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Title: Experimental evidence of edge intrinsic momentum source driven by kinetic ion loss and edge radial electric fields in tokamaks

Abstract

Here, bulk ion toroidal velocity profiles, V D+ ||, peaking at 40–60 km/s are observed with Mach probes in a narrow edge region of DIII-D discharges without external momentum input. This intrinsic rotation can be well reproduced by a first principle, collisionless kinetic loss model of thermal ion loss that predicts the existence of a loss-cone distribution in velocity space resulting in a co-Ip directed velocity. We consider two kinetic models, one of which includes turbulence-enhanced momentum transport, as well as the Pfirsch-Schluter (P-S) fluid mechanism. We measure a fine structure of the boundary radial electric field, Er, insofar ignored, featuring large (10–20 kV/m) positive peaks in the scrape off layer (SOL) at, or slightly inside, the last closed flux surface of these low power L- and H-mode discharges in DIII-D. The Er structure significantly affects the ion-loss model, extended to account for a non-uniform electric field. We also find that V D+ || is reduced when the magnetic topology is changed from lower single null to upper single null. The kinetic ion loss model containing turbulence-enhanced momentum transport can explain the reduction, as we find that the potential fluctuations decay with radius, while we need to invoke a topology-enhancedmore » collisionality on the simpler kinetic model. The P-S mechanism fails to reproduce the damping. We show a clear correlation between the near core V C6+ || velocity and the peak edge V D+ || in discharges with no external torque, further supporting the hypothesis that ion loss is the source for intrinsic torque in the present tokamaks. However, we also show that when external torque is injected in the core, it can complete with, and eventually overwhelm, the edge source, thus determining the near SOL flows. Finally, we show some additional evidence that the ion/electron distribution in the SOL is non-Maxwellian.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [3];  [3];  [3];  [1]; ORCiD logo [2];  [2];  [1];  [4];  [3]; ORCiD logo [5];  [6]
  1. Univ. of California-San Diego, La Jolla, CA (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  6. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Publication Date:
Research Org.:
US Department of Energy, Washington, D.C. (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE)
Contributing Org.:
DIII-D Team
OSTI Identifier:
1332295
Alternate Identifier(s):
OSTI ID: 1325841; OSTI ID: 1331213; OSTI ID: 1371911
Report Number(s):
DOE-GA-30200-1
Journal ID: ISSN 1070-664X; PHPAEN
Grant/Contract Number:
FC02-04ER54698; AC02-09CH11466; AC04-94AL85000; AC05-00OR22725; AC52-07NA27344; FC02- 04ER54698; FG02-07ER54917; FG02-95ER54309
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 23; Journal Issue: 9; 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; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; turbulence simulations; tokamaks; torque; collision theories; electric fields

Citation Formats

Boedo, J. A., deGrassie, J. S., Grierson, B., Stoltzfus-Dueck, T., Battaglia, D. J., Rudakov, D. L., Belli, E. A., Groebner, R. J., Hollmann, E., Lasnier, C., Solomon, W. M., Unterberg, E. A., and Watkins, J. Experimental evidence of edge intrinsic momentum source driven by kinetic ion loss and edge radial electric fields in tokamaks. United States: N. p., 2016. Web. doi:10.1063/1.4962683.
Boedo, J. A., deGrassie, J. S., Grierson, B., Stoltzfus-Dueck, T., Battaglia, D. J., Rudakov, D. L., Belli, E. A., Groebner, R. J., Hollmann, E., Lasnier, C., Solomon, W. M., Unterberg, E. A., & Watkins, J. Experimental evidence of edge intrinsic momentum source driven by kinetic ion loss and edge radial electric fields in tokamaks. United States. doi:10.1063/1.4962683.
Boedo, J. A., deGrassie, J. S., Grierson, B., Stoltzfus-Dueck, T., Battaglia, D. J., Rudakov, D. L., Belli, E. A., Groebner, R. J., Hollmann, E., Lasnier, C., Solomon, W. M., Unterberg, E. A., and Watkins, J. Wed . "Experimental evidence of edge intrinsic momentum source driven by kinetic ion loss and edge radial electric fields in tokamaks". United States. doi:10.1063/1.4962683. https://www.osti.gov/servlets/purl/1332295.
@article{osti_1332295,
title = {Experimental evidence of edge intrinsic momentum source driven by kinetic ion loss and edge radial electric fields in tokamaks},
author = {Boedo, J. A. and deGrassie, J. S. and Grierson, B. and Stoltzfus-Dueck, T. and Battaglia, D. J. and Rudakov, D. L. and Belli, E. A. and Groebner, R. J. and Hollmann, E. and Lasnier, C. and Solomon, W. M. and Unterberg, E. A. and Watkins, J.},
abstractNote = {Here, bulk ion toroidal velocity profiles, VD+||, peaking at 40–60 km/s are observed with Mach probes in a narrow edge region of DIII-D discharges without external momentum input. This intrinsic rotation can be well reproduced by a first principle, collisionless kinetic loss model of thermal ion loss that predicts the existence of a loss-cone distribution in velocity space resulting in a co-Ip directed velocity. We consider two kinetic models, one of which includes turbulence-enhanced momentum transport, as well as the Pfirsch-Schluter (P-S) fluid mechanism. We measure a fine structure of the boundary radial electric field, Er, insofar ignored, featuring large (10–20 kV/m) positive peaks in the scrape off layer (SOL) at, or slightly inside, the last closed flux surface of these low power L- and H-mode discharges in DIII-D. The Er structure significantly affects the ion-loss model, extended to account for a non-uniform electric field. We also find that VD+|| is reduced when the magnetic topology is changed from lower single null to upper single null. The kinetic ion loss model containing turbulence-enhanced momentum transport can explain the reduction, as we find that the potential fluctuations decay with radius, while we need to invoke a topology-enhanced collisionality on the simpler kinetic model. The P-S mechanism fails to reproduce the damping. We show a clear correlation between the near core VC6+|| velocity and the peak edge VD+|| in discharges with no external torque, further supporting the hypothesis that ion loss is the source for intrinsic torque in the present tokamaks. However, we also show that when external torque is injected in the core, it can complete with, and eventually overwhelm, the edge source, thus determining the near SOL flows. Finally, we show some additional evidence that the ion/electron distribution in the SOL is non-Maxwellian.},
doi = {10.1063/1.4962683},
journal = {Physics of Plasmas},
number = 9,
volume = 23,
place = {United States},
year = {Wed Sep 21 00:00:00 EDT 2016},
month = {Wed Sep 21 00:00:00 EDT 2016}
}

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  • Cited by 4
  • Here, bulk ion toroidal velocity profiles, V D+ ||, peaking at 40–60 km/s are observed with Mach probes in a narrow edge region of DIII-D discharges without external momentum input. This intrinsic rotation can be well reproduced by a first principle, collisionless kinetic loss model of thermal ion loss that predicts the existence of a loss-cone distribution in velocity space resulting in a co-Ip directed velocity. We consider two kinetic models, one of which includes turbulence-enhanced momentum transport, as well as the Pfirsch-Schluter (P-S) fluid mechanism. We measure a fine structure of the boundary radial electric field, Er, insofar ignored,more » featuring large (10–20 kV/m) positive peaks in the scrape off layer (SOL) at, or slightly inside, the last closed flux surface of these low power L- and H-mode discharges in DIII-D. The Er structure significantly affects the ion-loss model, extended to account for a non-uniform electric field. We also find that V D+ || is reduced when the magnetic topology is changed from lower single null to upper single null. The kinetic ion loss model containing turbulence-enhanced momentum transport can explain the reduction, as we find that the potential fluctuations decay with radius, while we need to invoke a topology-enhanced collisionality on the simpler kinetic model. The P-S mechanism fails to reproduce the damping. We show a clear correlation between the near core V C6+ || velocity and the peak edge V D+ || in discharges with no external torque, further supporting the hypothesis that ion loss is the source for intrinsic torque in the present tokamaks. However, we also show that when external torque is injected in the core, it can complete with, and eventually overwhelm, the edge source, thus determining the near SOL flows. Finally, we show some additional evidence that the ion/electron distribution in the SOL is non-Maxwellian.« less
  • Bulk ion toroidal velocity profiles, V|| D+ , peaking at 40-60 km/s are observed with Mach probes in a narrow edge region of DIII-D discharges without external momentum input. This intrinsic rotation can be well reproduced by a first principle, collisionless kinetic loss model of thermal ion loss that predicts the existence of a loss-cone distribution in velocity space resulting in a co-Ip directed velocity. We consider two kinetic models, one of which includes turbulence-enhanced momentum transport, as well as a third, the Pfirsch-Schluter (P-S) fluid mechanism. We measure a fine structure of the boundary radial electric field, Er, previouslymore » ignored, featuring large (10–20 kV/m) positive peaks in the scrape off layer (SOL) at, or slightly inside, the last closed flux 2 surface (LCFS) of these low power L- and H-mode discharges in DIII-D. The Er structure significantly affects the ion-loss model, extended to account for a non-uniform electric field. We also find that V|| D+ is reduced when the magnetic topology is changed from lower single null (LSN) to upper single null (USN). The kinetic ion loss model containing turbulence-enhanced momentum transport can explain the reduction, as we find that the potential fluctuation profile differs between USN and LSN discharges, while we need to invoke a topology-enhanced collisionality on the simpler kinetic model. The P-S mechanism fails to reproduce the damping. We show a clear correlation between the near core V|| C6+ velocity and the peak edge V|| D+ in discharges with no external torque, further supporting the hypothesis that ion loss is the source for intrinsic torque in present tokamaks. However, we also show that when external torque is injected in the core, it can compete with, and eventually overwhelm, the edge source. Finally, we show some additional evidence that the ion/electron distribution in the SOL is non-Maxwellian.« less
  • Particle orbit simulations are carried out to study the ion orbits and loss at the edge of a tokamak plasma. The ion loss conditions are examined as a function of {upsilon}{sub PLL}/{upsilon}{sub 0} and the distance of ion launching points form the magnetic separatrix. The simulation results are compared with the theoretical ones. Good agreements and detailed features are shown in the simulations. 8 refs., 6 figs.
  • An investigation of the effect of ion orbit loss of thermal ions and the compensating return ion current directly on the radial ion flux flowing in the plasma, and thereby indirectly on the toroidal and poloidal rotation velocity profiles, the radial electric field, density, and temperature profiles, and the interpretation of diffusive and non-diffusive transport coefficients in the plasma edge, is described. Illustrative calculations for a high-confinement H-mode DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] plasma are presented and compared with experimental results. Taking into account, ion orbit loss of thermal ions and the compensating return ion current ismore » found to have a significant effect on the structure of the radial profiles of these quantities in the edge plasma, indicating the necessity of taking ion orbit loss effects into account in interpreting or predicting these quantities.« less