On the Issue of Existence of a Soft X-Ray Pit in the Ohmic and ECR Plasma Heating Regimes at the L-2M Stellarator

An attempt to detect the soft X-ray pit (SXR-pit) phenomenon at the L-2M stellarator has been made in different plasma heating regimes using direct spectral measurements. The abnormally strong absorption of soft X-ray plasma radiation in its passing through beryllium foils with thicknesses of 90 μm or more is called the SXR-pit phenomenon; it has been observed at the T-11M tokamak and a number of other tokamaks. A scanning spectrometer and multichord diagnostics of soft X-rays were used in the experiment. It is shown that the SXR-pit phenomenon was not observed at the L-2M stellarator with the plasma parameters similar to those at the T-11M tokamak either in the ohmic heating regime or in the regime of electron-cyclotron-resonance plasma heating.