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Title: Initiation and sustainment of tokamak plasmas with local helicity injection as the majority current drive

Local helicity injection (LHI) is a non-solenoidal current drive capable of achieving high- I p tokamak startup with non-invasive current injectors in the plasma scrape-off layer. The choice of injector location within the edge region is flexible but has a profound influence on the nature of the current drive in LHI discharges. New experiments on the Pegasus ST with injection in the high-field-side, lower divertor region produce plasmas dominated by helicity injection current drive, static plasma geometry, and negligible inductive drive. Peak plasma current up to 200 kA, and a sustained plasma current of 100 kA for up to 18 ms, is demonstrated. Maximum achievable plasma current is found to scale approximately linearly with the effective loop voltage from LHI. A newly-observed MHD regime for LHI-driven plasmas in which large-amplitude n = 1 fluctuations at 20–50 kHz are abruptly reduced on the outboard side results in improved current drive. In conclusion, a simultaneous increase in high frequency fluctuations (>400 kHz) inside the plasma edge suggests short wavelength turbulence as an important current drive mechanism during LHI.
Authors:
ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1]
  1. Univ. of Wisconsin-Madison, Madison, WI (United States)
Publication Date:
Grant/Contract Number:
FG02-96ER54375; SC0006928
Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 58; Journal Issue: 9; Related Information: J.M. Perry, G.M. Bodner, M.W. Bongard, M.G. Burke, R.J. Fonck, J.L. Pachicano, C. Pierren, J.A. Reusch, A.T. Rhodes, N.J. Richner, C. Rodriguez Sanchez, C.E. Schaefer, and J.D. Weberski, "Public Data Set: Initiation and Sustainment of Tokamak Plasmas with Local Helicity Injection as the Majority Current Drive," DOI: 10.18138/1419641; Journal ID: ISSN 0029-5515
Publisher:
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
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; tokamak; non-inductive current drive; magnetic helicity; helicity injection; spherical tokamak
OSTI Identifier:
1461535

Perry, Justin M., Bodner, Grant M., Bongard, Michael W., Burke, Marcus G., Fonck, Raymond J., Pachicano, Jessica L., Pierren, Christopher, Reusch, Joshua A., Rhodes, Alexander T., Richner, Nathan J., Sanchez, Cuauhtemoc Rodriguez, Schaefer, Carolyn E., and Weberski, Justin D.. Initiation and sustainment of tokamak plasmas with local helicity injection as the majority current drive. United States: N. p., Web. doi:10.1088/1741-4326/aac72e.
Perry, Justin M., Bodner, Grant M., Bongard, Michael W., Burke, Marcus G., Fonck, Raymond J., Pachicano, Jessica L., Pierren, Christopher, Reusch, Joshua A., Rhodes, Alexander T., Richner, Nathan J., Sanchez, Cuauhtemoc Rodriguez, Schaefer, Carolyn E., & Weberski, Justin D.. Initiation and sustainment of tokamak plasmas with local helicity injection as the majority current drive. United States. doi:10.1088/1741-4326/aac72e.
Perry, Justin M., Bodner, Grant M., Bongard, Michael W., Burke, Marcus G., Fonck, Raymond J., Pachicano, Jessica L., Pierren, Christopher, Reusch, Joshua A., Rhodes, Alexander T., Richner, Nathan J., Sanchez, Cuauhtemoc Rodriguez, Schaefer, Carolyn E., and Weberski, Justin D.. 2018. "Initiation and sustainment of tokamak plasmas with local helicity injection as the majority current drive". United States. doi:10.1088/1741-4326/aac72e.
@article{osti_1461535,
title = {Initiation and sustainment of tokamak plasmas with local helicity injection as the majority current drive},
author = {Perry, Justin M. and Bodner, Grant M. and Bongard, Michael W. and Burke, Marcus G. and Fonck, Raymond J. and Pachicano, Jessica L. and Pierren, Christopher and Reusch, Joshua A. and Rhodes, Alexander T. and Richner, Nathan J. and Sanchez, Cuauhtemoc Rodriguez and Schaefer, Carolyn E. and Weberski, Justin D.},
abstractNote = {Local helicity injection (LHI) is a non-solenoidal current drive capable of achieving high-Ip tokamak startup with non-invasive current injectors in the plasma scrape-off layer. The choice of injector location within the edge region is flexible but has a profound influence on the nature of the current drive in LHI discharges. New experiments on the Pegasus ST with injection in the high-field-side, lower divertor region produce plasmas dominated by helicity injection current drive, static plasma geometry, and negligible inductive drive. Peak plasma current up to 200 kA, and a sustained plasma current of 100 kA for up to 18 ms, is demonstrated. Maximum achievable plasma current is found to scale approximately linearly with the effective loop voltage from LHI. A newly-observed MHD regime for LHI-driven plasmas in which large-amplitude n = 1 fluctuations at 20–50 kHz are abruptly reduced on the outboard side results in improved current drive. In conclusion, a simultaneous increase in high frequency fluctuations (>400 kHz) inside the plasma edge suggests short wavelength turbulence as an important current drive mechanism during LHI.},
doi = {10.1088/1741-4326/aac72e},
journal = {Nuclear Fusion},
number = 9,
volume = 58,
place = {United States},
year = {2018},
month = {7}
}