Soft X-Ray Spectra of Plasma in High-Power ECR Heating Regime

The effect of the induced longitudinal (along the toroidal magnetic field) electric field on the shape of soft X-ray spectra in the regime of electron cyclotron resonance (ECR) heating of plasma in the L-2M stellarator is considered. Causes of the appearance of non-Maxwellian two-slope spectra of soft X-rays measured in the axial ECR plasma heating regimes at the introduced microwave powers of 200–400 kW are analyzed. In the authors' opinion, the two-temperature spectral shape arises due to the fact that radiation coming from two plasma regions falls in the field of view of the spectrometer when measuring the spectra along the central chord. A radiation fraction comes from the axial plasma region; another fraction comes from the heating region which in the high-power ECRH regime is approximately at half the plasma radius, rather than at the plasma center.