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

The present paper reports on studies of short-wave turbulence in plasma of 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 10¹³ /cm^-3. The energy lifetime was ∼ 3.5 ms at P₀ = 100 kW and dropped to about 2 ms at a P₀ = 200 kW. When the limiter was introduced inside the plasma to a depth of 2 cm from the last closed flux surface, τ_e decreased by a factor of 1.3 - 1.4. Plasma density fluctuations were measured from the scattering spectra of gyrotron radiation at the second harmonic of operating frequency (∼ 150 GHz). A quasioptical receiving system allowed measurements of scattered radiation from plasma regions r/a ≤ 0.6 at scattering angles π/ 4 ≤ θ ≤ π/ 2(24cm^-1 ≤ k_{perpendicular} ≤ 44cm^-1) . The short-wave turbulence was studied for two radial positions -perpendicular of the scattering region: r/a = 0.3 - 0.4 and r/a = 0.5 - 0.6. Short-wave turbulence related connected with ETG instability in core plasma of L-2M stellarator was investigated by the method of collective scattering of gyrotron radiation on the second harmonic of operating frequency. It is shown, that short-wave turbulence is close to the type of strong plasma turbulence. It is shown, that decreasing of energy lifetime power at doubling of the power of ECR heating correlates with growth of energy of short-wave noise. It is established, that cooling of plasma near last close surface by means of a sector limiter causes decreasing of falling energy lifetime and growth of short-wave turbulence in core plasma. Thus, it is experimentally established, that change of energy lifetime in L-2M stellarator correlates with the level of short-wave turbulence. (author)