The WATer CHerenkov Monitor for Anti-Neutrinos (WATCHMAN) is the first experiment planned for the Advanced Instrumentation Testbed (AIT) facility just starting construction at the Boulby Underground Lab. The main purpose of WATCHMAN is to develop technology and data analysis techniques to demonstrate the ability to monitor nuclear reactors from distances of 10's of kilometers as part of future Nuclear Non-Proliferation Treaties. WATCHMAN will be able to use the Hartlepool Nuclear Power Station (a distance of 25 kilometers away from the Boulby Lab) as the source of reactor anti-neutrinos for this study.
WATCHMAN consists of a cylindrical tank of gadolinium sulfate doped pure water located near the existing lab at a depth more than 1 kilometer underground. The tank size is still being determined, but will be between 20-25 meters in diameter with roughly the same dimension in height. This volume will have a inner fiducial volume of 1-2 kilotons, and between 3500-4500 large format photomultiplier tubes. There will be an outer veto (similar to previous large water detectors) to reject cosmic ray muons and also provide passive shielding from external gamma rays from the rock and steel components. An artist's concept of the detector is shown on the right.
It is expected that WATCHMAN will be upgraded as new technology is tested to improve performance. This is expected to include Water-based Liquid Scintillator (WbLS), large format fast photosensors such as the Large Area Picosecond PhotoDetectors (LAPPDs), and improved conventional Photomultiplier Tubes. Thes developments will allow WATCHMAN to serve as a 5% scale prototype for the proposed THEIA experiment.
WATCHMAN has been approved for construction by the US Department of Energy in collaboration with sister agencies in the UK. The kickoff meeting to move towards a preliminary design was held at Sheffield University in January 2018. This was followed by a visit the Boulby Lab . The picture to the right shows UC Davis students Julie He and Teal Pershing inside the lab with Professor Bob Svoboda.
At UC Davis, we lead the Photomultiplier Working Group and also have repsonsibilites associated with material compatibility of detector materials with gadolinium sulfate and pure water. In addition, we are leading the effort to make sure WATCHMAN is upward compatible with WbLS.
The WATCHMAN Colalboration currently consists of a consortium of universities in the US and UK, with Lawrence Livermore National Lab (LLNL) taking the lead for the construction project. The picture below is of about 2/3 of the collaboration underground at the Boulby Lab in january, 2018.