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Energy stability in recirculating, energy-recovering linacs

Description: Recirculating, energy-recovering linacs can be used as driver accelerators for high power FELs. Instabilities which arise from fluctuations of the cavity fields are investigated. Energy changes can cause beam loss on apertures, or, when coupled to M{sub 56}, phase oscillations. Both effects change the beam induced voltage in the cavities and can lead to unstable variations of the accelerating field. Stability analysis for small perturbations from equilibrium is performed and threshold currents are determined. Furthermore, the analytical model is extended to include amplitude and phase feedback, with the transfer function in the feedback path presently modeled as a low-pass filter. The feedback gain and bandwidth required for stability are calculated for the high power UV FEL proposed for construction at CEBAF. 4 refs.
Date: July 1, 1996
Creator: Merminga, L.; Bisognano, J.J. & Delayen, J.R.
Partner: UNT Libraries Government Documents Department

Nevada Test Site Sensor Test Facility

Description: A Sensor Test Facility (STF) was recently established at the Department of Energy`s Nevada Test Site (NTS). It has been used for a series of sensor tests that have demonstrated the usefulness of the testbed. The facility consists of a cut-and-cover bunker complex and the two square mile surrounding area. The STF was developed as a scientific testbed optimized for the development and evaluation of advanced sensor systems, including ground sensor systems designed to identify and detect hardened underground facilities. This was accomplished by identifying a facility in a remote location where seismic, acoustic, and electromagnetic interference would be minimal, establishing a testbed that would be accommodating to field testing, and conducting a thorough geophysical characterization of the area surrounding the facility in order to understand the local geology and its effects on geophysical signals emanating from the facility. The STF is representative of a number of cut-and-cover bunkers around the world that are used for the manufacture and/or storage of weapons of mass destruction. This paper provides a general description of the Nevada Test Site, the Sensor Test Facility, and the Geophysical Site Characterization.
Date: December 1, 1996
Creator: Gomez, B.J. & Boyer, W.B.
Partner: UNT Libraries Government Documents Department

Cold test results of a standing wave muffin-tin structure at X-band

Description: A muffin-tin structure is chosen to study high gradient acceleration in the millimeter wavelength range. In order to understand the electromagnetic field characteristics, a standing wave structure operating at a frequency around 11.4 GHz was built. Cold test measurements were performed and results are presented. Comparisons with theoretical predictions based on computer simulation are shown.
Date: November 1, 1996
Creator: Chou, P.J.; Hanna, S.M.; Henke, H.; Menegat, A.; Siemann, R.H. & Whittum, D.
Partner: UNT Libraries Government Documents Department

Impedance of accelerator components

Description: As demands for high luminosity and low emittance particle beams increase, an understanding of the electromagnetic interaction of these beams with their vacuum chamber environment becomes more important in order to maintain the quality of the beam. This interaction is described in terms of the wake field in time domain, and the beam impedance in frequency domain. These concepts are introduced, and related quantities such as the loss factor are presented. The broadband Q = 1 resonator impedance model is discussed. Perturbation and coaxial wire methods of measurement of real components are reviewed.
Date: May 1, 1996
Creator: Corlett, J.N.
Partner: UNT Libraries Government Documents Department

The team workshops: What`s old? What`s new?

Description: A short history of the TEAM workshops is presented, with emphasis on the first two rounds of workshops and the recent workshops in Berlin and Okayama. New problems provide benchmarks for new applications and interest, but old problems continue to provide benchmarks for new methods and approaches. There is a trend to attempt to solve more and more complicated problems on a personal computer (PC). Problem 8 (a slot in a conducting plate) has been solved on a PC using the eddy- current code ELEKTRA.
Date: October 29, 1996
Creator: Turner, L.R.
Partner: UNT Libraries Government Documents Department

Parallel processing ITS

Description: This report provides a users` guide for parallel processing ITS on a UNIX workstation network, a shared-memory multiprocessor or a massively-parallel processor. The parallelized version of ITS is based on a master/slave model with message passing. Parallel issues such as random number generation, load balancing, and communication software are briefly discussed. Timing results for example problems are presented for demonstration purposes.
Date: September 1, 1996
Creator: Fan, W.C. & Halbleib, J.A. Sr.
Partner: UNT Libraries Government Documents Department

Subspace angles: a metric for comparisons in EEG and MEG

Description: In forward head modeling, various approximations are made in order to keep the problem tractable. Simplifications can yield models ranging from simple spherical models to multi-tessellated arbitrary surfaces in a boundary element model (BEM). Spherical head models differ in the number of shells and the assumed conductivities. Other assumptions in the BEM include the choice of basis sets, such as constant, linear, or quadratic variations of the voltages across the individual areal elements, or the selection of error-weighting method, such as collocation, Galerkin, or `direct` methods. Numerical versus analytic integration can also yield numerical differences. These differences in parameters and approximations can yield models whose external fields (EEG potentials or MEG magnetic fields) differ for the same internal source configuration. Quantitative measures are needed to determine if these differences are significant.
Date: July 1, 1996
Creator: Mosher, J. C.
Partner: UNT Libraries Government Documents Department

QUICKSILVER - a general tool for electromagnetic PIC simulation

Description: The dramatic increase in computational capability that has occurred over the last ten years has allowed fully electromagnetic simulations of large, complex, three-dimensional systems to move progressively from impractical, to expensive, and recently, to routine and widespread. This is particularly true for systems that require the motion of free charge to be self-consistently treated. The QUICKSILVER electromagnetic Particle-In-Cell (EM-PIC) code has been developed at Sandia National Laboratories to provide a general tool to simulate a wide variety of such systems. This tool has found widespread use for many diverse applications, including high-current electron and ion diodes, magnetically insulated power transmission systems, high-power microwave oscillators, high-frequency digital and analog integrated circuit packages, microwave integrated circuit components, antenna systems, radar cross-section applications, and electromagnetic interaction with biological material. This paper will give a brief overview of QUICKSILVER and provide some thoughts on its future development.
Date: October 1, 1996
Creator: Seidel, D.B.; Coats, R.S. & Johnson, W.A.
Partner: UNT Libraries Government Documents Department

Comparing a 2D fluid model of the DC planar magnetron cathode to experiments

Description: Planar magnetron cathodes have arching magnetic field lines which concentrate plasma density near the electrode surface. This enhances the ion bombardment of the surface and the yield of sputtered atoms. Magnetron cathodes are used in the Plasma Electrode Pockels Cell (PEPC) devices of the Laser Program because they provide for significantly higher conduction than do glow discharges. An essential feature of magnetron cathodes is that the vector product of the perpendicular electric field, E[sub y], with the parallel component of the magnetic field, B[sub x], forms a closed track with a circulating current along the cathode surface. An analytical, 2D, two component, quasi-neutral, continuum model yields formulas for the plasma density, the total and component current densities, the electric field, and the positive electrical potential, between the cathode surface and a distant, uniform plasma. For a specific gas, the free parameters are electron temperature, gas number density, and total current. The model is applied to the interpretation of experimental data from the PEPC device, as well as a small vacuum facility for testing magnetron cathodes. Finally, the model has been applied to generate cross sectional views of a PEPC magnetron cathode track.
Date: May 1, 1996
Creator: Garcia, M.
Partner: UNT Libraries Government Documents Department

TRACE 3-D code improvements

Description: TRACE 3-D is an interactive beam-transport code for bunched beams that includes accelerating elements and linear space-charge forces. It has been integrated with an improved GUI (graphic user interface) based on the Shell for Particle Accelerator Related Codes. Recent modifications to the code include centroid tracking and an improved beam description consisting of a set of beam slices, each having its own 6D centroid and sigma matrix. This allows one to study some nonlinear effects, such as wakefields, that are related to the variation of the beam bunch along the longitudinal direction.
Date: November 1, 1996
Creator: Lysenko, W.P.; Rusthoi, D.P.; Chan, K.C.D.; Gillespie, G.H. & Hill, B.W.
Partner: UNT Libraries Government Documents Department

Evaluation of the discrete complex-image method for a NEC-like moment-method solution

Description: The discrete image approximation for the field of a half-space is tested in the NEC antenna modeling program as an alternative to the interpolation method presently used. The accuracy and speed of the discrete image approximation are examined for varying number of images and approximation contour, and the solution for current is obtained on a horizontal wire approaching the interface.
Date: January 5, 1996
Creator: Burke, G.J.
Partner: UNT Libraries Government Documents Department

High accuracy 3D electromagnetic finite element analysis

Description: A high accuracy 3D electromagnetic finite element field solver employing quadratic hexahedral elements and quadratic mixed-order one-form basis functions will be described. The solver is based on an object-oriented C++ class library. Test cases demonstrate that frequency errors less than 10 ppm can be achieved using modest workstations, and that the solutions have no contamination from spurious modes. The role of differential geometry and geometrical physics in finite element analysis will also be discussed.
Date: November 1, 1996
Creator: Nelson, E.M.
Partner: UNT Libraries Government Documents Department

The integral equation for a high gain FEL

Description: The theory of a high gain free electron laser (FEL) is now well developed. In this paper I derive the equation for the electron distribution function, which is valid for FELs with a longitudinally inhomogeneous magnetic system (which may include, in particular, dispersive sections, quadrupole lenses, and simply empty spaces between the undulator sections), magnetic field errors in undulators, and some other options. The integral form of the equation may be useful for numerical calculations.
Date: July 1, 1996
Creator: Vinokurov, N.A.
Partner: UNT Libraries Government Documents Department

Microwave analysis of the damped detuned accelerator structure

Description: Damped and detuned accelerating structures (DDS), designed to minimize the effects of long range wakefields excited by bunchtrains, are presently under investigations at SLAC. The authors report the first studies of beam-induced microwave signals in a prototype DDS. The DDS is a 206 cell, nearly constant gradient structure, employing Gaussian detuning, and four symmetrically placed waveguide manifolds to damp the first-band dipole modes. They describe the manifold and output coupler design, bench measurements, and measurements with beam during the ASSET experiment. Dipole mode signals have been used to steer the beam to the structure center and minimize the wakefield kick.
Date: September 1, 1996
Creator: Seidel, M.; Adolphsen, C. & Fowkes, W.R.
Partner: UNT Libraries Government Documents Department

Environmental testing of an experimental digital safety channel

Description: This document presents the results of environmental stress tests performed on an experimental digital safety channel (EDSC) assembled at the Oak Ridge National Laboratory (ORNL) as part of the NRC-sponsored Qualification of Advanced Instrumentation and Controls (W) System program. The objective of this study is to investigate failure modes and vulnerabilities of microprocessor-based technologies when subjected to environmental stressors. The study contributes to the technical basis for environmental qualification of safety-related digital I&C systems. The EDSC employs technologies and digital subsystems representative of those proposed for use in advanced light-water reactors (ALWRs) or for retrofits in existing plants. Subsystems include computers, electrical and optical serial communication links, fiber-optic network links, analog-to-digital and digital-to-analog converters, and multiplexers. The EDSC was subjected to selected stressors that are a potential risk to digital equipment in a mild environment. The selected stressors were electromagnetic and radio-frequency interference (EMYRFI), temperature, humidity, and smoke exposure. The stressors were applied over ranges that were considerably higher than what the channel is likely to experience in a normal nuclear power plant environment. Ranges of stress were selected at a sufficiently high level to induce errors so that failure modes that are characteristic of the technologies employed could be identified.
Date: September 1996
Creator: Korsah, K.; Tanaka, T.J.; Wilson, T.L. Jr. & Wood, R.T.
Partner: UNT Libraries Government Documents Department

Correct chromaticities of circular accelerators without sextupoles

Description: A new method of correcting chromaticities of circular accelerators is introduced. Instead of using two families of sextupoles, as the standard way to correct chromaticities, two pairs of TM(210) mode RF cavities are used. The betatron phase advances (both horizontal and vertical) between the two cavities are set to be a multiple of it, and a proper momentum compaction is required. With this method, sextupole nonlinear terms are eliminated. There are octupole terms left by this method. However, they are explicit and should be easy to compensate. An example lattice demonstrates the method. The power required for the RF cavities is estimated.
Date: June 1, 1996
Creator: Chen, Tong
Partner: UNT Libraries Government Documents Department

NASA Boeing 757 HIRF test series low power on-the-ground tests

Description: The data acquisition phase of a program intended to provide data for the validation of computational, analytical, and experimental techniques for the assessment of electromagnetic effects in commercial transports; for the checkout of instrumentation for following test programs; and for the support of protection engineering of airborne systems has been completed. Funded by the NASA Fly-By-Light/ Power-By-Wire Program, the initial phase involved on-the-ground electromagnetic measurements using the NASA Boeing 757 and was executed in the LESLI Facility at the USAF Phillips Laboratory. The major participants in this project were LLNL, NASA Langley Research Center, Phillips Laboratory, and UIE, Inc. The tests were performed over a five week period during September through November, 1994. Measurements were made of the fields coupled into the aircraft interior and signals induced in select structures and equipment under controlled illumination by RF fields. A characterization of the ground was also performed to permit ground effects to be included in forthcoming validation exercises. This report and the associated test plan that is included as an appendix represent a definition of the overall on-the-ground test program. They include descriptions of the test rationale, test layout, and samples of the data. In this report, a detailed description of each executed test is provided, as is the data identification (data id) relating the specific test with its relevant data files. Samples of some inferences from the data that will be useful in protection engineering and EM effects mitigation are also presented. The test plan which guided the execution of the tests, a test report by UIE Inc., and the report describing the concrete pad characterization are included as appendices.
Date: August 1, 1996
Creator: Poggio, A.J.; Pennock, S.T.; Zacharias, R.A.; Avalle, C.A. & Carney, H.L.
Partner: UNT Libraries Government Documents Department

Diffraction model of a step-out transition

Description: The diffraction model of a cavity, suggested by Lawson, Bane and Sands is generalized to a step out transition. Using this model, the high frequency impedance is calculated explicitly for the case that the transition step is small compared with the beam pipe radius. In the diffraction model for a small step out transition, the total energy is conserved, but, unlike the cavity case, the diffracted waves in the geometric shadow and the pipe region, in general, do not always carry equal energy. In the limit of small step sizes, the impedance derived from the diffraction model agrees with that found by Balakin, Novokhatsky and also Kheifets. This impedance can be used to compute the wake field of a round collimator whose half aperture is much larger than the bunch length, as existing in the SLC final focus.
Date: June 1, 1996
Creator: Chao, A.W. & Zimmermann, F.
Partner: UNT Libraries Government Documents Department

Collimator wake fields in the SLC final focus

Description: The SLC final focus system accommodates 29 fixed or adjustable collimators for machine protection and background reduction. By amplifying pulse to pulse orbit variations and by generating emittance growth, collimator wake fields may degrade the beam quality at the interaction point (IP). In the SLC final focus, collimator half apertures are larger than the bunch length, so that the standard collimator wake formula of Bane and Morton does not apply. Numerical wake field calculations for SLC parameters agree quite well with the high frequency impedance of a step out transition. Due to the nature of a final focus system, the wake field kicks from all collimators add coherently, and the overall impact on luminosity can be significant. This paper suggests that collimator wake fields in the final focus provide a possible explanation for the 30% discrepancy between expected and measured luminosity in the 1994/95 SLC run.
Date: June 1, 1996
Creator: Zimmermann, F.; Bane, K.L.F. & Ng, C.K.
Partner: UNT Libraries Government Documents Department

Optimization and nonlinear solver experiences in high-intensity rf ion linac problems

Description: Optimization techniques and nonlinear equation solvers have long been used as tools for advanced problems in high-intensity rf ion linacs. It is expected that the use of these tools will increase dramatically in the future, as computer software and hardware facilitates their development and use. Three such problems are discussed: development of an rf field tuning method to work around a systematic error in the LAMPF linac, investigation of this tuning method to identify why it does not always converge, and investigations of the fundamental space-charge physics of linacs for minimizing beam losses.
Date: October 1, 1996
Creator: Jameson, R.A.
Partner: UNT Libraries Government Documents Department

Detection of underground structures and tunnels

Description: This is the final report of a one year, Laboratory Directed Research and Development project at Los Alamos National Laboratory. There is a continuing need in the United States defense and drug interdiction for effective over, convert, and standoff means of detecting underground tunnels, structures, and objects. This project sought to begin an assessment of electromagnetic and gravitational gradient detection approaches to the detection of underground structures and tunnels.
Date: September 1, 1996
Creator: Mack, J.M.; Moses, R.W.; Kelly, R.E.; Flynn, E.R.; Kraus, R.H.; Cogbill, A.H. et al.
Partner: UNT Libraries Government Documents Department

Investigation of charge transport and electromagnetic effects in advanced microelectronics and optoelectronics

Description: This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The next generation of electronic microchips will utilize components with sub-micron feature size and optoelectronic devices with picosecond response time. Fundamental understanding of the device performance can only be obtained through first principles physics modeling of charge transport and electromagnetic effects in realistic geometries with material interfaces and dispersive properties. We have developed a general model incorporating important physics such as charge transport processes in materials with multilevel band structures and electromagnetic effects to simulate device characteristics. Accurate treatment of material interfaces and boundaries is included. The Monte Carlo charge transport is coupled self-consistently to Maxwell`s equations to accurately model scattering processes in the presence of an externally biased potential. This detailed multidimensional simulation capability is compared with and verified by experimental data, and could become an industrial standard for benchmarking and improving the {open_quotes}reduced model{close_quotes} codes used for semiconductor design. Specific tasks are the extension of existing capabilities in particle-in-cell plasma simulation technique and Monte Carlo charge transport to study the physics of charged particle dynamics in realistic microelectronic devices, such as bipolar semiconductors, heterojunction transistors, and optoelectronic switches. Our approach has been based on the coupled particle-in-cell/Monte Carlo technique, which can simultaneously treat both electromagnetic wave propagation and charged-particle transport.
Date: July 1, 1996
Creator: Kwan, T.; Booth, T. & Gray, M.
Partner: UNT Libraries Government Documents Department

Engineering Research, Development and Technology, FY95: Thrust area report

Description: The mission of the Engineering Research, Development, and Technology Program at Lawrence Livermore National Laboratory (LLNL) is to develop the knowledge base, process technologies, specialized equipment, tools and facilities to support current and future LLNL programs. Engineering`s efforts are guided by a strategy that results in dual benefit: first, in support of Department of Energy missions, such as national security through nuclear deterrence; and second, in enhancing the nation`s economic competitiveness through their collaboration with US industry in pursuit of the most cost-effective engineering solutions to LLNL programs. To accomplish this mission, the Engineering Research, Development, and Technology Program has two important goals: (1) identify key technologies relevant to LLNL programs where they can establish unique competencies, and (2) conduct high-quality research and development to enhance their capabilities and establish themselves as the world leaders in these technologies. To focus Engineering`s efforts, technology thrust areas are identified and technical leaders are selected for each area. The thrust areas are comprised of integrated engineering activities, staffed by personnel from the nine electronics and mechanical engineering divisions, and from other LLNL organizations. This annual report, organized by thrust area, describes Engineering`s activities for fiscal year 1995. The report provides timely summaries of objectives methods, and key results from eight thrust areas: computational electronics and electromagnetics; computational mechanics; microtechnology; manufacturing technology; materials science and engineering; power conversion technologies; nondestructive evaluation; and information engineering.
Date: February 1, 1996
Partner: UNT Libraries Government Documents Department