Study of MARFE during lower hybrid current drive in HT-7 tokamak

Abstract

Lower hybrid current drive (LHCD) experiments have been carried out to achieve high performance for long pulse operation in the HT-7 superconducting tokamak. Multifaceted asymmetric radiation from the edge (MARFE) phenomena, is observed in LHCD plasmas when P LH > 160 kW and edge safety factor q ( a ) is slightly less than 6.5 and has been studied in this Letter. Studies show that the critical density of MARFE onset is observed in the region of Z eff 1 / 2 f GW = 0.6 – 0.9 , where f GW = n ¯ e n GW (here n ¯ e is the maximum line average electron density and n GW is the Greenwald density). These MARFEs generally appear to have the same characteristics as high f GW MARFEs and are positionally stable throughout the LHCD pulse.