[Halld-pid] TOF PMT bases and gain

[Beni Zihlmann]

Hi All,
looking at the PMT specifications it is recommended to keep the 
operating parameters
such that the overall current is below 0.1mA.
I did some estimations based on a few assumptions and summarized the 
conclusions in

http://www.jlab.org/Hall-D/software/wiki/index.php/Detector_Rates_and_Lifetime

the assumptions are that we want a mean signal amplitude for MIPs of 
about 1000mV
when they pass through the middle of the paddle. I used GlueX-Doc 1471 
to get the
background rates and mean relative signal hight. I assume a signal 
length of about 25ns
with a triangular shape and a 50Ohm load.

The conclusion is that we should have special bases for the innermost 3 
full paddles
(closest to the beam line) as well as for the short paddles.
These special bases should be operated at a much lower gain so that the 
amplitude
of the mean background signals is below 100mV but then add an amplifier 
at the
location of the base maybe integrated into the voltage divider.

cheers,
Beni