We are developing a new high explosive pulsed power (HEPP) system based on the 1.4 m long Ranchero generator which was developed in 1999 for driving solid density z-pinch loads. The new application requires approximately 40 MA to implode similar liners, but the liners cannot tolerate the 65 mu s, 3 MA current pulse associated with delivering the initial magnetic flux to the 200 nH generator. To circumvent this problem, we have designed a system with an internal start switch and four explosively formed fuse (EFF) opening switches. The integral start switch is installed between the output glide plane and the armature. It functions in the same manner as a standard input crowbar switch when armature motion begins, but initially isolates the load. The circuit is completed during the flux loading phase using post hole convolutes. Each convolute attaches the inner (coaxial) output transmission line to the outside of the outer coax through a penetration of the outer coaxial line. The attachment is made with the conductor of an EFF at each location. The EFFs conduct 0.75 MA each, and are actuated just after the internal start switch connects to the load. EFFs operating at these parameters have been tested in the past. The post hole convolutes must withstand as much as 80 kV at peak dI/dt during the Ranchero load current pulse. We describe the design of this new HEPP system in detail, and give the experimental results available at conference time. In addition, we discuss the work we are doing to test the upper current limits of a single standard size Ranchero module. Calculations have suggested that the generator could function at up to similar to 120 MA, the rule of thumb we follow (1 MA/cm) suggests 90 MA, and simple flux compression calculations, along with the similar to 4 MA seed current available from our capacitor bank, suggests 118 MA is the currently available upper limit.

Experiments performed at the Sandia National Laboratories (SNL) Z-machine, located in Albuquerque, New Mexico produce hot (approximately 220 eV) plasmas. X-ray emission from the plasma is used to drive radiation flow experiments. Our standard plasma diagnostic suite consists of x-ray diodes (XRDs), silicon photodiodes, and nickel thin film bolometers. Small diagnostic holes allow us to view the hot plasma from the side, top axial anode side, and bottom axial cathode side. Computer software has been written to process the raw data to calculate data quality, fold in detector spectral response and experiment geometry for emitted flux, calculate a multidetector spectral unfold, and yield an equivalent time-dependent Planckian temperature profile. Spectral unfolds of our XRD data generally yield a Planckian-like spectrum. In our presentation we will compare our diagnostic techniques, analysis, and results to more accurately characterize spectral unfolds in order to establish better drive conditions for our experiments.

The photoemissive cathode type of x-ray diode (XRD) is popular for measuring time and spectrally resolved output of pulsed power experiments. Vitreous carbon XRDs currently used on the Sandia National Laboratories Z-machine were designed in the early 1980s and use materials and processes no longer available. Additionally cathodes used in the high x-ray flux and dirty vacuum environment of a machine such as Z suffer from response changes requiring recalibration. In searching for a suitable replacement cathode, we discovered very high purity vitreous-carbon planchets are commercially available for use as biological substrates in scanning electron microscope (SEM) work. After simplifying the photocathode mounting to use commercially available components, we constructed a set of 20 XRDs using SEM planchets that were then calibrated at the National Synchrotron Light Source at Brookhaven National Laboratory. We present comparisons of the reproducibility and absolute calibrations between the current vitreous-carbon XRDs and our new design.

Blast waves (BWs) form when the wave speed of an initially diffusive, supersonic radiation wave becomes subsonic and creates a radiographically-visible, hydrodynamic shock wave. BWs are a novel diagnostic in radiation-flow, code validation experiments that use Sandia's Z-accelerator's dynamic hohlraum (DH) as a radiative source. The physics models being tested are sensitive to delivered energy and power changes of better than +/- 10%; therefore, precise in-situ radiative power and energy measurements are required for quantitative comparisons between simulation and experiment. The energy sensitive BW diagnostic complements bolometric and x-ray radiometric diagnostics in providing these measurements. Recent comparisons between BW qualification experiments and simulations have revealed a spatial dependence on the radiation source. We discuss the experimental design and sensitivities for the BW diagnostic and experimental results in comparison to simulations and other diagnostics.

The plastic response of beryllium was investigated during loading by laser-induced shock waves, using surface velocimetry and in-situ x-ray diffraction. Results from loading by thermal x-rays (hohlraum) were consistent with more extensive studies using laser ablation. Strong elastic waves were observed, up to ~1 km/s in free surface speed, with significant structure before the arrival of the plastic shock. The magnitude and shape of the precursor could be reproduced with a plasticity model based on dislocation dynamics. Changes in lattice spacing measured from the x-ray diffraction pattern gave a direct measurement of uniaxial compression in the elastic wave, triaxial flow from the decay of the precursor, and triaxial compression in the plastic shock; these were consistent with the velocity data. The dynamic strength behavior deduced from the laser experiments was used to help interpret surface velocity data around the onset of shock-induced melting. A model of heterogeneous mixtures is being extended to treat anisotropic components, and spall.

We have characterized kilo-electron-volt (keV) emission from Al plasmas for various laser illuminations at the OMEGA laser with the goal of optimizing the ability to backlight low-atomic-number materials such as beryllium for fusion ignition studies. The plasma is diagnosed by spectral-measurement comparisons to detailed theoretical atomic physics models. It is found that a significant fraction of the radiation is due to the x-ray continuum, that the electron temperature Te depends weakly on laser energy and power, and that the conversion efficiency to Lyman α (Lα, the N=2→1 transition in H-like Al) at 1.73 keV is reduced as laser energy is increased. As the number of beams is increased, the extra laser energy goes into a larger, higher-density plasma in which He-like and H-like ions are more effectively ionized.

As calculational capabilities mature the data accuracy requirements become more stringent. Typical Z-pinch power measurements use multiple sets of filtered X-Ray Diodes 1 (XRD) to provide temporally and spectrally resolved information on the pinch performance within a +/− 12% error bar. Integrated power measurements are provided by Ni-foil bolometers2 with +/− 10% accuracy

We performed a series of dynamic loading experiments on iron with pressures of 5–40 GPa at the Trident Laser Laboratory. We used 2.4 ns laser pulses of varying shapes and irradiances of 2 to 1000 GW/cm2 to load a 5‐mm diameter region of rolled iron foils that were 25–50 microns thick. The temporal characteristic of the laser irradiance was tailored to produce shock or quasi‐isentropic loading histories. Line‐imaging VISAR was used to time‐resolve free surface velocities. In several experiments, two different thickness samples, placed side‐by‐side, were subjected to the same irradiance history. We describe the experiment configuration, analysis, and results.