Jefferson Lab Weekly Briefs
April 8, 2009
12 GeV Upgrade
A total of 3,200 km of SCSF-78M 1mm-diameter scintillating fibers were ordered for use in the Hall D barrel calorimeter detector. The fibers are made in rods 4.1 meters in length. One hundred first-article fibers were received in February for evaluation of conformance with specifications. The fibers were tested at JLab and the University of Regina in Saskatchewan, Canada, for light output and transparency. The fiber performance was measured to be uniform from fiber to fiber and in all cases exceeded specifications, as determined by measurements of the light output in response to a Strontium-90 radioactive source.
The tentative schedule for April-June consists of three Quasi-Elastic scattering experiments off polarized helium-3 (E05-015, E08-005 and E05-102) in Hall A. These experiments require a configuration with the BigBite spectrometer at large angles and the right High Resolution Spectrometer at small angles. This configuration is opposite to the one used by the just-completed experiments, and it requires dismantling BigBite, moving the right HRS and re-installing BigBite. Most of the operation has been completed, and it is expected that BigBite will be re-assembled and operational soon. A Danfysik field engineer is modifying the two Q1 power supplies to adapt new Zero-Field Current Transformers to these supplies. The original ZFCT from one of the supplies as well as a spare unit have failed. These units are no longer manufactured and Danfysik could not warrant their repair. Work on the Compton electron detector upgrade is also proceeding.
In Hall B, preparation of the hall for the second part of the eg1-DVCS run is in progress. Work consists of repair to drift chambers (region 3 sector 2), replacement of the target heat shield and re-alignment of the target and inner calorimeter. The first prototype gas electron multiplier assembly of the new radial time projection chamber is completed. The method of self-supporting foils with foam rings worked well, and the GEMs were assembled practically without wrinkles. Procurement of the CLAS12 detector components are in progress.
In Hall C, the raised concrete floor has been extended to a larger area, with spectrometers for the hypernuclear experiment (E05-115) to be moved into position. The shielding wall at the entrance to the hall has been partially disassembled, allowing start of work on reconfiguring the beamline for the horizontal chicane used in E05-115.
The third week of the scheduled accelerator down went well. The new photocathode of Gun2 was activated. The Gun3 cathode electrode was replaced. Commissioning of C50-refurbished cryomodules NL12 and SL07 started. Owl shifts were used to measure the quality factors of superconducting radiofrequency cavities. General maintenance items continued to be addressed.
Free-Electron Laser (FEL)
Fixing the low-conductivity water leak behind the FEL in the eight-inch pipe has led to a major shift in our operations schedule. The lab had planned to replace this pipe during a shutdown in June/July, but that plan has been accelerated, with the shutdown taking place now. If weather cooperates with the contractor, the FEL will be running by May 18. FEL staffers will take advantage of the shutdown to improve the drive laser, install UV components and fix a number of other items.
In a new Theory Center paper <arXiv:0903.2990 [hep-lat]>, the ground state octet baryon masses are extracted with fully quantified uncertainties that are at or below the 0.2 percent level at one particular value of the quark mass, lattice spacing and lattice volume. The primary focus of this work is to fully understand the statistical and systematic uncertainties that are encountered in lattice QCD calculations with very high statistics (300,000 measurements are used in this study), as will be required to make an impact on quantities of interest to nuclear physics. The lowest-lying negative-parity states are also extracted, albeit with a somewhat lower level of precision.
Environment, Safety, Health & Quality
Eighty percent of individuals will experience at least one episode of back pain during their lives. Lower back pain (LBP) is the most costly musculoskeletal disorder in industrial nations, ranging in severity from completely debilitating to a temporary annoyance. More than $50 billion is spent annually for back care-related pain and disability. The exact cause of this type of pain goes undiagnosed in 85 percent of cases; therefore, considerable guesswork is often involved in selecting treatment options (e.g., ice, rest, gentle activity, manipulative therapies, therapeutic exercise or surgery).
Lower back pain is caused by chemical or mechanical irritation of pain-sensitive nerve endings in structures of the lumbar spine and is exacerbated by common practices, such as heavy physical work, static work postures, frequent bending or twisting, lifting, pushing and pulling arm extension with a load, repetitive work, vibrations and psychological/psychosocial aspects of work. Some general observations on back pain and avoidance practices include:
Computing and Networking Infrastructure (CNI)
Maintenance Day on Tuesday, April 14, 5-10 p.m.
12 GeV Upgrade Groundbreaking Ceremony
Take a Break for Quark Cafe's Spring Bake Sale on April 9
Want to Be JLab's "Biggest Loser"?
JLab's Safety Numbers
93 Days since Last Recordable Accident (JLab record: 331)
JLab Calendar of Events
April 14: 12 GeV Upgrade Groundbreaking