Jefferson Lab Weekly Briefs
March 28, 2012
12 GeV Upgrade
Pre-planning of work activities greatly improves the overall safety of the task. Recently, the two Central Helium Liquefier (CHL-2) cold boxes that were delivered and placed into final positions required complex lifts. The operation took two large cranes, several riggers and other support personnel working in unison to complete the task. Through extensive pre-planning and clear communication of the roles and responsibilities for the people involved, these complex lifts were completed without incident.
Hall A has been down this week while staffers recovered from the septum magnet incident. The incident happened on Saturday, March 17. A connection from the right-septum magnet to the power supply became loose, developing a resistive contact, and overheated. A thermal runaway destroyed this connection. A second damage occurred on the magnet windings, about 1 meter away from the connector. There, due to the sudden drop in current, a spike in voltage caused a short between the magnet windings and the iron yolk. The power supply tripped off. Three coil windings (out of 28) are shorted. To repair the magnet, Hall A workers have jumpered over these three windings and replaced the connector. A ground fault circuit interrupter is being installed on the power supply, and heat-sensitive switches are being installed in various locations, including the connectors. The connectors have been torqued to specification and will be regularly re-torqued to ensure a tight connection. A panel of two electrical engineers from Engineering and a Hall C physicist has reviewed the incident. Once this panel is satisfied with the repairs, Hall A will be certified to continue running. With three windings jumpered out, the magnet will have 11 percent less field for a given current, but the field quality and magnetic optics should still be sufficient.
In Hall C, the Q-weak experiment continued with production data taking on hydrogen intermixed with occasional background runs with an aluminum target. Some studies of the effects of beam halo were done by blocking one of the eight Q-weak detector octants with a tungsten shutter.
Minority Undergraduate Research Assistantship
Multiple unsuccessful attempts to reconfigure Hall B for five-pass beam during the past week were traced to a shorted quadrupole magnet at the 9A20 girder in Arc 9. Beam has not been at 5 pass since before the start of the summer down. C100 RF zones continue to be challenging to operate, as Operations staff attempt to raise them to their nominal 98 MeV gradients. On Saturday, March 24, a beam strike resulted in a vacuum event, which interrupted beam to both operating halls for several shifts. By Sunday, beam was restored to Hall C at its requested pass and to Hall B at 4 pass due to an inability to transport beam beyond Arc 9. On Monday morning, the accelerator was opened up to reactivate the cathode. The 9A20 quadrupole problem was found and various other maintenance activities were performed.
The FEL ran well this week, and the team started the infrared experimental program by measuring mirror performance at 1.6 microns.
Center for Theoretical and Computational Physics
In a new paper, QCD calculations of the heavy-hadron axial couplings g1, g2, and g3 are reported. These quantities are the low-energy constants of heavy-hadron chiral perturbation theory and determine the strong decay widths of charm and bottom baryons. The analysis makes use of lattice QCD at light quark masses and chiral perturbation theory to control all systematic uncertainties.
The alignment group has been busy in Hall A supporting the g2p experiment. The field crews have aligned the chicane magnets and diagnostics through four energy changes. Additionally, alignment has carried out an initial inspection/fiducialization of the Hall D CDC detector at Carnegie Mellon University. For Hall D, the group surveyed the solenoid and control monuments in the hall. For Hall B, the region 3 drift chambers were surveyed. Additionally, the group is transitioning and readying data and software files to prepare for the upcoming 12 GeV Upgrade down. The magnet measurement group has finished measuring 11 of the 20 new spreader and recombiner magnets. In addition, magnet measurement is preparing for the upcoming down when they will have to refurbish many of the existing machine magnets.
Environment, Safety, Health and Quality
Eliminating Your Car's Blind Spots
Time Collection Server Upgrade Set for Thursday
Tornado Drill Survey
Interactive Shipping Authorization Form Now Available
Volunteers Needed for May 19 JLab Open House
Seminar on Women in Physics Offered April 5
Tracking Thomas at JLab
Congratulations this week go to Pashupati Dhakal and Samika Hawkins, who were the first to correctly identify the March 21 location. Honorable mentions go to Jim Follkie, Subashini De Silva and Robert Martin. 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
March 29: Newport News Public Schools Business & Education STEM Summit