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Title: Disruption thermal load mitigation with shattered pellet injection on the Joint European Torus (JET)

Abstract

Disruption mitigation remains a critical, unresolved challenge for ITER. To aid in addressing this challenge, a shattered pellet injection (SPI) system was installed on JET and experiments conducted at a range of thermal energy fractions and stored energies in excess of 7 MJ. The primary goals of these experiments were to investigate the efficacy of the SPI on JET and the ability of the plasma to assimilate multiple pellets. Single pellet injections produced a saturation in total radiated energy (Wrad) with increasing injected neon content, suggesting total radiation of stored thermal energy. Further increases in injected neon quantities resulted in reduced cooling times and current quench (CQ) durations, indicating higher impurity assimilation. No significant variation in CQ duration or Wrad was observed when varying the deuterium content at fixed neon quantities. Additionally, higher assimilation, inferred by shorter CQ durations, was measured when a mechanical punch was used to launch the pellets and this was attributed to a lower pellet velocity leading to higher solid content in the pellet plume and larger fragments penetrating deeper into the plasma. Radiation asymmetries averaged over the cooling time were inferred from Emis3D and ranged from 1.6 to 1.9. Asymmetries averaged over the entire disruptionmore » sequence were found to increase at higher thermal energy fractions. The radiated energy fractions decreased with increasing thermal energy fractions but this trend was eliminated when toroidal asymmetries were accounted for with Emis3D. Pure deuterium pellets were able to produce cooling times of up to 75 ms with a gradual loss in thermal stored energy of up to 80%. Experiments with multiple pellet injection indicated Wrad can be increased through pellet superposition and density can be increased with an additional D2 injection without a reduction in Wrad. KPRAD modelling accurately reproduced the cooling times and the CQ duration at high thermal energies. Assimilation estimates from KPRAD indicated CQ rates scale strongly whilst Wrad scales weakly and saturates with assimilated neon content. Comparable Wrad can be achieved with lower assimilated neon quantities as longer cooling times are attained. Thus reduced neon content can be preferential in a thermal load mitigation scheme as it may reduce radiation asymmetries and prevent flash melting.« less

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3];  [4];  [5];  [6]; ORCiD logo [5];  [3]; ORCiD logo [6]; ORCiD logo [4]
+ Show Author Affiliations
  1. Ecole Polytechnique Federale Lausanne (Switzerland). Swiss Plasma Center
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  4. Culham Science Centre, Abingdon (United Kingdom). Culham Centre for Fusion Energy (CCFE), EURATOM/UKAEA Fusion Association
  5. ITER Organization, St. Paul Lez Durance (France)
  6. CEA, IRFM, Saint Paul Lez Durance (France)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE; EUROfusion Consortium
OSTI Identifier:
1865736
Grant/Contract Number:  
AC05-00OR22725; 633053
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 61; Journal Issue: 12; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Sheikh, U. A., Shiraki, D., Sweeney, R., Carvalho, P., Jachmich, S., Joffrin, E., Lehnen, M., Lovell, J., Nardon, E., and Silburn, S. Disruption thermal load mitigation with shattered pellet injection on the Joint European Torus (JET). United States: N. p., 2021. Web. doi:10.1088/1741-4326/ac3191.
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Sheikh, U. A., Shiraki, D., Sweeney, R., Carvalho, P., Jachmich, S., Joffrin, E., Lehnen, M., Lovell, J., Nardon, E., & Silburn, S. Disruption thermal load mitigation with shattered pellet injection on the Joint European Torus (JET). United States. https://doi.org/10.1088/1741-4326/ac3191
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Sheikh, U. A., Shiraki, D., Sweeney, R., Carvalho, P., Jachmich, S., Joffrin, E., Lehnen, M., Lovell, J., Nardon, E., and Silburn, S. Fri . "Disruption thermal load mitigation with shattered pellet injection on the Joint European Torus (JET)". United States. https://doi.org/10.1088/1741-4326/ac3191. https://www.osti.gov/servlets/purl/1865736.
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@article{osti_1865736,
title = {Disruption thermal load mitigation with shattered pellet injection on the Joint European Torus (JET)},
author = {Sheikh, U. A. and Shiraki, D. and Sweeney, R. and Carvalho, P. and Jachmich, S. and Joffrin, E. and Lehnen, M. and Lovell, J. and Nardon, E. and Silburn, S.},
abstractNote = {Disruption mitigation remains a critical, unresolved challenge for ITER. To aid in addressing this challenge, a shattered pellet injection (SPI) system was installed on JET and experiments conducted at a range of thermal energy fractions and stored energies in excess of 7 MJ. The primary goals of these experiments were to investigate the efficacy of the SPI on JET and the ability of the plasma to assimilate multiple pellets. Single pellet injections produced a saturation in total radiated energy (Wrad) with increasing injected neon content, suggesting total radiation of stored thermal energy. Further increases in injected neon quantities resulted in reduced cooling times and current quench (CQ) durations, indicating higher impurity assimilation. No significant variation in CQ duration or Wrad was observed when varying the deuterium content at fixed neon quantities. Additionally, higher assimilation, inferred by shorter CQ durations, was measured when a mechanical punch was used to launch the pellets and this was attributed to a lower pellet velocity leading to higher solid content in the pellet plume and larger fragments penetrating deeper into the plasma. Radiation asymmetries averaged over the cooling time were inferred from Emis3D and ranged from 1.6 to 1.9. Asymmetries averaged over the entire disruption sequence were found to increase at higher thermal energy fractions. The radiated energy fractions decreased with increasing thermal energy fractions but this trend was eliminated when toroidal asymmetries were accounted for with Emis3D. Pure deuterium pellets were able to produce cooling times of up to 75 ms with a gradual loss in thermal stored energy of up to 80%. Experiments with multiple pellet injection indicated Wrad can be increased through pellet superposition and density can be increased with an additional D2 injection without a reduction in Wrad. KPRAD modelling accurately reproduced the cooling times and the CQ duration at high thermal energies. Assimilation estimates from KPRAD indicated CQ rates scale strongly whilst Wrad scales weakly and saturates with assimilated neon content. Comparable Wrad can be achieved with lower assimilated neon quantities as longer cooling times are attained. Thus reduced neon content can be preferential in a thermal load mitigation scheme as it may reduce radiation asymmetries and prevent flash melting.},
doi = {10.1088/1741-4326/ac3191},
journal = {Nuclear Fusion},
number = 12,
volume = 61,
place = {United States},
year = {Fri Nov 12 00:00:00 EST 2021},
month = {Fri Nov 12 00:00:00 EST 2021}
}
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Publisher's Version of Record
https://doi.org/10.1088/1741-4326/ac3191
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Works referenced in this record:

The Development of Shattered Pellet Injector on HL-2A
journal, November 2018

Automating the design of tokamak experiment scenarios
journal, October 2019

MHD stability in X-point geometry: simulation of ELMs
journal, June 2007

Deployment of multiple shattered pellet injection systems in KSTAR
journal, May 2020

Radiation asymmetry and MHD destabilization during the thermal quench after impurity shattered pellet injection
journal, January 2021

Shatter Thresholds and Fragment Size Distributions of Deuterium–Neon Mixture Cryogenic Pellets for Tokamak Thermal Mitigation
journal, September 2020

Demonstration of rapid shutdown using large shattered deuterium pellet injection in DIII-D
journal, September 2010

Design and performance of shattered pellet injection systems for JET and KSTAR disruption mitigation research in support of ITER *
journal, August 2021

Methods to determine the radiated power in SPI-mitigated disruptions in JET
journal, February 2021

  • Lovell, J.; Reinke, M. L.; Sheikh, U. A.
  • Review of Scientific Instruments, Vol. 92, Issue 2
  • DOI: 10.1063/5.0014654

Disruption mitigation efficiency and scaling with thermal energy fraction on ASDEX Upgrade
journal, October 2020

Impact and mitigation of disruptions with the ITER-like wall in JET
journal, August 2013

Design of a shattered pellet injection system on J-TEXT tokamak
journal, October 2018

  • Li, Y.; Chen, Z. Y.; Wei, Y. N.
  • Review of Scientific Instruments, Vol. 89, Issue 10
  • DOI: 10.1063/1.5035186
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