Measurement of the toroidal radiation asymmetry during massive gas injection triggered disruptions on J-TEXT

Tong, R. H.; Chen, Z Y; Jiang, Zhonghe; Zhang, X L; Cheng, Zhifeng; Liu, L Z; Li, W; Yan, Wei; Wei, Yunong; Lin, Z.; Huang, Yuan; Yang, Zhoujun

doi:10.1063/1.5035187

Cited by 12 publications

(13 citation statements)

References 22 publications

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“…Radiation asymmetry during disruption mitigation is one of the most serious problems, and can result in substantial heat loads on the first wall of ITER [40]. AXUV arrays located at four different toroidal positions have been developed to study the toroidal radiation peaking factors (TPFs) during disruption [31]. The TPF is defined as:…”

Section: Resultsmentioning

confidence: 99%

“…The penetration process of the gas jet from the plasma boundary to the core can be monitored by a fast visible camera filtered by a He II (468.2 nm) filter with a tangential view. AXUV arrays are developed to study the toroidal radiation asymmetry during the MGI impurity injection [31]. The arrays are located at four different toroidal positions, which cover the full poloidal cross section.…”

Section: Key Diagnosticsmentioning

confidence: 99%

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The impact of an m/n = 2/1 locked mode on the disruption process during a massive gas injection shutdown on J-TEXT

et al. 2019

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Locked modes (LMs) will be one of the major causes of disruptions in the ITER tokamak. Disruption mitigation systems (DMSs), such as massive gas injection (MGI) or shattered pellet injection (SPI), are expected to be deployed in pre-disruption discharges with large pre-existing locked modes. A series of target plasmas with an m/n = 2/1 locked mode induced by resonant magnetic perturbation (RMP) penetration was terminated by an MGI on the J-TEXT tokamak. The penetration of the injected impurities during the process was diagnosed using a fast frame visible camera and a multi-channel polarimeter-interferometer (POLARIS) in combination. The electron temperature evolution during thermal quench (TQ) is also shown in detail. It is found that both the phase and width of the 2/1 mode have an effect on MGI shutdown dynamics. When the mode is larger than the critical width, the penetration depth and assimilation of impurities can be enhanced during pre-TQ, leading to a faster quenching process if the relative phase between the O-point of the 2/1 mode and the MGI valve is ∆φ = +90°. Conversely, the penetration depth and assimilation of impurities are suppressed, leading to a slower TQ when the relative phase is ∆φ = −90°. The toroidal radiation asymmetry is worse with the locked mode. The results suggest that the 3D effect between the injected impurities and the 2/1 locked mode is important during the disruption mitigation process.

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Section: Resultsmentioning

confidence: 99%

Section: Key Diagnosticsmentioning

confidence: 99%

The impact of an m/n = 2/1 locked mode on the disruption process during a massive gas injection shutdown on J-TEXT

et al. 2019

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“…Without proper mitigation, disruptions can deposit substantial heat loads, unbalanced electromagnetic forces, and runaway electron current to the first wall and plasma facing components, causing disastrous damage to the machine [1]. Disruption mitigation schemes based on the massive gas injection (MGI) method have been widely studied on major tokamaks including JET [2,3], DIII-D [4][5][6][7], ASDEX-Upgrade [8,9], KSTAR [10], EAST [11], J-TEXT [12][13][14][15]. Although recent designs for the ITER disruption mitigation scheme have opted toward the more efficient shattered pellet injection system, the MGI system has remained viable and effective for disruption mitigation on most tokamaks, at least during the thermal quench (TQ) phase [16].…”

Section: Introductionmentioning

confidence: 99%

MHD simulations of cold bubble formation from 2/1 tearing mode during massive gas injection in a tokamak

Zeng

Zhu

Izzo³

et al. 2021

Nucl. Fusion

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Massive gas injection (MGI) experiments have been carried out in many tokamaks to study disruption dynamics and mitigation schemes. Two events often observed in those experiments are the excitation of the m = 2, n = 1 magnetohydrodynamic (MHD) mode, and the formation of cold bubble structure in the temperature distribution before the thermal quench (TQ). Here m is the poloidal mode number, n the toroidal mode number. The physics mechanisms underlying those phenomena, however, have not been entirely clear. In this work, our recent NIMROD simulations of the MGI process in a tokamak have reproduced the main features of both events, which has allowed us to examine and establish the causal relation between them. In these simulations, the 3/1 and 2/1 islands are found to form successively after the arrival of impurity ion cold front at the corresponding q = 3 and q = 2 rational surfaces. At the interface between impurity and plasma, a local thin current sheet forms due to an enhanced local pressure gradient and moves inward following the gas cold front, this may contribute to the formation of a dominant 2/1 mode. Following the growth of the 2/1 tearing mode, the impurity penetration into the core region inside the q = 2 surface gives rise to the formation of the cold bubble temperature structure and initiates the final TQ. A subdominant 1/1 mode developed earlier near the q = 1 surface alone does not cause such a cold bubble formation, however, the exact manner of the preceding impurity penetration depends on the nature of the 1/1 mode: kink-tearing or quasi-interchange.

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“…The electron temperature can be measured by an electron cyclotron emission (ECE) system which is located at port 5 (but now the ECE system has been moved to port 9) [27]. Four extreme ultraviolet (AXUV) arrays installed in ports 3, 5, 6, 13 are used to measure the total radiation power [28]. The Ar SPI system is located at the equatorial port 10.…”

Section: Methodsmentioning

confidence: 99%

“…The detector arrays at port 3 consist of four AXUV 16ELG detectors and the other three arrays are located at ports 5, 6, and 13, each of which contains two sets of AXUV 20ELG detector arrays, located at the upper-right windows of the vacuum vessel. All detectors cover the full poloidal crosssection from −0.28 m to 0.28 m with a spatial resolution o f ∼20 mm [28].…”

Section: Comparison Of Disruption Characteristics With Spi and Mgimentioning

confidence: 99%

Comparison of disruption mitigation from shattered pellet injection with massive gas injection on J-TEXT

Li¹,

Chen²,

Yan³

et al. 2021

Nucl. Fusion

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The mitigation of disruption damage is essential to the safe operation of a large-scale tokamak. In order to achieve the safe operation of ITER, the shattered pellet injection (SPI) has been considered as a primary measure of disruption mitigation. A dedicated argon SPI system, focusing on disruption mitigation has been designed for the J-TEXT tokamak. In the J-TEXT SPI system, a pure argon pellet can be formed in the freezing tube, then separated from the tube and accelerated by a punch mechanism. The pellet can be injected with a speed of 150–300 m s−1. The performance of disruption mitigation by Ar SPI has been compared with Ar massive gas injection (MGI). The cooling process observed from the ECE indicates that the SPI has deeper deposition, with the cold front that can reach the q = 1 rational surface in case of SPI, but stops at the q = 2 profile in MGI. The increase of core plasma density during a fast shutdown is higher than that with Ar MGI, which proves a deeper penetration of SPI. In disruption, the magnetohydrodynamic (MHD) activities, measured at the Mirnov coils, have similar behavior in both MGI and SPI shots. The m/n = 2/1 mode dominates the MHD activities from the penetration to the end of the thermal quench (TQ). Subsequently, in the current quench (CQ) phase, the m/n = 3/1 mode grows to become the dominant mode. The radiation power is much stronger in the SPI shot. The radiation asymmetry is compared in the two plasma disruption mitigation methods. Changing the pellet velocity can effectively adjust the TQ process and CQ rate, which can achieve a higher impurity assimilation rate when the pellet velocity increases in a certain range.

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Measurement of the toroidal radiation asymmetry during massive gas injection triggered disruptions on J-TEXT

Cited by 12 publications

References 22 publications

The impact of an m/n = 2/1 locked mode on the disruption process during a massive gas injection shutdown on J-TEXT

The impact of an m/n = 2/1 locked mode on the disruption process during a massive gas injection shutdown on J-TEXT

MHD simulations of cold bubble formation from 2/1 tearing mode during massive gas injection in a tokamak

Comparison of disruption mitigation from shattered pellet injection with massive gas injection on J-TEXT

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