Near-Ideal Dechirper for Plasma-Based Electron and Positron Acceleration Using a Hollow Channel Plasma

Abstract

Plasma-based electron and positron wakefield acceleration has made great strides in the past decade. However one major challenge for its applications to coherent light sources and colliders is the relatively large energy spread of the accelerated beams, currently at a few percent level. This energy spread is usually correlated with particle position in the beam arising from the longitudinal chirp of the wakefield amplitude. Therefore a dechirper is highly desirable for reducing this spread down to ∼ 0.1% level, while at the same time for maintaining the emittance of the accelerated beam. Here we propose that a low-density hollow channel plasma can act as a near-ideal dechirper for both electrons and positrons. We demonstrate the concept through large-scale three-dimensional particle-in-cell simulations.We show that the initial positive correlated energy spread (chirp) on the beam exiting a plasma accelerator can be compensated by the nearly linear self-wake induced by the beam in the hollow channel from few percent level down to ≤ 0.1%. Meanwhile, the beam emittance can be preserved due to the negligible transverse field inside the channel. This passive method may significantly improve the beam quality of plasma-based accelerators, paving the way for their applications to future compact free electron lasers and colliders.A plasma wake driven by an intense laser pulse or a charged particle beam can be utilized to accelerate electrons and positrons at extremely large accelerating fields of ≥ 100 GV/m, which are orders of magnitude larger than those in state-of-the-art radio-frequency microwave based accelerators [1,2]. In the past decade, plasma-based wakefield acceleration has achieved many significant milestones, such as multi-GeV electron acceleration in laser driven wakes [3][4][5][6][7][8][9][10], and high-energy, high-efficiency electron/positron acceleration in beam driven wakes [11][12][13][14]. However, for the beams produced by plasma accelerators to be useable for critical applications like X-ray free electron lasers (X-FELs) and linear colliders, many challenges still remain. One of these is the relatively large energy spread of the accelerated electron/positron beams produced by plasma arXiv:1805.07031v2 [physics.acc-ph]

Determining the duration of an ultra-intense laser pulse directly in its focus

“…We show how an ultra-intense laser’s pulse duration can in principle be measured directly in its focus at ultra-high field strengths, providing an order-of-magnitude benchmark for conventional indirect pulse metrology. Its basic working principle is to imprint a temporal structure onto the electron bunch to be scattered from the ultra-intense laser pulse, in the form of an energy chirp as are common in laser-accelerated electron bunches and need to be mitigated with great effort 46,47 . Keeping the electron bunch chirped, the particles’ changing energy will lead to a temporal evolution of the angular range into which the electrons emit radiation.…”

Features and futures of X-ray free-electron lasers

“…The first is to utilize a tenuous uniform or hollow channel plasma de-chirper to reduce the beam energy spread. 166 , 167 , 168 This works because, in PBAs, the energy chirp induced by the acceleration phase variance is the dominant part of the total energy spread. The second works on the basis that, because the PBA generated electron beam has a very small emittance, its entire phase space brightness is sufficiently high to drive the XFEL.…”

High efficiency uniform positron beam loading in a hollow channel plasma wakefield accelerator

“…4e plots the spectrum of the energy gain of the e + beam, where the induced rms energy spread can be measured as 0.29%, 0.42% and 0.55% for I 1 = 0.2kA, 1kA, 5kA respectively. Since E z is uniform in the transverse dimension, the induced slice energy spread for all cases is less than 0.1%, allowing the next step manipulation of the phase space such as energy dechirper to further reduce the total energy spread [29,30]. Energy transfer efficiency, i.e., the ratio between energy loss of the electron beam and energy gain of the positron beam, for the 3 cases is 95.7%, 81.5% and 46.3% for I 1 = 0.2kA, 1kA, 5kA respectively.…”