Simultaneous ion temperature and flow measurements using a retarding field analyzer in the HL-2A tokamak

A retarding field analyzer (RFA) was designed and built for use on the HL-2A tokamak to simultaneously measure the ion temperature and plasma flow velocities in the scrape-off layer via a reciprocating probe drive. The probe was built with many off-the-shelf components, making it even more attractive as a diagnostic tool. The probe consisted of two back-to-back RFA analyzers aligned along the toroidal magnetic field lines to measure the downstream and upstream ion temperatures. The true ion temperature was obtained by averaging the two temperatures. RFA measurements on HL-2A have consistently reported ion temperatures higher than electron temperature with ion-to-electron temperature ratios in the range 1-3. The entrance slit plates of the RFA were used as Mach probes for plasma flow measurements, a first among published RFA experiments.