The system is a part of the MicroBooNE experiment, a 170 ton liquid argon time projection chamber being built inside a 12 meter long steel cryostat at the Fermi National Accelerator Laboratory in Illinois. The detector will record the interactions of neutrinos in the 1 GeV energy range, looking for signs of oscillation anomalies and developing US experience with liquid argon neutrino technology. The light detection system, which is supported by the National Science Foundation, is a vital component of the detector and will act as a trigger for the experiment, allowing the separation of activity caused by neutrino interactions from a pervasive, much higher rate background of cosmic rays.
As of December 19th, the optical system will not be seen again for several years. On this date the time projection chamber, a 2.5 x 2.5 x 10 m steel box weighing several tons, was installed in the MicroBooNE cryostat. With this component in place, the optical system has become permanently inaccessible for maintenance or adjustments until after the experiment has completed its three year neutrino run. The optical system group, which is formed primarily from MIT graduate students and postdocs, spent the last weeks of 2013 carefully testing the completed system during the night times and making final tweaks and tune-ups during the day.
Once all groups were ready, the time projection chamber was slowly rolled into the open end of the vessel on a hydraulic cart. This several hour procedure involved the support structure passing within less than an inch of the delicate glass photomultiplier tubes and quartz fibers, and within two inches of the vessel walls. Postdoc Matt Toups, and myself, an LNS graduate student, were a part of the team which performed the installation.
My role in the operation was to be one of two team members, the other a Fermilab engineer, who would be inside the cryostat as the chamber was rolled in. For most of the operation I retreated steadily behind the back corner of the steel structure, looking for any mechanical interferences with a flashlight as the cart advanced. For the final few feet of the insertion there was no longer standing room, and I found myself squeezed into the back rim of the cylindrical vessel in order to view the chamber passing last few optical units. After the roll-in was complete, I shuffled underneath the chamber to confirm the alignment of the support pins, after which the steel structure above me was lowered into place on the hydraulic lifts. After a final check on the positioning of the optical units, I army-crawled out of narrow space under the chamber and emerged to celebrate successful installation of the two MicroBooNE sensitive detector systems with the rest of the team.
In January 2014 the end cap of the vessel will be welded closed and the complete detector will be transported to its permanent home in the booster neutrino beam line. It will then be filled with high purity liquid argon, ready to begin detecting neutrinos events in summer 2014.
Plates coated with wavelength shifter (which shifts the 128 nm light
produced in liquid argon to the visible) are placed in front of the PMTs
before the TPC slides in.
Ben's view of the TPC as it is pushed into the Cryostat. You are
looking through the HV field cage. The phototubes
are on the right.
The view from the outside, in the clean tent, as the TPC is pushed
into the cryostat.