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We present calculations for the field of view (FOV), image fluence, image monochromaticity, spectral acceptance, and image aberrations for spherical crystal microscopes, which are used as self-emission imaging or backlighter systems at large-scale high energy density physics facilities. Our analytic results are benchmarked with ray-tracing calculations as well as with experimental measurements from the 6.151 keV backlighter system at Sandia National Laboratories. The analytic expressions can be used for x-ray source positions anywhere between the Rowland circle and object plane. This enables quick optimization of the performance of proposed but untested, bent-crystal microscope systems to find the best compromise between FOV, image fluence, and spatial resolution for a particular application.

The magnetized liner inertial fusion concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)] utilizes a magnetic field and laser heating to relax the pressure requirements of inertial confinement fusion. The first experiments to test the concept [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] were conducted utilizing the 19 MA, 100 ns Z machine, the 2.5 kJ, 1 TW Z Beamlet laser, and the 10 T Applied B-field on Z system. Despite an estimated implosion velocity of only 70 km/s in these experiments, electron and ion temperatures at stagnation were as high as 3 keV, and thermonuclear deuterium-deuterium neutron yields up to 2 × 1012 have been produced. X-ray emission from the fuel at stagnation had widths ranging from 50 to 110 μm over a roughly 80% of the axial extent of the target (6–8 mm) and lasted approximately 2 ns. X-ray yields from these experiments are consistent with a stagnation density of the hot fuel equal to 0.2–0.4 g/cm3. In these experiments, up to 5 × 1010 secondary deuterium-...

Magnetized Liner Inertial Fusion experiments performed at Sandia's Z facility have demonstrated significant thermonuclear fusion neutron yields (∼1012 DD neutrons) from multi-keV deuterium plasmas inertially confined by slow (∼10 cm/μs), stable, cylindrical implosions. Effective magnetic confinement of charged fusion reactants and products is signaled by high secondary DT neutron yields above 1010. Analysis of extensive power, imaging, and spectroscopic x-ray measurements provides a detailed picture of ∼3 keV temperatures, 0.3 g/cm3 densities, gradients, and mix in the fuel and liner over the 1–2 ns stagnation duration.

By magnetizing the fusion fuel in inertial confinement fusion (ICF) systems, the required stagnation pressure and density can be relaxed dramatically. This happens because the magnetic field insulates the hot fuel from the cold pusher and traps the charged fusion burn products. This trapping allows the burn products to deposit their energy in the fuel, facilitating plasma self-heating. Here, we report on a comprehensive theory of this trapping in a cylindrical DD plasma magnetized with a purely axial magnetic field. Using this theory, we are able to show that the secondary fusion reactions can be used to infer the magnetic field-radius product, BR, during fusion burn. This parameter, not ρR, is the primary confinement parameter in magnetized ICF. Using this method, we analyze data from recent Magnetized Liner Inertial Fusion experiments conducted on the Z machine at Sandia National Laboratories. We show that in these experiments BR ≈ 0.34(+0.14/−0.06) MG · cm, a ∼ 14× increase in BR from the initial value, and confirming that the DD-fusion tritons are magnetized at stagnation. This is the first experimental verification of charged burn product magnetization facilitated by compression of an initial seed magnetic flux.

We have developed a diagnostic system that measures the spectrally integrated (i.e. the total) energy and power radiated by a pulsed blackbody x-ray source. The total-energy-and-power (TEP) diagnostic system is optimized for blackbody temperatures between 50 and 350 eV. The system can view apertured sources that radiate energies and powers as high as 2 MJ and 200 TW, respectively, and has been successfully tested at 0.84 MJ and 73 TW on the $Z$ pulsed-power accelerator. The TEP system consists of two pinhole arrays, two silicon-diode detectors, and two thin-film nickel bolometers. Each of the two pinhole arrays is paired with a single silicon diode. Each array consists of a $38\ifmmode\times\else\texttimes\fi{}38$ square array of 10-$\ensuremath{\mu}\mathrm{m}$-diameter pinholes in a 50-$\ensuremath{\mu}\mathrm{m}$-thick tantalum plate. The arrays achromatically attenuate the x-ray flux by a factor of $\ensuremath{\sim}1800$. The use of such arrays for the attenuation of soft x rays was first proposed by Turner and co-workers [Rev. Sci. Instrum. 70, 656 (1999)]. The attenuated flux from each array illuminates its associated diode; the diode's output current is recorded by a data-acquisition system with 0.6-ns time resolution. The arrays and diodes are located 19 and 24 m from the source, respectively. Because the diodes are designed to have an approximately flat spectral sensitivity, the output current from each diode is proportional to the x-ray power. The nickel bolometers are fielded at a slightly different angle from the array-diode combinations, and view (without pinhole attenuation) the same x-ray source. The bolometers measure the total x-ray energy radiated by the source and---on every shot---provide an in situ calibration of the array-diode combinations. Two array-diode pairs and two bolometers are fielded to reduce random uncertainties. An analytic model (which accounts for pinhole-diffraction effects) of the sensitivity of an array-diode combination is presented.

Using the physical process of ultraintense field ionization of high charge states of inert gas ions, we have developed a method of peak intensity measurement at the focus of high energy short pulse lasers operating in single shot mode. The technique involves detecting ionization products created from a low pressure gas target at the laser focus via time of flight detector. The observation of high ion charge states collected by the detector yields peak intensity at the focus when compared with the results obtained from well established tunnel ionization models. An initial peak intensity measurement of 5× 1016 W cm-2 was obtained for a 1.053 μm center wavelength, 0.4 J pulse with 1 ps pulse duration focused with an f5.5 off-axis parabola. Experiments with multijoule level, 500 fs laser pulses are on the way. © 2006 American Institute of Physics.

We have improved deformable mirror approach to allow good parabolic deformation for efficient thermal lens compensation. Our design uses an annulus to push onto the back surface of a flat mirror substrate, simply supported at the outer edge, thereby creating a parabolic deformation within the encircled area. We built an assembly using a 25.4 mm diameter, 1 mm thick mirror with a wedge of less than 10 arc seconds that was deformed with a 12 mm diameter annulus at the back of the mirror. Using a Shack-Hartman wavefront sensor we performed careful measurements to characterize the performance of the mirrors.

Greater control over complex weapons systems, and the elements which comprise them , such as ne tworks of manned and unmanned vehicles, including intelligent sensors and weapons, requires special attention to s ystems integration issues . This includes software safety and other technical challenges and risks , such as schedule and costs associat ed with acquisition and total ow ne rship . How to carry out such programs and retain the requisite level of control , is a special and somewhat new problem . Similar issues exist for the U.S. and the Australian militar y. These issues, and how they are integral to the whole realm of Systems Engineering are discussed, with examples from specific complex weapons programs such as t he U.S Army's Future Combat System . The top five perceived risks , and how software safety plays a significant role in these risks, for Systems o f Systems in general are discussed , Potential Systems Engineering approaches and processes which can be applied toward reducing these risks are described .

A combination of a 400 ns, 300 mJ, 640 nm dye laser, and an optical streak camera have been used to demonstrate that time-resolved shadowgrams can be made of the implosion phase of tungsten wire arrays. Initial experiments have shown that mirror lifetime and spatial resolution are issues for this diagnostic technique. Nonetheless, these experiments have provided new information on wire array dynamics; specifically, they show that even with a 0.46 mm wire spacing, the high density regions formed by the wires, are separate until 30 ns into the main drive current. Peak currents of 6.6 MA were obtained 40 ns after the start of the current, while peak radiated powers of 85 TW were measured at 50 ns.

We have performed two sets of experiments looking at laser-driven radiating blast waves. In the first set of experiments the effect of a drive laser’s passage through a background gas on the hydrodynamical evolution of blast waves was examined. The laser’s passage heated a channel in the gas, creating a region where a portion of the blast wave front had an increased velocity, leading to the formation of a bump-like protrusion on the blast wave. The second set of experiments involved the use of regularly spaced wire arrays used to induce perturbations on a blast wave surface. The decay of these perturbations as a function of time was measured for various wave number perturbations and found to be in good agreement with theoretical predictions.

The authors have explored the high velocity implosion limit of krypton gas-puff z-pinch implosions in an effort to efficiently generate K-shell radiation from high-Z elements. Using Saturn, a fast electrical generator, they imploded krypton gas-puff z pinches attaining implosion velocities as high as 125 cm/{mu}s. They observed the magneto Raleigh-Taylor instability in the fastest implosions. Despite the high implosion velocities, the plasma was never observed to attain the He-like ionization state, most likely because of inadequate density giving too long an ionization time. The dominant ionization state at peak compression was Ne-like Kr. They measured radiation yields as high as 100 J from Kr K{sub {alpha}} transitions. They used two different nozzle configurations for these experiments: 2.5-cm mean diameter nozzles and 3.5-cm mean diameter nozzles. Both sets of nozzles had exits with a 1-cm width. These nozzles are designed to have a 5-degree inward tilt to reduce the effect of zippering. The gas valve timing was adjusted relative to the generator so that the implosion occurred during the time when the gas density was increased. This also acted to reduce the effect of zippering. VUV preionization of the Kr was used for all of these shots. The pinch length wasmore » 2 cm. Current in the z pinch was measured with both B-dot current monitors and piezoelectric pressure transducers.« less

We have developed wire-array $z$-pinch scaling relations for plasma-physics and inertial-confinement-fusion (ICF) experiments. The relations can be applied to the design of $z$-pinch accelerators for high-fusion-yield $(\ensuremath{\sim}0.4\phantom{\rule{0.3em}{0ex}}\mathrm{GJ∕shot})$ and inertial-fusion-energy $(\ensuremath{\sim}3\phantom{\rule{0.3em}{0ex}}\mathrm{GJ∕shot})$ research. We find that $({\ensuremath{\delta}}_{a}∕{\ensuremath{\delta}}_{\mathrm{RT}})\ensuremath{\propto}{(m∕\ensuremath{\ell})}^{1∕4}{(R\ensuremath{\Gamma})}^{\ensuremath{-}1∕2}$, where ${\ensuremath{\delta}}_{a}$ is the imploding-sheath thickness of a wire-ablation-dominated pinch, ${\ensuremath{\delta}}_{\mathrm{RT}}$ is the sheath thickness of a Rayleigh-Taylor-dominated pinch, $m$ is the total wire-array mass, $\ensuremath{\ell}$ is the axial length of the array, $R$ is the initial array radius, and $\ensuremath{\Gamma}$ is a dimensionless functional of the shape of the current pulse that drives the pinch implosion. When the product $R\ensuremath{\Gamma}$ is held constant the sheath thickness is, at sufficiently large values of $m∕\ensuremath{\ell}$, determined primarily by wire ablation. For an ablation-dominated pinch, we estimate that the peak radiated x-ray power ${P}_{r}\ensuremath{\propto}{(I∕{\ensuremath{\tau}}_{i})}^{3∕2}R\ensuremath{\ell}\ensuremath{\Phi}\ensuremath{\Gamma}$, where $I$ is the peak pinch current, ${\ensuremath{\tau}}_{i}$ is the pinch implosion time, and $\ensuremath{\Phi}$ is a dimensionless functional of the current-pulse shape. This scaling relation is consistent with experiment when $13\phantom{\rule{0.3em}{0ex}}\mathrm{MA}\ensuremath{\leqslant}I\ensuremath{\leqslant}20\phantom{\rule{0.3em}{0ex}}\mathrm{MA}$, $93\phantom{\rule{0.3em}{0ex}}\mathrm{ns}\ensuremath{\leqslant}{\ensuremath{\tau}}_{i}\ensuremath{\leqslant}169\phantom{\rule{0.3em}{0ex}}\mathrm{ns}$, $10\phantom{\rule{0.3em}{0ex}}\mathrm{mm}\ensuremath{\leqslant}R\ensuremath{\leqslant}20\phantom{\rule{0.3em}{0ex}}\mathrm{mm}$, $10\phantom{\rule{0.3em}{0ex}}\mathrm{mm}\ensuremath{\leqslant}\ensuremath{\ell}\ensuremath{\leqslant}20\phantom{\rule{0.3em}{0ex}}\mathrm{mm}$, and $2.0\phantom{\rule{0.3em}{0ex}}\mathrm{mg}∕\mathrm{cm}\ensuremath{\leqslant}m∕\ensuremath{\ell}\ensuremath{\leqslant}7.3\phantom{\rule{0.3em}{0ex}}\mathrm{mg}∕\mathrm{cm}$. Assuming an ablation-dominated pinch and that $R\ensuremath{\ell}\ensuremath{\Phi}\ensuremath{\Gamma}$ is held constant, we find that the x-ray-power efficiency ${\ensuremath{\eta}}_{x}\ensuremath{\equiv}{P}_{r}∕{P}_{a}$ of a coupled pinch-accelerator system is proportional to ${({\ensuremath{\tau}}_{i}{P}_{r}^{7∕9})}^{\ensuremath{-}1}$, where ${P}_{a}$ is the peak accelerator power. The pinch current and accelerator power required to achieve a given value of ${P}_{r}$ are proportional to ${\ensuremath{\tau}}_{i}$, and the requisite accelerator energy ${E}_{a}$ is proportional to ${\ensuremath{\tau}}_{i}^{2}$. These results suggest that the performance of an ablation-dominated pinch, and the efficiency of a coupled pinch-accelerator system, can be improved substantially by decreasing the implosion time ${\ensuremath{\tau}}_{i}$. For an accelerator coupled to a double-pinch-driven hohlraum that drives the implosion of an ICF fuel capsule, we find that the accelerator power and energy required to achieve high-yield fusion scale as ${\ensuremath{\tau}}_{i}^{0.36}$ and ${\ensuremath{\tau}}_{i}^{1.36}$, respectively. Thus the accelerator requirements decrease as the implosion time is decreased. However, the x-ray-power and thermonuclear-yield efficiencies of such a coupled system increase with ${\ensuremath{\tau}}_{i}$. We also find that increasing the anode-cathode gap of the pinch from $2\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}4\phantom{\rule{0.3em}{0ex}}\mathrm{mm}$ increases the requisite values of ${P}_{a}$ and ${E}_{a}$ by as much as a factor of 2.

Nested wire-array Z pinches are shown to generate soft x-ray radiation pulse shapes required for three-shock isentropic compression and hot-spot ignition of high-yield inertial confinement fusion capsules. We demonstrate a reproducible and tunable foot pulse (first shock) produced by interaction of the outer and inner arrays. A first-step pulse (second shock) is produced by inner array collision with a central CH{sub 2} foam target. Stagnation of the inner array at the axis produces the third shock. Capsules optimized for several of these shapes produce 290-900 MJ fusion yields in 1D simulations.

A large-aperture (30-cm) kilojoule-class Nd:glass laser system known as Z-Beamlet has been constructed to perform x-ray radiography of high-energy-density science experiments conducted on the Z facility at Sandia National Laboratories, Albuquerque, New Mexico. The laser, operating with typical pulse durations from 0.3 to 1.5 ns, employs a sequence of successively larger multipass amplifiers to achieve up to 3-kJ energy at 1054 nm. Large-aperture frequency conversion and long-distance beam transport can provide on-target energies of up to 1.5 kJ at 527 nm.

Using a micro channel plate (MCP), we have developed a sensitive method for measuring the onset of laser damage by detecting liberated surface ions and XUV radiation from the laser induced surface plasma. This method is insensitive to optical alignment and therefore assures good repeatability over numerous measurements.

Nested tungsten wire arrays (20-mm on 12-mm diam.) are shown for the first time to operate in a current-transfer mode at 16-19 MA, even for azimuthal interwire gaps of 0.2 mm that are the smallest typically used for any array experiment. After current transfer, the inner wire array shows discrete wire ablation and implosion characteristics identical to that of a single array, such as axially nonuniform ablation, delayed acceleration, and trailing mass and current. The presence of trailing mass from the outer and the inner arrays may play a role in determining nested array performance.

To explore the validity of theories forwarded to explain the dynamics of hydrodynamic perturbations on high Mach number blast waves, we have studied the decay rate of perturbations on blast waves traveling through nitrogen gas. In our experiments, 1 kJ pulses from the Z-Beamlet laser at Sandia National Laboratories illuminated solid targets immersed in gas and created blast waves. The polytropic index implied by comparing experiment to theoretical predictions is compared to simulation results.

We present the first comprehensive study of high wire-number, wire-array Z-pinch dynamics at 14-18 MA using x-ray backlighting and optical shadowgraphy diagnostics. The cylindrical arrays retain slowly expanding, dense wire cores at the initial position up to 60% of the total implosion time. Azimuthally correlated instabilities at the array edge appear during this stage which continue to grow in amplitude and wavelength after the start of bulk motion, resulting in measurable trailing mass that does not arrive on axis before peak x-ray emission.

We have measured the x-ray power and energy radiated by a tungsten-wire-array $z$ pinch as a function of the peak pinch current and the width of the anode-cathode gap at the base of the pinch. The measurements were performed at 13- and 19-MA currents and 1-, 2-, 3-, and 4-mm gaps. The wire material, number of wires, wire-array diameter, wire-array length, wire-array-electrode design, normalized-pinch-current time history, implosion time, and diagnostic package were held constant for the experiments. To keep the implosion time constant, the mass of the array was increased as ${I}^{2}$ (i.e., the diameter of each wire was increased as $I),$ where $I$ is the peak pinch current. At 19 MA, the mass of the 300-wire 20-mm-diam 10-mm-length array was 5.9 mg. For the configuration studied, we find that to eliminate the effects of gap closure on the radiated energy, the width of the gap must be increased approximately as $I.$ For shots unaffected by gap closure, we find that the peak radiated x-ray power ${P}_{r}\ensuremath{\propto}{I}^{1.24\ifmmode\pm\else\textpm\fi{}0.18},$ the total radiated x-ray energy ${E}_{r}\ensuremath{\propto}{I}^{1.73\ifmmode\pm\else\textpm\fi{}0.18},$ the x-ray-power rise time ${\ensuremath{\tau}}_{r}\ensuremath{\propto}{I}^{0.39\ifmmode\pm\else\textpm\fi{}0.34},$ and the x-ray-power pulse width ${\ensuremath{\tau}}_{w}\ensuremath{\propto}{I}^{0.45\ifmmode\pm\else\textpm\fi{}0.17}.$ Calculations performed with a time-dependent model of an optically thick pinch at stagnation demonstrate that the internal energy and radiative opacity of the pinch are not responsible for the observed subquadratic power scaling. Heuristic wire-ablation arguments suggest that quadratic power scaling will be achieved if the implosion time ${\ensuremath{\tau}}_{i}$ is scaled as ${I}^{\ensuremath{-}1/3}.$ The measured 1\ensuremath{\sigma} shot-to-shot fluctuations in ${P}_{r},$ ${E}_{r},$ ${\ensuremath{\tau}}_{r},$ ${\ensuremath{\tau}}_{w},$ and ${\ensuremath{\tau}}_{i}$ are approximately 12%, 9%, 26%, 9%, and 2%, respectively, assuming that the fluctuations are independent of $I.$ These variations are for one-half of the pinch. If the half observed radiates in a manner that is statistically independent of the other half, the variations are a factor of ${2}^{1/2}$ less for the entire pinch. We calculate the effect that shot-to-shot fluctuations of a single pinch would have on the shot-success probability of the double-pinch inertial-confinement-fusion driver proposed by Hammer et al. [Phys. Plasmas 6, 2129 (1999)]. We find that on a given shot, the probability that two independent pinches would radiate the same peak power to within a factor of $1\ifmmode\pm\else\textpm\fi{}\ensuremath{\alpha}$ (where $0l~\ensuremath{\alpha}\ensuremath{\ll}1)$ is equal to $\mathrm{erf}(\ensuremath{\alpha}/2\ensuremath{\sigma}),$ where \ensuremath{\sigma} is the 1\ensuremath{\sigma} fractional variation of the peak power radiated by a single pinch. Assuming \ensuremath{\alpha} must be $l~7%$ to achieve adequate odd-Legendre-mode radiation symmetry for thermonuclear-fusion experiments, \ensuremath{\sigma} must be $l3%$ for the shot-success probability to be $g~90%.$ The observed ${(12/2}^{1/2})%=8.5%$ fluctuation in ${P}_{r}$ would provide adequate symmetry on 44% of the shots. We propose that three-dimensional radiative-magnetohydrodynamic simulations be performed to quantify the sensitivity of the x-ray emission to various initial conditions, and to determine whether an imploding $z$ pinch is a spatiotemporal chaotic system.

Annular wire array implosions on the Sandia Z-machine can produce >200 TW and 1-2 MJ of soft x rays in the 0.1-10 keV range. The x-ray flux and debris in this environment present significant challenges for radiographic diagnostics. X-ray backlighting diagnostics at 1865 and 6181 eV using spherically-bent crystals have been fielded on the Z-machine, each with a ~ 0.6 eV spectral bandpass, 10 μm spatial resolution, and a 4 mm by 20 mm field of view. The Z-Beamlet laser, a 2-TW, 2-kJ Nd:glass laser (λ=527 nm), is used to produce 0.1-1 J x-ray sources for radiography. The design, calibration, and performance of these diagnostics is presented.

A kilojoule-class Nd:Glass laser known as Z-Beamlet has been constructed to perform x-ray radiography of high energy density science experiments conducted on the megajoule-class z-pinch Z facility at Sandia National Laboratories. The combination of Z-Beamlet and Z provide a unique platform for studying high energy density science in the laboratory.

Summary form only given. The z-pinch driven hohlraum high-yield concept is in the process of being experimentally validated on the Z accelerator, qualifying its performance with respect to hohlraum energetics, radiation symmetry, pulse shaping, capsule preheat, and z-pinch physics scaling. Key parts of the assessment effort are the measurement and simulation of capsule radiation symmetry on Z, and the theoretical scaling of radiation symmetry from the hohlraum conditions on Z (70-90 eV) to the 200-250 eV hohlraum temperatures characteristic of a device for driving high yield capsules. Recently, we have begun to use the Z-beamlet laser (ZBL) to create high-energy (4.75 - 6.7 keV) X-rays for backlighting capsule implosion experiments on Z in point projection mode. The hohlraum geometry is a single-sided power feed analog to the high-yield concept, in which a central secondary hohlraum containing the capsule is driven by a z-pinch primary hohlraum at each end. Images at 4.75 and 6.7 keV backlighting energies have been obtained, mapping the trajectory and distortion of a 2-mm initial diameter plastic ablator capsule over multiple shots.

Summary from only given. The Z-machine is a Z-pinch device, using pulsed power methods to implode wire arrays and create high density plasmas and consequent x-ray emission. Small cavities (holhraums) are used to symmetrically bathe capsules in this radiation, causing the capsules compress for ICF studies. Radiography performed during an accelerator shot shows implosion symmetry and a factor of 2 compression at 14 ns after peak accelerator radiation The new radiography ability provided by a Z-beamlet laser allows this implosion symmetry to be studied and improved.

We present observations for 20-MA wire-array z pinches of an extended wire ablation period of 57%+/-3% of the stagnation time of the array and non-thin-shell implosion trajectories. These experiments were performed with 20-mm-diam wire arrays used for the double- z -pinch inertial confinement fusion experiments [M. E. Cuneo, Phys. Rev. Lett. 88, 215004 (2002)] on the Z accelerator [R. B. Spielman, Phys. Plasmas 5, 2105 (1998)]. This array has the smallest wire-wire gaps typically used at 20 MA (209 microm ). The extended ablation period for this array indicates that two-dimensional (r-z) thin-shell implosion models that implicitly assume wire ablation and wire-to-wire merger into a shell on a rapid time scale compared to wire acceleration are fundamentally incorrect or incomplete for high-wire-number, massive (>2 mg/cm) , single, tungsten wire arrays. In contrast to earlier work where the wire array accelerated from its initial position at approximately 80% of the stagnation time, our results show that very late acceleration is not a universal aspect of wire array implosions. We also varied the ablation period between 46%+/-2% and 71%+/-3% of the stagnation time, for the first time, by scaling the array diameter between 40 mm (at a wire-wire gap of 524 mum ) and 12 mm (at a wire-wire gap of 209 microm ), at a constant stagnation time of 100+/-6 ns . The deviation of the wire-array trajectory from that of a thin shell scales inversely with the ablation rate per unit mass: f(m) proportional[dm(ablate)/dt]/m(array). The convergence ratio of the effective position of the current at peak x-ray power is approximately 3.6+/-0.6:1 , much less than the > or = 10:1 typically inferred from x-ray pinhole camera measurements of the brightest emitting regions on axis, at peak x-ray power. The trailing mass at the array edge early in the implosion appears to produce wings on the pinch mass profile at stagnation that reduces the rate of compression of the pinch. The observation of precursor pinch formation, trailing mass, and trailing current indicates that all the mass and current do not assemble simultaneously on axis. Precursor and trailing implosions appear to impact the efficiency of the conversion of current (driver energy) to x rays. An instability with the character of an m = 0 sausage grows rapidly on axis at stagnation, during the rise time of pinch power. Just after peak power, a mild m = 1 kink instability of the pinch occurs which is correlated with the higher compression ratio of the pinch after peak power and the decrease of the power pulse. Understanding these three-dimensional, discrete-wire implosion characteristics is critical in order to efficiently scale wire arrays to higher currents and powers for fusion applications.

Summary form only given. The high-yield inertial confinement fusion concept based on a double-ended Z-pinch driven hohlraum tolerates the degree of spatial inhomogeneity present in Z-pinch plasma radiation sources by utilizing a relatively large hohlraum wall surface to provide spatial smoothing of the radiation delivered to the fusion capsule. The Z-pinch radiation sources are separated from the capsule by radial spoke arrays. Key physics issues for this concept are the behavior of the spoke array (effect on the Z-pinch performance, X-ray transmission) and the uniformity of the radiation flux incident on the surface of the capsule. Experiments are underway on the Z accelerator at Sandia National Laboratories to gain understanding of these issues in a single-sided drive geometry. These experiments seek to measure the radiation coupling among the Z-pinch, source hohlraum, and secondary hohlraum, as well as the uniformity of the radiation flux striking a foam witness ball diagnostic positioned in the secondary hohlraum.

Summary form only given as follows. Fast, high current Z-pinch implosions are used to produce intense X-ray pulses for various applications. For high-energy photon production and for inertial fusion applications, the imploding Z pinch can achieve velocities between 50 and 100 cm//spl mu/s. To image such implosions, a high time resolution is needed. Furthermore, the final pinches formed can be only 1 to 1.5 mm in diameter but 20 mm long. Given a basic microchannel plate resolution of 80 /spl mu/m, then a high magnification (>1.5) is required to maintain good spatial resolution. To satisfy these requirements, we have designed and fielded a nine-frame, gated-MCP pinhole camera on the 20-MA Z accelerator. Each MCP frame is 6 cm by 2 cm, and is gated with a 100 ps duration pulse. We will describe the design and operation of this camera, in addition to showing data from Z-pinch and hohlraum experiments using this camera.

Summary form only given. Recent development of high power Z-pinches (>150 TW) on the Z driver has permitted the study of high-temperature, radiation-driven hohlraums. Three complementary, Z-pinch source-hohlraum-ICF capsule configurations are being developed to harness the X-ray output of these Z-pinch's. These are the dynamic-hohlraum, static-wall hohlraum, and Z-pinch-driven hohlraum concepts. Each has different potential strengths and concerns. In this paper, we report on the first experiments with the Z-pinch-driven hohlraum (ZPDH) concept. A high-yield ICF capsule design for this concept appears feasible, when driven by Z-pinches from a 60 MA-class driver.

We report experiments on high power laser driven radiative blast waves. By focusing 100J – 1 kJ laser pulses onto pin targets immersed in gases we attempted to produce the pressure-driven thin shell overstability thought to play a major role in supernova remnant hydrodynamics.

The US Department of Energy has supported a substantial research program in Inertial Confinement Fusion (ICF) since the early 1970s. Over the ensuing 25 years, pulsed power approaches to inertial fusion have remained of interest primarily because of the high energy, efficiency, and relatively low cost of the technology when compared to the mainline ICF approach involving large glass lasers. These compelling advantages, however, have been tempered with the difficulty in concentrating the energy in space and time to create the high energy and power density required to achieve temperatures useful in indirect drive ICF. Since the Beams '96 meeting, the situation has changed dramatically, and extremely high X-ray power (290 TW) and energy (1.8 MJ) have been produced in fast z-pinch implosions on the Z accelerator. These sources have been utilized to heat hohlraums to >150 eV and have opened the door to important ICF capsule experiments. Although light ion beams offer a long term potential for fusion energy, we are suspending our ion beam research this year to maximize progress with z pinches.

Summary form only given. Pulsed power, such as the Sandia Z-machine, is contributing our understanding of where codes model reality. Fine-zoned Eulerian (and ALE) calculations, for a wide variety of geometries, show elaborate structure such as jets and instabilities, which are not calculated by Lagrangian codes. More and faster computers allow these fine-zoned (1.0 micron or less on a side) calculations to be done. The Z-machine, along with modern diagnostics, which obtain time-dependent images for more than one photon energy response, are well suited to helping us understand, in at least one case, how much of this structure is real. The geometry considered here is a CH tamped hole in a Au hohlraum for which Eulerian calculations show a jet of Au forming at a corner of the Au and moving through the CH tamping. Subsequently, large amounts of Au move into the hole. Lagrangian calculations show the Au to have only minimal motion. Here pulsed power enables us to determine the better computer model.

In the past three years, tremendous strides have been made in X-ray production using high-current Z-pinches. Today, the X-ray energy and power output of the Z accelerator (formerly PBFA II) is the largest available in the laboratory. These Z-pinch X-ray sources have great potential to drive high-yield inertial confinement fusion (ICF) reactions at affordable cost if several challenging technical problems can be overcome. Technical challenges in three key areas are discussed in this paper: the design of a target for high yield, the development of a suitable pulsed power driver, and the design of a target chamber capable of containing the high fusion yield.

An inertial-confinement-fusion (ICF) concept using two 60-MA $Z$ pinches to drive a cylindrical hohlraum to 220 eV has been recently proposed. The first capsule implosions relevant to this concept have been performed at the same physical scale with a lower 20-MA current, yielding a $70\ifmmode\pm\else\textpm\fi{}5\text{ }\text{ }\mathrm{e}\mathrm{V}$ capsule drive. The capsule shell shape implies a polar radiation symmetry, the first high-accuracy measurement of this type in a pulsed-power-driven ICF configuration, within a factor of 1.6--4 of that required for scaling to ignition. The convergence ratio of 14--21 is to date the highest in any pulsed-power ICF system.

Summary form only given. We are now performing imploding annular wire-array experiments on the PBFA-Z accelerator. The experimental diagnostics include X-ray diode detectors (XRDs), photoconducting diode detectors (PCDs), and X-ray pinhole cameras both time-integrating and time-dependent. We have set up a pulsed-laser x-ray source for calibration of these diagnostics. A pulsed 10-joule Nd:YAG laser is shot onto a low-Z target, and a combination of filters then provides a large-area, mono-energetic source with a one-nanosecond pulse width. Measurements of the diagnostic's sensitivity between 160 eV and 3 keV can be determined with this source with the appropriate combination of target and filter. The reference standard is a 1024/spl times/1024 pixel X-ray CCD that measures the source intensity and is calibrated at 100 eV to 2500 eV.

Summary form only given, as follows. Capsule radiation symmetry is a crucial issue in the design of the z-pinch driven hohlraum approach to high-yield inertial confinement fusion. Capsule symmetry may be influenced by the power imbalance of the two z-pinch X-ray sources, and by hohlraum effects (geometry, time-dependent albedo, wall motion). 2-D and 3-D radiosity ("viewfactor") models have been used to design hohlraums that optimize the capsule radiation symmetry for experiments on Z as well as for high-yield targets. The goals of capsule symmetry experiments on Z include commissioning the Z-beamlet backlighter laser and requisite initial imaging detectors, measuring capsule flux asymmetry at the several percent level, and demonstrating understanding of the factors influencing capsule asymmetry in z-pinch hohlraums. Design and simulation efforts have focused on: (a) hohlraum radiation transport models to determine the sensitivity of capsule flux asymmetry to hohlraum geometry, top-bottom pinch power imbalance, and pinch mistiming, (a) 2-mm diameter, 60-/spl mu/m thick plastic shells designed to implode within 10 ns after the secondary hohlraum reaches its peak drive temperature of 75-85 eV, providing a suitable target for initial experiments at lower backlighting energies (2.5-3 keV), (b) 3- to 5-mm diameter thin (20-40 /spl mu/m) Ge-doped plastic shells designed for backlighting with Ti K-shell X-rays to assess symmetry early in the capsule implosion, and (c) uniform density foam spheres (/spl sim/50-100 mg/cc) also designed for Ti backlighting to image the trajectory of the shock/ablation front feature throughout the drive pulse. We present the results of postprocessed 1- and 2-D radiation-hydrodynamics calculations for each type of symmetry target, describing their advantages and disadvantages, and show comparisons with preliminary experimental data.

Summary form only given. In Z-pinch experiments on the Z accelerator, we are evaluating the feasibility of using a radiation-driven vacuum secondary hohlraum for indirect-drive ICF. To develop a system with the potential to scale to ignition and high yield, we must demonstrate a high degree of radiation flux symmetry at the capsule position. In initial experiments with single-sided illumination of the secondary, we have used a 5.0-mm-diameter low density foam ball imaged by a gated X-ray framing pinhole camera looking through a 6.5-mm tamped aperture to diagnose the large time-dependent asymmetry in polar radiation flux. For peak hohlraum radiation temperatures in the range of 70 100 eV, foams of about 50 mg/cc will support a transonic radiation front propagating with a sharp total transmission edge (combined foam self-emission and transmitted hohlraum wall backlight). The transmission edge can be tracked for comparison with radiation-hydrodynamics and 3D radiosity simulations.

Summary form only given. Radiation environments characteristic of those encountered during the low-temperature foot pulse and subsequent higher-temperature early-step pulses required for indirect-drive ICF ignition on the National Ignition Facility (NIF) are desired in order to provide a platform to better understand the dynamics of NIF hohlraums and capsules prior to NIF completion. In this paper, we show that an axial hohlraum using the static-wall-hohlraum geometry heated by X-rays from a Z-pinch on the Z generator is capable of providing environments for such pre-NIF studies as well as for diagnostic applications.

Simulations of a double Z-pinch hohlraum, relevant to the high-yield inertial-confinement-fusion concept, predict that through geometry design the time-integrated P 2 Legendre mode drive asymmetry can be systematically controlled from positive to negative coefficient values. Studying capsule elongation, recent experiments on Z confirm such control by varying the secondary hohlraum length. Since the experimental trend and optimum length are correctly modeled, confidence is gained in the simulation tools; the same tools predict capsule drive uniformity sufficient for high-yield fusion ignition.

A double Z pinch driving a cylindrical secondary hohlraum from each end has been developed which can indirectly drive intertial confinement fusion capsule implosions with time-averaged radiation fields uniform to 2%-4%. 2D time-dependent view factor and 2D radiation hydrodynamic simulations using the measured primary hohlraum temperatures show that capsule convergence ratios of at least 10 with average distortions from sphericity ofDelta r/ror=30% are possible on the Z accelerator and may meet radiation symmetry requirements for scaling to fusion yields of200 MJ.

The U. S. Department of Energy is supporting research at Sandia National Laboratories (SNL) to investigate the possibility of using pulsed power driven magnetic implosions (z-pinches) to drive inertial confinement fusion (ICF) targets.1 This research is being conducted on SNL’s Z facility that is capable of delivering peak currents of 20 MA in z-pinch loads producing implosion velocities as high as 7.5×107 cm/s, x-ray energies of 1.6 MJ, and x-ray powers exceeding 200 TW. Several different target concepts that employ DT cryogenic capsules (2–4 mm in diameter) indirectly driven by radiation fields generated by z-pinch hohlraum sources are being pursued.1

Existing monochromatic X-ray backlighting diagnostics at 1.865 and 6.151 keV have been combined to create a two-color monochromatic X-ray backlighting diagnostic. The use of different photon energies can allow a much broader range of areal densities to be observed in a single experiment. Here, we apply the two-color backlighter to the study of instability growth on the outside edge of an initially solid copper rod target driven by a 100-ns rise-time current pulse with a peak value of 20 MA. The different opacity of Cu at these two photon energies allows a dynamic range of ~ 1600x to be surveyed instead of ~ 60x (assuming a useful transmission range of 5%-95%).

Monochromatic 6.151-keV radiographs of a highly unstable inertial confinement fusion capsule are shown. The capsule was driven by a 70-eV peak radiation temperature and exhibits numerous small-scale features down to the resolution of the backlighting diagnostic (about 15 μm ). The capsule experiment was done using the double-ended Z -pinch-driven hohlraum on the Sandia Z facility.

Imploding wire arrays on the 20 MA Z generator have recently provided some of the most powerful and energetic laboratory sources of multi-keV photons, including ∼375 kJ of Al K-shell emission (hν ∼ 1–2 keV), ∼80 kJ of stainless steel K-shell emission (hν ∼ 5–9 keV) and a kJ-level of Mo K-shell emission (hν ∼ 17 keV). While the global implosion dynamics of these different wire arrays are very similar, the physical process that dominates the emission from these x-ray sources fall into three broad categories. Al wire arrays produce a column of plasma with densities up to ∼3 × 1021 ions/cm3, where opacity inhibits the escape of K-shell photons. Significant structure from instabilities can reduce the density and increase the surface area, therefore increase the K-shell emission. In contrast, stainless steel wire arrays operate in a regime where achieving a high pinch temperature (achieved by thermalizing a high implosion kinetic energy) is critical and, while opacity is present, it has less impact on the pinch...

Summary form only given, as follows. We have developed an electromagnetic driven fast shutter for purposes of debris mitigation on Z. This shutter was developed to prevent debris generated by the z-pinch implosion from damaging an x-ray imaging system used with the Z backlighter systems. The shutter uses a capacitor-driven pulsed electromagnet to accelerate an aluminum tube across the 24-mm diameter line of sight, completely closing the line of sight 185 microseconds after the z-pinch implosion. After the shutter crosses the line of sight, a tapered high-strength steel catcher slows the shutter to a stop and locks the shutter in a position covering the line of sight. The design, operation, and limitations of the shutter system are described. Concepts for faster, more efficient electromagnetic shutter systems are also discussed.

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.

PBFA Z, a new 60-TW/5-MJ electrical accelerator located at Sandia National Laboratories, is now the world’s most powerful z-pinch driver. PBFA Z stores 11.4 MJ in its 36 Marx generators, couples 5 MJ into a 60-TW/105-ns FWHM pulse to the 120-mΩ water transmission lines, and delivers 3.0 MJ and 50 TW of electrical energy to the z-pinch load. Depending on load parameters, we attain peak load currents of 16–20 MA with a current rise time of ∼105 ns with wire-array z-pinch loads. We have extended the x-ray performance of tungsten wire-array z pinches from earlier Saturn experiments. Using a 2-cm-radius, 2-cm-long tungsten wire array with 240, 7.5-μm diameter wires (4.1-mg mass), we achieved an x-ray power of 210 TW and an x-ray energy of 1.9 MJ. Preliminary spectral measurements suggest a mostly optically-thick, Planckian-like radiator below 1000 eV. Data indicate ∼100 kJ of x rays radiated above 1000 eV. An intense z-pinch x-ray source with an overall coupling efficiency greater than 15% has been demonstrated.

Multiple experimental campaigns have been executed to study the implosions of initially solid beryllium (Be) liners (tubes) on the Z pulsed-power accelerator. The implosions were driven by current pulses that rose from 0 to 20 MA in either 100 or 200 ns (200 ns for pulse shaping experiments). These studies were conducted in support of the recently proposed Magnetized Liner Inertial Fusion concept [Slutz et al., Phys. Plasmas 17, 056303 (2010)], as well as for exploring novel equation-of-state measurement techniques. The experiments used thick-walled liners that had an aspect ratio (initial outer radius divided by initial wall thickness) of either 3.2, 4, or 6. From these studies, we present three new primary results. First, we present radiographic images of imploding Be liners, where each liner contained a thin aluminum sleeve for enhancing the contrast and visibility of the liner's inner surface in the images. These images allow us to assess the stability of the liner's inner surface more accurately and more directly than was previously possible. Second, we present radiographic images taken early in the implosion (prior to any motion of the liner's inner surface) of a shockwave propagating radially inward through the liner wall. Radial mass density profiles from these shock compression experiments are contrasted with profiles from experiments where the Z accelerator's pulse shaping capabilities were used to achieve shockless (“quasi-isentropic”) liner compression. Third, we present “micro-B” measurements of azimuthal magnetic field penetration into the initially vacuum-filled interior of a shocked liner. Our measurements and simulations reveal that the penetration commences shortly after the shockwave breaks out from the liner's inner surface. The field then accelerates this low-density “precursor” plasma to the axis of symmetry.

AIAA, Fluid Dynamics Conference, 27th, New Orleans, LA, June 17-20, 1996 The results of a series of workshops sponsored by the Joint Army/Navy/NASA/Air Force (JANNAF) Airbreathing Propulsion Committee are reviewed. The results address the need for, and the process needed for establishing, archival benchmark experiments; the definition of the validation process; the process of establishing CFD code validation/verification test programs; and information management of the CFD experimental archival data. The results are presented from the points of view of experimentalists, code developers, and generalists/managers. The issues associated with the validation process are also discussed and summarized. The coordination of the workshop activities with other organizations, including AGARD, SAE, and the AIAA, is also described. Developments regarding publication standards being addressed by the AIAA CFD Committee on Standards (CFD/COS) are described. Key steps required to help CFD play a more viable role in engineering design and performance processes are discussed in the paper's summary. (Author)