Runaway electron generation during disruptions in the J-TEXT tokamak

Zeng, Long; Chen, Zhiyi; Dong, Y.B.; Koslowski, H. R.; Liang, Y.; Zhang, Y.P.; Zhuang, Hui; Huang, Dan; Gao, Xiang

doi:10.1088/1741-4326/aa57d9

Cited by 42 publications

(41 citation statements)

References 40 publications

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“…Some qualitative trends in RE seed formation can be inferred from RE plateau current JT-60U, ASDEX-U, and JET have observed data supporting a B ∼ 2 T toroidal field threshold for RE seed formation [206,235,243], leading to speculation that excitation of whistler waves could prevent RE formation below B = 2 T [158]. However, later experiments in JET [244], KSTAR [245], TEXTOR [246], and J-TEXT [247] found that there is no clear toroidal field threshold, so that B = 2 T is not a prerequisite for RE formation. Nevertheless, a robust trend is observed across all machines that higher toroidal magnetic field does elevate the RE plateau levels.…”

Section: E Re Seed Formation During Tqmentioning

confidence: 99%

Physics of runaway electrons in tokamaks

et al. 2019

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Of all electrons, runaway electrons have long been recognized in the fusion community as a distinctive population. They now attract special attention as a part of ITER mission considerations. This review covers basic physics ingredients of the runaway phenomenon and the ongoing efforts (experimental and theoretical) aimed at runaway electron taming in the next generation tokamaks. We emphasize the prevailing physics themes of the last 20 years: the hot-tail mechanism of runaway production, runaway electron interaction with impurity ions, the role of synchrotron radiation in runaway kinetics, runaway electron transport in presence of magnetic fluctuations, micro-instabilities driven by runaway electrons in magnetized plasmas, and vertical stability of the plasma with runaway electrons. The review also discusses implications of the runaway phenomenon for ITER and the current strategy of runaway electron mitigation.

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Section: E Re Seed Formation During Tqmentioning

confidence: 99%

Physics of runaway electrons in tokamaks

et al. 2019

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“…Significant work has been done to prevent REs in ITER (Putvinski et al 1997;Boozer 2015Boozer , 2017. The Dreicer generation (Connor & Hastie 1975), hot tails (Smith & Verwichte 2008;Zeng et al 2017) and avalanche mechanisms (Jayakumar, Fleischmann & Zweben 1993; are three main runaway generation processes. The Dreicer mechanism plays a major role when the collisional drag force on an energetic electron is less than the driving force by the toroidal electric field.…”

Section: Runaway Modementioning

confidence: 99%

On the breakdown modes and parameter space of ohmic tokamak start-up

et al. 2018

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Tokamak start-up is strongly dependent on the state of the initial plasma formed during plasma breakdown. We have investigated through numerical simulations the effects that the pre-filling pressure and induced electric field have on pure ohmic heating during the breakdown process. Three breakdown modes during the discharge are found, as a function of different initial parameters: no breakdown mode, successful breakdown mode and runaway mode. No breakdown mode often occurs with low electric field or high pre-filling pressure, while runaway electrons are usually easy to generate at high electric field or low pre-filling pressure (${<}1.33\times 10^{-4}$ Pa). The plasma behaviours and the physical mechanisms under the three breakdown modes are discussed. We have identified the electric field and pressure values at which the different modes occur. In particular, when the electric field is $0.3~\text{V}~\text{m}^{-1}$ (the value at which ITER operates), the pressure range for possible breakdown becomes narrow, which is consistent with Lloyd’s theoretical prediction. In addition, for $0.3~\text{V}~\text{m}^{-1}$, the optimal pre-filling pressure range obtained from our simulations is $1.33\times 10^{-3}\sim 2.66\times 10^{-3}$ Pa, in good agreement with ITER’s design. Besides, we also find that the Townsend discharge model does not appropriately describe the plasma behaviour during tokamak breakdown due to the presence of a toroidal field. Furthermore, we suggest three possible operation mechanisms for general start-up scenarios which could better control the breakdown phase.

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“…2013) and in J-TEXT (Zeng et al. 2017). Kinetic instabilities driven by the runaways themselves can also induce local magnetic perturbations increasing the radial transport.…”

Section: Introductionmentioning

confidence: 99%

Effects of magnetic perturbations and radiation on the runaway avalanche

et al. 2021

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The electron runaway phenomenon in plasmas depends sensitively on the momentum- space dynamics. However, efficient simulation of the global evolution of systems involving runaway electrons typically requires a reduced fluid description. This is needed, for example, in the design of essential runaway mitigation methods for tokamaks. In this paper, we present a method to include the effect of momentum-dependent spatial transport in the runaway avalanche growth rate. We quantify the reduction of the growth rate in the presence of electron diffusion in stochastic magnetic fields and show that the spatial transport can raise the effective critical electric field. Using a perturbative approach, we derive a set of equations that allows treatment of the effect of spatial transport on runaway dynamics in the presence of radial variation in plasma parameters. This is then used to demonstrate the effect of spatial transport in current quench simulations for ITER-like plasmas with massive material injection. We find that in scenarios with sufficiently slow current quench, owing to moderate impurity and deuterium injection, the presence of magnetic perturbations reduces the final runaway current considerably. Perturbations localised at the edge are not effective in suppressing the runaways, unless the runaway generation is off-axis, in which case they may lead to formation of strong current sheets at the interface of the confined and perturbed regions.

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Runaway electron generation during disruptions in the J-TEXT tokamak

Cited by 42 publications

References 40 publications

Physics of runaway electrons in tokamaks

Physics of runaway electrons in tokamaks

On the breakdown modes and parameter space of ohmic tokamak start-up

Effects of magnetic perturbations and radiation on the runaway avalanche

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