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Taritree Wongjirad, 10/05/2015 10:15 AM

PMT - Overview

As a shifter, your responsibilities will be to alert the light collection experts about PMT alarms, start calibration runs, and help ramp the PMT HV up and down. Eventually, shifters will be able to ramp the PMT HV up and down themselves during normal operation (i.e. not after HV trips). However, to start off with, any requests to ramp the HV up or down will require calling the on-call light collection expert. The expert will then do it. This even includes in the middle of the night. It's OK we don't mind! Try the on-call expert first. If the expert cannot be reached try the following experts (in order):

  • Taritree: 701-471-0048
  • Jarrett: 208-407-6680
  • Matt Toups: 919-451-2633

In the event of a trip, please log the trip into the e-log and then call the on-call expert. If the expert cannot be reached, try calling the above experts. For information on the alarms, please see the PMT-guide page.

Some background information

The light collection system consists of 36 optical detectors: 32 8" PMTs and 4 2" PMTs. The 8" PMTs look at a TPB-coated acrylic plate that shifts 128 nm scintillation light to the visible (blue) that the PMTs can see. The 2" PMTs look at TPB-coated acrylic light guide paddles.

The following diagram shows how the PMTs are arranged in the cryostat. The upstream portion of the detector is to the right of the diagram.

Below shows a schematic of the cable connections for one PMT between the PMT, its HV source, and the readout electronics. The signal comes out of the PMT, through the cold and warm RG316 cables that connect at FT11, and into one of 48 splitter circuits located in a box installed in the PMT/TRIG rack. The splitter circuit guides the HV from the supply and splits off any signals through the coupling capacitor. Note that for each splitter, and therefore each PMT, there are 4 copies of the waveform that leave the splitter and go into the PMT readout. Two copies go through a 0.18 attenuating circuit (in the splitter); the other two go through a 0.018 attenuation circuit. The former copies are referred to as the "high gain" signals, while the other two are the "low gain" signals. Each copy then leaves the splitter and goes into a shaping amplifier. The output of the shaping amplifier then goes to the FEM (front-end module) which digitizes the signal coming from the cable and performs trigger logic on the digitized waveforms.