Generation of debris from targets and by x-ray ablation of surrounding materials will be a matter of concern for experimenters and the operations staff at the National Ignition Facility (NIF). Target chamber and final optics protection, for example debris shield damage, and efficient facility operation drive the interest for the NIF staff. Experimenters are primarily concerned with diagnostic survivability, separation of mechanical versus radiation induced test object response in the case of effects tests, and radiation transport through the debris field when the net radiation output is used to benchmark computer codes. In addition, radiochemical analysis of activated capsule debris during ignition shots can provide a measure of the ablator. Conceptual design of the Debris Monitor and Rad-Chem Station, one of the NIF core diagnostics, is presented. Methods of debris collection, particle size and mass analysis, impulse measurement, and radiochemical analysis are given. A description of recent experiments involving debris collection and impulse measurement on the OMEGA and Pharos lasers is also provided

Barnes, C. W.

Celeste, J. R.

Davis, J. F.

Grun, J.

Miller, M. C.

Stroyer, M. A.

Suter, L. J.

Tobin, M. T.

Wilson, D. C.

UNT Digital Library

U.S.Departmentof Energy&LawrenceL1vermOreNationalLaboratoryPreprintUCRL-JC-137945Debris characterizationdiagnostic for the NationalIgnition FacilityM. C. Miller, J.R. Celeste, M.A. Stoyer, L.J. Suter,M. T. Tobin, J. Grun, J.F. Davis, C. W. Barnes, andD.C WilsonThis article was submitted to13’h Topical Conference on High-Temperature Plasma Diagnostics,Tucson, AZ, June 19–22, 2000June 7,2000Approved for public release; further dissemination unlimitedDISCLAIMERThis document waa prepared as an account of work sponsored by an agency of the United StatesGovernment. Neither the United States Government nor the University of California nor any of theiremployees, makes any warranty, express or implied, or assumes any legal liability or responsibility forthe accuracy, completeness, or usefulness of my information, apparatus, product, or process disclosed, orrepresents that its use would not infringe privately owned rights. Reference herein to any specificcommercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does notnecessarily constitute or imply its endorsement, recommendation, or favoring .by the United StatesGovernment or the University of California. The views and opinions of authors expressed herein do notnecessarily state or reflect those of the United States Government or the University of California, andshall not be used for advertising or product endorsement purposes.This is a preprint of a paper intended for publication in a journal or proceedings. Since changes maybemade before publication, this preprint is made available with the understanding that it will not be citedor reproduced without the permission of the author.This report has been reproduceddirectly from the best available copy.Available to DOE and DOE contractors from theOffice of Scientificand Technical InformationP.O. Box 62, Oak Ridge, TN 37831priCes available from (423) 576.S401ht~//apollo.osti. gov/bridge/Available to the public from theNational Technical Information ServiceU.S. Department of Commerce5285 Port Royal Rd.,Springfield, VA 22161http/ /www.ntis.gov/ORLawrence Livermore National LaboratoryTechnical Information Department’s Digital Libra~htqx/ /wwwJnl.gov/tid/Libra~.htm3Debris characterization diagnostic for the National IgnitionFacilityM. C. Miller, J. R. Celeste, M. A. Stoyer, L. J. Suter, and M. T. TobinLawrence Livermore National Laboratoy, Livermore, California 94550J. GrunNaval Research Laboratory, Washington D. C. 20375J. F. DavisAlme & Associates, Alexandria, Virginia 22303C. W. Barnes and D. C. WilsonLos Alamos National Laboratory, Los Alamo., New Mexico 87545Generation of debris from targets and by x-ray ablation of surrounding materials will be amatter of concern for experimenters and the operations staff at the National IgnitionFacility (NIF). Target chamber and final optics protection, for example debris shielddamage, and efficient facility operation drive the interest for the NIF staff.Experimenters are primarily concerned with diagnostic survivability, separation ofmechanical versus radiation induced test object response in the case of effects tests, andradiation transport through the debris field when the net radiation output is used to1—-—.benchmark computer codes. In addition, radiochemical analysis of activated capsuledebris during ignition shots can provide a measure of the ablator <pr>. Conceptualdesign of the Debris Monitor and Rad-Chem Station, one of the NIF core diagnostics, ispresented. Methods of debris collection, particle size and mass analysis, impulsemeasurement, and radiochemical analysis are given. A description of recent experimentsinvolving debris collection and impulse measurement on the OMEGA and Pharos lasersis also provided.52.55.Pi, 52.70.-m, 82.55.+eINTRODUCTIONDebris generation from NIF experiments is important for a variety of reasons: targetchamber and final optics protection,’ interpretation of radiation effects test results,2’3diagnostic survivability y, and computer simulations of net radiation output. In addition,radiochemical analysis of debris collected from ignition shots is diagnostic of capsuleperformance. The Debris Monitor and Rad-Chem Station addresses these interests bycollecting debris for characterization of mass and particle size distribution, measurementof debris impulse, and radiochemical analysis of activated debris. The diagnostic iscomposed of a suite of collectors and sensors that maybe placed at various Iocations onthe target chamber to cover multiple lines of sight. Capabilities of the diagnostic will befielded in stages, the first being mass, particle size distribution, and impulsemeasurement. Detailed tecluiques for performing radiochemical analysis of collected2samples remain to be developed as specific experiments are defined. As a result thecapability is being protected as “not to preclude”, meaning that implementation of debriscollection will not unreasonably constrain the ability to perform radiochemical analysison collected samples. This paper describes the conceptual design of the Debris Monitorand Rad-Chem Station and recent experimental experience at the University of RochesterOMEGA and the Naval Research Laboratory Pharos laser facilities with debris collectionand impulse sensors.DEBRIS MASS AND PARTICLE SIZEDebris mass and particle size distribution analysis will be accomplished by collection ofdebris onto a glass slide or silicon wafer housed in a clean box, followed by opticalinspection. The clean box is loaded in a class 100 clean room, then placed on adiagnostic instrument manipulator (DIM) 4 cart. The DIM allows insertion of diagnosticsinto the NIY target chamber and the cart is a removable portion for offline diagnosticloading, alignment, etc. Figure 1 shows a schematic of the clean box with two collectors.Once the chamber/DIM is under vacuum the clean box is opened remotely. It is keptopen for one or more shots, then remotely closed and removed from the DIM cart. Thebox is then transported to the clean room, placed on a microscope, and automatedcounting of sizes and shapes is performed. The slide is returned for forther rmalysis asneeded. Specifications for the debris mass and particle size analysis are presented inTable I.3Another collection mechanism that has been recently investigated is medium- and higb-density silicon aerogel obtained from NASA.5 This approach has the advantage ofpreserving the particle track so that an analysis of its velocity can be performed inaddition to mass and size. We have fielded a pair of these collectors on OMEGA shots.Figure 2 is a schematic of the experimental set up and Fig. 3 shows particulate that wascollected during these shots. The exposure area of each aerogel was 5 cm2, with nominalthickness of 3 cm. Post-shot inspection of the surfaces of the aerogels indicate theimportance of maintaining clean conditions for quantitative measurements. Analysis ofthe particulate tracks and composition is currently being performed by NASA.DEBRIS IMPULSEPassive impulse gauges fielded on the ‘Nova laser demonstrated the capability to makethis type of measurement using a simple technique, tkee from electrical noise issues oftenassociated with a high-power laser environment.6 On NIF however, automation ofdiagnostics is highly desirable and we are focusing our efforts on active methods using avariety of sensors, allowing a large dynamic range to be covered. In general, the sensoris imbedded into a puck whose equation of state is well known. The puck is placed intoNIF via a DIM cart. Pressure waves in the puck generated by impacting debris aremeasured by the sensor and the impulse of the debris is backed out from the data utilizing4the equation of state of the puck. The diagnostic is remotely controlled by computer andthe pressure signal is recorded on a scope.Three types of sensors are currently under evaluation, etalon probes’, ruby sensors, andpolyvinylidene fluoride (PVDF) gauges.s The etalon probes consist of microchipinterferometers attached to 50 pm core optical fibers and have a sensitivity range of-1 –1000 bar. Ruby sensors (custom mated to fiber optics by NRL) are sensitive to higherpressures, covering -2 – 100 kbar. The piezoelectric PVDF gauges compliment theetalon probes and ruby sensors, with operational pressure range of-0.5 –500 bar. TableII contains the specifications for the debris impulse measurement.hnpulse measurement experiments have recently been carried out on the OMEGA andPharos lasers. On OMEGA, a PVDF sensor was fielded on Au hohlranm shots anddemonstrated operation in a laser environment with very low noise (<1 mV). Aschematic of the PVDF sensor is shown in Fig. 4. On the Pharos laser, an experimentwas performed that compared an etalon gauge with an electrical carbon gauge on thesame shot. The shock was generated by focusing a laser beam into water, so that theelectrical environment was that of a laser. Figure 5 shows the results. The first pulse onthe etalon trace is laser light at t=O, the second pulse is the pressure response, and thethird pulse is a reflection from nearby material. The carbon trace shows a small pressurepulse and a much larger set of signals arising from electrical noise.5RADIOCHEMISTRYThe (n,2n) production of 62CUand ‘Cu from naturally occurring 63CUand 65CUin the Cu-doped Be ablator is proportional to the ablator <pr> and neutron Yield.g Themeasurement would be performed by capturing a fraction of the capsule explosion debrisand counting the decay of activated copper, then using a chemical analysis of Cu or Be inthe sample to determine the capsule fraction obtained. The collected sample would becounted quickly because of the relatively short half-lives of 62CUand ‘Cu (9.7 min and12.9 br respectively).Both 62CUand ‘Cu decay by positron emission, accompanied by annihilation radiation(511 keV), and each emits discrete gamma rays that maybe used for identification andquantification. Coincidence counting of the annihilation radiation covering a period of afew half-lives is an established method for measuring 62CUand 64CUactivation.’” Thismethod has the advantage of being most sensitive to lower yields, but lacks theunambiguous isotope identification that comes from measuring discrete gamma rays,which may be performed with a high-purit y intrinsic Ge detector. Recent experiments onthe Petawatt laser at Livermore have demonstrated the feasibility of measuring 62CUand64CU directly via the 1173-keV and 1345-keV gamma rays respectively, at levels wellbelow those of nominal full yield on NE.’ 1 Yields as low as lE-6 of nominal full yieldwill produce enough activity for ablator <pr> determination using the coincidence6counting technique. We also anticipate that radiochemical analysis of a variety ofactivation products will be useful in diagnosing experiments well before ignition isachieved on NIP. Table III presents specifications for the Rad-Chem Station.SUMMARYThe Debris Monitor and Rad-Chem Station is being developed for the National IgnitionFacility as one of the core diagnostics. Methods of debris collection proposed and undercurrent investigation include glass slides, silicon wafers, and silicon aerogels. Impulsesensors to cover a wide dynamic range are being evaluated and include etalon probes,rub y sensors, and PVDF gauges. Radiochemical analysis of activated debris will enablea measurement of the ablator <pr> for ignition shots as well as providing a generalcapability to diagnose experiments that produce activation products. Offlinedevelopment and testing on the OMEGA and Pharos lasers will continue so that thediagnostic may be completed and operational for first use on NIF in 2004. Table IVshows the current schedule of milestones based on the recently announced NIF startupschedule.ACKNOWLEDGEMENTS7The authors would like to thank the OMEGA operations staff, and in particular JackArmstrong, for assistance in fielding the debris collectors and impulse gauges. This workwas carried out under the auspices of the United States Department of Energy by theUniversity of California Lawrence Livermore National Laboratory under contract numberW-7405 -ENG-48 and is supported in part by the United States Defense Threat ReductionAgency under contract number IACRC) 00-3003, Work Unit 6172. Naval ResearchLaboratory is supported by the United States Defense Threat Reduction Agency under aseparate contract.8TABLE L Specifications for debris mass and particle size analysisDebris size distribution 1 – 500 ~mMass limit 1 pgTemporal response NoneCollector area >1 cm2TABLE II. Specifications for debris impulse measurementPressure range 1 bw– 100kbwGauge diameter <500pn-2cmTemporal response <15 ns9TABLE III. Specifications for radiochemical analysisGeometric collection efficiency >lE-6Maximum removal timeDetector resolutionMDL (atoms)62CU63CU64CU65CU9Be10BeTemporal response2 – 20 min.<2.5 keV @ 1173 keV1E41.3E111E56E1O-lE1l-lE11None10TABLE IV. Milestones for the Debris Monitor and Rad-Chem StationMilestone Description DateMlM2M3M4aM4bM5M6M7M8Conceptual design review65V0 design review100’% design reviewFabrication complete, begin offline testingOffline testing complete, ship to NIFDry run reviewFirst use on NIFFunctional operationFacility acceptance1/1016/1/0110/1/019/1/024/1/049/1/0412/1/041/1/067/1/0611FIG. 1. Schematic of clean box and debris collection surfaces. Box is housed in aDIM and opened remotely before shot.FIG. 2. Experimental setup for the aerogel collectors at the OMEGA laser facility.FIG. 3. Aerogel debris collector showing particle and associated track. This samplewas recently collected from a Au hohlraum target shot on the OEMGA laser.FIG. 4. Schematic of the PVDF impulse gauge recently fielded on OEMGA.FIG. 5. EtaIon probe results versus carbon gauge for a laser-induced shock in waterat the Pharos laser facility at the Naval Research Laboratory.1 M. Tobin, D. Eder, I. Thomas, J. Latkowski, S. Brereton, B. MacGowan, R. Horton, T.Duewer, F. Zaka, S. Davis, and J. Ertel, Lawrence Livermore National Laboratorydocument UCRL-JC-135650 (September 1999).122 D. E. Johnson, E. A. Smith, F. W. Davies, and E. D. Stretanski, “Debris EnvironmentsAssociated with Plasma Radiation Sources,” Proceedings of the Joint SNTJDSWAPlasma Radiation Source Workshop, November 1996.3 P. D. LePell, T. T. Covert, D. L. Reeder, E. A. Smith, and F. W. Davies, J. Rad. Effects(to be published).4 W. Hibbard, M. Larrdon, M. Verginc,, D. Lee, and J. Chael, Rev. Sci. Instrum. (theseproceedings).5 F. Horz, G. Cress, M. Zolensky, T. H. Lee, R. P. Bernhard, and J. L. Warren, “OrbitalAnalysis of Impact Features in Aerogel from the Orbital Debris Collection Experiment onthe MIR Station,” National Aeronautics and Space Administration document NASA/TM-1999-209372 (August 1999).6 M. Gerassimenko and F. Serduke, “Impulse Measurements on Nova,” LawrenceLivermore National Laboratory document DDV-95-0021 (October 1995).7 Photonetics Inc., modified by NRL for fast response.8 F. W. Davies, D. E. Johnson, E. Stretanski, and D. Reeder, J. Rad. Effects 16,242(1998).9 D. C. Wilson, P. A. Bradley, N. M. Hoffman, F. J. Swenson, D. P. Smitherman, R. E.Chrien, R. W. Margevicius, D. J. Thoma, L. R. Foreman, J. K. Hoffer, S. R. Goldman, S.E. Caldwell, T. R. Dittrich, S. W. Haan, M. M. Marinak, S. M. Pollaine, and J. J.Sanchez, Phys. Plasmas 5, 1953 (1998).1310H. G. Ahlstrom, in Physics of Laser Fusion, Vol. II, Diagnostics of Experiments onLaser Fusion Targets at LLNL, Lawrence Liverrnore National Laboratory docmnentUCRL-53106 (1982).11M.A. Stoyer, T.C, Sangster, E.A. Henry, M.D. Cable, T.E. Cowan,S.P. Hatchett, M.H. Key, M.J. Moran, D.M. Permington, M.D. Perry, T.W. Phillips,M.S. Singh, R.A. Snavely, M. Tabak and S.C. Wilks, Rev. Sci. Instrurn. (theseproceedings).14Portableclean box‘eby,~yco,,ect.rsI 1Remotely controlledvacuum-tight valveFig 1 M.C. Miller et al., Rev. Sci. Instrurn.Al cans-- ... . to hold aerogels“-..-’... /-’Fig 2 M.C. Miller et al., Rev. Sci. Instrum.Fig 3 M.C. Miller et al., Rev. Sci. Instrum.,.’Metal shield 25micron PVDF sensor sandwichedar...d.d t. W between K. f-F discs wnh AJ h.uslnaStandard Impulse s.nsorfrom Ktech Corp.~ I“S”MM(W-Y)Fig 4 M.C. Miller et al., Rev. Sci. Instrum.-0.8 — EtaIon Gauge-1 b-2 18 38 56 78 98Time (p)Fig 5 M.C. Miller et al., Rev. Sci. Instrum,

Debris Characterization Diagnostic for the National Ignition Facility

Debris Characterization Diagnostic for the National Ignition Facility

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