High-speed 2-D image measurement for plasma-wall interaction studies

A movable carbon target with a head diameter of 9 cm was inserted into the peripheral region of a Heliotron J plasma. High-speed, two-dimensional images of filtered visible light emission near this target were taken by a C-MOS video camera. In high-density ECH discharges (70 GHz, 0.3 MW, n ¯ e > 1.5 × 10 19 m−3) it was observed that a striped pattern of Hα light moved along the poloidal direction. Simultaneously, other diagnostic data (ECE signals, line integral electron density, ion saturation currents of Langmuir probes) showed plasma oscillation at a frequency of 5–6 kHz. Individual signals from pixels of the visible camera images indicate that the oscillation phase is approximately constant along the field line, suggesting that coherent structure phenomena along the field line are present in the high-density plasmas of Heliotron J.