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Plasma stability

In plasma physics, plasma stability concerns the stability properties of a plasma in equilibrium and its behavior under small perturbations. The stability of the system determines if the perturbations will grow, oscillate, or be damped out. It is an important consideration in topics such as nuclear fusion and astrophysical plasma.

In many cases, a plasma can be treated as a fluid and analyzed with the theory of magnetohydrodynamics (MHD). MHD stability is necessary for stable operation of magnetic confinement fusion devices and places certain operational limits. The beta limit, for example, sets the maximum achievable plasma beta in tokamaks.

On the other hand, small-scale plasma instabilities (typically described by kinetic theory), such as the drift wave instability, are believed to be the driving mechanism of turbulent transport in tokamaks, which leads to high rate of particle and energy transport across the confining magnetic fields. Plasma instabilities described by kinetic theory can contain aspects such as finite Larmor radius (FLR) effects and resonant wave-particle interactions, which is not captured in fluid models such as MHD.

Plasma instabilities
Plasma instabilities can be divided into two general groups:
 * 1) hydrodynamic instabilities
 * 2) kinetic instabilities.

Plasma instabilities are also categorised into different modes (e.g. with reference to a particle beam):

List of plasma instabilities

 * Buneman instability,
 * Farley–Buneman instability,
 * Jeans–Buneman instability,
 * Relativistic Buneman instability,
 * Cherenkov instability,
 * Coalescence instability,
 * Non-linear coalescence instability
 * Chute instability,
 * Collapse instability,
 * Cyclotron instabilities, including:
 * Alfven cyclotron instability
 * Cyclotron maser instability,
 * Electron cyclotron instability
 * Electrostatic ion cyclotron Instability
 * Ion cyclotron instability
 * Magnetoacoustic cyclotron instability
 * Proton cyclotron instability
 * Non-resonant beam-type cyclotron instability
 * Relativistic ion cyclotron instability
 * Whistler cyclotron instability
 * Diocotron instability, (similar to the Kelvin-Helmholtz fluid instability).
 * Disruptive instability (in tokamaks)
 * Double emission instability,
 * Edge-localized modes,
 * Explosive instability (or Ballooning instability),
 * Double plasma resonance instability,
 * Drift instability (a.k.a. drift-wave instability, or universal instability )
 * Lower hybrid (drift) instability (in the Critical ionization velocity mechanism)
 * Magnetic drift instability,
 * Slow Drift Instability
 * Electrothermal instability
 * Fan instability,
 * Firehose instability (a.k.a. hose instability), not to be confused with the similarly named Firehose instability in galactic dynamics
 * Fish instability,
 * Free electron maser instability,
 * Gyrotron instability,
 * Helical (Helix) instability,
 * Jeans instability,
 * Magnetic buoyancy instability
 * Interchange instability (a.k.a. flute instability),
 * Parker instability (a.k.a. undular instability or magnetic Rayleigh–Taylor instability)
 * Mixed instability (a.k.a. quasi-interchange instability)
 * Magnetorotational instability (in accretion disks)
 * Magnetothermal instability (Laser-plasmas),
 * Modulational instability
 * Non-Abelian instability,
 * Pair instability (in supernovae)
 * Peratt instability (stacked toroids)
 * Pinch instability (a.k.a. Bennett pinch instability),
 * Sausage instability (m=0)
 * Kink instability (m=1)
 * Helical kink instability (a.k.a. helical instability)
 * Rayleigh–Taylor instability (RTI, a.k.a. gravitational instability)
 * Rotating instability,
 * Tearing mode instability (or resistive tearing instability )
 * Two-stream instability (a.k.a. beam-plasma instability, counter-streaming instability)
 * Beam acoustic instability
 * Bump-on-tail instability
 * Ion beam instability
 * Weak beam instability
 * Weibel instability
 * Chromo–Weibel instability (i.e. non-abelian instability)
 * Filamentation instability (a.k.a. beam-Weibel instability),

MHD Instabilities
Beta is a ratio of the plasma pressure over the magnetic field strength. $$\beta = \frac{p}{p_\text{mag}} = \frac{n k_B T}{(B^2/2\mu_0)}$$

MHD stability at high beta is crucial for a compact, cost-effective magnetic fusion reactor. Fusion power density varies roughly as $$\beta^2$$ at constant magnetic field, or as $$\beta_N^4$$ at constant bootstrap fraction in configurations with externally driven plasma current. (Here $$\beta_N = \beta / (I / a B)$$ is the normalized beta.) In many cases MHD stability represents the primary limitation on beta and thus on fusion power density. MHD stability is also closely tied to issues of creation and sustainment of certain magnetic configurations, energy confinement, and steady-state operation. Critical issues include understanding and extending the stability limits through the use of a variety of plasma configurations, and developing active means for reliable operation near those limits. Accurate predictive capabilities are needed, which will require the addition of new physics to existing MHD models. Although a wide range of magnetic configurations exist, the underlying MHD physics is common to all. Understanding of MHD stability gained in one configuration can benefit others, by verifying analytic theories, providing benchmarks for predictive MHD stability codes, and advancing the development of active control techniques.

The most fundamental and critical stability issue for magnetic fusion is simply that MHD instabilities often limit performance at high beta. In most cases the important instabilities are long wavelength, global modes, because of their ability to cause severe degradation of energy confinement or termination of the plasma. Some important examples that are common to many magnetic configurations are ideal kink modes, resistive wall modes, and neoclassical tearing modes. A possible consequence of violating stability boundaries is a disruption, a sudden loss of thermal energy often followed by termination of the discharge. The key issue thus includes understanding the nature of the beta limit in the various configurations, including the associated thermal and magnetic stresses, and finding ways to avoid the limits or mitigate the consequences. A wide range of approaches to preventing such instabilities is under investigation, including optimization of the configuration of the plasma and its confinement device, control of the internal structure of the plasma, and active control of the MHD instabilities.

Ideal Instabilities
Ideal MHD instabilities driven by current or pressure gradients represent the ultimate operational limit for most configurations. The long-wavelength kink mode and short-wavelength ballooning mode limits are generally well understood and can in principle be avoided.

Intermediate-wavelength modes (n ~ 5–10 modes encountered in tokamak edge plasmas, for example) are less well understood due to the computationally intensive nature of the stability calculations. The extensive beta limit database for tokamaks is consistent with ideal MHD stability limits, yielding agreement to within about 10% in beta for cases where the internal profiles of the plasma are accurately measured. This good agreement provides confidence in ideal stability calculations for other configurations and in the design of prototype fusion reactors.

Resistive Wall Modes
Resistive wall modes (RWM) develop in plasmas that require the presence of a perfectly conducting wall for stability. RWM stability is a key issue for many magnetic configurations. Moderate beta values are possible without a nearby wall in the tokamak, stellarator, and other configurations, but a nearby conducting wall can significantly improve ideal kink mode stability in most configurations, including the tokamak, ST, reversed field pinch (RFP), spheromak, and possibly the FRC. In the advanced tokamak and ST, wall stabilization is critical for operation with a large bootstrap fraction. The spheromak requires wall stabilization to avoid the low-m, n tilt and shift modes, and possibly bending modes. However, in the presence of a non-ideal wall, the slowly growing RWM is unstable. The resistive wall mode has been a long-standing issue for the RFP, and has more recently been observed in tokamak experiments. Progress in understanding the physics of the RWM and developing the means to stabilize it could be directly applicable to all magnetic configurations. A closely related issue is to understand plasma rotation, its sources and sinks, and its role in stabilizing the RWM.

Resistive instabilities
Resistive instabilities are an issue for all magnetic configurations, since the onset can occur at beta values well below the ideal limit. The stability of neoclassical tearing modes (NTM) is a key issue for magnetic configurations with a strong bootstrap current. The NTM is a metastable mode; in certain plasma configurations, a sufficiently large deformation of the bootstrap current produced by a “seed island” can contribute to the growth of the island. The NTM is already an important performance-limiting factor in many tokamak experiments, leading to degraded confinement or disruption. Although the basic mechanism is well established, the capability to predict the onset in present and future devices requires better understanding of the damping mechanisms which determine the threshold island size, and of the mode coupling by which other instabilities (such as sawteeth in tokamaks) can generate seed islands. Resistive Ballooning Mode, similar to ideal ballooning, but with finite resistivity taken into consideration, provides another example of a resistive instability.

Configuration
The configuration of the plasma and its confinement device represent an opportunity to improve MHD stability in a robust way. The benefits of discharge shaping and low aspect ratio for ideal MHD stability have been clearly demonstrated in tokamaks and STs, and will continue to be investigated in experiments such as DIII-D, Alcator C-Mod, NSTX, and MAST. New stellarator experiments such as NCSX (proposed) will test the prediction that addition of appropriately designed helical coils can stabilize ideal kink modes at high beta, and lower-beta tests of ballooning stability are possible in HSX. The new ST experiments provide an opportunity to test predictions that a low aspect ratio yields improved stability to tearing modes, including neoclassical, through a large stabilizing “Glasser effect” term associated with a large Pfirsch-Schlüter current. Neoclassical tearing modes can be avoided by minimizing the bootstrap current in quasi-helical and quasi-omnigenous stellarator configurations. Neoclassical tearing modes are also stabilized with the appropriate relative signs of the bootstrap current and the magnetic shear; this prediction is supported by the absence of NTMs in central negative shear regions of tokamaks. Stellarator configurations such as the proposed NCSX, a quasi-axisymmetric stellarator design, can be created with negative magnetic shear and positive bootstrap current to achieve stability to the NTM. Kink mode stabilization by a resistive wall has been demonstrated in RFPs and tokamaks, and will be investigated in other configurations including STs (NSTX) and spheromaks (SSPX). A new proposal to stabilize resistive wall modes by a flowing liquid lithium wall needs further evaluation.

Internal Structure
Control of the internal structure of the plasma allows more active avoidance of MHD instabilities. Maintaining the proper current density profile, for example, can help to maintain stability to tearing modes. Open-loop optimization of the pressure and current density profiles with external heating and current drive sources is routinely used in many devices. Improved diagnostic measurements along with localized heating and current drive sources, now becoming available, will allow active feedback control of the internal profiles in the near future. Such work is beginning or planned in most of the large tokamaks (JET, JT–60U, DIII–D, C–Mod, and ASDEX–U) using RF heating and current drive. Real-time analysis of profile data such as MSE current profile measurements and real-time identification of stability boundaries are essential components of profile control. Strong plasma rotation can stabilize resistive wall modes, as demonstrated in tokamak experiments, and rotational shear is also predicted to stabilize resistive modes. Opportunities to test these predictions are provided by configurations such as the ST, spheromak, and FRC, which have a large natural diamagnetic rotation, as well as tokamaks with rotation driven by neutral beam injection. The Electric Tokamak experiment is intended to have a very large driven rotation, approaching Alfvénic regimes where ideal stability may also be influenced. Maintaining sufficient plasma rotation, and the possible role of the RWM in damping the rotation, are important issues that can be investigated in these experiments.

Feedback Control
Active feedback control of MHD instabilities should allow operation beyond the “passive” stability limits. Localized RF current drive at the rational surface is predicted to reduce or eliminate neoclassical tearing mode islands. Experiments have begun in ASDEX–U and COMPASS-D with promising results, and are planned for next year in DIII–D. Routine use of such a technique in generalized plasma conditions will require real-time identification of the unstable mode and its radial location. If the plasma rotation needed to stabilize the resistive wall mode cannot be maintained, feedback stabilization with external coils will be required. Feedback experiments have begun in DIII–D and HBT-EP, and feedback control should be explored for the RFP and other configurations. Physics understanding of these active control techniques will be directly applicable between configurations.

Disruption Mitigation
The techniques discussed above for improving MHD stability are the principal means of avoiding disruptions. However, in the event that these techniques do not prevent an instability, the effects of a disruption can be mitigated by various techniques. Experiments in JT–60U have demonstrated reduction of electromagnetic stresses through operation at a neutral point for vertical stability. Pre-emptive removal of the plasma energy by injection of a large gas puff or an impurity pellet has been demonstrated in tokamak experiments, and ongoing experiments in C–Mod, JT–60U, ASDEX–U, and DIII–D will improve the understanding and predictive capability. Cryogenic liquid jets of helium are another proposed technique, which may be required for larger devices. Mitigation techniques developed for tokamaks will be directly applicable to other configurations.

title: Plasma stability


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Magnetohydrodynamics

Magnetohydrodynamics (MHD; also called magneto-fluid dynamics or hydromagnetics) is a model of electrically conducting fluids that treats all interpenetrating particle species together as a single continuous medium. It is primarily concerned with the low-frequency, large-scale, magnetic behavior in plasmas and liquid metals and has applications in multiple fields including space physics, geophysics, astrophysics, and engineering.

The word magnetohydrodynamics is derived from ' meaning magnetic field, ' meaning water, and  meaning movement. The field of MHD was initiated by Hannes Alfvén, for which he received the Nobel Prize in Physics in 1970.

History
The MHD description of electrically conducting fluids was first developed by Hannes Alfvén in a 1942 paper published in Nature titled "Existence of Electromagnetic–Hydrodynamic Waves" which outlined his discovery of what are now referred to as Alfvén waves. Alfvén initially referred to these waves as "electromagnetic–hydrodynamic waves"; however, in a later paper he noted, "As the term 'electromagnetic–hydrodynamic waves' is somewhat complicated, it may be convenient to call this phenomenon 'magneto–hydrodynamic' waves."

Equations
In MHD, motion in the fluid is described using linear combinations of the mean motions of the individual species: the current density $$\mathbf{J}$$ and the center of mass velocity $$\mathbf{v}$$. In a given fluid, each species $$\sigma$$ has a number density $$n_\sigma$$, mass $$m_\sigma$$, electric charge $$q_\sigma$$, and a mean velocity $$\mathbf{u}_\sigma$$. The fluid's total mass density is then $\rho = \sum_\sigma m_\sigma n_\sigma$, and the motion of the fluid can be described by the current density expressed as
 * $$\mathbf{J} = \sum_\sigma n_\sigma q_\sigma \mathbf{u}_\sigma$$

and the center of mass velocity expressed as:
 * $$\mathbf{v} = \frac{1}{\rho} \sum_\sigma m_\sigma n_\sigma \mathbf{u}_\sigma .$$

MHD can be described by a set of equations consisting of a continuity equation, an equation of motion, an equation of state, Ampère's Law, Faraday's law, and Ohm's law. As with any fluid description to a kinetic system, a closure approximation must be applied to highest moment of the particle distribution equation. This is often accomplished with approximations to the heat flux through a condition of adiabaticity or isothermality.

In the adiabatic limit, that is, the assumption of an isotropic pressure $$p$$ and isotropic temperature, a fluid with an adiabatic index $$\gamma$$, electrical resistivity $$\eta$$, magnetic field $$\mathbf{B}$$, and electric field $$\mathbf{E}$$ can be described by the continuous equation
 * $$ \frac{\partial \rho}{\partial t} + \nabla \cdot \left(\rho\mathbf{v}\right)=0,$$

the equation of state
 * $$\frac{\mathrm{d}}{\mathrm{d}t} \left(\frac{p}{\rho^\gamma}\right) = 0,$$

the equation of motion
 * $$ \rho\left(\frac{\partial }{\partial t} + \mathbf{v}\cdot\nabla \right)\mathbf{v} = \mathbf{J}\times\mathbf{B} - \nabla p,$$

the low-frequency Ampère's law
 * $$\mu_0 \mathbf{J} = \nabla\times\mathbf{B},$$

Faraday's law
 * $$\frac{\partial \mathbf{B}}{\partial t} = - \nabla \times \mathbf{E},$$

and Ohm's law
 * $$\mathbf{E} + \mathbf{v}\times\mathbf{B} = \eta\mathbf{J}.$$

Taking the curl of this equation and using Ampère's law and Faraday's law results in the induction equation,
 * $$\frac{\partial\mathbf{B}}{\partial t} = \nabla\times(\mathbf{v}\times\mathbf{B}) + \frac{\eta}{\mu_0}\nabla^2\mathbf{B},$$

where $$\eta/\mu_0$$ is the magnetic diffusivity.

In the equation of motion, the Lorentz force term $$\mathbf{J}\times\mathbf{B}$$ can be expanded using Ampère's law and a vector calculus identity to give
 * $$\mathbf{J}\times\mathbf{B} = \frac{\left(\mathbf{B}\cdot\nabla\right)\mathbf{B}}{\mu_0} - \nabla\left(\frac{B^2}{2\mu_0}\right),$$

where the first term on the right hand side is the magnetic tension force and the second term is the magnetic pressure force.

Ideal MHD
The simplest form of MHD, ideal MHD, assumes that the resistive term $$\eta\mathbf{J}$$ in Ohm's law is small relative to the other terms such that it can be taken to be equal to zero. This occurs in the limit of large magnetic Reynolds numbers during which magnetic induction dominates over magnetic diffusion at the velocity and length scales under consideration. Consequently, processes in ideal MHD that convert magnetic energy into kinetic energy, referred to as ideal processes, cannot generate heat and raise entropy.

A fundamental concept underlying ideal MHD is the frozen-in flux theorem which states that the bulk fluid and embedded magnetic field are constrained to move together such that one can be said to be "tied" or "frozen" to the other. Therefore, any two points that move with the bulk fluid velocity and lie on the same magnetic field line will continue to lie on the same field line even as the points are advected by fluid flows in the system. The connection between the fluid and magnetic field fixes the topology of the magnetic field in the fluid—for example, if a set of magnetic field lines are tied into a knot, then they will remain so as long as the fluid has negligible resistivity. This difficulty in reconnecting magnetic field lines makes it possible to store energy by moving the fluid or the source of the magnetic field. The energy can then become available if the conditions for ideal MHD break down, allowing magnetic reconnection that releases the stored energy from the magnetic field.

Ideal MHD equations
In ideal MHD, the resistive term $$\eta\mathbf{J}$$ vanishes in Ohm's law giving the ideal Ohm's law,
 * $$\mathbf{E} + \mathbf{v}\times\mathbf{B} = 0.$$

Similarly, the magnetic diffusion term $$\eta\nabla^2\mathbf{B}/\mu_0$$ in the induction equation vanishes giving the ideal induction equation,
 * $$\frac{\partial\mathbf{B}}{\partial t} = \nabla\times(\mathbf{v}\times\mathbf{B}).$$

Applicability of ideal MHD to plasmas
Ideal MHD is only strictly applicable when:

 * 1) The plasma is strongly collisional, so that the time scale of collisions is shorter than the other characteristic times in the system, and the particle distributions are therefore close to Maxwellian.
 * 2) The resistivity due to these collisions is small. In particular, the typical magnetic diffusion times over any scale length present in the system must be longer than any time scale of interest.
 * 3) Interest in length scales much longer than the ion skin depth and Larmor radius perpendicular to the field, long enough along the field to ignore Landau damping, and time scales much longer than the ion gyration time (system is smooth and slowly evolving).

Importance of resistivity
In an imperfectly conducting fluid the magnetic field can generally move through the fluid following a diffusion law with the resistivity of the plasma serving as a diffusion constant. This means that solutions to the ideal MHD equations are only applicable for a limited time for a region of a given size before diffusion becomes too important to ignore. One can estimate the diffusion time across a solar active region (from collisional resistivity) to be hundreds to thousands of years, much longer than the actual lifetime of a sunspot—so it would seem reasonable to ignore the resistivity. By contrast, a meter-sized volume of seawater has a magnetic diffusion time measured in milliseconds.

Even in physical systems —which are large and conductive enough that simple estimates of the Lundquist number suggest that the resistivity can be ignored—resistivity may still be important: many instabilities exist that can increase the effective resistivity of the plasma by factors of more than 109. The enhanced resistivity is usually the result of the formation of small scale structure like current sheets or fine scale magnetic turbulence, introducing small spatial scales into the system over which ideal MHD is broken and magnetic diffusion can occur quickly. When this happens, magnetic reconnection may occur in the plasma to release stored magnetic energy as waves, bulk mechanical acceleration of material, particle acceleration, and heat.

Magnetic reconnection in highly conductive systems is important because it concentrates energy in time and space, so that gentle forces applied to a plasma for long periods of time can cause violent explosions and bursts of radiation.

When the fluid cannot be considered as completely conductive, but the other conditions for ideal MHD are satisfied, it is possible to use an extended model called resistive MHD. This includes an extra term in Ohm's Law which models the collisional resistivity. Generally MHD computer simulations are at least somewhat resistive because their computational grid introduces a numerical resistivity.

Structures in MHD systems

In many MHD systems most of the electric current is compressed into thin nearly-two-dimensional ribbons termed current sheets. These can divide the fluid into magnetic domains, inside of which the currents are relatively weak. Current sheets in the solar corona are thought to be between a few meters and a few kilometers in thickness, which is quite thin compared to the magnetic domains (which are thousands to hundreds of thousands of kilometers across). Another example is in the Earth's magnetosphere, where current sheets separate topologically distinct domains, isolating most of the Earth's ionosphere from the solar wind.

Waves
The wave modes derived using the MHD equations are called magnetohydrodynamic waves or MHD waves. There are three MHD wave modes that can be derived from the linearized ideal-MHD equations for a fluid with a uniform and constant magnetic field:
 * Alfvén waves
 * Slow magnetosonic waves
 * Fast magnetosonic waves

These modes have phase velocities that are independent of the magnitude of the wavevector, so they experience no dispersion. The phase velocity depends on the angle between the wave vector $v_{A} > v_{s}$ and the magnetic field $v_{A} < v_{s}$. An MHD wave propagating at an arbitrary angle $θ$ with respect to the time independent or bulk field $k$ will satisfy the dispersion relation
 * $$\frac{\omega}{k} = v_A \cos\theta$$

where
 * $$v_A = \frac{B_0}{\sqrt{\mu_0\rho}}$$

is the Alfvén speed. This branch corresponds to the shear Alfvén mode. Additionally the dispersion equation gives
 * $$\frac{\omega}{k} = \left( \tfrac12\left(v_A^2+v_s^2\right) \pm \tfrac12\sqrt{\left(v_A^2+v_s^2\right)^2 - 4v_s^2v_A^2\cos^2\theta}\right)^\frac12$$

where
 * $$v_s = \sqrt{\frac{\gamma p}{\rho}}$$

is the ideal gas speed of sound. The plus branch corresponds to the fast-MHD wave mode and the minus branch corresponds to the slow-MHD wave mode. A summary of the properties of these waves is provided:

The MHD oscillations will be damped if the fluid is not perfectly conducting but has a finite conductivity, or if viscous effects are present.

MHD waves and oscillations are a popular tool for the remote diagnostics of laboratory and astrophysical plasmas, for example, the corona of the Sun (Coronal seismology).

Extensions

 * Resistive
 * Resistive MHD describes magnetized fluids with finite electron diffusivity ($B$). This diffusivity leads to a breaking in the magnetic topology; magnetic field lines can 'reconnect' when they collide.  Usually this term is small and reconnections can be handled by thinking of them as not dissimilar to shocks; this process has been shown to be important in the Earth-Solar magnetic interactions.

 * Extended
 * Extended MHD describes a class of phenomena in plasmas that are higher order than resistive MHD, but which can adequately be treated with a single fluid description. These include the effects of Hall physics, electron pressure gradients, finite Larmor Radii in the particle gyromotion, and electron inertia.

 * Two-fluid
 * Two-fluid MHD describes plasmas that include a non-negligible Hall electric field. As a result, the electron and ion momenta must be treated separately.  This description is more closely tied to Maxwell's equations as an evolution equation for the electric field exists.

 * Hall
 * In 1960, M. J. Lighthill criticized the applicability of ideal or resistive MHD theory for plasmas. It concerned the neglect of the "Hall current term" in Ohm's law, a frequent simplification made in magnetic fusion theory. Hall-magnetohydrodynamics (HMHD) takes into account this electric field description of magnetohydrodynamics, and Ohm's law takes the form
 * $$\mathbf{E} + \mathbf{v}\times\mathbf{B}\underbrace{-\frac{1}{n_e e}(\mathbf{J}\times\mathbf{B})}_{\text{Hall current term}} = \eta\mathbf{J},$$
 * where $$n_e$$ is the electron number density and $$e$$ is the elementary charge. The most important difference is that in the absence of field line breaking, the magnetic field is tied to the electrons and not to the bulk fluid.

 * Electron MHD
 * Electron Magnetohydrodynamics (EMHD) describes small scales plasmas when electron motion is much faster than the ion one. The main effects are changes in conservation laws, additional resistivity, importance of electron inertia. Many effects of Electron MHD are similar to effects of the Two fluid MHD and the Hall MHD. EMHD is especially important for z-pinch, magnetic reconnection, ion thrusters, neutron stars, and plasma switches.

 * Collisionless
 * MHD is also often used for collisionless plasmas. In that case the MHD equations are derived from the Vlasov equation.

 * Reduced
 * By using a multiscale analysis the (resistive) MHD equations can be reduced to a set of four closed scalar equations. This allows for, amongst other things, more efficient numerical calculations.

Importance of kinetic effects
Another limitation of MHD (and fluid theories in general) is that they depend on the assumption that the plasma is strongly collisional (this is the first criterion listed above), so that the time scale of collisions is shorter than the other characteristic times in the system, and the particle distributions are Maxwellian. This is usually not the case in fusion, space and astrophysical plasmas. When this is not the case, or the interest is in smaller spatial scales, it may be necessary to use a kinetic model which properly accounts for the non-Maxwellian shape of the distribution function. However, because MHD is relatively simple and captures many of the important properties of plasma dynamics it is often qualitatively accurate and is therefore often the first model tried.

Effects which are essentially kinetic and not captured by fluid models include double layers, Landau damping, a wide range of instabilities, chemical separation in space plasmas and electron runaway. In the case of ultra-high intensity laser interactions, the incredibly short timescales of energy deposition mean that hydrodynamic codes fail to capture the essential physics.

Geophysics
Beneath the Earth's mantle lies the core, which is made up of two parts: the solid inner core and liquid outer core. Both have significant quantities of iron. The liquid outer core moves in the presence of the magnetic field and eddies are set up into the same due to the Coriolis effect. These eddies develop a magnetic field which boosts Earth's original magnetic field—a process which is self-sustaining and is called the geomagnetic dynamo.

Based on the MHD equations, Glatzmaier and Paul Roberts have made a supercomputer model of the Earth's interior. After running the simulations for thousands of years in virtual time, the changes in Earth's magnetic field can be studied. The simulation results are in good agreement with the observations as the simulations have correctly predicted that the Earth's magnetic field flips every few hundred thousand years. During the flips, the magnetic field does not vanish altogether—it just gets more complex.

Earthquakes
Some monitoring stations have reported that earthquakes are sometimes preceded by a spike in ultra low frequency (ULF) activity. A remarkable example of this occurred before the 1989 Loma Prieta earthquake in California, although a subsequent study indicates that this was little more than a sensor malfunction. On December 9, 2010, geoscientists announced that the DEMETER satellite observed a dramatic increase in ULF radio waves over Haiti in the month before the magnitude 7.0 Mw 2010 earthquake. Researchers are attempting to learn more about this correlation to find out whether this method can be used as part of an early warning system for earthquakes.

Space Physics
The study of space plasmas near Earth and throughout the Solar System is known as space physics. Areas researched within space physics encompass a large number of topics, ranging from the ionosphere to auroras, Earth's magnetosphere, the Solar wind, and coronal mass ejections.

MHD forms the framework for understanding how populations of plasma interact within the local geospace environment. Researchers have developed global models using MHD to simulate phenomena within Earth's magnetosphere, such as the location of Earth's magnetopause (the boundary between the Earth's magnetic field and the solar wind), the formation of the ring current, auroral electrojets, and geomagnetically induced currents.

One prominent use of global MHD models is in space weather forecasting. Intense solar storms have the potential to cause extensive damage to satellites and infrastructure, thus it is crucial that such events are detected early. The Space Weather Prediction Center (SWPC) runs MHD models to predict the arrival and impacts of space weather events at Earth.

Astrophysics
MHD applies to astrophysics, including stars, the interplanetary medium (space between the planets), and possibly within the interstellar medium (space between the stars) and jets. Most astrophysical systems are not in local thermal equilibrium, and therefore require an additional kinematic treatment to describe all the phenomena within the system (see Astrophysical plasma).

Sunspots are caused by the Sun's magnetic fields, as Joseph Larmor theorized in 1919. The solar wind is also governed by MHD. The differential solar rotation may be the long-term effect of magnetic drag at the poles of the Sun, an MHD phenomenon due to the Parker spiral shape assumed by the extended magnetic field of the Sun.

Previously, theories describing the formation of the Sun and planets could not explain how the Sun has 99.87% of the mass, yet only 0.54% of the angular momentum in the Solar System. In a closed system such as the cloud of gas and dust from which the Sun was formed, mass and angular momentum are both conserved. That conservation would imply that as the mass concentrated in the center of the cloud to form the Sun, it would spin faster, much like a skater pulling their arms in. The high speed of rotation predicted by early theories would have flung the proto-Sun apart before it could have formed. However, magnetohydrodynamic effects transfer the Sun's angular momentum into the outer solar system, slowing its rotation.

Breakdown of ideal MHD (in the form of magnetic reconnection) is known to be the likely cause of solar flares. The magnetic field in a solar active region over a sunspot can store energy that is released suddenly as a burst of motion, X-rays, and radiation when the main current sheet collapses, reconnecting the field.

Magnetic confinement fusion
MHD describes a wide range of physical phenomena occurring in fusion plasmas in devices such as tokamaks or stellarators.

The Grad-Shafranov equation derived from ideal MHD describes the equilibrium of axisymmetric toroidal plasma in a tokamak. In tokamak experiments, the equilibrium during each discharge is routinely calculated and reconstructed, which provides information on the shape and position of the plasma controlled by currents in external coils.

MHD stability theory is known to govern the operational limits of tokamaks. For example, the ideal MHD kink modes provide hard limits on the achievable plasma beta (Troyon limit) and plasma current (set by the $$q > 2$$ requirement of the safety factor).

Sensors
Magnetohydrodynamic sensors are used for precision measurements of angular velocities in inertial navigation systems such as in aerospace engineering. Accuracy improves with the size of the sensor. The sensor is capable of surviving in harsh environments.

Engineering
MHD is related to engineering problems such as plasma confinement, liquid-metal cooling of nuclear reactors, and electromagnetic casting (among others).

A magnetohydrodynamic drive or MHD propulsor is a method for propelling seagoing vessels using only electric and magnetic fields with no moving parts, using magnetohydrodynamics. The working principle involves electrification of the propellant (gas or water) which can then be directed by a magnetic field, pushing the vehicle in the opposite direction. Although some working prototypes exist, MHD drives remain impractical.

The first prototype of this kind of propulsion was built and tested in 1965 by Steward Way, a professor of mechanical engineering at the University of California, Santa Barbara. Way, on leave from his job at Westinghouse Electric, assigned his senior-year undergraduate students to develop a submarine with this new propulsion system. In the early 1990s, a foundation in Japan (Ship & Ocean Foundation (Minato-ku, Tokyo)) built an experimental boat, the Yamato-1, which used a magnetohydrodynamic drive incorporating a superconductor cooled by liquid helium, and could travel at 15 km/h.

MHD power generation fueled by potassium-seeded coal combustion gas showed potential for more efficient energy conversion (the absence of solid moving parts allows operation at higher temperatures), but failed due to cost-prohibitive technical difficulties. One major engineering problem was the failure of the wall of the primary-coal combustion chamber due to abrasion.

In microfluidics, MHD is studied as a fluid pump for producing a continuous, nonpulsating flow in a complex microchannel design.

MHD can be implemented in the continuous casting process of metals to suppress instabilities and control the flow.

Industrial MHD problems can be modeled using the open-source software EOF-Library. Two simulation examples are 3D MHD with a free surface for electromagnetic levitation melting, and liquid metal stirring by rotating permanent magnets.

Magnetic drug targeting
An important task in cancer research is developing more precise methods for delivery of medicine to affected areas. One method involves the binding of medicine to biologically compatible magnetic particles (such as ferrofluids), which are guided to the target via careful placement of permanent magnets on the external body. Magnetohydrodynamic equations and finite element analysis are used to study the interaction between the magnetic fluid particles in the bloodstream and the external magnetic field.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Magnetohydrodynamics


text:
Great Chicago Fire

The Great Chicago Fire was a conflagration that burned in the American city of Chicago during October 8–10, 1871. The fire killed approximately 300 people, destroyed roughly 3.3 sqmi of the city including over 17,000 structures, and left more than 100,000 residents homeless. The fire began in a neighborhood southwest of the city center. A long period of hot, dry, windy conditions, and the wooden construction prevalent in the city, led to the conflagration. The fire leapt the south branch of the Chicago River and destroyed much of central Chicago and then leapt the main stem of the river, consuming the Near North Side.

Help flowed to the city from near and far after the fire. The city government improved building codes to stop the rapid spread of future fires and rebuilt rapidly to those higher standards. A donation from the United Kingdom spurred the establishment of the Chicago Public Library.

Origin

The fire is said to have started at about 8:30 p.m. on October 8, in or around a small barn belonging to the O'Leary family that bordered the alley behind 137 W. DeKoven Street. The shed next to the barn was the first building to be consumed by the fire. City officials never determined the cause of the blaze, but the rapid spread of the fire due to a long drought in that year's summer, strong winds from the southwest, and the rapid destruction of the water pumping system, explain the extensive damage of the mainly wooden city structures. There has been much speculation over the years on a single start to the fire. The most popular tale blames Mrs. O'Leary's cow, who allegedly knocked over a lantern; others state that a group of men were gambling inside the barn and knocked over a lantern. Still other speculation suggests that the blaze was related to other fires in the Midwest that day.

The fire's spread was aided by the city's use of wood as the predominant building material in a style called balloon frame. More than two-thirds of the structures in Chicago at the time of the fire were made entirely of wood, with most of the houses and buildings being topped with highly combustible tar or shingle roofs. All of the city's sidewalks and many roads were also made of wood. Compounding this problem, Chicago received only 1 in of rain from July 4 to October 9, causing severe drought conditions before the fire, while strong southwest winds helped to carry flying embers toward the heart of the city.

In 1871, the Chicago Fire Department had 185 firefighters with just 17 horse-drawn steam pumpers to protect the entire city. The initial response by the fire department was timely, but due to an error by the watchman, Matthias Schaffer, the firefighters were initially sent to the wrong place, allowing the fire to grow unchecked. An alarm sent from the area near the fire also failed to register at the courthouse where the fire watchmen were, while the firefighters were tired from having fought numerous small fires and one large fire in the week before. These factors combined to turn a small barn fire into a conflagration.

Spread
When firefighters finally arrived at DeKoven Street, the fire had grown and spread to neighboring buildings and was progressing toward the central business district. Firefighters had hoped that the South Branch of the Chicago River and an area that had previously thoroughly burned would act as a natural firebreak. All along the river, however, were lumber yards, warehouses, and coal yards, and barges and numerous bridges across the river. As the fire grew, the southwest wind intensified and became superheated, causing structures to catch fire from the heat and from burning debris blown by the wind. Around midnight, flaming debris blew across the river and landed on roofs and the South Side Gas Works.

With the fire across the river and moving rapidly toward the heart of the city, panic set in. About this time, Mayor Roswell B. Mason sent messages to nearby towns asking for help. When the courthouse caught fire, he ordered the building to be evacuated and the prisoners jailed in the basement to be released. At 2:30 a.m. on the 9th, the cupola of the courthouse collapsed, sending the great bell crashing down. Some witnesses reported hearing the sound from a mile (1.6 km) away.

As more buildings succumbed to the flames, a major contributing factor to the fire's spread was a meteorological phenomenon known as a fire whirl. As overheated air rises, it comes into contact with cooler air and begins to spin, creating a tornado-like effect. These fire whirls are likely what drove flaming debris so high and so far. Such debris was blown across the main branch of the Chicago River to a railroad car carrying kerosene. The fire had jumped the river a second time and was now raging across the city's north side.

Despite the fire spreading and growing rapidly, the city's firefighters continued to battle the blaze. A short time after the fire jumped the river, a burning piece of timber lodged on the roof of the city's waterworks. Within minutes, the interior of the building was engulfed in flames and the building was destroyed. With it, the city's water mains went dry and the city was helpless. The fire burned unchecked from building to building, block to block.

Finally, late into the evening of October 9, it started to rain, but the fire had already started to burn itself out. The fire had spread to the sparsely populated areas of the north side, having thoroughly consumed the densely populated areas.

Aftermath

Once the fire had ended, the smoldering remains were still too hot for a survey of the damage to be completed for many days. Eventually, the city determined that the fire destroyed an area about 4 mi long and averaging 3/4 mi wide, encompassing an area of more than 2000 acre. Destroyed were more than 73 mi of roads, 120 mi of sidewalk, 2,000 lampposts, 17,500 buildings, and $222 million in property, which was about a third of the city's valuation in 1871.

On October 11, 1871, General Philip H. Sheridan came quickly to the aid of the city and was placed in charge by a proclamation, given by mayor Roswell B. Mason: "'The Preservation of the Good Order and Peace of the city is hereby intrusted to Lieut. General P.H. Sheridan, U.S. Army.'"To protect the city from looting and violence, the city was put under martial law for two weeks under Gen. Sheridan's command structure with a mix of regular troops, militia units, police, and a specially organized civilian group "First Regiment of Chicago Volunteers." Former Lieutenant-Governor William Bross, and part owner of the Tribune, later recollected his response to the arrival of Gen. Sheridan and his soldiers: "'Never did deeper emotions of joy overcome me. Thank God, those most dear to me and the city as well are safe.'"

For two weeks Sheridan's men patrolled the streets, guarded the relief warehouses, and enforced other regulations. On October 24 the troops were relieved of their duties and the volunteers were mustered out of service.

Of the approximately 324,000 inhabitants of Chicago in 1871, 90,000 Chicago residents (about 28% of the population) were left homeless. 120 bodies were recovered, but the death toll may have been as high as 300. The county coroner speculated that an accurate count was impossible, as some victims may have drowned or had been incinerated, leaving no remains.

In the days and weeks following the fire, monetary donations flowed into Chicago from around the country and abroad, along with donations of food, clothing, and other goods. These donations came from individuals, corporations, and cities. New York City gave $450,000 along with clothing and provisions, St. Louis gave $300,000, and the Common Council of London gave 1,000 guineas, as well as £7,000 from private donations. In Greenock, Scotland (pop. 40,000) a town meeting raised £518 on the spot. Cincinnati, Cleveland, and Buffalo, all commercial rivals, donated hundreds and thousands of dollars. Milwaukee, along with other nearby cities, helped by sending fire-fighting equipment. Food, clothing and books were brought by train from all over the continent. Mayor Mason placed the Chicago Relief and Aid Society in charge of the city's relief efforts.

Operating from the First Congregational Church, city officials and aldermen began taking steps to preserve order in Chicago. Price gouging was a key concern, and in one ordinance, the city set the price of bread at 8¢ for a 12 oz loaf. Public buildings were opened as places of refuge, and saloons closed at 9 in the evening for the week following the fire. Many people who were left homeless after the incident were never able to get their normal lives back since all their personal papers and belongings burned in the conflagration.

After the fire, A. H. Burgess of London proposed an "English Book Donation", to spur a free library in Chicago, in their sympathy with Chicago over the damages suffered. Libraries in Chicago had been private with membership fees. In April 1872, the City Council passed the ordinance to establish the free Chicago Public Library, starting with the donation from the United Kingdom of more than 8,000 volumes.

The fire also led to questions about development in the United States. Due to Chicago's rapid expansion at that time, the fire led to Americans reflecting on industrialization. Based on a religious point of view, some said that Americans should return to a more old-fashioned way of life, and that the fire was caused by people ignoring traditional morality. On the other hand, others believed that a lesson to be learned from the fire was that cities needed to improve their building techniques. Frederick Law Olmsted observed that poor building practices in Chicago were a problem:

"Chicago had a weakness for 'big things', and liked to think that it was outbuilding New York. It did a great deal of commercial advertising in its house-tops. The faults of construction as well as of art in its great showy buildings must have been numerous. Their walls were thin, and were overweighted with gross and coarse misornamentation."

Olmsted also believed that with brick walls, and disciplined firemen and police, the deaths and damage caused would have been much less.

Almost immediately, the city began to rewrite its fire standards, spurred by the efforts of leading insurance executives, and fire-prevention reformers such as Arthur C. Ducat. Chicago soon developed one of the country's leading fire-fighting forces. Business owners and land speculators such as Gurdon Saltonstall Hubbard quickly set about rebuilding the city. The first load of lumber for rebuilding was delivered the day the last burning building was extinguished. By the World's Columbian Exposition 22 years later, Chicago hosted more than 21 million visitors. The Palmer House hotel burned to the ground in the fire 13 days after its grand opening. Its developer, Potter Palmer, secured a loan and rebuilt the hotel to higher standards, across the street from the original, proclaiming it to be "The World's First Fireproof Building".

In 1956, the remaining structures on the original O'Leary property at 558 W. DeKoven Street were torn down for construction of the Chicago Fire Academy, a training facility for Chicago firefighters, known as the Quinn Fire Academy or Chicago Fire Department Training Facility. A bronze sculpture of stylized flames, entitled Pillar of Fire by sculptor Egon Weiner, was erected on the point of origin in 1961.

Surviving structures

The following structures from the burned district are still standing:

 * St. Michael's Church, Old Town
 * Chicago Water Tower
 * Chicago Avenue Pumping Station
 * St. Ignatius College Prep.
 * Police Constable Bellinger's cottage at 21 Lincoln Place (2121 North Hudson, today).
 * 2323 and 2339 North Cleveland Avenue also survived the blaze.

St. Michael's Church and the Pumping Station were both gutted in the fire, but their exteriors survived, and the buildings were rebuilt using the surviving walls. Additionally, though the inhabitable portions of the building were destroyed, the bell tower of St. James Cathedral survived the fire and was incorporated into the rebuilt church. The stones near the top of the tower are still blackened from the soot and smoke.

Precise start

Almost from the moment the fire broke out, various theories about its cause began to circulate. The most popular and enduring legend maintains that the fire began in the O'Leary barn as Mrs. O'Leary was milking her cow. The cow kicked over a lantern (or an oil lamp in some versions), setting fire to the barn. The O'Leary family denied this, stating that they were in bed before the fire started, but stories of the cow began to spread across the city. Catherine O'Leary seemed the perfect scapegoat: she was a poor, Irish Catholic immigrant. During the latter half of the 19th century, anti-Irish sentiment was strong in Chicago and throughout the United States. This was intensified as a result of the growing political power of the city's Irish population.

Furthermore, the United States had been distrustful of Catholics (or papists, as they were often called) since its beginning, carrying over attitudes in England in the 17th century;    as an Irish Catholic, Mrs. O'Leary was a target of both anti-Catholic and anti-Irish sentiment. This story was circulating in Chicago even before the flames had died out, and it was noted in the Chicago Tribune's first post-fire issue. In 1893 the reporter Michael Ahern retracted the "cow-and-lantern" story, admitting it was fabricated, but even his confession was unable to put the legend to rest. Although the O'Learys were never officially charged with starting the fire, the story became so engrained in local lore that Chicago's city council officially exonerated them—and the cow—in 1997.

Amateur historian Richard Bales has suggested the fire started when Daniel "Pegleg" Sullivan, who first reported the fire, ignited hay in the barn while trying to steal milk. Part of Bales's evidence includes an account by Sullivan, who claimed in an inquiry before the Fire Department of Chicago on November 25, 1871, that he saw the fire coming through the side of the barn and ran across DeKoven Street to free the animals from the barn, one of which included a cow owned by Sullivan's mother. Bales's account does not have consensus. The Chicago Public Library staff criticized his account in their web page on the fire. Despite this, the Chicago city council was convinced of Bales's argument and stated that the actions of Sullivan on that day should be scrutinized after the O'Leary family was exonerated in 1997.

Anthony DeBartolo reported evidence in two articles of the Chicago Tribune (October 8, 1997, and March 3, 1998, reprinted in Hyde Park Media) suggesting that Louis M. Cohn may have started the fire during a craps game. Following his death in 1942, Cohn bequeathed $35,000 which was assigned by his executors to the Medill School of Journalism at Northwestern University. The bequest was given to the school on September 28, 1944, and the dedication contained a claim by Cohn to have been present at the start of the fire. According to Cohn, on the night of the fire, he was gambling in the O'Learys' barn with one of their sons and some other neighborhood boys. When Mrs. O'Leary came out to the barn to chase the gamblers away at around 9:00, they knocked over a lantern in their flight, although Cohn states that he paused long enough to scoop up the money. The argument is not universally accepted.

An alternative theory, first suggested in 1882 by Ignatius L. Donnelly in Ragnarok: The Age of Fire and Gravel, is that the fire was caused by a meteor shower. This was described as a "fringe theory" concerning Biela's Comet. At a 2004 conference of the Aerospace Corporation and the American Institute of Aeronautics and Astronautics, engineer and physicist Robert Wood suggested that the fire began when a fragment of Biela's Comet impacted the Midwest. Biela's Comet had broken apart in 1845 and had not been observed since. Wood argued that four large fires took place, all on the same day, all on the shores of Lake Michigan (see related events), suggesting a common root cause. Eyewitnesses reported sighting spontaneous ignitions, lack of smoke, "balls of fire" falling from the sky, and blue flames. According to Wood, these accounts suggest that the fires were caused by the methane that is commonly found in comets.

Meteorites are not known to start or spread fires and are cool to the touch after reaching the ground, so this theory has not found favor in the scientific community. Methane-air mixtures become flammable only when the methane concentration exceeds 5%, at which point the mixtures also become explosive, a situation unlikely to occur from meteorites. Methane gas is lighter than air and thus does not accumulate near the ground; any localized pockets of methane in the open air rapidly dissipate. Moreover, if a fragment of an icy comet were to strike the Earth, the most likely outcome, due to the low tensile strength of such bodies, would be for it to disintegrate in the upper atmosphere, leading to an air burst explosion analogous to that of the Tunguska event.

The specific choice of Biela's Comet does not match with the dates in question, as the 6-year period of the comet's orbit did not intersect that of the Earth until 1872, one full year after the fire, when a large meteor shower was indeed observed. A common cause for the fires in the Midwest in late 1871 is that the area had suffered through a tinder-dry summer, so that winds from the front that moved in that evening were capable of generating rapidly expanding blazes from available ignition sources, which were plentiful in the region.

Related events
On that hot, dry, and windy autumn day, three other major fires occurred along the shores of Lake Michigan at the same time as the Great Chicago Fire. Some 250 mi to the north, the Peshtigo Fire consumed the town of Peshtigo, Wisconsin, along with a dozen other villages. It killed 1,200 to 2,500 people and charred approximately 1.5 e6acre. The Peshtigo Fire remains the deadliest in American history but the remoteness of the region meant it was little noticed at the time, due to the fact that one of the first things that burned were the telegraph lines to Green Bay.

Across the lake to the east, the town of Holland, Michigan, and other nearby areas burned to the ground. Some 100 mi to the north of Holland, the lumbering community of Manistee also went up in flames in what became known as the Great Michigan Fire.

Farther east, along the shore of Lake Huron, the Port Huron Fire swept through Port Huron, Michigan and much of Michigan's "Thumb". On October 9, 1871, a fire swept through the city of Urbana, Illinois, 140 mi south of Chicago, destroying portions of its downtown area. Windsor, Ontario, likewise burned on October 12.

The city of Singapore, Michigan, provided a large portion of the lumber to rebuild Chicago. As a result, the area was so heavily deforested that the land deteriorated into barren sand dunes that buried the town, and the town had to be abandoned.

In popular culture

 * The University of Illinois at Chicago athletic teams are named the Flames since 1982, in commemoration of the Great Chicago Fire.
 * Although set in Philadelphia, Theodore Dreiser's 1912 novel The Financier portrays the nationwide impact the 1871 Chicago fire had on the stock markets and the financial world.
 * The 1938 film In Old Chicago is centered on the fire, with a highly fictionalized portrayal of the O'Leary family as the main characters.
 * A Dudley Do-Right segment in The Adventures of Rocky and Bullwinkle and Friends featured a bear character named Stokey who was hypnotized by the segment's villain and lights fires instead of preventing fires. In the end of the segment, Do-Right took Stokey to Chicago to stay with a friend but ends up starting major fires convicting that he started the Great Chicago Fire. The segment was later banned for more than four decades due to protests from the U.S. Forest Service who disliked the parody of Smokey the Bear shortly after its original airing in 1961.
 * In 1974, the Chicago Fire football team played in the short-lived World Football League. Another Chicago Fire played in the American Football Association.
 * The 1976 made-for-TV movie Time Travelers has two doctors sent back to 1871 Chicago to find a cure for a disease thought lost to the fire. The Fire is shown starting when flames burst out from the O'Leary's barn and various attempts to stop the fire with a fire carriage and dynamiting buildings are depicted.
 * Events of the 1986 novel Illinois! by Noel Gerson writing as Dana Fuller Ross occur around the Great Chicago Fire.
 * The 1987 Williams pinball "Fire!" was inspired by the Great Chicago Fire.
 * The 1995 book The Great Fire by Jim Murphy tells the story of the fire for children, and was a Newbery Honor book in 1996.
 * A 1998 episode of the American television series Early Edition depicted Gary Hobson finding himself back in time in 1871 trying to prevent the fire. While he initially succeeds and stops the fire after the lantern is kicked over, subsequent events lead to the fire restarting, preserving the historical event while changing its origin.
 * The Major League Soccer team Chicago Fire was founded on October 8, 1997, the 126th anniversary of the Great Chicago Fire.
 * In 2014, the city of Chicago and Redmoon Theater partnered to create The Great Chicago Fire Festival. Held on October 4, 2014, the event fell victim to technical difficulties as replicas of 1871 houses on floating barges in the Chicago River failed to ignite properly due to electrical problems and heavy rain on the preceding days.
 * The Beach Boys' instrumental track titled "Mrs. O'Leary's Cow" was inspired by the fabled cause of the Great Chicago Fire, and served as the representation for the classical element fire on their abandoned project Smile.
 * Adopted on April 4, 1917, the flag of Chicago represents the Great Chicago fire with one of the four red stars present on the flag.

title: Great Chicago Fire


text:
Universal grammar

Universal grammar (UG), in modern linguistics, is the theory of the innate biological component of the language faculty, usually credited to Noam Chomsky. The basic postulate of UG is that there are innate constraints on what the grammar of a possible human language could be. When linguistic stimuli are received in the course of language acquisition, children then adopt specific syntactic rules that conform to UG. The advocates of this theory emphasize and partially rely on the poverty of the stimulus (POS) argument and the existence of some universal properties of natural human languages. However, the latter has not been firmly established, as some linguists have argued languages are so diverse that such universality is rare, and the theory of universal grammar remains controversial among linguists.

Overview
The term "universal grammar" is placeholder for whichever domain-specific features of linguistic competence turn out to be innate. Within generative grammar, it is generally accepted that there must be some such features, and one of the goals of generative research is to formulate and test hypotheses about which aspects those are. In day-to-day generative research, the notion that universal grammar exists motivates analyses in terms of general principles. As much as possible, facts about particular languages are derived from these general principles rather than from language-specific stipulations.

Evidence
The idea that at least some aspects are innate is motivated by poverty of the stimulus arguments. For example, one famous poverty of the stimulus argument concerns the acquisition of yes-no questions in English. This argument starts from the observation that children only make mistakes compatible with rules targeting hierarchical structure even though the examples which they encounter could have been generated by a simpler rule that targets linear order. In other words, children seem to ignore the possibility that the question rule is as simple as "switch the order of the first two words" and immediately jump to alternatives that rearrange constituents in tree structures. This is taken as evidence that children are born knowing that grammatical rules involve hierarchical structure, even though they have to figure out what those rules are.

Theories of universal grammar
Within generative grammar, there are a variety of theories about what universal grammar consists of. One notable hypothesis proposed by Hagit Borer holds that the fundamental syntactic operations are universal and that all variation arises from different feature-specifications in the lexicon. On the other hand, a strong hypothesis adopted in some variants of Optimality Theory holds that humans are born with a universal set of constraints, and that all variation arises from differences in how these constraints are ranked. In a 2002 paper, Noam Chomsky, Marc Hauser and W. Tecumseh Fitch proposed that universal grammar consists solely of the capacity for hierarchical phrase structure.

Relation to the evolution of language
In an article entitled "The Faculty of Language: What Is It, Who Has It, and How Did It Evolve?" Hauser, Chomsky, and Fitch present the three leading hypotheses for how language evolved and brought humans to the point where they have a universal grammar.

The first hypothesis states that the faculty of language in the broad sense (FLb) is strictly homologous to animal communication. This means that homologous aspects of the faculty of language exist in non-human animals.

The second hypothesis states that the FLb is a derived and uniquely human adaptation for language. This hypothesis holds that individual traits were subject to natural selection and came to be specialized for humans.

The third hypothesis states that only the faculty of language in the narrow sense (FLn) is unique to humans. It holds that while mechanisms of the FLb are present in both human and non-human animals, the computational mechanism of recursion has evolved recently, and solely in humans. This hypothesis aligns most closely with the typical theory of universal grammar championed by Chomsky.

Presence of creole languages
The presence of creole languages is sometimes cited as further support for this theory, especially by Bickerton's controversial language bioprogram theory. Creoles are languages that develop and form when disparate societies with no common language come together and are forced to devise a new system of communication. The system used by the original speakers is typically an inconsistent mix of vocabulary items, known as a pidgin. As these speakers' children begin to acquire their first language, they use the pidgin input to effectively create their own original language, known as a creole. Unlike pidgins, creoles have native speakers (those with acquisition from early childhood) and make use of a full, systematic grammar.

According to Bickerton, the idea of universal grammar is supported by creole languages because certain features are shared by virtually all in the category. For example, their default point of reference in time (expressed by bare verb stems) is not the present moment, but the past. Using pre-verbal auxiliaries, they uniformly express tense, aspect, and mood. Negative concord occurs, but it affects the verbal subject (as opposed to the object, as it does in languages like Spanish). Another similarity among creoles can be seen in the fact that questions are created simply by changing the intonation of a declarative sentence, not its word order or content.

However, extensive work by Carla Hudson-Kam and Elissa Newport suggests that creole languages may not support a universal grammar at all. In a series of experiments, Hudson-Kam and Newport looked at how children and adults learn artificial grammars. They found that children tend to ignore minor variations in the input when those variations are infrequent, and reproduce only the most frequent forms. In doing so, they tend to standardize the language that they hear around them. Hudson-Kam and Newport hypothesize that in a pidgin-development situation (and in the real-life situation of a deaf child whose parents are or were disfluent signers), children systematize the language they hear, based on the probability and frequency of forms, and not that which has been suggested on the basis of a universal grammar. Further, it seems to follow that creoles would share features with the languages from which they are derived, and thus look similar in terms of grammar.

Many researchers of universal grammar argue against a concept of relexification, which says that a language replaces its lexicon almost entirely with that of another. This goes against universalist ideas of a universal grammar, which has an innate grammar.

Criticism
Recent work has also suggested that some recurrent neural network architectures are able to learn hierarchical structure without an explicit constraint. This shows that it may in fact be possible for human infants to acquire natural language syntax without an explicit universal grammar.

The empirical basis of poverty of the stimulus arguments has been challenged by Geoffrey Pullum and others, leading to back-and-forth debate in the language acquisition literature.

Language acquisition researcher Michael Ramscar has suggested that when children erroneously expect an ungrammatical form that then never occurs, the repeated failure of expectation serves as a form of implicit negative feedback that allows them to correct their errors over time such as how children correct grammar generalizations like goed to went through repetitive failure.

In addition, it has been suggested that people learn about probabilistic patterns of word distributions in their language, rather than hard and fast rules (see Distributional hypothesis). For example, children overgeneralize the past tense marker "ed" and conjugate irregular verbs as if they were regular, producing forms like goed and eated and correct these deviancies over time. It has also been proposed that the poverty of the stimulus problem can be largely avoided, if it is assumed that children employ similarity-based generalization strategies in language learning, generalizing about the usage of new words from similar words that they already know how to use.

Neurogeneticists Simon Fisher and Sonja Vernes consider Chomsky's "Universal Grammar" as an example of a romantic simplification of genetics and neuroscience. According to them, the link from genes to grammar has not been consistently mapped by scientists. What has been established by research relates primarily to speech pathologies. The arising lack of certainty has provided an audience for unconstrained speculations that have fed the myth of "so-called grammar genes".

Geoffrey Sampson maintains that universal grammar theories are not falsifiable and are therefore pseudoscientific. He argues that the grammatical "rules" linguists posit are simply post-hoc observations about existing languages, rather than predictions about what is possible in a language. Similarly, Jeffrey Elman argues that the unlearnability of languages assumed by universal grammar is based on a too-strict, "worst-case" model of grammar, that is not in keeping with any actual grammar. In keeping with these points, James Hurford argues that the postulate of a language acquisition device (LAD) essentially amounts to the trivial claim that languages are learnt by humans, and thus, that the LAD is less a theory than an explanandum looking for theories.

Morten H. Christiansen and Nick Chater have argued that the relatively fast-changing nature of language would prevent the slower-changing genetic structures from ever catching up, undermining the possibility of a genetically hard-wired universal grammar. Instead of an innate universal grammar, they claim, "apparently arbitrary aspects of linguistic structure may result from general learning and processing biases deriving from the structure of thought processes, perceptuo-motor factors, cognitive limitations, and pragmatics".

Wolfram Hinzen summarizes the most common criticisms of universal grammar:
 * Universal grammar has no coherent formulation
 * Universal grammar cannot have evolved by standardly accepted neo-Darwinian evolutionary principles.
 * Apparent variation at all levels of linguistic organization, which lies at the heart of human faculty of language.

In the domain of field research, Daniel Everett has claimed that the Pirahã language is a counterexample to the basic tenets of universal grammar because it lacks clausal embedding. According to Everett, this trait results from Pirahã culture emphasizing present-moment concrete matters. Other linguists have responded that Pirahã does in fact have clausal embedding, and that even if it did not this would be irrelevant to current theories of universal grammar.

History
The modern conception of universal grammar is generally attributed to Noam Chomsky. However, similar ideas are found in older work. A related idea is found in Roger Bacon's c. 1245 Overview of Grammar and c. 1268 Greek Grammar, where he postulates that all languages are built upon a common grammar, even though it may undergo incidental variations. In the 13th century, the speculative grammarians postulated universal rules underlying all grammars.

The concept of a universal grammar or language was at the core of the 17th century projects for philosophical languages. An influential work in that time was Grammaire générale by Claude Lancelot and Antoine Arnauld. They tried to describe a general grammar for languages, coming to the conclusion that grammar has to be universal. There is a Scottish school of universal grammarians from the 18th century, as distinguished from the philosophical language project, which included authors such as James Beattie, Hugh Blair, James Burnett, James Harris, and Adam Smith. The article on grammar in the first edition of the Encyclopædia Britannica (1771) contains an extensive section titled "Of Universal Grammar".

In the late 19th and early 20th century, Wilhelm Wundt and Otto Jespersen responded to these earlier arguments, arguing that their view of language was overly influenced by Latin and ignored the breadth of worldwide linguistic variation. Jesperson did not fully dispense with the idea of a "universal grammar", but reduced it to universal syntactic categories or super-categories, such as number, tenses, etc.

During the rise of behaviorism, the idea of a universal grammar was discarded in light of the idea that language acquisition, like any other kind of learning, could be explained by a succession of trials, errors, and rewards for success. In other words, children learned their mother tongue by simple imitation, through listening and repeating what adults said. For example, when a child says "milk" and the mother will smile and give her child milk as a result, the child will find this outcome rewarding, thus enhancing the child's language development.

In 2016 Chomsky and Berwick co-wrote their book titled Why Only Us, where they defined both the minimalist program and the strong minimalist thesis and its implications to update their approach to UG theory. According to Berwick and Chomsky, the strong minimalist thesis states that "The optimal situation would be that UG reduces to the simplest computational principles which operate in accord with conditions of computational efficiency. This conjecture is ... called the Strong Minimalist Thesis (SMT)." The significance of SMT is to significantly shift the previous emphasis on universal grammars to the concept which Chomsky and Berwick now call "merge". "Merge" is defined in their 2016 book when they state "Every computational system has embedded within it somewhere an operation that applies to two objects X and Y already formed, and constructs from them a new object Z. Call this operation Merge." SMT dictates that "Merge will be as simple as possible: it will not modify X or Y or impose any arrangement on them; in particular, it will leave them unordered, an important fact... Merge is therefore just set formation: Merge of X and Y yields the set {X, Y}."

title: Universal grammar


text:
Munro

A Munro (Rothach ) is defined as a mountain in Scotland with a height over 3000 ft, and which is on the Scottish Mountaineering Club (SMC) official list of Munros; there is no explicit topographical prominence requirement. The best known Munro is Ben Nevis (Beinn Nibheis), the highest mountain in the British Isles at 4,411 ft (1,345 m).

Munros are named after Sir Hugh Munro, 4th Baronet (1856–1919), who produced the first list of such hills, known as Munro's Tables, in 1891. Also included were what Munro considered lesser peaks, now known as Munro Tops, which are also over 3,000 feet but are lower than the nearby primary mountain. The publication of the original list is usually considered to be the epoch event of modern peak bagging. The list has been the subject of subsequent variation and, the Scottish Mountaineering Club has listed 282 Munros and 226 Munro Tops.

"Munro bagging" is the activity of climbing all the listed Munros. , 7,651 people had reported completing a round. The first continuous round was completed by Hamish Brown in 1974, whilst the record for the fastest continuous round is held by ultra runner Jamie Aarons, who completed a round in 31 days 10 hours 27 min in June 2023. Furths are mountains in England, Wales or Ireland recognized by the SMC as meeting the Munro classification.

History

Before the publication of Munro's Tables in 1891, there was much uncertainty about the number of Scottish peaks over 3,000 feet. Estimates ranged from 31 (in M.J.B. Baddeley's guides) to 236 (listed in Robert Hall's third edition of The Highland Sportsman and Tourist, published in 1884). When the Scottish Mountaineering Club was formed in 1889, one of its aims was to remedy this by accurately documenting all of Scotland's mountains over 3,000 feet. Sir Hugh Munro, a founding member of the club, took on the task using his own experience as a mountaineer, as well as detailed study of the Ordnance Survey six-inch-to-the-mile (1:10,560) and one-inch-to-the-mile (1:63,360) maps.

Munro researched and produced a set of tables that were published in the Scottish Mountaineering Club Journal in September 1891. The tables listed 538 summits over 3,000 feet, 282 of which were regarded as "separate mountains". The term Munro applies to separate mountains, while the lesser summits are known as Munro Tops. Munro did not set any measure of topographic prominence by which a peak qualified as a separate mountain, so there has been much debate about how distinct two hills must be if they are to be counted as two separate Munros.

The Scottish Mountaineering Club has revised the tables, both in response to new height data on Ordnance Survey maps and to address the perceived inconsistency as to which peaks qualify for Munro status. In 1992, the publication of Alan Dawson's book Relative Hills of Britain, showed that three Munro Tops not already considered summits, had a prominence of more than 500 ft. Given this they would have qualified as Corbett summits had they been under 3,000 feet. In the 1997 tables these three Munro Tops, on Beinn Alligin, Beinn Eighe and Buachaille Etive Beag, gained full Munro summit status. Dawson's book also highlighted a number of significant Munro Tops with as much as 60 m of prominence which were not listed as Munro Tops. The 1997 tables promoted five of these to full Munro status.

A total of 197 Munros have a topographic prominence of over 150 m and are regarded by peakbaggers as Real Munros. 130 Scottish mountains over 1000m, with a topographic prominence of over 100 m have been termed Metric Munros.

Other classification schemes in Scotland, such as the Corbetts 2500 to(-) and Grahams 2000 to(-), require a peak to have a prominence of at least 500 ft for inclusion. The Munros, however, lack a rigid set of criteria for inclusion, with many summits of lesser prominence listed, principally because their summits are hard to reach.

Between April 2007 and July 2015 the Munro Society re-surveyed twenty mountains and tops that were known to be close to the 3,000 ft figure to determine their height more accurately. On 10 September 2009 the society announced that the mountain Sgùrr nan Ceannaichean, south of Glen Carron, had a height of 913.43 m. Therefore, the Scottish Mountaineering Club removed the Munro status of Sgùrr nan Ceannaichean and this mountain is now a Corbett. In a Summer 2011 height survey by The Munro Society, Beinn a' Chlaidheimh was found to be 914 m and thus short of the Munro mark. On 6 September 2012, the Scottish Mountaineering Club demoted it from Munro to Corbett status. On 26 August 2020, the SMC confirmed that Beinn a' Chroin West Top at 938m was deleted as a Munro Top and Beinn a' Chroin East Top became the new Munro Top at 940.1m. The summit height of Beinn a' Chroin was also changed to 941.4m. As of 10 December 2020, there were 226 Scottish Munro Tops after Stob Coire na Cloiche, a Munro Top to Parent Peak Sgùrr nan Ceathramhnan, was surveyed at 912.5m and was deleted as a Munro Top and downgraded to a Corbett Top.

As of 2 July 2024, the Scottish Mountaineering Club lists 282 Munros and 226 Munro Tops. The current SMC list; totals 508 summits.

Notable peaks
The most famous Munro is Ben Nevis (Beinn Nibheis) in the Lochaber area. It is the highest peak in the British Isles, with an elevation of 4,411 ft (1,345 m)

Other well-known Munros include:

 * Ben Macdui (Beinn Macduibh), 4,296 ft (1,309.3 m), is the second highest peak in the British Isles; Braeriach (Am Bràigh Riabhach), 4,252 ft (1,296 m), is the third highest peak in the British Isles and Cairn Gorm (An Càrn Gorm), 4,084 ft (1,244.8 m), is the sixth highest peak in the British Isles. These three Munros are located together in the Cairngorms
 * Beinn Teallach, 3,001 ft (914.6 m), in Lochaber is the lowest Munro
 * Ben Hope (Beinn Hòb), 3,041 ft (927 m), in Sutherland is the most northerly Munro
 * Mount Keen (Monadh Caoin), 3,082 ft (939.4 m), in Glen Mark is the most easterly Munro
 * Ben Lomond (Beinn Laomainn), 3,195 ft (973.7 m), at Loch Lomond and The Trossachs National Park is the most southerly Munro
 * Sgùrr na Banachdaich, 3,166 ft (965 m), in the Black Cuillin on the Isle of Skye is the most westerly Munro
 * Schiehallion (Sìdh Chailleann), 3,554 ft (1,083.3 m), in Perth and Kinross, is a Munro often described as lying at the centre of Scotland
 * Bidean nam Bian, 3,771 ft (1,149.4 m); Buachaille Etive Mòr (Buachaille Èite Mòr) (Stob Dearg), 3,351 ft (1021.4 m), at the entrance to Glen Coe, is the most photographed mountain in the British Isles/Buachaille Etive Mòr (Buachaille Èite Mòr) (Stob na Bròige), 3,128 ft (953.4 m); Aonach Eagach (Sgor nam Fiannaidh), 3,175 ft (967.7 m) /Aonach Eagach (Meall Dearg), 3,124 ft (952.3 m), are regarded as the two most difficult Munros for extreme exposure while scrambling including the longest and narrowest ridge on mainland Britain, though it competes with Liathach and An Teallach for this title; and finally Buachaille Etive Beag (Buachaille Èite Beag) (Stob Dubh), 3,143 ft (958 m) /Buachaille Etive Beag (Buachaille Èite Beag) (Stob Coire Raineach), 3,033 ft (924.5 m). These seven Munros are located together in Glen Coe
 * Sgùrr Alasdair, 3,255 ft (992 m); Sgùrr Dearg – Inaccessible Pinnacle, 3,234 ft (985.8 m), is the hardest Munro and the only Munro with a peak that can only be reached by rock climbing and abseiling; Sgùrr a' Ghreadaidh, 3,189 ft (972.1 m); Sgùrr nan Gillean, 3,170 ft (966.1 m); Bruach na Frìthe, 3,146 ft (958.8 m); Sgùrr Mhic Choinnich, 3,111 ft (948.1 m); Sgùrr Dubh Mòr, 3,097 ft (944 m); Am Basteir (Am Baisteir), 3,064 ft (934 m); Sgùrr nan Eag, 3,039 ft (926.3 m) and Sgùrr a' Mhadaidh, 3,012 ft (918 m). These ten Munros including one other (Sgùrr na Banachdaich, as shown above) provide part of the most spectacular, toughest and longest single mountaineering challenge anywhere in the British Isles and are located together in the Black Cuillin on the Isle of Skye
 * Blà Bheinn (Blaven), 3,048 ft (929 m), in the Black Cuillin Outlier (Blaven group) on the Isle of Skye
 * Liathach (Spidean a' Choire Lèith), 3,461 ft (1,054.8 m) /Liathach (Mullach an Rathain), 3,359 ft (1,023.8 m); Beinn Eighe (Ruadh-stac Mòr), 3,314 ft (1,010 m) /Beinn Eighe (Spidean Coire nan Clach), 3,258 ft (993 m) and Beinn Alligin (Beinn Àilleagan) (Sgùrr Mhòr), 3,235 ft (986 m) /Beinn Alligin (Beinn Àilleagan) (Tom na Gruagaich), 3,025 ft (922 m). These six Munros are located together in Torridon
 * An Teallach (Bidean a' Ghlas Thuill), 3,486 ft (1,062.6 m) /An Teallach (Sgùrr Fiona), 3,473 ft (1,058.7 m). These two Munros are located together in Dundonnell
 * Sgùrr na Cìche, 3,413 ft (1,040.2 m) and Ladhar Bheinn, 3,346 ft (1,020 m). These two Munros are located in Knoydart
 * The Saddle (An Dìollaid), 3,318 ft (1,011.4 m), in Glen Shiel
 * A' Mhaighdean, 3,173 ft (967 m), and Slioch (Sleaghach), 3,219 ft (981 m). These two Munros are located together in Wester Ross between the Fisherfield Forest and Letterewe Forest
 * Ben Cruachan (Cruach na Beinne), 3,698 ft (1,127 m), at Loch Awe, gives its name to the Cruachan Power Station (also known as the Cruachan Dam), a pumped-storage hydroelectric power station located in a cavern inside the mountain

Remotest Munros

 * Carn an Fhidhleir, 3,261 ft (994 m), from Linn of Dee via White Bridge has a distance of 11.40 miles
 * A' Mhaighdean, 3,173 ft (967 m), from Incheril via Gleann Bianasdail has a distance of 10.98 miles
 * Beinn Bheoil, 3,343 ft (1,019 m), from Rannoch Lodge via Ben Alder Cottage has a distance of 10.46 miles
 * Ruadh Stac Mor (Ruadh-Stac Mòr), 3,014 ft (918.7 m), from A832 near Corrie Hallie via Shenavall has a distance of 10.37 miles
 * Ben Alder (Beinn Eallair), 3,766 ft (1,148 m), from Corrour railway station via Loch Ossian has a distance of 10.34 miles
 * Mullach na Dheiragain, 3,222 ft (982 m), from A87 near Cluanie Inn via Alltbeithe has a distance of 10.25 miles
 * An Sgarsoch, 3,302 ft (1,006.5 m), from Linn of Dee via White Bridge has a distance of 10.16 miles

Peak bagging
When compared to continental ranges, such as The Alps, Scottish peaks are generally lesser in height. However, walking and climbing in them can still be dangerous and difficult to navigate the recommended routes due to their latitude and exposure to Atlantic and Arctic weather systems. Even in summer, the weather can change quickly in the mountains and conditions can be atrocious; thunderstorms, thick fog, strong winds, driving rain and freezing summit temperatures close to 0°C are not unusual.

Winter ascents of some Munros are serious undertakings due to the unpredictable weather, the likelihood of ice and snow, and poor visibility. Each ascent becomes a test of skill, endurance, and determination, as trekkers navigate through snowdrifts, icy slopes, and unpredictable weather conditions. Some hikers try even unprepared for extreme weather on the exposed tops and fatalities are recorded every year, often resulting from slips on wet rock or ice.

The activity of attempting to climb every Munro is known as "Munro bagging". Munro-bagging is a form of peak bagging. A walker who has climbed all Munros is entitled to be called a Munroist. Descending a Munro by funicular is known as de-bagging.

Notable completions
The Scottish Mountaineering Club maintains a list of walkers who have reported completing the Munros. , there are 7,581 names on the list. (The club uses the spelling compleator for someone who has completed the Munros.)

Hugh Munro never completed his own list, missing out on Càrn an Fhidhleir and Càrn Cloich-mhuillin (downgraded to a Munro Top in 1981). Sir Hugh is said to have missed the Inaccessible Pinnacle of Sgùrr Dearg, on the Isle of Skye, which he never climbed. However the "In Pinn", as it is known colloquially within Scottish mountaineering, was only listed as a Munro Top on his list (despite being several metres higher than Sgùrr Dearg, which was listed as the main Munro Top).

The first "completionist" was to be the Reverend A. E. Robertson, in 1901, later minister at Braes of Rannoch from 1907. However, research has cast doubt on this claim, and it is not certain that he reached the summit of Ben Wyvis. Also it is known that Robertson did not climb the Inaccessible Peak of Sgùrr Dearg. If Robertson is discounted, the first Munroist is Ronald Burn, who completed in 1923. Burn is also (indisputably) the first person to climb all the Munro Tops.

The person with the most rounds of Munros is Steven Fallon from Edinburgh, who has completed 16 rounds as of 1 October 2019.

Chris Smith became the first Member of Parliament to complete the Munros when he reached the summit of Sgùrr nan Coireachan on 27 May 1989.

Ben Fleetwood is probably the youngest person to have completed a round. He climbed the final Munro of his round – Ben More – on 30 August 2011 at the age of 10 years and 3 months. The youngest completionist to have done the round without the presence of a parent or a guardian is probably Andy Nisbet, who finished his round in 1972 aged 18 years and 1 month.

Continuous rounds
Hamish Brown did the first continuous self-propelled round of the Munros (except for the Skye and Mull ferries) between 4 April and 24 July 1974 with 449000 ft of ascent and mostly walking 1639 mi – just 150 mi were on a bicycle. The journey is fully documented in his book Hamish's Mountain Walk. The average time taken to bag all the Munros is eight years.

In 1984 George Keeping accomplished the first continuous round of the Munros entirely on foot (and ferry) in 135 days. He went on to complete the English and Welsh 3,000 foot peaks in a further 29 days.

The first reported completion of all the Munros plus the Munro Tops in one continuous expedition was by Chris Townsend in 1996. His trip lasted between 18 May and 12 September (118 days), he covered a distance of 1770 mi (240 mi by bicycle) with 575000 ft of ascent. The round was broken twice for spells at the office, which could be regarded as stretching the meaning of "continuous".

The first person to complete a winter round (all the Munros in one winter season) was Martin Moran in 1984–85. His journey lasted between 21 December 1984 and 13 March 1985 (83 days), he walked 1028 mi with 412000 ft of ascent. He used motor transport (campervan) to link his walk.

In the winter of 2005–06, Steve Perry completed a continuous unsupported round entirely on foot (and ferry). He is also the first person to have completed two continuous Munro rounds, having also walked Land's End to John O'Groats via every mainland 3,000 ft mountain between 18 February 2003 and 30 September 2003.

Fastest rounds
In 1990, international fell runner and maths teacher Hugh Symonds of Sedbergh, Yorkshire, ran all 277 Munros starting from Ben Hope. It took him 66 days and 22 hours. This also included running the other 3,000 foot peaks in Great Britain. Having achieved this in the short time of 83 days, when his target had been a hundred, he decided to add the Republic of Ireland tops to the list and still finished all 303 peaks in 97 days.

In July 1992, Andrew Johnstone of Aberdeen and Rory Gibson of Edinburgh completed their mountain triathlon across the Munros, the 277 Scottish peaks over 3,000 ft, beating the existing record by five days. They began on 29 May and finished at 8.30pm on 15 July on the summit of Ben Hope, the most northerly Munro, completing a journey which began 51 days and 10 hours earlier on the Isle of Mull. After swimming lochs, cycling highland roads and running across some of the most desolate and dangerous terrain in Britain, they covered 1,400 miles.

Charlie Campbell, a former postman from Glasgow, held the record for the fastest round of the Munros between 2000 and 2010. He completed his round in 48 days, 12 hours and 0 minutes, finishing on 16 July 2000, on Ben Hope. He cycled and swam between Munros; no motorised transport was used.

Campbell's record was broken by Stephen Pyke of Stone, Staffordshire, in 2010 who completed the round in 39 days, 9 hours and 6 minutes. Pyke's round started on the Isle of Mull on 25 April 2010 and finished on Ben Hope in Sutherland on 3 June 2010. He cycled and kayaked between Munros; no motorised transport was used. He was backed by a support team in a motor home, but had to camp out in the more remote areas.

On 18 September 2011, Alex Robinson and Tom O'Connell finished a self-propelled continuous round on Ben Hope in a time of 48 days, 6 hours and 56 minutes. At the age of just 21, Alex became the youngest person to have completed a continuous round without the use of any motorised transport.

On 17 September 2017, the women's self-propelled, continuous record was broken by Libby Kerr and Lisa Trollope in 76 days and 10 hours. This record would later be vastly broken by Jamie Aarons on 26 June 2023 who would also break the record for both the male and female fastest ever round.

On 2 September 2020, Pyke's record was broken by Donnie Campbell of Inverness. He completed his round in 31 days, 23 hours and 2 minutes, starting on the Isle of Mull on 1 August 2020 and finished on Ben Hope on 2 September 2020. Campbell ran the 282 Munros and cycled and kayaked between them. On day 29, he was joined by previous record holder Stephen Pyke. Whilst ticking off Mòruisg in the cloud, he mistook the big cairn for the summit and had to head back up and so climbed the Munro twice. On day 31, he completed 18 Munros. He was supported by a crew travelling in his motorhome, who also shuttled his bike for him to follow a more linear route.

On 26 June 2023, Jamie Aarons of California broke the previous record of fastest ever round held by former marine Donnie Campbell by more than 12 hours by completing a self-propelled continuous round in 31 days, 10 hours and 27 minutes. She also ran, cycled and kayaked between each of the Munros, covering a total of around 932 miles (1,500 km) on foot and about the same distance by bike. She began at Ben More on Mull and ended at Ben Klibreck in Sutherland, raising £14,000 for World Bicycle Relief.

Furths
The SMC recognises six peaks in England, fifteen in Wales and thirteen in Ireland that would be Munros or Munro Tops if they were in Scotland. These are referred to as Furth Munros, i.e. the Munros furth of Scotland. The first recorded Furthist is James Parker, who completed on Tryfan (Snowdonia) on 19 April 1929.

General references

 * The Munros (SMC Guide), Donald Bennet et al., ISBN 0-907521-13-4

title: Munro


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