Behaviour of runaway electrons in the ''Tuman-2'' device

In a tokamak with plasma compression by an increasing toroidal field runaway electrons were observed by excited hard X radiation. By shifting plasma with the aid of a rapidly varying transverse field it was established that at the stage of joule heating runaway electrons are usually localized near plasma surface in a layer of thickness approximately 1 cm. The oscillations in the intensity of the X radiation made it possible to determine some characteristics of the instability which causes them. Under plasma compression by the toroidal magnetic field the energy of the runaway electrons increases from 400-500 keV to 1 MeV within approximately 100 μs. This increase cannot be attributed to longitudinal electron acceleration alone; it is assumed that the electrons possess a considerable transverse energy, which increases with the toroidal field in compression. Thus, the experiments carried out point to the existence in tokamak plasma of a group of electrons with an energy of several hundred keV, a considerable part of which is the energy of the Larmor rotation. The abrupt increase in the energy of such electrons on magnetic compression speeds up their arrival at the diaphragm