Of the proton beam density cross section caused by

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Unformatted text preview: lerators have also been employed on some occasions for electric Rev. Mod. Phys., Vol. 85, No. 2, April–June 2013 field measurements in plasmas, via the detection of the proton deflection, e.g., by Mendel and Olsen (1975). In practice, the difficulties and high cost involved in coupling externally produced particle beams of sufficiently high energy to laser-plasma experiments (or indeed magnetic confinement experiments) and the relatively long duration of ion pulses produced from conventional accelerators have limited the application of such diagnostic techniques. The unique properties of protons from high-intensity lasermatter interactions, particularly in terms of spatial quality and temporal duration, have opened up a totally new area of application of proton probing or radiography. As seen in Sec. III.B, TNSA protons from a laser-irradiated foil can be described as emitted from a virtual, pointlike source located in front of the target (Borghesi et al., 2004). A pointprojection imaging scheme is therefore automatically achieved with magnification M set by the geometrical distances at play. Backlighting with laser-driven protons has intrinsically high spatial resolution, which, for negligible scattering in the investigated sample, is determined by the size d of the virtual proton source and the width s of the point spread function of the detector (mainly due to scattering near the end of the proton range), offering the possibility of resolving details with spatial dimensions of a few m. As discussed in Sec. II.E multilayer detector arrangements employing RCFs or CR39 layers offer the possibility of energyresolved measurements despite the broad spectrum. Energy dispersion provides the technique with an intrinsic multiframe capability. In fact, since the sample to be probed is situated at a finite distance from the source, protons with different energies reach it at different times. As the detector performs spectral selection, each RCF layer contains, in a first approximation, information pertaining to a particular time, so that a movie of the interaction made up of discrete frames can be taken in a single shot. Depending on the experimental conditions, 2D proton deflection map frames spanning up to 100 ps can be obtained. The ultimate limit of the temporal resolution is given by the duration of the proton burst at the source, which is of the order of the laser pulse duration. Several radiographic applications of laser-produced protons have been reported to date and radiographs of objects for various size and thickness (down to a few $m) have been obtained (Cobble et al., 2002; Roth et al., 2002; Borghesi et al., 2004; Mackinnon et al., 2006). Density diagnosis via proton radiography has potential application in ICF. A preliminary test studying the compression of empty CH shells under multibeam isotropic irradiation at the moderate irradiance of 1013 W cmÀ2 has been carried out at the Rutherford Appleton Laboratory (Mackinnon et al.,...
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This document was uploaded on 09/28/2013.

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