Feedback-assisted extension of the tokamak operating space to low safety factor

Hanson, Jeremy M.; Bialek, James M.; Baruzzo, M.; Bolzonella, Tommaso; Hyatt, Alan W.; Jackson, Gary L.; King, J.; La Haye, Robert J.; Lanctot, Matthew J.; Marrelli, Lionello; Martin, Piero; Navratil, Gerald A.; Okabayashi, Michio; Olofsson, K. Erik J.; Paz-Soldan, Carlos; Piovesan, Paolo; Piron, Chiara; Piron, Lidia; Shiraki, Daisuke; Strait, Edward J.; Terranova, D.; Turco, Francesca; Turnbull, Alan D.; Zanca, Paolo

doi:10.1063/1.4886796

Title: Feedback-assisted extension of the tokamak operating space to low safety factor

Full Record
Other Related Research

Abstract

Recent DIII-D and RFX-mod experiments have demonstrated stable tokamak operation at very low values of the edge safety factor q(a) near and below 2. The onset of n = 1 resistive wall mode (RWM) kink instabilities leads to a disruptive stability limit, encountered at q(a) = 2 (limiter plasmas) and q₉₅ = 2 (divertor plasmas). However, passively stable operation can be attained for q(a) and q₉₅ values as low as 2.2. RWM damping in the q(a) = 2 regime was measured using active MHD spectroscopy. Although consistent with theoretical predictions, the amplitude of the damped response does not increase significantly as the q(a) = 2 limit is approached, in contrast with damping measurements made approaching the pressure-driven RWM limit. Applying proportional gain magnetic feedback control of the n = 1 modes has resulted in stabilized operation with q₉₅ values reaching as low as 1.9 in DIII-D and q(a) reaching 1.55 in RFX-mod. In addition to being consistent with the q(a) = 2 external kink mode stability limit, the unstable modes have growth rates on the order of the characteristic wall eddy-current decay timescale in both devices, and a dominant m = 2 poloidal structure that is consistent with ideal MHDmore »« less

Authors:

Hanson, Jeremy M. ^[1]; Bialek, James M. ^[1]; Baruzzo, M. ^[2]; Bolzonella, Tommaso ^[2]; Hyatt, Alan W. ^[3]; Jackson, Gary L. ^[3]; King, J. ^[4]; La Haye, Robert J. ^[3]; Lanctot, Matthew J. ^[3]; Marrelli, Lionello ^[2]; Martin, Piero ^[2]; Navratil, Gerald A. ^[1]; Okabayashi, Michio ^[5]; Olofsson, K. Erik J. ^[1]; Paz-Soldan, Carlos ^[4]; Piovesan, Paolo ^[2]; Piron, Chiara ^[2]; Piron, Lidia ^[2]; Shiraki, Daisuke ^[6]; Strait, Edward J. ^[3] more »

Columbia Univ., New York, NY (United States)
Consorzio RFX, Padova (Italy)
General Atomics, San Diego, CA (United States)
Oak Ridge Inst. for Science and Education (ORISE), Oak Ridge, TN (United States)
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Columbia Univ., New York, NY (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Publication Date:: Mon Jul 07 00:00:00 EDT 2014

Research Org.:: General Atomics, San Diego, CA (United States)

Sponsoring Org.:: USDOE Office of Nuclear Energy (NE)

OSTI Identifier:: 1354831

Grant/Contract Number:: FC02-04ER54698; AC05-06OR23100; AC02-09CH11466

Resource Type:: Accepted Manuscript

Journal Name:: Physics of Plasmas

Additional Journal Information:: Journal Volume: 21; Journal Issue: 7; Journal ID: ISSN 1070-664X

Publisher:: American Institute of Physics (AIP)

Country of Publication:: United States

Language:: English

Subject:: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats


                    Hanson, Jeremy M., Bialek, James M., Baruzzo, M., Bolzonella, Tommaso, Hyatt, Alan W., Jackson, Gary L., King, J., La Haye, Robert J., Lanctot, Matthew J., Marrelli, Lionello, Martin, Piero, Navratil, Gerald A., Okabayashi, Michio, Olofsson, K. Erik J., Paz-Soldan, Carlos, Piovesan, Paolo, Piron, Chiara, Piron, Lidia, Shiraki, Daisuke, Strait, Edward J., Terranova, D., Turco, Francesca, Turnbull, Alan D., and Zanca, Paolo. Feedback-assisted extension of the tokamak operating space to low safety factor.  United States: N. p., 2014. 
Web.  doi:10.1063/1.4886796.

Copy to clipboard


                    Hanson, Jeremy M., Bialek, James M., Baruzzo, M., Bolzonella, Tommaso, Hyatt, Alan W., Jackson, Gary L., King, J., La Haye, Robert J., Lanctot, Matthew J., Marrelli, Lionello, Martin, Piero, Navratil, Gerald A., Okabayashi, Michio, Olofsson, K. Erik J., Paz-Soldan, Carlos, Piovesan, Paolo, Piron, Chiara, Piron, Lidia, Shiraki, Daisuke, Strait, Edward J., Terranova, D., Turco, Francesca, Turnbull, Alan D., & Zanca, Paolo. Feedback-assisted extension of the tokamak operating space to low safety factor.  United States.  https://doi.org/10.1063/1.4886796

Copy to clipboard


                    Hanson, Jeremy M., Bialek, James M., Baruzzo, M., Bolzonella, Tommaso, Hyatt, Alan W., Jackson, Gary L., King, J., La Haye, Robert J., Lanctot, Matthew J., Marrelli, Lionello, Martin, Piero, Navratil, Gerald A., Okabayashi, Michio, Olofsson, K. Erik J., Paz-Soldan, Carlos, Piovesan, Paolo, Piron, Chiara, Piron, Lidia, Shiraki, Daisuke, Strait, Edward J., Terranova, D., Turco, Francesca, Turnbull, Alan D., and Zanca, Paolo. Mon .  
"Feedback-assisted extension of the tokamak operating space to low safety factor".  United States.  https://doi.org/10.1063/1.4886796.  https://www.osti.gov/servlets/purl/1354831.

Copy to clipboard


                    
@article{osti_1354831,

  title        = {Feedback-assisted extension of the tokamak operating space to low safety factor},

  author       = {Hanson, Jeremy M. and Bialek, James M. and Baruzzo, M. and Bolzonella, Tommaso and Hyatt, Alan W. and Jackson, Gary L. and King, J. and La Haye, Robert J. and Lanctot, Matthew J. and Marrelli, Lionello and Martin, Piero and Navratil, Gerald A. and Okabayashi, Michio and Olofsson, K. Erik J. and Paz-Soldan, Carlos and Piovesan, Paolo and Piron, Chiara and Piron, Lidia and Shiraki, Daisuke and Strait, Edward J. and Terranova, D. and Turco, Francesca and Turnbull, Alan D. and Zanca, Paolo},

  abstractNote = {Recent DIII-D and RFX-mod experiments have demonstrated stable tokamak operation at very low values of the edge safety factor q(a) near and below 2. The onset of n = 1 resistive wall mode (RWM) kink instabilities leads to a disruptive stability limit, encountered at q(a) = 2 (limiter plasmas) and q95 = 2 (divertor plasmas). However, passively stable operation can be attained for q(a) and q95 values as low as 2.2. RWM damping in the q(a) = 2 regime was measured using active MHD spectroscopy. Although consistent with theoretical predictions, the amplitude of the damped response does not increase significantly as the q(a) = 2 limit is approached, in contrast with damping measurements made approaching the pressure-driven RWM limit. Applying proportional gain magnetic feedback control of the n = 1 modes has resulted in stabilized operation with q95 values reaching as low as 1.9 in DIII-D and q(a) reaching 1.55 in RFX-mod. In addition to being consistent with the q(a) = 2 external kink mode stability limit, the unstable modes have growth rates on the order of the characteristic wall eddy-current decay timescale in both devices, and a dominant m = 2 poloidal structure that is consistent with ideal MHD predictions. As a result, the experiments contribute to validating MHD stability theory and demonstrate that a key tokamak stability limit can be overcome with feedback.},

  doi          = {10.1063/1.4886796},

  journal      = {Physics of Plasmas},

  number       = 7,

  volume       = 21,

  place        = {United States},

  year         = {Mon Jul 07 00:00:00 EDT 2014},

  month        = {Mon Jul 07 00:00:00 EDT 2014}

}

Copy to clipboard

Journal Article:

Free Publicly Available Full Text

Accepted Manuscript (DOE)

Publisher's Version of Record

https://doi.org/10.1063/1.4886796

Other availability

Search WorldCat to find libraries that may hold this journal

Citation Metrics:

Cited by: 13 works

Citation information provided by
Web of Science

Save / Share:

Export Metadata

Save to My Library

Similar Records in DOE PAGES and OSTI.GOV collections:

Feedback-assisted extension of the tokamak operating space to low safety factor

Journal Article Hanson, J. M., E-mail: jmh2130@columbia.edu ; Bialek, J. M. ; Navratil, G. A. ; ... - Physics of Plasmas

Recent DIII-D and RFX-mod experiments have demonstrated stable tokamak operation at very low values of the edge safety factor q(a) near and below 2. The onset of n = 1 resistive wall mode (RWM) kink instabilities leads to a disruptive stability limit, encountered at q(a) = 2 (limiter plasmas) and q{sub 95} = 2 (divertor plasmas). However, passively stable operation can be attained for q(a) and q{sub 95} values as low as 2.2. RWM damping in the q(a) = 2 regime was measured using active MHD spectroscopy. Although consistent with theoretical predictions, the amplitude of the damped response does not increase significantly as the q(a) = 2 limit is approached,more »« less
https://doi.org/10.1063/1.4886796
Stability of DIII-D high-performance, negative central shear discharges

Journal Article Hanson, Jeremy M. ; Berkery, John W. ; Bialek, James M. ; ... - Nuclear Fusion

Tokamak plasma experiments on the DIII-D device demonstrate high-performance, negative central shear (NCS) equilibria with enhanced stability when the minimum safety factor q_min exceeds 2, qualitatively confirming theoretical predictions of favorable stability in the NCS regime. The discharges exhibit good confinement with an L-mode enhancement factor H₈₉ = 2.5, and are ultimately limited by the ideal-wall external kink stability boundary as predicted by ideal MHD theory, as long as tearing mode (TM) locking events, resistive wall modes (RWMs), and internal kink modes are properly avoided or controlled. Although the discharges exhibit rotating TMs, locking events are avoided as long asmore »« less
Cited by 7
https://doi.org/10.1088/1741-4326/aa6266

Full Text Available
Stabilization of the external kink and control of the resistive wall mode in tokamaks

Conference Garofalo, A M ; Turnbull, A D ; Strait, E J

One promising approach to maintaining stability of high beta tokamak plasmas is the use of a conducting wall near the plasma to stabilize low-n ideal MHD instabilities. However, with a resistive wall, either plasma rotation or active feedback control is required to stabilize the more slowly growing resistive wall modes (RWMs). Experiments in the DIII-D, PBHX-M, and HBT-EP tokamaks have demonstrated that plasmas with a nearby conducting wall can remain stable to the n = 1 ideal external kink above the beta limit predicted with the wall at infinity, with durations in DIII-D up to 30 times {tau}{sub w}, themore »« less
Full Text Available
Interaction of external n = 1 magnetic fields with the sawtooth instability in low-q RFX-mod and DIII-D tokamaks

Journal Article Piron, C. ; Martin, P. ; Bonfiglio, D. ; ... - Nuclear Fusion

External n = 1 magnetic fields are applied in RFX-mod and DIII-D low safety factor Tokamak plasmas to investigate their interaction with the internal MHD dynamics and in particular with the sawtooth instability. In these experiments the applied magnetic fields cause a reduction of both the sawtooth amplitude and period, leading to an overall stabilizing effect on the oscillations. In RFX-mod sawteeth eventually disappear and are replaced by a stationary m = 1, n = 1 helical equilibrium without an increase in disruptivity. However toroidal rotation is significantly reduced in these plasmas, thus it is likely that the sawtooth mitigationmore »« less
Cited by 9
https://doi.org/10.1088/0029-5515/56/10/106012

Full Text Available
Cross-machine comparison of resonant field amplification and resistive wall mode stabilization by plasma rotation

Journal Article Reimerdes, H ; Sabbagh, S A ; Bialek, J M ; ... - Physics of Plasmas

Dedicated experiments in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion, 42, 614 (2002)], the Joint European Torus (JET) [P. H. Rebut, R. J. Bickerton, and B. E. Keen, Nucl. Fusion 25, 1011 (1985)], and the National Spherical Torus Experiment (NSTX) [M. Ono, S. M. Kaye, Y.-K. M. Peng et al., Nucl. Fusion 40, 557 (2000)] reveal the commonalities of resistive wall mode (RWM) stabilization by sufficiently fast toroidal plasma rotation in devices of different size and aspect ratio. In each device the weakly damped n=1 RWM manifests itself by resonant field amplification (RFA) of externally applied n=1 magnetic fields,more »« less
https://doi.org/10.1063/1.2177134

Similar Records