Figure 1

(a) Comparison of proton spectra from the heated (dotted line) and unheated Al targets (solid line). (b) Comparison of the ${\mathrm{\text{carbon}}}^{6+}$ spectrum from heated and unheated Al targets. A clear reduction in proton and carbon numbers is visible. Carbon energies are enhanced due to the reduction of protons. These spectra were measured at the front of the target along the surface normal using a Thomson parabola (collection angle $2\times {10}^{-8}\mathrm{s}\mathrm{r}$, $B=0.1\mathrm{T}$, $E=3.5\mathrm{k}\mathrm{V}/\mathrm{c}\mathrm{m}$, and a CR39 detector). The numbers on the abscissa assume isotropic emission. Details on the total number of protons ($\approx {10}^{12}>1\mathrm{M}\mathrm{e}\mathrm{V}$) and their distribution can be found in 5.Reuse & Permissions

Figure 2

(a)–(c) images from a detector stack showing the typical features observed for cold targets for $I={10}^{19}\mathrm{W}\mathrm{c}{\mathrm{m}}^{\mathrm{-}\mathrm{2}}$, $100\mu \mathrm{m}$ Al target. (a) Data taken using RCF film (proton energy $E\ge 3\mathrm{M}\mathrm{e}\mathrm{V}$. (b) CR39 data ($E=5\mathrm{M}\mathrm{e}\mathrm{V}$). (c) $E=12\mathrm{M}\mathrm{e}\mathrm{V}$ (CR39). Three spatially distinct contributions are indicated. (d),(e) Series of corresponding data taken from a heated Al target under otherwise identical conditions. (d) $E\ge 1\mathrm{M}\mathrm{e}\mathrm{V}$ (RCF); (e)$E=3\mathrm{M}\mathrm{e}\mathrm{V}$ (CR39); and (f) $E=6\mathrm{M}\mathrm{e}\mathrm{V}$ (CR39). The signal level is significantly reduced on the heated target and the rings visible in (b) have (almost) disappeared. The absence of the cross pattern is due to the significantly larger spatial extent of the heated target. Angles indicated in (b) are half angles and apply to (a)–(g). (g) shows the dose derived from (a); (h) shows an enlarged view of the central feature in (b). Heavy ion contamination can be ruled out due to the proton$/$carbon ratio (Fig. 1) and the low carbon energies from the rear surface [20].Reuse & Permissions

Figure 3

(a) shows a comparison of the angular divergence of ring structure and central feature. The error bars include the variation over multiple shots and the feature width for each shot. (b) shows a comparison of the radially integrated signal for different angles for the case with PEEK on the front and PEEK on the back.Reuse & Permissions

Figure 4

Comparison of data from heated target ($20\mu \mathrm{m}$ PEEK on $100\mu \mathrm{m}$ Al). The PEEK coating was on the front side in the first case (a)–(c), and on the back side of the target (d)–(f) in the second. Proton energies (a),(d) $\ge 1\mathrm{M}\mathrm{e}\mathrm{V}$ (RCF behind $25\mu \mathrm{m}$ Al filter); (b),(e) 3 MeV (CR39); (c),(f) 6 MeV (CR39). Angles indicated in (c) are half angles and apply to (a)–(f).Reuse & Permissions