skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

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

Abstract

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:
Research Org.:
General Atomics, San Diego, CA (United States); U.S. Dept. of Energy
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24); USDOE Office of Nuclear Energy (NE)
OSTI Identifier:
1371758
Alternate Identifier(s):
OSTI ID: 1259368; OSTI ID: 1399582
Grant/Contract Number:
FC02-04ER54698; AC05-00OR22725; FG02-07ER54917; AC52-07NA27344
Resource Type:
Journal Article: 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)
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

Citation Formats

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., 2016. 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. Mon . "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 = {Mon Jun 27 00:00:00 EDT 2016},
month = {Mon Jun 27 00:00:00 EDT 2016}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Citation Metrics:
Cited by: 4works
Citation information provided by
Web of Science

Save / Share:
  • 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 demonstrates 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 ratemore » 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. This mixed species SPI technique provides a possible approach for tuning disruption properties to remain within the limited ranges allowed in the ITER design.« less
  • Cited by 4
  • 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 demonstrates 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 ratemore » 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. This mixed species SPI technique provides a possible approach for tuning disruption properties to remain within the limited ranges allowed in the ITER design.« less
  • A severe consequence of a disruption on large tokamaks such as ITER could be the generation of multi-megaelectronvolt electron beams that could damage the vacuum vessel and the structures of the machine if they hit the wall unmitigated. The mitigation of runaway electron beams is thus a key requirement for reliable operation of ITER. In order to achieve reliable disruption mitigation, a new fast shutdown technique has been developed: the injection of a large shattered cryogenic pellet in the plasma, which is expected to increase the electron density up to levels where the beam generation processes are mitigated by collisionalmore » losses. This technique has been implemented and tested for the first time ever on DIII-D. The first tests show evidence of an almost instantaneous deposition of more than 260 Pa m(3) of deuterium deep in the core. Record local densities during the thermal quench were observed for each injection with a very high reliability. Pellet mass and plasma energy content scans show an improvement of the assimilation of the particles for higher plasma energy and larger pellet mass.« less