Divertor detachment and asymmetry in H-mode operation with an ITER-like tungsten divertor in EAST

Abstract

The detached divertor has recently been achieved in H-mode plasmas in EAST with an ITER-like tungsten divertor, which is essential for high power long pulse operation in the near future. The divertor detachment is indicated by the rollover of particle flux and the drop in electron temperate down to ~5 eV, as measured by the Langmuir probes at the divertor target, as the plasma density increases. The density threshold of detachment increases with heating power, and is higher with combined neutral beam injection (NBI) and radiofrequency heating than NBI only. The divertor detachment exhibits a strong in–out asymmetry for favorable BT, i.e. with the ion B × drift direction toward the X-point. In contrast, with reverse toroidal field, the particle flux near the outer strike point first increases with density, then maintains nearly constant, without pronounced roll-over, when the divertor plasma enters the detachment regime, and the onset of detachment between inner and outer divertors becomes nearly balanced, as expected from the effect of drifts.