Resolving runaway electron distributions in space, time, and energy

Paz-Soldan, C.; Cooper, C. M.; Aleynikov, P.; Eidietis, N. W.; Lvovskiy, A.; Pace, D. C.; Brennan, D. P.; Hollmann, E. M.; Liu, Chang; Moyer, R. A.; Shiraki, D.

doi:10.1063/1.5024223

Cited by 35 publications

(62 citation statements)

References 48 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Similar findings are reported from J-TEXT [247]. More recently, it was observed at DIII-D that the absence of a runaway current plateau is correlated with the existence of Alfvén-like instabilities [289].…”

Section: H Other Runaway Electron Mitigation Techniquessupporting

confidence: 87%

“…Saturation in the achievable dissipation rates have been seen in experiments (e.g. [289]) that is likely caused by long transport times to bring the impurities into the background plasma of the runaway beam. First attempts to inject impurities with SPI into a runaway beam confirm the expectation that also the ice fragments are not penetrating the beam since similar dissipation rates were achieved as for MGI [237].…”

Section: Runaway Electron Energy Dissipationmentioning

confidence: 99%

See 1 more Smart Citation

Physics of runaway electrons in tokamaks

et al. 2019

View full text Add to dashboard Cite

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.

show abstract

Section: H Other Runaway Electron Mitigation Techniquessupporting

confidence: 87%

Section: Runaway Electron Energy Dissipationmentioning

confidence: 99%

Physics of runaway electrons in tokamaks

et al. 2019

View full text Add to dashboard Cite

show abstract

“…Comparing the f e obtained by experiment and modeling in Fig. 6, qualitative trends with n e and B T are captured and some discrepancies identified [33,36]. Non-monotonic f e features are found at the E RE predicted by time-dependent 0-D 2-V FP modeling [see purple arrows in Fig.…”

Section: Re Distribution Measurement Via Bremsstrahlungmentioning

confidence: 91%

“…At the time, the most complete 0-D 2-V FP treatments including additional effects such as synchrotron damping and pitch angle scattering predicted E φ /E crit values of just under 2 being sufficient for RE decay in these conditions [13,57]. Later energy-resolved HXR growth and decay measurements further clarified this picture by finding the strongest anomalous dissipation to low energy [36,33]. These measurements were hypothesized to be explained by either spatial transport of REs, or by modification of the RE f e and dissipation rate by kinetic instabilities.…”

Section: Re Dissipation Via Kinetic Instabilitiesmentioning

confidence: 98%

Recent DIII-D advances in runaway electron measurement and model validation

Paz-Soldan¹,

Eidietis²,

Hollmann³

et al. 2019

Nucl. Fusion

Self Cite

View full text Add to dashboard Cite

Novel measurements and modeling of runaway electron (RE) dynamics in DIII-D have resolved experimental discrepancies and validated predictions for ITER, improving confidence that RE avoidance and mitigation can be predictably achieved. Considering RE formation, first experimental assessments of the RE seed current demonstrates that present hot-tail theories are not yet accurate and require improved treatment of the pellet dynamics. Novel measurements of kinetic instabilities in the MHz-range have been made in the RE formation phase, with the intensity of these modes correlated with previously unexplained empirical thresholds for RE generation. Controlled RE dissipation experiments in quiescent regimes have validated RE distribution function dependencies on collisional and synchrotron damping, both in terms of distribution function shape and dissipation rates. Measurements of RE bremsstrahlung and synchrotron emission are now used in tandem to resolve energy and pitch-angle effects. A resolution to long-standing dissipation anomalies in the quiescent regime is offered by taking into account kinetic instability effects on RE phase-space dynamics. Kinetic instabilities in the 100-200 MHz range are directly observed, though modeling finds the largest dissipation arises from GHz range instabilities that are beyond the reach of existing diagnostics. Kinetic instabilities are also observed in the mature post-disruption RE plateau phase, so long as the collisional damping rate is reduced with low-Z injection. Experiments with high-Z injection find that the dissipation rate saturates with injection quantity, likely due to neutral diffusion rates being slower than vertical instability rates in DIII-D. Considering the final loss, a 0D model for first-wall Joule heating is found to be in agreement with experiment, and controlled access to RE equilibria with edge safety factor of two identifies novel dynamics brought about by large-scale kink instabilities. These dynamics are typified by fast (tens of microseconds) RE loss rates without RE beam regeneration. The above measurements and comparison with theory represent significant advances in the understanding of RE dynamics and indicate possible new opportunities for RE avoidance or mitigation via kinetic instabilities.

show abstract

“…As most of the FI in the MeV range lead to nuclear reactions, a single gamma-ray spectrum from a tokamak plasma is a diagnostics of different FI species simultaneously, and the number, intensity and shape of the lines embeds information on their distribution functions. MeV range REs are instead manifested by the bremsstrahlung radiation they emit as they collide with the plasma ions or impurities [12,13]. Unlike the case of FI driven reactions, the MeV range energy spectrum of this so called hard x-ray (HXR) emission is continuous and there is interest in measuring its shape and spatio-temporal evolution, which again depends on the distribution function of the REs.…”

Section: Introductionmentioning

confidence: 99%

MeV range particle physics studies in tokamak plasmas using gamma-ray spectroscopy

Contributers

Team

Nocente

et al. 2019

Plasma Phys. Control. Fusion

Self Cite

View full text Add to dashboard Cite

Gamma-ray spectroscopy (GRS) has become an established technique to determine properties of the distribution function of the energetic particles in the MeV range, which are fast ions from heating and fusion reactions or runaway electrons born in disruptions.In this paper we present a selection of recent results where GRS is key to investigate the physics of MeV range particles. These range from radio-frequency heating experiments, where theoretical models can be tested with an unprecedented degree of accuracy, to disruption mitigation studies, where GRS sheds light on the effect of the actuators on the runaway electron velocity space. We further discuss the unique observational capabilities offered by the technique in deuterium-tritium plasmas, particularly with regard to the inference of the energyand pitch-resolved distribution function of the α particles born from fusion reactions in the plasma core.

show abstract

Resolving runaway electron distributions in space, time, and energy

Cited by 35 publications

References 48 publications

Physics of runaway electrons in tokamaks

Physics of runaway electrons in tokamaks

Recent DIII-D advances in runaway electron measurement and model validation

MeV range particle physics studies in tokamak plasmas using gamma-ray spectroscopy

Contact Info

Product

Resources

About