Hot-Tail Runaway Seed Landscape during the Thermal Quench in Tokamaks

Svenningsson, Ida; Embréus, Ola; Hoppe, Mathias; Newton, Sarah; Fülöp, Tünde

doi:10.1103/physrevlett.127.035001

Cited by 22 publications

(23 citation statements)

References 35 publications

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“…It has already been shown that the transport of runaway electrons – also caused by the chaotic magnetic field – has a major impact on the evolution of the runaway current density (Svenningsson et al. 2021), but studies concerning the effect of the current relaxation are lacking. To capture current relaxation through fast magnetic reconnection in a model that only retains the radial (i.e.…”

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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Section: Introductionmentioning

confidence: 99%

Runaway dynamics in tokamak disruptions with current relaxation

2022

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“…However, disruptions are MHD active events; increased RE transport can be expected due to magnetic field stochasticity during the thermal and current quenches. The final RE beam magnitude is sensitive to the losses of RE seed population during the thermal quench [6], and the beam is suppressed altogether if losses overcome avalanche generation during the current quench [7,8,9].…”

Section: Introductionmentioning

confidence: 99%

Confinement of passing and trapped runaway electrons in the simulation of an ITER current quench

Särkimäki,

Artola,

Hoelzl

2022

Preprint

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“…The hot-tail runaway seed generated during the thermal quench varies over many orders of magnitude, depending on the injected densities and seed losses arising from perturbations of the magnetic field [9,10]. Regions of parameter space with sufficiently small hottail seeds have been found previously, which are not expected to result in an excessive final runaway current despite the strong avalanche gain [10]. However, these studies did not model the consistent build-up of the injected density following SPI and the subsequent current quench dynamics.…”

Section: Introductionmentioning

confidence: 99%

Effect of Two-Stage Shattered Pellet Injection on Tokamak Disruptions

Vallhagen,

Pusztai,

Hoppe

et al. 2022

Preprint

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An effective disruption mitigation system in a tokamak reactor should limit the exposure of the wall to localized heat losses and to the impact of high current runaway electron beams, and avoid excessive forces on the structure. We evaluate with respect to these aspects a two-stage deuterium-neon shattered pellet injection in an ITER-like plasma, using simulations with the Dream framework [M. Hoppe et al (2021) Comp. Phys. Commun. 268, 108098]. To minimize the obtained runaway currents an optimal range of injected deuterium quantities is found. This range is sensitive to the opacity of the plasma to Lyman radiation, which affects the ionization degree of deuterium, and thus avalanche runaway generation. The two-stage injection scheme, where dilution cooling is produced by deuterium before a radiative thermal quench caused by neon, reduces both the hot-tail seed and the localized transported heat load on the wall. However, during nuclear operation, additional runaway seed sources from the activated wall and tritium make it difficult to reach tolerably low runaway currents.

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Hot-Tail Runaway Seed Landscape during the Thermal Quench in Tokamaks

Cited by 22 publications

References 35 publications

Runaway dynamics in tokamak disruptions with current relaxation

Runaway dynamics in tokamak disruptions with current relaxation

Confinement of passing and trapped runaway electrons in the simulation of an ITER current quench

Effect of Two-Stage Shattered Pellet Injection on Tokamak Disruptions

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