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

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, previously 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 LSNmore » 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
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Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 23; Journal Issue: 9; Related Information: Boedo, J.A., deGrassie, J., Grierson, B.A., Stoltzfus-Dueck, T., Battaglia, J., Rudakov, D.L., Belli, E.A., Groebner, R.J., Hollmann, E., Lasnier, C., Solomon, W.M., Untergerg, E.A., Watkins, J. and DIII-Team, "Experimental Evidence of Edge Intrinsic Momentum Source Driven by Kinetic Ion Loss and Edge Radial Electric Fields in Tokamaks" Phys. Plasmas, 23, 092506 (2016); Journal ID: ISSN 1070-664X
American Institute of Physics (AIP)
Research Org:
General Atomics, San Diego, CA (United States)
Sponsoring Org:
Contributing Orgs:
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1371911