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Title: Confinement improvement in the high poloidal beta regime on DIII-D and application to steady-state H-mode on EAST

Abstract

Systematic experimental and modeling investigations on DIII-D and EAST show attractive transport properties of fully non-inductive high β p plasmas. Experiments on DIII-D show that the large-radius internal transport barrier (ITB), a key feature providing excellent confinement in the high β p regime, is maintained when the scenario is extended from q 95 ~ 12 to 7 and from rapid to near-zero toroidal rotation. The robustness of confinement versus rotation was predicted by gyro fluid modeling showing dominant neoclassical ion energy transport even without E B shear effect. The physics mechanism of turbulence suppression, we found, is the Shafranov shift, which is essential and sets a β p threshold for large-radius ITB formation in the high β p scenario on DIII-D. This is confirmed by two different parameter-scan experiments, one for β N scan and the other for q 95 scan. They both give the same p threshold at 1.9 in the experiment. Furthermore, the experiment trend of increasing thermal transport with decreasing β p is consistent with transport modeling. The very first step of extending high β p scenario on DIII-D to long pulse on EAST is to establish long pulse H-mode with ITB on EAST. Our paper showsmore » the first 61 sec fully non-inductive H-mode with stationary ITB feature and actively cooled ITER-like tungsten divertor in the very recent EAST experiment. The successful use of lower hybrid wave (LWH) as a key tool to optimize current profile in EAST experiment is also introduced. Results show that as the electron density is increased, the fully non-inductive current profile broadens on EAST. The improved understanding and modeling capability is also used to develop advanced scenarios for CFETR. These results provide encouragement that the high β p regime can be extended to lower safety factor and very low rotation, providing a potential path to high performance steady state operation in future devices.« less

Authors:
ORCiD logo [1];  [2];  [3];  [4];  [5];  [1];  [1];  [1];  [6]; ORCiD logo [1];  [1];  [7];  [1]; ORCiD logo [2];  [2];  [2]; ORCiD logo [2];  [2];  [1];  [1] more »;  [1]; ORCiD logo [1] « less
  1. Chinese Academy of Sciences (CAS), Beijing (China). Inst. of Plasma Physics
  2. General Atomics, San Diego, CA (United States)
  3. Institute of Plasma Physics, Chinese Academy of Sciences, P. O. Box 1126, Hefei, Anhui 230031, China
  4. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  6. Univ. of Wisconsin, Madison, WI (United States)
  7. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24); National Magnetic Confinement Fusion Science Program of China
OSTI Identifier:
1374574
Grant/Contract Number:
FC02-04ER54698; 2015GB103001; 2015GB102004; 2015GB101000; 2015GB110001; 2015GB110005; FC02- 04ER54698
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 5; 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

Ding, Siye, Garofalo, A. M., Qian, J., Cui, L., McClenaghan, J. T., Pan, C., Chen, J., Zhai, X., McKee, G., Ren, Q., Gong, X., Holcomb, C. T., Guo, W., Lao, L., Ferron, J., Hyatt, A., Staebler, G., Solomon, W., Du, H., Zang, Q., Huang, J., and Wan, B. Confinement improvement in the high poloidal beta regime on DIII-D and application to steady-state H-mode on EAST. United States: N. p., 2017. Web. doi:10.1063/1.4982058.
Ding, Siye, Garofalo, A. M., Qian, J., Cui, L., McClenaghan, J. T., Pan, C., Chen, J., Zhai, X., McKee, G., Ren, Q., Gong, X., Holcomb, C. T., Guo, W., Lao, L., Ferron, J., Hyatt, A., Staebler, G., Solomon, W., Du, H., Zang, Q., Huang, J., & Wan, B. Confinement improvement in the high poloidal beta regime on DIII-D and application to steady-state H-mode on EAST. United States. doi:10.1063/1.4982058.
Ding, Siye, Garofalo, A. M., Qian, J., Cui, L., McClenaghan, J. T., Pan, C., Chen, J., Zhai, X., McKee, G., Ren, Q., Gong, X., Holcomb, C. T., Guo, W., Lao, L., Ferron, J., Hyatt, A., Staebler, G., Solomon, W., Du, H., Zang, Q., Huang, J., and Wan, B. 2017. "Confinement improvement in the high poloidal beta regime on DIII-D and application to steady-state H-mode on EAST". United States. doi:10.1063/1.4982058.
@article{osti_1374574,
title = {Confinement improvement in the high poloidal beta regime on DIII-D and application to steady-state H-mode on EAST},
author = {Ding, Siye and Garofalo, A. M. and Qian, J. and Cui, L. and McClenaghan, J. T. and Pan, C. and Chen, J. and Zhai, X. and McKee, G. and Ren, Q. and Gong, X. and Holcomb, C. T. and Guo, W. and Lao, L. and Ferron, J. and Hyatt, A. and Staebler, G. and Solomon, W. and Du, H. and Zang, Q. and Huang, J. and Wan, B.},
abstractNote = {Systematic experimental and modeling investigations on DIII-D and EAST show attractive transport properties of fully non-inductive high βp plasmas. Experiments on DIII-D show that the large-radius internal transport barrier (ITB), a key feature providing excellent confinement in the high βp regime, is maintained when the scenario is extended from q95 ~ 12 to 7 and from rapid to near-zero toroidal rotation. The robustness of confinement versus rotation was predicted by gyro fluid modeling showing dominant neoclassical ion energy transport even without E B shear effect. The physics mechanism of turbulence suppression, we found, is the Shafranov shift, which is essential and sets a βp threshold for large-radius ITB formation in the high βp scenario on DIII-D. This is confirmed by two different parameter-scan experiments, one for βN scan and the other for q95 scan. They both give the same p threshold at 1.9 in the experiment. Furthermore, the experiment trend of increasing thermal transport with decreasing βp is consistent with transport modeling. The very first step of extending high βp scenario on DIII-D to long pulse on EAST is to establish long pulse H-mode with ITB on EAST. Our paper shows the first 61 sec fully non-inductive H-mode with stationary ITB feature and actively cooled ITER-like tungsten divertor in the very recent EAST experiment. The successful use of lower hybrid wave (LWH) as a key tool to optimize current profile in EAST experiment is also introduced. Results show that as the electron density is increased, the fully non-inductive current profile broadens on EAST. The improved understanding and modeling capability is also used to develop advanced scenarios for CFETR. These results provide encouragement that the high βp regime can be extended to lower safety factor and very low rotation, providing a potential path to high performance steady state operation in future devices.},
doi = {10.1063/1.4982058},
journal = {Physics of Plasmas},
number = 5,
volume = 24,
place = {United States},
year = 2017,
month = 5
}

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  • Cited by 3
  • Recent experiments on EAST have achieved the first long pulse H-mode (61 s) with zero loop voltage and an ITER-like tungsten divertor, and have demonstrated access to broad plasma current profiles by increasing the density in fully-noninductive lower hybrid current-driven discharges. These long pulse discharges reach wall thermal and particle balance, exhibit stationary good confinement (H 98y2~1.1) with low core electron transport, and are only possible with optimal active cooling of the tungsten armors. In separate experiments, the electron density was systematically varied in order to study its effect on the deposition profile of the external lower hybrid current drivemore » (LHCD), while keeping the plasma in fully-noninductive conditions and with divertor strike points on the tungsten divertor. A broadening of the current profile is found, as indicated by lower values of the internal inductance at higher density. A broad current profile is attractive because, among other reasons, it enables internal transport barriers at large minor radius, leading to improved confinement as shown in companion DIII-D experiments. These experiments strengthen the physics basis for achieving high performance, steady state discharges in future burning plasmas.« less
  • 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