Tallents et al 2009 and shock compression kritcher et

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Unformatted text preview: eams, which can heat the material in depth, are in principle better suited to this purpose than the methods described above. Heating of solid-density material with ions can be achieved with accelerator-based or electrical-pulsed ion sources; see, e.g., Bailey et al. (1990), Hoffmann et al. (2000), and Tahir et al. (2006). However, the relatively Rev. Mod. Phys., Vol. 85, No. 2, April–June 2013 FIG. 33 (color online). Heating of solid targets by protons. (a) Experimental setup for flat and focusing target geometries. Each target consists of a flat or hemispherical 10 m thick Al foil irradiated by the laser, and a flat 10 m thick Al foil to be heated by the protons. (b) Corresponding streak camera images showing space- and time-resolved thermal emission at 570 nm from the rear side of the proton-heated foil. Proton focusing by the hemispherical foil leads to a stronger, more localized heating. From Patel et al., 2003. long durations of ion pulses from these sources (1–10 ns) imply that the materials undergo significant hydrodynamic expansion already during the heating period. On the contrary, laser-generated proton beams, emitted in ps bursts, provide a means of very rapid heating, on a time scale shorter than the hydrodynamic time scale. By minimizing the distance between the ion source and the sample to be heated, it is possible to limit the heating time to tens of ps. The target then stays at near-solid density before significant expansion occurs, and the WDM properties can be investigated within this temporal window. The first demonstration of laser-generated proton heating was obtained by Patel et al. (2003). In this experiment a 10 J pulse from the 100 fs JanUSP laser at LLNL was focused onto an Al foil producing a 100–200 mJ proton beam used to heat a second Al foil. Target heating was monitored via timeresolved rear surface emission, as shown in Fig. 33. A focused proton beam, produced from a spherically shaped target (see Sec. III.E.3), was seen to heat a small target region to a temperature (of $23 eV). With a similar ion focusing arrangement on a higher energy laser system, Gekko at ILE Osaka, Snavely et al. (2007) demonstrated secondary target heating up to 80 eV by imaging both visible and extreme-ultraviolet Planckian emission from the target’s rear surface. Subsequent experiments have investigated the properties of the WDM produced with this approach with a number of diagnostics, either passive or in pump-probe configurations, combined to self-consistent modeling of sample heating and expansion. Warm solid Al at temperatures up to 15–20 eV ˇ´ (Dyer et al., 2008; Mancic et al., 2010b) and carbon up to $2 eV (Roth et al., 2009) have been produced in this manner. Dyer et al. (2008) reconstructed the EOS of the heated material by measuring the temperature and expansion rate of the heated Andrea Macchi, Marco Borghesi, and Matteo Passoni: Ion acceleration by superintense laser-plasma . . . FIG. 34 (color online). Setu...
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