Transport of intense beam pulses through background plasma

Summary form only given.This paper presents a survey of the present numerical modeling techniques and theoretical understanding of plasma neutralization of intense particle beams. Several particle-in- cell (PIC) codes have been used for modeling of beam propagation in a background plasma. Numerous issues in using PIC codes for simulation of beam-plasma interaction will be reviewed. Investigations of intense beam pulse interaction with a background plasma have identified the operating regimes for stable and neutralized propagation of intense charged particle beams. The proposed theoretical models can predict self-electric and magnetic field of the beam propagating in the target plasma in wide range of parameters. For IFE it is critical to develop a basic understanding of the conditions for quiescent beam propagation over large distances, controlling pinching and filamentation effects, and minimizing the degradation of beam quality due to instabilities and particle loss. We previously developed a reduced analytical model of beam charge and current neutralization for an ion beam pulse propagating in a cold background plasma. The model made use of the conservation of generalized fluid vorticity. The predictions of the analytical model agree very well with numerical simulation results. The model predicts very good charge neutralization during quasi-steady-state propagation, provided the beam pulse duration is much longer than the electron plasma period. In the opposite limit, the beam pulse excites large-amplitude plasma waves. If the beam density is larger than the background plasma density, the plasma waves break, which leads to electron heating. The reduced-fluid description provides an important benchmark for numerical codes and yields useful scaling relations for different beam and plasma parameters. This model has been extended to include the additional effects of a solenoidal magnetic field, gas ionization and the transition regions during beam pulse entry and exi- - t from the plasma. Analytical studies show that a sufficiently large solenoidal magnetic field can increase the degree of current neutralization of the ion beam pulse. However, simulations also show that the self-magnetic field structure of the ion beam pulse propagating through background plasma can be complex and non-stationary. Plasma waves generated by the beam head are greatly modified, and whistler waves propagating ahead of the beam pulse are excited during beam entry into the plasma. Accounting for plasma production by gas ionization yields a larger self-magnetic field of the ion beam compared to the case without ionization, and a wake of the current density and self-magnetic field are generated behind the beam pulse. Beam propagation in a dipole magnetic field configuration and background plasma has also been studied.