The TORCH PMT:
Photek are currently in a three year development program with CERN to produce a novel square PMT for the proposed TORCH detector which is aimed at the upgrade of the LHCb experiment. The PMT will be MCP based for the inherent timing accuracy that this brings, and has three main novel features that need to be developed:
- Long lifetime, it should be able to produce 5 C / cm$^2$ of accumulated anode charge without noticeable degradation in sensitivity.
- Multi-anode output with a spatial resolution in the “y” direction of 0.4 mm and 6 mm in the “x” direction.
- Close packing on 2 opposing sides with an active area fill factor target of 88% in the “x” direction. We will describe the work completed so far including the building and testing of lifetime prototypes, multi-anode prototypes and high fill factor (square) tube body shape developments. Previous work published by Photek has demonstrated a significant lifetime improvement in an MCP-PMT when the MCP is coated by Atomic layer Deposition (ALD). We believe that the ALD layer forms a barrier that prevents the outgassing of material from the MCP under heavy electron bombardment that, from an uncoated MCP, gets ionised and reacts with the photocathode, thus reducing the sensitivity. The front-end read-out of choice is currently the NINO ASIC and we will describe our developed method of efficiently coupling the PMT output pads to a PCB through an ACF film that minimises any parasitic input capacitance by allowing very close proximity between the NINO and the detector. We will also report on preliminary results from a charge sharing technique that enables position resolution that exceeds the granularity of the multi-anode.