[Sbs_gems] [EXTERNAL] Efficiency plots from SBS-14 GEM studies

[Gnanvo, Kondo (kg6cq)]

Dear all,
I produced a couple of efficiency plots from the GEM scan studies performed during SBS-9 with LD2 with beam current from 1 to 10 uA.

Please check out the attached slides:
1-) Slide 1:

  *   on the left: is the GEM current vs. beam current for each of the 8 GEM chambers so basically a different way to look at Anu linearity plots. So of course the current increases (negative value ==> drop on the plots) as the beam current increases  and the drop is more significant for the UV layers than the 4 X-Y modules of the back layer



  *   On the right: is the efficiency for the same layers vs. beam current. The trend is the similar although not necessarily correlated with the current drop (or excess current). For example UV layer 3 efficiency drops more faster than the other 3 layers even though the GEM current drop (or excess current) is less pronounced.


2-) Silde 2:

  *   This is more interesting, Here I am plotting the efficiency as a function of the excess current (relative to the measured current for 1 uA) for each chamber
  *   I keep both x and y axis to the same scale so that we can concentrate on the amplitude of efficiency drop for same range of excess current



  *   Here, it more interesting to look at the 4 bottom plots for the XY modules where the GEM current drop is less than 10 uA for all 4 modules which represent less than 1.5% of the nominal GEM so this should not cause any efficiency drop, but we are still looking at 20 percentage point drop at the minimum for each of these modules



  *   This 20 point drops in efficiency for such small current increase can only be explained by fake tracks from the 4 U-V layer. My hypothesis is that these fake tracks are partially caused by the negative pulses impact on the common mode calculation



  *   Efficiency drop on the 4 UV-module for a excess current range of 10 uA is limited to a couple of percentage point typically less than 5% which is 4 time smaller and I suspect that the XY layer which is less prone to these negative pulses reduce the probability of fake tracks and therefore the efficiency drop.


I think this is another clear indication that solving the divider hardware issue is only going to get us that far unless we address the negative pulses issues.

It will also be good that the similar plots are produced for the other GEM studies and correlated with the common mode calculation. I would not have time to do so though

Best regards
Kondo



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