Jefferson Lab Weekly Briefs
February 16, 2011
The installation for the five experiments scheduled to run in Hall A this spring was completed last week on schedule. On Friday evening, beam delivery started and great progress has been made on commissioning the various detector systems (HRS-L, HRS-R, BigBite and BigHAND, the Hall A neutron detector). On Monday, the hall was open to install the lead shielding in front of BigHAND.
In addition to production running on the liquid hydrogen target, the Q-weak experiment in Hall C made measurements of the asymmetries from a transversely polarized beam on both the LH2 and aluminum targets. Also, a series of rate measurements at different toroid magnetic fields was made to measure inelastic backgrounds. Both the transverse asymmetry and inelastic measurements serve to constrain backgrounds in the measurement of Q-weak. The Accelerator Operations group restored beam to the Compton Polarimeter chicane, achieving low backgrounds in the Compton detectors.
The accelerator has been running well, delivering beam to all three halls, although there was some downtime. On Tuesday, the beam polarization was changed from horizontal to vertical for Hall C and was changed back to horizontal two days later. Also in the last week, the Arc9 box supply tripped off due to a water leak, which was fixed; a spin dance was performed to optimize the beam polarization; and a few hours were spent to optimize beam quality. Radiofrequency zone 2L05 interrupted beam delivery for a few hours (a control module was replaced and cracked waveguide pressure line was repaired). On Monday, the laser spot was moved to support the high current run to Hall C.
The FEL group spent the week continuing installation of systems to support ultraviolet and vacuum UV optical transport to the labs, including installation of optical transport lines, controls, vacuum controls and changes required by the Laser Personnel Safety System.
Theoretical and Computational Physics
The so-called Witten diagrams are one of the main tools for nonperturbative QCD calculations in the Anti-de Sitter/QCD model. Using the Mellin representation of AdS propagators, one can reduce the Witten diagrams to the more familiar Feynman diagrams used in perturbative calculations. The Mellin representation for the AdS propagator of the graviton is derived in a new paper <arXiv:1102.0577 [hep-th]>, which is relevant for the description of high-energy processes in nonperturbative QCD.
Engineering and 12 GeV Upgrade
First article testing at the vendor for the new 12 GeV radiofrequency system cathode power supplies was witnessed last week by RF group engineers. Testing went as expected with minor issues to be resolved, but overall performance validated. Delivery of the first unit is expected by the end of February or in early March. The South Linac, which had been cleaned out, is now prepared for RF equipment installation activities. Equipment racks and AC power installation was completed earlier and will support the new hardware.
Environment, Safety, Health and Quality
As Hampton Roads moves into spring, many of us will be applying lawn and garden chemical products to either promote growth or eliminate growth in our lawns and gardens. However, fertilizers, herbicides and pesticides can have a significant adverse effect on the health of the fish and wildlife that live in and on our waterways. You can prevent pollution in local streams, rivers and bays, and also achieve cost savings, by simply following the label directions for mixing ratios and following the proper application method.
Computing and Networking Infrastructure
CNI Maintenance Day Set for Tuesday, Feb. 22
jlabs2 To Be Decommissioned
2011 Benefits Open Enrollment Underway
JLab Calendar of Events
Feb. 21: Presidents Day holiday: JLab closed