Effect of supersonic molecular beam injection deposition on edge localized mode mitigation in the HL-2A H-mode plasmas

Abstract

The ELM (edge localized mode) mitigation by SMBI (supersonic molecular beam injection) has been studied in the HL-2A H-mode plasmas. The ELM mitigation effect and its relationship with the deposition position of SMBI in the H-mode pedestal are reported for the first time experimentally. We found that when the deposition of SMBI is about 20% into the pedestal, the best ELM mitigation effect is achieved, which is identified by a significant increase of the ELM frequency and also a decrease of the ELM amplitude. The theoretical inference that no deep injection is needed is confirmed. The sand-pile model is used to simulate the ELM burst and explain the mitigation effect for different SMBI deposited positions. It is found that the gradient threshold is a key parameter in the process of the ELM mitigation, and there should be a local gradient threshold in the middle of the pedestal. When the deposition of SMBI is close to the edge of this region, the best ELM mitigation effect can be observed.

A review of supersonic molecular beam injection for plasma fueling and physical studies in magnetic fusion devices

“…SMBI has also been demonstrated to be an effective and flexible approach to control ELMs on HL-2A (Xiao et al , 2014bYang et al 2016), KSTAR (Xiao et al 2014b;Kim et al 2012) . and EAST (Hu et al 2015) (Wan et al 2015), in which the SMBI-induced minor instabilities such as turbulence and high-frequency bursts can prevent large ELMs.…”

“…37 Deposition of SMB and its effect on ELMs. The electron density profile of edge plasma (black line), and the ratio of frequency, energy lost, and heat flux changed during SMBI (Yang et al 2016) distinct possibility that the pedestal turbulence-related particle transport is responsible for ELM mitigation.…”

“…The depth is related to the operation scenario. A shallower deposition is usually observed in H-mode discharges than in L-mode discharges Yang et al 2016).…”

Simulation of helium supersonic molecular beam injection in tokamak plasma*

“…Specifically, supersonic molecular beam injection (SMBI) has been a promising technique for ELM mitigation. [6] The deposition location [7] and the cooling effect [8] of SMBI are relevant to ELM mitigation. According to the experimental results on HL-2A, it is found that the performance of ELM mitigation by the helium (He) is better than that by the deuterium due to the fact that the duration of ELM mitigation with helium SMBI (∼ 40 ms) is much longer than with deuterium SMBI (∼ 10 ms).…”

Simulations of fast component and slow component of SMBI on HL-2A tokamak

“…An improved SMBI with clusters, which are like micro-pellets, can be injected more deeply. [5] Besides being used in the plasma fuelling, SMBI can also be applied to study plasma impurity transport, [6][7][8] L-H transition and confinement improvement, [9][10][11] edge localized mode (ELM) mitigation, [12][13][14][15][16][17][18] and nonlocal heat transport. [19][20][21][22] Since the fuelling efficiency depends on the penetration depth, some experiments have been carried out to improve the SMBI penetration depth on the HL-2A tokamak.…”