Injected mass deposition thresholds for lithium granule instigated triggering of edge localized modes on EAST

Abstract

The ability of an injected lithium granule to promptly trigger an edge localized mode (ELM) has been established in multiple experiments. By horizontally injecting granules ranging in diameter from 200 microns to 1mm in diameter into the low field side of EAST H-mode discharges we have determined that granules with diameter > 600 microns are successful in triggering ELMs more than 95% of the time. It was also demonstrated that below 600 microns the triggering efficiency decreased roughly with granule size. Granules were radially injected from the outer midplane with velocities ~ 80 m/s into EAST upper single null discharges with an ITER like tungsten monoblock divertor. These granules were individually tracked throughout their injection cycle in order to determine their efficacy at triggering an ELM. For those granules of sufficient size, ELM triggering was a prompt response to granule injection. By simulating the granule injection with an experimentally benchmarked neutral gas shielding (NGS) model, the ablatant mass deposition required to promptly trigger an ELM is calculated and the fractional mass deposition is determined.

Numerical simulation of Li-pellet injection experiments for ELM-pacing in EAST

“…The parameter θ is the angle between magnetic field direction and the toroidal direction, and it can be derived from averaged magnetic field pitch provided by SOLPS. Simulations are carried out by using those parameters reported originally in [18]. to fit as closely as possible to EAST experiments.…”

“…Besides, advantages of low-Z impurity for improving plasma performance by wall conditioning had been reported in lithium related experiments [12][13][14][15]. Following these pioneering works, many positive results of Li-pellet ELM triggering were then obtained in several important fusion devices, such as EAST [16][17][18], DIII-D [19], ASDEX-U [20] and NSTX-U [21].…”

“…ELM triggering requires that the injected pellet provide a sufficient perturbation to the background plasma, but the perturbation must be well controlled, avoiding deteriorating the energy confinement severely. Recent experiments on EAST show that substantial progress has been made in narrowing down the parameter range of Li pellet injections for ELM triggering, but there are still some uncertainties in choosing the parameters for Li pellet injections such as pellet size and injection velocity [17,18]. Correspondingly, the efficiency of Li pellet ELM triggering in EAST experiments exhibited some probabilistic behavior.…”

Observations of dust fragmentations in the Experimental Advanced Superconducting Tokamak

“…2018; Block & Melzer 2019), particle injections and transports (Delzanno & Tang 2014; Lunsford et al. 2018) and the characteristics of dust particles (Arnas et al. 2017; Pardanaud et al.…”

“…In recent years, studies of dust particles in fusion devices have been carried out in many aspects, including the generation and re-deposition of dust particles (Tolias et al 2016;Ratynskaia et al 2016Ratynskaia et al , 2018, the interaction between dust particles and plasma (Laux, Balden & Siemroth 2014;Autricque et al 2018;Block & Melzer 2019), particle injections and transports (Delzanno & Tang 2014;Lunsford et al 2018) and the characteristics of dust particles (Arnas et al 2017;Pardanaud et al 2020;Pan et al 2022). The applications of fast cameras provide an important method for particle and plasma diagnosis (Ratynskaia et al 2011;Shalpegin et al 2015).…”