Runaway electron beam control

Carnevale, D.; Ariola, M.; Artaserse, G.; Bagnato, F.; Bin, W.; Boncagni, L.; Bolzonella, T.; Bombarda, F.; Buratti, P.; Calacci, L.; Causa, F.; Coda, S.; Cordella, F.; Decker, J.; Tommasi, G. De; Duval, B.P.; Esposito, B.; Ferro, Giulio; Ficker, O.; Gabellieri, L.; Gabrielli, Andrea; Galeani, Sergio; Galperti, C.; Garavaglia, S.; Havránek, A.; Gobbin, M.; Gospodarczyk, M.; Granucci, G.; Joffrin, E.; Lennholm, M.; Lier, A.; Macúšová, E.; Martin-Solís, J.R.; Martı́n-Solı́s, J. R.; Mlynář, J.; Panaccione, L.; Papp, G.; Passeri, M.; Pautasso, G.; Popović, Ž.; Possieri, Corrado; Pucella, G.; Sheikh, U.; Ramogida, G.; Reux, C.; Rimini, F.; Романо, А.; Sassano, Mario; Tilia, B.; Tudisco, O.; Valcárcel, D.; Contributors, Jet

doi:10.1088/1361-6587/aaef53

Cited by 33 publications

(49 citation statements)

References 28 publications

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“…This provides an approximate boundary between instabilities that act on REs in real space (< 30 MHz) and those that act on REs in phase space (> 30 MHz). Consequently both few MHz instabilities, 10-100s kHz MHD instabilities, and stationary applied 3-D fields can deconfine REs in effectively the same manner [42,8,82,70,43,16,41].…”

Section: General Prospects For Kinetic Instabilitiesmentioning

confidence: 98%

“…In the time domain, increasing B T increases the decay rate at high E RE while increasing n e increases the RE decay rate at all E RE . Considering information in the spatial domain, energy-dependent radial gradients of the RE population are observed, enabling future model validation efforts to specifically target RE spatial transport effects due to either MHD instabilities [39,40,16,41], imposed 3-D fields [42,43], or inherent processes [44]. Furthermore, simultaneously viewing the same flux surface with different sight-line angles to the magnetic field enables deconvolution of pitch-angle information.…”

Section: Re Distribution Measurement Via Bremsstrahlungmentioning

confidence: 99%

“…A successful RE mitigation would dissipate the RE kinetic energy and magnetic energy (RE current) prior to the RE beam coming into contact with the tokamak first-wall. This has been achieved in long-duration RE plateaus under shape control [14,15,16], though as will be described, challenges are encountered when the RE beam is vertically unstable [6].…”

Section: Introductionmentioning

confidence: 99%

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Recent DIII-D advances in runaway electron measurement and model validation

Paz-Soldan¹,

Eidietis²,

Hollmann³

et al. 2019

Nucl. Fusion

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Novel measurements and modeling of runaway electron (RE) dynamics in DIII-D have resolved experimental discrepancies and validated predictions for ITER, improving confidence that RE avoidance and mitigation can be predictably achieved. Considering RE formation, first experimental assessments of the RE seed current demonstrates that present hot-tail theories are not yet accurate and require improved treatment of the pellet dynamics. Novel measurements of kinetic instabilities in the MHz-range have been made in the RE formation phase, with the intensity of these modes correlated with previously unexplained empirical thresholds for RE generation. Controlled RE dissipation experiments in quiescent regimes have validated RE distribution function dependencies on collisional and synchrotron damping, both in terms of distribution function shape and dissipation rates. Measurements of RE bremsstrahlung and synchrotron emission are now used in tandem to resolve energy and pitch-angle effects. A resolution to long-standing dissipation anomalies in the quiescent regime is offered by taking into account kinetic instability effects on RE phase-space dynamics. Kinetic instabilities in the 100-200 MHz range are directly observed, though modeling finds the largest dissipation arises from GHz range instabilities that are beyond the reach of existing diagnostics. Kinetic instabilities are also observed in the mature post-disruption RE plateau phase, so long as the collisional damping rate is reduced with low-Z injection. Experiments with high-Z injection find that the dissipation rate saturates with injection quantity, likely due to neutral diffusion rates being slower than vertical instability rates in DIII-D. Considering the final loss, a 0D model for first-wall Joule heating is found to be in agreement with experiment, and controlled access to RE equilibria with edge safety factor of two identifies novel dynamics brought about by large-scale kink instabilities. These dynamics are typified by fast (tens of microseconds) RE loss rates without RE beam regeneration. The above measurements and comparison with theory represent significant advances in the understanding of RE dynamics and indicate possible new opportunities for RE avoidance or mitigation via kinetic instabilities.

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Section: General Prospects For Kinetic Instabilitiesmentioning

confidence: 98%

Section: Re Distribution Measurement Via Bremsstrahlungmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Recent DIII-D advances in runaway electron measurement and model validation

Paz-Soldan¹,

Eidietis²,

Hollmann³

et al. 2019

Nucl. Fusion

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“…For this reason, much effort is directed towards the development of schemes to avoid, limit or mitigate the formation of such a beam. One proposed measure is using massive material injection (MMI) in the form of gas (massive gas injection – MGI) or frozen pellets (shattered pellet injection) to avoid or dissipate the runaway electrons (Hollmann et al 2015 a ; Lehnen et al 2015), and its efficiency has been demonstrated in medium-sized tokamaks (Hollmann et al 2015 b ; Reux et al 2015; Pautasso et al 2016; Esposito et al 2017; Paz-Soldan et al 2017; Carnevale et al 2018; Coda et al 2019; Mlynar et al 2019; Pautasso et al 2020). However, the plasma currents, temperatures and densities of future devices such as ITER will be significantly larger than what can be achieved in current experiments, and simulations are necessary to foresee the effectiveness of massive material injections for disruption mitigation under such conditions.…”

Section: Introductionmentioning

confidence: 99%

Kinetic modelling of runaway electron generation in argon-induced disruptions in ASDEX Upgrade

et al. 2020

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Massive material injection has been proposed as a way to mitigate the formation of a beam of relativistic runaway electrons that may result from a disruption in tokamak plasmas. In this paper we analyse runaway generation observed in eleven ASDEX Upgrade discharges where disruption was triggered using massive gas injection. We present numerical simulations in scenarios characteristic of on-axis plasma conditions, constrained by experimental observations, using a description of the runaway dynamics with a self-consistent electric field and temperature evolution in two-dimensional momentum space and zero-dimensional real space. We describe the evolution of the electron distribution function during the disruption, and show that the runaway seed generation is dominated by hot-tail in all of the simulated discharges. We reproduce the observed dependence of the current dissipation rate on the amount of injected argon during the runaway plateau phase. Our simulations also indicate that above a threshold amount of injected argon, the current density after the current quench depends strongly on the argon densities. This trend is not observed in the experiments, which suggests that effects not captured by zero-dimensional kinetic modelling – such as runaway seed transport – are also important.

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“…go has the ability to model elongated plasmas [39], however, this capacity was not used in the presented simulations. The modelled discharges featured slightly elongated plasmas, κ ≈ 1.16 in the JET discharges, according to pre-disruption equilibrium reconstructions 7 . Inclusion of the elongation in Toroidal magnetic field on axis B (T) 2.5 3 the simulations did not result in any qualitative changes in the simulation results, and thus it was decided to reduce the parameter space by omitting this parameter.…”

Section: Plasma Elongationmentioning

confidence: 71%

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

Björk

Vallhagen

Papp

et al. 2021

Plasma Phys. Control. Fusion

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Disruptions in tokamak plasmas may lead to the generation of runaway electrons that have the potential to damage plasma-facing components. Improved understanding of the runaway generation process requires interpretative modelling of experiments. In this work we simulate eight discharges in the ASDEX Upgrade and JET tokamaks, where argon gas was injected to trigger the disruption. We use a fluid modelling framework with the capability to model the generation of runaway electrons through the hot-tail, Dreicer and avalanche mechanisms, as well as runaway electron losses. Using experimentally based initial values of plasma current and electron temperature and density, we can reproduce the plasma current evolution using realistic assumptions about temperature evolution and assimilation of the injected argon in the plasma. The assumptions and results are similar for the modelled discharges in ASDEX Upgrade and JET. For the modelled discharges in ASDEX Upgrade, where the initial temperature was comparatively high, we had to assume that a large fraction of the hot-tail runaway electrons were lost in order to reproduce the measured current evolution.

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Runaway electron beam control

Abstract: Plasma Physics and Controlled Fusion

Cited by 33 publications

References 28 publications

Recent DIII-D advances in runaway electron measurement and model validation

Recent DIII-D advances in runaway electron measurement and model validation

Kinetic modelling of runaway electron generation in argon-induced disruptions in ASDEX Upgrade

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

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