Energetic electron transport in the presence of magnetic perturbations in magnetically confined plasmas

Papp, G.; Drevlak, M.; Pokol, Gergö; Fülöp, Tünde

doi:10.1017/s0022377815000537

Cited by 24 publications

(30 citation statements)

References 19 publications

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“…It is still unfeasible for the existing codes and computers to simulate the randomized field directly, because of severe resolution requirements and the need for a kinetic rather than MHD description of the emerging short scales. This situation motivates numerous sensitivity studies of the fast electron transport to magnetic fluctuations produced by the MHD codes, created by external magnetic coils or to the arbitrarily postulated ones [21,[25][26][27][28][29][30][31].…”

Section: B Resonant Mhd Perturbationsmentioning

confidence: 99%

Physics of runaway electrons in tokamaks

et al. 2019

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Of all electrons, runaway electrons have long been recognized in the fusion community as a distinctive population. They now attract special attention as a part of ITER mission considerations. This review covers basic physics ingredients of the runaway phenomenon and the ongoing efforts (experimental and theoretical) aimed at runaway electron taming in the next generation tokamaks. We emphasize the prevailing physics themes of the last 20 years: the hot-tail mechanism of runaway production, runaway electron interaction with impurity ions, the role of synchrotron radiation in runaway kinetics, runaway electron transport in presence of magnetic fluctuations, micro-instabilities driven by runaway electrons in magnetized plasmas, and vertical stability of the plasma with runaway electrons. The review also discusses implications of the runaway phenomenon for ITER and the current strategy of runaway electron mitigation.

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Section: B Resonant Mhd Perturbationsmentioning

confidence: 99%

Physics of runaway electrons in tokamaks

et al. 2019

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“…The time evolution of the modes and their saturation amplitude is a critical question to determine their potency for runaway transport. Earlier studies showed that a magnetic perturbation with an amplitude of about δB/B ≈ 0.1% is sufficient to suppress runaway avalanche [71,72], while more recent research [73] decreases this threshold by about a factor of 2.…”

Section: Interaction Of Alpha Particles and Alfvén Wavesmentioning

confidence: 98%

“…Recent studies [73] suggest that the perturbation amplitudes and particle displacement caused by the modes discussed in this paper can lead to runaway avalanche mitigation (or even suppression). If the core transport is enhanced by for example alpha-driven modes, runaways are more easily transported to the edge, where other methods, such as resonant magnetic perturbations [58,72] could further aid the removal of runaways.…”

Section: Transport Of Runaway Electronsmentioning

confidence: 99%

Alpha particle driven Alfvénic instabilities in ITER post-disruption plasmas

et al. 2021

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Fusion-born alpha particles in ITER disruption simulations are investigated as a possible drive of Alfvénic instabilities. The ability of these waves to expel runaway electron (RE) seed particles is explored in the pursuit of a passive, inherent RE mitigation scenario. The spatiotemporal evolution of the alpha particle distribution during the disruption is calculated using the linearized Fokker-Planck solver CODION coupled to a fluid disruption simulation. These simulations are done in the limit of no alpha particle transport during the thermal quench, which can be seen as a most pessimistic situation where there is also no RE seed transport. Under these assumptions, the radial anisotropy of the resulting alpha population provides free energy to drive Alfvénic modes during the quench phase of the disruption. We use the linear gyrokinetic magnetohydrodynamic code LIGKA to calculate the Alfvén spectrum and find that the equilibrium is capable of sustaining a wide range of modes. The self-consistent evolution of the mode amplitudes and the alpha distribution is calculated utilizing the wave-particle interaction tool HAGIS. Intermediate mode number (n = 7-15, 22-26) toroidal Alfvén eigenmodes are shown to saturate at an amplitude of up to δB/B ≈ 0.1% in the spatial regimes crucial for RE seed formation. We find that the mode amplitudes are predicted to be sufficiently large to permit the possibility of significant radial transport of REs.

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“…Furthermore, it has been shown that modelling the transport as purely diffusive is insufficient in mixed magnetic topologies containing both islands and stochastic regions (Papp et al. 2015), but this can be addressed by including an advection term in the model (Särkimäki et al. 2016).…”

Section: Radial Diffusion Of Runaway Electrons In the Presence Of Radmentioning

confidence: 99%

“…In such circumstances, the transport will no longer be well described by the expression given by Rechester & Rosenbluth (1978) and a more general transport model consisting of spatially dependent diffusive and advective components is often formulated, based on particle following simulations (Papp et al. 2015; Särkimäki et al. 2016).…”

Section: Transport In An Inhomogeneous Plasmamentioning

confidence: 99%

Effects of magnetic perturbations and radiation on the runaway avalanche

et al. 2021

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The electron runaway phenomenon in plasmas depends sensitively on the momentum- space dynamics. However, efficient simulation of the global evolution of systems involving runaway electrons typically requires a reduced fluid description. This is needed, for example, in the design of essential runaway mitigation methods for tokamaks. In this paper, we present a method to include the effect of momentum-dependent spatial transport in the runaway avalanche growth rate. We quantify the reduction of the growth rate in the presence of electron diffusion in stochastic magnetic fields and show that the spatial transport can raise the effective critical electric field. Using a perturbative approach, we derive a set of equations that allows treatment of the effect of spatial transport on runaway dynamics in the presence of radial variation in plasma parameters. This is then used to demonstrate the effect of spatial transport in current quench simulations for ITER-like plasmas with massive material injection. We find that in scenarios with sufficiently slow current quench, owing to moderate impurity and deuterium injection, the presence of magnetic perturbations reduces the final runaway current considerably. Perturbations localised at the edge are not effective in suppressing the runaways, unless the runaway generation is off-axis, in which case they may lead to formation of strong current sheets at the interface of the confined and perturbed regions.

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Energetic electron transport in the presence of magnetic perturbations in magnetically confined plasmas

Cited by 24 publications

References 19 publications

Physics of runaway electrons in tokamaks

Physics of runaway electrons in tokamaks

Alpha particle driven Alfvénic instabilities in ITER post-disruption plasmas

Effects of magnetic perturbations and radiation on the runaway avalanche

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