2D-VPIC simulation results (1 μm average over z) of a 58 nm diamond target with 5% protons at t = 759.2 fs when peak target density has classical critical density: (a) electric field Ex ; (c) absolute value of charge density of electrons (ne, black), C6+ ions (nC, red), and proton (nP, blue); (b) and (d) kinetic energy distribution of C6+ ions ( ) and protons ( ); (e) and (f) momentum phase space of C6+ ions ( ) and protons ( ). See text for details.
Carbon C6+ spectra from 2D-VPIC simulation shown in Fig. 1 from a 58 nm diamond target mixed with 5% protons in number density (blue solid line) and a pure diamond target shown in Fig. 3 (red solid line); 1 μm average over z along the laser axis. Maximum carbon energies are 600 MeV and 1 Gev, respectively.
2D-VPIC simulation, same conditions as for simulation shown in Fig. 1 , but using a diamond target without protons (box length of 50 μm, t = 759.2 fs at end of acceleration when peak target density has classical critical density, 1 μm average over z): (a) electric field Ex ; (b) x-component of C6+ momentum phase space; (c) C6+ kinetic energy (black:1 μm average, red: entire z-domain).
2D-VPIC simulation, same conditions as for simulation shown in Fig. 3 , but using a box length of 75 μm. Plots are at t = 759.2 fs, the end of acceleration when peak target density has classical critical density and from a 1 μm average over z: (a) electric field Ex ; (b) x-component of C6+ momentum phase space; (c) C6+ kinetic energy (solid black:1 μm average, solid red: entire z-domain, dotted lines are results from Fig. 3 with a simulation box of 50 μm).
Raw IP data from the ion wide angle spectrometer for a heated (cleaned) diamond target (left) and an unheated diamond target (right), both with thickness 225 nm. The IP shows protons and ions with energy high enough to pass the filtering in front of the IP ( for H+ and for C6+). Energy increases from top to bottom, some energies are given as a guide for the eye; angle is from left to right; flux is color coded with blue = none to red = high. While the right image shows a strong proton distribution for the unheated target, the left image is devoid of any protons. In the lower portion of the image, a carbon distribution is visible for both targets; however, the one for the cleaned target extends to much higher energies. Note that the raw IP signal is a convolution of the IP response, the ion stopping power and the filtering; see Ref. 33 for a detailed explanation of the raw data.
Carbon C6+ spectra extracted from CR39 nuclear track detector in front of the IP in the ion wide angle spectrometer for an unheated 225 nm target (blue solid line) and a pre-heated 225 nm target (red solid line), i.e., without hydro-carbon surface contamination. The background for the heated spectrum is given by the grey solid line; the spectrum for the uncleaned target hast the background already subtracted. Maximum energies are (600± 32) MeV and (1050 ± 75) MeV, respectively. Error bars represent minimum instrument error. The spectrum is an average from 4° to 6° of the angularly resolved spectrum that covers −2° to 20° with respect to the laser propagation direction and orthogonal to the laser polarization plane.
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