Abstract
Theoretical and numerical studies of the transport in vacuum of multi-nC, multi-MeV electron beams are performed using several methods, including envelope models, a novel semianalytic approach using ellipsoidal shell decomposition, a modified electrostatic particle-in-cell method, and a point-to-point interaction model. The effects of space-charge forces on the longitudinal and transverse bunch properties are evaluated for various bunch lengths, energies, energy spreads, and charges. An evaluation of the various methods for studying space-charge effects in large energy spread, high charge beams is summarized. Examples are given for beam distributions typical of those generated by plasma-based accelerators. It is found that, for the highly correlated beams produced in the self-modulated regime, the high energy portion of the beam can gain significant energy while propagating in vacuum due to space-charge effects.
Highlights
The propagation in vacuum of dense electron beams, typical of those produced by plasma-based accelerators, is examined
These methods will be further used for the simulation of vacuum transport of electron beams produced by plasma sources
In a laser wakefield accelerators (LWFAs), space-charge effects may not be of concern while the bunch is in the plasma wave, since the longitudinal and transverse fields of the wake are typically much greater than the space-charge forces of the bunch
Summary
The propagation in vacuum of dense electron beams, typical of those produced by plasma-based accelerators, is examined. The bunch typical transverse dimensions are 10 m, and the bunch half-length is 2:5 m, corresponding to a number density of 2:5 1017 cm3 This is 2 orders of magnitude smaller than in the selfmodulated regime, but the longitudinal quality of the beam is much better because of the small relative energy spread. Several algorithms for computing space-charge forces have been proposed and intensively used over the past years to model electron beam dynamics in linacs and storage rings [6 –8] Such methods generally assume that the electron beam has a small energy spread. Appendices are included to discuss further aspects of these topics
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