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We present experimental results from the first systematic study of performance scaling with drive parameters for a magnetoinertial fusion concept. In magnetized liner inertial fusion experiments, the burn-averaged ion temperature doubles to 3.1 keV and the primary deuterium-deuterium neutron yield increases by more than an order of magnitude to 1.1×10^{13} (2 kJ deuterium-tritium equivalent) through a simultaneous increase in the applied magnetic field (from 10.4 to 15.9 T), laser preheat energy (from 0.46 to 1.2 kJ), and current coupling (from 16 to 20 MA). Individual parametric scans of the initial magnetic field and laser preheat energy show the expected trends, demonstrating the importance of magnetic insulation and the impact of the Nernst effect for this concept. A drive-current scan shows that present experiments operate close to the point where implosion stability is a limiting factor in performance, demonstrating the need to raise fuel pressure as drive current is increased. Simulations that capture these experimental trends indicate that another order of magnitude increase in yield on the Z facility is possible with additional increases of input parameters.

Neutron bang times ${t}_{\text{bang}}$ and mean neutron speeds $\overline{u}$ have been measured at the $Z$ facility for a series of ${D}_{2}$-filled targets, in magnetized liner inertial fusion experiments. Measurements were made by a novel neutron time-of-flight (nTOF) diagnostic, adapted for use at this facility, and consisted of detecting the neutron times in flight at seven independent scintillator--photomultiplier tube detectors (channels), located on three noncoplanar lines of sight, with distances to the neutron source varying between 690 and 2510 cm. The nTOF signals were analyzed by identifying fiducials on the detector traces to quantify the time in flight to each distance, using a nonrelativistic model for a uniformly thermalized, Maxwellian plasma distribution. The measured neutron arrival times were then linearly regressed on distance with the bang time and mean speed estimated from the fit parameters. A particular shot, 2584, is analyzed here to illustrate the method and the issues encountered in these measurements. On this particular shot, six usable channel traces were obtained. The standard errors of the parameter fits were as follows: ${t}_{\text{bang}}=3102.95\ifmmode\pm\else\textpm\fi{}0.97\text{ }\text{ }\mathrm{ns}$ (standard error) with six nTOF traces on the system clock and $\overline{u}=2.1524\ifmmode\pm\else\textpm\fi{}0.0032\text{ }\text{ }\mathrm{cm}/\mathrm{ns}$ (standard error), from which the mean, nonrelativistic, kinetic energy $\overline{E}$ of the neutrons was $2.4216\ifmmode\pm\else\textpm\fi{}0.0144\text{ }\text{ }\mathrm{MeV}$ (standard error). The estimates of $\overline{u}$ and $\overline{E}$ here agree within 1% of the published values for the $D{(d,n)}^{3}\mathrm{He}$ reaction. Hence, these measurements are consistent with the production of a thermalized, Maxwellian D-D fusion plasma in this experiment. The source duration was estimated to be $3.25\ifmmode\pm\else\textpm\fi{}0.84\text{ }\text{ }\mathrm{ns}$ (standard error) from six pulse-width measurements.

The one-dimensional imager of neutrons (ODIN) at the Sandia Z facility consists of a 10-cm block of tungsten with rolled edges, creating a slit imager with slit widths of either 250, 500, or 750 μm. Designed with a 1-m neutron imaging line of sight, we achieve about 4:1 magnification and 500-μm axial spatial resolution. The baseline inertial confinement fusion concept at Sandia is magnetized liner inertial fusion, which nominally creates a 1-cm line source of neutrons. ODIN was designed to determine the size, shape, and location of the neutron producing region, furthering the understanding of compression quality along the cylindrical axis of magnetized liner implosions. Challenges include discriminating neutrons from hard x-rays and gammas with adequate signal-to-noise in the 2 × 1012 deuterium-deuterium (DD) neutron yield range, as well as understanding the point spread function of the imager to various imaging detectors (namely, CR-39). Modeling efforts were conducted with MCNP6.1 to determine neutron response functions for varying configurations in a clean DD neutron environment (without x-rays or gammas). Configuration alterations that will be shown include rolled-edge slit orientation and slit width, affecting the resolution and response function. Finally, the experiment to determine CR-39 neutron sensitivity, with and without a high density polyethylene (n, p) converter, an edge spread function, and resolution will be discussed.The one-dimensional imager of neutrons (ODIN) at the Sandia Z facility consists of a 10-cm block of tungsten with rolled edges, creating a slit imager with slit widths of either 250, 500, or 750 μm. Designed with a 1-m neutron imaging line of sight, we achieve about 4:1 magnification and 500-μm axial spatial resolution. The baseline inertial confinement fusion concept at Sandia is magnetized liner inertial fusion, which nominally creates a 1-cm line source of neutrons. ODIN was designed to determine the size, shape, and location of the neutron producing region, furthering the understanding of compression quality along the cylindrical axis of magnetized liner implosions. Challenges include discriminating neutrons from hard x-rays and gammas with adequate signal-to-noise in the 2 × 1012 deuterium-deuterium (DD) neutron yield range, as well as understanding the point spread function of the imager to various imaging detectors (namely, CR-39). Modeling efforts were conducted with MCNP6.1 to determine neutron r...

High current pulsed-power generators efficiently store and deliver magnetic energy to z-pinch targets. We review applications of magnetically driven implosions (MDIs) to inertial confinement fusion. Previous research on MDIs of wire-array z-pinches for radiation-driven indirect-drive target designs is summarized. Indirect-drive designs are compared with new targets that are imploded by direct application of magnetic pressure produced by the pulsed-power current pulse. We describe target design elements such as larger absorbed energy, magnetized and pre-heated fuel, and cryogenic fuel layers that may relax fusion requirements. These elements are embodied in the magnetized liner inertial fusion (MagLIF) concept [Slutz “Pulsed-power-driven cylindrical liner implosions of laser pre-heated fuel magnetized with an axial field,” Phys. Plasmas, 17, 056303 (2010), and Stephen A. Slutz and Roger A. Vesey, “High-Gain Magnetized Inertial Fusion,” Phys. Rev. Lett., 108, 025003 (2012)]. MagLIF is in the class of magneto-inertial fusion targets. In MagLIF, the large drive currents produce an azimuthal magnetic field that compresses cylindrical liners containing pre-heated and axially pre-magnetized fusion fuel. Scientific breakeven may be achievable on the Z facility with this concept. Simulations of MagLIF with deuterium-tritium fuel indicate that the fusion energy yield can exceed the energy invested in heating the fuel at a peak drive current of about 27 MA. Scientific breakeven does not require alpha particle self-heating and is therefore not equivalent to ignition. Capabilities to perform these experiments will be developed on Z starting in 2013. These simulations and predictions must be validated against a series of experiments over the next five years. Near-term experiments are planned at drive currents of 16 MA with D2 fuel. MagLIF increases the efficiency of coupling energy (=target absorbed energy/driver stored energy) to targets by 10-150X relative to indirect-drive targets. MagLIF also increases the absolute energy absorbed by the target by 10-50X relative to indirect-drive targets. These increases could lead to higher fusion gains and yields. Single-shot high yields are of great utility to national security missions. Higher efficiency and higher gains may also translate into more compelling (lower cost and complexity) fusion reactor designs. We will discuss the broad goals of the emerging research on the MagLIF concept and identify some of the challenges. We will also summarize advances in pulsed-power technology and pulsed-power driver architectures that double the efficiency of the driver.

We report on the progress made to date for a Laboratory Directed Research and Development (LDRD) project aimed at diagnosing magnetic flux compression on the Z pulsed-power accelerator (0-20 MA in 100 ns). Each experiment consisted of an initially solid Be or Al liner (cylindrical tube), which was imploded using the Z accelerator's drive current (0-20 MA in 100 ns). The imploding liner compresses a 10-T axial seed field, B z ( 0 ) , supplied by an independently driven Helmholtz coil pair. Assuming perfect flux conservation, the axial field amplification should be well described by B z ( t ) = B z ( 0 ) x [ R ( 0 ) / R ( t )] 2 , where R is the liner's inner surface radius. With perfect flux conservation, B z ( t ) and dB z / dt values exceeding 10 4 T and 10 12 T/s, respectively, are expected. These large values, the diminishing liner volume, and the harsh environment on Z, make it particularly challenging to measure these fields. We report on our latest efforts to do so using three primary techniques: (1) micro B-dot probes to measure the fringe fields associated with fluxmore » compression, (2) streaked visible Zeeman absorption spectroscopy, and (3) fiber-based Faraday rotation. We also mention two new techniques that make use of the neutron diagnostics suite on Z. These techniques were not developed under this LDRD, but they could influence how we prioritize our efforts to diagnose magnetic flux compression on Z in the future. The first technique is based on the yield ratio of secondary DT to primary DD reactions. The second technique makes use of the secondary DT neutron time-of-flight energy spectra. Both of these techniques have been used successfully to infer the degree of magnetization at stagnation in fully integrated Magnetized Liner Inertial Fusion (MagLIF) experiments on Z [P. F. Schmit et al. , Phys. Rev. Lett. 113 , 155004 (2014); P. F. Knapp et al. , Phys. Plasmas, 22 , 056312 (2015)]. Finally, we present some recent developments for designing and fabricating novel micro B-dot probes to measure B z ( t ) inside of an imploding liner. In one approach, the micro B-dot loops were fabricated on a printed circuit board (PCB). The PCB was then soldered to off-the-shelf 0.020- inch-diameter semi-rigid coaxial cables, which were terminated with standard SMA connectors. These probes were recently tested using the COBRA pulsed power generator (0-1 MA in 100 ns) at Cornell University. In another approach, we are planning to use new multi-material 3D printing capabilities to fabricate novel micro B-dot packages. In the near future, we plan to 3D print these probes and then test them on the COBRA generator. With successful operation demonstrated at 1-MA, we will then make plans to use these probes on a 20-MA Z experiment.« less

The apparent ion temperature and neutron-reaction history are important characteristics of a fusion plasma. Extracting these quantities from a measured neutron-time-of-flight signal requires accurate knowledge of the instrument response function (IRF). This work describes a novel method for obtaining the IRF directly for single DT neutron interactions by utilizing n-alpha coincidence. The t(d,α)n nuclear reaction was produced at Sandia National Laboratories' Ion Beam Laboratory using a 300 keV Cockcroft-Walton generator to accelerate a 2.5 μA beam of 175 keV D+ ions into a stationary ErT2 target. The average neutron IRF was calculated by taking a time-corrected average of individual neutron events within an EJ-228 plastic scintillator. The scintillator was coupled to two independent photo-multiplier tubes operated in the current mode: a Hamamatsu 5946 mod-5 and a Photek PMT240. The experimental setup and results will be discussed.

We recently developed a one-dimensional imager of neutrons on the Z facility. The instrument is designed for Magnetized Liner Inertial Fusion (MagLIF) experiments, which produce D-D neutrons yields of ∼3 × 1012. X-ray imaging indicates that the MagLIF stagnation region is a 10-mm long, ∼100-μm diameter column. The small radial extents and present yields precluded useful radial resolution, so a one-dimensional imager was developed. The imaging component is a 100-mm thick tungsten slit; a rolled-edge slit limits variations in the acceptance angle along the source. CR39 was chosen as a detector due to its negligible sensitivity to the bright x-ray environment in Z. A layer of high density poly-ethylene is used to enhance the sensitivity of CR39. We present data from fielding the instrument on Z, demonstrating reliable imaging and track densities consistent with diagnosed yields. For yields ∼3 × 1012, we obtain resolutions of ∼500 μm.

The Z-pinch dynamic hohlraum (ZPDH) is a high-power x-ray source that has been used in a variety of high energy-density experiments including inertial confinement fusion (ICF) studies. The system consists of a tungsten wire-array Z pinch that implodes onto a low-density CH2 foam converter launching a radiating shock that heats the hohlraum to radiation temperatures >200 eV. Through time-gated pinhole camera measurements, the mean shock speed is measured from 28 experiments to be 326 ± 4 µm ns−1 with a shot-to-shot standard deviation of 7%. Broad-band x-ray measurements indicate that the shot-to-shot reproducibility in the power emission and pulse-shape of the source shock is 40 kJ of x-ray energy, within a factor of 4 of the energy believed sufficient for ICF ignition. The capsule types imploded by the ZPDH have evolved over four years culminating in a design that produces record indirect-drive DD thermonuclear neutron yields of up to 3.5E11.

Deuterium-filled capsule implosion experiments that employ the dynamic hohlraum are presently being conducted on the Z facility at Sandia National Laboratories. This paper will address the evidence for thermonuclear neutron production in the initial series and subsequent series of experiments that have been conducted to date employing Be, plastic, and glass capsules. The novelty of this approach motivated using several techniques to determine that the neutrons were thermonuclear in origin. The diagnostic techniques employed consist of measuring the average neutron energy and yield isotropy in two directions that were separated by a polar angle of 102 degrees. Additional "null" experiments were also employed that used the addition of Xe gas to the deuterium gas fill to suppress fusion neutron yields from the capsules by an order of magnitude. Use of these techniques are of particular importance because alternative, nonthermonuclear neutron processes were previously found to exist in Z-pinch and dense plasma focus plasmas. Such processes typically involved the creation of directed energetic ions leading to the production of nonthermal, "ion beam" generated neutrons. If not properly diagnosed, neutrons produced by these nonthermal processes could be misinterpreted as thermonuclear in origin.

An accurate interpretation of DD or DT fusion neutron time-of-flight (nTOF) signals from current mode detectors employed at the Z-facility at Sandia National Laboratories requires that the instrument response functions (IRF’s) be deconvolved from the measured nTOF signals. A calibration facility that produces detectable sub-ns radiation pulses is typically used to measure the IRF of such detectors. This work, however, reports on a simple method that utilizes cosmic radiation to measure the IRF of nTOF detectors, operated in pulse-counting mode. The characterizing metrics reported here are the throughput delay and full-width-at-half-maximum. This simple approach yields consistent IRF results with the same detectors calibrated in 2007 at a LINAC bremsstrahlung accelerator (Idaho State University). In particular, the IRF metrics from these two approaches and their dependence on the photomultipliers bias agree to within a few per cent. This information may thus be used to verify if the IRF for a given nTOF detector employed at Z has changed since its original current-mode calibration and warrants re-measurement.

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.

Inertial confinement fusion capsule implosions absorbing up to 35 kJ of x-rays from a ~220 eV dynamic hohlraum on the Z accelerator at Sandia National Laboratories have produced thermonuclear D–D neutron yields of (2.6±1.3) × 1010. Argon spectra confirm a hot fuel with Te ~ 1 keV and ne ~ (1–2) × 1023 cm−3. Higher performance implosions will require radiation symmetry control improvements. Capsule implosions in a ~70 eV double-Z-pinch-driven secondary hohlraum have been radiographed by 6.7 keV x-rays produced by the Z-beamlet laser (ZBL), demonstrating a drive symmetry of about 3% and control of P2 radiation asymmetries to ±2%. Hemispherical capsule implosions have also been radiographed in Z in preparation for future experiments in fast ignition physics. Z-pinch-driven inertial fusion energy concepts are being developed. The refurbished Z machine (ZR) will begin providing scaling information on capsule and Z-pinch in 2006. The addition of a short pulse capability to ZBL will enable research into fast ignition physics in the combination of ZR and ZBL-petawatt. ZR could provide a test bed to study NIF-relevant double-shell ignition concepts using dynamic hohlraums and advanced symmetry control techniques in the double-pinch hohlraum backlit by ZBL.

A dynamic hohlraum is formed when an imploding annular cylindrical Z-pinch driven plasma collides with an internal low density convertor. This collision generates an inward traveling shock wave that emits x rays, which are trapped by the optically thick Z-pinch plasma and can be used to drive an inertial fusion capsule embedded in the convertor. This scheme has the potential to efficiently drive high yield capsules due to the close coupling between the intense radiation generation and the capsule. In prior dynamic hohlraum experiments [J. E. Bailey et al., Phys. Rev Lett. 89, 095004 (2002)] the convertor shock wave has been imaged with gated x-ray pinhole cameras. The shock emission was observed to be very circular and to be quite narrow in the radial direction. This implies that there is minimal Rayleigh–Taylor imprinting on the shock wave. Thus, the dominant source of radiation asymmetry is not random and in principle could be significantly decreased by proper design. Due to the closed geometry of the d...

This Letter presents results from the first fully integrated experiments testing the magnetized liner inertial fusion concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)], in which a cylinder of deuterium gas with a preimposed 10 Taxial magnetic field is heated by Z beamlet, a 2.5 kJ, 1 TW laser, and magnetically imploded by a 19 MA, 100 ns rise time current on the Z facility. Despite a predicted peak implosion velocity of only 70 km = s, the fuel reaches a stagnation temperature of approximately 3 keV, with T(e) ≈ T(i), and produces up to 2 x 10(12) thermonuclear deuterium-deuterium neutrons. X-ray emission indicates a hot fuel region with full width at half maximum ranging from 60 to 120 μm over a 6 mm height and lasting approximately 2 ns. Greater than 10(10) secondary deuterium-tritium neutrons were observed, indicating significant fuel magnetization given that the estimated radial areal density of the plasma is only 2 mg = cm(2).

Magnetizing the fuel in inertial confinement fusion relaxes ignition requirements by reducing thermal conductivity and changing the physics of burn product confinement. Diagnosing the level of fuel magnetization during burn is critical to understanding target performance in magneto-inertial fusion (MIF) implosions. In pure deuterium fusion plasma, 1.01 MeV tritons are emitted during deuterium-deuterium fusion and can undergo secondary deuterium-tritium reactions before exiting the fuel. Increasing the fuel magnetization elongates the path lengths through the fuel of some of the tritons, enhancing their probability of reaction. Based on this feature, a method to diagnose fuel magnetization using the ratio of overall deuterium-tritium to deuterium-deuterium neutron yields is developed. Analysis of anisotropies in the secondary neutron energy spectra further constrain the measurement. Secondary reactions also are shown to provide an upper bound for the volumetric fuel-pusher mix in MIF. The analysis is applied to recent MIF experiments [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] on the Z Pulsed Power Facility, indicating that significant magnetic confinement of charged burn products was achieved and suggesting a relatively low-mix environment. Both of these are essential features of future ignition-scale MIF designs.

The National Ignition Facility (NIF), currently under construction at the Lawrence Livermore National Laboratory, will provide unprecedented opportunities for the use of nuclear diagnostics in inertial confinement fusion experiments. The completed facility will provide 2 MJ of laser energy for driving targets, compared to the approximately 40 kJ that was available on Nova and the approximately 30 kJ available on Omega. Ignited NIF targets are anticipated to produce up to 1019 DT neutrons. In addition to a basic set of nuclear diagnostics based on previous experience, these higher NIF yields are expected to allow innovative nuclear diagnostic techniques to be utilized, such as neutron imaging, recoil proton techniques, and gamma-ray-based reaction history measurements.

We have designed a total neutron yield diagnostic for the National Ignition Facility (NIF) which is based on the activation of In and Cu samples. The particular approach that we have chosen is one in which we calibrate the entire counting system and which we call the “F factor” method. In this method, In and/or Cu samples are exposed to known sources of DD and DT neutrons. The activated samples are then counted with an appropriate system: a high purity Ge detector for In and a NaI coincidence system for Cu. We can then calculate a calibration factor, which relates measured activity to total neutron yield. The advantage of this approach is that specific knowledge of such quantities as cross sections and detector efficiencies is not needed. Unless the actual scattering environment of the NIF can be mocked up in the calibration experiment, the F factor will have to be modified using the results of a numerical simulation of the NIF scattering environment. In this article, the calibration factor methodology will be discussed and experimental results for the calibration factors will be presented. Total NIF neutron yields of 109–1019 can be measured with this method assuming a 50 cm stand-off distance can be employed for the lower yields.

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.

Recent advances in Inertial Confinement Fusion (ICF) experiments at Lawrence Livermore National Laboratory's National Ignition Facility (NIF) have underscored the need for accurate total yield measurements of DT neutrons because yield measurements provide a measure of the predicted performance of the experiments. Future gas-puff DT experiments at Sandia National Laboratory's Z facility will also require similar measurements. For ICF DT experiments, the standard technique for measuring the neutron (14.1MeV) yield, counts the activity (counts/minute) induced in irradiated copper samples. This activity occurs by the 63 Cu(n,2n) 62 Cu reaction where 62 Cu decays by positrons ( +) with a half-life of 9.67 minutes. The calibrations discussed here employ the associated-particle method (APM), where the ( 4 He) particles from the T(d,n) 4 He reaction are measured to infer neutron fluxes on a copper sample. The flux induces 62 Cu activity, measured in a coincidence counting system. The method leads to a relationship between a DT neutron yield and copper activity known as the F-factor. The goal in future experiments is to apply this calibration to measure the yield at NIF with a combined uncertainty approaching 5%.

Neutron yields at the National Ignition Facility (NIF) are measured with a suite of diagnostics, including activation of ∼20–200 g samples of materials undergoing a variety of energy-dependent neutron reactions. Indium samples were mounted on the end of a Diagnostic Instrument Manipulator (DIM), 25–50 cm from the implosion, to measure 2.45 MeV D-D fusion neutron yield. The 336.2 keV gamma rays from the 4.5 hour isomer of 115m In produced by (n,n′) reactions are counted in high-purity germanium detectors. For capsules producing D-T fusion reactions, zirconium and copper are activated via (n,2n) reactions at various locations around the target chamber and bay, measuring the 14 MeV neutron yield to accuracies on order of 7%. By mounting zirconium samples on ports at nine locations around the NIF chamber, anisotropies in the primary neutron emission due to fuel areal density asymmetries can be measured to a relative precision of 3%.

Recent success with the Sandia Z machine has renewed interest in utilizing fast Z -pinches for ICF. One promising concept places the ICF capsule internal to the imploding Z -pinch. At machine parameters relevant to achieving high yield, the imploding Z -pinch mass has sufficient opacity to trap radiation giving rise to a `dynamic hohlraum'. Our concept utilizes a 12 MJ, 54 MA Z -pinch driver producing a capsule drive temperature exceeding 300 eV to realize a 550 MJ thermonuclear yield. We present the current high-yield design and its development that supports high-yield ICF with a Z -pinch driven dynamic hohlraum.

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 review of recent progress on the design of a diagnostic system proposed for ignition target experiments on the National Ignition Facility (NIF) will be presented. This diagnostic package contains an extensive suite of optical, x ray, gamma ray, and neutron diagnostics that enable measurements of the performance of both direct and indirect driven NIF targets. The philosophy used in designing all of the diagnostics in the set has emphasized redundant and independent measurement of fundamental physical quantities relevant to the operation of the NIF target. A unique feature of these diagnostics is that they are being designed to be capable of operating in the high radiation, electromagnetic pulse, and debris backgrounds expected on the NIF facility. The diagnostic system proposed can be categorized into three broad areas: laser characterization, hohlraum characterization, and capsule performance diagnostics. The operating principles of a representative instrument from each class of diagnostic employed in this package will be summarized and illustrated with data obtained in recent prototype diagnostic tests.

A replacement Marx generator for one of AWE's flash radiographic machines is required to mitigate component obsolescence. The design uses twelve 250 nF capacitors to charge a 14 nF Blumlein to 700 kV. For ease of maintenance the generator is removable from the oil tank by use of a rail system. Electrostatic codes have been used to design a new earthing system with access to the hidden capacitor terminals. The paper describes the design and the results of the Marx construction and high voltage commissioning into a resistive load.

We investigate the generation and propagation of intense pulsed ion beams at the 6 MeV level and above using the Hermes III facility at Sandia National Laboratories. While high-power ion beams have previously been produced using Hermes III, we have conducted systematic studies of several ion diode geometries for the purpose of maximizing focused ion energy for a number of applications. A self-field axial-gap diode of the pinch reflex type and operated in positive polarity yielded beam power below predicted levels. This is ascribed both to power flow losses of unknown origin upstream of the diode load in Hermes positive polarity operation, and to anomalies in beam focusing in this configuration. A change to a radial self-field geometry and negative polarity operation resulted in greatly increased beam voltage (> 6 MeV) and estimated ion current. A comprehensive diagnostic set was developed to characterize beam performance, including both time-dependent and time-integrated measurements of local and total beam power. A substantial high-energy ion population was identified propagating in reverse direction, i.e. from the back side of the anode in the electron beam dump. While significant progress was made in increasing beam power, further improvements in assessing the beam focusing envelope will bemore » required before ultimate ion generation efficiency with this geometry can be completely determined.« less

A novel method for modeling the neutron time of flight (nTOF) detector response in current mode for inertial confinement fusion experiments has been applied to the on-axis nTOF detectors located in the basement of the Z-Facility. It will be shown that this method can identify sources of neutron scattering, and is useful for predicting detector responses in future experimental configurations, and for identifying potential sources of neutron scattering when experimental set-ups change. This method can also provide insight on how much broadening neutron scattering contributes to the primary signals, which is then subtracted from them. Detector time responses are deconvolved from the signals, allowing a transformation from dN/dt to dN/dE, extracting neutron spectra at each detector location; these spectra are proportional to the absolute yield.

DT neutron yield (Y(n)), ion temperature (T(i)), and down-scatter ratio (dsr) determined from measured neutron spectra are essential metrics for diagnosing the performance of inertial confinement fusion (ICF) implosions at the National Ignition Facility (NIF). A suite of neutron-time-of-flight (nTOF) spectrometers and a magnetic recoil spectrometer (MRS) have been implemented in different locations around the NIF target chamber, providing good implosion coverage and the complementarity required for reliable measurements of Y(n), T(i), and dsr. From the measured dsr value, an areal density (ρR) is determined through the relationship ρR(tot) (g∕cm(2)) = (20.4 ± 0.6) × dsr(10-12 MeV). The proportionality constant is determined considering implosion geometry, neutron attenuation, and energy range used for the dsr measurement. To ensure high accuracy in the measurements, a series of commissioning experiments using exploding pushers have been used for in situ calibration of the as-built spectrometers, which are now performing to the required accuracy. Recent data obtained with the MRS and nTOFs indicate that the implosion performance of cryogenically layered DT implosions, characterized by the experimental ignition threshold factor (ITFx), which is a function of dsr (or fuel ρR) and Y(n), has improved almost two orders of magnitude since the first shot in September, 2010.

Several magnetized liner inertial fusion (MagLIF) experiments have been conducted on the Z accelerator at Sandia National Laboratories since late 2013. Measurements of the primary DD (2.45 MeV) neutrons for these experiments suggest that the neutron production is thermonuclear. Primary DD yields up to 3e12 with ion temperatures ~2-3 keV have been achieved. Measurements of the secondary DT (14 MeV) neutrons indicate that the fuel is significantly magnetized. Measurements of down-scattered neutrons from the beryllium liner suggest ρRliner ~ 1g/cm2. Neutron bang times, estimated from neutron time-of-flight (nTOF) measurements, coincide with peak x-ray production. Furthermore, plans to improve and expand the Z neutron diagnostic suite include neutron burn-history diagnostics, increased sensitivity and higher precision nTOF detectors, and neutron recoil-based yield and spectral measurements.

C.B. Yeamans, W. Cassata, J.A. Church, D.N. Fittinghoff, M. Gatu Johnson, N. Gharibyan, R. Hatarik, D.B. Sayre, H.W. Sio, R.M. Bionta, D.L. Bleuel, J.A. Caggiano, C.J. Cerjan, G.W. Copper, M.J. Eckart, E.R. Edwards, S.A. Faye, C.J. Forrest, J.A. Frenje, V.Yu. Glebov, P.F. Grant, G.P. Grim, E.P. Hartouni, H.W. Herrmann, J.D. Kilkenny, J.P. Knauer, A.J. Mackinnon, F.E. Merrill, K.J. Moody, M.J. Moran, R.D. Petrasso, T.W. Phillips, H.G. Rinderknecht, D. H. G. Schneider, S.M. Sepke, D.A. Shaughnessy, W. Stoeffl, C.A. Velsko, P. Volegov 1 Lawrence Livermore National Laboratory, Livermore, California, USA 2 General Atomics, San Diego, California, USA 3 Los Alamos National Laboratory, Los Alamos, New Mexico, USA 4 Massachusetts Institute of Technology, Cambridge, Massachusetts, USA 5 University of California, Berkeley, Berkeley, California, USA 6 University of New Mexico, Albuquerque, New Mexico, USA 7 University of Rochester, Laboratory for Laser Energetics, Rochester, New York, USA yeamans1@llnl.gov

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.

The National Ignition Facility has been used to compress deuterium-tritium to an average areal density of ~1.0±0.1 g cm(-2), which is 67% of the ignition requirement. These conditions were obtained using 192 laser beams with total energy of 1-1.6 MJ and peak power up to 420 TW to create a hohlraum drive with a shaped power profile, peaking at a soft x-ray radiation temperature of 275-300 eV. This pulse delivered a series of shocks that compressed a capsule containing cryogenic deuterium-tritium to a radius of 25-35 μm. Neutron images of the implosion were used to estimate a fuel density of 500-800 g cm(-3).

A new, accurate, neutron activation detection scheme for measuring pulsed neutrons has been designed and tested. The detection system is sensitive to neutrons with energies above 10 MeV; importantly, it is insensitive to gamma radiation 141 Pr, an element that has a single, naturally occurring isotope, a significant n,2n cross-section, and decays by positron emission that result in two coincident 511 keV photons. Neutron fluences are thus inferred by relating measured reaction product decay activity to fluence. Specific sample activity is measured using the sum-peak method to count gamma-ray coincidences from the annihilation of the positron decay products. The system was tested using 14 and 2.45 MeV neutron bursts produced by NSTec Dense Plasma Focus Laboratory fusion sources. Lead, copper, beryllium, and silver activation detectors were compared. The detection method allows measurement of 14 MeV neutron yield with a total error of ≈18%.

A multiinstitution collaboration is developing a neutron imaging system for the Sandia Z facility. The initial system design is for slit aperture imaging system capable of obtaining a one-dimensional image of a 2.45 MeV source producing 5x10(12) neutrons with a resolution of 320 microm along the axial dimension of the plasma, but the design being developed can be modified for two-dimensional imaging and imaging of DT neutrons with other resolutions. This system will allow us to understand the spatial production of neutrons in the plasmas produced at the Z facility.

Summary form only given. Development of intense electron beam-driven diodes for flash X-ray radiography is being carried out at 7.5-12 MV on the RITS-6 accelerator at Sandia National Laboratories. One of several diodes under investigation is the paraxial diode, which employs a gas-filled transport cell to focus an electron beam onto a high-atomic-number target to generate X-rays. Three key objectives are to produce a small spot size, 600 rads at 1 m, and efficiently couple this relatively high-impedance diode to the lower-impedance RITS-6 accelerator. Particle-in-cell (PIC) simulations have shown that the primary limitation in spot size is due to the finite decay of the plasma return current which causes the beam focal location to sweep axially during the timescale of the pulse, hence leading to an increasing spot size. Time-resolved measurements of the spot size which convey this trend are reported. Interpretation of these results was aided by PIC simulations in which additional physics was included. Other outstanding issues for the paraxial diode on RITS-6 are also presented which include electron powerflow coupling to the diode, cavity modes which may affect focusing, and gas-breakdown models. Measurements of dose, dose rate, time-integrated (and time-resolved) spot size, and current are reported for experimental results at 7.5 and 10.5 MV.

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.

Summary form only given. In electron beam driven flash X-ray radiography, an electron beam is focused onto a high atomic number target to generate high dose X-rays while achieving small

A methodology for obtaining empirical curves relating absolute measured scintillation light output to beta energy deposited is presented. Output signals were measured from thin plastic scintillator using NIST traceable beta and gamma sources and MCNP5 was used to model the energy deposition from each source. Combining the experimental and calculated results gives the desired empirical relationships. To validate, the sensitivity of a beryllium/scintillator-layer neutron activation detector was predicted and then exposed to a known neutron fluence from a Deuterium-Deuterium fusion plasma (DD). The predicted and the measured sensitivity were in statistical agreement.

In the light-ion-beam fusion program at Sandia National Laboratories an intense lithium beam is being developed to drive inertial confinement fusion targets. An important issue is the purity of the beam. To assess this concern, direct nuclear activation diagnostics based on the reactions 7Li(p,n)7Be, 10B(p,α)7Be, and 19F(7Li,d)24Na were fielded to measure the energy densities of hydrogen and lithium in the beam. The hydrogen beam energy density was measured to be less than 2% of the lithium beam energy density on a majority (10) of the 19 LiF anode shots taken and was always less than 10%. The total hydrogen energy in the beam ranged from only 0.5–10 kJ. Over this shot series increasing efforts were made to clean the anode prior to each shot. In general, there was a modest reduction in the hydrogen energy fraction with improved cleaning, but no corresponding increase in the lithium energy density was seen. The lithium energy density as a function of location was also measured and found to typically vary b...

Summary form only given. The paraxial diode is one of several candidate diodes being investigated to meet the X-radiography requirements of the CPF at AWE. The long term requirement is to produce a 2 mm X-ray source with a dose of 1000 rads at 1 metre. The paraxial diode currently produces around 500 R @ 1 m in a 5 mm spot. To help meet the long term requirement stated above the paraxial diode is currently being studied in detail with the aid of the large-scale-plasma PIC code Lsp in order to see if improvements can be made to spot and dose. It will be shown how the concept of emittance can be used as a powerful tool in understanding the behavior of the beam as it propagates in the diode. Emittance results in degradation of an electron's trajectory, which ultimately leads to an increased spot on the high Z, target. Previous work suggests that focal sweeping, because of time-varying net currents, is the main contributor. However, it will be demonstrated with the aid of Lsp simulations that emittance growth from non-linear focussing and foil scatter will set fundamental limits on the spot size achievable (typically 5 mm when operating at 1.1 torr air in the drift cell). Suggestions to reduce emittance and spot are presented by using a high pressure air fill ~20 torr inside the drift cell

Summary form only given. Experiments have been performed at the Z accelerator to study the neutron production from a deuterium gas puff. The current scaling of the neutron production was of primary interest, so shots were fielded at approximately 12 MA, and 16 MA. The shots at both current levels were fielded with similar implosion times. The gas puff nozzle used was a nested shell configuration, with the inner shell extending from 3 to 2 cm, and the outer shell from 3 to 4 cm; the load length was 2 cm. Dopant gases were added to the deuterium (argon and chlorine) to track the implosion characteristics of the gas through X-ray yield and spectroscopy measurements. Indium detectors, as well as lead and beryllium probes were fielded. Neutron time-of-flight measurements were also obtained. Neutron outputs near 1e13 were measured for the 12 MA shot, and greater than 1e13 was observed for the 16 MA shot. These results will be compared with computational predictions and previous neutron measurements from Z-pinch sources

Sandia National Laboratories is investigating and developing high-dose, high-brightness flash radiographic sources. The immersed-Bz diode employs large-bore, high-field solenoid magnets to help guide and confine an intense electron beam from a needle-like cathode "immersed" in the axial field of the magnet. The electron beam is focused onto a high-atomic-number target/anode to generate an intense source of bremsstrahlung X-rays. Historically, these diodes have been unable to achieve high dose (> 500 rad @ m) from a small spot (< 3 mm diameter). It is believed that this limitation is due in part to undesirable effects associated with the interaction of the electron beam with plasmas formed at either the anode or the cathode. Previous research concentrated on characterizing the behavior of diodes, which used untreated, room temperature (RT) anodes. Research is now focused on improving the diode performance by modifying the diode behavior by using cryogenic anodes that are coated in-situ with frozen gases. The objective of these cryogenically treated anodes is to control and limit the ion species of the anode plasma formed and hence the species of the counter-streaming ions that can interact with the electron beam. Recent progress in the development, testing and fielding of the cryogenically cooled immersed diodes at Sandia is described.

Summary form only given. In flash X-ray radiography, one of the key goals is to focus an electron beam onto a high-Z-target to generate X-rays. One of several goals is to create a small radiographic spot. The paraxial diode, which utilizes a gas-filled transport cell to focus the beam into a small spot, has been investigated for several decades. It has been shown in simulations using LSP, a particle-in-cell code, that the primary limitation to achieving a small spot size is due to time-dependent net currents in the transport cell which cause the beam's focal plane to shift axially during the timescale of the pulse. This movement, often referred to as ''beam sweep", smears out the radiographic spot, leading to a larger size than is desired. Recently, calculations with LSP, demonstrate that replacing the gas with a pre-ionized plasma with density on the order of 1016 cm-3 significantly slows down the net current evolution, and yields a more stable focal plane and thus decreased time-integrated spot size. Recent experiments utilizing gas and plasma-filled transport cells have been performed on the RITS accelerator (4.5 MV, 20-30 kA beam current 60 ns FWHM) to study these predictions. The most recent results and analysis from these experiments are presented

Summary form only given. Sandia National Laboratories is investigating and developing high-dose, high-brightness flash radiographic sources. One of the candidate sources being developed is the magnetically immersed diode. These diodes employ large-bore, high-field solenoid magnets to help produce an intense electron beam from a needle-like cathode "immersed" in the strong Bz field of the magnet. Sandia's RITS-3 accelerator (4-MV, 150-kA, 70-ns) has been used to fully characterize the diode behavior and radiographic performance of Sandia's 20-T large bore immersed diode over a wide range of diode parameters including cathode diameter, A-K gap, magnetic field strength, anode materials, base vacuum pressures and accelerator pre-pulse. Key results from this extensive survey are described.

Summary form only given. Determination of ion temperatures is essential to further understand basic physics of the fusion process. To better calculate ion temperatures, MCNPX, a Monte-Carlo, all-particle, high-energy transport code was used to model neutron detector energy deposition response signals. These calculated signals will be compared to experimental signals received during a series of OMEGA reactor shots performed at the Laboratory for Laser Energetics at the University of Rochester. In addition to neutron detector response, ion temperature calculations from experimental and computational data will be compared and presented.

Summary form only given. The paraxial diode has been identified as one of the potential candidates capable of reaching the short-term radiographic source requirement for the proposed Hydrodynamic Research Facility at AWE. The off axis dose produced in the AWE paraxial diode is partly attenuated by a local Tungsten shielding cone. Shielding requirements to minimise the off axis dose reaching detectors has been calculated for the paraxial diode at 14 MeV, which suggest a minimum areal mass of 350g/cm/sup 2/ (17 cm of Tungsten) is required. This thickness is required at all angles from the X-ray source outside of the main collimated beam. Clearly, it would be beneficial to place as much of the shielding as possible around the X-ray source. The simplest way to achieve this is to increase the angle of the shielding cone (45/spl deg/ for Mogul E), however, this is likely to alter the electric field distribution in the A-K region and possibly the electron beam trajectories at the anode foil plane. This paper describes the work carried out on RITS-3 to determine if increasing the diode shielding cone angle affects the performance of the diode.