Generation and diagnostics of fast electrons within tokamak plasma

The first part of this invited paper is devoted to mechanisms of the production of fast electrons in plasma experiments involving magnetic traps of the tokamak type. The phenomenon of generation of the so-called runaway electrons - which may reach energies up to several dozen MeV - is considered and basic characteristics of such electrons are described. In particular, the orbits of the runaway electrons and their energy limits are presented. Problems related to the cross-field transport in tokamak plasmas and interactions of the relativistic electrons with plasma oscillations are also considered. Production of the so-called ripple-born electrons, which may be observed in the energy range from approximately 50 keV to several hundreds keV, is analyzed separately. In the second part of this paper various diagnostic methods used for investigation of the runaway and ripple-born electrons are presented. Various techniques are described, which are based on different reactions induced by the runaway electrons, e.g., the emission of X-rays or neutrons, or the synchrotron radiation. Finally, a modern technique of electron measurements is described, which was developed by the author's team at the Andrzej Sołtan Institute for Nuclear Studies (IPJ) in Świerk (Poland), and which is based on the use of Cherenkov-type detectors. Examples of applications of the discussed techniques in different tokamak experiments are described. Particular attention is paid to the Cherenkov detectors, which have already been used in experiments at the small-size CASTOR device in Prague (Czech Republic), the ISTTOK machine in Lisbon (Portugal), as well as in the larger TORE-SUPRA facility in Cadarache (France).