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9,508 Matching Results
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Analysis of oxygen on and in beryllium using 2 MeV helium ions
Analysis of oxygen on beryllium can be routinely performed using helium-ion backscattering (RBS). However, determination of the bulk oxygen concentration by this technique is limited to about 350 atomic parts per million (appM). We have performed simultaneous RBS and particle-induced x-ray emission (PIXE) measurements to improve the detection limit for bulk oxygen. The RBS measurements allowed determination of the surface oxygen before and after in-situ sputter cleaning by argon ions in an ultra-high-vacuum system. PIXE measurements of specimens with surfaces maintained clean by sputtering permitted assessment of the concentration of oxygen in the bulk. For our geometry and detector sensitivities, 90% of the oxygen x-ray signal originated in the first 2.1 ..mu..m of the beryllium and a detection limit of 10 appM was found. 12 refs., 3 figs.
Date:
October 2, 1986
Creator:
Musket, R.G.
System:
The UNT Digital Library
Profile modification by the ponderomotive force in spherical targets
Experiments have been performed by LLL which indicate a definite density profile steepening. One possible mechanism for this effect is the ponderomotive force. LASNEX has been modified to include the light momentum deposition in the form rho dv/dt = -nabla P - nabla(radical epsilon + radical 1/epsilon) I/2c. Results will be presented from numerical simulations on spherical glass targets at laser intensities from 10/sup 14/ to 10/sup 16/ watts/cm/sup 2/. Emphasis is placed on the nature of the density profile near the critical region as a function of laser intensity and plasma conditions. The existence of this sharp step, whose scale length is of the order of a micrometer may imply a local reduction in the thermal conductivity.
Date:
October 26, 1977
Creator:
Larsen, J. T. & Harte, J.
System:
The UNT Digital Library
Data telecommunications at the CSCF
At Brookhaven National Laboratory data telecommunication for remote job entry, interactive time sharing, networking, graphics, and special purpose links became increasingly important--they now rival the more traditional over-the-counter traffic. The BNL Central Scientific Computing Facility (CSCF) responded to this need with a number of developments. The latest and most comprehensive of these is a ''front-end'' communications system built around MODCOMP II computers. To put this project into its proper framework, some historical background is presented describing predecessor systems, the development of specifications, and the factors considered in the decision to turn to MODCOMP. The hardware is based around dual MODCOMP II-233 processors with a specially developed link to the larger CSCF machines, two Control Data 6600 computers and one CDC 7600. The MODCOMP software is based upon an existing system developed by Chrysler Corporation, running under MAXCOM. On the Control Data side Scope 3.4/INTERCOM 4 is used as a basis. The developments and modifications, both hardware and software, necessary for these components to meet Brookhaven's specifications are described. Certain related special-purpose data link applications are described. Among them are a research project in national resource sharing networks using ARPANET, and a connection to the National Weather Service machines in Suitland, …
Date:
October 1, 1977
Creator:
Peskin, A. M.
System:
The UNT Digital Library
A Broad View of Model Validation
The safety assessment of a nuclear waste repository requires the use of models. Such models need to be validated to ensure, as much as possible, that they are a good representation of the actual processes occurring in the real system. In this paper we attempt to take a broad view by reviewing step by step the modeling process and bringing out the need to validating every step of this process. This model validation includes not only comparison of modeling results with data from selected experiments, but also evaluation of procedures for the construction of conceptual models and calculational models as well as methodologies for studying data and parameter correlation. The need for advancing basic scientific knowledge in related fields, for multiple assessment groups, and for presenting our modeling efforts in open literature to public scrutiny is also emphasized. 16 refs.
Date:
October 1, 1989
Creator:
Tsang, C. F.
System:
The UNT Digital Library
Hanford Waste Vitrification Plant
The Hanford Waste Vitrification Plant (HWVP) is being designed to immobilize pretreated Hanford high-level waste and transuranic waste in borosilicate glass contained in stainless steel canisters. Testing is being conducted in the HWVP Technology Development Project to ensure that adapted technologies are applicable to the candidate Hanford wastes and to generate information for waste form qualification. Empirical modeling is being conducted to define a glass composition range consistent with process and waste form qualification requirements. Laboratory studies are conducted to determine process stream properties, characterize the redox chemistry of the melter feed as a basis for controlling melt foaming and evaluate zeolite sorption materials for process waste treatment. Pilot-scale tests have been performed with simulated melter feed to access filtration for solids removal from process wastes, evaluate vitrification process performance and assess offgas equipment performance. Process equipment construction materials are being selected based on literature review, corrosion testing, and performance in pilot-scale testing. 3 figs., 6 tabs.
Date:
October 1, 1991
Creator:
Larson, D. E.; Allen, C. R. (Pacific Northwest Lab., Richland, WA (United States)); Kruger, O. L. & Weber, E. T. (Westinghouse Hanford Co., Richland, WA (United States))
System:
The UNT Digital Library
Lead-Glass Wall addition to the Spear Mark I Magnetic Detector
A ''Lead-Glass Wall,'' consisting of 318 lead-glass Cherenkov shower counters and three wire spark chambers, has been added to one octant of the SPEAR Mark I Magnetic Detector. The wall covers a solid angle of approximately 6 percent of 4..pi.. steradians and has been used to identify and measure the energies of electrons and photons produced in electron-positron collisions. The design, calibration, gain-monitoring, and performance of the system are described.
Date:
October 1, 1977
Creator:
Feller, J. M.; Barbaro-Galtieri, A. & Dorfan, J. M.
System:
The UNT Digital Library
Analytical model for the dynamic resistivity of electrically-exploded conductors
A detailed model for the dynamic resistivity of an exploding conductor presents many difficulties. An electrically-exploded conductor undergoes significant hydrodynamic expansion as it is heated. Resistivity is a function of both the temperature and density of a conductor and realistic models for resistivity over the range of parameter space experienced by an exploding conductor are quite complex. See for example, the model of Lee and More (1984). Calculation of the hydrodynamic expansion of the conductor during and subsequent to the explosion is likewise dependent on detailed knowledge of the equation of state for the conductor in a range where few experimental data exist. A further complication is the strong magnetic field which couples the hydrodynamic expansion to the currents flowing in the expanding material. In spite of the difficulties, progress is being made on detailed modeling of fuses and exploding conductors (Lidemuth and co-workers, 1985). A simpler approach has proved to be quite useful for modeling the electrical behavior of exploding bridgewire and slapper detonators and for modeling the explosionss of large conductors exploded with large capacitor banks. In the work described here, a simple, empirical model was developed which can be expressed as a closed-form algebraic expression involving four …
Date:
October 10, 1986
Creator:
Lee, R. S.
System:
The UNT Digital Library
Prototype photon position monitors for undulator beams at the Advanced Light Source
Design criteria are described, and test results are presented, for prototype ALS undulator beam position monitors. The design is based on monitors presently in use at NSLS, with modifications to account for the widely varying and large K values of the undulators to be installed at the ALS. In particular, we have modified the design to simplify the thermal engineering and we have explored techniques to suppress the response of the monitors to soft photons, so that the beam position can be determined by measuring the higher energy photons which are better collimated. 4 refs., 8 figs.
Date:
October 17, 1990
Creator:
Warwick, T.; Shu, D. (Lawrence Berkeley Lab., CA (United States)); Rodricks, B. (Argonne National Lab., IL (United States)) & Johnson, E.D. (Brookhaven National Lab., Upton, NY (United States))
System:
The UNT Digital Library
Notes on Luminosity Variation at ISABELLE
In the present ISABELLE design, the luminosity at each insertion will be the same, unless special efforts are taken to get a low-..beta.. insertion or reduced crossing angle. These can only change the luminosity by factors of 2 to 4 from insertion to insertion. An estimation of the range of desired luminosities is given.
Date:
October 19, 1977
Creator:
Herrera, J. C.; Marx, M.; Roe, B. & Rosenberg, E. I.
System:
The UNT Digital Library
Time resolution performance studies of contemporary high speed photomultipliers
The time resolution capabilities of prototype microchannel plate and static crossed-field photomultipliers have been investigated. Measurements were made of electron transit time, rise time, time response, single photoelectron time spread and multiphotoelectron time spread for LEP HR350 proximity focused high gain curved microchannel plate and VPM-154A/1.6L static crossed-field photomultipliers. The experimental data have been compared with results obtained with conventionally designed RCS 8850 and C31024 high speed photomultipliers. Descriptions are given of both the measuring techniques and the measuring systems.
Date:
October 5, 1977
Creator:
Leskovar, B. & Lo, C.C.
System:
The UNT Digital Library
Performance of the short-pulse oscillators for Argus and Shiva
The large Nd:glass laser-fusion systems, such as Argus and Shiva, require short-pulse oscillators that are very reliable and predictable. The requirements go well beyond what can reasonably be expected from a passively mode-locked laser. An actively mode-locked and Q-switched oscillator has now been developed that is extremely reliable and predictable, and satisfies all the requirements for the present Nd:glass laser systems. These systems require pulses that are adjustable from less than 100 ps to more than 1 ns, with less than 5% shot-to-shot variation in pulse energy and pulse width. Single-pulse energy from 100 ..mu..J to 1 mJ is sufficient. In this paper we will describe the principle of operation of this short-pulse oscillator, describe the Argus laser configuration, and the results obtained with this oscillator. We will then indicate further developments for the Shiva oscillator and discuss the performance of this laser.
Date:
October 1, 1977
Creator:
Kuizenga, D.J. & Martin, W.E.
System:
The UNT Digital Library
Design studies of a laser fusion power plant
The conceptual design of a laser fusion power plant has been undertaken to exploit recent developments in target design. Advanced high-gain targets which have been developed make it possible to significantly relax the laser and optical system requirements. The power plant design features a reactor concept which utilizes a thick falling region of liquid lithium to protect the first-wall from the neutrons, x-rays, and charged particles that are produced in the thermonuclear microexplosion. The lithium waterfall has also been designed to be thick enough to significantly reduce the effects of 14 MeV neutrons and cyclical stresses on the blanket structure; thereby allowing us to consider smaller blanket structures which could last the lifetime of the plant. Fusion targets producing 700 MJ of thermonuclear energy are ignited by a 2 percent efficient, 1 MJ laser system at the rate of 1.4 Hz. Schemes for protecting the final focusing optics are described which are both compatible with this reactor system, and show promise of surviving a full year in order to minimize costly downtime.
Date:
October 7, 1977
Creator:
Maniscalco, J. A.; Meier, W. R. & Monsler, M. J.
System:
The UNT Digital Library
Electron cyclotron resonance heating (ECRH) in the TMX-Upgrade tandem-mirror experiment
Results are described of engineering tests of operation of two gyrotrons from one power supply, tests of waveguide components and antennae, antenna design, and the x-ray shielding concept. Finally, we describe considerations of interaction with other system components.
Date:
October 1, 1981
Creator:
Griffin, D.H.; Rubert, R.R.; Simonen, T.C.; Stallard, B.W. & Wieskamp, T.F.
System:
The UNT Digital Library
Requirements and new materials for fusion laser systems
Higher focusable power in neodymium glass fusion lasers can be obtained through the use of new materials with lower nonlinear index (n/sub 2/) and better energy storage capabilities than the presently employed silicate glass. Silicate, phosphate, fluorophosphate, and beryllium fluoride glasses are discussed in terms of fusion laser requirements, particularly those for the proposed Nova laser. Examples of the variation in spectroscopic and optical properties obtainable with compositional changes are given. Results of a system evaluation of potential laser materials show that fluorophosphate glasses have many of the desired properties for use in Nova. These glasses are now being cast in large sizes (30-cm diameter) and will be tested in prototype amplifiers in 1978.
Date:
October 1, 1977
Creator:
Stokowski, S. E.; Weber, M. J.; Saroyan, R. A. & Hagen, W. F.
System:
The UNT Digital Library
New method to determine the chemical composition and structure of non-elemental acceptor and donor centers in ultra-pure germanium
A new approach towards the understanding of hitherto unknown, non-elemental acceptors and donors which can limit the purity of ultra-pure germanium has been explored for a specific pair of shallow centers, designated A/sub 2/ and D. Using photoelectric spectroscopy, we have demonstrated that an isotope shift in the ground-state binding energy occurs when the germanium crystals are grown in pure deuterium instead of in the usual pure hydrogen atmosphere. This isotope shift is the most direct proof of the presence of hydrogen atoms in the centers A/sub 2/ and D. Applying uniaxial stress to Ge samples containing A/sub 2/ and D, we show that the symmetry and structure of the centers can be explored. The knowledge of the chemical composition and the structure of the non-elemental centers will allow development of methods to reduce and keep their concentrations to acceptable levels.
Date:
October 1, 1977
Creator:
Haller, E.E.
System:
The UNT Digital Library
50th Anniversary, 1931-1981: symposium and banquet speeches
The proceedings includes talks given at the symposium and the banquet. They include examples of technology at the laboratory and speculation on the future at the laboratory. (GHT)
Date:
October 3, 1981
Creator:
unknown
System:
The UNT Digital Library
Energy balance measurements for Shiva
The Lawrence Livermore Laboratory Shiva laser-target interaction facility is designed for experiments at 20 to 30 terawatts. At this power level there will be larger fluxes of neutrons, x-rays, electrons and ions than have been previously measured. The measurements of energy converted into the various reaction products is crucial both in target design and performance analysis of the actual experiment. The total energy absorbed is measured by a box calorimeter surrounding the target except for beam input holes. This measurement prevents the use of other diagnostics, so for normal operation an energy balance module was designed for location on ports on the Shiva target chamber. This module monitors the energy in scattered light at 10640 A and 5320 A or 7118 A. It also contains a faraday cup and plasma and x-ray calorimeters. The distribution of energy in scattered light, plasma and x-rays will be mapped by 58 such modules.
Date:
October 24, 1977
Creator:
Glaros, S.S.; Rupert, V.C.; Gunn, S.R.; Phillion, D.W. & Kornblum, H.N.
System:
The UNT Digital Library
MLE (Maximum Likelihood Estimator) reconstruction of a brain phantom using a Monte Carlo transition matrix and a statistical stopping rule
In order to study properties of the Maximum Likelihood Estimator (MLE) algorithm for image reconstruction in Positron Emission Tomographyy (PET), the algorithm is applied to data obtained by the ECAT-III tomograph from a brain phantom. The procedure for subtracting accidental coincidences from the data stream generated by this physical phantom is such that he resultant data are not Poisson distributed. This makes the present investigation different from other investigations based on computer-simulated phantoms. It is shown that the MLE algorithm is robust enough to yield comparatively good images, especially when the phantom is in the periphery of the field of view, even though the underlying assumption of the algorithm is violated. Two transition matrices are utilized. The first uses geometric considerations only. The second is derived by a Monte Carlo simulation which takes into account Compton scattering in the detectors, positron range, etc. in the detectors. It is demonstrated that the images obtained from the Monte Carlo matrix are superior in some specific ways. A stopping rule derived earlier and allowing the user to stop the iterative process before the images begin to deteriorate is tested. Since the rule is based on the Poisson assumption, it does not work well …
Date:
October 1, 1987
Creator:
Veklerov, E.; Llacer, J. & Hoffman, E.J.
System:
The UNT Digital Library
MTX (Microwave Tokamak Experiment) facility and machine grounding plan
A key issue in the design of fusion research experiments and their related facilities is the control of ground currents. Because of the large magnetic field, high voltages and high currents present in most of these installations, it is essential to avoid ground loops, and to control ground currents during both normal operations and fault conditions. This paper describes the grounding policy that was developed for MTX. The vault area was divided into zones, and each of the four walls was treated as a separate grounding area. Cable runs and magnet buss bars were run into the machine radially. The paper also describes the steps taken to isolate diagnostic signals and power for pumps and instruments. The paper outlines some of the field calculations used to predict problem areas, and to reveal voltage isolation levels that were required. The paper includes the active ground fault detection system used to insure the integrity of the ground system. 2 refs., 5 figs.
Date:
October 7, 1987
Creator:
Bell, H.H.; Rice, B.W.; Petersen, D.E. & Herrera, C.H.
System:
The UNT Digital Library
A measurement of the p p total cross section at radical s = 1800 GeV
The {bar p}p differential elastic scattering cross section was measured at {radical}{bar s} = 1800 GeV, using an improved accelerator luminosity determination and CDF small angle data in the range of 0.05 {le} t {le} 0.2(GeV/c){sup 2}. By extrapolating the differential cross sections to t=0 and using the optical theorem we obtain a total cross section of {sigma}{sub tot}({bar p}p) = 72.0 {plus minus} 3.6 mb. This result is preliminary in the sense that we expect to further reduce the systematic error on the optical point. 9 refs., 8 figs.
Date:
October 1, 1991
Creator:
White, S. (Rockefeller Univ., New York, NY (United States))
System:
The UNT Digital Library
Electrostatically driven plasma hydrodynamic instability. I. The failure of vacuum-insulated, long wavelength laser fusion pellets
Longer wavelength (e.g., lambda = 10.5 ..mu..m) laser radiation generates relatively large fluxes of superthermal electrons that penetrate and preheat the cores of such pellets at early times in their implosion history, precluding their efficient subsequent compression. It has been proposed to separate the outermost shell of such pellets (onto which the laser light is directed) from its inner regions by a vacuum layer, thereby ''insulating'' these inner portions from superthermal electron degradation. We consider this proposal analytically and computationally, and find it to be questionable, due to the rapid penetration of the vacuum insulation layer by plasma streamers from the laser heated shells, which are accelerated to velocities of the order of those of the superthermal electrons by an electrostatic analog of the Rayleigh-Taylor instability. Results of such considerations are presented. The results developed also apply to a variety of formally similar phenomena, ranging from the relativistic edge of supernova photospheres to diode breakdown in REB machines.
Date:
October 1, 1977
Creator:
Levermore, C. D.; Caflisch, R. E. & Wood, L. L.
System:
The UNT Digital Library
Direct electron heating by 60 MHz fast waves on DIII-D
Efficient direct electron heating by fast waves has been observed on the DIII-D tokamak. A four strap antenna with (0,{pi},0,{pi}) phasing launched up to 1.6 MW of fast wave power with {vert bar}n{sub {parallel}}{vert bar} {approx} 11. This {vert bar}n{sub {parallel}}{vert bar} is suitable for strong electron interaction in ohmic target plasmas (T{sub e} {le} 2 keV). Ion cyclotron absorption was minimized by keeping the hydrogen fraction low ({lt}3%) in deuterium discharges and by operating at high ion cyclotron harmonics ({omega} = 4{Omega}{sub H} = 8{Omega}{sub D} at 1T). The fast wave electron heating was weak for central electron temperatures below 1 keV, but improved substantially with increasing T{sub e}. Although linear theory predicts a strong inverse magnetic field scaling of the first pass absorption, the measured fast-wave heating efficiency was independent of magnetic field. Multiple pass absorption of the fast waves appears to be occurring since at 2.1 T nearly 100% efficient plasma heating is observed while the calculated first pass absorption is 6% to 8%. The central electron temperature during fast wave heating also increased with magnetic field. The improved electron heating at higher magnetic fields may be due in part to a peaking of the ohmic plasma …
Date:
October 1, 1991
Creator:
Petty, C. C.; Pinsker, R. I.; Mayberry, M. J.; Chiu, S. C.; Luce, T. C.; Prater, R. (General Atomics, San Diego, CA (United States)) et al.
System:
The UNT Digital Library
Management policy decision analysis with system dynamics
None
Date:
October 1, 1974
Creator:
Addison, L E; Litchfield, J W & Hansen, J V
System:
The UNT Digital Library
Comparison of predicted and measured fission product behavior in the Fort St. Vrain HTGR during the first three cycles of operation
Fission product release from the reactor core has been predicted by the reference design methods and compared with reactor surveillance measurements and with the results of postirradiation examination (PIE) of spent FSV fuel elements. Overall, the predictive methods have been shown to be conservative: the predicted fission gas release at the end of Cycle 3 is about five times higher than observed. The dominant source of fission gas release is as-manufactured, heavy-metal contamination; in-service failure of the coated fuel particles appears to be negligible which is consistent with the PIE of spent fuel elements removed during the first two refuelings. The predicted releases of fission metals are insignificant compared to the release and subsequent decay of their gaseous precursors which is consistent with plateout probe measurements.
Date:
October 1, 1985
Creator:
Hanson, D. L.; Jovanovic, V. & Burnette, R. D.
System:
The UNT Digital Library