ELM elimination via lithium pellet gravitational injection into H-mode plasmas using the ITER-like tungsten divertor on EAST*

A reproducible, fully non-inductive, low q95, H-mode regime devoid of large ELMs has been achieved by Li granule gravitational injection in EAST with tungsten divertor, extending previous results with Li powder [J.S. Hu et al., PRL 114 (2015) 055001, R. Maingi et al. Nucl. Fusion 58 (2018) 024003]. Spherical Li pellets with 0.7mm diameter were gravitationally delivered by a new impurity powder dropper above the top X-point. Li pellets injected into the scrape-off layer of low q95(3.8), low natural ELM frequency(70Hz) and high auxiliary heating (8MW) plasmas successfully eliminated ELMs for 2.5s. These discharges did not suffer from density or impurity accumulation and constant core radiated power was maintained. The observed ELM elimination is correlated with a decrease in particle recycling with significantly reduced Dα baseline emission, with a stronger effect on wall conditioning than Li powder injection. Because granules can penetrate farther into the scape-off layer than powder, their extrapolability to future devices is more promising than pure powder injection.