Experimental study of disruption mitigation using massive injection of noble gases on Tore Supra

Abstract

Disruptions are a major threat for future tokamaks, including ITER. Disruption-generated heat loads, electromagnetic forces and runaway electrons will not be tolerable for next-generation devices. Massive noble gas injection is foreseen as a standard mitigation system for these tokamaks. Disruption mitigation experiments have been carried out on Tore Supra to study various injection scenarios and to investigate gas jet penetration and mixing. Comparisons of different gases (He, Ne, Ar, He/Ar mixture) and amounts (from 5 to 500 Pa m3) were made, showing that light gases are more efficient regarding runaway electron suppression than heavier gases. Eddy currents in the limiter are moderately reduced by all the gases, and may be more dependent on the time constants of the structures than on the gas species. The density rise induced by the massive injection before the thermal quench is higher and faster with light gases. Gas jet penetration in the cooling phase is observed to be shallow and independent of the gas nature and amount. The gas cold front is stopped along the q = 2 surface where it triggers MHD instabilities, expelling thermal energy from the plasma core.

Disruptions in ITER and strategies for their control and mitigation

“…Two injection schemes are presently under consideration, massive gas injection (MGI) and Shattered Pellet Injection (SPI). A broad experimental database exists for MGI [7,15,[32][33][34]14] and we will focus mainly on these results in the following. Cryogenic pellet injection has proven in the past to be capable of reducing loads [35][36][37][38], but it is not considered an option for ITER because of the high risk of generating RE.…”

Three-dimensional non-linear magnetohydrodynamic modeling of massive gas injection triggered disruptions in JET

“…MGI aims at spreading heat loads by radiating most of the plasma stored energy, preventing the generation of REs by increasing the electron density and controlling the CQ duration (in order to limit mechanical loads) by controlling the impurity content and thus the temperature and resistivity of the CQ plasma. A large body of experimental work on MGI exists, including experiments on JET, [6][7][8][9] ASDEX Upgrade, 10 Tore Supra, 11 DIII-D, 12 TEXTOR, 13 Alcator C-MOD, 14 and other devices. Results have shown the capability of MGI to fulfill part of the objectives of the ITER DMS, but not yet all of them.…”

WEST Physics Basis

“…The system is designed to inject gas mixes (up to 5 bar l), with a delay of 5-10 ms to extinguish the plasma. Disruption mitigation experiments have been carried out previously with this system on Tore Supra to study various injection scenarios and to investigate gas jet penetration and mixing, showing in particular that runaway mitigation is more efficient using light gases [44]. Additional experiments on runaway mitigation have been performed using a high pressure cartridge [45].…”