Self-consistent PIC simulations of ultimate space charge compensation with electron lenses

Abstract

Further progress of fundamental particle physics requires high intensity and high brightness of accelerated proton and ion beams. This goal is essential for the FAIR hadron beams at GSI, for the neutrino production at the facilities such as Fermilab and JPARC, and for the Large Hadron Collider luminosity at CERN. One of the most formidable obstacles toward that goal is the beam's own space charge, whose forces cause beam emittance growth, losses and lifetime degradation. Typically, such effects become intolerable when the space charge tune-shift parameter Δ QSC exceeds ∼ - (0.25–0.5). To reduce these detrimental effects, it was suggested to use electron lenses to compensate the space charge forces. This paper reports on detailed particle-in-cell space charge and electron lens compensation simulations for extremely intense proton bunches whose space charge tune-shift parameter exceeds -1.0. Different scenarios were evaluated based on reduction in the emittance growth and particle loss at a 4σ aperture. We investigate phenomena and issues related to the focusing lattice errors, importance of the transverse and longitudinal matching of the electron beam profiles to the proton ones, and vary the strength and the number of the electron lenses distributed around a circular machine to optimize the reduction of harmful space charge effects.

Progress in space charge compensation using electron columns

“…In this regime, the measured beam potential was 10-30 V, compared to the 200 V measured without residual gas injection. The achieved number of stored protons ranged from 0.75×10 12 to 1.25×10 12 , depending on gas species, almost an order of magnitude increase from the uncompensated case. When an accelerating voltage was applied to the beam to compensate energy loss, the lifetime and number of stored protons increased.…”

“…For more information on ELs for SCC, see also refs. [11,12]. Although SCC using an EC has not been fully implemented in circular machines, there have been several experimental and computational efforts to study SCC in a ring, showing promising results.…”

Beam physics research with the IOTA electron lens

“…Space-charge neutralization and compensation are routinely used in one-pass systems, such as beam lines for low-energy beam transport (LEBT) and rf photoinjectors. In rings, SCC with electrons offers several advantages [32] and could enable higher intensities and brightnesses by reducing losses and emittance growth [51,[53][54][55][56][57][58][59][60]. Proof-of-principle experiments are needed to understand the limits of the method and to explore the stability of the system.…”

“…To reduce these detrimental effects, it was suggested to use electron lenses to compensate the space-charge forces [53]. Further analysis and computer modeling [51,54,[58][59][60] indicated that compensation with electron lenses may enable an accelerator to exceed the space-charge limit and to operate with much larger tune-shift parameters, up to −1.0. The SCC e-lens should have a transverse currentdensity profile close to that of the proton beam.…”

“…For instance, the optimal degree of compensation 𝜂, predicted to be less than 1, needs to be determined experimentally. Studies showed that the longitudinal profile of the electron current pulse is also critical [51,57,59,60]. One of the challenges lies in the generation of fast electron pulses that match the short bunches in a storage ring.…”