Speaker
Description
An R12860 photomultiplier tubes (PMTs) with a box-and-line dynode structure, manufactured by Hamamatsu Photonics, has been developed for the next-generation water Cherenkov detector, Hyper-Kamiokande. Detector operation is scheduled to begin in 2028, featuring the world’s largest target mass of 260 kton of ultra-pure water, enabling a broad physics program including neutrino studies and nucleon decay searches. The improved performance of the new photodetectors allows the construction of a deeper water tank, providing approximately twice the tolerance against high hydrostatic pressure. These PMTs deliver enhanced physics sensitivity through a factor-of-two improvement in timing resolution and single-photoelectron detection efficiency, as well as a uniform response under varying magnetic fields and light-injection positions.
To finalize the PMT design for mass production, the amplification structure was optimized to ensure stable gain under high-rate and high-light-yield conditions, as well as uniform performance in surrounding magnetic fields. Additional studies focused on reducing radioactive contamination and suppressing radon emanation through careful material selection. Quantum efficiency in the short-wavelength region was improved by enhancing the glass quality. Mechanical strength was evaluated through extensive hydrostatic pressure tests with controlled glass thickness. In addition, an anti-implosion protection cover was developed to ensure stable long-term operation in the 70-m-deep water tank. Long-term stability and in-water detection performance have been verified using more than 100 PMTs installed in the 50-kton water volume of Super-Kamiokande since 2018.
Mass production of about twenty thousand PMTs was carried out from 2020 to 2026. PMT performance over this six-year period was assured through a continuous quality-monitoring system, including two temperature-controlled 8-PMT test rooms, two 100-PMT dark-noise stability monitoring rooms, and a 16-PMT setup for year-long aging tests. Signal checks and visual inspections were performed to confirm adequate waterproofing and mechanical integrity. With installation planned for 2027, a full-scale screening system is currently under preparation.
This poster presents the achieved performance improvements and the quality-assurance results obtained during mass production, demonstrating the readiness of the PMTs for the successful operation of the Hyper-Kamiokande experiment.