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

[Lubomir Pentchev]

Hi Yves,

Thanks for your fast response and sorry about Germany.

Indeed you explained most of the problems. As for the energy/amplitude 
vs drift time plots you are right, they look as expected:
- the mean energy goes down as the path length of the particle crossing 
the tube goes down, as well,
- the maximum amplitude of the first peak (this is what you mean by 
amplitude, right?) 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.

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 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
>
>
>
>                          /--------------------------------
>                         /   Yves Van Haarlem
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