On the relativistic large-angle electron collision operator for runaway avalanches in plasmas

Embréus, Ola; Stahl, Adam; Fülöp, Tünde

doi:10.1017/s002237781700099x

Cited by 28 publications

(48 citation statements)

References 40 publications

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“…In general, the large logarithm requires some adjustment to avoid double counting, as detailed in Ref. [52].…”

Section: B Electron-electron Collisions and Stopping Powermentioning

confidence: 99%

“…Implementation of this bookkeeping is straightforward in Monte-Carlo simulations [53] but requires some extra care within a continuous formulation to preserve particle conservation properties in the kinetic equation. Reference [52] provides such a continuous formulation along with a procedure for solving the kinetic equation numerically.…”

Section: B Electron-electron Collisions and Stopping Powermentioning

confidence: 99%

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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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“…In general, the large logarithm requires some adjustment to avoid double counting, as detailed in Ref. [52].…”

Section: B Electron-electron Collisions and Stopping Powermentioning

confidence: 99%

Section: B Electron-electron Collisions and Stopping Powermentioning

confidence: 99%

Physics of runaway electrons in tokamaks

et al. 2019

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“…We follow the calculation of Helander et al (2002) under the approximation Γ ≈ Γ 0 E/E eff c where Γ 0 is independent of the electric field. Neglecting electric-field diffusion -which may however significantly affect the final runaway current profile (Eriksson et al 2004;Smith et al 2006) -the zero-dimensional induction equation is…”

Section: Effect On Avalanche Growth Rate and Runaway Distributionmentioning

confidence: 99%

“…These results were obtained by solving the kinetic equation using the numerical solver code (Landreman, Stahl & Fülöp 2014; Stahl et al. 2016), including avalanche generation using the field particle Boltzmann operator given in equation (2.17) of Embréus, Stahl & Fülöp (2018), which was also studied by Chiu et al. (1998).…”

Section: Effect On Avalanche Growth Rate and Runaway Distributionmentioning

confidence: 99%

Generalized collision operator for fast electrons interacting with partially ionized impurities

et al. 2018

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Accurate modelling of the interaction between fast electrons and partially ionized atoms is important for evaluating tokamak disruption mitigation schemes based on material injection. This requires accounting for the effect of screening of the impurity nuclei by the cloud of bound electrons. In this paper, we generalize the Fokker-Planck operator in a fully ionized plasma by accounting for the effect of screening. We detail the derivation of this generalized operator, and calculate the effective ion length-scales, which are needed in the components of the collision operator, for a number of ion species commonly appearing in fusion experiments. We show that for high electric fields, the secondary runaway growth rate can be substantially larger than in a fully ionized plasma with the same effective charge, although the growth rate is significantly reduced at near-critical electric fields. Furthermore, by comparison with the Boltzmann collision operator, we show that the Fokker-Planck formalism is accurate even for large impurity content. † Email address for correspondence: hesslow@chalmers.se

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“…2015; Stahl et al. 2015), bremsstrahlung (Embréus, Stahl & Fülöp 2016) and close collisions (Embréus, Stahl & Fülöp 2018).…”

Section: Kinetic Equation For Positronsmentioning

confidence: 99%

Dynamics of positrons during relativistic electron runaway

et al. 2018

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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]

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On the relativistic large-angle electron collision operator for runaway avalanches in plasmas

Cited by 28 publications

References 40 publications

Physics of runaway electrons in tokamaks

Physics of runaway electrons in tokamaks

Generalized collision operator for fast electrons interacting with partially ionized impurities

Dynamics of positrons during relativistic electron runaway

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