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The TEAM workshops: A short history

Description: Early in 1985, Sam Berk of the Office of Fusion Energy, US Department of Energy, suggested that the development and validation of 3-D eddy current codes would benefit from the compilation of benchmark problems that could be used to validate the codes and from a series of workshops for the comparison of solution methods and codes. (Two years later, at the first International Symposium on Fusion Nuclear Technology in Tokyo, Sam Berk proposed the acronym TEAM for the workshops.) At a three-day planning meeting at Argonne National Laboratory (ANL) in November 1985, eleven participants from five countries defined the goals, format, schedule and problems for the workshops. The ultimate goal is to show the effectiveness of numerical techniques and associated computer codes in solving electromagnetic field problems, and to gain confidence in their predictions. The workshops should also provide cooperation between workers, leading to an interchange of ideas. This note reviews the three cycles of workshops and the problems.
Date: August 28, 1990
Creator: Turner, L.R.
Partner: UNT Libraries Government Documents Department

3-D computer simulations of EM fields in the APS vacuum chamber: Part 1, Frequency-domain analysis

Description: The vacuum chamber proposed for the storage ring of the 7-GeV Advanced Photon Source (APS) basically consists of two parts: the beam chamber and the antechamber, connected to each other by a narrow gap. A sector of 1-meter-long chamber with dosed end plates, to which are attached the 1-inch-diameter beampipes centered at the beam chamber, has been built for experimental purposes. The 3-D code MAFIA has been used to simulate the frequency-domain behaviors of EM fields in this setup. The results are summarized in this note and are compared with that previously obtained from 2-D simulations and that from network analyzer measurements. They are in general agreement. A parallel analysis in the time-domain is reported in a separate note. The method of our simulations can be briefly described as follows. The 1-inch diameter beampipes are terminated by conducting walls at a length of 2 cm. The whole geometry can thus be considered as a cavity. The lowest RF modes of this geometry are computed using MAFIA. The eigenfrequencies of these modes are a direct output of the eigenvalue solver E3, whereas the type of each mode is determined by employing the postprocessor P3. The mesh sizes are chosen such that they are small enough for computations in the frequency region in which we are interested (the sampling theorem), while the total number of mesh points is still well within the range that our computer system can cope with.
Date: September 4, 1990
Creator: Chou, W. & Bridges, J.
Partner: UNT Libraries Government Documents Department

Electromagnetic penetration through narrow slots in conducting surfaces and coupling to structures on the shadow side

Description: Electromagnetic field penetration through a curved narrow slot in a planar conducting surface and coupling to a curved, loaded thin wire on the shadow side are determined in the time domain (TD) and the frequency domain (FD) by integral equation methods. Coupled integral equations are derived and solved numerically for the equivalent magnetic current in the slot and the electric current on the wire, from which the field that penetrates the slotted surface is determined. One employs a piecewise linear approximation of the unknown currents and performs equation enforcement by pulse testing. The resulting TD equations are solved by a scheme incorporating a finite-difference approximation for a second partial time derivative which allows one to solve for the unknown currents at a discrete time instant t + 1 in terms of the known excitation and currents calculated at a discrete time instant t and earlier. The FD equations are solved by the method of moments. A hybrid time-domain integral equation -- finite-difference time-domain solution technique is described whereby one solves for the field which penetrates a slotted cavity-backed surface. One models the fields in the exterior region and in the slot with integral operators and models the fields inside the cavity with a discretized form of Maxwell's equations. Narrow slots following various contours were chemically etched in thin bass sheets and an apparatus was fabricated to measure shadow-side fields, electric current on a thin wire on the shadow side, and, separately, fields inside a rectangular cavity which backed the slotted brass sheet. The experimentation was conducted at the Lawrence Livermore National Laboratory on a frequency-domain test range employing a monocone source over a large ground plane. One observes very good agreement among the experimental and theoretical results.
Date: July 1, 1990
Creator: Reed, E.K. & Butler, C.M. (Clemson Univ., SC (USA). Dept. of Electrical and Computer Engineering)
Partner: UNT Libraries Government Documents Department

Field error lottery

Description: The level of field errors in an FEL is an important determinant of its performance. We have computed 3D performance of a large laser subsystem subjected to field errors of various types. These calculations have been guided by simple models such as SWOOP. The technique of choice is utilization of the FELEX free electron laser code that now possesses extensive engineering capabilities. Modeling includes the ability to establish tolerances of various types: fast and slow scale field bowing, field error level, beam position monitor error level, gap errors, defocusing errors, energy slew, displacement and pointing errors. Many effects of these errors on relative gain and relative power extraction are displayed and are the essential elements of determining an error budget. The random errors also depend on the particular random number seed used in the calculation. The simultaneous display of the performance versus error level of cases with multiple seeds illustrates the variations attributable to stochasticity of this model. All these errors are evaluated numerically for comprehensive engineering of the system. In particular, gap errors are found to place requirements beyond mechanical tolerances of {plus minus}25{mu}m, and amelioration of these may occur by a procedure utilizing direct measurement of the magnetic fields at assembly time. 4 refs., 12 figs.
Date: January 1, 1990
Creator: Elliott, C.J.; McVey, B. (Los Alamos National Lab., NM (USA)) & Quimby, D.C. (Spectra Technology, Inc., Bellevue, WA (USA))
Partner: UNT Libraries Government Documents Department

Damped and Detuned Accelerator Structures

Description: This paper reports continuing work on accelerator structures for future TeV linear colliders. These structures, in addition to having to operate at high gradients, must minimize the effects of wakefield modes which are induced by e{sup {plus minus}} bunch trains. Two types of modified disk-loaded waveguides are under investigation: damped structures in which the wakefield power is coupled out to lossy regions through radial slots in the disks and/or azimuthal rectangular waveguides, whereby the external Q of the undesirable HEM{sub 11} mode is lowered to values below 20, and detuned structures in which the frequencies of these modes are modified from one end to the other of each section by {approximately}10%, thereby scrambling their effects on the beam. Beam dynamics calculations indicate that these two approaches are roughly equivalent. MAFIA, ARGUS and URMEL codes have been used extensively in conjunction with low-power tests on S- and X-band models to identify mode patterns, dispersion curves and Q values, and to demonstrate damping or detuning of the HEM modes. Results of calculations and measurements on the various structures are presented and evaluated.
Date: September 1, 1990
Creator: Deruyter, H.; Farkas, Z.D; Hoag, H.A.; Ko, K.; Kroll, N.; Loew, G.A. et al.
Partner: UNT Libraries Government Documents Department

On the longitudinal coupling impedance of a toroidal beam tube

Description: In this paper, the longitudinal coupling impedance of a smooth toroidal beam tube is derived. By treating the torus as a slow-wave structure, the well-known method of describing the impedance in terms of cavity resonances can be used. A simple analytical expression for the coupling impedance of a toroidal beam tube with square cross section valid in the low-frequency limit is obtained. The results from the present study are compared with previously published solutions and qualitative differences are pointed out. 16 refs., 3 figs., 1 tab.
Date: January 1, 1990
Creator: Hahn, H. & Tepikian, S.
Partner: UNT Libraries Government Documents Department

The determination of the 805 MHz side coupled cavity dimensions for the Fermilab Linac upgrade

Description: In order to achieve the proper frequencies and coupling in Side Coupled Accelerator Structures, it is often necessary to model the cavities. In order to reduce the number of modeling steps and hence reduce machine shop time and cost, we have drawn heavily upon previous LAMPF experience and present day numerical calculation programs. Using a few aluminum cavity models at selected machine energies, we have been able to predict the frequency and coupling of our structures with good accuracy. This paper will describe the steps used to determine the cavity dimensions that meet our structure requirements. 6 refs., 6 figs.
Date: September 1, 1990
Creator: Jurgens, Thomas G.; Miller, Harold W.; Moretti, Alfred & Zhou, Ping
Partner: UNT Libraries Government Documents Department

Kiowa Creek Switching Station

Description: The Western Area Power Administration (Western) proposes to construct, operate, and maintain a new Kiowa Creek Switching Station near Orchard in Morgan County, Colorado. Kiowa Creek Switching Station would consist of a fenced area of approximately 300 by 300 feet and contain various electrical equipment typical for a switching station. As part of this new construction, approximately one mile of an existing 115-kilovolt (kV) transmission line will be removed and replaced with a double circuit overhead line. The project will also include a short (one-third mile) realignment of an existing line to permit connection with the new switching station. In accordance with the Council on Environmental Quality (CEQ) regulations for implementing the procedural provisions of the National Environmental Policy Act of 1969 (NEPA), 40 CFR Parts 1500--1508, the Department of Energy (DOE) has determined that an environmental impact statement (EIS) is not required for the proposed project. This determination is based on the information contained in this environmental assessment (EA) prepared by Western. The EA identifies and evaluates the environmental and socioeconomic effects of the proposed action, and concludes that the advance impacts on the human environment resulting from the proposed project would not be significant. 8 refs., 3 figs., 1 tab.
Date: March 1, 1990
Partner: UNT Libraries Government Documents Department

ELF (extremely-low-frequency) field interactions at the animal, tissue and cellular levels

Description: A description is given of the fundamental physical properties of extremely-low-frequency (ELF) electromagnetic fields, and the mechanisms through which these fields interact with the human body at a macroscopic level. Biological responses to ELF fields at the tissue, cellular and molecular levels are summarized, including new evidence that ELF field exposure produces alterations in gene expression and the cytoplasmic concentrations of specific proteins.
Date: October 1, 1990
Creator: Tenforde, T.S.
Partner: UNT Libraries Government Documents Department

An experiment to study strong electromagnetic fields at RHIC

Description: We present a description of an experiment which can be used to search for effects of strong electromagnetic fields on the production of e{sup +}e{sup {minus}} pairs in the elastic scattering of two heavy ions at RHIC. A very brief discussion of other possible studies of electromagnetic phenomena at RHIC is also presented.
Date: January 1, 1990
Creator: Fatyga, M. (Brookhaven National Lab., Upton, NY (USA)) & Norbury, J.W. (Rider Coll., Lawrenceville, NJ (USA). Dept. of Physics)
Partner: UNT Libraries Government Documents Department

Time-domain calculation of sub-nanosecond pulse launched by a proton beam

Description: Using the finite-difference time-domain code TBCI, we have numerically calculated the radiation from a sub-nanosecond 800-MeV proton bunch as it is launched into space. The calculation is compared to measurements of the time history of the radiated fields and good agreement is found. A movie showing the development of the radiation pattern will be shown during the presentation at this conference, namely, the First Los Alamos Symposium on Ultra-Wideband Radar. 6 refs., 7 figs.
Date: January 1, 1990
Creator: Chan, Kwok-Chi Dominic & Cooper, R.K.
Partner: UNT Libraries Government Documents Department

Low energy aspects of circular accelerators

Description: Performance in circular accelerators can be limited by some of the same sorts of phenomena described by Miller and Wangler in their lectures on low energy behavior in linear accelerators. In general the strength of the perturbation required to degrade performance is reduced in circular accelerators due to the repetitive nature of the orbits. For example, we shall see that space-charge can severely limit performance in circular accelerators even when operating far from the space-charge dominated regime'' as defined in linear accelerators. We will be discussing two particular aspects of low energy operation in circular accelerators -- space-charge and transition. Low energy'' is defined within the context of these phenomena. We shall see that the phenomena are really only relevant in hadron accelerators.
Date: December 1, 1990
Creator: Holmes, S.D.
Partner: UNT Libraries Government Documents Department

Deflecting modes of the side-coupled cavity structure

Description: The deflecting modes of the 805 MHz side-coupled cavity structure with the relativistic factor 0.566 are studied. Our main concern is the dispersion properties among different configurations of side-coupling cells and their interpretations. It is shown that the ninety degree side-coupling cell configuration, so to speak, the Mickey Mouse configuration has a merit in reducing the HEM{sub 1} passband. Another concern is the magnitude of the transverse coupling impedance around the synchronization condition. It is shown that the existence of the coupling cell introduces the nonuniformity of the deflecting mode and gives different impedance relative to the beam axis and that the coupling impedance at {pi}/10 exceeds 50 M{Omega}/m if the quality value of the mode is around 12000.
Date: November 1, 1990
Creator: Inagaki, Shigemi.
Partner: UNT Libraries Government Documents Department

Electromagnetic PIC codes on unstructured grids

Description: This report discusses the following topics in relationships to plasma simulation: unstructed grids; particle tracking; and field propagation. (LSP)
Date: October 12, 1990
Creator: Ambrosiano, J.J.; Brandon, S.T. (Lawrence Livermore National Lab., CA (USA)) & Loehner, R. (George Washington Univ., Washington, DC (USA). School of Engineering and Applied Science)
Partner: UNT Libraries Government Documents Department

Computer simulations of new dielectric accelerator devices

Description: Recently, dielectric wakefield accelerator structures have been successfully demonstrated at the Argonne Advanced Accelerator Test Facility. This paper describes computer simulations of these experiments, including schemes for damping transverse deflecting forces in these devices. These simulations were performed using the MAFIA and ARRAKIS codes. MAFIA is a set of electromagnetic solvers in three dimensions widely used for designing accelerator components. The ARRAKIS codes are time-domain electromagnetic solvers which have recently developed and implemented on massively parallel computers such as the Connection Machine. 6 refs., 5 figs., 1 tab.
Date: January 1, 1990
Creator: Chan, K.C.D. (Los Alamos National Lab., NM (USA)) & Schoessow, P. (Argonne National Lab., IL (USA))
Partner: UNT Libraries Government Documents Department

Performance of the D0 end calorimeter electromagnetic module

Description: We have constructed a uranium liquid argon calorimeter which serves as the end calorimeter electromagnetic module for the DO experiment at Fermilab. We present details of the construction and the results of the tests made using electron beams ranging from 10 GeV to 150 GeV. We find the energy resolution is 15.5%/{radical}E(GeV) with a small constant term of {approximately}0.5% and the response is linear to better than {plus minus}0.5%. 5 refs., 7 figs.
Date: October 1, 1990
Creator: Aihara, Hiroaki.
Partner: UNT Libraries Government Documents Department

Mechanical and electromagnetic analysis of 50 millimeter designs for the SSC dipole

Description: Several designs for the Superconducting Super Collider dipole magnet have been analyzed. This note discusses the mechanical and electromagnetic features of each design. Electromagnetic and Mechanical analyses were performed using hand, computer programs and finite element techniques to evaluate the design. 10 refs., 6 figs., 3 tabs.
Date: September 1, 1990
Creator: Jayakumar, J.; Leung, K.; Nobrega, F.; Orrell, D.; Sanger, P.; Snitchler, G. et al.
Partner: UNT Libraries Government Documents Department

Techniques for beam impedance measurements above cutoff

Description: Methods for measuring beam impedance above cutoff have been very limited. For design work on the ALS we have developed two techniques that yield data in the frequency domain with high sensitivity. The first is an extension of the wire method; the second utilizes traveling TM waves to simulate the beam's fields at the wall, and thus avoids the mechanical difficulties of mounting the wire. It is also more sensitive than the other method but the interpretation is complicated by the presence of higher order modes. With either method we were able to detect resonant peaks smaller than 1 Ohm at 10 GHz.
Date: August 1, 1990
Creator: Lambertson, G.R.; Jacob, A.F.; Rimmer, R.A. & Voelker, F.
Partner: UNT Libraries Government Documents Department

Modified-Yee field solutions in the AMOS wakefield code

Description: A new numerical procedure by which field calculations in AMOS are upgraded to model rotationally symmetric cavity structures in a more accurate fashion is described. The development work is aimed at implementing a modified finite difference update scheme on an irregular grid system. Elements of an irregular grid may be chosen to better fit object boundaries, resulting in increased solution accuracy. Our approach involves the placement of field components on a non-orthogonal body fitting grid and on a dual grid which is orthogonal to the first grid. It is found that this procedure retains several important computational advantages, including the ability to exploit the implied spatial relationships between nodes. Propagating fields on an irregular grid system have been observed and comparisons between finite difference AMOS and Modified-Yee AMOS field calculations are provided.
Date: August 29, 1990
Creator: Shang, C.C. & DeFord, J.F.
Partner: UNT Libraries Government Documents Department

Damped time advance methods for particles and EM fields

Description: Recent developments in the application of damped time advance methods to plasma simulations include the synthesis of implicit and explicit adjustably damped'' second order accurate methods for particle motion and electromagnetic field propagation. This paper discusses this method.
Date: October 12, 1990
Creator: Friedman, A.; Ambrosiano, J.J.; Boyd, J.K.; Brandon, S.T.; Nielsen, D.E. Jr. & Rambo, P.W.
Partner: UNT Libraries Government Documents Department

Numerical modeling of time domain 3-D problems in accelerator physics

Description: Time domain analysis is relevant in particle accelerators to study the electromagnetic field interaction of a moving source particle on a lagging test particle as the particles pass an accelerating cavity or some other structure. These fields are called wake fields. The travelling beam inside a beam pipe may undergo more complicated interactions with its environment due to the presence of other irregularities like wires, thin slots, joints and other types of obstacles. Analytical solutions of such problems is impossible and one has to resort to a numerical method. In this paper we present results of our first attempt to model these problems in 3-D using our finite difference time domain (FDTD) code. 10 refs., 9 figs.
Date: June 1, 1990
Creator: Harfoush, F.A. & Jurgens, T.G.
Partner: UNT Libraries Government Documents Department

HEM sub 11 modes revisited

Description: Concern with emittance growth in future multi-bunch linear colliders has rekindled interest in HEM{sub 11} dipole modes (sometimes also called TM{sub 11}-like'' or TE{sub 11}-like'') in disk-loaded waveguides. The availability of modern computer codes (URMEL, MAFIA) makes it possible to gain a deeper understanding of these modes and their properties. This paper presents {omega}-{beta} dispersion diagrams, field configurations and transverse shunt impedances for the HEM{sub 11} modes as a function of iris aperture. The transition between forward and backward waves of the various branches is explored. This information serves as background material for another paper at this conference which reports recent work on linac structures in which these modes are damped or detuned. 5 refs., 3 figs., 1 tab.
Date: September 1, 1990
Creator: Wang, J.W. & Loew, G.A.
Partner: UNT Libraries Government Documents Department

Summary of 1990 Code Conference

Description: The Conference on Codes and the Linear Accelerator Community was held in Los Alamos in January 1990, and had approximately 100 participants. This conference was the second in a series which has as its goal the exchange of information about codes and code practices among those writing and actually using these codes for the design and analysis of linear accelerators and their components. The first conference was held in San Diego in January 1988, and concentrated on beam dynamics codes and Maxwell solvers. This most recent conference concentrated on 3-D codes and techniques to handle the large amounts of data required for three-dimensional problems. In addition to descriptions of codes, their algorithms and implementations, there were a number of paper describing the use of many of the codes. Proceedings of both these conferences are available. 3 refs., 2 tabs.
Date: January 1, 1990
Creator: Cooper, R.K. & Chan, Kwok-Chi D.
Partner: UNT Libraries Government Documents Department