Friday September 19 through Monday September 22
All shifts began in shutdown.
On Friday evening the temporary lighting in the NuMI stub failed.
On Saturday morning technicians powered down the Education Center, Linac, and MiniBooNE for maintenance. The power for the Education Center was only off for a couple of hours, but power remained off for MiniBooNE and Linac until late in the afternoon.
Early on Monday morning technicians began work on the Main Injector controls that will disable readbacks for each house that they work on throughout the day.
A problem was discovered with the Tevatron (TeV) cryogenic magnet dipoles. The cryostat suspension has sagged over the years, causing the coil package to be very slightly off center with respect to the iron. This offset distorts the field in a way that makes the beam think it's passing through a quadrupole magnet, which in turn causes the coupling to change. The TeV has special magnets (T:SQ) that correct for "skew quad errors," which is what this problem is called. Experts have noticed an increase in current use for these magnets over the years. At the present time these magnets are running rather hard to compensate for the effect. T:SQ can still compensate for the average coupling error, however around the Collider Detector Facility and D-zero experiments, several SQ magnets were removed to install low beta spools. Unfortunately, this means the correction is now not uniform around the ring.
Technicians are adding shims to the lower support bolts of the dipole magnets to lift the cryostats by about 4 mils in these non-uniform areas. Just for general information, in the above drawing the bolts on top are called "smart bolts," while the bolts on the bottom are called "dumb bolts." Dumb bolts are locked in; smart bolts have a spring arrangement to allow them to move with the expansion and contraction of the magnet's cryostat.
Here is a list of work for NuMI that's occurring during the shutdown:
- Install Lambertson magnet and power supply
- Various electrical work
- Equipment surveys
- Various mechanical work
- Install a magnet in stub
- Remove shielding wall
- Install a extraction line
- Install cables and terminations
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