X-ray powers on the order of 10 TW over an area of 4.5 mm2 are produced in the axial direction from the compression of a low-density foam target centered within a z-pinch on the Z generator.1 The x rays from this source are used for high-energy–density physics experiments, including the heating of hohlraums for inertial confinements fusion studies.2 In this article, detailed characteristics of this radiation source measured using an upgraded axial-radiation-diagnostic suite3 together with other on- and off-axis diagnostics are summarized and discussed in terms of Eulerian and Lagrangian radiation–magnetohydrodynamic code simulations. The source, characterized here, employs a nested array of 10-mm-long tungsten wires, at radii of 20 and 10 mm, having a total masses of 2 and 1 mg, and wire numbers of 240 and 120, respectively. The target is a 14 mg/cc CH2 foam cylinder of 5 mm diameter. The codes take into account the development of the Rayleigh–Taylor instability in the r–z plane, and provide integrated calculations of the implosion together with the x-ray generation. The radiation exiting the imploding target through the 4.5 mm2 aperture is measured primarily by the axial diagnostic suite that now includes diagnostics at an angle of ∼30° to the z axis. The near on-axis diagnostics include: (1) a seven-element filtered silicon-diode array,4 (2) a five-element filtered x-ray diffraction (XRD) array,5 (3) a six-element filtered PCD array,6 (4) a three-element bolometer,7 (5) time-resolved and time-integrating crystal spectrometers, and (6) two fast-framing x-ray pinhole cameras having 11 frames each. The filtered silicon diodes, XRDs, and PCDs are sensitive to 1–200, 140–2300, and 1000–4000 eV x rays, respectively. They (1) establish the magnitude of the prepluse generated during the run in of the imploding wire arrays, (2) measure the Planckian nature of the dominant thermal, and (3) nonthermal component of the emission. The bolometers and XRDs mounted on the near-normal and 30° LOS (line-of-sight) measure the total power and check the Lambertian nature of the emission. Additionally, a suite of filtered fast-framing x-ray pinhole cameras and silicon-diode arrays behind a transmission grating, mounted on LOSs nearly normal to the z axis, quantify the plasma plume exiting the aperture. The hard bremsstrahlung generated is estimated with both on- and off-axis shielded scintillator photomultiplier diagnostics.

Summary form only given. The Z-pinch driven hohlraum (ZPDH) has shown great promise for indirect-drive ICF. In this concept, a Z-pinch radiation source resides in one or two primary hohlraums. Radiation is coupled from the primaries into a secondary hohlraum through a transparent Be-spoke electrode. Experiments at Sandia on the Z accelerator have characterized the hohlraum energetics, the radiation coupling efficiency to the secondary, and the radiation drive symmetry in the secondary, for single- and two-sided configurations. We have demonstrated energetics and coupling efficiencies that are adequate to scale the system to ignition and high-yield. We have recently developed a two-sided, or "double-pinch" secondary illumination capability to study radiation symmetry control for the ZPDH [3]. In this geometry, one Z-pinch-driven primary is located above, and another below a high-yield size (>4500 mm/sup 3/) ICF secondary. These two pinches are fed from a single current feed for compatibility with Z.

The 100 ns, 20 MA pinch-driver Z is surrounded by an extensive set of diagnostics. There are nine radial lines of sight set at 12° above horizontal and each of these may be equipped with up to five diagnostic ports. Instruments routinely fielded viewing the pinch from the side with these ports include x-ray diode arrays, photoconducting detector arrays, bolometers, transmission grating spectrometers, time-resolved x-ray pinhole cameras, x-ray crystal spectrometers, calorimeters, silicon photodiodes, and neutron detectors. A diagnostic package fielded on axis for viewing internal pinch radiation consists of nine lines of sight. This package accommodates virtually the same diagnostics as the radial ports. Other diagnostics not fielded on the axial or radial ports include current B-dot monitors, filtered x-ray scintillators coupled by fiber optics to streak cameras, streaked visible spectroscopy, velocity interferometric system for any reflector, bremsstrahlung cameras, and active shock breakout measurement of hohlraum temperature. The data acquisition system is capable of recording up to 500 channels and the data from each shot is available on the Internet. A major new diagnostic presently under construction is the BEAMLET backlighter. We will briefly describe each of these diagnostics and present some of the highest-quality data from them.

In the concept of the dynamic hohlraum an imploding Z pinch is optically thick to its own radiation. Radiation may be trapped inside the pinch to give a radiation temperature inside the pinch greater than that outside the pinch. The radiation is typically produced by colliding an outer Z-pinch liner onto an inner liner. The collision generates a strongly radiating shock, and the radiation is trapped by the outer liner. As the implosion continues after the collision, the radiation temperature may continue to increase due to ongoing PdV (pressure times change in volume) work done by the implosion. In principal, the radiation temperature may increase to the point at which the outer liner burns through, becomes optically thin, and no longer traps the radiation. One application of the dynamic hohlraum is to drive an ICF (inertial confinement fusion) pellet with the trapped radiation field. Members of the dynamic hohlraum team at Sandia National Labs have used the pulsed power driver Z (20 MA, 100 ns) to create a dynamic hohlraum with temperature linearly ramping from 100 to 180 eV over 5 ns. On this shot zp214 a nested tungsten wire array of 4 and 2 cm diam with masses of 2 and 1 mg imploded onto a 2.5 mg plastic annulus at 5 mm diam. The current return can on this shot was slotted. It is likely the radiation temperature may be increased to over 200 eV by stabilizing the pinch with a solid current return can. A current return can with nine slots imprints nine filaments onto the imploding pinch. This degrades the optical trapping and the quality of the liner collision. A 1.6 mm diam capsule situated inside this dynamic hohlraum of zp214 would see 15 kJ of radiation impinging on its surface before the pinch itself collapses to a 1.6 mm diam. Dynamic hohlraum shots including pellets were scheduled to take place on Z in September of 1998.

Fusion research at Sandia’s z-pinch accelerator has produced an X-ray radiation source with a confirmed equivalent black body temperature of 1.8 000 000°C and an output of about 290 terawatts. This radiation source was created by containing the X-rays produced by a z-pinch plasma implosion in a special type of wire array radiation case, about the size of a spool of thread. By placing annular or cylindrical foam targets inside the wire array (a concept called dynamic or internal hohlraum), even higher temperatures can be attained by the rapidly compressing volume. The dynamic hohlraum as an X-ray source places stringent requirements on the quality of foam targets to minimize plasma instabilities during implosion. Nuclear microscopy, which used MeV-energy focused ion beams to characterize materials, provides unique capabilities for quantifying fabrication-induced defects in these targets with fine resolution. For example, the uniformity of representative annular and cylindrical foam targets has been nondestructively characterized in three dimensions by IMT (ion microtomography) with 50–100 μm spatial resolution. The uniformity of very large diameter annular targets (up to 24 mm outer diameter) was measured using STIM (scanning transmission ion microscopy) at several angular orientations. The distribution of diagnostic tracer elements used in some targets to probe the z-pinch plasma was measured by scanned PIXE (particle-induced X-ray emission) and RBS (Rutherford backscattering spectroscopy). The results of these analyses show that high quality foam targets are being delivered for z-pinch experiments, even when target development lead times are as short as 3 weeks.

Summary form only given. For many years, Sandia National Laboratories under contract to the Department of Energy has produced targets designed to understand complex ion beam and Z-pinch plasma physics. This poster focuses on the features of target designs that make them suitable for Z-pinch plasma physics applications. Precision diagnostic targets will prove critical in understanding the plasma physics model needed for future ion beam and Z-pinch design. Targets are designed to meet specific physics needs; in this case we have fabricated targets to maximize information about the end-on versus side-on X-ray emission and Z-pinch hohlraum development. In this poster we describe the fabrication and characterization techniques. We will include discussion of current targets under development as well as target fabrication capabilities.

A tentative schedule of experiments for the ignition campaign on the National Ignition Facility (NIF) has been developed. These experiments will be used to validate beam pointing and balance, to tune time history and symmetry of drive of NIF hohlraums, and to implode subignition and igniting targets. The initial target diagnostics are designed to validate beam pointing and to demonstrate the properties of the hohlraums.