Relativistic runaway electrons in tokamak plasmas

An experimental study of the generation of runaway electrons in TEXTOR has been perfonned. From the infrared synchrotron radiation emitted by relativistic electrons, the number of runaway electrons can be obtained as a function of time. In low density discharges cne < lxl019 m-3) runaways are created throughout the discharge and not predominantly in the start-up phase. From the exponential increase in the runaway population and the ongoing runaway production after increasing the density, it is concluded that the secondary generation, i.e. the creation of runaways through close collisions of already existing runaways with thennal electrons, provides an essential contribution to the runaway production. The effective avalanche time of this secondary process is determined to be leff = 0.9 ± 0.2 s.

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