Emittance preservation in plasma-based accelerators with ion motion

Abstract

In a plasma-accelerator-based linear collider, the density of matched, low-emittance, high-energy particle bunches required for collider applications can be orders of magnitude above the background ion density, leading to ion motion, perturbation of the focusing fields, and, hence, to beam emittance growth. By analyzing the response of the background ions to an ultrahigh density beam, analytical expressions, valid for nonrelativistic ion motion, are derived for the transverse wakefield and for the final (i.e., after saturation) bunch emittance. Analytical results are validated against numerical modeling. Initial beam distributions are derived that are equilibrium solutions, which require head-to-tail bunch shaping, enabling emittance preservation with ion motion.

Positron transport and acceleration in beam-driven plasma wakefield accelerators using plasma columns

“…We consider an electron drive beam and a positron witness beam, both with Gaussian transverse profiles, propagating in a finite radius plasma, and demonstrate emittance preservation at the percent-level in a strongly loaded wakefield. Further optimization is possible, e.g., the emittance growth can be reduced by slice-by-slice matching of the witness beam to the focusing field [27], and, by proper shaping of drive and witness beams, the transformer ratio and thus efficiency can be increased [29,30]. The initial plasma profile may also be optimized.…”

“…Extension to a round beam is straightforward following the theory presented in Ref. [27]. Under these hypotheses the motion in the horizontal x-plane decouples from the vertical y-plane, and is completely determined once the horizontal component of the transverse wake is specified.…”

“…The emittance growth can be completely suppressed if, for each slice, the transverse phase-space distribution is chosen to be a Vlasov equilibrium for the steplike wakefield instead of a Gaussian distribution, as discussed in Ref. [27].…”

Emittance growth due to misalignment in multistage laser-plasma accelerators

“…The exact evolution of the beam properties depends on a large number of parameters. The beam emittance would, in particular, depend on the beam evolution between stages, e.g., the propagation distance in free space as well as potential focusing optics, which are neglected in the scope of this work, as well as ion motion [37,38], beam or laser hosing, and cavitation. Since emittance growth in the x and y directions is independent, as shown in Fig.…”

Overview of plasma lens experiments and recent results at SPARC_LAB

“…Multi-GeV acceleration, both laser and particle beam driven, has been already demonstrated in cm-scale plasma structures [1,2,3,4]. Great efforts are currently ongoing in several groups [5,6,7,8] worldwide for the acceleration of high brightness electron beams, which need to be captured and transported up to the final application. The aim is the preservation of the quality of the 6D phase space, which is demanding in particular for FEL experiments.…”