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Title: Injection of multiple shattered pellets for disruption mitigation in DIII-D

Abstract

Plasma shutdown experiments in DIII-D have injected multiple shattered pellets at different toroidal locations for the first time, as is planned for the ITER disruption mitigation system. Systematically varying the relative timing of the two pellets suggests that simultaneously injected pellets may influence the assimilation of each other, altering the resulting disruption characteristics compared to a single pellet injecting similar neon quantities. Thermal quench (TQ) radiation measured near the injection location is reduced with the dual pellets, contrary to TQ radiation measured away from the injection ports, which does not show a clear difference between single or dual pellet injections. The mitigation of other disruption loads, such as the current quench (CQ) duration and divertor heat loads, decrease when the pellets enter the plasma simultaneously compared to single shattered pellet injections with similar neon quantities. This similar reduction in mitigation of CQ and conductive loads is consistent with the observed reduction in total TQ radiation. The time between initial pellet injection and the end of the TQ is shorter when both pellets are injected simultaneously compared to a single pellet. This lower cooling duration may limit the amount of the neon assimilated by the plasma prior to the end ofmore » the TQ, consistent with the observed reduction in radiation. The injected impurities spread primarily in the parallel direction, away from the source at the injection location. The addition of two shattered pellet injectors shows that the initial poloidal radiation is spread out into two distinct regions, cooling multiple flux tubes simultaneously, which may induce global MHD instabilities more rapidly than a single flux tube of impurities leading to a shorter cooling duration. The electron density increased by approximately a factor of two with the addition of multiple pellets, but is highly sensitive to the time between injections. Here, a maximum density increase is found when both pellets arrive at the plasma prior to the start of the TQ.« less

Authors:
ORCiD logo [1];  [1];  [1]; ORCiD logo [2];  [3];  [4];  [3]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Univ. of California San Diego, La Jolla, CA (United States)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES); USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1593101
Alternate Identifier(s):
OSTI ID: 1608090
Report Number(s):
DOE-GA-54698; LLNL-JRNL-806822
Journal ID: ISSN 0029-5515
Grant/Contract Number:  
FC02-04ER54698; AC05-00OR22725; FG02-07ER54917; AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 59; Journal Issue: 10; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; tokamak; disruption mitigation; shattered pellet injection; multiple shattered pellet injection

Citation Formats

Herfindal, J. L., Shiraki, D., Baylor, L. R., Eidietis, N. W., Hollmann, E. M., Lasnier, C. J., and Moyer, R. A. Injection of multiple shattered pellets for disruption mitigation in DIII-D. United States: N. p., 2019. Web. doi:10.1088/1741-4326/ab3693.
Herfindal, J. L., Shiraki, D., Baylor, L. R., Eidietis, N. W., Hollmann, E. M., Lasnier, C. J., & Moyer, R. A. Injection of multiple shattered pellets for disruption mitigation in DIII-D. United States. doi:10.1088/1741-4326/ab3693.
Herfindal, J. L., Shiraki, D., Baylor, L. R., Eidietis, N. W., Hollmann, E. M., Lasnier, C. J., and Moyer, R. A. Wed . "Injection of multiple shattered pellets for disruption mitigation in DIII-D". United States. doi:10.1088/1741-4326/ab3693. https://www.osti.gov/servlets/purl/1593101.
@article{osti_1593101,
title = {Injection of multiple shattered pellets for disruption mitigation in DIII-D},
author = {Herfindal, J. L. and Shiraki, D. and Baylor, L. R. and Eidietis, N. W. and Hollmann, E. M. and Lasnier, C. J. and Moyer, R. A.},
abstractNote = {Plasma shutdown experiments in DIII-D have injected multiple shattered pellets at different toroidal locations for the first time, as is planned for the ITER disruption mitigation system. Systematically varying the relative timing of the two pellets suggests that simultaneously injected pellets may influence the assimilation of each other, altering the resulting disruption characteristics compared to a single pellet injecting similar neon quantities. Thermal quench (TQ) radiation measured near the injection location is reduced with the dual pellets, contrary to TQ radiation measured away from the injection ports, which does not show a clear difference between single or dual pellet injections. The mitigation of other disruption loads, such as the current quench (CQ) duration and divertor heat loads, decrease when the pellets enter the plasma simultaneously compared to single shattered pellet injections with similar neon quantities. This similar reduction in mitigation of CQ and conductive loads is consistent with the observed reduction in total TQ radiation. The time between initial pellet injection and the end of the TQ is shorter when both pellets are injected simultaneously compared to a single pellet. This lower cooling duration may limit the amount of the neon assimilated by the plasma prior to the end of the TQ, consistent with the observed reduction in radiation. The injected impurities spread primarily in the parallel direction, away from the source at the injection location. The addition of two shattered pellet injectors shows that the initial poloidal radiation is spread out into two distinct regions, cooling multiple flux tubes simultaneously, which may induce global MHD instabilities more rapidly than a single flux tube of impurities leading to a shorter cooling duration. The electron density increased by approximately a factor of two with the addition of multiple pellets, but is highly sensitive to the time between injections. Here, a maximum density increase is found when both pellets arrive at the plasma prior to the start of the TQ.},
doi = {10.1088/1741-4326/ab3693},
journal = {Nuclear Fusion},
issn = {0029-5515},
number = 10,
volume = 59,
place = {United States},
year = {2019},
month = {9}
}

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