Recent DIII-D advances in runaway electron measurement and model validation
Artikel i vetenskaplig tidskrift, 2019

© 2019 IAEA, Vienna. 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.

tokamak

kinetic instability

disruption

runaway electron

Författare

C. Paz-Soldan

General Atomics

N. W. Eidietis

General Atomics

E M Hollmann

University of California

P B Aleynikov

Max Planck-institutet

L. Carbajal

Oak Ridge National Laboratory

W.W. Heidbrink

University of California at Irvine (UCI)

M. Hoppe

C. Liu

Princeton Plasma Physics Laboratory

A. Lvovskiy

Oak Ridge Associated Universities

D. Shiraki

Oak Ridge National Laboratory

D. Spong

Oak Ridge National Laboratory

D. P. Brennan

Princeton University

C. M. Cooper

Oak Ridge Associated Universities

Diego del-Castillo-Negrete

Oak Ridge National Laboratory

X. Du

General Atomics

Ola Embréus

Chalmers, Fysik, Subatomär fysik och plasmafysik

Tünde Fülöp

Chalmers, Fysik, Subatomär fysik och plasmafysik

J. Herfindal

Oak Ridge National Laboratory

R. A. Moyer

University of California

P. Parks

General Atomics

K. E. Thome

General Atomics

Nuclear Fusion

0029-5515 (ISSN)

Vol. 59 6 066025

Ämneskategorier

Atom- och molekylfysik och optik

Annan fysik

Fusion, plasma och rymdfysik

DOI

10.1088/1741-4326/ab1769

Mer information

Senast uppdaterat

2019-08-08