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Title: Ablation of solid pellets induced by supra-thermal ions in the far scrape-off layer of DIII-D plasmas

Abstract

Injection of solid pellets is a key element in several aspects of the operation of a magnetic confinement plasma reactor for fusion applications, including plasma fueling, control and diagnosis. This letter reports observations demonstrating that pellet ablation can begin outside the plasma boundary, by effect of supra-thermal ions, whose orbits, under appropriate conditions, can extend well into the vacuum region. The phenomenon was recorded during plasma discharges in the DIII-D tokamak, combining pulsed modulation of heating neutral beams, with high-frequency injection of sub-millimeter lithium pellets, and it is ascribed to the large fraction of trapped beam ions associated with counter current neutral beam injection. Furthermore, the effect was quantitatively evaluated by means of Monte-Carlo simulations of supra-thermal ion orbits, finding that the heat-deposition was of the order of 50–100 W mm –2, in the region traversed by the lithium pellets before reaching the plasma boundary, which is consistent with the severe pellet deterioration observed for low velocity pellets.

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1];  [1];  [1];  [1]; ORCiD logo [1]; ORCiD logo [2];  [2]; ORCiD logo [3]; ORCiD logo [3]; ORCiD logo [1]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. Univ. of California, San Diego, La Jolla, CA (United States)
  3. General Atomics, San Diego, CA (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE
Contributing Org.:
the DIII-D team
OSTI Identifier:
1558757
Grant/Contract Number:  
AC02-09CH114661; AC05-00OR227252; AC52-07NA273444; FC02-04ER54698; FC02-04ER546983; FG02-06ER54867
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 59; Journal Issue: 8; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; tokamak; pellet; fast-ion; ablation; scrape-off layer; lithium; DIII-D

Citation Formats

Bortolon, A., Kramer, G. J., Maingi, R., Mansfield, D. K., Nagy, A., Roquemore, A. L., Lunsford, R., Bykov, I., Moyer, R. A., Parks, P. B., Van Zeeland, M. A., and Nazikian, R. Ablation of solid pellets induced by supra-thermal ions in the far scrape-off layer of DIII-D plasmas. United States: N. p., 2019. Web. doi:10.1088/1741-4326/ab267f.
Bortolon, A., Kramer, G. J., Maingi, R., Mansfield, D. K., Nagy, A., Roquemore, A. L., Lunsford, R., Bykov, I., Moyer, R. A., Parks, P. B., Van Zeeland, M. A., & Nazikian, R. Ablation of solid pellets induced by supra-thermal ions in the far scrape-off layer of DIII-D plasmas. United States. doi:10.1088/1741-4326/ab267f.
Bortolon, A., Kramer, G. J., Maingi, R., Mansfield, D. K., Nagy, A., Roquemore, A. L., Lunsford, R., Bykov, I., Moyer, R. A., Parks, P. B., Van Zeeland, M. A., and Nazikian, R. Tue . "Ablation of solid pellets induced by supra-thermal ions in the far scrape-off layer of DIII-D plasmas". United States. doi:10.1088/1741-4326/ab267f. https://www.osti.gov/servlets/purl/1558757.
@article{osti_1558757,
title = {Ablation of solid pellets induced by supra-thermal ions in the far scrape-off layer of DIII-D plasmas},
author = {Bortolon, A. and Kramer, G. J. and Maingi, R. and Mansfield, D. K. and Nagy, A. and Roquemore, A. L. and Lunsford, R. and Bykov, I. and Moyer, R. A. and Parks, P. B. and Van Zeeland, M. A. and Nazikian, R.},
abstractNote = {Injection of solid pellets is a key element in several aspects of the operation of a magnetic confinement plasma reactor for fusion applications, including plasma fueling, control and diagnosis. This letter reports observations demonstrating that pellet ablation can begin outside the plasma boundary, by effect of supra-thermal ions, whose orbits, under appropriate conditions, can extend well into the vacuum region. The phenomenon was recorded during plasma discharges in the DIII-D tokamak, combining pulsed modulation of heating neutral beams, with high-frequency injection of sub-millimeter lithium pellets, and it is ascribed to the large fraction of trapped beam ions associated with counter current neutral beam injection. Furthermore, the effect was quantitatively evaluated by means of Monte-Carlo simulations of supra-thermal ion orbits, finding that the heat-deposition was of the order of 50–100 W mm–2, in the region traversed by the lithium pellets before reaching the plasma boundary, which is consistent with the severe pellet deterioration observed for low velocity pellets.},
doi = {10.1088/1741-4326/ab267f},
journal = {Nuclear Fusion},
issn = {0029-5515},
number = 8,
volume = 59,
place = {United States},
year = {2019},
month = {6}
}

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