University of California, San Diego Center for Energy Research

1. University of California, San Diego Center for Energy Research Simulations investigating the effect of a DT-ice-covered cone tip on the implosion of a re-entrant cone-guided ICF capsuleJ. Pasley - University of California San DiegoR. Stephens – General Atomics Abstract Previous simulations of re-entrant cone-guided fast ignition capsule implosions have investigated the interaction of the imploding shell with the gold cone. Here we present simulations showing the effect of DT-ice layering onto the cone tip itself: a situation that may be difficult to avoid in the manufacture of cryogenic targets. 2d radiation hydrodynamic simulation results using the new ‘h2d’ code show a range of possible outcomes. Preheat levels are shown to be of critical importance in determining late time behavior. 2-D spherical (fine) 1-D simulations of gas density sensitivity • Range of simulations : • 2-D h2d [1] multigroup radiation hydrodynamics simulations in rectangular geometry examining early time behavior at junction between cone and shell • 2-D h2d multigroup radiation hydrodynamics simulations of the implosion of a re-entrant cone guided in spherical geometry (180O) • - coarsely meshed ice/cone to examine motion of ice-on-cone into central gas over history of implosion • - higher resolution runs to examine effect of ice on motion of gold layer • 1-D HYADES [1] multigroup radiation hydrodynamics simulations of both Planckian and spectrally hot preheat onto ice-gold planar target • 1-D HYADES multigroup radiation hydrodynamics simulations of implosions with varying density of central gas fill to examine effect of ice layer expansion into central region With ice No ice Initial interface pos. Lineout of above at r=0 2-D rectangular ice (Early time point chosen to avoid errors associated with rezoning) laser • x-ray heated ice layer acts to tamp the gold ablation plume (similar situation to that presented in [2]) however the gold is strongly heated by harder components of the spectrum : efficacy of tamping is limited • The corner region of cone expands most violently due to the larger exposed surface/ volume ratio in this region of the cone. Au entrained ‘cone’ surface 1-D simulations of interface motion • Ice layer expands rapidly in cases where preheat is significant, having little impact on in-flight shell dynamics. • If ice remains cold then shell motion is impeded – a small effect unless the ice layer is thick. • Ablation and entrainment of Au from outer cone into shell ablation plume can bring gold into contact with laser rays => enhanced preheating inside capsule Compression is sensitive to density in central low density region – ablation of significant ice-on-cone layers could have a similar effect. 50mm thick ice 30mm thick ice Future work This was just a quick ‘look-see’ at the effects of the ice layer. Need to extend to optimised FI-specific capsule designs. H2d burn package presently incompatible with hydro package – this should be fixed soon. 2-D spherical (coarse) 20mm thick ice 10mm thick ice 1.5ns 2.0ns Power matched drives with different spectra: (note cone is too thin (10mm) and shock breaks through) Red: 120eV Planck spectrum Green: 400eV Planck spectrum Blue : 1keV Planck spectrum References [1] HYADES and h2d are commercial products of Cascade Applied Sciences Incorporated, 6325 Trevarton Drive, Longmont, CO 80503. Electronic mail: larsen@casinc.com. [2] J. Pasley et al, Physics of Plasmas 13, 032702 (2006) • As shell approaches stagnation, central low-density DT region shows significant density perturbation due to ice ablation off cone tip Gold motion is sensitive to thickness of ice layer but appears less sensitive to the preheat spectrum Supported by GA internal funds and the Fusion Science Center