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Schematic of the experimental arrangement showing the plasma mirror geometry and proton diagnostics. The spatial profile monitor only sampled the lower portion of the beam, enabling the magnetic spectrometers situated in the horizontal plane to be operated simultaneously. The inset shows the spatial profile data from a foil shot, corresponding to the star in Fig. 2. A filter mask consisting of strips of Al foil with different thicknesses, each stopping protons below a threshold energy, gives a staircase energy response in the vertical direction for the spatial profile.
Maximum proton energies obtained as a function of Al target thickness for on-target contrasts of (crosses). The solid line is a trend line fitted to the on-axis average for each thickness (circles). The 14° average data are represented by the triangles and the dotted trend line. The dashed line represents the detection limit. The inset shows typical proton spectra for the shot represented by the star symbol.
The effective temperature (a) and energy conversion efficiency to protons with (b) of the proton distribution as a function of target thickness. Both curves show maxima for targets of thickness.
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