(Color online) (a) The two-stage acceleration scheme. The initial density of the hydrogen foil is n 0/nc = 20, the thickness is d = 0.5λl , the density of the tenuous backside plasma is ne /nc = 0.01, its length is 12 000λl . (b) Sketch of the snowplow process, the dynamic density of the ions is ni and the electron density in the snowplow layer is n com. The position B indicates the laser pulse front and A is an arbitrary point in the snowplow region.
(Color online) (a) Electron density ne /nc , proton density np /nc , and the distance between the electron and PLs (see inset), and (b) longitudinal proton phase space px /mpc at t = 5.8Tl , where mp is proton mass. The longitudinal electrostatic field eEx /meωlc (dashed line) in the snowplow regime at (c) t = 5000Tl and (d) t = 12 000Tl . The initial plasma parameters are given in Fig. 1.
(Color online) Simulation results at t = 12 000Tl . (a) Proton phase space px /mpc versus x, and (b) energy spectrum of the trapped protons.
(Color online) (a) Distance between proton beam and the laser pulse front versus time for different gas densities, where stars, diamonds, crosses, and squares correspond to the gas densities 0.01nc , 0.025nc , 0.05nc , and 0.1nc , respectively, (b) longitudinal electrostatic field eEx /meωlc, (c) decoupling length, (d) maximum proton energy. Here the theoretical curves are given as solid lines and the simulation results are shown as stars, diamonds, crosses, and squares.
(Color online) 2D simulation results at t = 990Tl . (a) Electron density profile, (b) electrostatic field on the axis, (c) proton phase space, and (d) proton spectrum.
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