• H. Qin, R. C. Davidson, E. Startsev
  PPPL, Princeton, New Jersey

In 3D high-intensity bunched beams, the collective effects associated with strong coupling between the longitudinal and transverse dynamics are of fundamental importance. A direct consequence of this coupling is that the particle dynamics does not conserve transverse energy and longitudinal energy separately, and there exists no exact kinetic equilibrium which has an anisotropic energy in the transverse and longitudinal directions. The strong coupling also introduces a mechanism for the electrostatic Harris-type instability driven by strong temperature anisotropy, which exists naturally in beams that have been accelerated to large velocities. The self-consistent Vlasov-Maxwell equations are applied to high-intensity bunched beams, and a generalized low-noise delta-f particle simulation algorithm is developed for bunched beams with or without energy anisotropy. Systematic studies are carried out that determine the particle dynamics, the approximate equilibrium, and stability properties under conditions corresponding to strong 3D nonlinear space-charge force. Finite bunch-length effects on collective excitations and anisotropy-driven instabilities are also investigated.

• R. C. Davidson, H. Qin, E. Startsev
  PPPL, Princeton, New Jersey

This paper makes use of a one-dimensional kinetic model based on the Vlasov-Maxwell equations to describe nonlinear wave and soliton excitations in coasting charged particle beams. The kinetic description makes use of the recently-developed g-factor model [1] that incorporates self-consistently the effects of transverse density profile shape at moderate beam intensities. The nonlinear evolution of wave and soliton excitations is examined for disturbances both moving faster and moving slower than the sound speed, incorporating the important effects of wave dispersion [2]. Analytical solutions are obtained for nonlinear traveling wave pulses with and without trapped particles, and the results of nonlinear perturabtive particle-in-cell simulations are presented that describe the stability properties and long-time evolution.

[1] R. C. Davidson and E. A. Startsev, Phys. Rev. ST Accel. Beams 7, 024401 (2004).[2] R. C. Davidson, Phys. Rev. ST Accel. Beams 7, 054402 (2004).

• E. Startsev, R. C. Davidson, H. Qin
  PPPL, Princeton, New Jersey

A numerical scheme for the electromagnetic particle simulation of high-intensity charged-particle beams has been developed which is a modification of the Darwin model. The Darwin model neglects the transverse induction current in Ampere?s law and therefore eliminates fast electromagnetic (light) waves from the simulations. The model has been incorporated into the nonlinear delta-f Beam Equilibrium Stability and Transport(BEST) code. As a benchmark, we have applied the model to simulate the transverse electromagnetic Weibel-type instability in a single-species charged-particle beam with large temperature anisotropy. Results are compared with previous theoretical and numerical studies using the eighenmode code bEASt. The nonlinear stage of the Weibel instability is also studied using BEST code, and the mechanism for nonlinear saturation is identified.