Fast ions and shear Alfven waves

In order to study the interaction of ions of intermediate energies with plasma fluctuations, two plasma immersible lithium ion sources, based on solid-state thermionic emitters (Li aluminosilicate) were developed. Compared to discharge based ion sources, they are compact, have zero gas load, small energy dispersion, and can be operated at any angle with respect to an ambient magnetic field of up to 4.0 kG. Beam energies range from 400 eV to 2.0 keV with typical beam current densities in the 1 mA/cm2 range. Because of the low ion mass, beam velocities of 100--300 km/s are in the range of Alfven speeds in typical helium plasmas in the LArge Plasma Device (LAPD).; The Doppler-shifted cyclotron resonance (o -- k znuz = Of) between fast ions and shear Alfven waves is experimentally investigated. (o: wave frequency; kz: axial wavenumber; vz: fast-ion axial speed; O 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), with shear Alfven waves (SAW) (amplitude deltaB/B up to 1%) launched by a loop antenna. A collimated fast-ion energy analyzer measures the non-classical 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 oci. 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. Measurements of fast-ion signals on selected fast-ion energies confirm that the particles gain/lose energy from/to the wave.; A multiple magnetic mirror array is formed at the LAPD to study axial periodicity-influenced Alfven spectra. SAWs are launched by antennas inserted in the LAPD plasma and diagnosed by B-dot probes at many axial locations. Alfven wave spectral gaps and continua are farmed similar to wave propagation in other periodic media due to the Bragg effect. The measured width of the propagation gap increases with the modulation amplitude as predicted by the solutions to Mathieu's equation. A 2-D finite-difference code modeling SAW in a mirror array configuration shows similar spectral features. Machine end-reflection conditions and damping mechanisms including electron-ion Coulomb collision and electron Landau damping are important for simulation.