Abstract
The Doppler-shifted cyclotron resonance (ω- kz vz = 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.
Original language | English |
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Article number | 102112 |
Journal | Physics of Plasmas |
Volume | 15 |
Issue number | 10 |
DOIs | |
State | Published - 2008 |
Externally published | Yes |