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

[Yves Van Haarlem]

Hi Lubomir,

> - the maximum amplitude of the first peak (this is what you mean by 
> amplitude, right?)
Yes

> is almost constant, except at the extreme  track 
> positions. One expects this because this amplitude is related the cluster (or 
> few clusters) that is closest to the wire and should not depend on the path 
> length. To make sure that this correct, could you make a profile plot: the 
> mean amplitude vs drift time, excluding the overflow channels.
I added this plot (non-tracked and tracked version) on
http://www.jlab.org/Hall-D/software/wiki/index.php/Energy/Amplitude_as_a_function_of_drift_time

It is fairly constant, there is a slow trend downwards.

Cheers,
 	Yves



>
> Thanks,
> Lubomir
>
>
>
> On Wed, 7 Jul 2010, Yves Van Haarlem wrote:
>
>> 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 r?p?te: 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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