[Halld-cpp] [New Logentry] Continued Noise Investigation

[davidl at jlab.org]

Logentry Text:
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Some effort was made in the hall over the past few days to reduce the amount of noise in the MWPC. Several people 
were involved with numerous tests. One thing that seemed to reduce the amplitude of the noise was simply grabbing
the chamber itself, using the capacitance of the human body. I took a few runs this morning under various conditions.
These are described below. For all of these runs, the HV cable was connected to both the chamber and the CAEN
supply but the HV itself was off.

Run 257: Attached chamber ground plane to u-metal cylinder via large copper wire with copper clamps. The 
cylinder was found in the hall. It was made from a sheet that was rolled up into a cylinder that was approximately 
1 ft in diameter and 1ft tall.

Run 258: Grabbed the chamber firmly to use human body as capacitor to absorb noise. Gripped at roughly center of
HV side of chamber. Both upstream and downstream sides were in contact with skin.

Run 259: No additional capacitor/grounding attached.

Run 260: Attached a large metal trashcan using copper cable with clamps. The can was placed on some cloth to
make sure it was electrically disconnected from platform.


The figure below shows the maximum sample height vs. wire number for each of the 4 runs,.
[figure1]


The following figure is made by projecting wires 73-79 from the above plots onto the y-axis.  This indicates that the human
body and the trash can give similar improvements. While in the hall, the u-metal shield appeared to give an improvement
when observing from the scope, but that does not seem to be the case in these plots. One difference from the u-metal and 
the trash can is that the trash can was placed on cloth in order to insure electrical isolation from the platform itself. The u-metal
was left to sit on the platform. It is unclear if the paint on the platform gave sufficient resistance to isolate the u-metal.
[figure:2]


OBSERVATIONS:

1. There is still a strong dependence on wire number for the noise with wires near the center of the chamber being more affected.
One possible action is to solder additional cables to the HV board grounds and connect them to the ground planes as is already done
at the top and bottom of the chamber.

2. Several wires seem to have significantly lower noise (e.g. wires 63 and 64). It is not clear what is different about these wires.

3. A Number of people have commented on possible solutions. These all tend to involve installing good shielding around all of the
sense boards with thick, short contacts between the sense board ground and the shielding,



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This is a plain text email for clients that cannot display HTML.  The full logentry can be found online at https://logbooks.jlab.org/entry/3546081
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