Recent H-mode Results on ECH Plasmas in Heliotron J

Abstract

Recent 70-GHz, 0.4-MW ECH experiments in Heliotron J have revealed the existence of the spontaneous confinement transition, like that of the H-mode, at rather low threshold line-averaged densities of 1.2-1.6 × 10¹⁹ m^-3. The transition was discovered in two edge-iota windows: one is 0.54 < ι(a)/2π < 0.56 at separatrix discharge plasmas and the other is 0.62 < ι(a)/2π < 0.63 at partial walllimiter discharge plasmas. The energy confinement time for the separatrix discharge plasmas was found to be enhanced beyond the normal ISS95 scaling in the transient H-mode phase, being 50% longer than that in the “before transition” phase.