Role of Radiation Loss in Transport Processes in Self-Organized Plasma of the L-2M Stellarator

In many tokamaks, the effect of improving plasma energy confinement after injecting impurities, and accordingly, increasing radiation loss is observed. In this paper, we experimentally study whether this effect is observed at the L-2M stellarator. We ascertained that for the L-2M stellarator, in the range of operating parameters, the energy lifetime does not depend on the radiation loss power. We propose a mechanism for explaining the improvement in energy confinement observed in tokamaks with limiters after injecting light impurities. The safety factor gradient at the plasma edge increases after impurities are injected, as does the shear of poloidal rotation velocity. As a consequence, turbulent flows are suppressed, resulting in an improvement in plasma energy confinement. In stellarators, this mechanism does not work since the angle of rotational transformation is rigidly set by the coils of the facility magnetic system. The plasma confinement in the L-2M is not deteriorated after increasing radiation loss power due to the action of the plasma self-organization processes.