The Large Area Picosecond Photodetector (LAPPD) 8” MCP-PMT: Recent Results
Racetrack-WH7X - Wilson Hall 7th fl Crossover (Fermilab)
Racetrack-WH7X - Wilson Hall 7th fl Crossover
The LAPPD is a 400 cm^2 microchannel plate photomultiplier with a timing resolution better than 100 pS. It has sensitivity to single photoelectrons with a gain of ~7E6. It incorporates a bi-alkali Na2KSb photocathode, with a peak sensitivity near 360 nm. Photocathodes with quantum efficiencies as high as 30% have been fabricated. The anode has a parallel stripline configuration, with a position resolution of ~4mm or better.
The large area makes the LAPPD suitable for viewing large area scintillator radiation detectors. The high speed response makes it useful for applications such as neutron detectors (i.e. Weinfurther et al., 2018), or Cerenkov light detectors for high energy physics applications. Two LAPPDs were recently used as a telescope in a 150 MeV cancer therapy proton beam, in a project designed to verify beam targeting.
LAPPDs are manufactured with a borosilicate glass envelope, and a fused silica window. The microchannel plates are fabricated using a glass substrate, with 20 micron pores. Thin films are applied to the substrate with the Atomic Layer Deposition technique. These films impart the resistive and emissive qualities needed for charge multiplication within the microchannels. Recently, improvements in the deposition method for an MgO secondary electron emission film have provided a breakthrough in gain, as the MgO retains a high gain throughout the manufacturing process of the LAPPD.
Recent measurements of gain, timing, position and quantum efficiency will be shown, and applications discussed.