Spin Filter for Polarized Electron Acceleration in Plasma Wakefields

Abstract

We propose a filter method to generate electron beams of high polarization from bubble and blow-out wakefield accelerators. The mechanism is based on the idea to identify all electron-beam subsets with low-polarization and to filter them out by an X-shaped slit placed right behind the plasma accelerator.To find these subsets we investigate the dependence between the initial azimuthal angle and the spin of single electrons during the trapping process. This dependence shows that transverse electron spins preserve their orientation during injection if they are initially aligned parallel or anti-parallel to the local magnetic field. We derive a precise correlation of the local beam polarization as a function of the coordinate and the electron phase angle. Three-dimensional particle-in-cell simulations, incorporating classical spin dynamics, show that the beam polarization can be increased from 35% to about 80% after spin filtering. The injected flux is strongly restricted to preserve the beam polarization, e.g. <1kA in Ref.[27]. This limitation is removed by employing the proposed filter mechanism. The robust of the method is discussed that contains drive beam fluctuations, jitters, the thickness of the filter and initial temperature.This idea marks an efficient and simple strategy to generate energetic polarized electron beams based on wakefield acceleration.

Geometric particle-in-cell methods for the Vlasov–Maxwell equations with spin effects

“…Metallic and magnetic nano-objects have many potential technological applications, which include to biology and medicine where they can be used to absorb electromagnetic energy and release it as heat to destroy cancer cells (hyperthermia) (Mehdaoui et al 2013). In plasma physics, polarized electron beams of high spin polarization can now be created and precisely manipulated in the laboratory (Wu et al 2019(Wu et al , 2020Nie et al 2021). Recently, numerical simulations of spin-polarized electron beams interacting with strong laser pulses were performed by Wen, Keitel & Bauke (2017); Wen, Tamburini & Keitel (2019).…”

Generation of polarized particle beams at relativistic laser intensities

“…Wu et al [49] find that beam polarization depends on the azimuthal angle in a plasma wakefield due to the symmetric bubble field; see Figure 13. Accordingly, an X-shaped slit (spin filter) is proposed to significantly enhance beam polarization of the accelerated electrons.…”

“…These processes can be modeled with the help of full three-dimensional particle-in-cell (PIC) simulations, incorporating the spin dynamics via the Thomas-Bargmann Michel Telegdi (T-BMT) equation (see Equation (2) below) [47,48] . A couple of such codes have been developed recently, and used for the modeling of polarized electron [45,46,49,50] and proton [51][52][53][54] beam generation.…”

“…(3) The first applications of pre-polarized targets employed by Wen et al [45] and Wu et al [46,49,50] were actually aiming at the laser-induced acceleration of proton beams [51][52][53][54] . This is because protons have much smaller magnetic moments and, therefore, their spin alignment in the plasma magnetic fields is much more inert as compared to electrons.…”

“…Figure 13. Electron polarization distributions in the transverse phase space during laser-wakefield acceleration [49] .…”