Modelling of runaway electron dynamics during argon-induced disruptions in ASDEX Upgrade and JET

Björk, Klara Insulander; Vallhagen, O.; Papp, G.; Reux, C.; Embréus, Ola; Rachlew, Elisabeth; Fülöp, Tünde

doi:10.1088/1361-6587/ac07b5

Cited by 4 publications

(3 citation statements)

References 40 publications

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“…2020) or assume a flat electric field profile (Insulander Björk et al. 2021; Hoppe et al. 2021 b ) as their initial condition, which is then evolved in an inductive–resistive fashion.…”

Section: Introductionmentioning

confidence: 99%

Runaway dynamics in tokamak disruptions with current relaxation

2022

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The safe operation of tokamak reactors requires a reliable modelling capability of disruptions, and in particular the spatio-temporal dynamics of associated runaway electron currents. In a disruption, instabilities can break up magnetic surfaces into chaotic field line regions, causing current profile relaxation, as well as a rapid radial transport of heat and particles. Using a mean-field helicity transport model implemented in the disruption runaway modelling framework Dream, we calculate the dynamics of runaway electrons in the presence of current relaxation events. In scenarios where flux surfaces remain intact in parts of the plasma, a skin current is induced at the boundary of the intact magnetic field region. This skin current region becomes an important centre concerning the subsequent dynamics: it may turn into a hot ohmic current channel, or a sizeable radially localized runaway beam, depending on the heat transport. If the intact region is in the plasma edge, runaway generation in the countercurrent direction can occur, which may develop into a sizeable reverse runaway beam. Even when the current relaxation extends to the entire plasma, the final runaway current density profile can be significantly affected, as the induced electric field is reduced in the core and increased in the edge, thereby shifting the centre of runaway generation towards the edge.

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“…2020) or assume a flat electric field profile (Insulander Björk et al. 2021; Hoppe et al. 2021 b ) as their initial condition, which is then evolved in an inductive–resistive fashion.…”

Section: Introductionmentioning

confidence: 99%

Runaway dynamics in tokamak disruptions with current relaxation

2022

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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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“…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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Modelling of runaway electron dynamics during argon-induced disruptions in ASDEX Upgrade and JET

Cited by 4 publications

References 40 publications

Runaway dynamics in tokamak disruptions with current relaxation

Runaway dynamics in tokamak disruptions with current relaxation

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

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