Deviation of the electron energy distribution function from maxwellian during ECR heating in the L-2M stellarator in regimes with a high specific heating power

Abstract

In the previous experiments on ECR heating of a low-density plasma with n e =(0.3−0.5)×1019 m−3 in the L-2M stellarator, the electron temperature profile measured from the intensity of electron cyclotron emission was found to be asymmetric about the magnetic axis and the electron temperature measured by this diagnostics turned out to be higher than that expected from diamagnetic measurements. To find out the character of distortion of the electron energy distribution function, the soft X-ray spectrum was measured in regimes with large values of the specific heating power η (1.5 MW per 1019 particles). Under these conditions, the X-ray spectrum plotted on a semilogarithmic scale has no linear segments in the photon energy range from 1.5 to 12 keV. This indicates that the electron distribution function is non-Maxwellian over the entire energy range under study.