Fig. 1. (a) Schematic of the generation of collimated GeV positron jets by the interaction of two 10 PW laser pulses with a plasma channel filled with NCD plasma. The drive pulse (laser #1) and probe pulse (laser #2) are incident from the left and right sides, respectively. Two cases are considered: (b) a plasma channel with a radially symmetric density profile and (c) a uniform plasma slab.

Fig. 2. (a) Energy spectra of electrons at t=58T0. (b) Transverse electric fields along the laser propagation axis. The insets in (a) and (b) show the distributions of the trapped electron energy density and laser transverse electric field, respectively, in the case of a plasma channel (top) and a uniform plasma slab (bottom). (c) and (d) show the distributions of the parameter η along the x axis in the case of a plasma channel and a uniform plasma slab, respectively.

Fig. 3. (a) Energy spectra of γ rays at t=68T0. The insets show the energy density distribution of the γ-ray emission with a plasma channel (top) and a uniform plasma slab (bottom). (b) and (c) show the angular energy distributions of the emitted γ rays in the plasma channel and uniform plasma, respectively.

Fig. 4. (a) Energy spectra of positrons from a plasma channel (red curve) and a uniform plasma slab (black curve), where the inset shows the positron angular divergence. (b) Evolution of total yield and energy of positrons with the interaction time, where the solid curves are for a plasma channel and the dashed curves are for a uniform plasma slab. (c) and (d) show the energy density distributions of positrons generated from a plasma channel and from a uniform plasma slab, respectively. The insets present the density profiles of positrons in the x–y cross section.

Fig. 5. Yield Ne+, energy conversion efficiency ρe+, and cutoff energy Ee+ of positrons as functions of (a) laser amplitude a0 and (b) plasma channel length L.