CURRENT NEUTRALIZATION AND FOCUSING OF INTENSE ION-BEAMS WITH A PLASMA-FILLED SOLENOIDAL LENS .1.

The response of the magnetized plasma in an axisymmetric, plasma-fille d, solenoidal magnetic lens, to intense light ion beam injection is st udied. The lens plasma fill is modeled as an inertialess, resistive, e lectron magnetohydrodynamic (EMHD) fluid since characteristic beam tim es tau satisfy 2 pi/omega(pe), 2 pi/Omega(i) much less than tau less t han or equal to 2 pi/Omega(i) (omega(pe) is the electron plasma freque ncy and Omega(e,i) are the electron, ion gyrofrequencies). When the el ectron collisionality satisfies nu(e) much less than Omega(e), the lin ear plasma response is determined by whistler wave dynamics. In this c ase, current neutralization of the beam is reduced on the time scale f or whistler wave transit across the beam. The transit time is inversel y proportional to the electron density and proportional to the angle o f incidence of the beam with respect to the applied solenoidal field. In the collisional regime (nu(e) > Omega(e)) the plasma return current s decay on the normal diffusive time scale determined by the conductiv ity. The analysis is supported by two-and-one-half dimensional hybrid particle-in-cell simulations. (C) 1996 American Institute of Physics.