Advances in the physics of steady-state plasmas by long pulse experiments on Tore Supra

Abstract

Long pulse, multi-MW operation on Tore Supra, with active control of the main plasma parameters and new diagnostics, has allowed the investigation of several important issues relevant to the physics of steady-state plasmas, sometimes leading to the discovery of new physics effects. Results obtained in the most recent experimental campaigns are reported. Discharges lasting several resistive times, with combined LHCD and minority ICRH at high power level (>10 MW) in plasmas close to the Greenwald limit, at Te ∼ Ti, were realized. In these discharges, toroidal rotation velocities of the order of 50 km s−1 induced by ICRH were measured by charge exchange spectroscopy. Doppler backscattering was used to complete these measurements and to provide turbulence spectra. MHD phenomena characteristic of steady-state plasmas, such as double tearing modes, were studied using a new 32-channel ECE radiometer and correlation ECE. After the discovery of stationary regimes characterized by non-linearly coupled temperature and current oscillations, a new regime was observed, characterized by spontaneous transitions between two cycles of electron temperature oscillations: low-amplitude (ΔTe/Te ∼ 0.1) and giant (ΔTe/Te > 0.5).