Greifswald 2009 – scientific programme

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SYPA: Energetic Particle Acceleration in Space and Laboratory

SYPA 1: Particle Acceleration

SYPA 1.3: Invited Talk

Wednesday, April 1, 2009, 18:00–18:30, Zahnklinik

On runaway electrons — •Per Helander — Max Planck Instiut für Plasmaphysik, Greifswald

This talk will give a broad overview of the physics of runaway electron acceleration in fusion research, in the Earth's atmosphere and in solar flares. As is well known, the collisional friction that an electron experiences in a plasma decreases with energy. As a result, a steady electric field can lead to virtually unlimited acceleration of electrons above a certain energy threshold. In so-called tokamak "disruptions", this mechanism can convert several mega-amperes of plasma current into a beam of multi-MeV electrons, which can seriously damage the wall on impact. At the same time, it accidentally converts the tokamak into a laboratory for relativistic electron physics, where phenomena such as synchrotron radiation damping and electron-positron pair production take place. The situation is exacerbated by several mechanisms that provide the "seed" of fast electrons from which the runaway avalance can grow. Large-angle collisions, which are not accounted for by the usual Fokker-Planck equation, provide the most efficient mechanism for runaway electron generation in large tokamaks, and are also thought to be responsible for triggering lightning in thunderstorms.