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Title: Tokamak Operation with Safety Factor q 95 < 2 via Control of MHD Stability

Magnetic feedback control of the resistive-wall mode has enabled DIII-D to access stable operation at safety factor q95 = 1:9 in divertor plasmas for 150 instability growth times. Magnetohydrodynamic stability sets a hard, disruptive limit on the minimum edge safety factor achievable in a tokamak, or on the maximum plasma current at given toroidal magnetic eld. In tokamaks with a divertor, the limit occurs at q95 = 2, as con rmed in DIII-D. Since the energy con cement time scales linearly with current, this also bounds the performance of a fusion reactor. DIII-D has overcome this limit, opening a whole new high-current regime not accessible before. This result brings signi cant possible bene ts in terms of fusion performance, but it also extends resistive wall mode physics and its control to conditions never explored before. In present experiments, q95 < 2 operation is eventually halted by voltage limits reached in the feedback power supplies, not by intrinsic physics issues. Improvements to power supplies and to control algorithms have the potential to further extend this regime.
Authors:
 [1] ;  [2] ;  [1] ;  [2] ;  [2] ;  [2] ;  [3] ;  [3] ;  [4] ;  [5] ;  [3] ;  [3] ;  [1] ;  [1] ;  [1] ;  [3] ;  [3] ;  [1] ;  [1] ;  [2]
  1. Consorzio RFX, Padova (Italy)
  2. Columbia Univ., New York, NY (United States)
  3. General Atomics, San Diego, CA (United States)
  4. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  5. Oak Ridge Inst. for Science and Education (ORISE), Oak Ridge, TN (United States)
Publication Date:
Grant/Contract Number:
FC02-04ER54698
Type:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 113; Journal Issue: 4; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Research Org:
U.S. Department of Energy, Washington, DC (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
OSTI Identifier:
1367085

Piovesan, Paolo, Hanson, Jeremy M., Martin, Piero, Navratil, Gerald A., Turco, Francesca, Bialek, James, La Haye, Robert J., Lanctot, Matthew J., Okabayashi, Michio, Paz-Soldan, Carlos, Strait, Edward J., Turnbull, Alan D., Zanca, P., Baruzzo, M., Bolzonella, T., Hyatt, Alan W., Jackson, G. L., Marrelli, L., Piron, L., and Shiraki, Daisuke. Tokamak Operation with Safety Factor q95<2 via Control of MHD Stability. United States: N. p., Web. doi:10.1103/PhysRevLett.113.045003.
Piovesan, Paolo, Hanson, Jeremy M., Martin, Piero, Navratil, Gerald A., Turco, Francesca, Bialek, James, La Haye, Robert J., Lanctot, Matthew J., Okabayashi, Michio, Paz-Soldan, Carlos, Strait, Edward J., Turnbull, Alan D., Zanca, P., Baruzzo, M., Bolzonella, T., Hyatt, Alan W., Jackson, G. L., Marrelli, L., Piron, L., & Shiraki, Daisuke. Tokamak Operation with Safety Factor q95<2 via Control of MHD Stability. United States. doi:10.1103/PhysRevLett.113.045003.
Piovesan, Paolo, Hanson, Jeremy M., Martin, Piero, Navratil, Gerald A., Turco, Francesca, Bialek, James, La Haye, Robert J., Lanctot, Matthew J., Okabayashi, Michio, Paz-Soldan, Carlos, Strait, Edward J., Turnbull, Alan D., Zanca, P., Baruzzo, M., Bolzonella, T., Hyatt, Alan W., Jackson, G. L., Marrelli, L., Piron, L., and Shiraki, Daisuke. 2014. "Tokamak Operation with Safety Factor q95<2 via Control of MHD Stability". United States. doi:10.1103/PhysRevLett.113.045003. https://www.osti.gov/servlets/purl/1367085.
@article{osti_1367085,
title = {Tokamak Operation with Safety Factor q95<2 via Control of MHD Stability},
author = {Piovesan, Paolo and Hanson, Jeremy M. and Martin, Piero and Navratil, Gerald A. and Turco, Francesca and Bialek, James and La Haye, Robert J. and Lanctot, Matthew J. and Okabayashi, Michio and Paz-Soldan, Carlos and Strait, Edward J. and Turnbull, Alan D. and Zanca, P. and Baruzzo, M. and Bolzonella, T. and Hyatt, Alan W. and Jackson, G. L. and Marrelli, L. and Piron, L. and Shiraki, Daisuke},
abstractNote = {Magnetic feedback control of the resistive-wall mode has enabled DIII-D to access stable operation at safety factor q95 = 1:9 in divertor plasmas for 150 instability growth times. Magnetohydrodynamic stability sets a hard, disruptive limit on the minimum edge safety factor achievable in a tokamak, or on the maximum plasma current at given toroidal magnetic eld. In tokamaks with a divertor, the limit occurs at q95 = 2, as con rmed in DIII-D. Since the energy con cement time scales linearly with current, this also bounds the performance of a fusion reactor. DIII-D has overcome this limit, opening a whole new high-current regime not accessible before. This result brings signi cant possible bene ts in terms of fusion performance, but it also extends resistive wall mode physics and its control to conditions never explored before. In present experiments, q95 < 2 operation is eventually halted by voltage limits reached in the feedback power supplies, not by intrinsic physics issues. Improvements to power supplies and to control algorithms have the potential to further extend this regime.},
doi = {10.1103/PhysRevLett.113.045003},
journal = {Physical Review Letters},
number = 4,
volume = 113,
place = {United States},
year = {2014},
month = {7}
}