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Prospects for inertial fusion energy based on a diode-pumped solid-state laser (DPSSL) driver: Overview and development path

Description: It is now known with certainty that the type of fusion known as inertial fusion will work with sufficient energy input, so inertial fusion is really beyond the ``scientific breakeven`` point in many respects. The most important question that remains for inertial fusion energy (IFE) is whether this type of fusion can operate with sufficiently low input energy to make it economically feasible for energy production. The constraint for low input energy demands operation near the inertial fusion ignition threshold, and such operation creates enormous challenges to discover a target design that will produce sufficient energy gain. There are also multiple issues relating to the scientific feasibility of using a laboratory-type ``driver`` to energize a target, such as those concerning bandwidth and beam smoothing for ``direct drive,`` and extension of hohlraum plasma physics to the IFE scale for ``indirect drive.`` One driver that appears as though it will be able to meet the IFE requirements, assuming modest development and sufficient target gain, is a diode-pumped solid-state laser (DPSSL). We give an overview of this type of laser system, and explain what development remains for the economic production of electricity using this type of driver for IFE.
Date: March 1, 1997
Creator: Orth, C.D.
Partner: UNT Libraries Government Documents Department

Target area design issues for implementing direct drive on the National Ignition Facility

Description: NIF will be configured in its baseline design to achieve ignition and gain using the indirect drive approach. However, the requirements require the design to not preclude the conduct of inertial confinement fusion experiments using direct drive. This involves symmetrical illumination of an ICF capsule, where each beam fully subtends the capsule. The re-directing of 24 of the 48 NIF beamlines (2x2 beamlet group each) from 30 and 50{degree} cone angles to 75{degree} cone angles near the chamber `equator` is required. This would be done by adjusting intermediate transport mirrors so that the beams intercept different final mirrors in the Target Bay and be directed into final optics assemblies attached to chamber ports positioned at the new port locations. Space for converting from one irradiation scheme to another is a problem; also NIF user needs cannot be compromised by direct drive needs. Target for direct drive, absent a hohlraum, emits much fewer cold x rays than for indirect drive. Further, the irradiation scheme may not result in the absorption of all the 3{omega} light and this may create a hazard to the NIF chamber first wall. This paper describes possible design features of the NIF Target Area to allow conversion to direct drive and discusses some differences in post-shot conditions created compared to indirect drive.
Date: June 14, 1996
Creator: Tobin, M.; Karpenko, V.; Burnham, A. & Peterson, R.
Partner: UNT Libraries Government Documents Department

Developing inertial fusion energy - Where do we go from here?

Description: Development of inertial fusion energy (IFE) will require continued R&D in target physics, driver technology, target production and delivery systems, and chamber technologies. It will also require the integration of these technologies in tests and engineering demonstrations of increasing capability and complexity. Development needs in each of these areas are discussed. It is shown how IFE development will leverage off the DOE Defense Programs funded inertial confinement fusion (ICF) work.
Date: June 11, 1996
Creator: Meier, W.R. & Logan, G.
Partner: UNT Libraries Government Documents Department

Inertial fusion energy development approaches for direct and indirect-drive

Description: Consideration of different driver and target requirements for inertial fusion energy (IFE) power plants together with the potential energy gains of direct and indirect-drive targets leads to different optimal combinations of driver and target options for each type of target. In addition, different fusion chamber concepts are likely to be most compatible with these different driver and target combinations. For example, heavy-ion drivers appear to be well matched to indirect=drive targets with all-liquid-protected-wall chambers requiring two-sided illuminations, while diode-pumped, solid- state laser drivers are better matched to direct-drive targets with chambers using solid walls or flow-guiding structures to allow spherically symmetric illuminations. R&D on the critical issues of drivers, targets, and chambers for both direct and indirect-drive options should be pursued until the ultimate gain of either type of target for IFE is better understood.
Date: August 20, 1996
Creator: Logan, B.G.; Lindl, J.D. & Meier, W.R.
Partner: UNT Libraries Government Documents Department

NIF capsule design update

Description: We describe several ignition capsule designs, for use in the National Ignition Facility. We will compare these designs for ablator efficiency, ignition margin, implosion and stability performance. This study includes capsule designs driven by x-ray drive profiles with both 300 eV and 250 eV peak temperatures. All of the 300 eV designs are tuned to implode the DT fuel in a nearly identical manner. Capsule designs consist of an ablator material (CH with Br dopant; Be with Cu dopant; and B{sub 4}C) encasing a layer of solid DT. The dopants alter material opacities sufficiently to (1) shield the DT fuel from preheat effects; and (2) develop an ablation front density profile favorable to implosion stability. B{sub 4}C has sufficient opacity at 300 eV that a dopant is not necessary. Issues relating to material properties and fabrication will be described.
Date: October 1, 1996
Creator: Dittrich, T.R.; Haan, S.W.; Pollaine, S.; Burnham, A.K. & Strobel, G.L.
Partner: UNT Libraries Government Documents Department

All Solid State Optical Pulse Shaper for the OMEGA Laser Fusion Facility

Description: OAK-B135 All Solid State Optical Pulse Shaper for the OMEGA Laser Fusion Facility. The authors have developed an all-solid-state, compact, computer-controlled, flexible optical pulse shaper for the OMEGA laser facility. This pulse shaper produces high bandwidth, temporally shaped laser pulses that meet OMEGA requirements. The design is a significant simplification over existing technology with improved performance capabilities.
Date: July 24, 2000
Partner: UNT Libraries Government Documents Department

Edward Teller medal lecture: high intensity lasers and the road to ignition

Description: There has been much progress in the development of high intensity lasers and in the science of laser driven inertially confined fusion such that ignition is now a near term prospect. This lecture reviews the field with particular emphasis on areas of my own involvement.
Date: June 2, 1997
Creator: Key, M. H.
Partner: UNT Libraries Government Documents Department

Recent advances and challenges for diode-pumped solid-state lasers as an inertial fusion energy driver candidate

Description: We discuss how solid-state laser technology can serve in the interests of fusion energy beyond the goals of the National Ignition Facility (NIF), which is now being constructed to ignite a deuterium-tritium target to fusion conditions in the laboratory for the first time. We think that advanced solid-state laser technology can offer the repetition-rate and efficiency needed to drive a fusion power plant, in contrast to the single-shot character of NIF. As discuss below, we propose that a gas-cooled, diode-pumped Yb:S-FAP laser can provide a new paradigm for fusion laser technology leading into the next century.
Date: December 23, 1997
Creator: Payne, S.A.; Beach, R.J. & Bibeau, C.
Partner: UNT Libraries Government Documents Department

Multiple-beam pulse shaping and preamplification

Description: Glass fusion laser systems typically use a master oscillator-power amplifier (MOPA) architecture, where control of the optical pulse temporal and spatial parameters is accomplished mainly in the master oscillator and low power optics. The pulses from this low power ``front end`` are amplified in the power amplifier, which modifies the pulse shape temporally and spatially. Nonlinear frequency conversion crystals following the amplifier further change the pulse before it reaches the target. To effectively control the optical pulse on target for different types of experiments, and compensate for nonlinearity in the preceding optics, the front end system must be versatile enough to easily control many pulse parameters over a large range. The front end pulse generation system described in this article represents a new approach to this problem. The proposed National Ignition Facility (NIF) has 192 beamlines, each of which requires an input pulse of up to 12 Joules in around 4 ns equivalent square pulse length. Considerations of laser architecture for supplying each of these beamlines from a central oscillator system were crucial in the design of the front end. Previous lasers have used bulk optics to split a single oscillator signal and report beams to multiple amplifier chains. A key idea in the current design is to replace bulk optic transport with fibers, eliminating large opto-mechanical subsystems. Another important concept is convenient pulse forming using low voltage integrated optic modulators. The integrated optic and fiber optic concepts resulted in the current pulse generation designs for NEF. An important advantage is that each of the beamlines can have an independently controlled temporal pulse shape, which provides for precise balance of instantaneous power on target.
Date: November 9, 1994
Creator: Wilcox, R.B.; VanWonterghem, B.W.; Burkhart, S.C. & Davin, J.M.
Partner: UNT Libraries Government Documents Department

The use of an intermediate wavelength laser for alignment to inertial confinement fusion targets

Description: The conceptual design of the National Ignition Facility (NIF) 192 beam laser incorporates a low-power alignment beam injected in the pinhole plane of the final spatial filter with a wave length intermediate between the 1053 mn laser output and the 351 mn frequency-converted beam that illuminates the target Choosing the specific wavelength for which the spatial filter plane is reimaged in the same target chamber plane as the frequency-converted main laser pulse, achieves optimum accuracy without the need for additional means to insure precise overlap between the two beams. Insertion of the alignment beam after the last laser amplifier also allows alignment to the target while the amplifiers are still cooling from a previous shot.
Date: September 21, 1995
Creator: English, R.E. Jr.; Seppala, L.G.; Vann, C.S. & Bliss, E.S.
Partner: UNT Libraries Government Documents Department

Laser diagnostic for high-energy, laser fusion drivers

Description: A complete set of diagnostics for use on a frequency-tripled high-energy glass laser system is described. We employed high resolution imaging, temporal pulse-shape, beam bandwidth, phase-front, and precision energy instrumentation.
Date: November 8, 1994
Creator: Burkhart, S.C.; Behrendt, W. & Smith, I.
Partner: UNT Libraries Government Documents Department


Description: OAK-B135 Fast ignition is a novel scheme for achieving laser fusion. A class of these targets involves cone mounted CH shells. The authors have been fabricating such targets with shells with a wide variety of diameters and wall thicknesses for several years at General Atomics. In addition, recently such shells were needed for implosion experiments at Laboratory for Laser Energetics (LLE) that for the first time were required to be gas retentive. Fabrication of these targets requires producing appropriate cones and shells, assembling the targets, and characterization of the assembled targets. The cones are produced using micromachining and plating techniques. The shells are fabricated using the depolymerizable mandrel technique followed by micromachining a hole for the cone. The cone and the shell then need to be assembled properly for gas retention and precisely in order to position the cone tip at the desired position within the shell. Both are critical for the fast ignition experiments. The presence of the cone in the shell creates new challenges in characterization of the assembled targets. Finally, for targets requiring a gas fill, the cone-shell assembly needs to be tested for gas retention and proper strength at the glue joint. This paper presents an overview of the developmental efforts and technical issues addressed during the fabrication of fast ignition targets.
Date: June 1, 2003
Partner: UNT Libraries Government Documents Department

Large-aperture, high-damage-threshold optics for beamlet

Description: Beamlet serves as a test bed for the proposed NIF laser design and components. Therefore, its optics are similar in size and quality to those proposed for the NIF. In general, the optics in the main laser cavity and transport section of Beamlet are larger and have higher damage thresholds than the optics manufactured for any of our previous laser systems. In addition, the quality of the Beamlet optical materials is higher, leading to better wavefront quality, higher optical transmission, and lower-intensity modulation of the output laser beam than, for example, that typically achieved on Nova. In this article, we discuss the properties and characteristics of the large-aperture optics used on Beamlet.
Date: February 23, 1995
Creator: Campbell, J.H.; Atherton, L.J.; DeYoreo, J.J.; Kozlowski, M.R.; Maney, R.T.; Montesanti, R.C. et al.
Partner: UNT Libraries Government Documents Department

Penetrating radiation impact on NIF final optic components

Description: Goal of the National Ignition Facility (NIF) is to achieve thermonuclear ignition in a laboratory environment in inertial confinement fusion (ICF). This will enable NIF to service the DOE stockpile stewardship management program, inertial fusion energy goals, and advance scientific frontiers. All of these applications will make use of the extreme conditions that the facility will create in the target chamber. In the case of a prospected 20 MJ yield scenario, NIF will produce 10{sup 19} neutrons with DT fusion 14 MeV energy per neutron. There will also be high-energy x rays as well as solid, liquid, and gaseous target debris produced either directly or indirectly by the inertial confinement fusion process. A critical design issue is the protection of the final optical components as well as sophisticated target diagnostics in such a harsh environment.
Date: October 15, 1996
Creator: Marshall, C.D.; Speth, J.A.; DeLoach, L.D. & Payne, S.A.
Partner: UNT Libraries Government Documents Department

Wavefront correction for static and dynamic aberrations to within 1 second of the system shot in the NIF Beamlet demonstration facility

Description: The laser wavefront of the NIF Beamlet demonstration system is corrected for static aberrations with a wavefront control system. The system operates closed loop with a probe beam prior to a shot and has a loop bandwidth of about 3 Hz. However, until recently the wavefront control system was disabled several minutes prior to the shot to allow time to manually reconfigure its attenuators and probe beam insertion mechanism to shot mode. Thermally-induced dynamic variations in gas density in the Beamlet main beam line produce significant wavefront error. After about 5-8 seconds, the wavefront error has increased to a new, higher level due to turbulence- induced aberrations no longer being corrected- This implies that there is a turbulence-induced aberration noise bandwidth of less than one Hertz, and that the wavefront controller could correct for the majority of turbulence-induced aberration (about one- third wave) by automating its reconfiguration to occur within one second of the shot, This modification was recently implemented on Beamlet; we call this modification the t{sub 0}-1 system.
Date: October 1, 1996
Creator: Hartley, R.; Kartz, M. & Behrendt, W.
Partner: UNT Libraries Government Documents Department

Mechanical beam isolator

Description: Back-reflections from a target, lenses, etc. can gain energy passing backwards through a laser just like the main beam gains energy passing forwards. Unless something blocks these back-reflections early in their path, they can seriously damage the laser. A Mechanical Beam Isolator is a device that blocks back-reflections early, relatively inexpensively, and without introducing aberrations to the laser beam.
Date: October 1996
Creator: Post, R. F. & Vann, C. S.
Partner: UNT Libraries Government Documents Department

Small Inertial Fusion Energy (IFE) demonstration reactors

Description: ICF target design studies done for the Nova Upgrade have identified conditions under which the target ignition ``cliff`` is shifted to much lower drive energy albeit with the penalty that the gain achieved at a given energy is also smaller. These targets would repeatedly produce the output and spectra of a higher gain targets at low yield. They should, thus, allow building much smaller R&D reactors with full thermonuclear effects. Demonstration reactor at the 1 to 100 MW{sub e} level appear to be feasible with driver energies of 0.5 to 2.0 MJ per pulse. These smaller, less expensive test and demonstration facilities should result in lower IFE development cost. If the U.S. government builds a driver and target factory, it is also conceivable that commercial organizations could build their own scaled concepts of IFE reactors using the beams and targets supplied by the government`s facilities.
Date: October 3, 1991
Creator: Hogan, W.J.
Partner: UNT Libraries Government Documents Department

Electro-optical deflectors as a method of beam smoothing for Inertial Confinement Fusion

Description: The electro-optic deflector is analyzed and compared to smoothing by spectral dispersion for efficacy as a beam smoothing method for ICF. It is found that the electro-optic deflector is inherently somewhat less efficient when compared either on the basis of equal peak phase modulation or equal generated bandwidth.
Date: January 1, 1997
Creator: Rothenberg, J.E.
Partner: UNT Libraries Government Documents Department

Development and evaluation of first wall materials for the National Ignition Facility

Description: Several low-Z refractory materials are evaluated for use as the NIF first wall in terms of their cost and ability to survive laser light, target emissions and debris, as well as be cleanable and not outgas excessively. Best performers contain B, C, or both, with B{sub 4}C being the best overall. It appears possible at this time that plasma-sprayed B{sub 4}C can be fabricated with low enough porosity and cost to be preferred to hot-pressed B{sub 4}C, the conservative choice.
Date: June 12, 1996
Creator: Burnham, A.K.; Tobin, M.T.; Anderson, A.T.; Honea, E.C.; Skulina, K.M.; Milam, D. et al.
Partner: UNT Libraries Government Documents Department

Diode-pumped solid state lasers (DPSSLs) for Inertial Fusion Energy (IFE)

Description: The status of diode-pumped, transverse-gas-flow cooled, Yb-S-FAP slab lasers is reviewed. Recently acquired experimental performance data are combined with a cost/performance IFE driver design code to define a cost-effective development path for IFE DPSSL drivers. Specific design parameters are described for the Mercury 100J/10 Hz, 1 kW system (first in the development scenario).
Date: October 1, 1996
Creator: Krupke, W.F.
Partner: UNT Libraries Government Documents Department

Construction safety program for the National Ignition Facility

Description: The Construction Safety Program (CSP) for NIF sets forth the responsibilities, guidelines, rules, policies and regulations for all workers involved in the construction, special equipment installation, acceptance testing, and initial activation and operation of NIF at LLNL during the construction period of NIF. During this period, all workers are required to implement measures to create a universal awareness which promotes safe practice at the work site, and which will achieve NIF`s management objectives in preventing accidents and illnesses. Construction safety for NIF is predicated on everyone performing their jobs in a manner which prevents job-related disabling injuries and illnesses. The CSP outlines the minimum environment, safety, and health (ES&H) standards, LLNL policies and the Construction Industry Institute (CII) Zero Injury Techniques requirements that all workers at the NIF construction site shall adhere to during the construction period of NIF. It identifies the safety requirements which the NIF organizational Elements, construction contractors and construction subcontractors must include in their safety plans for the construction period of NIF, and presents safety protocols and guidelines which workers shall follow to assure a safe and healthful work environment. The CSP also identifies the ES&H responsibilities of LLNL employees, non-LLNL employees, construction contractors, construction subcontractors, and various levels of management within the NIF Program at LLNL. In addition, the CSP contains the responsibilities and functions of ES&H support organizations and administrative groups, and describes their interactions with the NIF Program.
Date: January 1, 1997
Creator: Cerruti, S.J.
Partner: UNT Libraries Government Documents Department

Towards predicting the laser damage threshold of large-area optics

Description: As the size of optics increases, such as in the optical coatings being developed for the National Ignition Facility in US and the Laser MegaJoules in France, the difficulty also increases in measuring and defining their laser damage threshold. Measuring the threshold on small witness samples ({le}cm) rather than full aperture optic (=m) is advantageous, and in this article, the threshold of large-area components is addressed in two ways. First, a model based on the R-on-l threshold distribution is shown to predict the threshold of a large optic with a high degree of confidence. The average R-on-l threshold provides a reliable, accurate value to evaluate coatings. An automated damage test bench has been developed at CEA. Secondly, the damage threshold has to be defined according to final use of the component. LLNL has defined a functional damage threshold to set limits on maximum damage size. An empirical power law dependence of average damage size on peak fluence was found; this can be used to predict the damage behavior of large-aperture optics exhibiting the same damage morphology.
Date: October 1, 1996
Creator: Hue, J.; Genin, F.Y.; Maricle, S.M. & Kozlowski, M.R.
Partner: UNT Libraries Government Documents Department

Optical pulse generation using fiber lasers and integrated optics

Description: We have demonstrated an optical pulse forming system using fiber and integrated optics, and have designed a multiple-output system for a proposed fusion laser facility. Our approach is an advancement over previous designs for fusion lasers, and an unusual application of fiber lasers and integrated optics.
Date: March 27, 1995
Creator: Wilcox, R. B.; Browning, D. F.; Burkhart, S. C. & VanWonterghem, B. W.
Partner: UNT Libraries Government Documents Department