Jefferson Lab Weekly Briefs
October 20, 2010
12 GeV Upgrade
The fourth group of four barrel calorimeter (BCAL) modules for Hall D has arrived at JLab from the University of Regina, Saskatchewan, Canada, meaning one-third of all the modules are on-site. The first units of the new Cockcroft-Walton type high-voltage synthesizer-and-divider bases for the Hall D forward calorimeter passed acceptance tests at Indiana University, thus 500 of the total 2800 have been ordered to start mass production. Tests of first-article preamplifiers for the central and forward drift chambers, using the custom application-specific integrated circuit developed in collaboration with the University of Pennsylvania, were completed successfully. Therefore, all key elements of the electronics chain for the Hall D tracking detectors are now entering mass production. Manufacture of the custom 16-channel 250 Megahertz flash analog-to-digital converter, key to calorimeter, time-of-flight array and tagger hodoscope readout, has also begun, with assembly of the first 20 production boards. The largest of the Hall D solenoid magnet coils has been installed in the Test Lab stand and is being prepared for cool-down and full-field tests later this fall.
Hall A continues commissioning E07-007 and E08-025 (deeply virtual Compton scattering).
Commissioning of Q-weak and the Compton polarimeter continues in Hall C. No significant boiling of the liquid hydrogen target is seen up to 150 microamps. Initial studies of the sensitivity of the detectors to beam motion are encouraging.
The accelerator has been delivering beam to all three halls, with some downtime. Monday was a scheduled maintenance day for reactivating the injector photocathode and reconfiguring the low-conductivity water for the end stations. Over the weekend, some misbehaving radiofrequency cavities caused a couple of hours of downtime. Last week, beam energy was slightly off after the Arc2 box supply was replaced. The problem was corrected in a timely manner. After gun high-voltage power cycling, sometimes the injector orbits do not reproduce. The experts are still investigating the problem, and a work-around method has been implemented.
The FEL team continued gain-scaling measurements last week, while operating at both the 400-nanometer region and 700 nanometers. The small signal gain appears to be significantly over 100 percent, and lasing is easily established each day. A power meter had to be replaced due to damage from the optical beam. The team also managed to find the source of an annoying phase jump in the injector system in an over-torqued splitter connection to a radiofrequency module.
Center for Theoretical and Computational Physics
Quarks, the building blocks of protons and pions, carry a property we call color that comes in three shades. However, theorists like to imagine how the world changes as the number of colors increases. This provides a way of telling the difference between mesons that are thought to be made of a quark and an antiquark and those that might have more complicated configurations. The lightest meson that is unstable under the strong interaction, the σ (sigma), a meson that is important in nuclear forces, is thought to be such a more complicated state. A recent study by JLab's Michael Pennington and collaborators <arXiv:1009.6204> provides evidence that in a world with a larger number of colors than three, the σ would be a quark-antiquark meson, just like most of the other mesons we know of. They then explain how the σ changes its nature as the variety of shades is reduced to its physical number three, while ensuring a property known as "semi-local duality" holds, whatever the number of colors.
Environment, Safety, Health & Quality
Halloween is a fun time for kids, but it is also an important time to be extra vigilant for possible safety hazards so that your children have a fun and safe holiday. Click the link for timely tips from the U.S. Product Safety Commission to keep your little trick-or-treaters out of harm's way.
Computing and Networking Infrastructure
Microsoft Patches Will Be Released Tuesday
Introduction to Mailman for List Owners/Administrators
Discontinuation of Dial-up Modem Pool (RAS) Service
Sentara Mobile Mammography Unit Onsite Dec. 6
Win an iPad in United Way Raffle
JLab Calendar of Events
Oct. 22: Safety Shoe vendor onsite
JLab's Safety Numbers
51 Days since Last Recordable Accident (JLab record: 331)