[Primexd] [New Comment] FCAL LED pulser

[gleasonc at jlab.org]

Comments:
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 - by gleasonc on Mon, 11/19/2018 - 18:18.

Sasha, is this for the - Sasha, is this for the standard production HV settings? Or are all channels set to the same HV?

One thing you will need to keep in mind around the beam hole when using LEDs is the amount of radiation damage in each block (see this image https://halldweb.jlab.org/wiki/images/e/ea/4x4_array.pdf for an image of radiation damage for each channel around the beam hole). The lower amplitude of the bottom row could be due to radiation damage and not a "wrong" HV set point (we know it's wrong in the sense that it is uncalibrated, but there may only be a small correction needed). For this row (27_30,27_29, and 27_28), the HV is set to the max EPICS value of 1800V with the production settings. 

 It would be interesting to check this with the green pulser, at say 25V, as that is not affected as much by the radiation damage. Nonetheless, I look forward to seeing the result with properly tuned HV.

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Logentry Text:
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FCAL FADC waveforms for 3 inner FCAL layers induced by a violet LED pulser operated at 15 V
(data is taken in a raw fadc mode). Each histogram represents the FCAL module. Histograms are 
normalized to 500 fadc counts. FADC amplitudes have different peak values even in the 3rd FCAL
layer, which can be accounted for either different light collection or PMT gains 
(we'll correlate amplitudes with the calibration coefficient obtained by Iliya).

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