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Pulsed power driven hohlraum research at Sandia National Laboratories

Description: Three pulsed power driven hohlraum concepts are being investigated at Sandia for application to inertial fusion research. These hohlraums are driven by intense proton and Li ion beams as well as by two different types of z-pinch x-ray sources. Research on these hohlraum systems will continue on Sandia`s PBFA II-Z facility.
Date: June 1, 1996
Creator: Leeper, R.J.; Alberts, T.E. & Allshouse, G.A.
Partner: UNT Libraries Government Documents Department

Target diagnostics for intense lithium ion hohlraum experiments on PBFA II

Description: A review of the diagnostics used at Sandia National Laboratories to measure the parameters of intense lithium ion-beam hohlraum target experiments on PBFA II will be presented. This diagnostic package contains an extensive suite of x-ray spectral and imaging diagnostics that enable measurements of target temperature and x-ray output. The x-ray diagnostics include time-integrated and time-resolved pinhole cameras, energy-resolved I-D streaked imaging, diagnostics, time-integrated and time-resolved grazing, incidence spectrographs, a transmission grating spectrograph, an elliptical crystal spectrograph, a bolometer array, an eleven-element x-ray diode (XRD) array, and an eleven-element PIN diode detector array. The incident Li beam symmetry and an estimate of incident Li beam power density can be measured from ion beam-induced characteristic x-ray line emission and neutron emission.
Date: December 31, 1994
Creator: Leeper, R.J.; Bailey, J.E. & Carlson, A.L.
Partner: UNT Libraries Government Documents Department

Analytic Models of High-Temperature Hohlraums

Description: A unified set of high-temperature-hohlraum models has been developed. For a simple hohlraum, P{sub s} = [A{sub s}+(1{minus}{alpha}{sub W})A{sub W}+A{sub H}]{sigma}T{sub R}{sup 4} + (4V{sigma}/c)(dT{sub R}{sup r}/dt) where P{sub S} is the total power radiated by the source, A{sub s} is the source area, A{sub W} is the area of the cavity wall excluding the source and holes in the wall, A{sub H} is the area of the holes, {sigma} is the Stefan-Boltzmann constant, T{sub R} is the radiation brightness temperature, V is the hohlraum volume, and c is the speed of light. The wall albedo {alpha}{sub W} {triple_bond} (T{sub W}/T{sub R}){sup 4} where T{sub W} is the brightness temperature of area A{sub W}. The net power radiated by the source P{sub N} = P{sub S}-A{sub S}{sigma}T{sub R}{sup 4}, which suggests that for laser-driven hohlraums the conversion efficiency {eta}{sub CE} be defined as P{sub N}/P{sub LASER}. The characteristic time required to change T{sub R}{sup 4} in response to a change in P{sub N} is 4V/C[(l{minus}{alpha}{sub W})A{sub W}+A{sub H}]. Using this model, T{sub R}, {alpha}{sub W}, and {eta}{sub CE} can be expressed in terms of quantities directly measurable in a hohlraum experiment. For a steady-state hohlraum that encloses a convex capsule, P{sub N} = {l_brace}(1{minus}{alpha}{sub W})A{sub W}+A{sub H}+[(1{minus}{alpha}{sub C})(A{sub S}+A{sub W}{alpha}{sub W})A{sub C}/A{sub T}]{r_brace}{sigma}T{sub RC}{sup 4} where {alpha}{sub C} is the capsule albedo, A{sub C} is the capsule area, A{sub T} {triple_bond} (A{sub S}+A{sub W}+A{sub H}), and T{sub RC} is the brightness temperature of the radiation that drives the capsule. According to this relation, the capsule-coupling efficiency of the baseline National-Ignition-Facility (NIF) hohlraum is 15% higher than predicted by previous analytic expressions. A model of a hohlraum that encloses a z pinch is also presented.
Date: November 29, 2000
Creator: Stygar, W.A.; Olson, R.E.; Spielman, R.B. & Leeper, R.J.
Partner: UNT Libraries Government Documents Department

Light ion hohlraum target experiments on PBFA II and Nova

Description: The goal of the National Inertial Confinement Fusion (ICF) Program in the United States is a target yield in the range of 200 to 1000 MJ. To address this goal, the near-term emphasis in the Light Ion Target Physics program is to design a credible high-gain target driven by ion beams. Based on this target design, we have identified ion beam spatial parameters, ion beam energy and power deposition, the conversion of ion-beam energy into soft x-ray thermal radiation, the conversion of ion-beam energy into hydrodynamic motion, radiation smoothing in low-density foams, and internal pulse shaping as the critical physics issues. These issues are currently being addressed in both ion- and laser-driven experiments.
Date: December 31, 1995
Creator: Leeper, R.J.; Bailey, J.E. & Barber, T.L.
Partner: UNT Libraries Government Documents Department

Target diagnostic system for the National Ignition Facility (NIF)

Description: 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, EMP, 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.
Date: July 1, 1996
Creator: Leeper, R.J.; Chandler, G.A.; Cooper, G.W. & Derzon, M.S.
Partner: UNT Libraries Government Documents Department

Proto-I axial-focusing experiments

Description: The time-integrated axial (z) focus of the 4.5-cm-radius Proto I (1.5 MV, 500 kA) radial proton diode is presently limited to approx. 3 mm FWHM. This result is obtained with current neutralized beam transport in a gas cell with 6 Torr argon. If the vertical local divergence were the same (1/sup 0/ or less) as the horizontal divergence, the local divergence alone would produce a 1.5 mm FWHM focus. The axial focal size is evidently limited by time-dependent effects. These are studied by observing the beam incident upon various targets with two time-resolved pinhole cameras. The first camera observes Rutherford-scattered protons from gold targets with an array of 11 siicon PIN detectors. The second camera observes K/sub ..cap alpha../-fluorescence from aluminum targets with 4 independently-gated microchannel plates imaging tubes.
Date: January 1, 1983
Creator: Johnson, D J; Leeper, R J; Stygar, W A & Slutz, S A
Partner: UNT Libraries Government Documents Department

An intense proton beam diagnostic using the {sup 7}Li(p,{gamma}{sup 8})Be {yields} {sup 141}Pr({gamma},n){sup 140}Pr({beta}{sup +}) nuclear reaction sequence

Description: An indirect nuclear activation diagnostic was developed to measure the proton fluence onto a thick target of lithium metal located in the diode region of pulsed power accelerators. This diagnostic uses the nuclear sequence {sup 7}Li(p,{gamma}){sup 8}Be=>{sup 14l}Pr({gamma},n){sup 140}Pr({beta}{sup +}) to relate the proton reaction fluence to induced {sup 140}Pr activity. This diagnostic was calibrated using a Van de Graaff accelerator. Energetic protons were focused onto a thick lithium target driving the {sup 7}Li(p,{gamma}){sup 8}Be reaction. The resulting prompt gamma rays activated a secondary {sup l4l}Pr target via the reaction {sup 141}Pr({gamma},n){sup 140}Pr({beta}{sup +}). A NaI gamma-gamma coincidence detector system was used to measure the induced {sup 140}Pr activity as a function of proton energy and proton fluence. These data yielded a calibration curve for proton energies ranging from 2 to 12 MeV. Since deuterium impurities can interfere with this diagnostic by driving the reaction sequence {sup 7}Li(d,n){sup 8}Be=> {sup 141}Pr(n,2n){sup 140}Pr, a similar calibration experiment was conducted using deuterium ions. These data yielded a correction factor that can be used to determine the deuterium contribution to the {sup 140}Pr activity providing that the deuterium beam fraction is known.
Date: May 1, 1994
Creator: Evans, C. B.; Cooper, G. W.; Ruiz, C. L. & Leeper, R. J.
Partner: UNT Libraries Government Documents Department

Shot-to-shot comparison of the first Li-beam driven hohlraum experiments

Description: Shot-to-shot comparison of the first Li-beam hohlraum experiments on PBFA II provides an opportunity to measure and determine the factors that the affect on-axis reproducibility of the Li ion beam. Both inner shell and thermal x-ray emission are used to estimate the relative beam power on target from shot to shot. The M- and L-shell Au x-ray yield measurements were made with an array of 11 filtered PIN detectors, and the thermal emission measurements were made with an array of three filtered bolometers. The analysis shows that the beam intensity on target varied by more than a factor of ten during the shot series. By correlating the results of the beam on target with other diagnostics and events, we have identified some potential causes for these variations. A slight difference in top-to-bottom timing appears critical in affecting relative peak power on target.
Date: August 1, 1994
Creator: Derzon, M. S.; Rochau, G. E.; Chandler, G. A.; Moats, A. R. & Leeper, R. J.
Partner: UNT Libraries Government Documents Department

Diagnostics program for a magnetically insulated ion diode for inertial confinement fusion

Description: Some of the diagnostics used to study ion beam composition and profiles from magnetically insulated ion diodes, developed at Sandia Laboratories through the drift section to the target, are described. The carbon activation technique, which is used to measure proton and carbon fluence and flux, is discussed. Time resolved x-ray pinhole cameras, time resolved optical spectral measurements of the anode plasma, holographic interferometry and soft x-ray, vacuum ultraviolet spectroscopy are considered.
Date: January 1, 1979
Creator: Burns, E.J.T.; Johnson, D.J.; Farnsworth, A.V. Jr.; Fehl, D.L.; Leeper, R.J.; Mix, L.P. et al.
Partner: UNT Libraries Government Documents Department

Absolute, soft x-ray calorimetry on the Z facility at Sandia National Laboratories

Description: Simple and reliable x-ray fluence measurements, in addition to time-resolved diagnostics, are needed to understand the physics of hot Z-pinch plasmas. A commercially available laser calorimeter has been modified for measuring soft x-ray fluence from the Z facility at Sandia National Laboratories. The x-ray absorber of this calorimeter is an aluminum disk, attached to a two-dimensional thermopile and surrounded by an isoperibol shroud. The time-integral and the maximum of the thermopile voltage signal are both proportional to the x-ray energy deposited. Data are collected for 90 seconds, and the instrument has, thus far, been used in the 1--25 mJ range. A wider dynamic measuring range for x-ray fluence (energy/area) can be achieved by varying the area of the defining aperture. The calorimeter is calibrated by an electrical substitution method. Calibrations are performed before and after each x-ray experiment on the Z facility. The calibration of the time-integral of the thermopile voltage vs. energy deposited (or the peak of thermopile voltage vs. energy deposited) is linear with zero offset at the 95% confidence level. The irreproducibility of the calibration is <2%, and the imprecision in the measurement of the incident x-ray energy (inferred from signal noise and the calibration) is estimated to be {approximately}0.9 mJ (95% confidence level). The inaccuracy is estimated at {+-}10%, due to correctable systematic errors (e.g., baseline shifts). Comparisons have been made of the calorimeter to time-resolved x-ray diagnostics, e.g., bolometers and XRD (x-ray diode) arrays, by integrating the flux measured by these instruments over time.
Date: May 1, 1998
Creator: Fehl, D.L.; Muron, D.J.; Leeper, R.J.; Chandler, G.A.; Deeney, C. & Spielman, R.B.
Partner: UNT Libraries Government Documents Department

Time-dependent, x-ray spectral unfolds and brightness temperatures for intense Li{sup +} ion beam-driven hohlraums

Description: X-ray-producing hohlraums are being studied as indirect drives for Inertial Confinement Fusion targets. In a 1994 target series on the PBFAII accelerator, cylindrical hohlraum targets were heated by an intense Li{sup +} ion beam and viewed by an array of 13 time-resolved, filtered x-ray detectors (XRDs). The UFO unfold code and its suite of auxiliary functions were used extensively in obtaining time- resolved x-ray spectra and radiation temperatures from this diagnostic. UFO was also used to obtain fitted response functions from calibration data, to simulate data from blackbody x-ray spectra of interest, to determine the suitability of various unfolding parameters (e.g., energy domain, energy partition, smoothing conditions, and basis functions), to interpolate the XRD signal traces, and to unfold experimental data. The simulation capabilities of the code were useful in understanding an anomalous feature in the unfolded spectra at low photon energies ({le} 100 eV). Uncertainties in the differential and energy-integrated unfolded spectra were estimated from uncertainties in the data. The time-history of the radiation temperature agreed well with independent calculations of the wall temperature in the hohlraum.
Date: July 1, 1996
Creator: Fehl, D.L.; Chandler, G.A.; Biggs, F.; Dukart, R.J.; Moats, A.R. & Leeper, R.J.
Partner: UNT Libraries Government Documents Department

Direct measurement of the energy spectrum of an intense proton beam

Description: A time-resolved magnetic spectrometer has been used to measure the energy spectrum of an intense (0.5 TW/cm/sup 2/) proton beam. A thin (2400 A) gold foil placed at the focus of an ion diode Rutherford scattered protons by 90/sup 0/ into the spectrometer, reducing the beam intensity to a level suitable for magnetic analysis. The scattered beam was collimated by two 1 mm diameter apertures separated by 12.3 cm. The collimated protons were deflected in a 12.7 cm diameter, 6.65 Kg samarium-cobalt permanent magnet. The deflected protons were recorded simultaneously on CR-39 and eight 1 mm/sup 2/ by 35 ..mu..m thick PIN diodes. A Monte Carlo computer code was used to calculate the sensitivity and resolution of the spectrometer. Data taken on Proto-I show a 150 keV to 250 keV wide proton energy spectrum at each instant in time.
Date: January 1, 1983
Creator: Leeper, R J; Lee, J R; Kissel, L; Johnson, D J; Stygar, W A; Hebron, D E et al.
Partner: UNT Libraries Government Documents Department

Experimental results and modeling of a dynamic hohlraum on SATURN

Description: Experiments were performed at SATURN, a high current z-pinch, to explore the feasibility of creating a hohlraum by imploding a tungsten wire array onto a low-density foam. Emission measurements in the 200--280 eV energy band were consistent with a 110--135 eV Planckian before the target shock heated, or stagnated, on-axis. Peak pinch radiation temperatures of nominally 160 eV were obtained. Measured early time x-ray emission histories and temperature estimates agree well with modeled performance in the 200--280 eV band using a 2D radiation magneto-hydrodynamics code. However, significant differences are observed in comparisons of the x-ray images and 2D simulations.
Date: June 1, 1998
Creator: Derzon, M.S.; Allshouse, G.O.; Deeney, C.; Leeper, R.J.; Nash, T.J.; Matuska, W. et al.
Partner: UNT Libraries Government Documents Department

Z-Pinch Generated X-Rays Demonstrate Indirect-Drive ICF Potential

Description: Hohlraums (measuring 6-mm in diameter by 7-mm in height) have been heated by x-rays from a z-pinch. Over measured x-ray input powers P of 0.7 to 13 TW, the hohlraum radiation temperature T increases from {approximately}55 to {approximately}130 eV, and is in agreement with the Planckian relation P-T{sup 4}. The results suggest that indirect-drive ICF studies involving NIF relevant pulse shapes and &lt;2-mm diameter capsules can he studied using this arrangement.
Date: June 16, 1999
Creator: Bowers, R.L.; Chandler, G.A.; Derzon, M.S.; Hebron, D.E.; Leeper, R.J.; Matzen, M.K. et al.
Partner: UNT Libraries Government Documents Department

Z-Pinch Generated X-Rays in Static-Wall Hohlraum Geometry Demonstrate Potential for Indirect-Drive ICF Studies

Description: Hohlraums of full ignition scale (6-mm diameter by 7-mm length) have been heated by x-rays from a z-pinch target on Z to a variety of temperatures and pulse shapes which can be used to simulate the early phases of the National Ignition Facility (NIF) temperature drive. The pulse shape is varied by changing the on-axis target of the z pinch in a static-wall-hohlraum geometry. A 2-{micro}m-thick walled Cu cylindrical target of 8-mm diameter filled with 10 mg/cm{sup 3} CH, for example, produces foot-pulse conditions of {minus}85 eV for a duration of {approximately} 10 ns, while a solid cylindrical target of 5-mm diameter and 14-mg/cm{sup 3} CH generates first-step-pulse conditions of {approximately} 122 eV for a duration of a few ns. Alternatively, reducing the hohlraum size (to 4-mm diameter by 4-mm length) with the latter target has increased the peak temperature to {approximately} 150 eV, which is characteristic of a second-step-pulse temperature. In general, the temperature T of these x-ray driven hohlraums is in agreement with the Planckian relation (T-(P/A){sup 1/4}). P is the measured x-ray input power and A is the surface area of the hohlraum. Fully-integrated 2-D radiation-hydrodynamic simulations of the z pinch and subsequent hohlraum heating show plasma densities within the useful volume of the hohlraums to be on the order of air or less.
Date: August 25, 1999
Creator: Sandord, T.W.L.; Olson, R.E.; Chandler, G.A.; Hebron, D.E.; Mock, R.C.; Leeper, R.J. et al.
Partner: UNT Libraries Government Documents Department

Ion beam generation and focusing on PBFA (Particle Beam Fusion Accelerator) II

Description: During the past year we have succeeded in obtaining a 5 TW/cm{sup 2} proton focus on Sandia National Laboratories' Particle Beam Fusion Accelerator (PBFA) II. This has allowed us to shift our experimental emphasis to the implementation of an improved ion diode geometry for higher voltage operation, full azimuthal beam characterization, and especially lithium ion source experiments. We have made significant progress in each of these areas during the past year, demonstrating 10 MV diode operation, {plus minus}10% azimuthal beam symmetry, and promising initial results from lithium ion source experiments. 8 refs., 6 figs.
Date: January 1, 1990
Creator: Stinnett, R.W.; Bailey, J.E.; Bieg, K.W.; Coats, R.S.; Chandler, G.; Derzon, M.S. et al.
Partner: UNT Libraries Government Documents Department

Light ion sources and target results on PBFA II (Particle Beam Fusion Accelerator II)

Description: Advances in ion beam theory, diagnostics, and experiments in the past two years have enabled efficient generation of intense proton beams on PBFA II, and focusing of the beam power to 5.4 TW/cm{sup 2} on a 6-mm-diameter target. Target experiments have been started with the intense proton beams, since the range of protons at 4--5 MeV is equivalent to that of lithium at 30 MeV. Three series of experiments have been conducted using planar, conical, and cylindrical targets. These tests have provided information on ion beam power density, uniformity, and energy deposition. In order to increase the power density substantially for target implosion experiments, we are now concentrating on development of high voltage lithium ion beams. 10 refs., 13 figs.
Date: January 1, 1990
Creator: Cook, D.L.; Bailey, J.E.; Bieg, K.W.; Bloomquist, D.D.; Coats, R.S.; Chandler, G.C. et al.
Partner: UNT Libraries Government Documents Department

Neutron spectrometry - An essential tool for diagnosing implosions at the National Ignition Facility

Description: DT neutron yield (Y{sub n}), ion temperature (T{sub 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 redundancy required for reliable measurements of Yn, Ti and dsr. From the measured dsr value, an areal density ({rho}R) is determined from the relationship {rho}R{sub tot} (g/cm{sup 2}) = (20.4 {+-} 0.6) x dsr{sub 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. The spectrometers are now performing to the required accuracy, as indicated by the good agreement between the different measurements over several commissioning shots. In addition, 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 {rho}R) and Y{sub n}, has improved almost two orders of magnitude since the first shot in September, 2010.
Date: May 2, 2012
Creator: Mackinnon, A J; Johnson, M G; Frenje, J A; Casey, D T; Li, C K; Seguin, F H et al.
Partner: UNT Libraries Government Documents Department

Z-Pinch Driven Inertial Confinement Fusion Target Physics Research at Sandia National Laboratories

Description: Three hohlraum concepts are being pursued at Sandia National Laboratories (SNL) to investigate the possibility of using pulsed power driven magnetic implosions (z-pinches) to drive high gain targets capable of yields in the range of 200-1000 MJ. This research is being conducted on SNL'S.Z facility that is capable of driving peak currents of 20 MA in z-pinch loads producing implosion velocities as high as 7.5X 107 cm/s, x-ray energies approaching 2 MJ, and x-ray powers exceeding 200 TW. This paper will discuss each of these hohlraum concepts and will overview the experiments that have been conducted on these systems to date.
Date: October 27, 1998
Creator: Alberts, T.E.; Asay, J.R.; Baca, P.M.; Baker, K.L.; Breeze, S.P.; Chandler, G.A. et al.
Partner: UNT Libraries Government Documents Department