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Publications (5)0 Total impact

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    ABSTRACT: Recent experiments at the University to Michigan are helping to elucidate the dynamics of electrons and protons produced by high-intensity-laser interactions with thin-film solid targets by examining proton beam characteristics from increasing thicknesses of Mylar and aluminum. The proton beam energy and spatial profile are found to vary with target thickness as well as initial target conductivity. Half the peak proton energy is observed from Mylar targets as compared to aluminum targets as well as a much sharper reduction in proton energy with increasing target thickness. These differences originate from the strong inhibition of the hot-electron forward and return currents in the initially highly resistive material, which limits electron recirculation and thus proton energy from the target rear surface. In addition, evidence from energy and beam profile data supports the existence of target independent 5-MeV-maximum-energy beam from the target front surface. Other effects on beam profile due to target conductivity such as beam hollowing, originating from the electrothermal instability, are also presented.
    11/2004;
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    ABSTRACT: We report on the dependence of high-intensity laser accelerated proton beams on material properties of various thin-film targets. Evidence of star-like filaments [1] and beam hollowing (predicted from the electrothermal instability theory [2]) is observed on Radiochromic Film (RCF) and CR-39 nuclear track detectors. The proton beam profile also varies with initial target conductivity and target thickness. These phenomenona are explained by the strong inhibition of current in resistive target material due to the lack of a return current. We have also observed filamentary structures in the proton beam like those expected from the Weibel [3,4] instability in the electron beam. This work was supported by the National Science Foundation. References: [1] L. Gremillet, G. Bonnaud, and F. Amiranoff, Physics of Plasma 9, 941 (2002). [2]M.G. Haines, Phys. Rev. Lett. 47, 917 (1981). [3]Y. Sentoku, K. Mima, P. Kaw, and K. Nishikawa, Phys. Rev. Lett. 90, 155001 (2003). [4]E. S. Weibel, Phys. Rev. Lett. 2, 83 (1959).
    10/2003;
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    12/2002: pages 925;
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    ABSTRACT: We report on multy-MeV ion beam generation from the interaction of a 400fs, 1.053 mu m laser focused onto thin foil targets at intensities ranging from 10^17 to mid 10^19W/cm^2. Ion beam characteristics were studied as a function of the preformed plasma scale-length and target material initial conductivity. We model energetic ion generation by a fully relativistic two dimensional (2D) particle-in-cell (PIC) simulation [1]. These simulations identify the mechanism for the hot electron generation at the laser-plasma interface. We also found that the theoretical dependencies of the front side ion-generation efficiency versus laser intensity and plasma profiles agree well with experiments [2,3]. [1] Y Sentoku, et. al., to be published in Phys. Plasmas (2001). [2] A. Maksimchuk, et. al, Phys. Rev Lett. 84, 4108 (2000). [3] K. Nemoto, et. al., Appl. Phys. Lett. 78, 595 (2001).
    10/2001;
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    ABSTRACT: We have conducted investigations of a collimated beam of fast protons, produced by a 10TW laser with frequencies of either ω<sub>0</sub> (corresponding to 1.053 micron light) or 2ω <sub>0</sub> (corresponding to 532 nm light) focused to an intensity of more the 3×10<sup>19</sup> W/cm<sup>2</sup> onto the surface of a thin-film target. Energies as high as 10 MeV and total number of 10<sup>9</sup>, confined in a cone angle of 40°±10° have been observed. The protons, which originate form impurities on the front side of the target and exit out the backside in a direction normal to the target surface. Acceleration field gradients of ~10 GeV/cm have been inferred. The maximum proton energy for 2ω<sub>0</sub> can be explained by the charge-separation electrostatic-field acceleration due to "vacuum heating". In another set of experiments when a deuterated polystyrene layer was deposited on a surface of a Mylar film and a <sup>10</sup>B sample was placed behind the target, we observed the production of ~10<sup>5</sup> atoms of positron active isotope <sup>11 </sup>C from the nuclear fusion reaction <sup>10</sup>B(d,n)<sup>11</sup>C. No activation was detected when only the proton beam was used. We also discuss the use of ions from these table-top sources for medical applications such as cancer radiotherapy and fundamental studies in radio-biology
    Particle Accelerator Conference, 2001. PAC 2001. Proceedings of the 2001; 02/2001