Debris and Shrapnel Assessments for National Ignition Facility Targets and Diagnostics PDF Download
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Languages : en
Pages : 6
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Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 6
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Book Description
Author:
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Category :
Languages : en
Pages : 6
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Book Description
A wide range of targets with laser energies spanning two orders of magnitude have been shot at the National Ignition Facility (NIF). The National Ignition Campaign (NIC) targets are cryogenic with Si supports and cooling rings attached to an Al thermo-mechanical package (TMP) with a thin (30 micron) Au hohlraum inside. Particular attention is placed on the low-energy shots where the TMP is not completely vaporized. In addition to NIC targets, a range of other targets has also been fielded on NIF. For all targets, simulations play a critical role in determining if the risks associated with debris and shrapnel are acceptable. In a number of cases, experiments were redesigned, based on simulations, to reduce risks or to obtain data. The majority of these simulations were done using the ALE-AMR code, which provides efficient late-time (100-1000X the pulse duration) 3D calculations of complex NIF targets.
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Languages : en
Pages : 6
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All experiments at the National Ignition Facility (NIF) will produce debris and shrapnel from vaporized, melted, or fragmented target/diagnostics components. For some experiments mitigation is needed to reduce the impact of debris and shrapnel on optics and diagnostics. The final optics, e.g., wedge focus lens, are protected by two layers of debris shields. There are 192 relatively thin (1-3 mm) disposable debris shields (DDS's) located in front of an equal number of thicker (10 mm) main debris shields (MDS's). The rate of deposition of debris on DDS's affects their replacement rate and hence has an impact on operations. Shrapnel (molten and solid) can have an impact on both types of debris shields. There is a benefit to better understanding these impacts and appropriate mitigation. Our experiments on the Omega laser showed that shrapnel from Ta pinhole foils could be redirected by tilting the foils. Other mitigation steps include changing location or material of the component identified as the shrapnel source. Decisions on the best method to reduce the impact of debris and shrapnel are based on results from a number of advanced simulation codes. These codes are validated by a series of dedicated experiments. One of the 3D codes, NIF's ALE-AMR, is being developed with the primary focus being a predictive capability for debris/shrapnel generation. Target experiments are planned next year on NIF using 96 beams. Evaluations of debris and shrapnel for hohlraum and capsule campaigns are presented.
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Languages : en
Pages : 3
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Activation of the Be-Cu or Ge-doped CH capsules is insignificant. DU generates higher dose rates than Au during the first day following a 20 MJ shot. Au produces higher dose rates after longer wait-periods. Contribution from activated target materials to the overall dose environment inside the Target Chamber is small. Fission gases generated from the use of DU will significantly decay away within one day after a 20 MJ shot. A typical wait period of 5 days is planned for all maintenance activities after 20 MJ shots, resulting in a significant reduction in hazards present inside the Target Bay due to the use of proposed target materials.
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Category :
Languages : en
Pages : 6
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The debris and shrapnel generated by laser targets are important factors in the operation of a large laser facility such as NIF, LMJ, and Orion. Past experience has shown that it is possible for such target debris to render diagnostics inoperable and also to penetrate or damage optical protection (debris) shields. We are developing the tools to allow evaluation of target configurations in order to better mitigate the generation and impact of debris, including development of dedicated modeling codes. In order to validate these predictive simulations, we briefly describe a series of experiments aimed at determining the amount of debris and/or shrapnel produced in controlled situations. We use glass and aerogel to capture generated debris/shrapnel. The experimental targets include hohlraums (halfraums) and thin foils in a variety of geometries. Post-shot analysis includes scanning electron microscopy and x-ray tomography. We show the results of some of these experiments and discuss modeling efforts.
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Category :
Languages : en
Pages : 12
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Lawrence Livermore National Laboratory' s (LLNL) Contained Firing Facility (CFF) is a facility to be constructed for explosives testing of up to 60 kg of explosives at LLNL' s Site 300 Explosives Test Site. The CFF will be a large, rectangular, reinforced concrete firing chamber, lined with steel for shrapnel protection. The CFF will contain several glass ports for cameras, lasers, and other diagnostic equipment to be used for data collection during planned explosives detonations. Glass is used due to the need for the greatest possible optical clarity. This study was performed during the CFF final design stage to determine probabilities and consequences (bounding and best estimate) of impact of shrapnel, due to concerns about the possible effects of rebounding shrapnel on these glass diagnostic ports. We developed a customized version of the Persistence of Vision{trademark} Ray-Tracer (POV-Ray{trademark}) version 3.02 code for the Macintosh TM Operating System (MacOS{trademark}). POV-Ray creates three- dimensional, very high quality (photo-realistic) images with realistic reflections, shading, textures, perspective, and other effects using a rendering technique called ray-tracing. It reads a text file that describes the objects and lighting in a scene and generates an image of that scene from the viewpoint of a camera, also described in the text file. The customized code (POV-Ray Shrapnel Tracker, V3.02 - Custom Build) generates fragment trajectory paths at user designated angle intervals in three dimensions, tracks these trajectory paths through any complex three-dimensional space, and outputs detailed data for each ray as requested by the user, including trajectory source location, initial direction of each trajectory, vector data for each surface/trajectory interaction, and any impacts with designated model target surfaces during any trajectory segment (direct path or reflected paths). This allows determination of the three-dimensional trajectory of each simulated particle, as well as overall and individual fragment probabilities of impact with any designated target(s) in the three-dimensional model. It also allows identification of any areas of particular concern due to grouping (in discrete areas) of fragment paths that lead to hits on the target areas of concern. The default code output includes data for specified fragment paths up through four reflections, with the number of target hits for each path segment listed. Output is grouped by target number, arbitrarily assigned in order as the target objects are declared in the input model text file. Hits on the targets are listed by path segments (e.g., direct path, one bounce, two bounces, etc.). The code has the capability to output a separate data file containing full x, y, and z directional data for each fragment path, to output just the data for a user specified number of reflections, or to output data for just the paths that lead to hits on the specified targets. The code assumes that the shrapnel originates from a point source located at the defined camera position in the model. The shrapnel pieces are assumed to be ideal, spherical, point-sized objects. Travel paths are assumed to be short and at high speed, i.e., gravitational curvature of the shrapnel paths is ignored. Reflections are assumed to be ideal, i.e., the reflection angle is equal to the incident angle. Both irregular fragment shapes and rotational momentum of the fragments would be expected to cause individual fragments to deviate from the ideal fragment paths. However, the aggregate real-world fragment paths would not be expected to significantly deviate from the ideal paths because of the averaging out of the deviations. Any collisions or other interactions between fragments are ignored. The analysis code has the capability to simulate non-ideal reflections caused by irregular fragment shapes by introducing either regular or random surface roughness or bumpiness. However, no simulation method available in the analysis code has been identified to simulate the effects of rotational energy.
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Category :
Languages : en
Pages :
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The purpose of this work is to computationally assess the threat from shrapnel generation on the National Ignition Facility (NIF) first wall, final optics, and ultimately other target chamber components. Shrapnel is defined as material.that is in a solid, liquid, or clustered-vapor phase with sufficient velocity to become a threat to exposed surfaces as a consequence of its impact. Typical NIF experiments will be of two types, low neutron yield shots in which the capsule is not cryogenically cooled, and high yield shots for which cryogenic cooling of the capsule is required. For non-cryogenic shots, shrapnel would be produced by spaIIing, melting and vaporizing of''shine shields'' by absorption and shock wave loading following 1-[omega] and 2-[omega] laser radiation. For cryogenic shots, shrapnel would be generated through shock wave splitting, spalling, and droplet formation of the cryogenic tubes following neutron energy deposition. Motion of the shrapnel is determined not only by particle velocities resulting from the neutron deposition, but also by both x-ray and debris loading arising from explosion of the hohlraum. Material responses of different target area components are computed from one- dimensional and two-dimensional stress wave propagation codes. Well developed rate-dependent spall computational models are used for stainless steel spall and splitting, . Severe cell distortion is accounted for in shine-shield and hohlraum-loading computations. Resulting distributions of shrapnel particles are traced to the first wall and optics and damage is estimated for candidate materials. First wall and optical material damage from shrapnel includes crater formation and associated extended cracking.
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Category :
Languages : en
Pages : 16
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The proposed National Ignition Facility (NIF) is a large (1.8 MJ on target at 0.35 [mu]m) multi-beam laser facility that will be used for Inertial Confinement Fusion (ICF). ICF implosions at this facility will produce core plasma temperatures over 10 keV and densities over 100 g/cm3. Properties of these plasmas can be measured by a variety of optical, x-ray, and nuclear diagnostic techniques such as those used at existing facilities like the Nova laser at the Lawrence Livermore National Laboratory (LLNL). Some of these currently used techniques will be directly applicable to NIF; others require significant development. Damage of components close to the target will be a much greater issue at NIF, necessitating the development of distant detector techniques. To penetrate the larger targets, x-ray-based core diagnostics will need to utilize substantially higher energies than are in routine use today. Penetrating nuclear-particle-based diagnostics will be particularly well suited to these implosions, and the higher nuclear yields will allow new techniques to be developed. Some examples of diagnostics used for high-density-implosion experiments at Nova and corresponding development of new techniques for NIF are discussed.
Author: National Research Council
Publisher: National Academies Press
ISBN: 0309270626
Category : Science
Languages : en
Pages : 119
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In the fall of 2010, the Office of the U.S. Department of Energy's (DOE's) Secretary for Science asked for a National Research Council (NRC) committee to investigate the prospects for generating power using inertial confinement fusion (ICF) concepts, acknowledging that a key test of viability for this concept-ignition -could be demonstrated at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) in the relatively near term. The committee was asked to provide an unclassified report. However, DOE indicated that to fully assess this topic, the committee's deliberations would have to be informed by the results of some classified experiments and information, particularly in the area of ICF targets and nonproliferation. Thus, the Panel on the Assessment of Inertial Confinement Fusion Targets ("the panel") was assembled, composed of experts able to access the needed information. The panel was charged with advising the Committee on the Prospects for Inertial Confinement Fusion Energy Systems on these issues, both by internal discussion and by this unclassified report. A Panel on Fusion Target Physics ("the panel") will serve as a technical resource to the Committee on Inertial Confinement Energy Systems ("the Committee") and will prepare a report that describes the R&D challenges to providing suitable targets, on the basis of parameters established and provided to the Panel by the Committee. The Panel on Fusion Target Physics will prepare a report that will assess the current performance of fusion targets associated with various ICF concepts in order to understand: 1. The spectrum output; 2. The illumination geometry; 3. The high-gain geometry; and 4. The robustness of the target design. The panel addressed the potential impacts of the use and development of current concepts for Inertial Fusion Energy on the proliferation of nuclear weapons information and technology, as appropriate. The Panel examined technology options, but does not provide recommendations specific to any currently operating or proposed ICF facility.
Author:
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ISBN:
Category : Power resources
Languages : en
Pages : 1364
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