High Frequency ELM Pacing by Lithium Pellet Injection on DIII-D

Full-shot, high-frequency pacing of edge localized modes (ELM) by lithium pellet injection has been demonstrated in DIII-D. A Lithium Granule Injector (LGI), recently installed on DIII-D to study pacing efficiency dependence on granule size and velocity, was tested in different ELMy scenarios ($\beta _{\mathrm{N}}=$1.2-2.0) injecting granules of nominal diameter 0.3-0.9~mm, with injection speed 50-120~m/s and injection rates up to 500~Hz. Robust ELM pacing was documented on time windows up to 3.5~s, with triggering efficiency close to 100{\%} obtained with 0.9~mm diameter granules, lower with smaller sizes and weakly dependent on granule velocity. Paced ELM frequencies up to 100~Hz were achieved, with a 2-5 fold increase over the natural ELM frequency and a consequent reduction of divertor peak heat flux. Overall, LGI high frequency pacing appeared to be compatible with high plasma performance, in terms of global confinement and pedestal characteristics.