Figure 1: Experimental setup.
From: Generation of neutral and high-density electron–positron pair plasmas in the laboratory
(a) The laser wakefield-accelerated electrons (green spheres) impact onto a solid target, initiating a quantum electrodynamic cascade involving electrons, positrons (red spheres) and photons (blue sinusoids). The escaping electrons and positrons are separated and spectrally resolved using a magnetic spectrometer (details in the text) and a pair of LANEX screens. Plastic and lead shielding was inserted to reduce the noise on the LANEX screens as induced by both the low-energy electrons and gamma-rays generated, at wide angles, during the laser–gas and electron–solid target interactions. (b) Typical measured spectra of the electron beam without the solid target. Dashed green lines depict single-shot electron spectra, whereas the solid brown line is an average over five consecutive shots. (c) Typical positron signal, as recorded by the LANEX screen, for 0.5 cm of Pb. The image is to scale. The white dashed lines depict the projection of the magnet gap, whereas the grey dashed lines depict the position of 0.2, 0.5 and 1 GeV positrons on the LANEX screen.
