Charge and current neutralization in the formation of ion rings in a background plasma

For typical field-reversed ion ring experiments, an intense ion beam is injected across a plasma-filled magnetic cusp and propagated into a solenoidal field downstream. During the initial phases of injection the characteristic time τ satisfies 2π/Ωe ≪ τ ≤ 2π/Ωi and the background plasma can be modeled as an electron magnetohydrodynamic (EMHD) fluid. In the nearly collision less regime, such that νe ≢ Ωe, the plasma response is governed by the whistler mode. It is found that for close enough conducting walls, such that the whistler transit time to the wall is short compared to the beam transit time, effective control of the return currents can be established such that current neutralization can be suppressed while maintaining good charge neutralization.