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Title: Application of Townsend avalanche theory to tokamak startup by coaxial helicity injection

Abstract

Townsend avalanche theory is employed to model and interpret plasma initiation in NSTX by Ohmic heating and coaxial helicity injection (CHI). The model is informed by spatially resolved vacuum calculations of electric field and magnetic field line connection length in the poloidal cross-section. The modelis shown to explain observations of Ohmic startup including the duration andlocation of breakdown. Adapting the model to discharges initiated by CHI offers insight into the causes of upper divertor (absorber) arcs in cases where the discharge fails to initiate in the lower divertor gap. Finally, upper and lower limits are established for vessel gas fill based on requirements for breakdown and radiation. It is predicted that CHI experiments on NSTX-U should beable to use as much as four times the amount of prefill gas employed in CHI experiments in NSTX. This should provide greater flexibility for plasma start-up, as the injector flux is projected to be increased in NSTX-U.

Authors:
; ;
Publication Date:
DOE Contract Number:  
AC02-09CH11466
Product Type:
Dataset
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
U. S. Department of Energy
Keywords:
NSTX
OSTI Identifier:
1562045
DOI:
https://doi.org/10.11578/1562045

Citation Formats

Hammond, K C, Raman, R, and Volpe, F A. Application of Townsend avalanche theory to tokamak startup by coaxial helicity injection. United States: N. p., 2017. Web. doi:10.11578/1562045.
Hammond, K C, Raman, R, & Volpe, F A. Application of Townsend avalanche theory to tokamak startup by coaxial helicity injection. United States. doi:https://doi.org/10.11578/1562045
Hammond, K C, Raman, R, and Volpe, F A. 2017. "Application of Townsend avalanche theory to tokamak startup by coaxial helicity injection". United States. doi:https://doi.org/10.11578/1562045. https://www.osti.gov/servlets/purl/1562045. Pub date:Fri Sep 01 00:00:00 EDT 2017
@article{osti_1562045,
title = {Application of Townsend avalanche theory to tokamak startup by coaxial helicity injection},
author = {Hammond, K C and Raman, R and Volpe, F A},
abstractNote = {Townsend avalanche theory is employed to model and interpret plasma initiation in NSTX by Ohmic heating and coaxial helicity injection (CHI). The model is informed by spatially resolved vacuum calculations of electric field and magnetic field line connection length in the poloidal cross-section. The modelis shown to explain observations of Ohmic startup including the duration andlocation of breakdown. Adapting the model to discharges initiated by CHI offers insight into the causes of upper divertor (absorber) arcs in cases where the discharge fails to initiate in the lower divertor gap. Finally, upper and lower limits are established for vessel gas fill based on requirements for breakdown and radiation. It is predicted that CHI experiments on NSTX-U should beable to use as much as four times the amount of prefill gas employed in CHI experiments in NSTX. This should provide greater flexibility for plasma start-up, as the injector flux is projected to be increased in NSTX-U.},
doi = {10.11578/1562045},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2017},
month = {9}
}