Electron runaway in ASDEX Upgrade experiments of varying core temperature

Linder, O.; Papp, G.; Fable, E.; Jenko, F.; Pautasso, G.

doi:10.1017/s0022377821000416

Cited by 7 publications

(6 citation statements)

References 40 publications

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“…Global disruption evolution simulations by codes such as GO [54][55][56][57], ASTRA [58,59] or DREAM [60] can benefit from the simplification of full conversion to RE-driven current. Conversely, further understanding of the RE dynamics and RE beam formation in this set of TCV experiments may be expected from ongoing modelling efforts, which have been initiated for each phase of the plasma evolution described in the paper text.…”

Section: Summary Discussion and Outlookmentioning

confidence: 99%

Full conversion from ohmic to runaway electron driven current via massive gas injection in the TCV tokamak

et al. 2022

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Full conversion from Ohmic to runaway electron (RE) driven current was observed in the TCV tokamak following massive injection of neon through a disruption mitigation valve into a low-density limited circular plasma. Following a partial disruption, a stable 200 kA RE beam is maintained for more than one second. Controlled ramp-down of the RE beam with adjustable decay rate was demonstrated. Control of the beam vertical position was achieved down to a RE current of 20 kA. RE beam formation is observed in elongated plasma configurations up to κ=1.5. A reproducible scenario for RE beam generation without loss of circulating current is of particular interest for disruption modelling applications.

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Section: Summary Discussion and Outlookmentioning

confidence: 99%

Full conversion from ohmic to runaway electron driven current via massive gas injection in the TCV tokamak

et al. 2022

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“…Such fast cooling of the background plasma is possible during the thermal quench phase of disruptions, and it has been indicated [27,34,35] that in ITER disruptions the hot-tail generation will dominate over the Dreicer generation. However, in ASDEX Upgrade and JET disruptions, the Dreicer generation can be comparable to the hot-tail generation [36,37], hence accurate simulation of the Dreicer generation rate is relevant and necessary in simulations of disruptions in current-day devices. In the other studied cases, the runaway seed is expected to be generated mostly by the Dreicer mechanism.…”

Section: Discussionmentioning

confidence: 99%

Validity of models for Dreicer generation of runaway electrons in dynamic scenarios

Olasz¹,

Embréus²,

Hoppe³

et al. 2021

Nucl. Fusion

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Runaway electron modelling efforts are motivated by the risk these energetic particles pose to large fusion devices. The sophisticated kinetic models can capture most features of the runaway electron generation but have high computational costs, which can be avoided by using computationally cheaper reduced kinetic codes. This paper compares the reduced kinetic and kinetic models to determine when the former solvers, based on analytical calculations assuming quasi-stationarity, can be used. The Dreicer generation rate is calculated by two different solvers in parallel in a workflow developed in the European integrated modelling framework, and this is complemented by calculations of a third code that is not yet integrated into the framework. Runaway Fluid, a reduced kinetic code, NORSE, a kinetic code using non-linear collision operator, and DREAM, a linearized Fokker–Planck solver, are used to investigate the effect of a dynamic change in the electric field for different plasma scenarios spanning across the whole tokamak-relevant range. We find that on time scales shorter than or comparable to the electron–electron collision time at the critical velocity for runaway electron generation, kinetic effects not captured by reduced kinetic models play an important role. This characteristic time scale is easy to calculate and can reliably be used to determine whether there is a need for kinetic modelling or cheaper reduced kinetic codes are expected to deliver sufficiently accurate results. This criterion can be automated, and thus it can be of great benefit for the comprehensive self-consistent modelling frameworks that are attempting to simulate complex events such as tokamak start-up or disruptions.

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“…They speculated that the increase of RE seeds during TQ strengthened the pellet ablation, leading to the shortening of TQ. In J-TEXT a similar process might be involved, as the penetration of gas jet into the plasma could be affected by the RE seeds [41].…”

Section: Mgi Shutdown Dynamicsmentioning

confidence: 99%

Elevation of runaway electron current by electron cyclotron resonance heating during disruptions on J-TEXT

Bai¹,

Yan²,

Chen³

et al. 2021

Plasma Phys. Control. Fusion

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Runaway electrons represent a serious problem for the reliable operation of future tokamaks. Radio frequency (RF) auxiliary heating can help suppress runaway electrons in the flat-top phase through a reduction in loop voltage. However, if a disruption occurs during RF auxiliary heating, it may lead to an increase in the runaway electron production due to the generation of a suprathermal population with energies in the order of ∼100 keV. The elevation of runaway current during disruptions by electron cyclotron resonance heating (ECRH) has been investigated on the J-TEXT tokamak. The results show that the conversion efficiency of runaway current increases with increased ECRH power. When the applied ECRH power is at the level of 400 kW, the conversion efficiency of Ohmic to runaway current increases from 35% to 75%, the thermal quench duration is decreased from 0.24 ms to 0.11 ms, and the Absolute Extreme Ultraviolet Spectrometer (AXUV) radiative power and electron density are about two times higher than the cases without ECRH heating.

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Electron runaway in ASDEX Upgrade experiments of varying core temperature

Cited by 7 publications

References 40 publications

Full conversion from ohmic to runaway electron driven current via massive gas injection in the TCV tokamak

Full conversion from ohmic to runaway electron driven current via massive gas injection in the TCV tokamak

Validity of models for Dreicer generation of runaway electrons in dynamic scenarios

Elevation of runaway electron current by electron cyclotron resonance heating during disruptions on J-TEXT

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