Delta-f Simulations of Electron-ion Two-stream Instability

Two-stream instabilities in intense charged particle beams, described self-consistently by the nonlinear Vlasov-Maxwell equations, are studied using a 3D multispecies perturbative particle simulation method. The beam equilibrium, stability, and transport (BEST) code is used to simulate the linear and nonlinear properties of the electron-proton (e-p) two-stream instability observed in the Proton Storage Ring (PSR) experiment as well as the electron-ion two-stream instability in the high intensity ion beams for heavy ion fusion drivers. Simulations show that the electron-ion instability has a typical dipole-mode * [email protected] structure, and that the instability threshold descreases with increasing fractional neutralization, and increases with increasing axial momentum spread of the beam particles. In the nonlinear phase, the simulations show that the instability first saturates at a relatively low level, and subsequently grows to a higher level. The nonlinear space-charge-induced transverse tune spread, which introduces a major growth-rate reduction effect on the instability, is studied for the self-consistent equilibrium populations of ions and electrons. Initial results on the two-stream instability for bunched beams and the interaction between the instability and the secondary electron yield will also be discussed.