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Title: Progress toward steady-state tokamak operation exploiting the high bootstrap current fraction regime

Abstract

Recent DIII-D experiments have increased the normalized fusion performance of the high bootstrap current fraction tokamak regime toward reactor-relevant steady state operation. The experiments, conducted by a joint team of researchers from the DIII-D and EAST tokamaks, developed a fully noninductive scenario that could be extended on EAST to a demonstration of long pulse steady-state tokamak operation. Improved understanding of scenario stability has led to the achievement of very high values of β p and β N despite strong ITBs. Good confinement has been achieved with reduced toroidal rotation. These high β p plasmas challenge the energy transport understanding, especially in the electron energy channel. A new turbulent transport model, named 2 TGLF-SAT1, has been developed which improves the transport prediction. Experiments extending results to long pulse on EAST, based on the physics basis developed at DIII-D, have been conducted. Finally, more investigations will be carried out on EAST with more additional auxiliary power to come online in the near term.

Authors:
ORCiD logo [1];  [2];  [1];  [3]; ORCiD logo [2];  [4];  [2]; ORCiD logo [2];  [5];  [1];  [5]; ORCiD logo [2];  [6];  [1];  [1];  [1];  [1]; ORCiD logo [1]
  1. Chinese Academy of Sciences (CAS), Beijing (China). Inst. of Plasma Physics
  2. General Atomics, San Diego, CA (United States)
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  4. Univ. of Wisconsin, Madison, WI (United States). Dept. of Engineering Physics
  5. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  6. Univ. of California, San Diego, CA (United States). Center for Energy Research
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE; National Magnetic Confinement Fusion Program of China
OSTI Identifier:
1371748
Grant/Contract Number:
FC02-04ER54698; AC52-07NA27344; FG02-08ER54999; AC02-09CH11466; FG02-07ER54917; FG02-06ER54871
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 23; Journal Issue: 6; 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; Internal transport barrier; Tokamaks; Torque; Turbulent transport processes; Toroidal plasma confinement

Citation Formats

Ren, Q. L., Garofalo, A. M., Gong, X. Z., Holcomb, C. T., Lao, L. L., McKee, G. R., Meneghini, O., Staebler, G. M., Grierson, B. A., Qian, J. P., Solomon, W. M., Turnbull, A. D., Holland, C., Guo, W. F., Ding, S. Y., Pan, C. K., Xu, G. S., and Wan, B. N. Progress toward steady-state tokamak operation exploiting the high bootstrap current fraction regime. United States: N. p., 2016. Web. doi:10.1063/1.4948724.
Ren, Q. L., Garofalo, A. M., Gong, X. Z., Holcomb, C. T., Lao, L. L., McKee, G. R., Meneghini, O., Staebler, G. M., Grierson, B. A., Qian, J. P., Solomon, W. M., Turnbull, A. D., Holland, C., Guo, W. F., Ding, S. Y., Pan, C. K., Xu, G. S., & Wan, B. N. Progress toward steady-state tokamak operation exploiting the high bootstrap current fraction regime. United States. doi:10.1063/1.4948724.
Ren, Q. L., Garofalo, A. M., Gong, X. Z., Holcomb, C. T., Lao, L. L., McKee, G. R., Meneghini, O., Staebler, G. M., Grierson, B. A., Qian, J. P., Solomon, W. M., Turnbull, A. D., Holland, C., Guo, W. F., Ding, S. Y., Pan, C. K., Xu, G. S., and Wan, B. N. 2016. "Progress toward steady-state tokamak operation exploiting the high bootstrap current fraction regime". United States. doi:10.1063/1.4948724. https://www.osti.gov/servlets/purl/1371748.
@article{osti_1371748,
title = {Progress toward steady-state tokamak operation exploiting the high bootstrap current fraction regime},
author = {Ren, Q. L. and Garofalo, A. M. and Gong, X. Z. and Holcomb, C. T. and Lao, L. L. and McKee, G. R. and Meneghini, O. and Staebler, G. M. and Grierson, B. A. and Qian, J. P. and Solomon, W. M. and Turnbull, A. D. and Holland, C. and Guo, W. F. and Ding, S. Y. and Pan, C. K. and Xu, G. S. and Wan, B. N.},
abstractNote = {Recent DIII-D experiments have increased the normalized fusion performance of the high bootstrap current fraction tokamak regime toward reactor-relevant steady state operation. The experiments, conducted by a joint team of researchers from the DIII-D and EAST tokamaks, developed a fully noninductive scenario that could be extended on EAST to a demonstration of long pulse steady-state tokamak operation. Improved understanding of scenario stability has led to the achievement of very high values of βp and βN despite strong ITBs. Good confinement has been achieved with reduced toroidal rotation. These high βp plasmas challenge the energy transport understanding, especially in the electron energy channel. A new turbulent transport model, named 2 TGLF-SAT1, has been developed which improves the transport prediction. Experiments extending results to long pulse on EAST, based on the physics basis developed at DIII-D, have been conducted. Finally, more investigations will be carried out on EAST with more additional auxiliary power to come online in the near term.},
doi = {10.1063/1.4948724},
journal = {Physics of Plasmas},
number = 6,
volume = 23,
place = {United States},
year = 2016,
month = 6
}

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  • Recent EAST/DIII-D joint experiments on the high poloidal beta tokamak regime in DIII-D have demonstrated fully noninductive operation with an internal transport barrier (ITB) at large minor radius, at normalized fusion performance increased by ≥30% relative to earlier work. The advancement was enabled by improved understanding of the “relaxation oscillations”, previously attributed to repetitive ITB collapses, and of the fast ion behavior in this regime. It was found that the “relaxation oscillations” are coupled core-edge modes 2 amenable to wall-stabilization, and that fast ion losses which previously dictated a large plasma-wall separation to avoid wall over-heating, can be reduced tomore » classical levels with sufficient plasma density. By using optimized waveforms of the plasma-wall separation and plasma density, fully noninductive plasmas have been sustained for long durations with excellent energy confinement quality, bootstrap fraction ≥ 80%, β N ≤ 4 , β P ≥ 3 , and β T ≥ 2%. Finally, these results bolster the applicability of the high poloidal beta tokamak regime toward the realization of a steady-state fusion reactor.« less
  • Recent EAST/DIII-D joint experiments on the high poloidal betamore » $${{\beta}_{\text{P}}}$$ regime in DIII-D have extended operation with internal transport barriers (ITBs) and excellent energy confinement (H 98y2 ~ 1.6) to higher plasma current, for lower q 95 ≤ 7.0, and more balanced neutral beam injection (NBI) (torque injection < 2 Nm), for lower plasma rotation than previous results. Transport analysis and experimental measurements at low toroidal rotation suggest that the E × B shear effect is not key to the ITB formation in these high $${{\beta}_{\text{P}}}$$ discharges. Experiments and TGLF modeling show that the Shafranov shift has a key stabilizing effect on turbulence. Extrapolation of the DIII-D results using a 0D model shows that with the improved confinement, the high bootstrap fraction regime could achieve fusion gain Q = 5 in ITER at $${{\beta}_{\text{N}}}$$ ~ 2.9 and q 95 ~ 7. With the optimization of q(0), the required improved confinement is achievable when using 1.5D TGLF-SAT1 for transport simulations. Furthermore, results reported in this paper suggest that the DIII-D high $${{\beta}_{\text{P}}}$$ scenario could be a candidate for ITER steady state operation.« less
  • The reactor potential of some advanced physics operating modes proposed for the TPX physics program are examined. A moderate aspect ratio (A = 4.5 as in TPX), 2 GW reactor is analyzed because of its potential for steady-state, non-inductive operation with high bootstrap current fraction. Particle, energy and toroidal current equations are evolved to steady-state conditions using the 1-1/2-D time-dependent WHIST transport code. The solutions are therefore consistent with particle, energy and current sources and assumed transport models. Fast wave current drive (FWCD) provides the axial seed current. The bootstrap current typically provides 80-90% of the current, while feedback onmore » the lower hybrid current drive (LHCD) power maintains the total current. The sensitivity of the plasma power amplification factor, Q {triple_bond} P{sub fus}/P{sub aux}, to variations in the plasma properties is examined. The auxiliary current drive power, P{sub aux} = P{sub LH} + P{sub FW}; bootstrap current fraction; current drive efficiency; and other parameters are evaluated. The plasma is thermodynamically stable for the energy confinement model assumed (a multiple of ITER89P). The FWCD and LHCD sources provide attractive control possibilities, not only for the current profile, but also for the total fusion power since the gain on the incremental auxiliary power is typically 10-30 in these calculations when overall Q {approx} 30.« less