Plasma Resonance Interaction with a Spatially Rotating Static Magnetic Field

The ion cyclotron resonance interaction of plasma with a rotating transverse magnetic perturbation on a longitudinal magnetic field is investigated experimentally and theoretically. The plasma is injected axially from a coaxial hydromagnetic gun along a longitudinal magnetic field on which there is superimposed a transverse spatially rotating perturbation field. A resonance transfer of ion energy from the longitudinal to the transverse direction is observed when the spatial period or wavelength of the perturbation field and the plasma velocity and ion cyclotron frequency satisfy the relation λ_z = 2πv_z/Ω_B. Measurements of plasma diamagnetism and transit time show an increase of up to a factor of two in diamagnetism coupled with a decrease in axial velocity corresponding to a reduction to half the initial longitudinal energy. Resonance may be observed over a range of longitudinal energies by varying the parameters of the system. For the plasma gun and perturbation field helix used in the experiment, optimum resonance was obtained with plasmas of longitudinal energy of ∼ 2.5 keV and particle densities of ∼ 10¹⁵cm⁻³(β ≳ 0.8). A theoretical account of the effect is given which considers the excitation by the perturbation field of circularly polarized electromagnetic waves in the plasma at ion cyclotron frequency and the transfer of longitudinal ion energy into transverse motion through the intermediate action of the waves.