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Title: Demonstration of Tokamak Discharge Shutdown with Shell Pellet Payload Impurity Dispersal

Abstract

The first rapid tokamak discharge shutdown using dispersive core payload deposition with shell pellets has been achieved in the DIII-D tokamak. Shell pellets are being investigated as a possible new path toward achieving tokamak disruption mitigation with both low conducted wall heat loads and slow current quench. Conventional disruption mitigation injects radiating impurities into the outer edge of the tokamak plasma, which tends to result in poor impurity assimilation and creates a strong edge cooling and outward heat flow, thus requiring undesirable high-$Z$ impurities to achieve low conducted heat loads. The shell pellet technique aims to produce a hollow temperature profile by using a thin, low-ablation shell surrounding a dispersive payload, giving a greatly increased impurity ablation (and radiation) rate when the payload is released in the plasma core. This principle was demonstrated successfully using 3.6 mm outer diameter, 40 μm thickness diamond shells holding boron powder. The pellets caused rapid (<10 ms) discharge shutdown with low conducted divertor heat fluence (~0.1 MJ/m 2). Confirmation of massive release of the boron powder payload into the plasma core was obtained spectroscopically. Some evidence for the formation of a hollow temperature profile during the shutdown was observed. Furthermore, these first results openmore » a new avenue for disruption mitigation research, hopefully enabling development of highly effective methods of avoiding disruption wall damage in future reactor-scale tokamaks.« less

Authors:
 [1];  [2];  [3];  [2];  [2];  [4];  [1]
  1. Univ. of California - San Diego, La Jolla, CA (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1542705
Alternate Identifier(s):
OSTI ID: 1494388
Report Number(s):
LLNL-JRNL-779527
Journal ID: ISSN 0031-9007; PRLTAO; 959496
Grant/Contract Number:  
AC52-07NA27344; FG02-07ER54917; FC02-04ER54698; AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 122; Journal Issue: 6; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Hollmann, E. M., Parks, P. B., Shiraki, D., Alexander, N., Eidietis, N. W., Lasnier, C. J., and Moyer, R. A. Demonstration of Tokamak Discharge Shutdown with Shell Pellet Payload Impurity Dispersal. United States: N. p., 2019. Web. doi:10.1103/PhysRevLett.122.065001.
Hollmann, E. M., Parks, P. B., Shiraki, D., Alexander, N., Eidietis, N. W., Lasnier, C. J., & Moyer, R. A. Demonstration of Tokamak Discharge Shutdown with Shell Pellet Payload Impurity Dispersal. United States. doi:10.1103/PhysRevLett.122.065001.
Hollmann, E. M., Parks, P. B., Shiraki, D., Alexander, N., Eidietis, N. W., Lasnier, C. J., and Moyer, R. A. Tue . "Demonstration of Tokamak Discharge Shutdown with Shell Pellet Payload Impurity Dispersal". United States. doi:10.1103/PhysRevLett.122.065001.
@article{osti_1542705,
title = {Demonstration of Tokamak Discharge Shutdown with Shell Pellet Payload Impurity Dispersal},
author = {Hollmann, E. M. and Parks, P. B. and Shiraki, D. and Alexander, N. and Eidietis, N. W. and Lasnier, C. J. and Moyer, R. A.},
abstractNote = {The first rapid tokamak discharge shutdown using dispersive core payload deposition with shell pellets has been achieved in the DIII-D tokamak. Shell pellets are being investigated as a possible new path toward achieving tokamak disruption mitigation with both low conducted wall heat loads and slow current quench. Conventional disruption mitigation injects radiating impurities into the outer edge of the tokamak plasma, which tends to result in poor impurity assimilation and creates a strong edge cooling and outward heat flow, thus requiring undesirable high-$Z$ impurities to achieve low conducted heat loads. The shell pellet technique aims to produce a hollow temperature profile by using a thin, low-ablation shell surrounding a dispersive payload, giving a greatly increased impurity ablation (and radiation) rate when the payload is released in the plasma core. This principle was demonstrated successfully using 3.6 mm outer diameter, 40 μm thickness diamond shells holding boron powder. The pellets caused rapid (<10 ms) discharge shutdown with low conducted divertor heat fluence (~0.1 MJ/m2). Confirmation of massive release of the boron powder payload into the plasma core was obtained spectroscopically. Some evidence for the formation of a hollow temperature profile during the shutdown was observed. Furthermore, these first results open a new avenue for disruption mitigation research, hopefully enabling development of highly effective methods of avoiding disruption wall damage in future reactor-scale tokamaks.},
doi = {10.1103/PhysRevLett.122.065001},
journal = {Physical Review Letters},
number = 6,
volume = 122,
place = {United States},
year = {2019},
month = {2}
}

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