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

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.

doi:10.1063/1.4962683

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

Journal Article · Wed Sep 21 00:00:00 EDT 2016 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4962683· OSTI ID:1331213

^[1]; ^[2]; Grierson, B. ^[3]; Stoltzfus-Dueck, T. ^[3]; Battaglia, D. J. ^[3]; Rudakov, D. L. ^[4]; ^[2]; Groebner, R. J. ^[2]; Hollmann, E. ^[4]; Lasnier, C. ^[5]; Solomon, W. M. ^[3]; ^[6]; Watkins, J. ^[7]

Univ. of California-San Diego, La Jolla, CA (United States); General Atomics
General Atomics, San Diego, CA (United States)
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Univ. of California-San Diego, La Jolla, CA (United States)
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

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-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.

View Accepted Manuscript (DOE)

Research Organization:: General Atomics, San Diego, CA (United States); Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

Sponsoring Organization:: USDOE; USDOE National Nuclear Security Administration (NNSA); USDOE Office of Nuclear Energy (NE); USDOE Office of Science (SC)

Contributing Organization:: DIII-D Team

Grant/Contract Number:: AC02-09CH11466; AC04-94AL85000; AC05-00OR22725; AC52-07NA27344; FC02-04ER54698; FG02-07ER54917; FG02-95ER54309

OSTI ID:: 1331213

Alternate ID(s):: OSTI ID: 1325841
OSTI ID: 1515662
OSTI ID: 1332295
OSTI ID: 1542111
OSTI ID: 1371911

Report Number(s):: DOE-GA--30200-1; LLNL-JRNL--736686

Journal Information:: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 9 Vol. 23; ISSN PHPAEN; ISSN 1070-664X

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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

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