Advanced schemes for underdense plasma photocathode wakefield accelerators: pathways towards ultrahigh brightness electron beams

Abstract

The 'Trojan Horse' underdense plasma photocathode scheme applied to electron beam-driven plasma wakefield acceleration has opened up a path which promises high controllability and tunability and to reach extremely good quality as regards emittance and five-dimensional beam brightness. This combination has the potential to improve the state-of-the-art in accelerator technology significantly. In this paper, we review the basic concepts of the Trojan Horse scheme and present advanced methods for tailoring both the injector laser pulses and the witness electron bunches and combine them with the Trojan Horse scheme. These new approaches will further enhance the beam qualities, such as transverse emittance and longitudinal energy spread, and may allow, for the first time, to produce ultrahigh six-dimensional brightness electron bunches, which is a necessary requirement for driving advanced radiation sources. This article is part of the Theo Murphy meeting issue 'Directions in particle beam-driven plasma wakefield acceleration'.

Keywords: energy spread compensation; plasma wakefield acceleration; simultaneous spatial and temporal focusing; underdense plasma photocathode.

Figure 1.

(a) Suggested set-up for the SSTF-TH scheme. A spatially chirped laser photocathode is focused at the location of the plasma blowout using an off-axis parabolic mirror. (b) Normalized pulse duration τ/τ₀, (c) the axial peak intensity I/I₀ and (d) transverse beam size w/w₀ of an SSTF pulse as a function of axial position z/z_R for different values of β_BA. The parameters are normalized to its corresponding non-spatially chirped pulse with axial Gaussian profile.

Figure 2.

Field propagation of an SSTF pulse with beams aspect ratio of 4. Fields are normalized to 1.

Figure 3.

Snapshots from three-dimensional PIC simulation immediately after (a) He generation and (b) after approximately 1 mm of acceleration.

Figure 4.

Longitudinal phase space of the witness bunch during at the position of minimum energy spread from ref. [38].

Figure 5.

Effect of the first TH laser pulse offset to the plasma-based dechirping techniques. The initial position of TH laser is offset transversely with respect to the blowout axis. Here, the plasma wavelength is 100 µm, thereby the maximum blowout radius, R_b,max, is 40 µm.