A water Cherenkov Detector prototype for the HAWC gamma-ray Observatory

A full-size Water Cherenkov Detector (WCD) prototype for the High Altitude Water Cherenkov (HAWC) gamma-ray Observatory was deployed and is being operated at Colorado State University. The HAWC Observatory will have 300 WCDs at the very high altitude site in Sierra Negra, Mexico. Each WCD will be instrumented with three 8" baffled upward-facing PMTs anchored to the bottom of a 5 m deep by 7.3 m diameter steel container with a self made multilayer hermetic plastic bag containing 200, 000 liters of purified water. The full size WCD prototype is instrumented with seven HAWC PMTs, and scintillators under and above the volume of water. Besides the additional instrumentation, this prototype has the same laser calibration system that the detectors deployed at the site in Mexico will have. This WCD prototype serves as a testbed for the different subsystems before deployment at high altitude, and for optimizing the location of the three PMTs, the design of the light collectors, deployment procedures, etc. Simulations of the light inside the detectors, and the expected signals in the PMTs can also be benchmarked with this prototype. The prototype started operation on March 1, 2011.