Modeling experiments of new compact hohlraum configuration with multiple parallel-driven x-ray sources with application of VisRad code
Résumé
A new compact Z-pinch x-ray hohlraum design with multiple parallel-driven x-ray sources was jointly proposed by the Sandia National Laboratories and the University of Nevada [1]. The first proof-of-principle experimental demonstration of the full configuration of this compact hohlraum with central reemission target and tailored shine shields (to provide a symmetric temperature distribution on the target) was achieved at the 1.7 MA UNR Zebra generator [2]. VisRad (PRISM Computational Sciences Co.), a 3-D view factor code, is used to simulate the multi-dimensional radiation environment within this new compact hohlraum configuration that incorporates multiple compact (mm-scale) planar wire array (PWA) x-ray sources that surround a reemission target in the center of the hohlraum cavity, allowing a reduction of hohlraum surface area and potentially providing a hotter x-ray environment. View factor modeling is a valuable design tool, allowing us to improve rapidly on experimental design and to demonstrate the feasibility of the concept for hohlraum and ICF studies on a 1-2 MA university-scale pulsed power platform. Double-PWA sources (DPWA) were modeled and used in experiments due to much better pulse shaping properties compared with single PWAs. Also, we are taking into account that the W DPWA is an anisotropic x-ray source and maximum radiation is emitted in the direction parallel to the wire planes. Different versions of compact hohlraum with two W DPWA sources and central cavity between them were analyzed using VisRad code. Simulations have predicted a reemission plastic target radiation temperature Trad ~ 39eV, showing good correlation to experimental data 37 3 eV The possibility of optimization of new compact configuration was demonstrated by changing relative volume of central cavity. Special emphasis is made on Trad uniformity at the reemission target surface by analysis of compact holraum configuration of 6 or more - PWA pinches proposed in Ref. [2] to reach better symmetry of hohlraum exposure. The scaling of this 6 DPWA sources hohlraum configuration using VisRad for higher current 20 MA generators (as Sandia National Laboratories Z facility) show that central target Trad ~ 85 eV is reachable. VisRad simulation has shown that x-ray power flux in new compact hohlraum might be ~1.3 times higher if W sources will be changed with Au sources.