Effect of ECRH regime on characteristics of short-wave turbulence in plasma of the L-2M stellarator

This paper reports on studies of short-wave turbulence in the plasma of the L-2M stellarator under markedly different conditions: with doubling the ECR heating power (100 and 200 kW) and with restricting the plasma radius by a sector limiter. The role of such short-wave turbulence in anomalous transport can appear important for conditions of a thermonuclear reactor. Experiments were carried out in a basic magnetic configuration of the L-2M stellarator during ECRH at the second harmonic of the electron gyrofrequency (75.3 GHz) at average electron densities of (1.5-1.7) x 10(13) cm(-3). The energy confinement time was similar to 3.5 ms at P-0 = 100 kW and was reduced to similar to 2 ms at P-0 = 200 kW. When the limiter was introduced inside the plasma to a depth of 2 cm from the last closed flux surface, tau(E) decreased by a factor of 1.3-1.4. Plasma density fluctuations were measured from the scattering of gyrotron radiation at the second harmonic of operating frequency (similar to 150 GHz). A quasioptical receiving system allowed measurements of scattered radiation from plasma regions r/a <= 0.6 at scattering angles pi/4 <= Theta <= pi/2 (24 cm(-1) <= k(perpendicular to) <= 44 cm(-1)). The short-wave turbulence was studied for two radial positions of the scattering region: r/a = 0.3-0.4 and r/a = 0.5-0.6. Short-wave turbulence exhibits features of strong plasma turbulence. It is experimentally established that a change in the energy confinement time in the L-2M stellarator correlates with the level of short-wave turbulence.