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The dynamics of runaway electrons in tokamaks are investigated theoretically by taking into account the acceleration in the toroidal electric field, the collisions with the plasma particles, the deceleration due to synchrotron radiation and the resonance of their gyromotion with the ripple of the toroidal magnetic field. With this ripple resonance mechanism the momentum parallel to the magnetic field is converted into momentum of the gyromotion. As a consequence the synchrotron radiation losses are increased and can balance the energy gain in the electric field, such that the energy of the runaways stays constant. So the maximum energy which is finally reached is much lower than the maximum possible energy of about 65 MeV, which is obtained if they move on a circle centred on the torus axis. The runaway electrons which are captured in a ripple resonance form a monoenergetic electron beam. These extremely monoenergetic runaways fulfil the conditions necessary for a free-electron maser. The maser radiation of the runaways, which lies in the microwave region, is clearly detected on ASDEX Upgrade.

Additional information

Authors: KURZAN B, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Report: IPP 1/287 DE (1995) 89 pp.
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
Record Number: 199510872 / Last updated on: 1995-08-03
Original language: de
Available languages: de