PMT module characterization test bench for the MAGIC IACT telescopes

摘要

The MAGIC experiment includes two imaging cameras capable of detecting faint (down to ＜ 20 photons) and short (≈ 2-3 ns) atmospheric Cherenkov radiation events. To achieve this, the MAGIC cameras employ high quantum efficiency 1 in. diameter hemispherical cathode photomultipliers arranged in 139 modules consisting of 7 pixels each for ease of assembly and maintenance. Each module was subjected to characterization and functional tests in the laboratory using a dedicated measurement setup before they were assembled into the camera. This paper describes the measurement setup and the characterization procedure applied. The measurement setup provides short (≈ 1 ns), stable optical pulses at a wavelength of 355 nm with uniform intensity over the module front surface. Optical pulse intensity is variable over a wide dynamic range in increments suitable for accurate photomultiplier linearity measurement Fixed, repeatable optical pulse intensities are used for single photoelectron spectrum and afterpulsing determination. Operation is automated, requiring around 20 min per module, and is expected to remain stable over the lifetime of the experiment