Sustained Detachment with the Self-Regulated Plasma Edge beneath the Last Closed Flux Surface in LHD

Abstract

Self-sustained detachment has been obtained in the Large Helical Devise (LHD). Strong hydrogen gas puffing of ˜200 P•am³/s after a density feedback phase successfully detaches the plasma from the divertor plate with high reproducibility. High electron density of over 1 × 10²⁰ m^-3 is sustained without gas puffing until the heating beam stops and the high-density flat top for 2 seconds has been demonstrated. Throughout the detachment phase, the minor radius of the hot plasma column shrinks to ˜90 % of the last closed flux surface, which corresponds to the ι/2π = 1/q = 1 rational surface.