3D Simulation Studies of the Two-Stream Instability in Intense Particle Beams Based on the Vlasov-Maxwell Equations

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 newly developed 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 for a long coasting beam. Simulations in a parameter regime characteristic of the PSR experiment show that the e-p instability has a dipole-mode 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.