Mark S. Derzon

High Temperature Dynamic Hohlraums on the Pulsed Power Driver Z

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...

Insights and applications of two-dimensional simulations to Z-pinch experiments

A two-dimensional (2D) Eulerian radiation-magnetohydrodynamic code has been used to successfully simulate hollow metallic z-pinch experiments fielded on several facilities with a wide variety of drive conditions, time scales, and loads. The 2D simulations of these experiments reproduce important quantities of interest including the radiation pulse energy, power, and pulse width. This match is obtained through the use of an initial condition: the amplitude of a random density perturbation imposed on the initial plasma shell. The perturbations seed the development of magnetically driven Rayleigh–Taylor instabilities which greatly affect the dynamics of the implosion and the resulting production of radiation. Analysis of such simulations allows insights into the physical processes by which these calculations reproduce the experimental results. As examples, the insights gained from the simulations of Sandia “Z” accelerator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] experiments have allowed for the ...

Z pinch driven inertial confinement fusion target physics research at Sandia National Laboratories

Three hohlraum concepts are being pursued at Sandia National Laboratories (SNL) to investigate the possibility of using pulsed power driven magnetic implosions (Z pinches) to drive targets capable of fusion yields in the range 200-1000 MJ. This research is being conducted on SNLs Z facility, which is capable of driving peak currents of 20 MA in various Z pinch load configurations that produce implosion velocities as high as 7.5 × 107cm/s, X ray energies of 1-2 MJ and X ray powers of 100-250 TW. The first concept, denoted dynamic hohlraum, has achieved a temperature of 180 ± 14 eV in a configuration suitable for driving capsules. In addition, this concept has also achieved a temperature of 230 ± 18 eV in an arrangement suitable for driving an external hohlraum. The second concept, denoted static walled hohlraum, has achieved temperatures of ~80-100 eV. Experimental investigation of the third concept, denoted Z pinch driven hohlraum, has recently begun. The article discusses each of these hohlraum concepts and provides an overview of the experiments that have been conducted on these systems to date.

Scaling and optimization of the radiation temperature in dynamic hohlraums

A quasianalytic model of the dynamic hohlraum is presented. Results of the model are compared to both experiments and full numerical simulations with good agreement. The computational simplicity of the model allows one to find the behavior of the hohlraum radiation temperature as a function of the various parameters of the system and thus find optimum parameters as a function of the driving current. The model is used to investigate the benefits of ablative standoff and quasispherical Z pinches.

ICF target diagnostics on PBFA II (invited)

Particle Beam Fusion Accelerator II is a light‐ion fusion accelerator that is presently capable of irradiating a 6‐mm‐diam sphere with ∼50 kJ of 5.5‐MeV protons in ∼15 ns. An array of particle and x‐ray diagnostics fielded on proton Inertial Confinement Fusion target experiments quantifies the incident particle beam and the subsequent target response. An overview of the ion and target diagnostic setup and capabilities will be given in the context of recent proton beam experiments aimed at studying soft x‐ray emission from foam‐filled targets and the hydrodynamic response of exploding‐pusher targets. Ion beam diagnostics indicate ∼100 kJ of proton beam energy incident within a 1.2‐cm radius of the center of the diode with an azimuthal uniformity which varied between 6% and 29%. Foam‐filled target temperatures of 35 eV and closure velocities of 4 cm/μs were measured.

High-efficiency magnetic particle focusing using dielectrophoresis and magnetophoresis in a microfluidic device

We describe a novel technique that utilizes simultaneous implementation of dielectrophoresis (DEP) and magnetophoresis (MAP) to focus magnetic particles into streams for optical analysis of biological samples. This technique does not require sheath flow and utilizes a novel interdigitated electrode array chip that yields multiple streams of flowing magnetic particles in single-file columns. The MAP force placed particles in close proximity to the microelectrodes where they were subjected to a strong DEP force that generated the particle focusing effect. Particle focusing efficiency was improved using this combination DEP–MAP technique compared to DEP alone: particle stream widths were reduced ~47% and stream width variability was reduced 80% for focused streams of 8.5 µm diameter magnetic particles. 3 µm diameter magnetic particles were strongly focused with DEP–MAP (~4 µm wide streams with sub-µm variability in stream width) while DEP alone provided minimal focusing. Additional components of a prototype detection system were also demonstrated including an integrated magnetic pelleting component, a hand-held MHz frequency signal generator and a bench-top near-confocal microscope for optical analysis of flowing particles. Preliminary testing of a sandwich assay performed on the surface of magnetic particles showed 50 ppb detection levels of a surrogate biotoxin (ovalbumin) in a raw milk sample.

Observation of K α. X-ray satellites from a target heated by an intense ion beam

We have made the first observation of K α X-ray satellites from a target heated by an intense ion beam. The satellites are produced when thermal ionization due to beam heating is accompanied by inner-shell ionization from beam ion impact. The Particle Beam Fusion Accelerator II was used to irradiate a conical aluminum target with a proton beam. The nominal beam parameters were 50–75 kJ in a 1-cm spot, 15–20-ns pulse length, and 4–5-MeV protons at peak power. An elliptical crystal X-ray spectrograph inside a 1000-kg tungsten shield was used to record the spectra. The peak ion stage reached by the aluminum target was +8. Collisional radiative calculations were performed, which indicate a peak electron temperature of 20–60 eV.

Fast z-pinches as dense plasma, intense x-ray sources for plasma physics and fusion applications

As a result of advances in fast pulsed-power technology and cylindrical load fabrication, the Z pulsed-power accelerator at Sandia National Laboratories drives currents approaching 20 MA with a rise time of approximately 100 ns through cylindrically-symmetric loads (typically a cylindrical array consisting of a few hundred wires) to produce plasma densities in excess of , x-ray output energies approaching 2 MJ, radiation pulses as short as 4 ns and peak x-ray powers as high as . More than 15% of the stored electrical energy in the Z pulsed-power accelerator is converted into x-rays. The plasma pressures at peak compression are several TPa with electron temperatures that can exceed 3 keV at containment magnetic fields exceeding 1000 T. Depending on the atomic number and composition of the imploding plasma, these z-pinches can be tailored to produce intense sources of thermal x-rays, keV x-rays or neutrons. Although applications of these x-ray sources have included research in radiation material interaction, equations of state, opacity, astrophysics and x-ray lasers, the principal focus of the present research is to use them for indirect-drive inertial confinement fusion (ICF).

Spatially and temporally resolved crystal spectrometer for diagnosing high-temperature pinch plasmas on Z

We have developed a spatially and temporally resolved crystal spectrometer for analyzing a variety of pinch experiments on Z. The spectrometer uses a convex curved crystal to disperse spectra onto a flat microchannel plate (MCP) framing camera detector. A single wide, 1 cm, strip on the MCP is gated to provide temporal resolution. The spectral range governed by the 4 cm length of the MCP strip varies with the central Bragg angle and crystal. For a KAP crystal a typical range is 1500–2000 eV. This range can be shifted by translating the crystal along the optical axis to access different Bragg angles. The spectrometer can therefore measure K shell spectra of a wide variety of elements such as Al, Ti, and Fe. The short 1 cm width of the strip is spatially resolved with an imaging cross slit. With a 500 μm cross slit and magnification 1 the spatial resolution at the pinch is 1 mm. The instrument may also be fielded with seven time frames using a seven strip-line microchannel plate as the detector by sacrifici...

AXIAL DIAGNOSTIC PACKAGE FOR Z

The authors have developed and fielded an axial diagnostic package for the 20 MA, 100 ns, z-pinch driver Z. The package is used to diagnose dynamic hohlraum experiments which require an axial line of sight. The heart of the package is a reentrant cone originally used to diagnose ion-beam-driven hohlraums on PBFA-H. It has one diagnostic line of sight at 0 degrees, 4 at 6 degrees, and 4 at 9 degrees. In addition it has a number of viewing, alignment, and vacuum feedthrough ports. The front of the package sits approximately 5 feet from the pinch. This allows much closer proximity to the pinch, with inherently better resolution and signal, than is presently possible in viewing the pinch from the side. Debris that is preferentially directed along the axis is mitigated by two apertures for each line of sight, and by fast valves and imaging pinholes or cross slits for each diagnostic. In the initial run with this package they fielded a time resolved pinhole camera, a five-channel pinhole-apertured x-ray diode array, a bolometer, a spatially resolved time-integrated crystal spectrometer, and a spatially and temporally resolved crystal spectrometer. They present data obtained from these diagnostics in the dynamic hohlraum research conducted on Z.