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Excited Baryons and Chiral Symmetry Breaking of QCD

Description: N* masses in the spin-1/2 and spin-3/2 sectors are computed using two non-perturbative methods: lattice QCD and QCD sum rules. States with both positive and negative parity are isolated via parity projection methods. The basic pattern of the mass splittings is consistent with experiments. The mass splitting within the same parity pair is directly linked to the chiral symmetry breaking QCD.
Date: April 1, 2002
Creator: Lee, Frank X.
Partner: UNT Libraries Government Documents Department

Parallel simulation of beam-beam interaction in high energy accelerators

Description: In this paper, we present a self-consistent simulation model of beam-beam interaction in high energy accelerators. Using a parallel particle-in-cell approach, we have calculated the electromagnetic fields between two colliding beams. Dynamic load balance is implemented to improve the parallel efficiency. A preliminary performance test on IBM SP Power3, Cray T3E and PC cluster is presented. As an application, we studied the coherent beam-beam oscillation in the proposed Large Hadron Collider.
Date: February 2, 2002
Creator: Qiang, Ji; Furman, Miguel A. & Ryne, Robert D.
Partner: UNT Libraries Government Documents Department

High Frequency Electromagnetic Impedance Imaging for Vadose Zone and Groundwater Characterization

Description: Accurate description of transport pathways on the gross scale, the location of contamination, and characterization of heterogeneity within the vadose zone, are now realized as vital for proper treatment, confinement and stabilization of subsurface contamination at Department of Energy (DOE) waste sites. Electromagnetic (EM) methods are ideal for these tasks since they are directly sensitive to the amount of fluid present in porous media, as well as fluid composition. At many DOE sites it is necessary to employ lower frequency (<1 MHz) or diffusive electromagnetic fields because of the inability of ground penetrating radar (GPR) to penetrate to sufficient depths. The high frequency impedance method, which operated in the diffusive frequency range (10 Hz to 1 MHz), as well as the low end of the spectrum employed by GPR (1MHz-10 MHz), is an ideal technique to delineate and map the aforementioned targets. The method has clearly shown the potential to provide needed information on variations in subsurface saturation due to local storage tanks and perched water zones, as well as mapping geological structures related to the subsurface hydrological properties and heterogeneity within the vadose zone. Although it exhibits certain advantages over other EM methods, the impedance method comes with a set of assumptions and practices that can limit its potential. The first is the desire to locate receivers in the far-field of the transmitter which allows the use of magnetotelluric (MT) inversion codes to interpret the data. Unfortunately, one does not precisely know when one is in the far-field of the transmitter, because this depends on the geology we wish to image. The second limiting factor is the scarcity of complete 2D and 3D inversion schemes necessary to properly invert the data. While approximate 2D schemes are now emerging, rigorous 2D and 3D inversion codes are needed to bound the ...
Date: June 7, 2002
Creator: Newman, Gregory A.; Nichols, Edward; Alumbaugh, David L. & Hoversten, G. Michael
Partner: UNT Libraries Government Documents Department

Strong-strong beam-beam simulation using a green function approach

Description: In this paper we present a news approach, based on a shifted Green function, to evaluate the electromagnetic field in a simulation of colliding beams. Unlike a conventional particle-mesh code, we use a method in which the computational mesh covers only the largest of the two colliding beams. This allows us to study long-range parasitic collisions accurately and efficiently. We have implemented this algorithm in a new parallel strong-strong beam-beam simulation code. As an application, we present a study of a beam sweeping scheme for the LBNL luminosity monitor of the Large Hadron Collider.
Date: September 8, 2002
Creator: Qiang, Ji; Furman, Miguel A. & Ryne, Robert D.
Partner: UNT Libraries Government Documents Department

Assembly of LIGA using Electric Fields

Description: The goal of this project was to develop a device that uses electric fields to grasp and possibly levitate LIGA parts. This non-contact form of grasping would solve many of the problems associated with grasping parts that are only a few microns in dimensions. Scaling laws show that for parts this size, electrostatic and electromagnetic forces are dominant over gravitational forces. This is why micro-parts often stick to mechanical tweezers. If these forces can be controlled under feedback control, the parts could be levitated, possibly even rotated in air. In this project, we designed, fabricated, and tested several grippers that use electrostatic and electromagnetic fields to grasp and release metal LIGA parts. The eventual use of this tool will be to assemble metal and non-metal LIGA parts into small electromechanical systems.
Date: April 1, 2002
Partner: UNT Libraries Government Documents Department

Quantitative measurements of magnetic vortices using position resolved diffraction in Lorentz STEM

Description: A number of electron column techniques have been developed over the last forty years to permit visualization of magnetic fields in specimens. These include: Fresnel imaging, Differential Phase Contrast, Electron Holography and Lorentz STEM. In this work we have extended the LSTEM methodology using Position Resolved Diffraction (PRD) to quantitatively measure the in-plane electromagnetic fields of thin film materials. The experimental work reported herein has been carried out using the ANL AAEM HB603Z 300 kV FEG instrument 5. In this instrument, the electron optical column was operated in a zero field mode, at the specimen, where the objective lens is turned off and the probe forming lens functions were reallocated to the C1, C2, and C3 lenses. Post specimen lenses (P1, P2, P3, P4) were used to magnify the transmitted electrons to a YAG screen, which was then optically transferred to a Hamamatsu ORCA ER CCD array. This CCD was interfaced to an EmiSpec Data Acquisition System and the data was subsequently transferred to an external computer system for detailed quantitative analysis. In Position Resolved Diffraction mode, we digitally step a focused electron probe across the region of interest of the specimen while at the same time recording the complete diffraction pattern at each point in the scan.
Date: March 5, 2002
Creator: Zaluzec, N. J.
Partner: UNT Libraries Government Documents Department

Advanced visualization technology for terascale particle accelerator simulations

Description: This paper presents two new hardware-assisted rendering techniques developed for interactive visualization of the terascale data generated from numerical modeling of next generation accelerator designs. The first technique, based on a hybrid rendering approach, makes possible interactive exploration of large-scale particle data from particle beam dynamics modeling. The second technique, based on a compact texture-enhanced representation, exploits the advanced features of commodity graphics cards to achieve perceptually effective visualization of the very dense and complex electromagnetic fields produced from the modeling of reflection and transmission properties of open structures in an accelerator design. Because of the collaborative nature of the overall accelerator modeling project, the visualization technology developed is for both desktop and remote visualization settings. We have tested the techniques using both time varying particle data sets containing up to one billion particle s per time step and electromagnetic field data sets with millions of mesh elements.
Date: November 16, 2002
Creator: Ma, K-L; Schussman, G.; Wilson, B.; Ko, K.; Qiang, J. & Ryne, R.
Partner: UNT Libraries Government Documents Department

805 MHz and 201 MHz RF cavity development for MUCOOL

Description: A muon cooling channel calls for very high acceleratinggradient RF structures to restore the energy lost by muons in theabsorbers. The RF structures have to be operated in a strong magneticfield and thus the use of superconducting RF cavities is excluded. Toachieve a high shunt impedance while maintaining a large enough apertureto accommodate a large transverse emittance muon beam, the cavity designadopted is a pillbox-like geometry with thin Be foils to terminate theelectromagnetic field at the cavity iris. The possibility of using gridsof thin-walled metallic tubes for the termination is also being explored.Many of the RF-related issues for muon cooling channels are being studiedboth theoretically and experimentally using an 805 MHz cavity that has apillbox-like geometry with thin Be windows to terminate the cavityaperture. The design and performance of this cavity are reported here.High-power RF tests of the 805 MHz cavity are in progress at Lab G inFermilab. The cavity has exceeded its design gradient of 30 MV/m,reaching 34 MV/m without external magnetic field. No surface damage wasobserved at this gradient. The cavity is currently under conditioning atLab G with an external magnetic field of 2.5 T. We also present here a201 MHz cavity design for muoncooling channels. The proposed cavitydesign is also suitable for use in a proof-of-principle Muon IonizationCooling Experiment (MICE).
Date: October 10, 2002
Creator: DLi@lbl.gov
Partner: UNT Libraries Government Documents Department

The National Ignition Facility: Status and Plans for Laser Fusion and High-Energy-Density Experimental Studies

Description: The National Ignition Facility (NIF), currently under construction at the University of California's Lawrence Livermore National Laboratory, is a stadium-sized facility containing a 192-beam, 1.8-Megajoule, 500-Terawatt, 351-nm laser system and a 10-meter diameter target chamber with room for nearly 100 experimental diagnostics. NIF is being built by the National Nuclear Security Administration and when completed will be the world's largest laser experimental system, providing a national center to study inertial confinement fusion and the physics of matter at extreme energy densities and pressures. NIF will provide 192 energetic laser beams that will compress small fusion targets to conditions where they will ignite and burn, liberating more energy than is required to initiate the fusion reactions. NIF experiments will allow the study of physical processes at temperatures approaching 100 million K and 100 billion times atmospheric pressure. These conditions exist naturally only in the interior of stars and in nuclear weapons explosions. In the course of designing the world's most energetic laser system, a number of significant technology breakthroughs have been achieved. Research is also underway to develop a shorter pulse capability on NIF for very high power and extreme electromagnetic field research and applications. We discuss here the technology challenges and solutions that have made NIF possible, along with enhancements to NIF's design that could lead to near-exawatt power levels.
Date: October 16, 2002
Creator: Moses, E I & Wuest, C R
Partner: UNT Libraries Government Documents Department

Exploring the Limits of the Dipole Approximation with Angle-Resolved Electron Time-of-Flight Spectrometry

Description: Understanding the electronic structure of atoms and molecules is fundamental in determining their basic properties as well as the interactions that occur with different particles such as light. One such interaction is single photoionization; a process in which a photon collides with an atom or molecule and an electron with a certain kinetic energy is emitted, leaving behind a residual ion. Theoretical models of electronic structures use the dipole approximation to simplify x-ray interactions by assuming that the electromagnetic field of the radiation, expressed as a Taylor-series expansion, can be simplified by using only the first term. It has been known for some time that the dipole approximation becomes inaccurate at high photon energies, but the threshold at which this discrepancy begins is ambiguous. In order to enhance our understanding of these limitations, we measured the electron emissions of nitrogen. Beamline 8.0.1 at the Advanced Light Source was used with an electron Time-of-Flight (TOF) end station, which measures the time required for electrons emitted to travel a fixed distance. Data were collected over a broad range of photon energies (413 - 664 eV) using five analyzers rotated to 15 chamber angles. Preliminary analysis indicates that these results confirm the breakdown of the dipole approximation at photon energies well below 1 keV and that this breakdown is greatly enhanced in molecules just above the core-level ionization threshold. As a result, new theoretical models must be made that use higher order terms that were previously truncated.
Date: January 1, 2002
Creator: Laidman, S.; Pangilinan, J.; Guillemin, R.; Yu, S.U.; Ohrwall, G.; Lindle, D. et al.
Partner: UNT Libraries Government Documents Department

Final report [The 15th Workshop on Electromagnetic Induction in the Earth, held 8/20-26/2000, and The 5th Magnetotelluric Data Interpretation Workshop, 8/17-19/2000]

Description: This document reports on how the DOE helped to support travel of students and scientists to the conferences in Brazil. Attendee names, funding, and session titles are listed.
Date: June 25, 2002
Creator: Alumbaugh, David L.
Partner: UNT Libraries Government Documents Department