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Computer simulations of electromagnetic ion instabilities in the plasma sheet boundary layer

Description: Linear Vlasov dispersion theory and one-dimensional hybrid computer simulations are used to study electromagnetic instabilities driven by hot, anisotropic counterstreaming proton components which model those observed from ISEE in the plasma sheet boundary layer of the near-Earth magnetotail. The proton anisotropies lead to the ion cyclotron anisotropy instability, which saturates at a low level of fluctuating fields and yields only weak proton scattering. Modest increases of the proton/proton relative drift, which might correspond to deeper tail conditions, excite the proton/proton nonresistant instability which attains larger fluctuation levels and more strongly heats the protons. If a relatively dense oxygen ion component is also introduced, the ion/ion right-hand resonant instability is excited; the consequent pitch-angle scattering of the protons resembles that indicated in the ISEE data. 6 refs., 5 figs.
Date: January 1, 1989
Creator: Gary, S.P. & Winske, D.
Partner: UNT Libraries Government Documents Department

Normalization of the scattered light from an isolated defect illuminated by a Gaussian beam

Description: The intensity distribution of the beam from a laser operated in the zero order configuration for the transverse electromagnetic field (TEM/sub 00/ mode) is Gaussian in a plane perpendicular to the axis of the beam. In some applications it is desirable to have a uniform intensity over a certain region in space. For example, when a Gaussian beam is incident on a smooth surface containing small isolated defects, the light scattered by a defect will depend on the position of the defect relative to the center of the beam. In the past, several techniques have been devised to convert a Gaussian intensity profile into a uniform intensity over a specified region in space. In the present work a different approach is taken. A method of normalization is described which makes direct use of the Gaussian intensity distribution of the TEM/sub 00/ mode. By this method the amount of light scattered by a defect can be normalized to the value which would be observed if the defect were located at the center of the beam, for a defect small in size compared with the 1/e/sup 2/ diameter of the Gaussian profile. The normalization requires that three measurements be made of the scattering by the defect for an arbitrary location of the defect relative to the center of the Gaussian beam, and that the 1/e/sup 2/ radius of the Gaussian beam and the interval between adjacent illuminated spots on the surface are known. Experimental data verifying the theory were obtained from isolated defects on a superfinished spherical surface.
Date: July 1, 1980
Creator: Klingsporn, P.E.
Partner: UNT Libraries Government Documents Department

Measurements of electromagnetic properties of LCT (Large Coil Task) coils in IFSMTF (International Fusion Superconducting Magnet Test Facility)

Description: Participants in the international Large Coil Task (LCT) have designed, built, and tested six different toroidal field coils. Each coil has a 2.5- by 3.5-m, D-shaped bore and a current between 10 and 18 kA and is designed to demonstrate stable operation at 8 T, with a superimposed averaged pulsed field of 0.14 T in 1.0 s and simulated nuclear heating. Testing of the full six-coil toroidal array began early in 1986 and was successfully completed on September 3, 1987, in the International Fusion Superconducting Magnet Test Facility (IFSMTF) at Oak Ridge National Laboratory (ORNL). This paper summarizes electromagnetic properties of LCT coils measured in different modes of energization and fast dump. Effects of mutual coupling and induced eddy currents are analyzed and discussed. Measurements of the ac loss caused by the superimposed pulsed fields are summarized. Finally, the interpretation of the test results and their relevance to practical fusion are presented. 11 refs., 10 figs., 4 tab.
Date: January 1, 1987
Creator: Shen, S.S.; Baylor, L.R.; Dresner, L.; Fehling, D.T.; Lubell, M.S.; Lue, J.W. et al.
Partner: UNT Libraries Government Documents Department

Modeling ferrite electromagnetic response in the time domain

Description: The behavior of ferrite loads commonly found in induction accelertors has important consequences for the performance of these accelerators. Previous work by the authors on modeling the electromagnetic fields in induction cavities has focussed upon use of a simple, phenomenological model for the process of magnetization reversal in these ferrite loads. In this paper we consider a model for magnetization reversal which is more deeply rooted in theory, and present a simulation of the reversal process based upon this model for an idealized set of boundary conditions. 7 refs., 3 figs.
Date: April 6, 1989
Creator: Johnson, J.; DeFord, J.F. & Craig, G.D.
Partner: UNT Libraries Government Documents Department

A modality-specific neuromagnetic P3

Description: Several studies indicate that in cases of psychopathology and alcoholism the amplitude and/or latency of endogenous, scalp-recorded P3 potentials elicited by rare events are abnormal. The P3 complex may normally be a valuable index of the brain's work-load and identification of the neural generator(s) of this late positive component would thus provide valuable insight into the substrates of both normal and abnormal information processes. Okada and his colleagues have recorded magnetic field correlates of P3 potentials evoked by visual and auditory stimuli. Data from a mapping study of a visually evoked magnetic P3 were consistent with a hippocampal source, but attempts to localize the generator(s) of the auditory magnetic P3 were unsuccessful. In an effort to independently confirm, extend, and clarify these results, the surface topographies of magnetic P3-like complexes evoked during the performance of auditory and visual detection tasks were examined. 6 refs., 2 figs.
Date: January 1, 1989
Creator: Flynn, E.R.; Lewine, J.D.; Oakley, M.T.; Roeder, S.B.; Arthur, D.L.; Aine, C.J. et al.
Partner: UNT Libraries Government Documents Department

Design of the electromagnetic fluctuations diagnostic for MFTF-B

Description: The Electromagnetic Fluctuations (EMF) diagnostic will be used to monitor ion fluctuations which could be unstable in MFTF-B. Each probe assembly includes a high impedance electrostatic probe to measure potential fluctuations, and a group of nested, single turn loops to measure magnetic fluctuations in three directions. Eventually, more probes and loops will be added to each probe assembly for making more detailed measurements. The sensors must lie physically close to the plasma edge and are radially positionable. Also, probes at separate axial locations can be positioned to connect along the same magnetic field line. These probes are similar in concept to the rf probes used on TMX, but the high thermal load for 30-second shots on MFTF-B requires a water-cooled design along with temperature monitors. Each signal channel has a bandwidth of .001 to 150 MHz and is monitored by up to four different data channels which obtain amplitude and frequency information. This paper describes the EMF diagnostic and presents the detailed mechanical and electrical designs.
Date: November 28, 1983
Creator: House, P.A.; Goerz, D.A. & Martin, R.
Partner: UNT Libraries Government Documents Department

Electromagnetic analysis for fusion reactors: status and needs

Description: Electromagnetic effects have far-reaching implications for the design, operation, and maintenance of future fusion reactors. Two-dimensional (2-D) eddy current computer codes are available, but are of limited value in analyzing reactors. Three-dimensional (3-D) codes are needed, but are only beginning to be developed. Both 2-D and 3-D codes need verification against experimental data, such as that provided by the upcoming FELIX experiments. Coupling between eddy currents and deflections has application in fusion reactor design and is being studied both by analysis and experiment.
Date: January 1, 1983
Creator: Turner, L.R.
Partner: UNT Libraries Government Documents Department

Unification of quantum theory and classical physics

Description: A program is described for unifying quantum theory and classical physics on the basis of the Copenhagen-interpretation idea of external reality and a recently discovered classical part of the electromagnetic field. The program effects an integration of the intuitions of Heisenberg, Bohr, and Einstein.
Date: July 1, 1985
Creator: Stapp, H.P.
Partner: UNT Libraries Government Documents Department

Results from the FELIX experiments on electromagnetic effects in hollow cylinders

Description: The early experiments with the FELIX (Fusion Electromagnetic Induction eXperiments) facility have been devoted to obtaining data which can be used to validate eddy current computer codes. This paper describes experiments on field variation inside conducting cylinders.
Date: January 1, 1985
Creator: Turner, L.R.; Gunderson, G.R.; Knott, M.J.; McGhee, D.G.; Praeg, W.F. & Wehrle, R.B.
Partner: UNT Libraries Government Documents Department

Solution of the field equations for 2-D electromagnetic direct implicit plasma simulation

Description: A direct implicit particle-in-cell (PIC) simulation model with full electromagnetic (EM) effects has been implemented in 2-D Cartesian geometry. The model, implemented with the D/sub 1/ time differencing scheme, was first implemented in a 1-D electrostatic (ES) version to gain some experience with spatial differencing in forms suitable for extension to the full EM field in two dimensions. The implicit EM field solve is considerably different from the implicit ES code. The EM field calculation requires an inductive part as well as the electrostatic and the B field must be self-consistently advanced.
Date: January 2, 1985
Creator: Hewett, D.W. & Langdon, A.B.
Partner: UNT Libraries Government Documents Department

Longitudinal impedance of a smooth toroidal chamber at low and intermediate frequencies

Description: We evaluate the longitudinal coupling impedance of a toroidal chamber with rectangular cross section in the frequency domain below the synchronous resonant modes. With infinite wall conductivity the impedance is purely reactive and consists of a ''space charge'' term, proportional to ..gamma../sup /minus/2/, and a ''curvature'' term which survives at large ..gamma... The curvature term is well represented as a quadratic function of frequency. 3 refs., 3 figs.
Date: March 1, 1989
Creator: Ng, King-Yuen & Warnock, R.
Partner: UNT Libraries Government Documents Department

Electromagnetic effects of plasma disruptions in tokamaks

Description: The tokamak is modeled as typically 100 mutually-coupled toroidal circuits. The self and mutual inductances and the currents and voltages are calculated. Using the calculated currents, the poloidal magnetic field and the electromagnetic forces as functions of space and time are calculated. The major conclusion of the analysis is that the torus sectors should be electrically connected to each other near the plasma. Such connections reduce the structural loads, eliminate arcing, and reduce the induced potentials in the poloidal field coils.
Date: January 1, 1981
Creator: Thomson, S.L.; Murray, J.G. & Bronner, G.
Partner: UNT Libraries Government Documents Department

Analysis of rf modes in the ANL APS vacuum chamber using computer simulation, electron beam excitation, and perturbation techniques

Description: The APS vacuum consists of a nearly elliptical beam chamber coupled to an antechamber through a 1-cm-high, 10-cm-long pumping slot over most of the 1104 m of storage ring circumference. Nonevaporable getter (NeG) strips in the antechamber are the pumping element. The 1-cm-high slot has two functions: to provide good conductance for vacuum pumping and for transmission of the photons into the beam ports. We thought that coupling of the beam to the antechamber might occur through the slot. Since the beam fields are transverse magnetic to the beam (TM/sub z/), no coupling occurs below the TM cutoff of the slot (15 GHz for 1 cm) because no wall currents are interrupted. Also, the frequency spectrum of a rigid bunch is well below 15 GHz. Both computer calculations and measurements were done to verify that no coupling occurs. Computer calculations in the frequency domain and two-arm wire measurements with picosecond pulses were previously reported. The wire measurements confirmed that little coupling occurs between the two chambers. In addition to those earlier studies, a real-time MAFIA-T3 study in 3D was done, and a measurement of modes excited by a 38-ps, 20-MeV electron beam has been completed. These results are the primary topic of this paper. Some measurements made with a network analyzer and bead perturbation equipment will also be discussed. 8 refs., 11 figs.
Date: January 1, 1989
Creator: Kustom, R.; Bridges, J.; Chou, W.; Cook, J.; Mavrogenes, G. & Nicholls, G.
Partner: UNT Libraries Government Documents Department

Beam-shape distortion caused by transverse wake fields

Description: As a particle bunch in a storage ring passes through a region with a transverse impedance, it generates a transverse wake electromagnetic field that is proportional to the transverse displacement of the bunch in the region. The field acts back on the bunch, causing various effects (such as instabilities) in the motion of the bunch. We study one such effect in which a transverse impedance causes the beam to be distorted in its shape. Observed at a fixed location in the storage ring, this distortion does not change from turn to turn; rather, the distortion is static in time. To describe the distortion, the bunch is considered to be divided longitudinally into many slices and the centers of change of the slices are connected into a curve. In the absence of transverse impedance, this curve is a straight line parallel to the direction of motion of the bunch. Perturbed by the transverse wake field, the curve becomes distorted. What we find in this paper is the shape of such a curve. The results obtained are applied to the PEP storage ring. The impedance is assumed to come solely from the rf cavities. We find that the beam shape is sufficiently distorted and hence that loss of luminosity due to this effect becomes a possibility.
Date: February 1, 1983
Creator: Chao, A.W. & Kheifets, S.
Partner: UNT Libraries Government Documents Department

Beam-strahlung effects in e-p collider

Description: The electromagnetic fields produced by one beam in an interaction point of a colliding-beam facility cause to the emission of synchrotron radiation by the other beam. This effect, the beam strahlung, for the e+e/sup -/ colliders has been considered by several authors, and they have pointed out that the effect is very important consideration at very-high-energy e+e/sup -/ colliders. At the first glance, the beam-strahlung effect can play an important role in the e-p collision due to the fact that the circulating currents in the collider are much higher than those of the e+e/sup -/ machine. However the detailed study shows that is not the case because of the collision geometry involved. What follows in this note is the beam-strahlung derivations using the method previously used by Hofmann and Keil. The difference between this note and that of Hofman and Keil is that in the case of e+e/sup -/ collider, equal mass particles are involved in the consideration and, in the e-p case, the electrons radiate and the protons provide the electromagnetic fields.
Date: September 1, 1982
Creator: Cho, Y.
Partner: UNT Libraries Government Documents Department

Limitation of Linear Colliders From Transverse RF Deflections

Description: Offaxis beam trajectories in a linear collider produce transverse wakefield and chromatic effects which cause emittance enlargement. One cause for non-centered trajectories in the accelerating structures is radial rf fields which produce transverse deflections. Static deflections can be compensated by static dipole magnetic fields. However, fluctuations of the rf fields cause variations in the deflections which must be managed or limited. Given the level of fluctuation of the phase and amplitude of an rf system, a limit on the allowable rf deflection can be calculated. Parameters, such as the beam emittance, lattice design, rf wavelength and the initial and final beam energies, influence the tolerances. Two tolerances are calculated: (1) one assumes that the wakefields are completely controlled, and that chromatic effects are the only enlarging mechanism (optimistic), and (2) the other assumes the limit is due to transverse wakefields without the aid of Landau damping (pessimistic).
Date: January 1, 1987
Creator: Seeman, J. T.
Partner: UNT Libraries Government Documents Department

MAGFOR: a magnetics code to calculate field and forces in twisted helical coils of constant cross section

Description: The machine-independent computer program MAGFOR calculates electromagnetic fields and forces in coil systems of arbitrary geometry. The coils may be modeled by using 20-node isoparametric hexahedrons; 8-node rectangular cross-sectional straight segments; rectangular cross-sectional circular arcs; and/or filamenting circular loops. A combination of analytical and numerical integration of the Biot-Savart law for a volume distribution of current is used for calculating magnetic fields. Volumetric body forces are calculated for the 20-node isoparametric brick by numerically integrating the vector product J x B over its volume, where the magnetic field at each Gauss point is obtained by interpolating the magnetic field at the node points by using shape functions. The force is distributed to the node points of the element, again using the shape functions in a consistent manner that maintains inter-element torsion. Body forces obtained from MAGFOR are compared with body forces from the computer code EFFI for several coil configurations considered in the design of the Advanced Toroidal Facility (ATF).
Date: January 1, 1983
Creator: Cain, W.D.
Partner: UNT Libraries Government Documents Department

Computer simulation of the lasertron with a ring model

Description: The lasertron is more efficient, lighter, and smaller than a klystron, especially at outputs below 2 GHz. Higher peak output powers are possible with the lasertron, and a separate modulator is not required. These advantages are useful for rf accelerators and linear colliders. The electron dynamics are simulated to estimate the device performance limits and to design an experimental lasertron. The relativistic electron dynamics are followed from the photocathode through the acceleration region and through the output region. The total fields are the sum of the space-charge, external magnetic, and acceleration or output-cavity fields. Wake fields are ignored, and the steady-state output fields are found. Lasertron performance as a function of acceleration field, charge per pulse nd frequency is calculated, showing its avantages and limitations. A preliminary design for the first Orsay lasertron experiment is presented.
Date: March 16, 1987
Creator: Tallerico, P.J. & Coulon, J.P.
Partner: UNT Libraries Government Documents Department

Higher-order modes calculation of rf cavity with cylindrical symmetry

Description: This paper represents a new computer calculating method for cylindrical symmetry cavities. This method can calculate not only the fundamental mode and longitudinal modes but also the transverse higher modes. The Hertz vector is used as fundamental quantity and the separated variable method is applied. An empty cylindrical cavity has been calculated. The calculating result is in accord with analytic solution fairly well.
Date: January 1, 1983
Creator: Zhou, W.; Xuanwen, C. & Mingda, Z.
Partner: UNT Libraries Government Documents Department

Superconducting cavities and modulated RF

Description: If a cavity has an infinite Q/sub o/, 81.5% of the energy contained in a pulse incident upon the cavity is transferred into the cavity by the end of the pulse if the cavity Q/sub e/ is chosen so that the cavity time constant is 0.796 pulse width (T/sub a/). As Q/sug o/ decreases, the energy in the cavity at the end of the pulse decreases very slowly as long as T/sub a/ is much less than the unloaded cavity time constant, T/sub co/. SC cavities with very high Q/sub o/ enable one to obtain very high gradients with a low power cw source. At high gradients, however, one often does not attain the high Q/sub o/ predicted by theory. Therefore, if one is inteerested in attaining maximum energy in the cavity, as is the case for RF processing and diagnostics, for a given available source energy there is no point in keeping the power on for longer than 0.1 T/sub co/ because the energy expended after 0.1 T/sub co/ is wasted. Therefore, to attain high fields at moderate Q/sub o/, pulsed operation is indicated. This note derives the fields and energy stored and dissipated in the cavity when Q/sub e/ is optimized for a given T/sub a/. It shows how to use this data to measure Q/sub o/ of an SC cavity as a function of field level, how to process the cavity with high RF fields, how to operate SC cavities in the pulsed mode to obtain higher efficiencies and gradients. Experimental results are also reported.
Date: February 1, 1981
Creator: Farkas, Z.D.
Partner: UNT Libraries Government Documents Department

SUPERFISH: a status report

Description: The computer code SUPERFISH was developed to calculate various parameters associated with rf fields in axially symmetrical cavities of arbitrary shapes. Since the introduction of the code in 1976, it has been in continuous use at Los Alamos National Laboratory. Over the intervening years there have been numerous utility improvements, and several technical additions to the program. These modifications and additions are described, and the basic capabilities of SUPERFISH are reviewed.
Date: January 1, 1981
Creator: Reid, D.W.; Harvey, A.A.; Rodenz, G.W. & Holsinger, R.F.
Partner: UNT Libraries Government Documents Department

Effects of spatial attention on the visual-evoked neuromagnetic response

Description: A number of studies have shown that selective attention to spatial location modulates the amplitudes of several visual evoked potential components recorded from posterior regions of the head (e.g., Eason, Harter White, 1969; Harter, Aine, Schroeder, 1982; Hillyard Munte, 1984; Mangun Hillyard, 1988). The early components, P1 and N1 (peak latencies: 90--135 and 140--170 msec, respectively), are thought to arise in one or more areas of visual cortex. Although it is generally assumed that such ERP effects reflect differential activation of populations of neurons at successive levels of the nervous system, little information is available about the neural structures responsible for such effects. We have employed neuromagnetic techniques in an attempt to identify more precisely the neural structures involved in selective attention to spatial location within the P1-N1 time sequence. In this study, effects of attention were assessed by comparing neural responses evoked by stimuli at a specified spatial location when subjects were required to attend and respond behaviorally to that location with neural responses to the same stimuli when subjects were required to attend and respond behaviorally to another location in the visual field. 7 refs., 3 figs.
Date: January 1, 1989
Creator: Aine, C.J.; George, J.S.; Oakley, M.T.; Medvick, P.A. & Flynn, E.R.
Partner: UNT Libraries Government Documents Department

Computation of electromagnetic effects in a tokamak due to a plasma disruption

Description: To model the consequences of a plasma disruption in a tokamak one must combine a code that computes the detailed MHD behavior of the plasma with one that treats the three-dimensional features of the conducting toroidal components around the plasma. The NET (Next European Torus) Team have undertaken a treatment of electromagnetic effects from plasma disruptions using both open loop and closed loop integration of codes. In America, workers at Oak Ridge National Laboratory, Idaho National Engineering Laboratory, and Argonne National Laboratory have looked at plasma disruption effects on the ITER blanket using the codes TSC and EDDYNET. Results show how the forces on a blanket segment depend on the number and size of the segments and on the gap between them. 9 refs., 4 figs., 1 tab.
Date: January 1, 1989
Creator: Turner, L.R.
Partner: UNT Libraries Government Documents Department