Observation of Critical-Gradient Behavior in Alfvén-Eigenmode-Induced Fast-Ion Transport

C. S. Collins, W. W. Heidbrink, M. E. Austin, G. J. Kramer, D. C. Pace, C. C. Petty, L. Stagner, M. A. Van Zeeland, R. B. White, Y. B. Zhu, and DIII-D team
Phys. Rev. Lett. 116, 095001 – Published 29 February 2016

Abstract

Experiments in the DIII-D tokamak show that fast-ion transport suddenly becomes stiff above a critical threshold in the presence of many overlapping small-amplitude Alfvén eigenmodes (AEs). The threshold is phase-space dependent and occurs when particle orbits become stochastic due to resonances with AEs. Above threshold, equilibrium fast-ion density profiles are unchanged despite increased drive, and intermittent fast-ion losses are observed. Fast-ion Dα spectroscopy indicates radially localized transport of the copassing population at radii that correspond to the location of midcore AEs. The observation of stiff fast-ion transport suggests that reduced models can be used to effectively predict alpha profiles, beam ion profiles, and losses to aid in the design of optimized scenarios for future burning plasma devices.

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  • Received 20 November 2015

DOI:https://doi.org/10.1103/PhysRevLett.116.095001

© 2016 American Physical Society

Physics Subject Headings (PhySH)

Plasma Physics

Authors & Affiliations

C. S. Collins1,*, W. W. Heidbrink1, M. E. Austin2, G. J. Kramer3, D. C. Pace4, C. C. Petty4, L. Stagner1, M. A. Van Zeeland4, R. B. White3, Y. B. Zhu1, and DIII-D team

  • 1University of California-Irvine, Irvine, California 92697, USA
  • 2University of Texas-Austin, Austin, Texas 78712, USA
  • 3Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543, USA
  • 4General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA

  • *collinscs@fusion.gat.com

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Vol. 116, Iss. 9 — 4 March 2016

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