A next-generation multi-PMT optical sensor for IceCube-Gen2

A new in-ice optical sensor, the Long Optical Module (LOM), is under development for IceCube-Gen2, the proposed expansion to the IceCube Neutrino Observatory at the South Pole. The sensor design encloses 16 new 4-inch Photomultiplier Tubes (PMTs) in a borosilicate glass pressure vessel, distributed homogeneously to guarantee full angular coverage. Challenges arise for the mechanical design from the tight constraints on the bore hole diameter and from the close packing of the PMTs. A support structure has been designed to enable precise alignment of the PMTs. The supports also aid in coupling PMTs to the pressure vessel using moulded optical gel ‘pads’. The conical gel pads provide an increase in photon collection efficiency, and enhance the module sensitivity.  Modular electronics have been custom-designed to fit into the available space and to minimize cost and power requirements for the ~10000  modules to be installed. We will provide an overview of our approach to these design considerations and summarize the results of our tests and simulations. Prototype modules will be installed in the upcoming IceCube Upgrade.