Disruption mitigation by injection of small quantities of noble gas in ASDEX Upgrade

Pautasso, G.; Bernert, M.; Dibon, M.; Duval, B. P.; Dux, R.; Fable, E.; Fuchs, Julien; Giannone, L.; Gude, A.; Herrmann, A.; Hoelzl, M.; McCarthy, Patrick J.; Mlynek, A.; Maraschek, M.; Nardon, E.; Papp, G.; Potzel, S.; Rapson, C.; Sieglin, B.; Suttrop, W.; Treutterer, W.

doi:10.1088/0741-3335/59/1/014046

Cited by 45 publications

(70 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Due to its experimental accessibility, we consider this scenario separately for a singly ionized argon-dominated plasma (Pautasso et al. 2016). For the runaway electron distribution we use the self-consistent slowing-down distribution of Hesslow et al.…”

Section: Radiation From Positrons In Tokamak Plasmasmentioning

confidence: 99%

Dynamics of positrons during relativistic electron runaway

et al. 2018

View full text Add to dashboard Cite

Sufficiently strong electric fields in plasmas can accelerate charged particles to relativistic energies. In this paper we describe the dynamics of positrons accelerated in such electric fields, and calculate the fraction of created positrons that become runaway accelerated, along with the amount of radiation that they emit. We derive an analytical formula that shows the relative importance of the different positron production processes, and show that above a certain threshold electric field the pair production by photons is lower than that by collisions. We furthermore present analytical and numerical solutions to the positron kinetic equation; these are applied to calculate the fraction of positrons that become accelerated or thermalized, which enters into rate equations that describe the evolution of the density of the slow and fast positron populations. Finally, to indicate operational parameters required for positron detection during runaway in tokamak discharges, we give expressions for the parameter dependencies of detected annihilation radiation compared to bremsstrahlung detected at an angle perpendicular to the direction of runaway acceleration. Using the full leading order pair production cross section, we demonstrate that previous related work has overestimated the collisional pair production by at least a factor of four. † Email address for correspondence: embreus@chalmers.se arXiv:1807.04460v1 [physics.plasm-ph]

show abstract

Section: Radiation From Positrons In Tokamak Plasmasmentioning

confidence: 99%

Dynamics of positrons during relativistic electron runaway

et al. 2018

View full text Add to dashboard Cite

show abstract

“…In this paper, we examine synchrotron emission from REs in discharge #35628 of the ASDEX Upgrade tokamak, deliberately disrupted using an injection of neutral argon (Pautasso et al. 2016). The injection of argon leads to a rapid cooling – a thermal quench (TQ).…”

Section: Introductionmentioning

confidence: 99%

Spatiotemporal analysis of the runaway distribution function from synchrotron images in an ASDEX Upgrade disruption

et al. 2021

View full text Add to dashboard Cite

Synchrotron radiation images from runaway electrons (REs) in an ASDEX Upgrade discharge disrupted by argon injection are analysed using the synchrotron diagnostic tool Soft and coupled fluid-kinetic simulations. We show that the evolution of the runaway distribution is well described by an initial hot-tail seed population, which is accelerated to energies between 25–50 MeV during the current quench, together with an avalanche runaway tail which has an exponentially decreasing energy spectrum. We find that, although the avalanche component carries the vast majority of the current, it is the high-energy seed remnant that dominates synchrotron emission. With insights from the fluid-kinetic simulations, an analytic model for the evolution of the runaway seed component is developed and used to reconstruct the radial density profile of the RE beam. The analysis shows that the observed change of the synchrotron pattern from circular to crescent shape is caused by a rapid redistribution of the radial profile of the runaway density.

show abstract

“…the dissipation of the energy of fast electrons via Coulomb scattering by increasing the density, is considered to be the main solution. Several techniques directed to this end are extensively investigated in the tokamak community, for instance Massive Gas Injection (MGI) [15][16][17][18][19][20] and shattered pellet injection [21,22].…”

Section: Introductionmentioning

confidence: 99%

Runaway electron mitigation by 3D fields in the ASDEX-Upgrade experiment

Gobbin

Liu

et al. 2017

Plasma Phys. Control. Fusion

Self Cite

View full text Add to dashboard Cite

Disruption-generated runaway electron (RE) beams represent a severe threat for tokamak plasma-facing components in high current devices like ITER, thus motivating the search of mitigation techniques. The application of 3D fields might aid this purpose and recently was investigated also in the ASDEX Upgrade experiment by using the internal active saddle coils (termed B-coils). Resonant magnetic perturbations (RMPs) with dominant toroidal mode number n = 1 have been applied by the B-coils, in a RE specific scenario, before and during disruptions, which are deliberately created via massive gas injection. The application of RMPs affects the electron temperature profile and seemingly changes the dynamics of the disruption; this results in a significantly reduced current and lifetime of the generated RE beam. A similar effect is observed also in the hard-X-ray (HXR) spectrum, associated to runaway electron emission, characterized by a partial decrease of the energy content below 1MeV when RMPs are applied. The strength of the observed effects strongly depends on the upper-to-lower B-coil phasing, i.e. on the poloidal spectrum of the applied RMPs, which has been reconstructed including the plasma response by the code MARS-F. A crude vacuum approximation fails in the interpretation of the experimental findings: despite the relatively low β (< 0.5%) of these discharges, a modest amplification (factor of 2) of the edge kink response occurs, which has to be considered to explain the observed suppression effects.PACS numbers:

show abstract

Disruption mitigation by injection of small quantities of noble gas in ASDEX Upgrade

Cited by 45 publications

References 13 publications

Dynamics of positrons during relativistic electron runaway

Dynamics of positrons during relativistic electron runaway

Spatiotemporal analysis of the runaway distribution function from synchrotron images in an ASDEX Upgrade disruption

Runaway electron mitigation by 3D fields in the ASDEX-Upgrade experiment

Contact Info

Product

Resources

About