Numerical modeling of Hohlraum radiation conditions: Spatial and spectral variations due to sample position, beam pointing, and Hohlraum geometry

Abstract

View-factor simulations are presented of the spatially varying radiation conditions inside double-ended gold hohlraums and single-ended gold hohlraums ("halfraums") used in inertial confinement fusion (ICF) and high energy density (HED) physics experiments [J. Lindl, Phys. Plasmas 11, 339 (2004); M. D. Rosen, Phys. Plasmas 3, 1803(1996]. It is shown that in many circumstances, the common assumption that the hohlraum "drive" can be characterized by a single temperature is too simplistic. Specifically, the radiation conditions seen by an experimental package can differ significantly from the wall reemission measured through diagnostic holes or laser entrance holes (LEHs) by absolutely calibrated detectors. Furthermore, even in situations where the radiation temperature is roughly the same for diagnostics and experimental packages, or for packages at different locations, the spectral energy distributions can vary significantly, due to the differing fractions of reemitting wall, laser hot spots, and LEHs seen from different locations. We find that the spatial variation of temperature, and especially the differences between what diagnostics looking in the LEH measure vs. the radiation temperature on wall-mounted experimental packages, is generally greater for double-ended hohlraums than it is for halfraums. View-factor simulations can also be used to explore experimental variables (halfraum length and geometry, sample position, and beam pointing) that can be adjusted in order to, for example, maximize the radiation flux onto a sample, or other package. In this vein, simulations of hohlraums and halfraums with LEH shields are also presented.

Capsule implosion optimization during the indirect-drive National Ignition Campaign

“…Figure 7 compares 3D Hydra 46 calculations including all the above-mentioned differences between the incident P 2 =P 0 flux inferred from a reemission sphere and the incident P 2 =P 0 flux on an ignition capsule averaged over the first 2 ns as a function of inner cone fraction. We note that the surro-gacy offset in P 2 is relatively small, þ 8%, because the viewfactor 78 between the patch areas and the Bi sphere limb from which the equatorial view data is extracted is small. The error in this offset is estimated based on 10% uncertainties in 100 eV low 55 Z and high 61 Z albedoes at 62%, well within the requirement to tune to 65% in P 2 .…”

Development of a thermal X-radiation source using “hot” hohlraums

“…The measured flux is a combination of non-thermal emission from the hot laser spots and thermal emission from the hohlraum wall. The contributions of laser spots observed are strongly dependent on the angle-of-observation [27] and thus the measured radiation flux is not necessarily the same as that seen by a volume element inside the hohlraum. In addition, the measured flux may under predict the internal flux if the size of the hole through which it is observed closes as plasma fills the hohlraum.…”

Long duration X-ray drive hydrodynamics experiments relevant for laboratory astrophysics

“…Variations in the peak temperature ware explained by beam to beam energy variations and also by slightly different mDMX viewfactors. A simplify viewfactor calculation with Visrad [38] shows the different emission zones viewed by mDMX (see Fig. 5c).…”