[Halld-cpp] [New Logentry] More HV cable noise investigation.

[davidl at jlab.org]

Logentry Text:
--
I spent a little time looking into the noise issue, trying to follow up on Ilya's investigation of the HV cable.
I tried a few things:

1. wrapped a thick copper braid around the SHV connector (chamber end) shielding while it was plugged into the chamber. I wrapped the other end around one of the large cylindrical posts sticking out from the chamber. The braid was secured in both places with a tie wrap to hold it firmly against the metal I was trying make. contact with.

2. Same as above, but wrapped it around an exposed structural point of the unistruct support. 

3. Routed a different HV cable under the stairs and plugged that in.

 To check the effect, I ran the DAQ and viewed single, live events with the fmwpcview program. None of the changes appeared to have a significant effect other than when I disconnected the cable completely. These tests were all done while run 251 was in progress.

To get clean samples, I also took some dedicated runs with different conditions as listed below.

Note: These were all done with 90/10 gas that had been flowing through the chamber for a week.
Note: The HV was always turned OFF



Run   #events     Conditrions
-----  ------------   --------------------
252     4.7k        No HV cable plugged in at Chamber.
253     2.1k        Normal HV cable plugged in (chamber end only)
254     2.0k        Alternative HV cable (routed under stairs) plugged in (chamber end only)
255     2.0k        Same as 254 but with Al tape connecting HV board to grounding plane in middle of chamber
256     2.0k        Same as 255 but with Al tape connected better (touching strip connecting boards rather than just taped to through-holes)


Runs 255 and 256 were taken after noticing that the HV ground has connections to the outside of the grounding planes only at the top and bottom of the chamber. The figures below show where the connections are and how they are made. The thinking was that this could explain the asymmetry in the noise levels between the center and edges of the chamber. An attempt was made to connect the centermost jumper to the grounding planes with Al tape. This may not have made a very good connection though.

[figure:1]
[figure:2]


Before leaving, the nominal HV cable was reconnected on both ends. The HV to the chamber was left off, but the HV to the
PMTs was left on. 


---

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/3544983
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