Analysis of Sources of Dark Noise from Quartz PMTs in JLab Hall B CLAS12 HTCC

The High Threshold Cherenkov Counter (HTCC) at Thomas Jefferson National Accelerator Facility (JLab) in experimental Hall B is one of the detector systems of the CLAS12 spectrometer used to generate fast trigger signal in electron experiments. The CLAS12 HTCC has 48 channels with 5” PMTs with quartz faceplate to detect Cherenkov light. Our plans are to re-calibrate and study overall performance of the PMTs, to replace them as needed, and to run some tests to find ways to reduce the dark noise in the HTCC channels. Several potential sources of the noise could be the presence of helium, the features of the power supply, or temperature-dependence of the components. It has been observed after-pulses in some PMTs while re-calibrating. We suspect that the culprit could be helium gas in the PMTs. The HTCC is mounted between a superconducting Central Solenoid and a superconducting Torus magnets. Helium in the experimental hall could be from small leaks, as well as from magnet quenches or their tests. This talk is a culmination of our efforts in both identifying and reducing the dark noise in the HTCC channels.