Whistler wave excitation and effects of self-focusing on ion beam propagation through a background plasma along a solenoidal magnetic field

This paper extends studies of ion beam transport through a background plasma along a solenoidal magnetic field by Kaganovich [Phys. Plasmas 15, 103108 (2008)] to the important regime of moderate magnetic field strength satisfying ω_ce 2 Β_b ω_pe. Here, ω_ce and ω_pe are the electron cyclotron frequency and electron plasma frequency, respectively, and Β_b = v_b /c is the directed ion beam velocity normalized to the speed of light. The electromagnetic field perturbations excited by the ion beam pulse in this regime are calculated analytically and verified by comparison with the numerical simulations. The degrees of beam charge neutralization and current neutralization are estimated, and the transverse component of the Lorentz force associated with the excited electromagnetic field is calculated. It is found that the plasma response to the ion beam pulse is significantly different depending on whether the value of the solenoidal magnetic field is below or above the threshold value specified by ω _ce ^cr =2 Β_b ω_pe, and corresponding to the resonant excitation of large-amplitude whistler waves. The use of intense whistler wave excitations for diagnostic purposes is also discussed.