Jefferson Lab Weekly Briefs
May 23, 2012
12 GeV Upgrade
The Hall D complex is being equipped with services and beamline items, including the pair spectrometer magnet and collimator system. The tagger magnet coils and steel cores are under production, with delivery expected in late summer. Wire-stringing of the straw tubes for the Central Drift Chamber (CDC) has been completed at Carnegie Mellon University. The third chamber package (of four total) is being built for the Forward Drift Chamber (FDC). The manufacturing contract for the several hundred FADC-125 read-out modules for the FDC and CDC is out for bid. A readout module for the Barrel Calorimeter (BCAL) has been extensively tested using beam parasitically during a Hall B run. The final units of the 3,840 silicon photo-multipliers for the BCAL are arriving, and machining and polishing of the similar number of lightguides is underway. Production quantities of high-voltage modules, low-voltage modules, cables, and VXS and VME-64 crates are arriving.
Data taking for Q-weak, the lab's most ambitious experiment to date, was completed in Hall C on Friday. During the long run, a large amount of parity-mode data was accumulated on the world's highest-power liquid hydrogen target. In addition, background and auxiliary measurements were made with a variety of targets, beam energies, beam conditions and Q-weak spectrometer settings. As well as being crucial to the extraction of the proton weak charge from the data, many of these measurements have a physics interest of their own. The success of the experiment was due to the efforts of the people, lab and collaboration that designed, built, installed, commissioned, operated and maintained the many components of the experiment, including the polarized source, accelerator, beamline, Compton polarimeter, cryogenics, target, Qtor magnet and the experimental apparatus. More than 20 graduate students have written or plan to write Ph.D. theses based on the Q-weak experiment.
Accelerator operations personnel started the week with a pass change for Hall A, from 2-pass to 3-pass beam. A bad power supply and controller board caused a phantom fault that would not clear (the fault propagated down the chain of controllers, but the source was not shown). This resulted in almost two hours of down time. A control module for a superconducting radiofrequency cavity failed, which required replacement and another two of the dwindling hours of 6 GeV beam time remaining. At the end of the day on Tuesday, the heavens opened up and the rain poured out. The end stations took the worst of it, with storm water flowing down the Hall B truck ramp, through the hall, and out into the other halls covering the floors in places with several inches of water. The accelerator remained dry but did have some glitches on several systems due to nearby lightning strikes. Personnel from Radiation Control, the Safety Systems Group and Engineering Support came in or stayed after to assist in the recovery, and beam was back to Hall A shortly after midnight, with Halls B and C coming up later that afternoon. A rack of magnet controllers for the injector had issues all week, with some magnets randomly failing to maintain the set currents. The operators became very efficient at recovering the magnets and restoring the beam, giving up only minutes of precious beam time as compared to the possible hours it may have taken to troubleshoot and repair the magnet rack. Thursday night at 8:30 p.m., beam was terminated to the halls. Hall C was changed to 3-pass beam, and the injector was set up for transverse spin polarization. The zone 2L25 C100 superconducting cavities were raised to 108 MeV and run with a total of 465 microamps for one hour, exceeding the 12 GeV Upgrade requirement for the new modules. On Friday, May 18, at 8:18:46, Lab Director Hugh Montgomery pushed the button that terminated the final 6 GeV beam.
The FEL team performed installation activities and some beam dynamics studies while awaiting delivery of a repaired wiggler controller. The machine achieved lasing while accelerating beam past crest, which is probably the first time anyone has accomplished this trick. Significant activities are underway in designing a robust gun and preparing superconducting radiofrequency cavities for reprocessing for the refurbished cryomodule.
Center for Theoretical and Computational Physics
The anomaly observed in recent quasi-elastic neutrino scattering data on carbon-12 — the excess of measured cross section relative to theoretical calculations — has led to speculations that our present understanding of the nuclear response to weak probes may be incomplete. However, the calculations that these speculations have been inferred from use rather crude models of nuclear structure and simplistic treatments of the reaction mechanism. In a new paper, inclusive neutrino scattering from the simplest nucleus, the deuteron, is studied over a wide energy range and within a realistic approach to nuclear dynamics. The motivations are twofold: the first is to provide a benchmark for quantum Monte Carlo studies of electro-weak inclusive response in light nuclei, including 12C, that will be carried out in the near future; the second has to do with plans to determine the neutrino flux in accelerator-based experiments from measurements of inclusive cross sections on the deuteron. Clearly, accurate predictions for these cross sections are crucial for a reliable determination of the flux.
Hall D Cryogenics Design and Installation
Environment, Safety, Health and Quality
Limited Approach Boundaries
Get Your Hurricane Season Supplies - Tax Free!
Computing and Networking Infrastructure
Web Maintenance Period Set for Tuesday, May 29
Email Migrations into New System Continue
Open House Pictures Posted to JLab's flickr Account
New JLab Emergency Management Page Now Live!
6 GeV End of an Era Party June 6 for Lab Staff, Students & Users
Tracking Thomas at JLab
Congratulations this week go to Michael Haddox-Schatz, Brita Hampton, Casey Heck and Samika Hawkins, who were the first to correctly identify the May 16 location. Honorable mentions go to Michelle Shinn, Maurizio Ungaro, Dana Cochran, Susan Brown, Jim Boyce, Stephanie Vermeire, Mike Legg, Greg Nowicki, Anusha Liyanage, Rob Mahurin and Andrea Celentano. Check out the Tracking Thomas webpage for a better view of his last location and this week's new mystery photo.
JLab Calendar of Events
May 28: Memorial Day holiday, JLab closed