A powerbalance model for local helicity injection startup in a spherical tokamak
A 0D circuit model for predicting I _{p}( t) in Local Helicity Injection (LHI) discharges is developed. Analytic formulas for estimating the surface flux of finiteA plasmas developed are modified and expanded to treat highly shaped, ultralowA tokamak geometry using a database of representative equilibria. Model predictions are compared to sample LHI discharges in the A ~ 1 Pegasus spherical tokamak, and are found to agree within 15% of experimental I _{p}( t). High performance LHI discharges are found to follow the Taylor relaxation current limit for approximately the first half of the current ramp, or I _{p} ≲ 75 kA. The second half of the current ramp follows a limit imposed by powerbalance as plasmas expand from high A to ultralow A. Here, this shape evolution generates a significant drop in external plasma inductance, effectively using the plasma’s initially high inductance to drive the current ramp and provide > 70% of the current drive Vs. Projections using this model indicate the relative influences of higher helicity input rate and injector current on the attainable total plasma current.
 Authors:

^{[1]}
;
^{[1]}
;
^{[1]}
;
^{[1]}
;
^{[1]}
;
^{[1]}
;
^{[1]}
 Univ. of WisconsinMadison, Madison, WI (United States)
 Publication Date:
 Grant/Contract Number:
 FG0296ER54375; SC0006928
 Type:
 Accepted Manuscript
 Journal Name:
 Nuclear Fusion
 Additional Journal Information:
 Journal Volume: 58; Journal Issue: 7; Related Information: J.L. Barr, M.W. Bongard, M.G. Burke, R.J. Fonck, E.T. Hinson, J.M. Perry, and J.A. Reusch, "Public Data Set: A PowerBalance Model for Local Helicity Injection Startup in a Spherical Tokamak," DOI: 10.18138/1345037; Journal ID: ISSN 00295515
 Publisher:
 IOP Science
 Research Org:
 Univ. of WisconsinMadison, Madison, WI (United States)
 Sponsoring Org:
 USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC24)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; plasma startup; spherical tokamaks; current drive; helicity injection; Taylor relaxation; tokamaks
 OSTI Identifier:
 1456911
Barr, Jayson L., Bongard, Michael W., Burke, Marcus G., Fonck, Raymond J., Hinson, Edward T., Perry, Justin M., and Reusch, Joshua A.. A powerbalance model for local helicity injection startup in a spherical tokamak. United States: N. p.,
Web. doi:10.1088/17414326/aac0a0.
Barr, Jayson L., Bongard, Michael W., Burke, Marcus G., Fonck, Raymond J., Hinson, Edward T., Perry, Justin M., & Reusch, Joshua A.. A powerbalance model for local helicity injection startup in a spherical tokamak. United States. doi:10.1088/17414326/aac0a0.
Barr, Jayson L., Bongard, Michael W., Burke, Marcus G., Fonck, Raymond J., Hinson, Edward T., Perry, Justin M., and Reusch, Joshua A.. 2018.
"A powerbalance model for local helicity injection startup in a spherical tokamak". United States.
doi:10.1088/17414326/aac0a0.
@article{osti_1456911,
title = {A powerbalance model for local helicity injection startup in a spherical tokamak},
author = {Barr, Jayson L. and Bongard, Michael W. and Burke, Marcus G. and Fonck, Raymond J. and Hinson, Edward T. and Perry, Justin M. and Reusch, Joshua A.},
abstractNote = {A 0D circuit model for predicting Ip(t) in Local Helicity Injection (LHI) discharges is developed. Analytic formulas for estimating the surface flux of finiteA plasmas developed are modified and expanded to treat highly shaped, ultralowA tokamak geometry using a database of representative equilibria. Model predictions are compared to sample LHI discharges in the A ~ 1 Pegasus spherical tokamak, and are found to agree within 15% of experimental Ip(t). High performance LHI discharges are found to follow the Taylor relaxation current limit for approximately the first half of the current ramp, or Ip ≲ 75 kA. The second half of the current ramp follows a limit imposed by powerbalance as plasmas expand from highA to ultralowA. Here, this shape evolution generates a significant drop in external plasma inductance, effectively using the plasma’s initially high inductance to drive the current ramp and provide > 70% of the current drive Vs. Projections using this model indicate the relative influences of higher helicity input rate and injector current on the attainable total plasma current.},
doi = {10.1088/17414326/aac0a0},
journal = {Nuclear Fusion},
number = 7,
volume = 58,
place = {United States},
year = {2018},
month = {5}
}