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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 <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

X-ray Conversion Efficiency of high-Z hohlraum wall materials for indirect drive ignition

Description: We measure the conversion efficiency of 351 nm laser light to soft x-rays (0.1-5 keV) for Au, U and high Z mixtures 'cocktails' used for hohlraum wall materials in indirect drive ICF. We use spherical targets in a direct drive geometry, flattop laser pulses and laser smoothing with phase plates to achieve constant and uniform laser intensities of 10{sup 14} and 10{sup 15} W/cm{sup 2} over the target surface that are relevant for the future ignition experiments on NIF. The absolute time and spectrally-resolved radiation flux is measured with a multichannel soft x-ray power diagnostic. The conversion efficiency is then calculated by dividing the measured x-ray power by the incident laser power from which the measured laser backscattering losses is subtracted. After {approx}0.5 ns, the time resolved x-ray conversion efficiency reaches a slowly increasing plateau of 95% at 10{sup 14} W/cm{sup 2} laser intensity and of 80% at 10{sup 15} W/cm{sup 2}. The M-band flux (2-5 keV) is negligible at 10{sup 14} W/cm{sup 2} reaching {approx}1% of the total x-ray flux for all target materials. In contrast, the M-band flux is significant and depends on the target material at 10{sup 15} W/cm{sup 2} laser intensity, reaching values between 10% of the total flux for U and 27% for Au. Our LASNEX simulations show good agreement in conversion efficiency and radiated spectra with data when using XSN atomic physics model and a flux limiter of 0.15, but they underestimate the generated M-band flux.
Date: February 22, 2008
Creator: Dewald, E; Rosen, M; Glenzer, S H; Suter, L J; Girard, F; Jadaud, J P et al.
Partner: UNT Libraries Government Documents Department

Wire-number effects on high-power annular z-pinches and some characteristics at high wire number

Description: Characteristics of annular wire-array z-pinches as a function of wire number and at high wire number are reviewed. The data, taken primarily using aluminum wires on Saturn are comprehensive. The experiments have provided important insights into the features of wire-array dynamics critical for high x-ray power generation, and have initiated a renaissance in z-pinches when high numbers of wires are used. In this regime, for example, radiation environments characteristic of those encountered during the early pulses required for indirect-drive ICF ignition on the NIF have been produced in hohlraums driven by x-rays from a z-pinch, and are commented on here.
Date: May 23, 2000
Creator: SANFORD,THOMAS W. L.
Partner: UNT Libraries Government Documents Department

Scaling and optimization of the radiation temperature in dynamic hohlraums

Description: The authors have constructed a quasi-analytic model of the dynamic hohlraum. Solutions only require a numerical root solve, which can be done very quickly. Results of the model are compared to both experiments and full numerical simulations with good agreement. The computational simplicity of the model allows one to find the behavior of the hohlraum temperature as a function the various parameters of the system and thus find optimum parameters as a function of the driving current. The model is used to investigate the benefits of ablative standoff and axial convergence.
Date: April 13, 2000
Creator: SLUTZ,STEPHEN A.; DOUGLAS,MELISSA R.; LASH,JOEL S.; VESEY,ROGER A.; CHANDLER,GORDON A.; NASH,THOMAS J. et al.
Partner: UNT Libraries Government Documents Department

High yield ICF target design for a Z-pinch driven hohlraum

Description: We describe calculations for a high yield inertial fusion design, employing indirect drive with a double-ended z-pinch-driven hohlraum radiation source. A high current ({approximately}60 MA) accelerator implodes z-pinches within an enclosing hohlraum. Radial spoke arrays and shine shields isolate the capsule from the pinch plasma, magnetic field and direct x-ray shine. Our approach places minimal requirements on z-pinch uniformity and stability, usually problematic due to magneto-Rayleigh Taylor (MRT) instability. Large inhomogeneities of the pinch and spoke array may be present, but the hohlraum adequately smooths the radiation field at the capsule. Simultaneity and reproducibility of the pinch x-ray output to better than 7% are required, however, for good symmetry. Recent experiments suggest a pulse shaping technique, through implosion of a multishell z-pinch. X-ray bursts are calculated and observed to occur at each shell collision. A capsule absorbing 1 MJ of x-rays at a peak drive temperature of 210 eV is found to have adequate stability and to produce 400 MJ of yield.
Date: November 13, 1998
Creator: Bailey, D.S.; Hammer, J.H.; Lindl, J.D.; Rambo, P.W.; Tabak, M.; Toor, A. et al.
Partner: UNT Libraries Government Documents Department

EXPERIMENTAL TARGET INJECTION AND TRACKING SYSTEM CONSTRUCTION AND SINGLE SHOT TESTING

Description: Targets must be injected into an IFE power plant at a rate of approximately 5 to 10 Hz. Targets must be tracked very accurately to allow driver beams to be aligned with defined points on the targets with accuracy {+-} 150 {micro}m for indirect drive and {+-} 20 {micro}m for direct drive. An experimental target injection and tracking system has been constructed at General Atomics. The injector system will be used as a tool for testing the survivability of various target designs and provide feedback to the target designers. Helium gas propels the targets down an 8 m gun barrel up to 400 m/s. Direct-drive targets are protected in the barrel by sabots that are spring loaded to separate into two halves after acceleration. A sabot deflector directs the sabot halves away from the target injection path. Targets will be optically tracked with laser beams and line-scan cameras. Target position and arrival time will be predicted in real time based on early target position measurements. The system installation will be described. System testing to overcome excessive projectile wear and debris in the gun barrel is presented.
Date: September 1, 2003
Creator: PETZOLDT,R.W; ALEXANDER,N.B; DRAKE,T.J; GOODIN,D.T; JONESTRACK,K & VERMILLION,B.A
Partner: UNT Libraries Government Documents Department

IMPLOSION OF INDIRECTLY DRIVEN REENTRANT CONE SHELL TARGET

Description: OAK-B135 The authors have examined the implosion of an indirectly driven reentrant-cone shell target to clarify the issues attendant on compressing fuel for a fast ignition target. The target design is roughly hydrodynamic equivalent to a NIF cryo-ignition target, but scaled down to be driven by Omega. A sequence of backlit x-radiographs recorded each implosion. The collapse was also modeled with LASNEX, generating simulated radiographs. They compare experimental and simulated diameter, density and symmetry as functions of time near stagnation. The simulations were generally in good agreement with the experiments with respect to the shell, but did not show the opacity due to ablation of gold off the cone; non-thermal gold M-line radiation from the hohlraum wall penetrates the shell and drives this ablation causing some Au to mix into the low density center of the core and into the region between the core and cone. This might be a problem in a cryo-ignition target.
Date: August 1, 2003
Creator: STEPHENS,RB
Partner: UNT Libraries Government Documents Department

O-d energetics scaling models for Z-pinch-driven hohlraums

Description: Wire array Z-pinches on the Z accelerator provide the most intense laboratory source of soft x-rays in the world. The unique combination of a highly-Planckian radiation source with high x-ray production efficiency (15% wall plug), large x-ray powers and energies ( >150 TW, {ge}1 MJ in 7 ns), large characteristic hohlraum volumes (0.5 to >10 cm{sup 3}), and long pulse-lengths (5 to 20 ns) may make Z-pinches a good match to the requirements for driving high-yield scale ICF capsules with adequate radiation symmetry and margin. The Z-pinch driven hohlraum approach of Hammer and Porter [Phys.Plasmas, 6, 2129(1999)] may provide a conservative and robust solution to the requirements for high yield, and is currently being studied on the Z accelerator. This paper describes a multiple region, 0-d hohlraum energetic model for Z-pinch driven hohlraums in four configurations. The authors observe consistency between the models and the measured x-ray powers and hohlraum wall temperatures to within {+-}20% in flux, for the four configurations.
Date: June 8, 2000
Creator: CUNEO,MICHAEL E.; VESEY,ROGER A.; HAMMER,J.H. & PORTER,JOHN L.
Partner: UNT Libraries Government Documents Department

Z-pinch driven fusion energy

Description: The Z machine at Sandia National Laboratories (SNL) is the most powerful multi-module synchronized pulsed-power accelerator in the world. Rapid development of z-pinch loads on Z has led to outstanding progress in the last few years, resulting in radiative powers of up to 280 TW in 4 ns and a total radiated x-ray energy of 1.8 MJ. The present goal is to demonstrate single-shot, high-yield fusion capsules. Pulsed power is a robust and inexpensive technology, which should be well suited for Inertial Fusion Energy, but a rep-rated capability is needed. Recent developments have led to a viable conceptual approach for a rep-rated z-pinch power plant for IFE. This concept exploits the advantages of going to high yield (a few GJ) at low rep-rate ({approximately} 0.1 Hz), and using a Recyclable Transmission Line (RTL) to provide the necessary standoff between the fusion target and the power plant chamber. In this approach, a portion of the transmission line near the capsule is replaced after each shot. The RTL should be constructed of materials that can easily be separated from the liquid coolant stream and refabricated for a subsequent shots. One possibility is that most of the RTL is formed by casting FLiBe, a salt composed of fluorine, lithium, and beryllium, which is an attractive choice for the reactor coolant, with chemically compatible lead or tin on the surface to provide conductivity. The authors estimate that fusion yields greater than 1 GJ will be required for efficient generation of electricity. Calculations indicate that the first wall will have an acceptable lifetime with these high yields if blast mitigation techniques are used. Furthermore, yields above 5 GJ may allow the use of a compact blanket direct conversion scheme.
Date: May 30, 2000
Creator: SLUTZ,STEPHEN A.; OLSON,CRAIG L.; ROCHAU,GARY E.; DERZON,MARK S.; PETERSON,P.F.; DEGROOT,J.S. et al.
Partner: UNT Libraries Government Documents Department

Target technologies for indirect drive ignition on the NIF

Description: X-ray driven ignition targets for the NIF will include fuel capsule materials different from those used up to now in ICF experiments. They will contain cryogenic fuel layers, and will be enclosed in cryogenic hohlraums. These hohlraums must provide the thermal environment required to shape the fuel layers, and must be supported by cryogenic equipment in the NIF target chamber. The methods for filling and delivering the targets to the NIF chamber will combine high-temperature diffusion with cryogenic transport. A program is in place in the US to design and develop the ignition targets, and the cryogenic support and fill systems needed to field them. This program includes participation from Lawrence Livermore National Laboratory, Los Alamos National Laboratory, and General Atomics.
Date: September 9, 1999
Creator: Bernat, T P
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 magnet 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 {approx}85 eV for a duration of {approx}10 ns, while a solid cylindrical target of 5-mm diameter and 14-mg/cm{sup 3} CH generates first-step-pulse conditions of {approx}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 {approx}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{approx}(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: November 1, 1999
Creator: BOWERS,RICHARD; CHANDLER,GORDON A.; HEBRON,DAVID E.; LEEPER,RAMON J.; MATUSLKA,WALTER; MOCK,RAYMOND CECIL et al.
Partner: UNT Libraries Government Documents Department

Baseline unconverted light management (indirect drive configuration)

Description: This document defines the baseline plan for the management of unconverted light in the NIF target chamber. It includes a detailed description of the characteristics of the diffractive optics (color separation grating) and their orientation for each beam. The resulting unconverted light distribution is then described in a form that will ease experiment planning.
Date: March 30, 1999
Creator: Dixit, S & Kalantar, D
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

Characteristics of ICF Relevant Hohlraums Driven by X-Rays from a Z-Pinch

Description: Radiation environments characteristic of those encountered during the low-temperature foot pulse and subsequent higher-temperature early-step pulses (without the foot pulse) required for indirect-drive ICF ignition on the National ignition Facility have been produced in hohlraums driven by x-rays from a z-pinch. These environments provide a platform to better understand the dynamics of full-scale NIF hohlraums, ablator material, and capsules prior to NIF completion. Radiation temperature, plasma fill, and wall motion of these hohlraums are discussed.
Date: November 3, 1999
Creator: BOWERS,R.L.; CHANDLER,GORDON A.; HEBRON,DAVID E.; LEEPER,RAMON J.; MATUSKA,W.; MOCK,RAYMOND CECIL et al.
Partner: UNT Libraries Government Documents Department

ICF quarterly report October-December 1998 volume 8, number 1

Description: This issue of the ICF Quarterly Report focuses on the final section of the 192-arm, 1.8-MJ National Ignition Facility (NIF). We describe both technological advances necessary for optimal utilization of the delivered energy and the hohlraum physics resulting from extremely high energy densities. Two articles belong to the first category. The conversion of infrared light to ultraviolet occurs at the tripler in the NIF's Final Optics Assembly. It is then necessary to separate any unconverted (first- and second-harmonic) light from the tripled-frequency light passed to the target. Large-Aperture Color-Separation Gratings for Diverting Unconverted Light Away from the NIF Target describes the design and fabrication of novel diffraction gratings that fulfill this function. In both direct- and indirect-drive ICF, the symmetry of the capsule as it compresses is crucial. The NIF will have 48 clusters of four beams incident on targets. Optimization of Beam Angles for the National Ignition Facility (p. 15) presents the rationale used to assign beam angles for cylindrical indirect drive while still allowing direct-drive and tetrahedral indirect-drive experiments to be performed.
Date: September 8, 1998
Creator: Feit, M
Partner: UNT Libraries Government Documents Department

Stockpile Stewardship and the National Ignition Facility

Description: The National Ignition Facility (NIF), the world's most energetic laser system, is operational at Lawrence Livermore National Laboratory (LLNL). Since the completion of the construction project in March 2009, NIF has completed nearly 150 target experiments for the National Ignition Campaign (NIC), High Energy Density Stewardship Science (HEDSS) in the areas of radiation transport, material dynamics at high pressure in the solid state, as well as fundamental science and other national security missions. NIF capabilities and infrastructure are in place to support all of its missions with over 50 X-ray, optical and nuclear diagnostic systems and the ability to shoot cryogenic targets and DT layered capsules. NIF is now qualified for use of tritium and other special materials as well as to perform high yield experiments and classified experiments. DT implosions with record indirect-drive neutron yield of 4.5 x 10{sup 14} neutrons have been achieved. A series of 43 experiments were successfully executed over a 27-day period, demonstrating the ability to perform precise experiments in new regimes of interest to HEDSS. This talk will provide an update of the progress on the NIF capabilities, NIC accomplishments, as well as HEDSS and fundamental science experimental results and an update of the experimental plans for the coming year.
Date: January 4, 2012
Creator: Moses, E.
Partner: UNT Libraries Government Documents Department

Suppression of Stimulated Brillouin Scattering in multiple-ion species inertial confinemen fusion Hohlraum Plasmas

Description: A long-standing problem in the field of laser-plasma interactions is to successfully employ multiple-ion species plasmas to reduce stimulated Brillouin scattering (SBS) in inertial confinement fusion (ICF) hohlraum conditions. Multiple-ion species increase significantly the linear Landau damping for acoustic waves. Consequently, recent hohlraum designs for indirect-drive ignition on the National Ignition Facility investigate wall liner material options so that the liner gain for parametric instabilities will be below threshold for the onset SBS. Although the effect of two-ion species plasmas on Landau damping has been directly observed with Thomson scattering, early experiments on SBS in these plasmas have suffered from competing non-linear effects or laser beam filamentation. In this study, a reduction of SBS scattering to below the percent level has been observed in hohlraums at Omega that emulate the plasma conditions in an indirect drive ICF experiments. These experiments have measured the laser-plasma interaction processes in ignition-relevant high-electron temperature regime demonstrating Landau damping as a controlling process for SBS. The hohlraums have been filled with various fractions of CO{sub 2} and C{sub 3}H{sub 8} varying the ratio of the light (H) to heavy (C and O) ion density from 0 to 2.6. They have been heated by 14.5 kJ of 351-nm light, thus increasing progressively Landau damping by an order of magnitude at constant electron density and temperature. A delayed 351-nm interaction beam, spatially smoothed to produce a 200-{micro}m laser spot at best focus, has propagated along the axis of the hohlraum. The backscattered light, both into the lens and outside, the transmitted light through the hohlraum plasma and the radiation temperature of the hohlraum has been measured. For ignition relevant laser intensities (3-9 10{sup 14} Wcm{sup -2}), we find that the SBS reflectivity scales as predicted with Landau damping from >30% to <1%. Simultaneously, the hohlraum radiation temperature ...
Date: May 14, 2007
Creator: Neumayer, P
Partner: UNT Libraries Government Documents Department

Thermal Infrared Exposure of Cryogenic Indirect Drive ICF Targets

Description: Cryogenic inertial confinement fusion targets at the National Ignition Facility and the Laser Megajoule will be protected from thermal infrared radiation by a cold shroud. As the shroud is removed just before the laser pulse, infrared radiation will heat and possibly degrade the symmetry of the solid hydrogen fuel layer. A lumped component mathematical model has been constructed to calculate how long an indirect drive target can be exposed to thermal radiation before the fuel layer degrades. The allowed exposure time sets the maximum shroud removal time and therefore has important implications for the design of the cryogenic shroud systems. The model predicts that the maximum exposure time is approximately 0.18 s for plastic capsules inside hohlraums with transparent laser entrance holes. By covering the laser entrance holes with a partially reflective coating, the exposure time can be increased to approximately 1 s. The exposure time can be increased to about 2 s by using beryllium capsules. Several other design concepts could increase the exposure time even further. Lengthening of the allowed exposure time to 1 s or longer could allow a significant cost savings for the shroud system.
Date: July 8, 2005
Creator: London, R A; Moody, J D; Sanchez, J J; Sater, J D; Haid, B J & Bittner, D N
Partner: UNT Libraries Government Documents Department