A 0D circuit model for predicting Ip(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 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 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.
Barr, Jayson L., et al. "A power-balance model for local helicity injection startup in a spherical tokamak." Nuclear Fusion, vol. 58, no. 7, May. 2018. https://doi.org/10.1088/1741-4326/aac0a0
Barr, Jayson L., Bongard, Michael W., Burke, Marcus G., Fonck, Raymond J., Hinson, Edward T., Perry, Justin M., & Reusch, Joshua A. (2018). A power-balance model for local helicity injection startup in a spherical tokamak. Nuclear Fusion, 58(7). https://doi.org/10.1088/1741-4326/aac0a0
Barr, Jayson L., Bongard, Michael W., Burke, Marcus G., et al., "A power-balance model for local helicity injection startup in a spherical tokamak," Nuclear Fusion 58, no. 7 (2018), https://doi.org/10.1088/1741-4326/aac0a0
@article{osti_1456911,
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.},
title = {A power-balance model for local helicity injection startup in a spherical tokamak},
annote = {A 0D circuit model for predicting Ip(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 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 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.},
doi = {10.1088/1741-4326/aac0a0},
url = {https://www.osti.gov/biblio/1456911},
journal = {Nuclear Fusion},
issn = {ISSN 0029-5515},
number = {7},
volume = {58},
place = {United States},
publisher = {IOP Science},
year = {2018},
month = {05}}
Pegasus-Supplementary information for journal article at DOI: https://doi.org/10.1088/1741-4326/aac72e, 1 file (17.1 MB)https://doi.org/10.18138/1419641
Pegasus-Supplementary information for journal article at DOI: https://doi.org/10.1088/1741-4326/aac72e, 1 file (17.1 MB)https://doi.org/10.18138/1419641