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Report of the SSC impedance workshop

Description: This workshop focused attention on the transverse, single-bunch instability and the detailed analysis of the broadband impedance which would drive it. Issues discussed included: (1) single bunch stability -- impact of impedance frequency shape, coupled-mode vs. fast blowup regimes, possible stopband structure; (2) numerical estimates of transverse impedance of inner bellows and sliding contact shielded bellows; (3) analytic estimates of pickup and kicker impedance contributions; and (4) feasibility studies of wire and beam measurements of component impedance.
Date: October 28, 1985
Partner: UNT Libraries Government Documents Department

3-D computer simulations of EM field sin the APS vacuum chamber. Part 2: Time-domain analysis

Description: Our simulations suggest that the strong peak around 4 GHz in the narrow gap observed in the measurements is generated by TE modes. Therefore, one should not worry about this peak insofar as the coupling impedance is concerned. On the other hand, some discrepancies between our simulations and the measurements are noticed and remain to be resolved.
Date: January 20, 1989
Creator: Chou, W.
Partner: UNT Libraries Government Documents Department

An introduction to acceleration mechanisms

Description: This paper discusses the acceleration of charged particles by electromagnetic fields, i.e., by fields that are produced by the motion of other charged particles driven by some power source. The mechanisms that are discussed include: Ponderamotive Forces, Acceleration, Plasma Beat Wave Acceleration, Inverse Free Electron Laser Acceleration, Inverse Cerenkov Acceleration, Gravity Acceleration, 2D Linac Acceleration and Conventional Iris Loaded Linac Structure Acceleration. (LSP)
Date: May 1, 1987
Creator: Palmer, R.B.
Partner: UNT Libraries Government Documents Department

Argonne plasma wake-field acceleration experiments

Description: Four years after the initial proposal of the Plasma Wake-field Accelerator (PWFA), it continues to be the object of much investigation, due to the promise of the ultra-high accelerating gradients that can exist in relativistic plasma waves driven in the wake of charged particle beams. These wake-fields are of interest both in the laboratory, for acceleration and focusing of electrons and positrons in future linear colliders, and in nature as a possible cosmic ray acceleration mechanism. The purpose of the present work is to review the recent experimental advances made in PWFA research at Argonne National Laboratory. Some of the topics discussed are: the Argonne Advanced Accelerator Test Facility; linear plasma wake-field theory; measurement of linear plasma wake-fields; review of nonlinear plasma wave theory; and experimental measurement of nonlinear plasma wake-fields. 25 refs., 11 figs.
Date: March 14, 1989
Creator: Rosenzweig, J.B.; Cole, B.; Gai, W.; Konecny, R.; Norem, J.; Schoessow, P. et al.
Partner: UNT Libraries Government Documents Department

EBQ code: transport of space-charge beams in axially symmetric devices

Description: Such general-purpose space charge codes as EGUN, BATES, WOLF, and TRANSPORT do not gracefully accommodate the simulation of relativistic space-charged beams propagating a long distance in axially symmetric devices where a high degree of cancellation has occurred between the self-magnetic and self-electric forces of the beam. The EBQ code was written specifically to follow high current beam particles where space charge is important in long distance flight in axially symmetric machines possessing external electric and magnetic field. EBQ simultaneously tracks all trajectories so as to allow procedures for charge deposition based on inter-ray separations. The orbits are treated in Cartesian geometry (position and momentum) with z as the independent variable. Poisson's equation is solved in cylindrical geometry on an orthogonal rectangular mesh. EBQ can also handle problems involving multiple ion species where the space charge from each must be included. Such problems arise in the design of ion sources where different charge and mass states are present.
Date: November 1, 1982
Creator: Paul, A.C.
Partner: UNT Libraries Government Documents Department

CBEAM. 2-D: a two-dimensional beam field code

Description: CBEAM.2-D is a two-dimensional solution of Maxwell's equations for the case of an electron beam propagating through an air medium. Solutions are performed in the beam-retarded time frame. Conductivity is calculated self-consistently with field equations, allowing sophisticated dependence of plasma parameters to be handled. A unique feature of the code is that it is implemented on an IBM PC microcomputer in the BASIC language. Consequently, it should be available to a wide audience.
Date: May 1, 1985
Creator: Dreyer, K.A.
Partner: UNT Libraries Government Documents Department

Blanket technology experiments at Argonne National Laboratory

Description: Argonne National Laboratory has the largest US program for the development of blanket technology. The goals of the program are to resolve critical issues for different blanket concepts, to develop the understanding and predictive capability of blanket behavior, and to develop the technology needed to build and operate advanced fusion blankets. The projects within the program are liquid metal MHD, breeder neutronics, tritium oxidation, transient electromagnetics, FLIBE chemistry, and insulator coatings. The present status and recent results of the projects are described.
Date: February 1, 1988
Creator: Mattas, R.F.; Reed, C.B.; Picologlou, B.; Finn, P.; Clemmer, R.; Porges, K. et al.
Partner: UNT Libraries Government Documents Department

Nonperturbative analysis of the two-level atom: Applications to multiphoton excitation

Description: Selective excitation in an atomic system subjected to a slowly varying external electromagnetic field is studied using a two-level model. Time evolution of the system is found using an approach which is nonperturbative in the field strength. There is no constraint to small values of the applied field, that is, the field (in appropriate energy units) need not be small compared to the difference in energies of the two levels. Rather, we prey upon the fact that the situation of interest to us is where the frequency of the exciting field is small compared to the frequency associated with the level difference. Transition probabilities and resonance conditions are found which circumscribe both the large and small field limits. In the weak field limit the previous results of high-order perturbation theory are readily recovered. For a monochromatic field the characteristic features of resonance excitation at high harmonic number of the applied field are (a) extremely narrow resonance widths and (b) shifts in resonance positions which are strong functions of field intensity. Because of this sensitivity, we are able to demonstrate that when slow temporal evolution of the field amplitude is taken into account (e.g., due to finite pulse duration) the appropriate mean excitation rate is that due to the uncorrelated contribution of many resonances. The results of this analysis are used to estimate excitation rates in a specific atomic system, Cd/sup 12 +/, which are then compared to multiphoton ionization rates. Our calculations suggest that the ionization rate exceeds the excitation rate by several orders of magnitude. 15 refs., 3 figs.
Date: August 1, 1987
Creator: Duvall, R.E.; Valeo, E.J. & Oberman, C.R.
Partner: UNT Libraries Government Documents Department

Ion radial transport induced by ICRF waves in tokamaks

Description: The wave-induced fluxes of energetic-trapped ions during ICRF heating of tokamak plasmas are calculated using quasilinear equations. A simple single particle model of this transport mechanism is also given. Both a convective flux proportional to k/sub phi/vertical bar E/sub +/vertical bar/sup 2/ and a diffusive flux proportional to k/sub phi//sup 2/vertical bar E/sub +/vertical bar/sup 2/ are found. Here, k/sub phi/ is the toroidal wave number and E/sub +/ is the left-hand polarized wave field. The convective flux may become significant for large k/sub phi/ if the wave spectrum is asymmetric in k/sub phi/. But for the conditions of most previous experiments, these calculations indicate that radial transport driven directly by the ICRF wave is unimportant.
Date: May 1, 1987
Creator: Chen, L.; Vaclavik, J. & Hammett, G.W.
Partner: UNT Libraries Government Documents Department

Linear optimal control of tokamak fusion devices

Description: The control of plasma position, shape and current in a tokamak fusion reactor is examined using linear optimal control. These advanced tokamaks are characterized by non up-down symmetric coils and structure, thick structure surrounding the plasma, eddy currents, shaped plasmas, superconducting coils, vertically unstable plasmas, and hybrid function coils providing ohmic heating, vertical field, radial field, and shaping field. Models of the electromagnetic environment in a tokamak are derived and used to construct control gains that are tested in nonlinear simulations with initial perturbations. The issues of applying linear optimal control to advanced tokamaks are addressed, including complex equilibrium control, choice of cost functional weights, the coil voltage limit, discrete control, and order reduction. Results indicate that the linear optimal control is a feasible technique for controlling advanced tokamaks where the more common classical control will be severely strained or will not work. 28 refs., 13 figs.
Date: May 1, 1989
Creator: Kessel, C.E.; Firestone, M.A. & Conn, R.W.
Partner: UNT Libraries Government Documents Department

Beamline considerations for a compact, high current, high power linear RF electron accelerator

Description: A design for a compact, high current, high power linear electron accelerator using an rf power source is investigated. It consists of adjacent cavities into which rf power is injected and through which electron pulses pass. The source is assumed to be capable of delivering sufficient rf power to the desired location at the proper phase. Beamline issues such as cavity loading, energy extraction, longitudinal and transverse pulse focusing, and beam breakup are considered. A device which, given the required source, can deliver beam parameters comparable to existing induction accelerators but which is more than an order of magnitude smaller appears feasible.
Date: June 1, 1987
Creator: Marder, B.
Partner: UNT Libraries Government Documents Department

Introduction to wakefields and wake potentials

Description: What are wakefields and wake potentials, and why are these concepts useful in the physics of linear accelerators and storage rings We approach this question by first reviewing the basic physical concepts which underlie the mathematical formalism. We then present a summary of the various techniques that have been developed to make detailed calculations of wake potentials. Finally, we give some applications to current problems of interest in accelerator physics. No attempt at completeness can be made in an introductory article of modest length. Rather, we try to give a broad overview and to list key references for more detailed study. It will also be apparent that the last chapter on this subject, with all the loose ends neatly tied up, has yet to be written. There are subtle points, there are controversial questions, and active calculations to resolve these questions are continuing at the time of this writing. 61 refs., 10 figs., 1 tab.
Date: January 1, 1989
Creator: Wilson, P.B.
Partner: UNT Libraries Government Documents Department

Wake field accelerators

Description: In a wake field accelerator a high current driving bunch injected into a structure or plasma produces intense induced fields, which are in turn used to accelerate a trailing charge or bunch. The basic concepts of wake field acceleration are described. Wake potentials for closed cavities and periodic structures are derived, as are wake potentials on a collinear path with a charge distribution. Cylindrically symmetric structures excited by a beam in the form of a ring are considered. (LEW)
Date: February 1, 1986
Creator: Wilson, P.B.
Partner: UNT Libraries Government Documents Department

Measurements of the electrostatic and electromagnetic fields of Faraday shielding half-turn loop type ICRF antennae

Description: Detailed measurements of both the electrostatic and electromagnetic fields are performed for various types of Faraday shields mounted on PLT ICRF antennae. The data show that the shields have little effect on the electromagnetic fields when the antenna is driven such that it is generating a constant total flux for the various cases. A new type of shield (Type II) is investigated that has no effect on the antenna inductance and performs equally as well as the conventional shields (Type I) in shielding out the electrostatic fields. Measurements indicate, for the shields investigated, that each layer of shield strips degrade the Q by approximately a factor of two.
Date: December 1, 1984
Creator: Fortgang, C.M. & Hwang, D.Q.
Partner: UNT Libraries Government Documents Department

Minimized emittance growth with elliptical beam pipes in FEL (free-electron-laser)

Description: Wakefield effects can cause emittance growth in free-electron-laser systems and reduce free-electron-laser gain. This paper explains that, by using beam pipes with elliptical cross sections, discontinuities can be allowed along a beam pipe without introducing wakefields. To use a beam pipe with an elliptical cross section, wakefield-less transitions between beam pipes with circular and elliptical cross sections are also needed. A concept to achieve such a transition is discussed. 4 refs., 7 figs.
Date: January 1, 1989
Creator: Chan, K.C.
Partner: UNT Libraries Government Documents Department

Different ways of looking at the electromagnetic vacuum

Description: Some thoughts on the electromagnetic vacuum are presented in connection with the vacuum and source fields as alternative physical bases for understanding spontaneous emission, the Lamb shift, Casimir effects, van der Waals forces, and the ''thermalization'' of vacuum fluctuations for a uniformly accelerated observer.
Date: January 1, 1987
Creator: Milonni, P.W.
Partner: UNT Libraries Government Documents Department

Measurement of the longitudinal parameters of an electron beam in a storage ring

Description: We discuss the determination of the longitudinal parameters of a bunched beam of electrons or positrons circulating in a storage ring. From the analysis of the beam current observed at a fixed azimuthal location, one can learn much about the longitudinal behavior. We present an elementary analysis of the time-dependence of the current. In particular, we discuss the determination of the average current, bunch length, synchrotron oscillation frequency, and the coherent synchrotron oscillation modes associated with longitudinal instabilities. A brief discussion is also given of the incoherent synchrotron oscillations, or Schottky noise. We review the electromagnetic field traveling with a charge in uniform motion, and introduce some of the most common devices used to detect this field: capacitive pick-up, stripline monitor, and DC beam current transformer. Our paper is organized as follows: We discuss the analysis of the time-dependence of the beam current. Then, the measurement of the current is considered. Finally, we describe some measurements of energy spread and bunch lengthening made recently at SLAC on the SLC damping ring. 12 refs., 6 figs.
Date: January 1, 1989
Creator: Krinsky, S.
Partner: UNT Libraries Government Documents Department

High-power, high-efficiency FELs

Description: High power, high efficiency FELs require tapering, as the particles loose energy, so as to maintain resonance between the electromagnetic wave and the particles. They also require focusing of the particles (usually done with curved pole faces) and focusing of the electromagnetic wave (i.e. optical guiding). In addition, one must avoid transverse beam instabilities (primarily resistive wall) and longitudinal instabilities (i.e sidebands). 18 refs., 7 figs., 3 tabs.
Date: April 1, 1989
Creator: Sessler, A.M.
Partner: UNT Libraries Government Documents Department

Choice of parameters for linear colliders in multi-bunch mode

Description: The energy efficiency of a linear collider in multi-bunch mode is calculated for the case that the bunches in each of the two interacting beams are identical in all interaction points, a configuration which can be realized by taking advantage of the beam-beam effect between beams of opposite electric charge. The maximization of the efficiency is discussed, the maximum appears to increase nearly linearly with beam brightness and accelerating gradient, and about quadratically with the length of the ir. The optimum operating frequency for the linacs increases also, while the pulse repetition rate and the beam current needed for fixed luminosity, decrease. The increasing brightness and the decreasing current needed for higher efficiency lead to smaller transverse spotsizes in the crossing points; this imposes tighter tolerances on the relative transverse coordinates of the two beam-axes. Pillbox or similar resonators, excited in the TM01 mode, may be preferable to quadrupoles for transverse focusing, at the high frequencies and gradients that seem desirable, particularly in the final focus. 4 refs., 7 figs.
Date: January 1, 1987
Creator: Claus, J.
Partner: UNT Libraries Government Documents Department

Geometrical properties of an internal local octonionic space in curved space time

Description: A geometrical treatment on a flat tangent space local to a generalized complex, quaternionic, and octonionic space-time is constructed. It is shown that it is possible to find an Einstein-Maxwell-Yang-Mills correspondence in this generalized (Minkowskian) tangent space. 9 refs.
Date: April 1, 1986
Creator: Marques, S. & Oliveira, C.G.
Partner: UNT Libraries Government Documents Department

An investigation of the usefulness of extremely low-frequency electromagnetic measurements for treaty verification

Description: From FY 1986 through FY 1988, we monitored extremely low-frequency (ELF) electromagnetic (EM) fields to determine whether these signals could be detected from underground nuclear explosions. Signals clearly related to underground tests were detected only when the ELF field sensors were located within 10 km of surface ground zero. Theoretical analysis, based on the results of these measurements, shows that the ELF impulse signals from underground nuclear tests are of longer duration than those from lightning sources and are, therefore, less efficient in exciting resonances in the earth-ionosphere cavity, even though the source strength for each may be the same. Thus, ELF signals from underground nuclear tests with yields of <150 kT are generally lower than the background signals caused by worldwide lightning activity. Our conclusion is that ELF monitoring probably will not be useful for detecting underground nuclear tests at distances >10 km from the tests. 16 refs., 24 figs., 3 tabs.
Date: January 1, 1989
Creator: Sweeney, J.J.
Partner: UNT Libraries Government Documents Department

Free electron laser amplifier driven by an induction linac

Description: This paper discusses the use of a free-electron laser amplifier as a means of converting the kinetic energy of an electron beam into coherent radiation. In particular, the use of an induction linear accelerator is discussed. The motion of the elections in the tapered and untapered wiggler magnets is discussed as well as the beam emittance, and the radiation fields involved. (LSP)
Date: June 3, 1986
Creator: Neil, V.K.
Partner: UNT Libraries Government Documents Department

Theory of atoms in strong, pulsed electromagnetic fields: 2, A free electron and a harmonically bound electron

Description: Multiple scale methods are used to treat several ingredients of the theory of atoms in strong electromagnetic fields. First, a focused electromagnetic field is expanded. Second, a classical electron is described giving the ponderomotive potential. Third, the quantum electron is treated in the WKB approximation. Fourth, the one dimensional quantum harmonic oscillator is solved; and last the one dimensional square well, showing the low intensity limit of the theory.
Date: July 1, 1987
Creator: Szoeke, A. & Garrison, J.
Partner: UNT Libraries Government Documents Department