Simulations of beam emittance growth from the collectiverelaxation of space-charge nonuniformities
Beams injected into a linear focusing channel typically have some degree of space-charge nonuniformity. For unbunched beams with high space-charge intensity propagating in linear focusing channels, Debye screening of self-field interactions tends to make the transverse density profile flat. An injected particle distribution with a large systematic charge nonuniformity will generally be far from an equilibrium of the focusing channel and the initial condition will launch a broad spectrum of collective modes. These modes can phase-mix and experience nonlinear interactions which result in an effective relaxation to a more thermal-equilibrium-like distribution characterized by a uniform density profile. This relaxation transfers self-field energy from the initial space-charge nonuniformity to the local particle temperature, thereby increasing beam phase space area (emittance growth). Here they employ two-dimensional electrostatic particle in cell (PIC) simulations to investigate the effects of initial transverse space-charge nonuniformities on the equality of beams with high space-charge intensity propagating in a continuous focusing channel. Results are compared to theoretical bounds of emittance growth developed in previous studies. Consistent with earlier theory, it is found that a high degree of initial distribution nonuniformity can be tolerated with only modest emittance growth and that beam control can be maintained. The simulations also provide information on the rate of relaxation and characteristic levels of fluctuations in the relaxed states. This research suggests that a surprising degree of initial space-charge nonuniformity can be tolerated in practical intense beam experiments.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Director. Office of Science. Office of Fusion EnergySciences. Contracts DE-AC03-76SF00098 and W-7405-ENG-48 andDE-ACO2-76-CHO-3073
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 861352
- Report Number(s):
- LBNL-55962; HIFAN 1358; R&D Project: Z41003; BnR: AT5015031; TRN: US200601%%834
- Resource Relation:
- Conference: 15th International Symposium on Heavy IonInertial Fusion, Princeton, NJ, June 7-11,2004
- Country of Publication:
- United States
- Language:
- English
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