Generating high-current monoenergetic proton beams by a circularly polarized laser pulse in the phase-stable acceleration regime

A new ion acceleration method, namely, phase-stable acceleration, usingcircularly-polarized laser pulses is proposed. When the initial target density n0 and thickness D satisfy aL∼(n0/nc)D/λL and D>ls with aL, λL, ls, and nc the normalized laser amplitude, the laser wavelength invacuum, the plasma skin depth, and the critical density of the incident laserpulse, respectively, a quasiequilibrium for the electrons is established bythe light pressure and the space charge electrostatic field at the interactingfront of the laser pulse. The ions within the skin depth of the laser pulseare synchronously accelerated and bunched by the electrostatic field, andthereby a high-intensity monoenergetic proton beam can be generated. The protondynamics is investigated analytically and the results are verified by one-and two-dimensional particle-in-cell simulations.