Setup a photomultiplier tube test bench for use at LHAASO-KM2A

To fulfill the requirements of testing the photomultiplier tubes of the electromagnetic detector at the Large High Altitude Air Shower Observatory (LHAASO), a multi-functional PMT test bench with a two-dimensional scanning system is developed. With this 2D scanning system, 16 PMTs are scanned simultaneously to test their uniformity and cathode transit time difference, and we can also perform PMT tests of SPE spectrum, gain vs. high voltage, linear behavior and dark noise. The programmable hardware and intelligent software of the test bench make it convenient to use and provide reliable results. The test methods are described in detail and primary results are presented.