Improvement of proton acceleration via collisionless shock acceleration by laser-foil interaction with an external magnetic field

Abstract

Effects of the external intense axial magnetic field on collisionless shock acceleration (CSA) are investigated by using two-dimensional particle-in-cell simulations. Proton beams accelerated by CSA show different properties when left-hand circularly polarized (LHCP) or right-hand circularly polarized (RHCP) lasers are individually applied to a foil target with or without the magnetic field. It can be attributed to the difference of the dispersion relationship for the laser propagating in a plasma. Protons achieve more efficient acceleration when magnetized plasma is irradiated by the RHCP laser compared with the LHCP laser. Furthermore, the effect of different amplitudes of the magnetic field is studied numerically. It shows that the induced electrostatic charge-separation field arises deep in the target with huge strength of the magnetic field. Protons in the upstream are accelerated before the shock arrives, leading to less efficient acceleration. As a result, an appropriate magnetic field should be applied to enhance the CSA regime.