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Confinement through a relativistic generalization of the linear interaction

Description: Generalizing a covariant framework previously developed, it is shown that confinement insures that meson {r_arrow} q + {anti q} decay amplitudes vanish when both quarks are on-shell. Regularization of singularities in a covariant linear potential associated with nonzero energy transfers (i.e. q{sup 2}=0, q{sup {mu}} {ne} 0) is improved.
Date: June 1, 1998
Creator: Savkli, Cetin & Gross, Franz
Partner: UNT Libraries Government Documents Department

The deuteron: a mini-review

Description: We review some recent results for elastic electron deuteron scattering (deuteron form factors) and photodisintegration of the deuteron, with emphasis on the recent high energy data from Jefferson Laboratory (JLab).
Date: July 1, 2001
Creator: Gross, Franz & Gilman, R.
Partner: UNT Libraries Government Documents Department

Performance of 1300 Mhz KEK-type single cell niobium cavities

Description: Four single cell niobium cavities fabricated from Tokyo-Denkai material of RRR=200 have been tested repeatedly with the purpose to evaluate different fabrication and processing techniques used at KEK and Jefferson Lab, respectively. Two cavities--K-15 and K-16--have been manufactured completely at KEK prior to shipment to Jefferson Lab. In addition, K-16 had received a barrel polishing treatment at KEK, resulting in the removal of 40 {mu}m of material from the surface. Cavity K-17 was electron-beam welded at Jefferson Lab; the deep drawing of the half cells and the trimming of the cups for electron-beam welding were done at KEK, however. Cavity JL-1 was completely fabricated at Jefferson Lab. Often, some processing field levels related to electronic activity in the cavities, possibly multipacting, have been seen at KEK and the purpose of this investigation is a verification of such observations. In addition, a comparison of different fabrication procedures and surface treatments are of interest for optimizing cost and performance for larger scale application. In several cavities, accelerating gradients between 20 MV/m {<=} E{sub acc} {<=} 27 MV/m have been measured with only little field emission loading. In one of the cavities, resonant electron loading was ''provoked'' by rinsing it with oil contaminated acetone. The observed multipacting levels at E{sub acc}=13 MV/m and 25 MV/m could be identified with the help of simulation calculations as 1-point and 2-point multipacting across the equator of the cavity. There is - as previously reported - a rather strong dependence of the quench field levels on the amount of material removed from the surface, confirming a picture of a surface damage layer which becomes depleted of defects as more and more of it is removed.
Date: October 1, 1997
Creator: Kneisel, P.; Saito, K. & Parodi, R.
Partner: UNT Libraries Government Documents Department

Performance of a Rapid-Scan Vacuum Michelson Interferometer at the NSLS

Description: A commercial Nicolet Magna series rapid-scan Michelson Fourier Transform Infrared (FTIR) was installed in a vacuum housing and integrated into the U4IR beamline at the National Synchrotron Light Source at Brookhaven National Laboratory. The frequency reference laser was mounted outside vacuum, but the moving mirror mechanism and the dynamic alignment system for the fixed mirror were in vacuum. The performance of the instrument was measured in the usual way by measuring the repeatability of data collected under specific conditions of aperture, resolution and mirror scanning velocity. We briefly discuss the beamline design, to put the interferometer in context, then present signal to noise data which we discuss in terms of both instrument performance and also storage ring stability. Under optimal conditions, the instrument has a reproducibility of 0.01% in 1 minute of measuring time at a resolution of 2 cmss,{sup -1}, over a range from 100-3000 cm{sup -1}.
Date: September 1, 2001
Creator: Brierly, P.; Dumas, P.; Smith, M. & Williams, G.P.
Partner: UNT Libraries Government Documents Department

Performance of SRF Systems in Large Scale Applications

Description: In the last ten years superconducting RF (sc) cavities have become a viable acceleration technique used at many facilities. Applications include electron accelerators like CEBAF, heavy ion accelerators like Atlas, and e{sup +}e{sup -} storage rings such as Tristan. The advantage of sc cavities is twofold: one, they can supply high gradients with a nominal RF source, and two, the state of the art in the design and production techniques has risen to a level that is acceptable. Systems such as Atlas and Tristan have proven that a reliable machine can be produced and have increased the confidence of the operability of SRF technology. As new and larger systems come on line, system performance becomes an issue. Because of the nature of SRF systems, rigid machine protection interlocks, vacuum requirements etc., different limitations that may have not occurred in normal conducting accelerators are being observed. Problems concerning gas discharges, tuning, gradient degradation and other phenomena have to be dealt with. This paper discusses operational performance of large scale SRF systems worldwide. Facilities discussed include high beta machines such as Tristan (KEK), LEP (CERN), HERA (DESY) and CEBAF and heavy ion linacs such as Atlas (Argonne). Key operational issues concerning interlocks, controls and system reliability are included. Particular emphasis is placed on CEBAF's operational experience because the author is closest to it and CEBAF will have 80% of installed SRF cavities by January 1994.
Date: October 1, 1993
Creator: Hovater, Curt
Partner: UNT Libraries Government Documents Department

Performance of the accelerator driver of Jefferson Laboratory's free-electron laser

Description: The driver of Jefferson Lab's kW-level infrared free-electron laser (FEL) is a superconducting, recirculating accelerator that recovers about 75% of the electron-beam power and converts it to radiofrequency power. In achieving first lasing, the accelerator operated straight-ahead to deliver 38 MeV, 1.1 mA cw current through the wiggler for lasing at wavelengths in the vicinity of 5 {mu}m. Just prior to first lasing, measured rms beam properties at the wiggler were 7.5{+-}1.5 mm-mr normalized transverse emittance, 26{+-}7 keV-deg longitudinal emittance, and 0.4{+-}0.1 ps bunch length which yielded a peak current of 60{+-}15A. The waste beam was then sent directly to a dump, bypassing the recirculation loop. Stable operation at up to 311 W cw was achieved in this mode. Commissioning the recirculation loop then proceeded. As of this Conference, the machine has recirculated cw average current up to 4 mA, and has lased cw with energy recover up to 710 W.
Date: April 1, 1999
Creator: Bohn, C.L.; Benson, S. & Biallas, G.
Partner: UNT Libraries Government Documents Department

Performance of the accelerator driver of Jefferson Laboratory's Free-Electron Laser

Description: The driver for Jefferson Lab's infrared free-electron laser is a superconducting, recirculating accelerator that recovers about 75% of the electron-beam energy and converts it to radiofrequency power. It is designed to lase continuous-wave at 3--6 {mu}m at kW-level power. In achieving first light, the accelerator operated straight ahead to deliver 38 MeV, 1.1 mA cw current through the wiggler for lasing at wavelengths in the vicinity of 5 {mu}m. The waste beam was then sent directly to a dump, bypassing the recirculation loop. Stable operation at power levels up to 311 W cw have thus far been achieved in this mode. The accelerator has recently recirculated up to 0.6 mA cw current with energy recovery. In this mode it has lased pulsed and cw at low-power. It remains to clean up the transport for high-power cw lasing.
Date: September 1, 1998
Creator: Bohn, C.L.
Partner: UNT Libraries Government Documents Department

Performance of the CEBAF Arc Beam Position Monitors

Description: The first three quarters of the first CEBAF arc have been instrumented with beam position monitors. Thirty-seven monitors (of 450) have been installed and their noise measured. Resolution of 100 mu-m was obtained at the lowest operating current of 1 mu-A. The update time of the system is 1 sec, limited by computer interfacing with a potential bandwidth of greater than 10 kHz.
Date: May 1, 1993
Creator: Hofler, A.S.; Bowling, B.A.; Higgins, C.S.; Kloeppel, P.K.; Krafft, G.A. & Mahoney, K.L.
Partner: UNT Libraries Government Documents Department

Performance of the electron beam diagnostics at Jefferson Lab's high power free electron laser

Description: The authors describe the performance and current status of the electron beam diagnostic complement for Jefferson Lab's IR-FEL oscillator. In addition, measurements for the driver-accelerator are presented. Beam diagnostics devices include optical beam transition radiation profile monitors, multi-slit beam emittance measurement, coherent transition and synchrotron radiation based bunch length monitors, both strip-line and button antenna BPM's and pick-up cavities for longitudinal transfer function measurements. All devices are controlled via the EPICS control system.
Date: April 1, 1999
Creator: P.Piot; Krafft, G.A.; Jordan, K.; Grippo, A. & Song, J.
Partner: UNT Libraries Government Documents Department

Performance of the FEL cryomodules

Description: The Thomas Jefferson National Accelerator Facility (Jefferson Lab, formerly known as CEBAF) is building a highly efficient, kilowatt-level infrared free-electron laser, the IR Demo FEL. The IR FEL uses superconducting radio-frequency (SRF) cavities to accelerate the electron beam that provides energy for the laser. These cavities provide the high-gradient acceleration for the high average currents necessary for a compact FEL design. Currently, a quarter cryomodule injector and a full eight-cavity cryomodule have been installed in the FEL linac. These units were tested as part of the IR FEL commissioning process. The main focus of these tests was to determine the maximum stable operating gradient. The average maximum gradient reached by these ten cavities was 11 Mv/m. Other tests include measurement of cavity parameters such as the unloaded Q (Qo) vs. gradient, the input coupling, calibration of field probes and behavior of the tuner mechanisms. This paper presents the results of those tests.
Date: September 1, 1998
Creator: Drury, M.; Fischer, J. & Preble, J.
Partner: UNT Libraries Government Documents Department

Performance report of the U.S. Department of Energy's Jefferson Lab

Description: Jefferson Lab, the newest of the US Department of Energy's 16 national laboratories, has been functioning effectively since its inception in 1984, first during construction and later during operations. As shown in this report, JLab aligns itself directly with DOE's strategic planning, both in terms of laboratory visions and plans and in terms of actual laboratory performance. Most importantly, JLab contributes significantly to DOE's Science and Technology mission in the area of nuclear physics, under the Office of Science. The laboratory practices continuous improvement and has made a number of important effectiveness and efficiency enhancements in recent years. Laboratory performance has been demonstrated by completion of the construction phase on cost and schedule, by exceeding technical specifications when coming on-line for physics research, and then - during operations in the mid- and late- 1990's - by the application of the performance measures in the laboratory's performance-based contract with DOE.
Date: June 1, 1999
Creator: Lab, Jefferson
Partner: UNT Libraries Government Documents Department

Performance Report of the U.S. Department of Energy's Thomas Jefferson National Accelerator Facility

Description: Jefferson Lab (JLab), the newest of the U.S. Department of Energy's 16 national laboratories, has been functioning effectively since its inception in 1984, first during construction and now during operations. As shown in this report, JLab aligns itself directly with DOE's strategic planning, both in terms of laboratory visions and plans and in terms of actual laboratory performance. Most importantly, JLab contributes significantly to DOE's Science and Technology mission in the area of nuclear physics, under the Office of Science. The laboratory practices continuous improvement and has made a number of important effectiveness and efficiency enhancements in recent years. Laboratory performance has been demonstrated by completion of the construction phase on cost and schedule, by exceeding technical specifications when coming on-line for physics research, and now during operations by earning ratings of ''outstanding'' relative to the performance measures in the laboratory's performance-based contract with DOE.
Date: June 1, 2001
Creator: Murphy, Jim
Partner: UNT Libraries Government Documents Department

Petabyte class storage at Jefferson Lab (CEBAF)

Description: By 1997, this facility will collect over 1 Terabyte of raw information/day accelerator operation from three concurrently operating experimental halls. With post-processing, it means that about 250 TB raw and formatted experimental data will be generated each year. By the year 2000, a total of one Petabyte will be stored on-line. Critical to the program is the networking and computational capability to collect, store, retrieve, and reconstruct data on this scale. Design criteria include support of a raw data stream of 10-12 MB/second from Experimental Hall B, which will operate the CEBAF Large Acceptance Spectrometer. Keeping up with this data stream implies design strategies that provide storage guarantees during accelerator operation, minimize the number of times data is buffered, allow seamless access to specific data sets for the researcher, synchronize data retrievals with scheduling of postprocessing calculations on the data reconstruction CPU farms, as well as support the site capability for data reconstruction and reduction at same overall rate that new data is being collected. Current implementation uses state of the art StorageTek Redwood tape drives and robotics library integrated with the Open Storage Manager Hierarchical Storage Management software (Computer Associates, International), the use of Fibre Channel RAID disks dual-ported between Sun Microsystems SMP servers, and a network-based interface to a 10,000 SPECint92 data processing CPU farm. Issues of efficiency, scaleability, and manageability will become critical to meet the year 2000 requirements for a Petabyte of near-line storage interfaced to over 30,000 SPECint92 of data processing power.
Date: August 1, 1996
Creator: Chambers, R. & Davis, M.
Partner: UNT Libraries Government Documents Department

Preliminary Statistical Analysis of CEBAF's Cavity Pair Assembly Process Data

Description: CEBAF has been collecting much data during the cavity pair assembly process. Some process data has been entered and analyzed during the last two years as part of our attempt to apply statistical process control methods. Analysis is presented here on mechanical tolerances achieved by the industrial fabricator of the CEBAF superconducting rf cavities (Siemens). Suggestions for tolerances obtainable in future procurements are made. Influence of cooldown conditions during vertical test on field emission onset gradient is discussed. An increase in the mean gradient of 2 MV/m was seen after a simple change in procedure.
Date: December 1, 1993
Creator: Benesch, Jay
Partner: UNT Libraries Government Documents Department

Probing ''Generalized Parton Distributions'' with Jefferson Lab at 12 GeV

Description: We discuss plans for Jefferson Lab to explore GPDs in hard exclusive reactions. A broad experimental program is proposed with up to 11 GeV polarized electron beams. Such an upgraded CEBAF, with high precision, and high performance detectors, will be a suitable place to study deep virtual production of mesons and photons in the range of Q{sup 2} &lt; 8 GeV/c{sup 2}. These studies are proposed as a key program for the Hall B CLAS detector.
Date: September 1, 2000
Creator: Stepanyan, S.
Partner: UNT Libraries Government Documents Department

Optimization of Dedicated Scintimammography Procedure Using Detector Prototypes and Compressible Phantoms

Description: Results are presented on the optimization of the design and use of dedicated compact scintimammography gamma cameras. Prototype imagers with a field-of-view (FOV) of 5 cm x 5 cm, 10 cm x 10 cm and 15 cm x 20 cm were used in either a dual modality mode as an adjunct technique to digital x-ray mammography imagers or as stand-alone instruments such as dedicated breast SPECT and planar imagers. Experimental data was acquired to select the best imaging modality (SPECT or planar) to detect small lesions using Tc{sup 99m} radio-labeled pharmaceuticals. In addition, studies were preformed to optimize the imaging geometry. Results suggest that the preferred imaging geometry is planar imaging with two opposing detector heads while the breast is under compression, however further study of the dedicated breast SPECT is warranted.
Date: October 1, 2000
Creator: Majewski, S.; Kieper, D.; Curran, E.; Keppel, C.; Kross, B.; Palumbo, A. et al.
Partner: UNT Libraries Government Documents Department

Optimization of Orbit Correction Systems Using Generalized Response Matrices and its Application to the LHC Injection Transfer Lines

Description: The LHC injection transfer lines will transport intense high-energy beams over considerable distances. Their relatively tight apertures require precise control of the trajectory. An analytic method has been developed to optimize the performance, reliability and cost of these lines. This method invokes a comprehensive set of performance criteria, makes detailed predictions on orbit correction effectiveness, configuration defects and critical elements, and gives indications for improvement. A path approaching an optimized configuration can thus be established based on well-defined quantitative criteria.
Date: June 1, 2001
Creator: Chao, Yu-Chiu
Partner: UNT Libraries Government Documents Department

Optimizing Pinhole and Parallel Hole Collimation for Scintimammography with Compact Pixellated Detectors

Description: The relative advantages of pinhole and parallel hole collimators for scintimammography with compact, pixellated gamma detectors were investigated using analytic models of resolution and sensitivity. Collimator design was studied as follows. A desired object resolution was specified for a pixellated detector with a given crystal size and intrinsic spatial resolution and for a given object-to-collimator distance. Using analytic formulas, pinhole and parallel hole collimator parameters were calculated that satisfy this object resolution with optimal geometric sensitivity. Analyses were performed for 15 cm x 20 cm field of view detectors with crystal elements 1.0, 2.0 and 3.0 mm on a side and 140 keV incident photons. The sensitivity for a given object resolution was greater for pinhole collimation at smaller distances, as expected. The object distance at which the pinhole and parallel hole sensitivity curves cross each other is important. The crossover distances increased with larger crystal size for a constant object resolution and increased as the desired object resolution decreases for a constant crystal size. For example, for 4 mm object resolution these distances were 5.5 cm, 6.5 cm and 8 cm for the 1 mm, 2 mm and 3 mm crystal detectors, respectively. The results suggest a strategy of parallel hole collimation for whole breast imaging and pinhole collimation for imaging focal uptake. This could be accomplished with a dual detector system with a different collimator type on each head or a single head system equipped with two collimators and a rapid switching mechanism. Multipinhole collimators have the potential to increase sensitivity yet maintain high image resolution. An experimental SPECT phantom study with a four-pinhole collimator was acquired with a pixellated detector. The iterative maximum-likelihood expectation- maximization (MLEM) reconstruction of a hot sphere in a warm cylinder showed the potential of multipinhole collimation to improve sensitivity for tomographic pinhole ...
Date: November 1, 2002
Creator: Smith, Mark F.; Kieper, Douglas A.; Majewski, Stan; Weisenberger, Andrew G. & Welch, Benjamin
Partner: UNT Libraries Government Documents Department

Optimizing Pinhole and Parallel Hole Collimation for Scintimammography With Compact Pixellated Detectors

Description: The relative resolution and sensitivity advantages of pinhole and parallel hole collimators for planar scintimammography with compact, pixellated gamma detectors were investigated using analytic models. Collimator design was studied as follows. A desired object resolution was specified for a pixellated detector with a given crystal size and intrinsic spatial resolution and for a given object-to- collimator distance. Using analytic formulas, pinhole and parallel hole collimator parameters were calculated that satisfy this object resolution with optimal geometric sensitivity. Analyses were performed for 15 cm x 20 cm field of view detectors with crystal elements 1.0, 2.0 and 3.0 mm on a side and 140 keV incident photons. The sensitivity for a given object resolution was greater for pinhole collimation at smaller distances, as expected. The object distance at which the pinhole and parallel hole sensitivity curves cross each other is important. The crossover distances increased with larger crystal size for a constant object resolution and increased as the desired object resolution decreases for a constant crystal size. For example, for 4 mm object resolution and a pinhole collimator with focal length 13 cm, these distances were 5.5 cm, 6.5 cm and 8 cm for the 1 mm, 2 mm and 3 mm crystal detectors, respectively. The results suggest a strategy of parallel hole collimation for whole breast imaging and pinhole collimation for imaging focal uptake. This could be accomplished with a dual detector system with a different collimator type on each head or a single head system equipped with two collimators and a rapid switching mechanism.
Date: November 1, 2002
Creator: Smith, Mark F.; Majewski, Stan & Weisenberger, Andrew G.
Partner: UNT Libraries Government Documents Department

Orbit Correction Implementation at CEBAF

Description: CEBAF has recently performed automated beam orbit control in real time. This effort was achieved by exploiting the capabilities of the TACL control system, using the newly implemented STAR network, which easily yielded the required data transfer density needed. Also involved in this effort was the On-Line Envelope code OLE, which provided first-order transfer matrices that reflected the current machine optics. These tools made the implementation of the specific orbit-correction algorithms easier and increased reliability. The implemented algorithms include beamthreading, orbit-locks with 2 correctors/2 monitors, most-effective corrector, and eta-corrector/eta-monitor correction.
Date: May 1, 1993
Creator: Bickley, M.; Bowling, B.A.; Douglas, D.; Hofler, A.; Kewisch, J. & Krafft, G.A.
Partner: UNT Libraries Government Documents Department

Orbit Correction Methods - Basic Formulation, Current Applications at Jefferson Lab, and Future Possibilities

Description: A. Orbit Correction System Optimization: Recipes for optimizing an orbit correction system configuration at the design level are presented. Linear algebraic tools are applied to various flavors of response matrices to uniformly control unobservability, uncorrectability, and response matrix singularity. Application at Jefferson Lab is discussed. B. Orbit Correction at Jefferson Lab: Unique challenges posed by orbit correction, as well as algorithms and tools developed at the CEBAF accelerator at Jefferson Lab are discussed. C. Orbit Interpretation and Virtual Monitors: A new approach to developing an orbit correction package with software structural, algorithmic and operational advantages is introduced. It consists of an orbit interpretation module, a virtual monitor module, and a generic steering engine. Mathematical formulation, algorithms prototyped and tested on simulated and real data, and future possibilities are discussed.
Date: December 1, 1999
Creator: Chao, Y.C.
Partner: UNT Libraries Government Documents Department

Orbitally Excited Baryon Spectroscopy in the 1/Nc Expansion

Description: The discussion of the 70-plet of negative parity baryons illustrates the large N{sub c} QCD approach to orbitally excited baryons. In the case of the l = 1 baryons the existing data allows to make numerous predictions to first order in the SU(3) symmetry breaking. New relations between splittings are found that follow from the spin-flavor symmetry breaking. The Lambda(1405) is well described as a three-quark state and a spin-orbit partner of the Lambda(1520). Singlet states with higher orbital angular momentum l are discussed.
Date: April 1, 2002
Creator: Schat, C.L.
Partner: UNT Libraries Government Documents Department

Origin of relativistic effects in the reaction D(e, e{prime}p)n at GeV energies

Description: In a series of recent publications, a new approach to the non-relativistic reduction of the electromagnetic current operator in calculations of electro-nuclear reactions has been introduced. In one of these papers, the conjecture that at energies of a few GeV, the bulk of the relativistic effects comes from the current and not from the nuclear dynamics was made, based on the large relativistic effects in the transverse-longitudinal response. Here, the authors explicitly compare a fully relativistic, manifestly covariant calculation performed with the Gross equation, with a calculation that uses a non-relativistic wave function and a fully relativistic current operator. They find very good agreement up to missing momenta of 400 MeV/c, thus confirming the previous conjecture. They discuss slight deviations in cross sections for higher missing momenta and their possible origin, namely p-wave contributions and off-shell effects.
Date: November 1, 1999
Creator: Jeschonnek, S. & Van Orden, J.W.
Partner: UNT Libraries Government Documents Department

The origins of quark-hadron duality: How does the square of the sum become the sum of the squares?

Description: Bloom-Gilman duality demonstrates empirically that the electroproduction of N*'s at low momentum transfers averages smoothly around the scaling curve measured at large momentum transfers. The latter is proportional to the sum of the squares of the constituent charges whereas the former involves the coherent excitation of resonances and is driven by the square of summed constituent charges. We determine the minimal necessary conditions for this equality to be realized so that duality can occur and consider the implications for a range of processes that may be studied soon at CEBAF.
Date: January 30, 2001
Creator: Close, Frank E. & Isgur, Nathan
Partner: UNT Libraries Government Documents Department