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Descripción
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| Fast ignition involves transport of GA currents of laser-driven electrons through dense coronal plasma of imploded fusion targets [1, 2]. Recently, we have reported integrated simulations of target ignition by fast electrons by means of a hybrid approach that allowed us to investigate important transport features such as current filamentation and magnetic beam collimation simultaneously with ignition physics [3, 4]. In those simulations, we assumed that the electron kinetic energies are given by the ponderomotive scaling and considered an initial divergence half-angle of 22.5º, consistent with the experiments reported in Ref. [1]. We found minimum ignition energies from 25 to 30 kJ, depending on the distance from the cone tip to the compressed core. Assuming a laser-to-fast electron conversion efficiency of 40%, those energies correspond to laser beam energies from 60 to 75 kJ, of the same order than those envisioned for HiPER [5]. Recent experiments carried out at RAL [6] at laser intensities relevant to fast ignition have evidenced an enhancement of the beam divergence with the laser intensity and electron kinetic energies lower than those predicted by the ponderomotive scaling [7]. We have recomputed the ignition energies of fast electron beams taking into account those experimental results. We have taken divergence angles consistent with the experiments of Ref. [6] and mean energies of fast electrons from 1 to 2 MeV. In addition, we have accounted for the scattering of electrons with the cone tip, typically a gold layer of tens of microns, which may induce a beam divergence comparable with those measured in the experiments. In this talk, we will present a parametric study on fast electron energy deposition and actual ignition of an imploded target configuration for different mean kinetic energies and divergences of the relativistic electrons. References [1] R. Kodama et al., Nature 412, 798 (2001) and Nature 418, 933 (2002). [2] R.B. Stephens et al., Phys. Rev. Lett. 91, 185001 (2003). [3] J.J. Honrubia and J. Meyer-ter-Vehn, Nucl. Fusion 46, L25 (2006). [4] J.J. Honrubia and J. Meyer-ter-Vehn, IFSA 2007 Proceedings (2007). [5] M. Dunne, Nature Physics 2, 2 (2006). [6] J.S. Green et al., Phys. Rev. Lett. 100, 015003 (2008). [7] Y. Sentoku et al., IFSA 2007 Proceedings (2007). | |
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Internacional
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Si |
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ISSN o ISBN
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0741-3335 |
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Entidad relacionada
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35th European Physical Society Conference on Plasma Physics combined with the 10th International Workshop on Fast Ignition of Fusion Targets |
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Nacionalidad Entidad
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Sin nacionalidad |
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Lugar del congreso
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Hersonissos, Creta, Grecia |