A synchrotron radiation diagnostic to observe relativistic runaway electrons in a tokamak plasma

In present day tokamaks runaway electrons can be confined long enough to ga in energies in the order of several tens of megaelectron volts. At these en ergies synchrotron radiation is emitted in the infrared wavelength range wh ich can easily be detected by thermographic cameras. The spectral features of this synchrotron radiation are reviewed. On TEXTOR-94 a diagnostic explo iting this synchrotron radiation has been developed and is presented here. It is shown how to deduce the runaway parameters like runaway energy, pitch angle, runaway current and beam radius from the measurements. Based on the experience at TEXTOR-94 the feasibility of a similar synchrotron diagnosti c on the International Thermonuclear Experimental Reactor is discussed. The maximum emission is expected in the wavelength range from 1-5 mum. A beam of 10 MeV runaway electrons with a current of about 15 kA will already be d etectable. (C) 2001 American Institute of Physics.