Fig. 1.

Experimental configuration. The main target (see photo in a) consists of two CH foils doped with 6% chlorine in atomic number (b) that are separated by 8 mm. Each foil is illuminated by ten 500 J, 1 ns pulse length, frequency tripled (351 nm wavelength) laser beams with 800 μm spot diameter. The beams are stacked in time to achieve the two pulse profiles shown in c. An additional set of 17 beams, all fired simultaneously, are used to implode a 420 μm diameter capsule consisting of a 2-μm-thick SiO₂ shell filled with D₂ gas at 6 atm and ³He at 12 atm. The implosion produces mono-energetic protons at 3.3 and 15 MeV with ~40 μm diameter source size, which traverse the plasma and are then collected by a CR-39 nuclear track detector with a total magnification factor of 28. The plasma expansion towards the center of the target is perturbed by the presence of two grids, placed 4 mm apart, with a 300 μm hole width and 300 μm hole spacing. Grid A has the central hole aligned on the center axis connecting the two foils, while grid B has the hole pattern shifted so that the central axis crosses the middle point between two holes. Thomson scattering uses a 30 J, 1 ns, frequency doubled (wavelength λ = 526.5 nm) laser beam to probe the plasma on the axis of the flow, 400 μm from the center and in a 50 μm focal spot, towards grid B. The scattered light is collected with 63° scattering angle and the geometry is such that the scattering wavenumber k = k_scatter−k_probe, where $∣k_{\mathrm{scatter}}∣\approx ∣k_{\mathrm{probe}}∣=2\pi \mathrm{∕}\lambda$, is parallel to the axis of the flow