Thermal and mechanical analysis of the Faraday shield for the Compact Ignition Tokamak

The antenna for the ion cyclotron resonance heating (ICRH) system of the Compact Ignition Tokamak (CIT) is protected from the plasma environment by a Faraday shield, an array of gas-cooled metallic tubes. The plasma side of the tubes is armored with graphite tiles, which can be either brazed or mechanically attached to the tube. The Faraday shield has been analyzed using finite element codes to model thermal and mechanical responses to typical CIT heating and disruption loads. Four representative materials (Inconel 718, tantalum-10 tungsten, copper alloy C17510, and molybdenum alloy TZM) and several combinations of tube and armor thicknesses were used in the thermal analysis, which revealed that maximum allowable temperatures were not exceeded for any of the four materials considered. The two-dimensional thermal stress analysis indicated Von Mises stresses greater than twice the yield stress for a tube constructed of Inconel 718 (the original design material) for the brazed-graphite design. Analysis of stresses caused by plasma disruption ()rvec J) )times) )rvec B)) loads eliminated the copper and molybdenum alloys as candidate tube materials. Of the four materials considered, tantalum-10 tungsten performed the best for a brazed graphite design, showing acceptable thermal stresses (69% of yield) and disruption stresses (42% of yield). A preliminary thermal analysis of the mechanically attached graphite scheme predicts minimal thermal stresses in the tube. The survivability of the graphite tubes in this scheme is yet to be analyzed. 8 refs., 19 figs., 2 tabs

Validation of Z-pinch double-ended hohlraum energetics and capsule coupling models using Z data

The pulsed-power driven double-ended vacuum hohlraum allows highly symmetric capsule implosions, aided by the separation of the capsule from the z-pinch and its associated instabilities, spatial variations, and non-thermal spectral components. Experiments on Sandia National Laboratories' Z facility in a single-sided power feed configuration have been limited thus far to capsule drive temperatures of 75 eV or less. Nonetheless, these experiments have validated the hohlraum energetics, hohlraum coupling, and capsule coupling properties of this configuration. Implosion capsules and symmetry diagnostic capsules have provided a wealth of capsule energetics data in the form of implosion trajectories for comparison to simulation. These measurements have been compared to detailed two-dimensional Lasnex hohlraum simulations, which model the hohlraum radiation transport including the effects of z-pinch source motion as well as hohlraum absorption/re-emission and wall plasma motion

The role of strong coupling in z-pinch-driven approaches to high yield inertial confinement fusion

Peak x-ray powers as high as 280±40 TW have been generated from the implosion of tungsten wire arrays on the Z Accelerator at Sandia National Laboratories. The high x-ray powers radiated by these z-pinches provide an attractive new driver option for high yield inertial confinement fusion (ICF). The high x-ray powers appear to be a result of using a large number of wires in the array which decreases the perturbation seed to the magnetic Rayleigh-Taylor (MRT ) instability and diminishes other 3-D effects. Simulations to confirm this hypothesis require a 3-D MHD code capability, and associated databases, to follow the evolution of the wires from cold solid through melt, vaporization, ionization, and finally to dense imploded plasma. Strong coupling plays a role in this process, the importance of which depends on the wire material and the current time history of the pulsed power driver. Strong coupling regimes are involved in the plasmas in the convolute and transmission line of the powerflow system. Strong coupling can also play a role in the physics of the z-pinch-driven high yield ICF target. Finally, strong coupling can occur in certain z-pinch-driven application experiments

Simulation of heating-compressed fast-ignition cores by petawatt laser-generated electrons

In this work, unique particle-in-cell simulations to understand the relativistic electron beam thermalization and subsequent heating of highly compressed plasmas are reported. The simulations yield heated core parameters in good agreement with the GEKKO-PW experimental measurements, given reasonable assumptions of laser-to-electron coupling efficiency and the distribution function of laser-produced electrons. The classical range of the hot electrons exceeds the mass density-core diameter product $\rho$L by a factor of several. Anomalous stopping appears to be present and is created by the growth and saturation of an electromagnetic filamentation mode that generates a strong back-EMF impeding hot electrons on the injection side of the density maxima .This methodology is then applied to the design of experiments for the ZR machine coupled to the Z-Beamlet/PW laser.
Sandia National Laboratories is also developing a combination of experimental and theoretical capabilities useful for the study of pulsed-power-driven fast ignition physics. In preparation for these fast ignition experiments, the theory group at Sandia is modeling various aspects of fast ignition physics. Numerical simulations of laser/plasma interaction, electron transport, and ion generation are being performed using the LSP code. LASNEX simulations of the compression of deuterium/tritium fuel in various reentrant cone geometries are being performed. Analytic and numerical modeling has been performed to determine the conditions required for fast ignition breakeven scaling. These results indicate that to achieve fusion energy output equal to the deposited energy in the core will require about 5% of the laser energy needed for ignition and might be an achievable goal with an upgraded Z-beamlet laser in short pulse mode

Down regulation of epidermal growth factor receptors in liver proliferation induced by a mixture of triiodothyronine, amino acids, glucagon, and heparin (TAGH).

This study investigated the mechanisms by which TAGH solution (a mixture of triiodothyronine, amino acids, glucagon, and heparin) induces DNA synthesis in hepatocytes in the liver of intact rats, with particular reference to events at the epidermal growth factor (EGF) receptor. Both partial hepatectomy and infusion of TAGH stimulated DNA synthesis at 24 hours and both procedures resulted in a reduction of EGF receptors assessed in plasma membranes isolated from rat liver at this time. In cell cultures, while EGF strongly stimulated DNA synthesis and started EGF receptor down regulation, TAGH had only a minor effect (1.5 x basal) on DNA synthesis and did not interact with or down regulate the EGF receptor. Membrane phosphorylation studies, however, showed that TAGH induced phosphorylation of tyrosine residues in the EGF receptor. The in vivo action of TAGH seems to entail recruitment of similar changes in the EGF receptor to those that occur after partial hepatectomy

Cryogenic target development for fast ignition with Z-pinch-driven fuel assembly

We are developing an alternative approach to indirect-drive fast ignition fusion targets in which a liquid cryogenic fuel layer is condensed in situ from a low pressure external gas supply and confined between a thick outer ablator shell and a thin inner shell. The shape and surface quality of the liquid fuel layer is determined entirely by the characteristics of the bounding shells. Liquid fuel targets of this type have a number of potential advantages including greatly reduced temperature control requirements and drastically reduced cost and complexity of the cryogenic support system compared to $\beta$-layed DT targets. This liquid fuel concept is particularly appropriate for a hemispherical capsule configuration with single-sided x-ray drive by a z-pinch source. Technology issues for concentric-shell liquid cryogenic target development and progress in thin inner hemispherical shell fabrication are discussed