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Possibility of MGB2 application to superconducting cavities

Description: A metallic superconductor, magnesium diboride (MgB{sub 2}), which has a transition temperature of {approx}39 K, was discovered in early 2001. Published data taken at 10 GHz demonstrate that the material has a surface resistance comparable to niobium. This paper discusses the possibility of MgB{sub 2} as compared to Nb and Nb{sub 3}Sn. Also, a possible method of fabricating a MgB{sub 2} cavity using the hot isostatic press (HIP) technique is proposed.
Date: January 1, 2002
Creator: Tajima, T. (Tsuyoshi)
Partner: UNT Libraries Government Documents Department

Fokker-Planck transport in solid state accelerator concepts

Description: Particle transport in a crystalline solid under channeling conditions is considered by means of a Fokker-Planck description. The model includes electron multiple scattering, radiation damping and an accelerating electric field. Analytic solutions have been obtained using a harmonic potential model to describe the channeling forces. These solutions will be described.
Date: January 1, 1989
Creator: Newberger, B. & Tajima, T.
Partner: UNT Libraries Government Documents Department

Laser wakefield excitation and measurement on a femtosecond time scale: Theory and experiment. Progress report, September 1, 1994--August 31, 1995

Description: A brief discussion was given for each of the following topics: superluminous wake excitation; photon frequency-shift (photon accelerator) spectroscopy; focusing, diffraction and 2D spectral shift; Raman self-modulation effects; optical preaccelerator; accelerator physics developments; experimental facilities; experimental results--pressure-tunable harmonic generation; experiments in progress--time-domain Rayleigh interferometry; Russian collaboration; and technology transfer.
Date: April 1, 1995
Creator: Tajima, T. & Downer, M.
Partner: UNT Libraries Government Documents Department

The [delta]f algorithm for beam dynamics

Description: An algorithm is developed to study particle dynamics of beams including collective interaction with high accuracy and low noise. Particle dynamics with collective interactions is treated through particle simulation, where the main or average distribution f[sub 0] and the deviation away from it [delta]f are separately followed. The main distribution f[sub 0] is handled by an analytic equilibrium solution and the perturbation away from it [delta]f is followed by the method of characteristics. We call this the [delta]f algorithm. We specifically model a synchrotron collider which includes the collision section where collective effects of collisions are simulated by this [delta]f algorithm and the rest of the collider where single particle dynamics are treated by simple harmonic transport. The most important target of this simulation is to understand and predict the long-time behavior of the beam luminosity and lifetime. The [delta]f method allows the study the effect of small perturbations over long timescales on beam lifetime by eliminating the numerical noise problem inherent in Particle-in-Cell techniques. In the [delta]f code using the reference parameters of the SSC (Superconducting Super Collider), beam blow-up near resonances and oscillations in the tune shift, [Delta][nu], far from resonances are observed. In studying long timescale particle diffusion in the phase space of the beams away from resonances, the [delta]f code performance is compared with a tracking code which does not incorporate collective interaction.
Date: May 1, 1993
Creator: Koga, J. & Tajima, T.
Partner: UNT Libraries Government Documents Department

Electromagnetic waves in a strong Schwarzschild plasma

Description: The physics of high frequency electromagnetic waves in a general relativistic plasma with the Schwarzschild metric is studied. Based on the 3 + 1 formalism, we conformalize Maxwell`s equations. The derived dispersion relations for waves in the plasma contain the lapse function in the plasma parameters such as in the plasma frequency and cyclotron frequency, but otherwise look {open_quotes}flat.{close_quotes} Because of this property this formulation is ideal for nonlinear self-consistent particle (PIC) simulation. Some of the physical consequences arising from the general relativistic lapse function as well as from the effects specific to the plasma background distribution (such as density and magnetic field) give rise to nonuniform wave equations and their associated phenomena, such as wave resonance, cutoff, and mode-conversion. These phenomena are expected to characterize the spectroscopy of radiation emitted by the plasma around the black hole. PIC simulation results of electron-positron plasma are also presented.
Date: November 1, 1996
Creator: Daniel, J. & Tajima, T.
Partner: UNT Libraries Government Documents Department

Numerical study of compressible magnetoconvection with an open transitional boundary

Description: We study by computer simulation nonlinear evolution of magnetoconvection in a system with a dynamical open boundary between the convection region and corona of the sun. We study a model in which the fluid is subject to the vertical gravitation, magnetohydrodynamics (MHD), and high stratification, through an MHD code with the MacCormack-Donner cell hybrid scheme in order to well represent convective phenomena. Initially the vertical fluid flux penetrates from the convectively unstable zone at the bottom into the upper diffuse atmosphere. As the instability develops, the magnetic fields are twisted by the convection motion and the folding magnetic fields is observed. When the magnetic pressure is comparable to the thermal pressure in the upper layer of convective zone, strong flux expulsion from the convective cell interior toward the cell boundary appears. Under appropriate conditions our simulation exhibits no shock formation incurred by the fluid convected to the photosphere, in contrast to earlier works with box boundaries. The magnetic field patterns observed are those of concentrated magnetic flux tubes, accumulation of dynamo flux near the bottom boundary, pinched flux near the downdraft region, and the surface movement of magnetic flux toward the downdraft region. Many of these computationally observed features are reminiscent of solar observations of the fluid and magnetic structures of their motions.
Date: August 1, 1990
Creator: Hanami, H. & Tajima, T.
Partner: UNT Libraries Government Documents Department

Summary of the international Dawson' Symposium on the physics of plasmas

Description: The Dawson'' Symposium was held on September 24 and 25, 1990 in honor of John Dawson's 60th birthday to reflect on various physics of plasma that he had pioneered. The international speakers touched on a wide range of subjects: magnetic fusion, laser fusion, isotope separation, computer simulation, basic plasma physics, accelerators and light sources, space physics, and international scientific collaboration. Highlighted in this article are magnetic fusion and laser fusion investigation that Dawson has been engaged in and the reviews of the present status of their development. The impact of the two-component fusion plasma idea, reactor concepts for advanced fuels, hot electron production by lasers and other nonlinear effects in laser fusion are discussed. Dawson's contributions in the allied areas are also reviewed.
Date: December 1, 1990
Creator: Tajima, T.
Partner: UNT Libraries Government Documents Department

Implicit-particle simulation of magnetized plasmas

Description: A second-order accurate, direct method for the simulation of magnetized, multi-dimensional plasmas is developed. A time decentered particle push is combined with the direct method for implicit plasma simulation to include finite sized particle effects in an absolutely stable algorithm. A simple iteration (renormalized Poisson equation) is used to solve the field corrector equation. Details of the two-dimensional, electrostatic, constant magnetic field, periodic case are given. Numerical results for ion-acoustic fluctuations and for an unstable gravitational interchange confirm the accuracy and efficacy of the method applied to low-frequency plasma phenomena.
Date: September 1, 1982
Creator: Barnes, D.C.; Kamimura, T.; Leboeuf, J.N. & Tajima, T.
Partner: UNT Libraries Government Documents Department

1991 US-Japan workshop on Nuclear Fusion in Dense Plasmas. Proceedings

Description: The scientific areas covered at the Workshop may be classified into the following subfields: (1) basic theory of dense plasma physics and its interface with atomic physics and nuclear physics; (2) physics of dense z-pinches, ICF plasmas etc; (3) stellar interior plasmas; (4) cold fusion; and (5) other dense plasmas.
Date: October 1, 1991
Creator: Ichimaru, S. & Tajima, T.
Partner: UNT Libraries Government Documents Department

Magnetless magnetic fusion

Description: The authors propose a concept of thermonuclear fusion reactor in which the plasma pressure is balanced by direct gas-wall interaction in a high-pressure vessel. The energy confinement is achieved by means of the self-contained toroidal magnetic configuration sustained by an external current drive or charged fusion products. This field structure causes the plasma pressure to decrease toward the inside of the discharge and thus it should be magnetohydrodynamically stable. The maximum size, temperature and density profiles of the reactor are estimated. An important feature of confinement physics is the thin layer of cold gas at the wall and the adjacent transitional region of dense arc-like plasma. The burning condition is determined by the balance between these nonmagnetized layers and the current-carrying plasma. They suggest several questions for future investigation, such as the thermal stability of the transition layer and the possibility of an effective heating and current drive behind the dense edge plasma. The main advantage of this scheme is the absence of strong external magnets and, consequently, potentially cheaper design and lower energy consumption.
Date: February 1, 1994
Creator: Beklemishev, A. D. & Tajima, T.
Partner: UNT Libraries Government Documents Department

Particle simulation algorithms with short-range forces in MHD and fluid flow

Description: Attempts are made to develop numerical algorithms for handling fluid flows involving liquids and liquid-gas mixtures. In these types of systems, the short-range intermolecular interactions are important enough to significantly alter behavior predicted on the basis of standard fluid mechanics and magnetohydrodynamics alone. We have constructed a particle-in-cell (PIC) code for the purpose of studying the effects of these interactions. Of the algorithms considered, the one which has been successfully implemented is based on a MHD particle code developed by Brunel et al. In the version presented here, short range forces are included in particle motion by, first, calculating the forces between individual particles and then, to prevent aliasing, interpolating these forces to the computational grid points, then interpolating the forces back to the particles. The code has been used to model a simple two-fluid Rayleigh-Taylor instability. Limitations to the accuracy of the code exist at short wavelengths, where the effects of the short-range forces would be expected to be most pronounced.
Date: July 1, 1992
Creator: Cable, S.; Tajima, T. & Umegaki, K.
Partner: UNT Libraries Government Documents Department

Superluminous laser pulse in an active medium

Description: Physical conditions are obtained to make the propagation velocity of a laser pulse and thus the phase velocity of the excited wake be at any desired value, including that equal to or greater than the speed of light. The provision of an active-plasma laser medium with an appropriately shaped pulse allows not only replenishment of laser energy loss to the wakefield but also acceleration of the group velocity of photons. A stationary solitary solution in the accelerated frame is obtained from the model equations and simulations thereof for the laser, plasma and atoms. This approach has applications in photonics and telecommunications as well as wakefield accelerators.
Date: December 1, 1993
Creator: Fisher, D. L. & Tajima, T.
Partner: UNT Libraries Government Documents Department

Particle diffusion from the beam-beam interaction in synchrotron colliders

Description: The authors investigate the beam-beam interaction in a synchrotron collider, specifically studying slow particle diffusion in phase space away from tune resonances. Using the tune and tune shift of contemporary large hadron colliders as reference parameters. The computation shows all particles diffusive after 10{sup 5} rotations in contrast to previous single particle tracking results. The diffusion coefficients are several orders of magnitude higher than the tracking code and increase exponentially with the action, caused by the collision induced variation of the second moment of the beams (x{sup 2}).
Date: January 1, 1994
Creator: Koga, J. K. & Tajima, T.
Partner: UNT Libraries Government Documents Department

Space charge tracking code for a synchrotron accelerator

Description: An algorithm has been developed to compute particle tracking, including self-consistent space charge effects for synchrotron accelerators. In low-energy synchrotrons space charge plays a central role in enhancing emittance of the beam. The space charge effects are modeled by mutually interacting (through the Coulombic force) N cylindrical particles (2-{1/2}-dimensional dynamics) whose axis is in the direction of the equilibrium particle flow. On the other hand, their interaction with synchrotron lattice magnets is treated with the thin-lens approximation and in a fully 3-dimensional way. Since the existing method to treat space charge fully self-consistently involved 3-D space charge effect computation, the present method allows far more realistic physical parameters and runs in far shorter time (about 1/20). Some examples on space charge induced instabilities are presented.
Date: June 1, 1997
Creator: Ottinger, M.B.; Tajima, T. & Hiramoto, K.
Partner: UNT Libraries Government Documents Department

Microbunching and coherent acceleration of electrons by subcycle laser pulses

Description: The pick up and acceleration of all plasma electrons irradiated by an intense, subcyclic laser pulse is demonstrated via analytical and numerical calculations. It is shown that the initial low emittance of the plasma electrons is conserved during the process of acceleration, leading to an extremely cold, bunched electron beam. Compression of the electron bunch along the longitudinal coordinate is naturally achieved due to the interaction of electrons and laser pulse. In this paper, the authors find the localized solutions to Maxwell`s equations of a subcyclic laser pulse and use these to determine the acceleration of charged particles and they suggest future application for this acceleration mechanism as low energy particle injector and as electron source for coherent x-ray generation.
Date: May 1, 1997
Creator: Rau, B.; Tajima, T. & Hojo, H.
Partner: UNT Libraries Government Documents Department

On the quasihydrostatic flows of radiatively cooling self-gravitating gas clouds

Description: Two model problems are considered, illustrating the dynamics of quasihydrostatic flows of radiatively cooling, optically thin self-gravitating gas clouds. In the first problem, spherically symmetric flows in an unmagnetized plasma are considered. For a power-law dependence of the radiative loss function on the temperature, a one-parameter family of self-similar solutions is found. The authors concentrate on a constant-mass cloud, one of the cases, when the self-similarity indices are uniquely selected. In this case, the self-similar flow problem can be formally reduced to the classical Lane-Emden equation and therefore solved analytically. The cloud is shown to undergo radiative condensation, if the gas specific heat ratio {gamma} > 4/3. The condensation proceeds either gradually, or in the form of (quasihydrostatic) collapse. For {gamma} < 4/3, the cloud is shown to expand. The second problem addresses a magnetized plasma slab that undergoes quasihydrostatic radiative cooling and condensation. The problem is solved analytically, employing the Lagrangian mass coordinate.
Date: March 1, 1995
Creator: Meerson, B.; Megged, E. & Tajima, T.
Partner: UNT Libraries Government Documents Department

Quantum-beamsstrahlung laser collider

Description: An e{sup +}e{sup {minus}} linear collider at energies beyond a TeV runs into a problem of severe beamsstrahlung, characterized by {Upsilon} on the order of unity (and beyond). In the regime of extremely high {Upsilon} the beamsstrahlung may be largely suppressed due to the quantum effect. In the design of an e{sup +}e{sup {minus}} collider there are two ways to satisfy the collider physics constraints. One is to decrease the number of particles per bunch (and thus to increase the repetition rate) and the other is to decrease the longitudinal bunch length. The former approach can limit {Upsilon}, while the latter boosts it. (It may be useful to reevaluate the future collider parameters in view of this.) The laser wakefield driver for a collider in comparison with the microwave driver naturally offers a very short bunch length, which is appropriate for the latter collider option. The authors show that this choice of collider design with a short bunch length and high {Upsilon} has advantages and provide sample design parameters at 5 TeV. Such sample design parameters challenge them in a number of fronts, such as the preservation of high quality bunches, efficient high repetition rate lasers, etc. The collision point physics simulated by the CAIN code shows a surprisingly well preserved luminosity spectrum.
Date: November 1, 1997
Creator: Tajima, T.; Chattopadyay, S. & Xie, M.
Partner: UNT Libraries Government Documents Department

Cluster plasma and its dispersion relation

Description: It is shown that unlike a gas plasma or an electron plasma in a metal, an ionized cluster material ({open_quotes}cluster plasma{close_quotes}) permits propagation below the plasma cut-off of electromagnetic (EM) waves whose phase velocity is close to but below the speed of light. Its unique properties allow a variety of applications, including direct acceleration of particles with its EM fields and the phase matching of waves of high harmonic generation (HHG).
Date: February 13, 1998
Creator: Tajima, T.; Downer, M.C. & Kishimoto, Y.
Partner: UNT Libraries Government Documents Department

A nonlinear particle dynamics map of wakefield acceleration in a linear collider

Description: The performance of a wakefield accelerator in a high energy collider application is analyzed. In order to carry out this task, it is necessary to construct a strawman design system (no matter how preliminary) and build a code of the systems approach. A nonlinear dynamics map built on a simple theoretical model of the wakefield generated by the laser pulse (or whatever other method) is obtained and they employ this as a base for building a system with multi-stages (and components) as a high energy collider. The crucial figures of merit for such a system other than the final energy include the emittance (that determines the luminosity). The more complex the system is, the more opportunities the system has to degrade the emittance (or entropy of the beam). Thus the map gu ides one to identify where the crucial elements lie that affect the emittance. They find that a strong focusing force of the wakefield coupled with a possible jitter of the axis (or laser aiming) of each stage and a spread in the betatron frequencies arising from different phase space positions for individual particles leads to a phase space mixing. This sensitively controls the emittance degradation. They show that in the case of a uniform plasma the effect of emittance growth is large and may cause serious problems. They discuss possibilities to avoid it and control the situation.
Date: August 1, 1998
Creator: Tajima, T.; Cheshkov, S.; Horton, W. & Yokoya, K.
Partner: UNT Libraries Government Documents Department


Description: We have manufactured a total of six {beta}=0.64, 700-MHz 5-cell cavities. The APT (Accelerator Production of Tritium) specification requires Q{sub 0} &gt; 5 x 10{sup 9} at an accelerating field of 5 MV/m. So far, the results of vertical tests have shown maximum accelerating fields of 12 MV/m (peak surface field of 41 MV/m) and maximum low-field Q{sub 0} of 3.6 x 10{sup 10} at 2 K. The present limitations are available input power, field emission and quench. This type of cavities will also be used for an ADTF (Accelerator-Driven Test Facility) for AAA (Advanced Accelerator Applications) project.
Date: June 1, 2001
Creator: TAJIMA, T.; MONTOYA, D. I & AL, ET
Partner: UNT Libraries Government Documents Department


Description: Within the framework of the Advanced Accelerator Applications (AAA) project we are interested in building and testing low-{beta} spoke resonators (cavities). To familiarize us with the specifics of these structures Argonne National Laboratory (ANL) kindly loaned us one of their spoke cavities for evaluation. This is a {beta}=0.291 2-gap resonator at 340 MHz. We benchmarked our computer codes by comparing room temperature measurements of frequency, tuning sensitivity, tuning forces, etc. with our 3D simulation results. The cavity was tested at both 4 K and 2 K. The results showed maximum accelerating gradients of 12.5 MV/m (4 K) and 12.3 MV/m (2 K), which correspond to a peak electric field of 40 MV/m and a peak magnetic field of 1063 Oe. Q{sub 0} values at 5 MV/m also exceeded by more than a factor 2 of present AAA specification. These results encouraged us toward development of spoke cavities for the low energy section (6.7 MeV to 109 MeV) of ADTF (Accelerator-Driven Test Facility) of AAA project.
Date: June 1, 2001
Creator: TAJIMA, T.; MONTOYA, D. I & AL, ET
Partner: UNT Libraries Government Documents Department


Description: A new system to map temperature and X-ray radiation around the external surface of 700-MHz 5-cell superconducting cavities has been developed. It consists of an aluminum cylinder that is equipped with six modules of sensors. Eighty-one carbon resistors (temperature sensors) and seventy-one PIN diodes (X-ray sensors) are attached. This cylinder surrounds the 5-cell cavity and rotates about the cavity axis in about 6 minutes. A new feature, compared to the ones developed in the past, is its brush-contact mechanism on the outer surface of the aluminum cylinder, which enables the sensor array to rotate continuously in the same direction during the test. Although the present mechanism allows only one direction of rotation, it does not seem to be difficult to modify for both directions if electrical connections work in this manner. This paper describes the details of the structure and associated mechanisms as well as future schedule and plans of operation.
Date: June 1, 2001
Partner: UNT Libraries Government Documents Department