The first high-confinement mode (H-mode) with type-III edge localized modes at an H factor of HIPB98(y,2) ∼ 1 has been obtained with about 1 MW lower hybrid wave power on the EAST superconducting tokamak. The first H-mode plasma appeared after wall conditioning by lithium (Li) evaporation before plasma breakdown and the real-time injection of fine Li powder into the plasma edge. The threshold power for H-mode access follows the international tokamak scaling even in the low density range and a threshold in density has been identified. With increasing accumulation of deposited Li the H-mode duration was gradually extended up to 3.6 s corresponding to ∼30 confinement times, limited only by currently attainable durations of the plasma current flat top. Finally, it was observed that neutral density near the lower X-point was progressively reduced by a factor of 4 with increasing Li accumulation, which is considered the main mechanism for the H-mode power threshold reduction by the Li wall coatings. (Some figures in this article are in colour only in the electronic version)

http://iopscience.iop.org/article/10.1088/0029-5515/51/7/072001/pdf

Study on H-mode access at low density with lower hybrid current drive and lithium-wall coatings on the EAST superconducting tokamak

As an alternative choice of solid plasma facing components (PFCs), flowing liquid lithium can serve as a limiter or divertor PFC and offers a self-healing surface with acceptable heat removal and good impurity control. Such a system could improve plasma performance, and therefore be attractive for future fusion devices. Recently, a continuously flowing liquid lithium (FLiLi) limiter has been successfully designed and tested in the EAST superconducting tokamak. A circulating lithium layer with a thickness of <0.1 mm and a flow rate ~2 cm3 s−1 was achieved. A novel in-vessel electro-magnetic pump, working with the toroidal magnetic field of the EAST device, was reliable to control the lithium flow speed. The flowing liquid limiter was found to be fully compatible with various plasma scenarios, including high confinement mode plasmas heated by lower hybrid waves or by neutral beam injection. It was also found that the controllable lithium emission from the limiter was beneficial for the reduction of recycling and impurities, for the reduction of divertor heat flux, and in certain cases, for the improvement of plasma stored energy, which bodes well application for the use of flowing liquid lithium PFCs in future fusion devices.

https://iopscience.iop.org/article/10.1088/0029-5515/56/4/046011/pdf

First results of the use of a continuously flowing lithium limiter in high performance discharges in the EAST device

To achieve desirable plasma density control, a supersonic molecular beam injection (SMBI) feedback control system has been developed recently for the EAST tokamak The performance of the SMBI and gas puffing (GP) feedback systems were used and compared The performance of pulse width mode is better than that of pulse amplitude mode when GP was used for density feedback control During one-day experiments, the variation of gas input and wall retention can be clarified into two stages In the first stage the retention ratio is as high as 80–90%, and the gas input is about an order of 1022 D2 However, in the second stage, the retention ratio is at a range of 50–70% The gas input of a single discharge is small and the net wall retention grows slowly The results of the SMBI feedback control experiment was analyzed The shorter delay time of SMBI makes it faster at feeding back control the plasma density The result showed that, compared with GP, the gas input of SMBI was decreased ~30% and the wall retention was reduced ~40% This shows SMBI's advantage for the long pulse high density discharges in EAST

https://iopscience.iop.org/article/10.1088/0741-3335/55/11/115010/pdf

Comparison between gas puffing and supersonic molecular beam injection in plasma density feedback experiments in EAST

Reductions in H content and particle recycling are important for the improvement of ion cyclotron range of frequency (ICRF) minority heating efficiency and the enhancement of plasma performance of the EAST superconducting tokamak. During recent years several techniques of surface conditioning such as baking, glow discharge cleaning/ICRF discharge cleaning, surface coatings, such as boronization, siliconization and lithium coating, have all been attempted in order to reduce the H/(H+D) ratio and particle recycling in EAST. Even though boronization and siliconization were both reasonably effective methods to improve plasma performance, lithium coatings were observed to reduce the H content and particle recycling to levels low enough to allow the attainment of enhanced plasma parameters and operating modes on EAST. For example, by accomplishing lithium coating using either vacuum evaporation or the real-time injection of fine lithium powder, the H/(H+D) ratio could be routinely decreased to about 5%, which significantly improved ICRF minority heating efficiency during the autumn campaign of 2010. Due to the reduced H/(H+D) ratio and lower particle recycling, and a reduced H-mode power threshold, improved plasma confinement and the first EAST H-mode plasma were obtained. Furthermore, with increasing accumulation of deposited lithium, several new milestones of EAST performance, such as a 6.4 s-long H-mode, a 100 s-long plasma duration and a 1 MA plasma current, were achieved in the 2010 autumn campaign.

https://iopscience.iop.org/article/10.1088/0741-3335/54/1/015014/pdf

Comparison of various wall conditionings on the reduction of H content and particle recycling in EAST

Deuterium high-confinement (H-mode) plasmas, lasting up to 3.45 s, have been generated in the EAST by ion cyclotron range of frequency (ICRF) heating. H-mode access was achieved by coating the molybdenum-tiled first wall with lithium to reduce the hydrogen recycling from the wall. H-mode plasmas with plasma currents between 0.4 and 0.6 MA and axial toroidal magnetic fields between 1.85 and 1.95 T were generated by 27 MHz ICRF heating of deuterium plasma with hydrogen minority. The ICRF input power required to access the H-mode was 1.6–1.8 MW. The line-averaged density was in the range (1.83–2.3) × 1019 m−3. 200–500 Hz type-III edge localized mode activity was observed during the H-mode phase. The H-mode confinement factor, H98IPB(y, 2), was ~0.7.

First results from H-mode plasmas generated by ICRF heating in the EAST

Vacuum and wall conditioning system on EAST

Investigation of lithium as plasma facing materials on HT-7

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Vacuum and wall conditioning system on EAST

Investigation of lithium as plasma facing materials on HT-7