[Primexd] [Revised Logentry] CCAL LED/ALPHA trigger adjustment

[somov at jlab.org]

Logentry Text:
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We adjusted LED and Alpha triggers for two reference PMTs.
Each CCAL reference PMT detects light from the LED optical
fiber and YAP:Ce Am source (alpha source trigger) attached
to the PMT face.


1. LED trigger is generated by the CAEN 1495 module and 
is distributed to the TS front panel (bit 5).


2. The alpha trigger is produced by each reference PMT 
(we OR triggers from two PMTs). We use NIM modules to veto
PMT signals induced by the LED pulser, and select 
alpha-source signals only. The alpha-source trigger is 
subsequently sent to the TS FP ( bit 6 ). The trigger rate is 120 Hz 
(the discriminator threshold was set to 25 mV).

3. We adjusted HV on each reference PMT in such a way,
that both, the LED and alpha-source signals are within
the fadc  amplitude range. The LED bias voltage was set to the 
maximum value of 29 V.


HV (reference PMT1) = 850 V
HV (reference PMT2) = 790 V

Fig. 1 FADC waveforms induced by an LED trigger (TS FP bit 5)
The first pulse (around fadc sample 38) corresponds to 
the noise in the LED distribution system, and has to be reduced. 

Fig. 2 and Fig. 3 FADC waveforms induced by an Am alpha source.

Fig. 4 and Fig. 5 FADC peak amplitude for the LED and alpha source 
for two reference PMTs

Fig. 6  FADC peak amplitude produced by alpha sources for two PMTs
(zoom in distribution).

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run 60289  (data1)   LED      (TS FP bit 5 only) 
run 60291 (data3)    Alpha trigger   (TS FP bit 6 only) 
 

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