RevModPhys.85.751

Proton spectrum in standard tnsa experiments in which

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Unformatted text preview: elerated species (Hegelich et al., 2002). A more complete spectral characterization of multicomponent ion beams can be obtained with Thomson parabola spectrometers, based on the principle for mass spectrometry introduced by Thomson (1911). A schematic of the device is shown in Fig. 10(a). Ions are deflected by parallel E and B fields [with E $ 104 V=m (Sakabe et al., 1980)] resulting in a characteristic deflection pattern in which species with different charge-to-mass ratio form separated parabolic traces in the detector plane, as shown in the typical image of Fig. 10(b). Modified magnetic and Thomson spectrometers, having imaging and angular resolution capability, have also been developed (Ter-Avetisyan et al., 2009; Chen et al., 2010; Jung et al., 2011a). The detectors used in conjunction with these spectrometers are typically either CR39, image plates (IP), scintillating plates, or microchannel plates (MCPs). Photostimulable IPs are filmlike radiation image sensors, developed for x-ray medical imaging, which are composed of specially designed phosphors that trap and store radiation energy in metastable excited states and can be absolutely calibrated in terms of ˇ´ particle flux (Mancic et al., 2008; Freeman et al., 2011). Scintillating plates (Green et al., 2010) or MCPs (Ter-Avetisyan, Schnrer, and Nickles, 2005) are favored in situations where online detection is required (e.g., highrepetition laser systems), as the scintillator screen or the MCPs phosphor are imaged on a charge-coupled device (CCD) and the detector does not require replacing after exposure. Scintillators can also be used for beam profiling (Sakaki et al., 2010), with potential for energy range selection (Green et al., 2011). FIG. 10 (color online). Left: Schematic of a Thomson parabola (courtesy of S. ter-Avetisyan). Right: A typical example of ion traces obtained with the Thomson parabola. Rev. Mod. Phys., Vol. 85, No. 2, April–June 2013 761 A different approach also allowing online beam monitoring is the use of time-of-flight (TOF) techniques, where the broadband ions are left to propagate over a given distance and then detected employing scintillating plates coupled to a photomultiplier (Nakamura et al., 2006), Faraday cups, or semiconductor detectors (Margarone et al., 2011). The time-varying signal produced by the detectors maps the ion energy spectrum, although the finite response time of the detector and realistic propagation distances limits the energy range over which these measurements can be applied. State-of-the-art TOF-MCP detectors allow for measurements of protons with a kinetic energy up to $20 MeV=nucleon (Fukuda et al., 2009). III. TARGET NORMAL SHEATH ACCELERATION A. TNSA scenario: Main experimental observations As anticipated in Sec. II.C the TNSA process (Wilks et al., 2001) is a consequence of the large charge separation generated by hot electrons reaching the rear side of the target. There, a cloud of relativistic electrons is formed, extendin...
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This document was uploaded on 09/28/2013.

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