- Person
- Lev Landau
- Lived
- 1908–1968
- Field
- Theoretical Physics
- From
- Soviet
The story
A plasma is a hot gas of electrically charged particles, the state of matter found in the Sun, in lightning and inside fusion reactors. Waves of electric charge can travel through a plasma much as sound travels through air. In 1946 Lev Landau, then head of the theoretical division at the Institute for Physical Problems in Moscow and already one of the most versatile physicists in the world, analysed how such waves behave and found a surprising result.
Normally a wave dies away because the particles it passes through collide and turn its energy into heat. Landau showed that in a plasma, waves can lose energy and fade even when the particles almost never collide. The key lies in the particles moving at nearly the same speed as the wave. The wave speeds up particles travelling slightly slower than itself and slows down those travelling slightly faster. In a typical plasma the slower particles outnumber the faster ones, so on balance the particles absorb energy from the wave and it is damped.
The result was a striking piece of theory, worked out from the equations governing a collisionless plasma. Later the Dutch physicist Nico van Kampen showed that the same result could be obtained by a different mathematical route, and in 1964 the physicists John Malmberg and Charles Wharton demonstrated Landau damping experimentally, almost two decades after Landau's prediction.
Landau damping is now a fundamental concept of plasma physics. Because it removes energy from waves, it can stop instabilities from growing and keep a plasma stable. The astrophysicist Donald Lynden-Bell later argued that a similar process operates in galaxies, where a 'gas' of stars interacting through gravity takes the place of charged particles. The effect is reproduced in computer simulations used to model plasmas.
Landau's name is honoured in the field today: the American Physical Society's Landau-Spitzer Award, which recognises outstanding contributions to plasma physics and collaboration between Europe and the United States, is named in part after him.
Why it matters
Landau damping is essential to understanding fusion plasmas, space weather, particle accelerators and even the dynamics of galaxies.
About Lev Landau
Baku-born prodigy who founded the great Soviet school of theoretical physics, survived Stalin’s prison, explained superfluid helium and won the 1962 Nobel Prize.
More about Lev Landau
- Landau co-discovered the quantum density matrixIn the late 1920s, while still a teenager, Lev Landau independently introduced the density matrix, a basic tool of quantum physics, alongside John von Neumann.
- Lev Landau explained frictionless superfluid heliumLev Landau explained why liquid helium flows without friction below 2.17 K, introducing phonons and 'rotons'; it won him the 1962 Nobel Prize in Physics.
- Landau's Fermi liquid theory explains metalsIn 1956 Lev Landau introduced Fermi liquid theory, explaining why electrons in metals and atoms in liquid helium-3 behave almost like free particles.
- The Ginzburg–Landau theory explains superconductorsLev Landau and Vitaly Ginzburg created the Ginzburg–Landau theory of superconductivity, work that helped win Ginzburg and Landau's student Abrikosov the 2003 Nobel Prize.
- Landau levels underpin the quantum Hall effectIn 1930 Lev Landau showed that electrons in a magnetic field occupy discrete energy levels, now called Landau levels, key to explaining the quantum Hall effect.
- Landau and Lifshitz wrote physics' great textbook seriesWith his student Evgeny Lifshitz, Lev Landau began the ten-volume Course of Theoretical Physics, still used by graduate physics students worldwide.
- Landau's 'Theoretical Minimum' trained a generationLev Landau's famous 'Theoretical Minimum' exams, passed by only 43 candidates from 1934 to 1961, created the Soviet Union's greatest school of theoretical physics.
- Landau's theory explains how matter changes stateLev Landau's theory of second-order phase transitions introduced the 'order parameter', still a broad and powerful framework for how matter changes state.
Sources
- Landau damping Wikipedia
- Lev Landau Wikipedia
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