University of Wisconsin-Madison Physical Sciences Lab

Learn More: Daya Bay

[Conceptual drawing of cylindrical detector]

PSL and the UW team have primary responsibility for the design and fabrication of the anti-neutrino detectors (AD). The UW team led by Assistant Professor Karsten Heeger coordinates the activities of engineers and scientists at several universities and collaborates closely with Berkeley, Brookhaven National Laboratory and the Institute of High Energy Physics in Beijing. The unique engineering resources of PSL allow the UW to make the single largest university contribution to this project.

PSL has a broad range of project responsibilities. Key to the detectors is the construction of eight pairs of thin-walled, nested acrylic vessels that allow the detection of the faint light generated in the anti-neutrino interaction with the detector liquids. PSL mechanical engineer Lee Greenler is responsible for design and analysis of the thin-walled vessel. A prototype vessel was fabricated at Reynolds Polymer of Colorado, which proved to be very challenging. Late in October, a dimensional and leak check of the prototype was performed and it was on spec and the lid sealed perfectly. A contract has been placed for the fabrication of the eight production tanks; the first two are being built now. The 3m acrylic vessel to nest inside the 4m vessel is being built in Taiwan to the PSL design. The 3m inner vessel will be filled with the “target,” a special Gadolinium doped liquid scintillator. The space between the 4m and 3m will be filled with undoped liquid scintillator, and the outer space will be filled with mineral oil.

To meet the delicate structural constraints of this nested vessel system the liquids must be introduced into the various detector volumes at the correct rate so they are always at about the same level on both sides of the thin walls. PSL mechanical engineer Dan Wenman has been working with Tom Wise on designing a filling system that carefully controls this process and will measure the target mass to an unprecedented precision of <0.1%.

In addition to the vessel design, there are eight “dry boxes” on each AD to allow passing cables carrying high voltage and signal to the PMTs inside the tank. PSL has made over 1600 feedthrough plugs and shipped them to Hamamatsu for attachment to the PMT cables. Interface rings for mounting the dry boxes to the tanks were also manufactured at PSL and shipped to China to be welded into the outer stainless steel vessel. PSL mechanical engineer Jeff Cherwinka has been working on the dry box design and visited the plant as part of an international team to survey the progress and coordinate interfaces. PSL electrical engineer Dan Wahl has been working on the cables and connectors.

Civil construction of the tunnels and the surface facilities is progressing. The surface assembly building will be done by the end of 2008 so that the prototype 4m vessel can be shipped there and an assembly test can be performed with the first 5m stainless steel tank and a prototype 3m acrylic vessel. The assembly and filling of the first pair of detectors is scheduled for completion in late 2009.

The UW Physics Dept. also has a description available.