Observation of Highly Asymmetric Radiative Collapse of NBI Heated Plasma in LHD

摘要

During discharges in the Large Helical Device (LHD), the plasma radiated power has been measured by several bolometry systems mounted on different ports of the machine. The spatial structure of the radiation during the period prior to the termination of Neutral Beam Injected (NBI) heated plasmas was also investigated using multi-channel bolometric diagnostics. During discharges with strongly radiative collapse (RC) a highly asymmetric radiation profile which is stronger on the inboard side was observed beginning about 50 ms prior to the quench of the plasma. This asymmetry is spatially and temporally well correlated with the degradation of signal from the multi-chord interferometer, which presumably results from beam deflection due to large density gradients. Moreover, there is evidence that in LHD this poloidally asymmetric radiation distribution during RC may be toroidally symmetric. These results indicate that a phenomenon similar to Multifaceted Asymmetric Radiation from the Edge (MARFE), which has been observed widely in tokamaks, also exists in LHD.