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Title: Analysis of MHD stability and active mode control on KSTAR for high confinement, disruption-free plasma

Abstract

Long-pulse plasma operation at high normalized beta, βN, above the n= 1 ideal MHD no-wall stability limit in KSTAR is presently limited by tearing instabilities rather than resistive wall modes. H-mode plasma operation during the recent KSTAR device campaign produced discharges having strong m/n= 2/1 tearing instabilities at βN lower than the ideal MHD no-wall beta limit.The unstable tearing mode consequently reduced plasma confinement and toroidal plasma rotation significantly. The experiment confirmed that an extended duration of electron cyclotron heating (ECH) at the initial phase of the discharge plays a critical role in mode destabilization.To study destabilizing mechanisms that affect the mode growth, the stability of the observed tearing modes from plasmas with significantly different βN is computed by using the resistive DCON code and the M3D-C1code. Equilibrium reconstructions that include constraints from internal profile diagnostics, and computed fast particle pressure are used as input for reliable computation of stability. The classical tearing stability index, Δ', from resistive DCON is computed to be unstable when the island is fully saturated with large amplitude,while the unstable mode is not computed by M3D-C1. The modified Rutherford equation (MRE) describing the evolution of the island width has been constructed for KSTAR plasmas bymore » using plasma parameters computed by the TRANSP code.The MRE model estimates a saturated island width corresponding to ~10% of the plasma minor radius for equilibrium at high βN> 3 having a stable Δ' from the resistive DCON. In preparation for long-pulse plasma operation at higher beta utilizing increased plasma heating power, a resistive wall mode (RWM) active feedback control algorithm has been completed and enabled on KSTAR. To accurately determine the n= 1component produced by RWMs, an algorithm has been developed that includes magnetic sensor compensation of the prompt applied field and the field from the induced current on the passive conductors. Use of multiple toroidal sensor arrays is enabled by modifying the sensor toroidal angles assumed in mode decomposition to include the effect of varied mode helicities in the outboard region where the mode measurement is made. This analysis on stability, transport, and control provides the required foundation for disruption prediction and avoidance research on KSTAR.« less

Authors:
ORCiD logo [1];  [1]; ORCiD logo [1];  [2];  [2];  [1];  [1]; ORCiD logo [1];  [2]; ORCiD logo [3];  [2]; ORCiD logo [2]; ORCiD logo [2];  [2]; ORCiD logo [2];  [2]; ORCiD logo [4]; ORCiD logo [5];  [5]; ORCiD logo [5] more »;  [2] « less
  1. Columbia Univ., New York, NY (United States)
  2. National Fusion Research Institute, Daejeon (Korea, Republic of)
  3. Fusion Theory and Computation, Inc., Kingston, WA (United States)
  4. Ulsan National Institute of Science and Technology, Ulsan (Korea, Republic of)
  5. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1650665
Alternate Identifier(s):
OSTI ID: 1615129
Grant/Contract Number:  
SC0016614
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 60; Journal Issue: 5; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Park, Y. S., Sabbagh, S. A., Ahn, J. H., Park, B. H., Kim, H. S., Berkery, J. W., Bialek, J. M., Jiang, Y., Bak, J. G., Glasser, A. H., Kang, J. S., Lee, J., Han, H. S., Hahn, S. H., Jeon, Y. M., Kwak, J. G., Park, H. K., Wang, Z. R., Park, J. -K., Ferraro, N. M., and Yoon, S. W. Analysis of MHD stability and active mode control on KSTAR for high confinement, disruption-free plasma. United States: N. p., 2020. Web. https://doi.org/10.1088/1741-4326/ab79ca.
Park, Y. S., Sabbagh, S. A., Ahn, J. H., Park, B. H., Kim, H. S., Berkery, J. W., Bialek, J. M., Jiang, Y., Bak, J. G., Glasser, A. H., Kang, J. S., Lee, J., Han, H. S., Hahn, S. H., Jeon, Y. M., Kwak, J. G., Park, H. K., Wang, Z. R., Park, J. -K., Ferraro, N. M., & Yoon, S. W. Analysis of MHD stability and active mode control on KSTAR for high confinement, disruption-free plasma. United States. https://doi.org/10.1088/1741-4326/ab79ca
Park, Y. S., Sabbagh, S. A., Ahn, J. H., Park, B. H., Kim, H. S., Berkery, J. W., Bialek, J. M., Jiang, Y., Bak, J. G., Glasser, A. H., Kang, J. S., Lee, J., Han, H. S., Hahn, S. H., Jeon, Y. M., Kwak, J. G., Park, H. K., Wang, Z. R., Park, J. -K., Ferraro, N. M., and Yoon, S. W. Fri . "Analysis of MHD stability and active mode control on KSTAR for high confinement, disruption-free plasma". United States. https://doi.org/10.1088/1741-4326/ab79ca. https://www.osti.gov/servlets/purl/1650665.
@article{osti_1650665,
title = {Analysis of MHD stability and active mode control on KSTAR for high confinement, disruption-free plasma},
author = {Park, Y. S. and Sabbagh, S. A. and Ahn, J. H. and Park, B. H. and Kim, H. S. and Berkery, J. W. and Bialek, J. M. and Jiang, Y. and Bak, J. G. and Glasser, A. H. and Kang, J. S. and Lee, J. and Han, H. S. and Hahn, S. H. and Jeon, Y. M. and Kwak, J. G. and Park, H. K. and Wang, Z. R. and Park, J. -K. and Ferraro, N. M. and Yoon, S. W.},
abstractNote = {Long-pulse plasma operation at high normalized beta, βN, above the n= 1 ideal MHD no-wall stability limit in KSTAR is presently limited by tearing instabilities rather than resistive wall modes. H-mode plasma operation during the recent KSTAR device campaign produced discharges having strong m/n= 2/1 tearing instabilities at βN lower than the ideal MHD no-wall beta limit.The unstable tearing mode consequently reduced plasma confinement and toroidal plasma rotation significantly. The experiment confirmed that an extended duration of electron cyclotron heating (ECH) at the initial phase of the discharge plays a critical role in mode destabilization.To study destabilizing mechanisms that affect the mode growth, the stability of the observed tearing modes from plasmas with significantly different βN is computed by using the resistive DCON code and the M3D-C1code. Equilibrium reconstructions that include constraints from internal profile diagnostics, and computed fast particle pressure are used as input for reliable computation of stability. The classical tearing stability index, Δ', from resistive DCON is computed to be unstable when the island is fully saturated with large amplitude,while the unstable mode is not computed by M3D-C1. The modified Rutherford equation (MRE) describing the evolution of the island width has been constructed for KSTAR plasmas by using plasma parameters computed by the TRANSP code.The MRE model estimates a saturated island width corresponding to ~10% of the plasma minor radius for equilibrium at high βN> 3 having a stable Δ' from the resistive DCON. In preparation for long-pulse plasma operation at higher beta utilizing increased plasma heating power, a resistive wall mode (RWM) active feedback control algorithm has been completed and enabled on KSTAR. To accurately determine the n= 1component produced by RWMs, an algorithm has been developed that includes magnetic sensor compensation of the prompt applied field and the field from the induced current on the passive conductors. Use of multiple toroidal sensor arrays is enabled by modifying the sensor toroidal angles assumed in mode decomposition to include the effect of varied mode helicities in the outboard region where the mode measurement is made. This analysis on stability, transport, and control provides the required foundation for disruption prediction and avoidance research on KSTAR.},
doi = {10.1088/1741-4326/ab79ca},
journal = {Nuclear Fusion},
number = 5,
volume = 60,
place = {United States},
year = {2020},
month = {4}
}

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