Simulations and experiments with space-charge-dominated beams

Abstract

Beams in which space charge forces are stronger than the force from thermal pressure are nonneutral plasmas, since particles interact mostly via the long-range collective potential. An ever-increasing number of applications demand such high-brightness beams. The University of Maryland Electron Ring ͓P. G. O'Shea et al., Nucl. Instrum Methods Phys. Res. A 464, 646 ͑2001͔͒, currently under construction, is designed for studying the physics of space-charge-dominated beams. Indirect ways of measuring beam emittance near the UMER source produced conflicting results, which were resolved only when a direct measurement of phase space indicated a hollow velocity distribution. Comparison to self-consistent simulation using the particle-in-cell code WARP ͓D. P. Grote et al., 193 ͑1996͔͒ revealed sensitivity to the initial velocity distribution. Since the beam is born with nonuniformities and granularity, dissipation mechanisms and rates are of interest. Simulations found that phase mixing by means of chaotic particle orbits is possible in certain situations, and proceeds much faster than Landau damping. The implications for using beams to model other N-body systems are discussed.

Space charge effects in field emission: One dimensional theory

“…PIC is used to model the injection and acceleration of charge bunches especially when space charge complicates transport and causes emittance growth [19,[44][45][46][47][48]. Indeed, the needs of PIC codes suggest using the PCM approach to develop the "cathode" boundary of the PIC simulation.…”

Simulations of beam envelope dynamics in circular accelerators

“…COSY INFINITY has also been proposed to expand its code to deal with space charge force [10,11]. A few systematic emittance evolution experiments were done in LINACs [12], and fewer in circular accelerators [4,13]. Systematic measurements and analysis of the emittance evolution with different injection turns at the Fermilab Booster, see e.g., Fig.…”

Tomography as a diagnostic tool for phase space mapping of intense particle beams

“…Such a distribution has been experimentally observed in UMER [18]. In order to model such a beam profile, we rotate a Gaussian distribution with width th and offset from the origin around a circle of radius [18]. The parameters th and are obtained empirically such that rms size and emittance of the hollow distribution are the same as the semi-Gaussian distribution in the previous section.…”

“…Therefore, instead of using a S-G we model our tomography process for beams starting with a hollow velocity distribution. Such a distribution has been experimentally observed in UMER [18]. In order to model such a beam profile, we rotate a Gaussian distribution with width th and offset from the origin around a circle of radius [18].…”

“…We simulated the above experimental setup with the particle-in-cell code WARP [16], developed at the Lawrence Livermore National Laboratory. The advantage of WARP is that it self-consistently includes space charge effects and has been successfully benchmarked against UMER experimental data [18]. For each quadrupole current setting, we run a WARP simulation, collect a snapshot of the beam density in configuration space at the phosphor screen location, and then process it to look like a phosphor screen image.…”