Polarized Laser-WakeField-Accelerated Kiloampere Electron Beams

Abstract

High-flux polarized particle beams are of critical importance for the investigation of spin-dependent processes, such as in searches of physics beyond the Standard Model, as well as for scrutinizing the structure of solids and surfaces in material science. Here we demonstrate that kiloampere polarized electron beams can be produced via laser-wakefield acceleration from a gas target. A simple theoretical model for determining the electron beam polarization is presented and supported with self-consistent three-dimensional particle-in-cell simulations that incorporate the spin dynamics. By appropriately choosing the laser and gas parameters, we show that the depolarization of electrons induced by the laser-wakefield-acceleration process can be as low as 10%. Compared to currently available sources of polarized electron beams, the flux is increased by four orders of magnitude.

Polarized electron-beam acceleration driven by vortex laser pulses

“…injection time for Δt∼π|r i −r 0 |/〈β x 〉∼4π|r i −r 0 |/c LG case and Δt∼2πr i /c Gaussian case, which is close to previous studies where considering trapped electrons as a whole with Δt≈4a 1/2 λ p /πc [30,53,54]. Assuming the injection density is homogenous among whole injection region, the whole polarization after injection is given as:…”

“…As shown below, spin depolarization mainly happens in the injection phase, which is in line with previous studies [29]. Recently, a method is proposed to mitigate this issue by fine tuning the focal position of the Gaussian laser beam to weaken the electron injection [30]. Here we propose that compared to Gaussian lasers, vortex laser beams are capable of creating a unique topology in LWFA that significantly suppresses the beam depolarization without sacrifice of the injected electron charge.…”

“…The vortex beam produces a donut-shaped electron bunch in the vicinity of r 0 ±!r/2, as compared to a cylinder-like beam of radius !r for the Gaussian driver, corresponding to a cross-section area of 2πr 0 !r and π!r 2 , respectively. For a simple estimation, we use !r∼a 1/2 λ p (x p )/π∼4 μm [30,[48][49][50] as the bunch radius of the trapped electrons and r 0 =w 0 / 2 ≈7 μm as the center of the trapped region for the LG case [48,49]. Accordingly, the peak-current ratio between the LG and the Gaussian case is about 2r 0 /!r∼3.5, a factor that is well reproduced in simulations.…”

“…similar to the one used in [30], for better comparison. Here Θ(x) is the step function, ξ=x−x 0 , x 0 =20 μm, L=16 μm, ratio between the peak density of the ramp and the background density κ=n p /n 0 =4, n p is the peak density while n 0 =10 18 cm −3 is the background density, respectively.…”

Spin Filter for Polarized Electron Acceleration in Plasma Wakefields

“…Such field distributions are also seen in our simulations ( Fig.1 (a)). As already stated in previous works [27][28][29]45], the spin is preserved during steady acceleration but precesses dramatically during the injection phase. That is why we focus on the spin dynamics during injection, where typically one has γ<<1/a e [42,46] and the second term of Eq.…”