Proton acceleration in a laser-induced relativistic electron vortex

Abstract

We show that when a solid plasma foil with a density gradient on the front surface is irradiated by an intense laser pulse at a grazing angle, ${\sim}80^{\circ }$ , a relativistic electron vortex is excited in the near-critical-density layer after the laser pulse depletion. The vortex structure and dynamics are studied using particle-in-cell simulations. Due to the asymmetry introduced by non-uniform background density, the vortex drifts at a constant velocity, typically $0.2{-}0.3$ times the speed of light. The strong magnetic field inside the vortex leads to significant charge separation; in the corresponding electric field initially stationary protons can be captured and accelerated to twice the velocity of the vortex (100–200 MeV). A representative scenario – with laser intensity of $10^{21}~\text{W}~\text{cm}^{-2}$ – is discussed: two-dimensional simulations suggest that a quasi-monoenergetic proton beam can be obtained with a mean energy 140 MeV and an energy spread of ${\sim}10\,\%$ . We derive an analytical estimate for the vortex velocity in terms of laser and plasma parameters, demonstrating that the maximum proton energy can be controlled by the incidence angle of the laser and the plasma density gradient.

On annihilation of the relativistic electron vortex pair in collisionless plasmas

“…This mechanism is similar to the so-called magnetic vortex acceleration (MVA) (Fukuda et al 2009;Bulanov et al 2010;Nakamura et al 2010). An alternative mechanism of ion acceleration from relativistic electron vortex pairs was recently considered in Yi et al (2018). The simulation set-up used in the problem, such as a plasma density gradient, is implemented in order to consider the adiabatic switching on of the vortex interaction effects.…”

Dynamics of moving electron vortices and magnetic ring in laser plasma interaction

“…al. when they studied the ion acceleration driven by a moving electron vortex 21 with much higher laser intensity and different laser incidence direction. In our case the laser intensity is orders of magnitude smaller and there is no efficient ion acceleration observed in front of the vortex.…”

“…Along with the recent rapid development of intense laser technology 1,2 , such kind of structures can be generated and studied in detail in intense laser plasma interactions. Among them electron vortices formed in relativistic laser plasmas have recently aroused broad interests [3][4][5][6][7][8] due to their wide presence in nature and potential applications in the laser electron and ion acceleration [9][10][11][12][13][14][15][16][17][18][19][20][21] , as well as extremely strong magnetic field generation 22,23 . Compared with normal target sheath field in laser solid interaction, in addition to ion acceleration, the vortex field can also be used to collimate the accelerated ions 11 , and gena) minchen@sjtu.edu.cn b) Sergei.Bulanov@eli-beams.eu erate quasi-monoenergetic protons with energy of hundreds of MeV 21 .…”

Electrostatic shock waves driven by electron vortices in laser–plasma interactions

“…The fields can be used for ion acceleration. Quasimonoenergetic ion beams accelerated directly by a moving electron vortex (EV) along its propagation direction have also been found in some numerical simulations recently [30].…”