Performance Test of Fine Mesh PMT in Strong Magnetic Field

Abstract：

The performance of a fine mesh photomultiplier tube (PMT)—Hamamatsu R5924(FM) to be used for the time of flight (TOF) counter in the upgraded Beijing Spectrometer (BESⅢ) was investigated in a strong magnetic field up to 1T. The dependence of the PMT relative gain on the magnetic field intensity at both 0°and 180°directions were measured. It was found that the relative gain of the PMT is reduced by a factor of 50 or more at 1T magnetic field compared with no field case. The relative gain of the PMT vs. the working voltage at different magnetic field intensities (0,0.5,1T) were also measured. An exponential dependence of the relative gain on the working voltage was observed for a wide range of the working voltage. Moreover,the factor k in the secondary electron emission ratio δ is measured to be less than the nominal value due to the special fine mesh structure of PMT's dynodes and it decreases with the increasing magnetic field intensities. It is the important reason that the gain of PMT decreases in case of strong magnetic field existence.