Shrinking or contracting light guides is a problem when photomultiplier tubes (PMTs) are glued to the guides. If there is no way to allow movement of the PMTs, when the temperature goes down, the light guide contracts and breaks the glue joint. The PMTs cannot be left loose to rattle around inside the detector. They must be held precisely, yet gently, and allowed to move.
A device was developed to compensate for wide temperature variations that occur inside the detector volumes. The detectors and their glue joints are built at room temperature. During shipping and deployment, they may experience temperatures of +100 down to –70 °F (+38 down to –57 °C). This device compensates for the expansion and contraction that occurs during these wide variations in temperature.
The device is a precisely made PMT housing. It is housed in a Delrin slide mechanism that holds the PMT in correct alignment while allowing the attached light guide to expand and contract. It allows the light guide to maintain intimate contact with the face of the PMT.