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Comparative spectra and efficiencies of ions laser-accelerated forward from the front and rear surfaces of thin solid foils
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10.1063/1.2720373
/content/aip/journal/pop/14/5/10.1063/1.2720373
http://aip.metastore.ingenta.com/content/aip/journal/pop/14/5/10.1063/1.2720373

Figures

Image of FIG. 1.
FIG. 1.

1D hydrodynamic simulations of preheating of a solid target by the ASE pedestal of a laser pulse using the MULTI code (Ref. 78). (a) In this case the target is composed of Al and the intensity of the ASE is . (b) In this case the target is composed of CH and the intensity of the ASE is as in Ref. 22.

Image of FIG. 2.
FIG. 2.

(Color online) (a) Schematic of the experiment showing a double proton beam. For this shot, the RCFs sensitive layer is facing the proton beam. (b) and (c) RCF layers. (d)–(f) Same as (a)–(c) except that here the target is tilted by 30°. The observed structures in the proton beam are imprinted by the copper mesh.

Image of FIG. 3.
FIG. 3.

(Color online) same experiment as in Fig. 2 except that, as illustrated in (a), the asymmetric RCFs are swapped so that the sensitive layer is not facing the proton beam. (b) and (c) RCF layers. The observed structures in the proton beam are imprinted by the copper mesh.

Image of FIG. 4.
FIG. 4.

(Color online) (a) Simulated angularly integrated spectra overlaid with the experimental spectrum (limited by the number of used RCF layers). The RCF sensitivities used are indicated in color. The RSA spectrum low-energy cutoff is due to contaminant depletion in the simulation. (b) Simulated phase-space distribution of the FSA and RSA at after the peak of the P-pol laser interaction. The target is tilted by 25°. Each contour line corresponds to every of the ion number in a log scale.

Image of FIG. 5.
FIG. 5.

(Color online) (a) Setup of the activation experiment at . (b) Simulated spectra for a foil. The RSA have lower energy than if the layer would be absent since, due to their smaller mass, the are preferentially accelerated by RSA. (c) Experimental and simulated yield for FSA . (d) Simulated spectra overlaid with the RCF inferred spectrum, both for a foil. All spectra are angularly integrated. (e) The phase plots of ions at . The broken lines indicate the initial Al target surface.

Image of FIG. 6.
FIG. 6.

(Color online) FSA activation data for a shot on a thick Al. The target front surface is covered with a thick layer of .

Image of FIG. 7.
FIG. 7.

(Color online) Activation experiment at . (a) Simulated spectra for a foil, (b) RCF inferred experimental spectra for different Al foil thicknesses (the lines are guides for the eye), (c) yield for FSA , experimental (filled circles) and simulated with (empty circles) or without (diamonds) the contribution from in inferred from the spectra shown in (b). All spectra are angularly integrated.

Image of FIG. 8.
FIG. 8.

(a) Experimental setup of the proton radiograph. Target 2 is tilted at 45° with respect to the axis of beam 2. The distance between the focus points of beam 1 and beam 2 is . (b) and (c) Probing proton angular distributions (for the same shot) at from target 1 for the proton probe beam shown in (a) and for different times of arrival on the edge of target 2 (as indicated on each film). Magnification is 15.75. Time 0 refers to the irradiation of target 2 by beam 2.

Image of FIG. 9.
FIG. 9.

(Color online) Schematic of the deflection incurred by the probing protons and the comoving electron in the field structure induced by the plasma expansion from target 2 (see Fig. 8).

Image of FIG. 10.
FIG. 10.

(Color online) (a) Angular distribution of protons centered around accelerated from a thick Al flat target irradiated at and detected on the RCF film stack placed from the target. Beam fiducials induced by a 1D modulation (with a modulation period of and a depth of ) on the target rear surface map the emission zone at the source (Refs. 4 and 63). This gives, therefore, access, for each fiducial beamlet, to its emission position on the target surface and to its emission angle. (b) Reconstruction of each beamlet trajectory in a plane perpendicular to the target surface. The ion flow is from left to right. The target plane is indicated. Each beamlet can be prolonged backwards (i.e., toward the incident laser) to reconstruct the virtual proton source. The envelope of the reconstructed beamlets defines a minimum source size of diameter.

Image of FIG. 11.
FIG. 11.

Proton phase space obtained with a 1D PIC simulation of a , , for a target at 40 . The center of the target is composed of aluminum with proton layers on each side of thickness. There is an exponential preplasma on the target front surface extending from to 40 in . The simulation box is long. The mesh size is and there are 260 particles per species per cell. The time step is equal to . The temporal profile is Gaussian and the pulse is injected at the left-hand side of the simulation box. It interacts with the target at normal incidence, and its electric field is -polarized. The snapshot is obtained at after the time of the peak of the pulse has irradiated the front surface of the target.

Image of FIG. 12.
FIG. 12.

(Color online) Analytical estimates of RSA-produced maximum proton energy for various laser intensities and pulse duration. The target thickness is , the FWHM laser focal spot is , and the laser wavelength is . The contour lines are for a constant maximum proton energy in units of MeV.

Image of FIG. 13.
FIG. 13.

(Color online) Analytical estimates of RSA- and FSA-produced maximum proton energy for various target and laser parameters. For (a), and the target thickness is . For (b), the target thickness is and . For (c), and . To compute the FSA proton energy, the slowing down in the target of the FSA produced protons is taken into account. Note, however, that in the FSA estimates we do not take into account a boosting that could take place at the rear surface due to the sheath fields. For all calculations, a FWHM laser focal spot of is assumed. The laser wavelength is assumed to be .

Tables

Generic image for table
Table I.

Comparison of RSA- and FSA-produced maximum proton energy for various experiments. To compute the FSA proton energy, the slowing down in the target of the FSA produced protons is taken into account. Note that in the FSA estimates, we do not take into account a boosting that could take place at the rear surface due to the sheath fields. For laser pulse durations up to , the laser wavelength of the reported experiments is . Otherwise, it is . For each calculation, we use the laser focal spot size as given in each reference.

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/content/aip/journal/pop/14/5/10.1063/1.2720373
2007-05-17
2014-04-16
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Comparative spectra and efficiencies of ions laser-accelerated forward from the front and rear surfaces of thin solid foils
http://aip.metastore.ingenta.com/content/aip/journal/pop/14/5/10.1063/1.2720373
10.1063/1.2720373
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