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Title: Thermal quench mitigation and current quench control by injection of mixed species shattered pellets in DIII-D

Injection of large shattered pellets composed of variable quantities of the main ion species (deuterium) and high-Z impurities (neon) in the DIII-D tokamak demonstrate control of thermal quench (TQ) and current quench (CQ) properties in mitigated disruptions. As the pellet composition is varied, TQ radiation fractions increase continuously with the quantity of radiating impurity in the pellet, with a corresponding decrease in divertor heating. Post-TQ plasma resistivities increase as a result of the higher radiation fraction, allowing control of current decay timescales based on the pellet composition. Magnetic reconstructions during the CQ show that control of the current decay rate allows continuous variation of the minimum safety factor during the vertically unstable disruption, reducing the halo current fraction and resulting vessel displacement. Both TQ and CQ characteristics are observed to saturate at relatively low quantities of neon, indicating that effective mitigation of disruption loads by shattered pellet injection (SPI) can be achieved with modest impurity quantities, within injection quantities anticipated for ITER. In conclusion, this mixed species SPI technique provides apossible approach for tuning disruption properties to remain within the limited ranges allowed in the ITER design.
Authors:
 [1] ;  [1] ; ORCiD logo [1] ;  [2] ;  [3] ;  [4] ; ORCiD logo [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, CA (United States)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Report Number(s):
LLNL-JRNL-737057
Journal ID: ISSN 1070-664X
Grant/Contract Number:
FC02-04ER54698; AC05-00OR22725; FG02-07ER54917; AC52-07NA27344
Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 23; Journal Issue: 6; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Research Org:
General Atomics, San Diego, CA (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; tokamak; disruption mitigation; shattered pellet injection; Halo; Radiation safety; Divertors; Plasma diagnostics; Electrical resistivity; toroidal plasma confinement; plasma properties; surface reconstruction; Physics - Plasma physics
OSTI Identifier:
1371758
Alternate Identifier(s):
OSTI ID: 1259368; OSTI ID: 1399582; OSTI ID: 1458629

Shiraki, D., Commaux, N., Baylor, L. R., Eidietis, N. W., Hollmann, E. M., Lasnier, C. J., and Moyer, R. A.. Thermal quench mitigation and current quench control by injection of mixed species shattered pellets in DIII-D. United States: N. p., Web. doi:10.1063/1.4954389.
Shiraki, D., Commaux, N., Baylor, L. R., Eidietis, N. W., Hollmann, E. M., Lasnier, C. J., & Moyer, R. A.. Thermal quench mitigation and current quench control by injection of mixed species shattered pellets in DIII-D. United States. doi:10.1063/1.4954389.
Shiraki, D., Commaux, N., Baylor, L. R., Eidietis, N. W., Hollmann, E. M., Lasnier, C. J., and Moyer, R. A.. 2016. "Thermal quench mitigation and current quench control by injection of mixed species shattered pellets in DIII-D". United States. doi:10.1063/1.4954389. https://www.osti.gov/servlets/purl/1371758.
@article{osti_1371758,
title = {Thermal quench mitigation and current quench control by injection of mixed species shattered pellets in DIII-D},
author = {Shiraki, D. and Commaux, N. and Baylor, L. R. and Eidietis, N. W. and Hollmann, E. M. and Lasnier, C. J. and Moyer, R. A.},
abstractNote = {Injection of large shattered pellets composed of variable quantities of the main ion species (deuterium) and high-Z impurities (neon) in the DIII-D tokamak demonstrate control of thermal quench (TQ) and current quench (CQ) properties in mitigated disruptions. As the pellet composition is varied, TQ radiation fractions increase continuously with the quantity of radiating impurity in the pellet, with a corresponding decrease in divertor heating. Post-TQ plasma resistivities increase as a result of the higher radiation fraction, allowing control of current decay timescales based on the pellet composition. Magnetic reconstructions during the CQ show that control of the current decay rate allows continuous variation of the minimum safety factor during the vertically unstable disruption, reducing the halo current fraction and resulting vessel displacement. Both TQ and CQ characteristics are observed to saturate at relatively low quantities of neon, indicating that effective mitigation of disruption loads by shattered pellet injection (SPI) can be achieved with modest impurity quantities, within injection quantities anticipated for ITER. In conclusion, this mixed species SPI technique provides apossible approach for tuning disruption properties to remain within the limited ranges allowed in the ITER design.},
doi = {10.1063/1.4954389},
journal = {Physics of Plasmas},
number = 6,
volume = 23,
place = {United States},
year = {2016},
month = {6}
}