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Title: Spatiotemporal Evolution of Runaway Electron Momentum Distributions in Tokamaks

Novel spatial, temporal, and energetically resolved measurements of bremsstrahlung hard-x-ray (HXR) emission from runaway electron (RE) populations in tokamaks reveal nonmonotonic RE distribution functions whose properties depend on the interplay of electric field acceleration with collisional and synchrotron damping. Measurements are consistent with theoretical predictions of momentum-space attractors that accumulate runaway electrons. RE distribution functions are measured to shift to a higher energy when the synchrotron force is reduced by decreasing the toroidal magnetic field strength. Increasing the collisional damping by increasing the electron density (at a fixed magnetic and electric field) reduces the energy of the nonmonotonic feature and reduces the HXR growth rate at all energies. Higher-energy HXR growth rates extrapolate to zero at the expected threshold electric field for RE sustainment, while low-energy REs are anomalously lost. The compilation ofHXR emission from different sight lines into the plasma yields energy and pitch-angle-resolved RE distributions and demonstrates increasing pitch-angle and radial gradients with energy.
Authors:
 [1] ;  [2] ;  [3] ;  [1] ;  [1] ;  [4] ;  [5] ;  [6] ;  [4] ;  [2] ;  [6] ;  [7]
  1. General Atomics, San Diego, CA (United States)
  2. Oak Ridge Associated Univ., Oak Ridge, TN (United States)
  3. Max-Planck Inst. for Plasma Physics, Greifswald (Germany)
  4. Princeton Univ., NJ (United States)
  5. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  6. Univ. of California, San Diego, CA (United States)
  7. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Grant/Contract Number:
FC02-04ER54698; FG02-07ER54917; AC05-00OR22725; FC02-99ER54512; SC0016268
Type:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 118; Journal Issue: 25; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Research Org:
General Atomics, San Diego, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
OSTI Identifier:
1374548
Alternate Identifier(s):
OSTI ID: 1365606

Paz-Soldan, Carlos, Cooper, Christopher M., Aleynikov, Pavel, Pace, David C., Eidietis, Nicholas W., Brennan, Dylan P., Granetz, R. S., Hollmann, Eric M., Liu, C., Lvovskiy, Andrey, Moyer, Richard A., and Shiraki, Daisuke. Spatiotemporal Evolution of Runaway Electron Momentum Distributions in Tokamaks. United States: N. p., Web. doi:10.1103/PhysRevLett.118.255002.
Paz-Soldan, Carlos, Cooper, Christopher M., Aleynikov, Pavel, Pace, David C., Eidietis, Nicholas W., Brennan, Dylan P., Granetz, R. S., Hollmann, Eric M., Liu, C., Lvovskiy, Andrey, Moyer, Richard A., & Shiraki, Daisuke. Spatiotemporal Evolution of Runaway Electron Momentum Distributions in Tokamaks. United States. doi:10.1103/PhysRevLett.118.255002.
Paz-Soldan, Carlos, Cooper, Christopher M., Aleynikov, Pavel, Pace, David C., Eidietis, Nicholas W., Brennan, Dylan P., Granetz, R. S., Hollmann, Eric M., Liu, C., Lvovskiy, Andrey, Moyer, Richard A., and Shiraki, Daisuke. 2017. "Spatiotemporal Evolution of Runaway Electron Momentum Distributions in Tokamaks". United States. doi:10.1103/PhysRevLett.118.255002. https://www.osti.gov/servlets/purl/1374548.
@article{osti_1374548,
title = {Spatiotemporal Evolution of Runaway Electron Momentum Distributions in Tokamaks},
author = {Paz-Soldan, Carlos and Cooper, Christopher M. and Aleynikov, Pavel and Pace, David C. and Eidietis, Nicholas W. and Brennan, Dylan P. and Granetz, R. S. and Hollmann, Eric M. and Liu, C. and Lvovskiy, Andrey and Moyer, Richard A. and Shiraki, Daisuke},
abstractNote = {Novel spatial, temporal, and energetically resolved measurements of bremsstrahlung hard-x-ray (HXR) emission from runaway electron (RE) populations in tokamaks reveal nonmonotonic RE distribution functions whose properties depend on the interplay of electric field acceleration with collisional and synchrotron damping. Measurements are consistent with theoretical predictions of momentum-space attractors that accumulate runaway electrons. RE distribution functions are measured to shift to a higher energy when the synchrotron force is reduced by decreasing the toroidal magnetic field strength. Increasing the collisional damping by increasing the electron density (at a fixed magnetic and electric field) reduces the energy of the nonmonotonic feature and reduces the HXR growth rate at all energies. Higher-energy HXR growth rates extrapolate to zero at the expected threshold electric field for RE sustainment, while low-energy REs are anomalously lost. The compilation ofHXR emission from different sight lines into the plasma yields energy and pitch-angle-resolved RE distributions and demonstrates increasing pitch-angle and radial gradients with energy.},
doi = {10.1103/PhysRevLett.118.255002},
journal = {Physical Review Letters},
number = 25,
volume = 118,
place = {United States},
year = {2017},
month = {6}
}