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The N* Program at CEBAF

Description: The N* program at CEBAF is reviewed, and some preliminary experimental results are presented to illustrate the quality and capabilities of the CLAS detector.
Date: December 1, 1998
Creator: Minehart, Ralph
Partner: UNT Libraries Government Documents Department

HIGH POWER TEST OF RF SEPARATOR FOR 12 GEV UPGRADE OF CEBAF AT JLAB

Description: CEBAF at JLab is in the process of an energy upgrade from 6 GeV to 12 GeV. The existing setup of the RF separator cavities in the 5th pass will not be adequate to extract the highest energy (11 GeV) beam to any two existing halls (A, B or C) while simultaneously delivering to the new hall D in the case of the proposed 12 GeV upgrade of the machine. To restore this capability, we are exploring the possibility of extension of existing normal conducting 499 MHz TEM-type rf separator cavities. Detailed numerical studies suggest that six 2-cell normal conducting structures meet the requirements; each 2-cell structure will require up to 4 kW RF input power in contrast with the current nominal operating power of 1.0 to 2.0 kW. A high power test of 4 kW confirms that the cavity meet the requirement.
Date: July 1, 2012
Creator: Ahmed, S.; Wissmann, M.; Mammosser, J.; Hovater, C.; Spata, M.; Krafft, G. et al.
Partner: UNT Libraries Government Documents Department

Device control at CEBAF

Description: CEBAF has undergone a major conversion of its accelerator control system from TACL to EPICS, affecting device control for the RF system, magnets, the machine protection system, the vacuum and valves, and the diagnostic systems including beam position monitors, harps, and the camera and solenoid devices (beam viewers, faraday cups, optical transition radiation viewers, synchrotron radiation monitor, etc.). Altogether these devices require approximately 125,000 EPICS database records. The majority of these devices are controlled through CAMAC; some use embedded microprocessors (RF and magnets), and newer interfaces are in VME. The standard EPICS toolkit was extended to include a driver for CAMAC which supports dual processors on one serial highway, custom database records for magnets and BPMs, and custom data acquisition tasks for the BPMs. 2 refs., 1 tab.
Date: August 1, 1996
Creator: Schaffner, S.; Barker, D. & Bookwalter, V.
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

Light meson radial Regge trajectories

Description: A new physical mechanism is suggested to explain the universal depletion of high meson excitations. It takes into account the appearance of holes inside the string world sheet due to q{bar q} pair creation when the length of the string exceeds the critical value R{sub 1} {approx_equal} 1.4 fm. It is argued that a delicate balance between large N{sub c} loop suppression and a favorable gain in the action, produced by holes, creates a new metastable (predecay) stage with a renormalized string tension which now depends on the separation r. This results in smaller values of the slope of the radial Regge trajectories, in good agreement with the analysis of experimental data in references.
Date: August 1, 2002
Creator: Badalian, A.M.; Bakke, B.L.G. & Simonov, Yu.A.
Partner: UNT Libraries Government Documents Department

Naturalness of the Coleman-Glashow mass relation in the 1/N{sub c} expansion: An update

Description: A new measurement of the {Xi}{sup 0} mass verifies the accuracy of the Coleman-Glashow relation at the level predicted by the 1/N{sub c} expansion. Values for other baryon isospin mass splittings are updated, and continue to agree with the 1/N{sub c} hierarchy.
Date: May 1, 2000
Creator: Jenkins, E. & Lebed, R.F.
Partner: UNT Libraries Government Documents Department

Jefferson Laboratory: Maintenance overview

Description: Maintenance, repair, and upgrades to the Thomas Jefferson National Accelerator Facility, a DOE laboratory located in Newport News, VA, USA, is based upon a two-week run cycle followed by a one-shift maintenance period. The rationale for this approach will be presented including a brief look at the maintenance funding, support staff, and beam availability. Means for improving the machine will be presented including record keeping of downtime, compilation of data, dissemination of findings, and allocation of resources. Maintenance problems facing Jefferson Lab will be presented.
Date: May 1, 1998
Creator: F.Suhring, Steve
Partner: UNT Libraries Government Documents Department

Charge conjugation invariance of the spectator equations

Description: In response to recent criticism, the authors show how to define the spectator equations for negative energies so that charge conjugation invariance is preserved. The result, which emerges naturally from the application of spectator principles to systems of particles with negative energies, is to replace all factors of the external energies W {sub iota} by {radical} W{sup 2} {sub iota}, insuring that the amplitudes are independent of the sign of the energies W {sub iota}.
Date: August 1, 1999
Creator: Gross, F.
Partner: UNT Libraries Government Documents Department

Note on Nuclear Shadowing at Low Q{sup 2} and the Extraction of sin{sup 2} theta{sub w}

Description: In the light of a recent claim that models of nuclear shadowing which incorporate a vector meson dominance component at low Q{sup 2} are incompatible with nuclear deep inelastic scattering data, we compare the predictions of such a model with high precision data on the Q{sup 2} dependence of nuclear shadowing. Contrary to this claim, we find that models which incorporate both vector meson and partonic mechanisms are indeed consistent with both the magnitude and the Q{sup 2} slope of the shadowing data.
Date: August 1, 2002
Creator: Melnitchouk, Wally & Thomas, A.W.
Partner: UNT Libraries Government Documents Department

Measurement of G

Description: The ratio of the electric and magnetic form factors of the proton, G{sub E{sub p}}/G{sub M{sub p}}, was measured at the Thomas Jefferson National Accelerator Facility (JLab) using the recoil polarization technique. The ratio of the form factors is directly proportional to the ratio of the transverse to longitudinal components of the polarization of the recoil proton in the elastic {rvec e}p {yields} e{rvec p} reaction. The new data presented in this article span the range 3.5 < Q{sup 2} < 5.6 GeV{sup 2} and are well described by a linear Q{sup 2} fit. Also, the ratio QF{sub 2p}/F{sub 1p} reaches a constant value above Q{sup 2}=2 GeV{sup 2}.
Date: March 1, 2002
Creator: Gayou, Olivier; Brash, Ed J.; Jones, Mark K.; Perdrisat, Charles F.; Punjabi, Vina; Pentchev, L. et al.
Partner: UNT Libraries Government Documents Department

Regularization for effective field theory with two heavy particles

Description: A regularization for effective field theory with two propagating heavy particles is constructed. This regularization preserves the low-energy analytic structure, implements a low-energy power counting for the one-loop diagrams, and preserves symmetries respected by dimensional regularization.
Date: January 1, 2001
Creator: Goity, J.L.; Lehmann, D.; Prezeau, G. & Saez, J.
Partner: UNT Libraries Government Documents Department

Looking Back at International Synchrotron Radiation Instrumentation

Description: With the 11th International Synchrotron Radiation Instrumentation coming up in July 2012 in Lyons, France, we thought it might be of interest to our readers to review all the past meetings in this series. We thank Denny Mills of the APS, Argonne for putting the list together. Prior to these larger meetings, and in the early days, facilities held their own meetings similar to the user meetings of today. However, the meeting held at ACO in Orsay, France in 1977 was the first such meeting with an international flavor and so it is on the list. However it is not counted as number 1 since it was agreed way back to start the numbering with the 1982 DESY meeting. The 2005 USA National Meeting scheduled at CAMD in Baton Rouge had to be canceled due to Hurricane Katrina. It was ultimately held in 2007, with the CLS hosted meeting the following year. And a personal note from the magazine - Synchrotron Radiation News was born at the 1987 meeting in Madison, Wisconsin with a proposal that was put to a special session of the meeting organized by Susan Lord. Initial proposals were to model it after the CERN Courier, but it soon adopted its own distinct flavor.
Date: March 1, 2012
Creator: Williams, Gwyn
Partner: UNT Libraries Government Documents Department

12 GeV Upgrade Project - Cryomodule Production

Description: The Thomas Jefferson National Accelerator Facility (Jefferson Lab) is producing ten 100+MV SRF cryomodules (C100) as part of the CEBAF 12 GeV Upgrade Project. Once installed, these cryomodules will become part of an integrated accelerator system upgrade that will result in doubling the energy of the CEBAF machine from 6 to 12 GeV. This paper will present a complete overview of the C100 cryomodule production process. The C100 cryomodule was designed to have the major components procured from private industry and assembled together at Jefferson Lab. In addition to measuring the integrated component performance, the performance of the individual components is verified prior to being released for production and assembly into a cryomodule. Following a comprehensive cold acceptance test of all subsystems, the completed C100 cryomodules are installed and commissioned in the CEBAF machine in preparation of accelerator operations. This overview of the cryomodule production process will include all principal performance measurements, acceptance criterion and up to date status of current activities.
Date: July 1, 2012
Creator: J. Hogan, A. Burrill, G.K. Davis, M.A. Drury, M. Wiseman
Partner: UNT Libraries Government Documents Department

HIGH AVERAGE POWER UV FREE ELECTRON LASER EXPERIMENTS AT JLAB

Description: Having produced 14 kW of average power at {approx}2 microns, JLAB has shifted its focus to the ultraviolet portion of the spectrum. This presentation will describe the JLab UV Demo FEL, present specifics of its driver ERL, and discuss the latest experimental results from FEL experiments and machine operations.
Date: July 1, 2012
Creator: Douglas, David; Evtushenko, Pavel; Gubeli, Joseph; Hernandez-Garcia, Carlos; Legg, Robert; Neil, George et al.
Partner: UNT Libraries Government Documents Department

Performance experience with the CEBAF SRF cavities

Description: The full complement of 169 pairs of niobium superconducting cavities has been installed in the CEBAF accelerator. This paper surveys the performance characteristics of these cavities in vertical tests, commissioning in the tunnel, and operational experience to date. Although installed performance exceeds specifications, and 3.2 GeV beam has been delivered on target, present systems do not consistently preserve the high performance obtained in vertical dewar tests as operational capability. Principal sources of these limitations are discussed.
Date: December 31, 1995
Creator: Reece, C.; Benesch, J.; Drury, M.; Hovater, C.; Mammosser, J. & Preble, J.
Partner: UNT Libraries Government Documents Department

A program to research emittance growth in bends

Description: A research program to explore the phenomenon of emittance growth in bends due to noninertial space-charge effects has been defined and initiated. The program combines theoretical, numerical, and experimental investigations. This paper summarizes the motivation of the work and highlights CEBAF`s need for immediate results. The program`s key elements, some of which qualitatively differ from the standard approach used to investigate the production and effects of coherent synchrotron radiation in synchrotrons and storage rings, are enumerated and discussed. 1 fig.
Date: December 31, 1995
Creator: Bohn, C.L.
Partner: UNT Libraries Government Documents Department

Measuring and adjusting the path length at CEBAF

Description: Accurately setting the path length around the machine is central to the proper operation of the CEBAF accelerator. The CEBAF main accelerator consists of two recirculating superconducting linacs operating at 1497 MHz fundamental frequency. The electron beam can recirculate up to five times through the two linacs before it is extracted to the experimental halls. In order to obtain maximum energy gain and minimum energy spread through the linacs, all passes should arrive at the beginning of the linacs in phase at the crest of the RF cycle. In this paper we explain how the arrival times of higher pass beams are measured with respect to the first pass to less than one degree of RF phase and how the path length around the machine is adjusted. Following a brief introduction to the CEBAF design and some local nomenclature, these topics will be discussed: differential RF phase measurements of time delay, the energy method of cresting the higher pass beams, results obtained with the measurement techniques, future plans and improvements to the devices, and finally, a set of conclusions. 3 refs., 5 figs., 1 tab.
Date: December 31, 1995
Creator: Krafft, G.A.; Crofford, M. & Douglas, D.R.
Partner: UNT Libraries Government Documents Department

Arcing phenomena on CEBAF RF-windows at cryogenic temperatures

Description: During the CEBAF commissioning tests some of the superconducting cavities had light emitting discharges (arcing) which were observed in the guard vacuum space between a warm polymeric rf window and the cold ceramic rf window. A dedicated off-line test system was implemented to investigate the conditions under which arcing may occur and to gain some understanding of the mechanisms leading to this phenomenon through optical spectral analysis. This paper reports on the photoemission spectra observed during the dedicated tests on a single cell 1500 MHz niobium cavity with a ceramic window operated at 10 MV/m and 2 K. The light emission was detected using a spectrometer with an intensified photodiode array. The effect of moving the window away from the beam line using a waveguide elbow is reported. 12 refs.
Date: December 31, 1995
Creator: Powers, T.; Kneisel, P. & Allen, R.
Partner: UNT Libraries Government Documents Department

CEBAF cryogenic system

Description: The CEBAF cryogenic system consists of 3 refrigeration systems: Cryogenic Test Facility (CTF), Central Helium Liquefier (CHL), and End Station Refrigerator (ESR). CHL is the main cryogenic system for CEBAF, consisting of a 4.8 kW, 2.0 K refrigerator and transfer line system to supply 2.0 K and 12 kW of 50 K shield refrigeration for the Linac cavity cryostats and 10 g/s of liquid for the end stations. This paper describes the 9-year effort to commission these systems, concentrating on CHL with the cold compressors. The cold compressors are a cold vacuum pump with an inlet temperature of 3 K which use magnetic bearings, thereby eliminating the possibility of air leaks into the subatmospheric He.
Date: December 31, 1995
Partner: UNT Libraries Government Documents Department

Location and correction of 60 hz in the CEBAF injector

Description: CEBAF produces a continuous electron beam with an emittance of 2-3 nm-rad. Transverse low frequency magnetic oscillations act to dilute this emittance. These fields are typically associated with AC line conductors. The CEBAF injector is approximately 40 m long. To locate the source(s) of the beam motion, measured offsets were back propagated along the beamline using the DIMAD model. Field measurements were then made at the calculated field source positions and correlated with the measured effects. Corrections and final beam measurements were made to verify the corrections. 2 refs., 4 tabs.
Date: August 1, 1996
Creator: Legg, R.; Douglas, D.; Krafft, G.A. & Saulter, Q.
Partner: UNT Libraries Government Documents Department