Space charge modeling of dense electron beams with large energy spreads

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 spacecharge effects.

Design considerations for table-top, laser-based VUV and X-ray free electron lasers

“…We want to em-phasize here that studies of space-charge effects of such ultra-dense relativistic bunches can be simulated most accurately only with codes (such as GPT and CSRtrack [19]) which utilize point-to-point interactions (a result also found in Ref. [20]). In contrast, other codes merely based upon Poisson-solvers cannot cope with large relative particle motions within the bunch rest frame in case of large initial energy spreads and Coulomb explosioninduced motion.…”

MeV-Energy X Rays from Inverse Compton Scattering with Laser-Wakefield Accelerated Electrons

“…The source size of the e beam [2 m (rms)] was extrapolated from both the e-beam size measured at the Compton interaction point [6 m (rms)] and its average divergence angle (10 mrad), assuming the space-charge blowup is negligible for our e-beam charge density and average energy [27]. Using the inferred source size, and the measured divergence angle of 5 mrad (for the 250-MeVcomponent of the e beam), we estimate a normalized rms e-beam emittance (" N ¼ e-source 250 MeV ) of 1 mm-mrad at 250 MeV.…”

Control of Laser Plasma Based Accelerators up to 1 GeV

“…Although such a drastic modulation was observed from PIC simulations [195], no experimental evidence has been observed yet. Another possible explanation for smaller beam divergence with higher input intensity would be space charge effect of the injected electrons [109]. If space charge of the injected electron beam is stronger than the radial focusing force from the wakefield, Overall, the mean (maximum) output total energy U b was around 5 mJ (80 mJ), which was ∼ 0.3% (1.2%) of the input laser energy.…”

“…Although it was demonstrated that a SM-LWFA could provide sufficient charge to perform chemical studies, a femtosecond pump probe experiment was not realized, probably due to the broadband property and space charge effect in high charge e-beams [109]. E-beams from SM-LWFA contained a total charge of nC, and such a high charge e-beam would be stretched out longitudinally during propagation in addition to the velocity difference between low and high energy electrons.…”