Abstract
Positron trapping and acceleration in a plasma wake using a four-bunch scheme [X. Wang et al., Phys. Rev. Lett. 101, 124801 (2008)] is numerically investigated through 2D particle-in-cell simulations. This scheme that integrates positron generation, trapping, and acceleration into a single stage is a promising approach for investigating positron acceleration in an electron-beam-driven wake. It consists of a plasma with an embedded thin foil target into which two closely spaced electron beams are shot. The first beam creates a region for accelerating and focusing positrons and the second beam provides positrons to be accelerated. Some of the outstanding issues related to the quality of the accelerated positron beam load are discussed as a function of the beam and plasma parameters. Simulations show that a large number of positrons (10 7 ‐10 8 ) can be trapped when the plasma wake is modestly nonlinear, and the positrongenerating foil target must be immersed into the plasma. Beam loading can reduce the energy spread of the positron beam load. The quality of the positron beam load is not very sensitive to the exact bunch spacing between the drive electron bunch and the positron beam load.
Highlights
To realize a future plasma-based linear collider, high gradient and high quality acceleration of positron and electron bunches are important [1]
Wang et al [11] have recently proposed a new scheme to test the acceleration of a positron bunch in the plasma wake driven by an electron bunch before suitable electron/positron bunch trains become available from rf accelerators
We find that the beam loading of the wake can lead to a minimum energy spread for the positron beam load emerging from the plasma, albeit at a small expense to the acceleration gradient
Summary
To realize a future plasma-based linear collider, high gradient and high quality acceleration of positron and electron bunches are important [1]. Wang et al [11] have recently proposed a new scheme to test the acceleration of a positron bunch in the plasma wake driven by an electron bunch before suitable electron/positron bunch trains become available from rf accelerators This idea can be briefly described as follows (Fig. 1): two closely spaced but relativistic electron bunches are focused on a thin high-Z foil target placed at the entrance of plasma. The electron drive bunch and the positron beam load remain after a short propagation distance into the plasma In this way, the desirable configuration for accelerating and focusing a tightly focused positron beam load in the wake of an electron beam is established. We look at this scheme in a plasma field-ionized by the drive electron bunch, as opposed to a preionized plasma that was assumed for the previous study, and find that the continued acceleration of the positron bunch is limited by the beam head erosion of the drive electron bunch
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