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Title: Application of transient CHI plasma startup to future ST and AT devices

Abstract

Employment of non-inductive plasma start-up techniques would considerably simplify the design of a spherical tokamak fusion reactor. Transient coaxial helicity injection (CHI) is a promising method, expected to scale favorably to next-step reactors. Yet, the implications of reactor-relevant parameters on the initial breakdown phase for CHI have not yet been considered. Here, we evaluate CHI breakdown in reactor-like configurations using an extension of the Townsend avalanche theory. We find that a CHI electrode concept in which the outer vessel wall is biased to achieve breakdown, while previously successful on NSTX and HIT-II, may exhibit a severe weakness when scaled up to a reactor. On the other hand, concepts which employ localized biasing electrodes such as those used in QUEST would avoid this issue. Assuming that breakdown can be successfully attained, we then apply scaling relationships to predict plasma parameters attainable in the transient CHI discharge. Assuming the use of 1 Wb of injector flux, we discover that plasma currents of 1 MA should be achievable. Moreover, these plasmas are expected to Ohmically self-heat with more than 1 MW of power as they decay, facilitating efficient hand-off to steady-state heating sources. These optimistic scalings are confirmed by Tokamak Simulation Code simulations.

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]
  1. Max Planck Inst. for Plasma Physics, Greifswald (Germany)
  2. Univ. of Washington, Seattle, WA (United States)
  3. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1510298
Grant/Contract Number:  
AC02-09CH11466; FG02-99ER54519
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 26; Journal Issue: 3; 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

Citation Formats

Hammond, K. C., Raman, R., and Jardin, S. C. Application of transient CHI plasma startup to future ST and AT devices. United States: N. p., 2019. Web. doi:10.1063/1.5087259.
Hammond, K. C., Raman, R., & Jardin, S. C. Application of transient CHI plasma startup to future ST and AT devices. United States. doi:10.1063/1.5087259.
Hammond, K. C., Raman, R., and Jardin, S. C. Fri . "Application of transient CHI plasma startup to future ST and AT devices". United States. doi:10.1063/1.5087259. https://www.osti.gov/servlets/purl/1510298.
@article{osti_1510298,
title = {Application of transient CHI plasma startup to future ST and AT devices},
author = {Hammond, K. C. and Raman, R. and Jardin, S. C.},
abstractNote = {Employment of non-inductive plasma start-up techniques would considerably simplify the design of a spherical tokamak fusion reactor. Transient coaxial helicity injection (CHI) is a promising method, expected to scale favorably to next-step reactors. Yet, the implications of reactor-relevant parameters on the initial breakdown phase for CHI have not yet been considered. Here, we evaluate CHI breakdown in reactor-like configurations using an extension of the Townsend avalanche theory. We find that a CHI electrode concept in which the outer vessel wall is biased to achieve breakdown, while previously successful on NSTX and HIT-II, may exhibit a severe weakness when scaled up to a reactor. On the other hand, concepts which employ localized biasing electrodes such as those used in QUEST would avoid this issue. Assuming that breakdown can be successfully attained, we then apply scaling relationships to predict plasma parameters attainable in the transient CHI discharge. Assuming the use of 1 Wb of injector flux, we discover that plasma currents of 1 MA should be achievable. Moreover, these plasmas are expected to Ohmically self-heat with more than 1 MW of power as they decay, facilitating efficient hand-off to steady-state heating sources. These optimistic scalings are confirmed by Tokamak Simulation Code simulations.},
doi = {10.1063/1.5087259},
journal = {Physics of Plasmas},
number = 3,
volume = 26,
place = {United States},
year = {2019},
month = {3}
}

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