A Dynamic Hohlraum (DH) is formed when arrays of tungsten wires driven by a high-current pulse implode and compress a cylindrical foam target. The resulting radiation is confined by the wire plasma and forms an intense, ~200–250 eV Planckian x-ray source. The internal radiation can be used for indirect drive inertial confinement fusion. The radiation emitted from the ends can be employed for radiation flow and material interaction studies. This external radiation is accompanied by an expanding blowoff plasma. In this paper, we have diagnosed this blowoff plasma using K-shell spectra of Mg tracer layers placed at the ends of some of the Dynamic Hohlraum targets. A similar diagnosis of the interior hohlraum has been carried out using Al and Mg tracers placed at 2mm depth from the ends. It is found that the blowoff plasma is about 20–25% as dense as that of the interior hohlraum, and that its presence does not significantly affect the outward flow of the nearly Planckian radiation field generated in the hohlraum interior. Finally, however, the electron temperature of the blowoff region, at ~120 eV, is only about half that of the interior hohlraum plasma.
We present designs for dynamic hohlraum z-pinch loads on the 28 MA, 140 ns driver ZR. The scaling of axially radiated power with current in dynamic hohlraums is reviewed. With adequate stability on ZR this scaling indicates that 30 TW of axially radiated power should be possible. The performance of the dynamic hohlraum load on the 20 MA, 100 ns driver Z is extensively reviewed. The baseline z-pinch load on Z is a nested tungsten wire array imploding onto on-axis foam. Data from a variety of x-ray diagnostics fielded on Z are presented. These diagnostics include x-ray diodes, bolometers, fast x-ray imaging cameras, and crystal spectrometers. Analysis of these data indicates that the peak dynamic radiation temperature on Z is between 250 and 300 eV from a diameter less than 1 mm. Radiation from the dynamic hohlraum itself or from a radiatively driven pellet within the dynamic hohlraum has been used to probe a variety of matter associated with the dynamic hohlraum: the tungsten z-pinch itself, tungsten sliding across the end-on apertures, a titanium foil over the end aperture, and a silicon aerogel end cap. Data showing the existence of asymmetry in radiation emanating from the two ends of the dynamic hohlraum is presented, along with data showing load configurations that mitigate this asymmetry. 1D simulations of the dynamic hohlraum implosion are presented and compared to experimental data. The simulations provide insight into the dynamic hohlraum behavior but are not necessarily a reliable design tool because of the inherently 3D behavior of the imploding nested tungsten wire arrays.
Diagnostic tracer layers of Al and/or Mg have been embedded in Dynamic Hohlraum targets which are imploded on Sandia National Laboratories Z generator by surrounding them with nested arrays of tungsten wires. The K-shell lines of these elements are observed, usually in absorption, in both time-resolved and time-integrated spectra. The radiation physics of line formation in this environment is well understood and captured with a detailed model. A {chi}{sup 2} fit to the measured line intensities is used in conjunction with the model to determine the hohlraums intrinsic properties. Among other features, our analyses find no evidence of intrinsic top-bottom asymmetry in the Dynamic Hohlraums.
In recent dynamic hohlraum experiments on the Z facility, Al and MgF{sub 2} tracer layers were embedded in cylindrical CH{sub 2} foam targets to provide K-shell lines in the keV spectral region for diagnosing the conditions of the interior hohlraum plasma. The position of the tracers was varied: sometimes they were placed 2 mm from the ends of the foam cylinder and sometimes at the ends of the cylinder. Also varied was the composition of the tracers in the sense that pure Al layers, pure MgF{sub 2} layers, or mixtures of the elements were employed on various shots. Time-resolved K-shell spectra of both Al and Mg show mostly absorption lines. These data can be analyzed with detailed configuration atomic models of carbon, aluminum, and magnesium in which spectra are calculated by solving the radiation transport equation for as many as 4100 frequencies. We report results from shot Z1022 to illustrate the basic radiation physics and the capabilities as well as limitations of this diagnostic method.
A quasi-spherical z-pinch may directly compress foam or deuterium and tritium in three dimensions as opposed to a cylindrical z-pinch, which compresses an internal load in two dimensions only. Because of compression in three dimensions the quasi-spherical z-pinch is more efficient at doing pdV work on an internal fluid than a cylindrical pinch. Designs of quasi-spherical z-pinch loads for the 28 MA 100 ns driver ZR, results from zero-dimensional (0D) circuit models of quasi-spherical implosions, and results from 1D hydrodynamic simulations of quasi-spherical implosions heating internal fluids will be presented. Applications of the quasi-spherical z-pinch implosions include a high radiation temperature source for radiation driven experiments, a source of neutrons for treating radioactive waste, and a source of fusion energy for a power generator.
Progress in understanding the physics of dynamic-hohlraums is reviewed for a system capable of generating 13 TW of axial radiation for high temperature (>200 eV) radiation-flow experiments and ICF capsule implosions.
A z-pinch radiation source has been developed that generates 60 {+-} 20 KJ of x-rays with a peak power of 13 {+-} 4 TW through a 4-mm diameter axial aperture on the Z facility. The source has heated NIF (National Ignition Facility)-scale (6-mm diameter by 7-mm high) hohlraums to 122 {+-} 6 eV and reduced-scale (4-mm diameter by 4-mm high) hohlraums to 155 {+-} 8 eV -- providing environments suitable for indirect-drive ICF (Inertial Confinement Fusion) studies. Eulerian-RMHC (radiation-hydrodynamics code) simulations that take into account the development of the Rayleigh-Taylor instability in the r-z plane provide integrated calculations of the implosion, x-ray generation, and hohlraum heating, as well as estimates of wall motion and plasma fill within the hohlraums. Lagrangian-RMHC simulations suggest that the addition of a 6 mg/cm{sup 3} CH{sub 2} fill in the reduced-scale hohlraum decreases hohlraum inner-wall velocity by {approximately}40% with only a 3--5% decrease in peak temperature, in agreement with measurements.
Characteristics of annular wire-array z-pinches as a function of wire number and at high wire number are reviewed. The data, taken primarily using aluminum wires on Saturn are comprehensive. The experiments have provided important insights into the features of wire-array dynamics critical for high x-ray power generation, and have initiated a renaissance in z-pinches when high numbers of wires are used. In this regime, for example, radiation environments characteristic of those encountered during the early pulses required for indirect-drive ICF ignition on the NIF have been produced in hohlraums driven by x-rays from a z-pinch, and are commented on here.