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

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 PLH>160kW 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 Zeff1/2fGW=0.6-0.9, where fGW=n¯enGW (here n¯e is the maximum line average electron density and nGW is the Greenwald density). These MARFEs generally appear to have the same characteristics as high fGW MARFEs and are positionally stable throughout the LHCD pulse.