Photo Detector Development
The efficient detection of scintillation or Cerenkov light over large areas is a key requirement of several particle astrophysics experiments, including DEAP-3600, NEXO, and SNO+.
Photo-multiplier tubes (PMTs) are still the most widely used technology despite being costly, having relatively low efficiency (<35%), and being rather radioactive. New technologies are likely to displace the PMT technology in particle astrophysics applications if they can meet the specific requirements of: low radioactivity, large area coverage, high efficiency over a range of wavelengths (from the visible down to vacuum ultra-violet), the ability to detect single photons, and in some cases excellent timing resolution.
New technologies are becoming mature for our field as witnessed by the complete replacement of PMTs by silicon photo-multipliers (SiPMs) in medical Positron Emission Tomography scanners in the last 10 years following the development of these devices for particle physics in a few experiments and in particular in the T2K experiment that had a strong Canadian participation.
Scientists within the Canadian particle astrophysics community are at the leading edge of the technologies required for new photo-detectors. The efforts driven by particle astrophysics applications are expected to yield compelling solutions in other fields where large area photo-detectors are required, such as for the detection of radioactive material.
Through the CPARC initiative all aspects of photon detection pertaining to particle astrophysics applications will be developed by setting up a multi-institution collaboration.
One group focus will be the integration of components into a package that is suitable for particle astrophysics applications. This effort will concentrate on creating a low-radioactivity envelope considering material selection, electrical feedthrough designs, cryogenic properties and the development of high-tech manufacturing capabilities that will facilitate production of hundreds of square meters of photomultiplier devices.
Collaboration with groups developing large area micro-channel plates is foreseen. This group also intends to lead the development of hybrid photo-detectors combining a PMT envelope and photo-cathode with a silicon-based gain stage.
Collaboration with other groups in particle physics and nanotechnology to investigate candidate photo-cathode materials that might provide advantages in manufacturability, photo-efficiency, low background or cryogenic performance, will be essential and made possible with CPARC funding. This work will benefit greatly from the low-background counting technologies being developed in parallel, and plans include a facility at SNOLAB to test these packages in a low background environment.
Other efforts will be focused on hybrid PMTs. This device offers good coverage and timing and works at room and cryogenic temperatures. In the past a close collaboration with manufacturers Hamamatsu Photonics and Schott Glass was established to develop and characterize the PMTs for SNO, and then DEAP. This resulted in a significant improvement in terms of efficiency, timing charge resolution and low radioactivity. The effort to develop hybrid PMTs will build on this experience. The Si based parts are similar to those needed for making large arrays but have lower requirements in terms of noise and cross talk and are therefore easier to make.
Another effort will focus primarily on the development of a silicon-based solution for overall detection or as a gain stage in hybrid photodetectors. The investigation of large-area SiPMs planes for potential use in the next generation detectors with liquid Xenon (NEXO) and liquid Argon (DEAP next generation) is a priority. The work will be in collaboration with SiPMs manufacturers in Canada. The main focus will be on the development of 3-dimensionally integrated SiPMs that are being pioneered by University of Sherbrooke in collaboration with industry partners and promises to achieve outstanding performance in term of power dissipation and timing resolution. This work has important synergies with other projects at TRIUMF in nuclear physics, material science, (micro-PET MR and PET brain scanners) and particle physics (e.g. ATLAS Inner Tracker), and TRIUMF has the infrastructure to support detector design, engineering, fabrication, and electronics development.
A further program will focus on the integration of individual SiPM ‘tiles’ into modules of larger area. The performance of these integrated modules will be investigated in a cryogenic test chamber. Specialized low-photon-intensity light sources will be developed to measure cross-talk and detection efficiency of the modules. The mechanical sustainability during cool-down will be tested as well. These groups will develop the expertise and knowledge required for the mechanical integration and read-out of SiPM tiles, and the development of electronics associated with photodetector readout and large capacitance SiPMs.
The development of methods to employ these photo-detectors in noble liquids will benefit from the strong engineering and technical resources provided by CPARC to develop complete detector packages. There is also an interest in exploring their potential application for large area photodetection aimed at homeland security, for example for container scanning.
The development of a complete solution will require strong collaboration among all institutions and engagement with local industries, each contributing relevant expertise. The allocation of resources will maximize the contribution from each institution, create expertise across Canada, and provide opportunities for the training of HQP. The infrastructure for this research program will be a part of a CFI proposal by Carleton University.