Electron temperature measurement by Thomson scattering in a low-aspect-ratio RFP RELAX

A Thomson scattering diagnostic system has been developed for measuring electron temperatures in low-aspect-ratio reversed-field pinch (RFP) plasmas in REversed-field pinch of Low Aspect ratio eXperiment (RELAX). In the range of plasma currents I_p = 50 - 80 kA, the central electron temperature was around 100 eV and, showed a weakly increasing trend as I_p increases. To estimate the central electron pressure p_e0, a density calibration was performed from simultaneous measurements with a 104-GHz microwave interferometer. The maximum p_e0 increased with I_p up to ∼ 70 kA to preserve the approximate relation p_e0/B_θa² ∼ constant, where B_θa is the edge poloidal field. In the higher current region, p_e0 tended to saturate, which may be improved by optimizing minute control of equilibrium in the higher current region. (author)