Performance of fine mesh photomultiplier tubes designed for an undoped CsI endcap photon detector

Abstract We have developed two types of fine-mesh photomultiplier tubes for an undoped-CsI endcap photon detector installed in a strong axial magnetic field. These photomultiplier tubes have ultraviolet-transmitting glass windows, backed by large-area bialkali photocathodes, in order to efficiently detect scintillation light from undoped-CsI crystals. A gain of more than 2 × 10 5 , in a magnetic field of 1.0 T, was obtained from these tubes with 19-stage fine-mesh dynodes. Gain drops caused by the magnetic field and by high anode currents were investigated. Several performance criteria of the tubes were studied: gain, quantum efficiency, linearity, noise, and transit time spread.