The Large Area Picosecond Photodetector (LAPPD) 8" MCP-PMT: Recent Results

Abstract

The Large Area Picosecond PhotoDetector (LAPPD) is a 200 mm square microchannel plate photomultiplier (MCP-PMT). It is a large area, position-sensitive, high speed, high gain device. It is suitable for detection of light such as Cherenkov or scintillation light. The large area is well-matched to large detection volumes, or imaging applications where tiling of small detectors is undesirable because of cost or lost sensitive area. Time resolution has been measured as a function of both MCP and photocathode voltage. A rapid improvement was observed as the photocathode voltage was raised to 50 volts. At higher voltages, the time resolution continued to improve, but at a diminishing rate. A similar improvement occurred with an increase in MCP voltage, up to a point beyond which there was no further benefit. This point corresponded to a gain of 3.2x106. Gain has been measured as a function of light pulse repetition rate. As the laser trigger rate was increased, the LAPPD gain fell to approximately half of the initial value at repetition rates of 12 to 38 kHz/mm2. These gain measurements were made in the mid 106 gain range. Gain recovery time has also been measured. The LAPPD was triggered with a laser repeatedly at a high rate, then allowed to recover before the next laser pulse. The gain recovered to its initial value with a 15 mS recovery time, and half the initial value with a 5 mS recovery time.