Plasma confinement during ECR heating with a volume power density of 3 mW/m3 at the L-2M stellarator

The experiments on ECR plasma heating were carried out at the L-2M stellarator at very high volume power density (up to 3.0 MW/m3). Under these conditions, non-monotonous hollow density profiles were measured. At the maximum heating power of P = 0.75 MW, the concavity in the axial region becomes drastic ne(0)/ne max = 0.5. In these experiments, plasma temperature profiles measured in the axial plasma region r/ap < 0.4 occur to be rather flat. We have also measured two-slope SXR spectra in the range from 2 to 12 keV. The possible reasons for these observed phenomena were discussed. However, with growing ECRH power up to PECRH = 0.75 MW, we have not observed dramatic deterioration of plasma confinement at the L-2M stellarator. The measured energy lifetime is generally consistent with that determined from the international LHD scaling. © Published under licence by IOP Publishing Ltd.