Plasma profile evolution during disruption mitigation via massive gas injection on MAST

被引：20

作者：

Thornton, A. J. ^{[1
]}

Gibson, K. J. ^{[2
]}

Chapman, I. T. ^{[1
]}

Harrison, J. R. ^{[1
]}

Kirk, A. ^{[1
]}

Lisgo, S. W. ^{[3
]}

Lehnen, M. ^{[4
]}

Martin, R. ^{[1
]}

Scannell, R. ^{[1
]}

Cullen, A. ^{[1
]}

机构：

[1] EURATOM CCFE Fus Assoc, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England

[2] Univ York, Dept Phys, York Plasma Inst, York YO10 5DD, N Yorkshire, England

[3] ITER Org, St Paul Les Durance, France

[4] Assoc EURATOM FZJ, FZJ, Inst Energy Res Plasma Phys, D-52425 Julich, Germany

来源：

NUCLEAR FUSION | 2012年 / 52卷 / 06期

基金：

英国工程与自然科学研究理事会;

关键词：

ALCATOR C-MOD; DIII-D; JET; TOKAMAKS; IMPURITY;

D O I：

10.1088/0029-5515/52/6/063018

中图分类号：

O35 [流体力学]; O53 [等离子体物理学];

学科分类号：

070204 ; 080103 ; 080704 ;

摘要：

Massive gas injection (MGI) is one means of ameliorating disruptions in future devices such as ITER, where the stored energy in the plasma is an order of magnitude larger than in present-day devices. The penetration of the injected impurities during MGI in MAST is diagnosed using a combination of high-speed (20 kHz) visible imaging and high spatial (1 cm) and temporal (0.1 ms) resolution Thomson scattering (TS) measurements of the plasma temperature and density. It is seen that the rational surfaces, in particular q = 2, are the critical surfaces for disruption mitigation. The TS data shows the build-up of density on rational surfaces in the edge cooling period of the mitigation, leading to the collapse of the plasma in a thermal quench. The TS data are confirmed by the visible imaging, which shows filamentary structures present at the start of the thermal quench. The filamentary structures have a topology which matches that of a q = 2 field line in MAST, suggesting that they are located on the q = 2 surface. Linearized magnetohydrodynamic stability analysis using the TS profiles suggests that the large density build-up on the rational surfaces drives modes within the plasma which lead to the thermal quench. The presence of such modes is seen experimentally in the form of magnetic fluctuations on Mirnov coils and the growth of an n = 1 toroidal mode in the period prior to the thermal quench. These results support the observations of other machines that the 2/1 mode is the likely trigger for the thermal quench in a mitigated disruption and suggests that the mitigation process in spherical tokamaks is similar to that in conventional aspect ratio devices.

引用

页数：12

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