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<p class="MsoNormal">Dear all, <o:p></o:p></p>
<p class="MsoNormal">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.
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Please check out the attached slides:<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:4.8pt">1-) Slide 1: <o:p></o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">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 <span style="font-family:Wingdings">è</span> 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<o:p></o:p></li></ul>
<p class="MsoListParagraph"><o:p> </o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">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.
<o:p></o:p></li></ul>
<p class="MsoListParagraph"><o:p> </o:p></p>
<p class="MsoNormal">2-) Silde 2:<o:p></o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">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<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">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<o:p></o:p></li></ul>
<p class="MsoListParagraph"><o:p> </o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">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<o:p></o:p></li></ul>
<p class="MsoListParagraph"><o:p> </o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">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 <o:p></o:p></li></ul>
<p class="MsoListParagraph"><o:p> </o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1">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.
<o:p></o:p></li></ul>
<p class="MsoListParagraph"><o:p> </o:p></p>
<p class="MsoNormal">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.
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Best regards <o:p></o:p></p>
<p class="MsoNormal">Kondo<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">_______________________________________________<br>
Sbs_gems mailing list<br>
<a href="mailto:Sbs_gems@jlab.org" target="_blank">Sbs_gems@jlab.org</a><br>
<a href="https://mailman.jlab.org/mailman/listinfo/sbs_gems" target="_blank">https://mailman.jlab.org/mailman/listinfo/sbs_gems</a><o:p></o:p></p>
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