Jefferson Lab Weekly Briefs
November 5, 2008
After a successful installation, commissioning of the polarized helium-3 target and of the BigBite detector system has been initiated in Hall A. The target polarization has been measured to be close to 50 percent.
In Hall C, commissioning and detector checkout for the Spin Asymmetries of the Nucleon Experiment (SANE) is in progress. The 5 Tesla superconducting magnet in the polarized target has been cooled down and energized. Data to calibrate BETA (the Big Electron Telescope Array) has been acquired using elastic scattering events in coincidence with the High Momentum Spectrometer. By taking data with the target magnet on and off, a large region of the BETA detector has been "illuminated" with calibration events.
This period was marked by increasing amounts of beam delivery to all three experimental halls. The halls continued to work on commissioning efforts, while the accelerator provided 348 hours of beam availability. Accelerator staff continued work on optimizing the number of hours of beam by reducing radiofrequency (RF) trips, with electron beam quality always a high priority.
Free-Electron Laser (FEL)
FEL staff brought electron beam around the machine and are optimizing the setup. Most of the systems appear to be functioning well, although there are some discrepancies between measured current for a given laser power and the measured quantum efficiency (QE). The cathode lifetime is presently shorter than desired due to relatively bad vacuum in the front end. FEL staffers have re-installed the shielding blocks to the FEL truck ramp so that the FEL can now operate safely at full power. By the end of the week, the team had success at energy-recovering the beam, setting the stage for careful tuneup during this week's operations.
The relativistic quark model that was recently developed for the nucleon N and Δ(1232) resonance, based on a simple picture in which quarks move in relative S-waves, has been extended by including higher angular momenta (D-waves) in the Δ (arXiv:0810.4126 [hep-ph]). The introduction of the D-states generates nonzero contributions to the quadrupole N → Δ transition form factors (a signature of the Δ deformation), but is insufficient to explain the experimental data. Combining the effects of the D-waves with well-known relations between nucleon elastic and N → Δ form factors, which account for quark-antiquark (or pion cloud) effects, the model then leads to agreement with data.
Environment, Safety, Health & Quality
Over the past three months, three 1.5-inch die grinders have been found onsite with improper attachments. The attachments were later found to be significant safety hazards. Unsafe attachments were found on two Dewalt Model DW887 grinders and a Black and Decker Model 4287. These grinders were rated at an operating speed of 25,000 RPM. However, the max RPM values listed on the attachments were 18,000 and 10,000. Thus, the attachments were being used at up to 2.5 times their recommended safe speed.
Die grinders are designed for fine, high-speed grinding and polishing of dies, molds and other hard-to-reach areas. The spinning attachments do not have a guard or shield. Therefore, even if gloves are worn, if the wrong attachment is used, the user may be injured from:
Statistics show that nearly half of all grinder related injuries in the workplace are caused by human error. Our site has cyclical maintenance activity, so be aware of the dangers and act accordingly.
Smoke Alarm Battery Change Out
JLab's Safety Numbers
56 Days since Last Recordable Accident (JLab record: 331)
JLab Calendar of Events
Nov. 4-6: Director's Project Review of the 12 GeV Upgrade