August 26, 2009
12 GeV Upgrade
Jefferson Lab Facilities & Logistics personnel have completed the re-packaging of the North & South Access Building Additions to include the electrical upgrades for an FY10 procurement. The electrical upgrades had previously been planned as an FY11 procurement. The contract package is under review by ESH&Q, Facilities and Accelerator personnel.
Construction on the FY09 procurements continues to progress. On the Central Helium Liquefier (CHL) Building Addition, the concrete work is complete and the structural steel work started this week with setting of the columns. On the Hall D Complex, the groundwater dewatering system is fully operational and the Hall D excavation is near the required depth of approximately 20 feet.
In Hall A, the summer down, in which the polarized helium-3 target and the BigBite spectrometer were removed and the standard cryotarget was installed, has been completed on schedule. Experiment E05-109, HAPPEx-III, a measurement of the nucleon strange form factors at high Q2, has started taking commissioning data at one pass.
The third and final part of the eg1-dvcs run group started last weekend in Hall B. Polarized ammonia (NH3) and polarized triply deuterated ammonia (ND3) targets will be used during this run. As the beam polarization was low, part of the weekend was spent to administer a cold irradiation dose to the ND3 target sample. The cold dose is needed to achieve optimal deuteron polarization during production data taking. In addition to the original physics goal of the eg1-dvcs run group, the ND3 part of the run will also serve to partly achieve the physics goal of the A-rated Hall C experiment E07-011. This experiment was canceled to run in Hall C due to a major failure of the polarized target. If the ND3 part of the eg1-dvcs run goes well, it will significantly improve our knowledge of the polarized structure function g1d.
In Hall C, commissioning of the beamline and spectrometers for the hypernuclear experiment, E05-115, has started. Beam was tuned through the new chicane relatively easily, which is a credit to the design, installation and alignment of this beamline. Beam has been used to shakedown beamline instrumentation and checkout detectors.
On Aug. 18, the Accelerator was scaled to unbalanced linacs to provide the halls with the highest beam polarization. Some time was spent on optics, radiofrequency, RSEP8A, shunt adders, vacuum and viewers. On Friday, the beamline flange at MBZ9E02 developed a leak, most likely due to beam tuning, which caused several hours of down time. Ops delivered some continuous wave beam to Halls A and B. Hall C High Resolution Kaon Spectrometer commissioning started.
Staffers operated the FEL during the week for the Light Pseudoscalar and Scalar Search experiment, getting a calibration run in but were bothered by loss of quantum efficiency in the gun due to vacuum trips. The FEL team is setting up to do a krypton processing to remove a field emission site that has developed. The Gun Test Stand gun demonstrated over five hours soaking at 400 kiloVolts DC, with no evidence of field emission affecting the ultra-high-vacuum environment.
The probability distributions of quarks and gluons (or "partons") in nuclei are suppressed at small values of the partons' momentum fraction x (x < 0.05) compared to the free nucleon - known as nuclear shadowing. Nuclear shadowing is explained by the multiple interactions of the incoming virtual photon with the target nucleons. A recent paper <arXiv:0908.1149 [hep-ph]> develops a new approach to the treatment of such multiple interactions by using the formalism of color fluctuations and updates predictions for nuclear parton distributions at small x using the leading-twist theory of nuclear shadowing.
JLab's Safety Numbers
42 Days since Last Recordable Accident (JLab record: 331)
JLab Calendar of Events
Aug. 26: Colloquium and Public Lecture
Environment, Safety, Health & Quality
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Computing and Networking Infrastructure
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Nuclear and Particle Physics at the Spallation Neutron Source
Land Clearing Starts Near CEBAF Center for New Connector Road
Register for a Personal Finance Lunchtime Seminar: Stretching Your Dollar
School Tools Drive Ends Sept. 4