[Halld-tracking-hw] [CDC] preAmp follow up on todays meeting

[Yves Van Haarlem]

Hi All,

This is to follow up on the discussion we had on todays meeting.

After watching Germany lose I locked myself up the lab and noticed that:

1/ That weird noise peak, mentioned in the meeting, is caused by the 
thermo-couple. If I switch off the T-controller that peak disappears.  It 
makes sense because after we fixed a gas leak the thermocouple must have 
moved closer to the straws, it is around this time this noise appeared. -- 
problem solved at the moment by switching off the T monitoring. Also, the 
noise is higher in amplitude on straws close to the T-couple.

2/ By comparing drift time spectra of the old preamp (as in the published 
paper) with the new preAMp at 2100V and 50-50 gas. It can be seen:

http://www.jlab.org/Hall-D/software/wiki/index.php/Drift_time_comparison_(gas_check)

that the new preAmp shows that the longest drift times are 100~ns shorter 
compared to the old measurement, this means that the gas mixtures are 
different. L'histoire se répète: mysteries with the old pre-amp were 
explained by wrong settings of the gas flow controllers. Now the mystery 
of the new preAmp has again something to do with the gas mixture. Indeed 
Beni, it looks like a 60/40 Ar/CO2 gas: both drift-time as 
efficiency-curve wise. Back then the problem with the gas mixer was easily 
fixed because some settings were wrong, now it has to be something else.

Personally I do NOT think it is worth to send the preAmps back before we 
solve this gas problem. If you still want me to send them to J-lab please 
ask me to do so.

The way we can solve/avoid the gas problem is to compare with pre-mixed 
gas: we have 90-10 Ar-CO2 premixed. This will take time... Or we can order 
50-50 premixed and repeat our studies, or we just put the 90-10 premixed 
in and compare with the measurements done for the paper and track down 
problems with the gas mixer later. Personally I would go with the last 
options because this produces results concerning the new preAmp faster.


3/ The plots requested by Lubomir with Energy/amplitude as a function of 
energy (using cosmics) can be found here:

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

Expected behavior can be seen, this data is not tracked (to save time), so 
some noise hits are present. Let me know if you want the tracked version 
too.

Cheers,
 	Yves



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                          /   Yves Van Haarlem
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