Compact Multistage Plasma-Based Accelerator Design for Correlated Energy Spread Compensation

The extreme electromagnetic fields sustained by plasma-based accelerators could drastically reduce the size and cost of future accelerator facilities. However, they are also an inherent source of correlated energy spread in the produced beams, which severely limits the usability of these devices. We propose here to split the acceleration process into two plasma stages joined by a magnetic chicane in which the energy correlation induced in the first stage is inverted such that it can be naturally compensated in the second. Simulations of a particular 1.5-m-long setup show that 5.5 GeV beams with relative energy spreads of $1.2\times {10}^{-3}$ (total) and $2.8\times {10}^{-4}$ (slice) could be achieved while preserving a submicron emittance. This is at least one order of magnitude below the current state of the art and would enable applications such as compact free-electron lasers.

Figure 1

Schematic view of a possible implementation of the energy chirp compensation concept.

Figure 2

Working principle of a magnetic chicane with $R_{56}=2/\chi$. The bunch longitudinal phase space is shown at the chicane (a) entrance, (b) middle, and (c) exit. Darker color implies higher energy.

Figure 3

Evolution of beam parameters along the accelerator: (a) beta function, (b) normalized emittance, (c) energy spread, and (d) energy. Transverse parameters are shown for the $y$ plane, which is not affected by dispersion in the chicane. Final values in $x$ and $y$ planes are virtually identical (difference of $\ll 1\%$). Slice parameters grow in the chicane center due to shorter bunch duration because the slice length ($0.1\mu \mathrm{m}$) is kept constant.

Figure 4

Comparison of the final bunch properties with respect to a case with acceleration in a single LWFA (same driver and plasma profile but $\sim 20\mathrm{cm}$ long): (a) bunch current, (b) longitudinal phase space, and (c) energy profile normalized to the peak number of counts $N$. The energy spread evolution during acceleration can be seen in (d).