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

Abstract

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,more » 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.« less

Authors:
ORCiD logo [1]; ORCiD logo [1];  [2];  [3]; ORCiD logo [4]; ORCiD logo [5]; ORCiD logo [6]; ORCiD logo [7]; ORCiD logo [8]; ORCiD logo [4]; ORCiD logo [4];  [9];  [8]; ORCiD logo [4];  [1];  [6];  [6]; ORCiD logo [4];  [2];  [1] more »; ORCiD logo [1] « less
  1. General Atomics, San Diego, CA (United States)
  2. Univ. of California, San Diego, CA (United States)
  3. Max-Planck Inst. for Plasma Physics, Greifswald (Germany)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  5. Univ. of California, Irvine, CA (United States)
  6. Chalmers Univ. of Technology, Göteborg (Sweden)
  7. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  8. Oak Ridge Associated Univ., Oak Ridge, TN (United States)
  9. Princeton Univ., NJ (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); U.S. Dept. of Energy (USDOE), Washington D.C. (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1568772
Alternate Identifier(s):
OSTI ID: 1511907
Grant/Contract Number:  
AC05-00OR22725; FC02-04ER54698
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 59; Journal Issue: 6; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; runaway electron; tokamak; kinetic instability; disruption

Citation Formats

Paz-Soldan, C., Eidietis, N. W., Hollmann, E. M., Aleynikov, P., Carbajal, Leopoldo, Heidbrink, W. W., Hoppe, M., Liu, C., Lvovskiy, Andreas, Shiraki, Daisuke, Spong, Donald, Brennan, Dylan, Cooper, C. M., Del-Castillo-Negrete, Diego B., Du, X., Embreus, O., Fulop, T., Herfindal, Jeffrey L., Moyer, R.A., Parks, P. B., and Thome, K. E. Recent DIII-D advances in runaway electron measurement and model validation. United States: N. p., 2019. Web. doi:10.1088/1741-4326/ab1769.
Paz-Soldan, C., Eidietis, N. W., Hollmann, E. M., Aleynikov, P., Carbajal, Leopoldo, Heidbrink, W. W., Hoppe, M., Liu, C., Lvovskiy, Andreas, Shiraki, Daisuke, Spong, Donald, Brennan, Dylan, Cooper, C. M., Del-Castillo-Negrete, Diego B., Du, X., Embreus, O., Fulop, T., Herfindal, Jeffrey L., Moyer, R.A., Parks, P. B., & Thome, K. E. Recent DIII-D advances in runaway electron measurement and model validation. United States. doi:10.1088/1741-4326/ab1769.
Paz-Soldan, C., Eidietis, N. W., Hollmann, E. M., Aleynikov, P., Carbajal, Leopoldo, Heidbrink, W. W., Hoppe, M., Liu, C., Lvovskiy, Andreas, Shiraki, Daisuke, Spong, Donald, Brennan, Dylan, Cooper, C. M., Del-Castillo-Negrete, Diego B., Du, X., Embreus, O., Fulop, T., Herfindal, Jeffrey L., Moyer, R.A., Parks, P. B., and Thome, K. E. Wed . "Recent DIII-D advances in runaway electron measurement and model validation". United States. doi:10.1088/1741-4326/ab1769.
@article{osti_1568772,
title = {Recent DIII-D advances in runaway electron measurement and model validation},
author = {Paz-Soldan, C. and Eidietis, N. W. and Hollmann, E. M. and Aleynikov, P. and Carbajal, Leopoldo and Heidbrink, W. W. and Hoppe, M. and Liu, C. and Lvovskiy, Andreas and Shiraki, Daisuke and Spong, Donald and Brennan, Dylan and Cooper, C. M. and Del-Castillo-Negrete, Diego B. and Du, X. and Embreus, O. and Fulop, T. and Herfindal, Jeffrey L. and Moyer, R.A. and Parks, P. B. and Thome, K. E.},
abstractNote = {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.},
doi = {10.1088/1741-4326/ab1769},
journal = {Nuclear Fusion},
number = 6,
volume = 59,
place = {United States},
year = {2019},
month = {5}
}

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