Francesca Stocker 16 January 2019 What it should be and what it is for all APAs except APA 3 APA 3 has a disconnected GPlane After putting HV back last week 09January we did not see any signals on U V X Plane of APA 3 ID: 926498
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Slide1
APA 3, disconnected g-Plane Update
Francesca Stocker
16. January 2019
Slide2What it should be and what it is for all APAs except APA 3
Slide3APA 3 has a disconnected G-Plane
After putting HV back last week (09.January) we did not see any signals on U, V, X – Plane of APA 3.
no transparency , something wrong with the G - Plane
Measured capacitance of G-Plane connection on APA 3 = 0.97nF
For other APAs capacitance is around 3nF
Not a power supply problem, no cable issue outside the cryostat
--> G – Plane of APA 3 is NOT connected and can not be biased with a PS
Slide4Good News - we still see signals
We have a self healing system:
When HV is back to nominal the floating G-Plane starts collecting electrons on the wire and after some time it will become transparent and let the electrons from tracks pass through and induce signals on U, V, X.
Natural
self biasing if you want
We cannot measure the potential on the G-Plane, but it must be < -320 V (potential of U-Plane)
Slide5Important questions to be investigated ASAP
Since WHEN is the G-Plane of APA 3 disconnected?
Only after the Christmas break?
During the whole run and we never noticed because it would charge up naturally before we looked at the data?
What is the time that it takes for the APA 3 G-Plane to charge naturally?
How do pulse shapes and
dQ
/dx of APA 3 compare to other APAs?
Slide62018-09-22: G-plane bias voltage @ -665V
APA 1 G plane current
APA 2 G plane current
APA 3 G plane current
1) Since WHEN is the G-Plane of APA 3 disconnected?
Slide72019-01-13: Last Sunday
APA 1 G plane current
APA 2 G plane current
APA 3 G plane current
Moment bias voltage was turned off
1) Since WHEN is the G-Plane of APA 3 disconnected?
Slide81) Since WHEN is the G-Plane of APA 3 disconnected?
Look at the pulse shape and
dQ
/dx of runs during the whole data taking, from September 2018 until now.
How do APA 3 and APA 2 (adjacent APAs) compare?
APA switch
Slide92) What is the time that it takes for the APA 3 G-Plane to charge naturally?
Back of the envelope estimate gives the order of 6h for the G-plane to charge up
Run 6301 (after X-mas break, just after HV back on) should contain the charging up process of the G-Plane, can someone investigate??
Find other runs before Christmas that had a longer time HV off (around October 26/27 3 days off)
Slide103) How do pulse shapes and dQ/dx of APA 3 compare to other APAs?
Look at data