[Sbs_gems] [EXTERNAL] UV Layer 4 Overview

[Sean Jeffas]

Hi All,

I just wanted to elaborate on the situation on the 4th UV layer, which is
sitting in EEL and waiting as a spare. Each UV layer uses 12 4-slot
backplanes and 4 3-slot backplanes. The 3-slot BPs are defective so we are
using 4-slot BPs in their place. That means that for the three UV layers in
BB right now we have used up every single 4-slot BP. Therefore we do not
have the BPs to equip UV layer 4 to use as a replacement for anything.

I am not familiar with the fixes needed for the 3-slot BPs, but assuming
this is easy and can be done quickly, we still need to recover the 4-slot
BPs from the UV GEMs in BB. This can probably be done by sliding the GEMs
to the side in the BB frame, as we have done before, so we can reach them.
Then we would need to place all the 3-slot BPs on the UV GEMs and test
them. I would estimate we would need 2 days of downtime in the hall for
this. Then we would need to add all the electronics to UV layer 4 back in
EEL, and get it ready in one of the INFN frames and do a cosmic test on it.
Then we would need another day of down time to swap it with J0 in the hall
as we did with J2 earlier.

Overall I think it would take two weeks of work to do all of this. Again I
am completely assuming the fix to the 3-slot BPs is easy, I have no idea.
Maybe Anu can elaborate. Also we will have to wait until the new APVs
arrive to start any of this work. Between all of this and the holiday break
I don't see this layer being used for anything during this run group.

Also as a side note, I will have to dig through some old emails and notes,
but I am fairly certain we accounted for all APVs and there are not enough
to equip all 10 UVa SBS layers and 4 UV layers.

Best,
Sean
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