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This content will become publicly available on May 15, 2019

Title: A power-balance 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 finite-A plasmas developed are modified and expanded to treat highly shaped, ultralow-A 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 power-balance 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 V-s. Projections using this model indicate the relative influences of higher helicity input rate and injector current on the attainable total plasma current.
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  1. Univ. of Wisconsin-Madison, Madison, WI (United States)
Publication Date:
Grant/Contract Number:
FG02-96ER54375; SC0006928
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 Power-Balance Model for Local Helicity Injection Startup in a Spherical Tokamak," DOI: 10.18138/1345037; Journal ID: ISSN 0029-5515
IOP Science
Research Org:
Univ. of Wisconsin-Madison, Madison, WI (United States)
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Country of Publication:
United States
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; plasma startup; spherical tokamaks; current drive; helicity injection; Taylor relaxation; tokamaks
OSTI Identifier: