Guiding-centre transformation of the radiation–reaction force in a non-uniform magnetic field

This overview covers recent developments in the theory of runaway electrons in tokamaks. Its main purpose is to outline the intuitive basis for first-principle advancements in runaway electron physics. The overview highlights the following physics aspects of the runaway evolution: (1) survival and acceleration of initially hot electrons during thermal quench, (2) effect of magnetic perturbations on runaway confinement, (3) multiplication of the runaways via knock-on collisions with the bulk electrons, (4) slow decay of the runaway current, and (5) runaway-driven micro-instabilities. The scope of the reported studies is governed by the need to understand the behavior of runaway electrons as an essential physics element of the disruption events in ITER in order to develop an effective runaway mitigation scheme.

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“…[30] and then independently in Refs. [48], [49].This peaking is very likely to facilitate excitation of kinetic instabilities.…”

Section: Avalanche Threshold and Current Decaymentioning

confidence: 97%

Kinetics of relativistic runaway electrons

Breǐzman

Aleynikov

2017

Nucl. Fusion

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“…Although the guiding-centre drift motion is routinely solved for in modern orbit following codes, accurately accounting for the effects of drifts in simulations of synchrotron radiation images is non-trivial and has, to our knowledge, previously only been employed in calculating the effect of synchrotron radiation-reaction (Hirvijoki et al. 2015). The details of the recently implemented support for guiding-centre drifts in Soft are provided in appendix A.…”

Section: Synchrotron Radiation From Resmentioning

confidence: 99%

“…An expression for the Larmor radius vector to first order was given by Hirvijoki et al. (2015), and using expressions found therein one can also derive the following expression for the momentum vector of a particle with mass and charge (negative for electrons): with the guiding-centre momentum vector where and are the particle momenta parallel and perpendicular to the magnetic field, respectively, is the magnetic field strength, and are mutually perpendicular unit vectors in the direction of the magnetic field and (lowest-order) Larmor radius vector, respectively, , is the Larmor radius, is the magnetic moment, is the inverse curvature vector, , and the dyads and are defined as To lowest order, the momentum vector (A 1) describes circular gyro motion around the magnetic field line. However, when including terms, the gyro motion component picks up contributions which alter this circular motion.…”

mentioning

confidence: 99%

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

et al. 2021

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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.

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“…The final step necessary to formulate our problem, the transformation of the RR force, was given recently in Hirvijoki et al. (2015).…”

Section: Kinetic Equationmentioning

confidence: 99%

Radiation reaction induced non-monotonic features in runaway electron distributions

et al. 2015

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Runaway electrons, which are generated in a plasma where the induced electric field exceeds a certain critical value, can reach very high energies in the MeV range. For such energetic electrons, radiative losses will contribute significantly to the momentum space dynamics. Under certain conditions, due to radiative momentum losses, a non-monotonic feature -a "bump" -can form in the runaway electron tail, creating a potential for bump-on-tail-type instabilities to arise. Here we study the conditions for the existence of the bump. We derive an analytical threshold condition for bump appearance and give an approximate expression for the minimum energy at which the bump can appear. Numerical calculations are performed to support the analytical derivations.

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Guiding-centre transformation of the radiation–reaction force in a non-uniform magnetic field

Cited by 20 publications

References 20 publications

Kinetics of relativistic runaway electrons

Kinetics of relativistic runaway electrons

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

Radiation reaction induced non-monotonic features in runaway electron distributions

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