Intermittent convective transport suppressed by supersonic molecular beam injection on the HL-2A tokamak

Abstract

Edge localized mode (ELM)-filament statistical characteristics and intermittent convective transport are studied during ELM mitigation (10-30 ms) induced by supersonic molecular beam injection (SMBI) on the HL-2A tokamak. Langmuir probe data show that the burst rate of large amplitude filaments (δn e > 4σ ) decreases by 30-50% and their radial velocity decreases by 40-60%, which is an indication of an E × B amplitude reduction. A decrease of long-range correlation along the magnetic flux surface is observed after SMBI, indicating a role of electron-ion collisionality on the filament parallel current in the ELM mitigation time. The transient particle and heat fluxes decrease about 40-50% and 50-60%, respectively. These observations indicate that SMBI might be an effective method to suppress the intermittent convective transport.

Impact of impurity mixture gas seeded by supersonic molecular beam injection on edge-localized modes in the HL-2A tokamak

“…The D α in figure 3(d) displays a complex nature of ELM effluxes. It might be interpreted by that the number of small filaments are increased and that of the larger amplitude one is reduced during the ELM mitigation phase, as statistically studied by Langmuir probes in HL-2A [80]. The global plasma performance was not undergone noticeable degradation after the mixture SMBI as seen from figure 3(e).…”

The effects of magnetic topology on the scrape-off layer turbulence transport in the first divertor plasma operation of Wendelstein 7-X using a new combined probe

“…However, inside the green rectangle the particle flux is very weak, which also agrees well with the APSD of figure 4(e). When the probe goes to the near SOL, Γ r ( f , t) decreases significantly when R < 6.06 m, and the particle transport is dominated by low frequency turbulence (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). In this near SOL region, the turbulence transport reflects some intermittent structures, especially when getting close to the LCFS.…”

“…In the plasma edge and the scrape-off layer (SOL), intermittent events are also considered to play an important role in the cross-field transport due to its large scale and large fluctuation amplitude. The intermittent transport, also named as blobs, filaments or eddies, has been measured by several diagnostics in many fusion devices, such as the gas puff imaging (GPI) in NSTX, Alcator C-Mod, TEXTOR and EAST [5][6][7][8][9], beam emission spectroscopy (BES) in DIII-D and KSTAR [10,11], and Langmuir probes in W7-AS, LHD, TJ-K, JET, ASDEX Upgrade, HL-2A and DIII-D [10,[12][13][14][15][16][17][18]. As measured by different machines, the blobs typically have a size of 1-3 cm, radial velocity about 0.5-2 km s −1 .…”

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

“…Small-scale avalanches can be stimulated if the baseline fueling is low, preventing the pedestal from growing to profiles globally vulnerable to ballooning The link between filament burst rate and filament amplitude before (blue) and after (red) SMBI. (Nie et al 2014) instabilities. More experimental investigations should be conducted to support the conclusion of the simulation.…”