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Observation of fast-ion Doppler-shifted cyclotron resonance with shear Alfvén waves

  • Author(s): Zhang, Y
  • Heidbrink, WW
  • Boehmer, H
  • McWilliams, R
  • Vincena, S
  • Carter, TA
  • Gekelman, W
  • Leneman, D
  • Pribyl, P
  • et al.

Published Web Location Commons 'BY' version 4.0 license

The Doppler-shifted cyclotron resonance (ω- kzvz = f) between fast ions and shear Alfv́n waves is experimentally investigated (ω, wave frequency; kz, axial wavenumber; vz, fast-ion axial speed; f, fast-ion cyclotron frequency). A test particle beam of fast ions is launched by a Li+ source in the helium plasma of the LArge Plasma Device (LAPD) [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)], with shear Alfv́n waves (SAW) (amplitude δ B/B up to 1%) launched by a loop antenna. A collimated fast-ion energy analyzer measures the nonclassical spreading of the beam, which is proportional to the resonance with the wave. A resonance spectrum is observed by launching SAWs at 0.3-0.8 ωci. Both the magnitude and frequency dependence of the beam-spreading are in agreement with the theoretical prediction using a Monte Carlo Lorentz code that launches fast ions with an initial spread in real/velocity space and random phases relative to the wave. Measured wave magnetic field data are used in the simulation. © 2008 American Institute of Physics.

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