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Excitation of a TEM Cell by a Vertical Electric Hertzian Dipole

Description: From abstract: The excitation of a transverse electromagnetic (TEM) cell by a vertical electric Hertzian dipole is analyzed where the gap between the septum and side wall is assumed to be small. Approximate expressions for the field distribution and characteristic impedance are derived. These expressions are numerically evaluated for some typical geometries, and good agreement with previously published results is shown. The formation also allows a vertical offset for the septum position, thus offering more flexibility of increasing the size of the test area to accommodate larger pieces of test equipment.
Date: March 1981
Creator: Wilson, Perry F.; Chang, David C. & Ma, Mark T.
Partner: UNT Libraries Government Documents Department

Input Impedance of a Probe Antenna Exciting a TEM Cell

Description: Abstract: The input impedance of a probe antenna exciting a transverse electromagnetic (TEM) transmission line cell is formulated by a variational approach. The formulation also utilizes the results from a previous work on the field distribution inside a TEM cell excited by a vertical electrical Hertzian dipole. The final result of imoedance is shown to consist of two distinct terms, which are respectively contributed by the ordinary rectangular waveguide and the gap perturbation. Numerical results for both the real and imaginary parts of the impedance are given. The resistive part is found to be proportional to the square of the probe length, and the reactive part largely capacitive.
Date: April 1982
Creator: Wilson, Perry F.; Chang, David C. & Ma, Mark T.
Partner: UNT Libraries Government Documents Department

A protype dipole septum magnet for fast high current kicker systems

Description: A dipole "septum" magnet without a material septum has been designed and tested as part of a fast beam kicker system for use in intense, electron-beam induction accelerators. This septum magnet is a simple, iron-based electromagnet with two static, oppositely oriented dipole field regions used to provide further separation of beam centroids given a small angle kick by a fast beam kicker. The magnet geometry includes removable pole pieces to allow experimental flexibility. Field errors experienced by the beam depend crucially on the magnitude of the initial kick that provides displacement of the beam centroids from the transition region between the two dipole field regions. Results of simulations are reported.
Date: March 29, 1999
Creator: Wang, L F; Caporaso, G J; Chen, Y J; Lund, S M; Poole, B R & Brown, T F
Partner: UNT Libraries Government Documents Department

Resolution depths for some transmitter receiverconfigurations

Description: Away from a conductive body, secondary magnetic fields due to currents induced in the body by a time varying external magnetic field are approximated by (equivalent) magnetic dipole fields. Approximating the external magnetic field by its value at the location of the equivalent magnetic dipoles, the equivalent magnetic dipoles' strengths are linearly proportional to the external magnetic field, for a given time dependence of external magnetic field, and are given by the equivalent dipole polarizability matrix. The polarizability matrix and its associated equivalent dipole location is estimated from magnetic field measurements made with at least three linearly independent polarizations of external magnetic fields at the body. Uncertainties in the polarizability matrix elements and its equivalent dipole location are obtained from analysis of a linearized inversion for polarizability and dipole location. Polarizability matrix uncertainties are independent of the scale of the polarizability matrix. Dipole location uncertainties scale inversely with the scale of the polarizability matrix. Uncertainties in principal polarizabilities and directions are obtained from the sensitivities of eigenvectors and eigenvalues to perturbations of a symmetric matrix. In application to synthetic data from a magnetic conducting sphere and to synthetic data from an axially symmetric elliptic conducting body, the estimated polarizability matrices, equivalent dipole locations and principal polarizabilities and directions are consistent with their estimated uncertainties.
Date: August 28, 2002
Creator: Smith, J. Torquil; Morrison, H. Frank & Becker, Alex
Partner: UNT Libraries Government Documents Department

MEG (Magnetoencephalography) multipolar modeling of distributed sources using RAP-MUSIC (Recursively Applied and Projected Multiple Signal Characterization)

Description: We describe the use of truncated multipolar expansions for producing dynamic images of cortical neural activation from measurements of the magnetoencephalogram. We use a signal-subspace method to find the locations of a set of multipolar sources, each of which represents a region of activity in the cerebral cortex. Our method builds up an estimate of the sources in a recursive manner, i.e. we first search for point current dipoles, then magnetic dipoles, and finally first order multipoles. The dynamic behavior of these sources is then computed using a linear fit to the spatiotemporal data. The final step in the procedure is to map each of the multipolar sources into an equivalent distributed source on the cortical surface. The method is illustrated through an application to epileptic interictal MEG data.
Date: January 1, 2001
Creator: Mosher, John C.; Baillet, Sylvain; Jerbi, Karim & Leahy, Richard M.
Partner: UNT Libraries Government Documents Department

Hybrid MEG (Magnetoencephalography) source characterization by cortical remapping and imaging of parametric source models

Description: Reliable estimation of the local spatial extent of neural activity is a key to the quantitative analysis of MEG sources across subjects and conditions. In association with an understanding of the temporal dynamics among multiple areas, this would represent a major advance in electrophysiological source imaging. Parametric current dipole approaches to MEG (and EEG) source localization can rapidly generate a physical model of neural current generators using a limited number of parameters. However, physiological interpretation of these models is often difficult, especially in terms of the spatial extent of the true cortical activity. In new approaches using multipolar source models [3, 5], similar problems remain in the analysis of the higher-order source moments as parameters of cortical extent. Image-based approaches to the inverse problem provide a direct estimate of cortical current generators, but computationally expensive nonlinear methods are required to produce focal sources [1,4]. Recent efforts describe how a cortical patch can be grown until a best fit to the data is reached in the least-squares sense [6], but computational considerations necessitate that the growth be seeded in predefined regions of interest. In a previous study [2], a source obtained using a parametric model was remapped onto the cortex by growing a patch of cortical dipoles in the vicinity of the parametric source until the forward MEG or EEG fields of the parametric and cortical sources matched. The source models were dipoles and first-order multipoles. We propose to combine the parametric and imaging methods for MEG source characterization to take advantage of (i) the parsimonious and computationally efficient nature of parametric source localization methods and (ii) the anatomical and physiological consistency of imaging techniques that use relevant a priori information. By performing the cortical remapping imaging step by matching the multipole expansions of the original parametric source and the equivalent ...
Date: January 1, 2001
Creator: Baillet, S. (Sylvain); Mosher, J. C. (John C.); Jerbi, K. (Karim) & Leahy, R. M. (Richard M.)
Partner: UNT Libraries Government Documents Department

Heat leak performance of SSC collider dipole magnets

Description: The large number of superconducting dipoles in the SSC results in a stringent heat leak budget for each dipole. Ensuring that the dipoles meet this budget is vital to the successful operation or the collider. This work surveys heat leak measurements taken during 4 different magnet string tests. These tests involved both 40 mm and SO mm aperture dipoles. In these experiments the heat leak to the 80 K shield, 20 K shield and cold mass are measured. The results are compared to predictions from a computational thermal model of the dipole cryostat. Discrepancies are seen between the predicted and measured values. Possible explanations for these discrepancies are given.
Date: September 1, 1993
Creator: Weisend, J.G. II; Levin, M.; Franks, D.; Pletzer, R.; Augustynowicz, S.; McInturff, A.D. et al.
Partner: UNT Libraries Government Documents Department

Efficient imaging of single-hole electromagnetic data

Description: The extended Born, or localized nonlinear (LN) approximation, of integral equation (IE) solution has been applied to inverting single-hole electromagnetic (EM) data using a cylindrically symmetric model. The extended Born approximation is less accurate than a full solution but much superior to the simple Born approximation. When applied to the cylindrically symmetric model with a vertical magnetic dipole source, however, the accuracy of the extended Born approximation is shown to be greatly improved because the electric field is scalar and continuous everywhere. One of the most important steps in the inversion is the selection of a proper regularization parameter for stability. The extended Born solution provides an efficient means for selecting an optimum regularization parameter, because the Green's functions, the most time consuming part in IE methods, are repeatedly re-usable at each iteration. In addition, the IE formulation readily contains a sensitivity matrix, which can be revised at each iteration at little expense. In this paper we show inversion results using synthetic and field data. The result from field data is compared with that of a 3-D inversion scheme.
Date: April 1, 2002
Creator: Lee, Ki Ha; Kim, Hee Joon & Wilt, Mike
Partner: UNT Libraries Government Documents Department

Compendation of SSC lattice optics in the presence of dipole field errors: Report of the Correction Element Working Group

Description: The assignment of the Correction Element Working Group (CEWG) is to advance the designs of various candidate correction schemes to a point where they can be compared and distilled down to a single plan. Choosing among, the options often involves consideration of incommensurate factors such as cost, practicality, and theoretical performance. Except for minor issues, the CEWG purpose is to gather and array the facts in a form from which these decisions can be rationally made, but not to make the decisions. The present report analyses various schemes for compensating nonlinear multipole errors in the main arc dipoles of the Superconducting Super Collider. Emphasis is on comparing lumped and distributed compensation, on minimizing the total number of correction elements, and on reducing the sensitivity to closed-orbit errors.
Date: February 1, 1989
Creator: Bintinger, D.; Chao, A. & Forest, E.
Partner: UNT Libraries Government Documents Department

Tolerable systematic errors in Really Large Hadron Collider dipoles

Description: Maximum allowable systematic harmonics for arc dipoles in a Really Large Hadron Collider are derived. The possibility of half cell lengths much greater than 100 meters is justified. A convenient analytical model evaluating horizontal tune shifts is developed, and tested against a sample high field collider.
Date: December 1, 1996
Creator: Peggs, S. & Dell, F.
Partner: UNT Libraries Government Documents Department

Relativistic charged particle in the dipole-sphere configuration I. Classical and semiclassical surface orbits

Description: The classical and semiclassical orbits of a relativistic charged particle on a rotating sphere threaded by a magnetic dipole field are examined. The rotational and dipole axes are in general not aligned. Several physically distinct regimes emerge, depending on the relative sizes of the total energy, canonical azimuthal angular momentum, and magnetic field strength. Magnetic flux enclosed by orbits is quantised very close to the poles. Application of this system to neutron star magnetic fields and questions for future research are outlined.
Date: January 1, 1997
Creator: Gopinath, K.S.; Kennedy, D.C. & Gelb, J.M.
Partner: UNT Libraries Government Documents Department

Results from a prototype permanent magnet dipole-quadrupole hybrid for the PEP-II B-factory

Description: We describe the construction of a prototype hybrid permanent magnet dipole and quadrupole. The magnet consists of two concentric rings of Sm{sub 2}Co{sub 17} magnetic material 5 cm in length. The outer ring is made of 16 uniformly magnetized blocks assembled as a Halbach dipole and the inner ring has 32 blocks oriented in a similar fashion so as to generate a quadrupole field. The resultant superimposed field is an offset quadrupole field which allows us to center the field on the high-energy beam in the interaction region of the PEP-II B-factory. The dipole blocks are glued to the inside surface of an outer support collar and the quadrupole blocks are held in a fixture that allows radial adjustment of the blocks prior to potting the entire assembly with epoxy. An extensive computer model of the magnet has been made and from this model we developed a tuning algorithm that allowed us to greatly reduce the n=3 17 harmonics of the magnet.
Date: June 1, 1997
Creator: Sullivan, M.; Bowden, G. & Ecklund, S.
Partner: UNT Libraries Government Documents Department

Helical dipole magnets for polarized protons in RHIC

Description: Superconducting helical dipole magnets will be used in the Brookhaven Relativistic Heavy Ion Collider (RHIC) to maintain polarization of proton beams and to perform localized spin rotations at the two major experimental detector regions. Requirements for the helical dipole system are discussed, and magnet prototype work is reported.
Date: July 1, 1997
Creator: Syphers, M.; Courant, E. & Fischer, W.
Partner: UNT Libraries Government Documents Department

Quench antenna and fast-motion investigations during training of a 7T dipole magnet

Description: Equipment was installed to detect fast conductor motion and quench propagation in a 1 meter long superconducting dipole magnet (1) The fast-motion antenna, centered within the bore of the magnet, used three long dipole coils, mounted end-to-end to span the magnet length. Coil signals were nulled against a neighbor to produce low-ripple signals that were sensitive to local flux changes. A low-microphonic signal was used as an event trigger. (2) Nulling improvements were made for the magnet`s coil-imbalance signals for improved cross-correlation information. (3) A quench-propagation antenna was installed to observe current redistribution during quench propagation. It consisted of quadrupole/sextupole coil sets distributed at three axial locations within the bore of the magnet. Signals were interpreted in terms of the radius, angle, orientation, and rate of change of an equivalent dipole. The magnet was cooled to 1.8K to maximize the number of events. Twenty-four fast-motion events occurred before the first quench. The signals were correlated with the magnet-coil imbalance signals. The quench-propagation antenna was installed for all subsequent quenches. Ramp-rate triggered quenches produced adequate signals for analysis, but pole-turn quenches yielded such small signals that angular localization of a quench was not precise.
Date: October 17, 1994
Creator: Lietzke, A.F.; Benjegerdes, R.; Bish, P.; Krywinski, J.; Scanlan, R.; Schmidt, R. et al.
Partner: UNT Libraries Government Documents Department

Design study of 45-mm bore dipole magnet for 11 to 12 tesla field

Description: Two designs of 45mm bore dipole magnets are described about their magnetic characteristics. The first one has a 25mm thick collar with overall diameter of 520 mm. The other one has a 9-mm thin spacer with the overall diameter of 434 mm. Both of them have good field regions of 10{sup -4}, 28 mm wide horizontally and 24 mm wide vertically. With further adjustment of higher harmonics, the good field region can be horizontally increased to 33 mm. With the installation of a beam screen, the estimated vacuum space available for the beam operation is 33 mm wide horizontally and 22 mm wide vertically. If we assume that the total degradation of short sample data is 18.5%, the maximum central field values at quench current will be between 11.3 and 11.5 T.
Date: June 3, 1999
Creator: Moeller, Jonathan; Wake, Masayoshi & Yamada, Ryuji
Partner: UNT Libraries Government Documents Department

Quench performance of 50-mm aperture, 15-m-long SSC dipole magnets built at Fermilab

Description: The quench performance, ramp rate dependence, and mechanical behavior of ten full-length, 50-mm-aperture, SSC dipole magnets built at Fermilab are discussed. Cold testing of these magnets shows that the quench plateau established at 4.35 K exceeds the design value by more than 10%, virtually without training.
Date: July 1, 1992
Creator: Kuzminski, J.; Bush, T. & Coombes, R.
Partner: UNT Libraries Government Documents Department

Design parameters for a 7.2 tesla bending magnet for a 1.5 GeV compact light source

Description: This report describes the design for a 7.2 tesla superconducting dipole magnet for a compact synchrotron light source. The proposed magnet is a Vobly type modified picture frame dipole that has the flux returned through unsaturated iron. In this magnet, The iron in the pole pieces is highly saturated, Separately powered coils around the pole pieces are used to direct the flux lines until the flux can be returned through the unsaturated iron. The proposed dipole will develop a uniform field over a region that is 80 mm high by 130 mm wide over a range of central induction from 0.4 T to almost 8 T. Each dipole for the compact light source will have a magnetic length of about 0.38 meters.
Date: June 1, 1995
Creator: Green, M. A. & Madura, D.
Partner: UNT Libraries Government Documents Department

The magnet system of the Relativistic Heavy Ion Collider (RHIC)

Description: The Relativistic Heavy Ion Collider now under construction at Brookhaven National Laboratory (BNL) is a colliding ring accelerator to be completed in 1999. Through collisions of heavy ions it is hoped to observe the creation of matter at extremely high temperatures and densities, similar to what may have occurred in the original "Big Bang." The collider rings will consist of 1740 superconducting magnet elements. Some of elements are being manufactured by industrial partners (Northrop Grumman and Everson Electric). Others are being constructed or assembled at BNL. A description is given of the magnet designs, the plan for manufacturing and test results. In the manufacturing of the magnets, emphasis has been placed on uniformity of their performance and on quality. Results so far indicate that this emphasis has been very successful.
Date: July 1995
Creator: Greene, A.; Anerella, M. & Cozzolino, J.
Partner: UNT Libraries Government Documents Department

Eddy current and quench loads and stress of SSC collider 4-K liner and the bore tube during magnet quench

Description: This paper describes the response of the eddy current and quench loads on a proposed Superconducting SuperCollider 4-K liner system. The liner within a bore tube is designed to remove the radiated power and the photodesorbed gas that impair the beam tube vacuum. The bimetallic liner tube is subjected to cooldown and eddy current loads. The square liner tube is a two-shell laminated Nitronic-40 steel is used for strength and a copper inner layer for low impedance to the image currents. Perforated holes are used to remove the photodesorbed gases for vacuum maintenance. The holes are located in a low-stress area of the liner. Rectangular holes in a four-pole symmetry pattern are required for beam dynamic stability. The liner is conductivity cooled by the round steel bore tube with a 2-mm wall. The copper layer must not be stressed over the yield strength limit because copper properties such as conductivity are known to change when the copper is stressed over yield strength. This analysis will address liner system response under thermal, eddy current, and vaporized liquid helium loads in a quenching dipole magnet.
Date: July 1, 1993
Creator: Leung, K.K. & Shu, Q.S.
Partner: UNT Libraries Government Documents Department

Hybrid helical snakes and rotators for RHIC

Description: The spin rotators and Siberian snakes presently envisaged for RHIC utilize helical dipole magnets. The snakes and the rotators each consist of four helices, each with a full twist (360{degrees}) of the field. Here we investigate an alternate layout, namely combinations of helical and pure bending magnet, and show that this may have advantages.
Date: June 13, 1995
Creator: Courant, E.D.
Partner: UNT Libraries Government Documents Department

Supercollider program plan. Phase 1

Description: The purpose of this plan is to describe the Research and Development activities associated with the SSC (Superconducting Super Collider) Phase I program. This Phase I program will provide a comprehensive conceptual design report and is geared to accomplish specific research and development objectives that are required prior to initiation of Construction (Phase II). The overall program objectives are given in Section 2. The plan for assuring that these objectives are attained is described in the SSC Management Plan. An overall description of the planned. program is provided in Section 5. This Phase I program follows an extensive Reference Design Study conducted for the purpose of assessing technical feasibility and probable costs.
Date: January 1, 1985
Partner: UNT Libraries Government Documents Department

Industrial production of RHIC magnets

Description: ``Doing more with less`` has always been the signature of the military man and is especially true of Air Force weapons handlers. However, as the military drawdown continues, the phase takes on new meaning and becomes an unmistakable way of life for many. Unfortunately, all the resourcefulness in the world cannot overcome some obstacles, forcing a review of utility and mission effectiveness. How can we continue to reduce our resources and still meet our requirements? This paper documents the efforts under way to create a new tool for high fidelity, dexterous, heavy payload manipulation tasks. The ultimate goal of the Next Generation Munitions Handler Advanced Technology Demonstrator (ATD) is the identification and integration of the enabling technologies necessary to produce a system that reduces weapon loading times and operator workload while addressing mobility requirements.
Date: July 1, 1995
Creator: Anerella, M.D.; Fisher, D.H.; Sheedy, E. & McGuire, T.
Partner: UNT Libraries Government Documents Department

Synchrotron power supply light source note

Description: The ring magnet of the injector synchrotron consists of 68 dipole magnets. These magnets are connected in series and are energized from two feed points 180{degrees} apart by two identical 12-phase power supplies. The current in the magnet will be raised linearly to about 1 kA level, and after a small flat top (1 ms to 10 ms typical to provide sufficient time for the bridge to go to inversion mode) the current will be reduced to the injection level of 60 A. The repetition time for the current waveform is 500 ms. In this paper the theory of operation for the power supply along with its design characteristics will be given.
Date: March 1, 1991
Creator: Fathizadeh, M.
Partner: UNT Libraries Government Documents Department