Longitudinal Electric Field in the Ohmic and Electron Cyclotron Resonance Regimes of Plasma Heating at the L-2M Stellarator

Abstract

A method for determining the longitudinal electric field from the spectrum of soft X-ray radiation is used to measure the radial distribution of the longitudinal electric field. In the ohmic heating regime, statistically reliable spectra of soft X-ray radiation were measured at the L-2M stellarator. It was obtained that the longitudinal field is distributed approximately uniformly over the radius. Comparison of the measured soft X‑ray radiation (SXR) spectra with the model bremsstrahlung spectrum of magnetized plasma in the longitudinal electric field has shown that at energies W > 3 keV, the measured spectrum deviates markedly not only from the Maxwellian one but also from the model spectrum of magnetized plasma in an electric field. Using SXR spectra that were measured in the regime of electron cyclotron resonance (ECR) plasma heating (without the ohmic-heating current), estimates are made of the longitudinal electric field that may occur in plasma due to drag currents, which are created during ECR heating. The dependence of the electric field on the plasma density was measured and it was shown that it agrees with the dependence of the difference current flowing through the plasma on the density.