sPHENIX discussion of the superconducting solenoid

[Kin Yip <kinyip AT bnl.gov>]

Hello,

I encourage everyone to read the Elog (99% written by Zeynep) that you may see what we tried to do and were doing :

http://elog.pbn.bnl.gov:8080/elogs/entryList.jsp?ELOG=sPHENIX-Magnet-High-Field-Test_2018

Last Friday, the Cryo group tried to improve last Friday but it seemed that the improvement went "negative".  It seems that they (almost) couldn't re-generate LHe
at a point but later Friday evening, they managed to get it back to 0.41% (of their "tank") per hour.  So, before last midnight, the highest they got
was like 46.37% , instead of ~70% and that's what Paul Orfin had when he started the "slow" cool-down ~midnight.   So, we didn't have much time to start with
this morning, especially the consumption rate is > 8% per hour.

In any case, we ramped to 500A/1000 A at 2A/s and then at 1 A/s to 1200, 1400 .... 2000 A.  We stayed there for ~13 minutes before we did an intentional fast
discharge.    We heard the "Contactor" open and this time the Cryo also made some noise.   Paul told us the He vent.  Carl claimed that he was able to (run up to)
see some He but I was a couple seconds behind and missed it.

I showed a temperature rise (due to eddy current in the Al cylinder when it was superconducting ... and later by itself when it's "normal") of the magnet coil (MT01.jpg), > 14 K.
It took almost 30 minutes to recover.

But right after the "fast discharge", the tank had only 12% left.   And so we had to call it a day (as it took some time for the temperature to go down and the Cryo group
typically likes to avoid below 10%.

2018-2-5.gif shows you the current rise today.   I found that the magnetic field measurement logging was not there when I came to my office from 912 while the test
was happening.   Winston couldn't get it to work remotely.  I walked back to 912 and found that the power lead to the GPIB-to-network box was loose and I was
able to push in a bit (and heard a "click").   I had to switch it off and on to really turn it on again.    I put a tape on the power lead to hopefully prevent it from
accidentally getting loose ...  Anyway, this explains why the magnetic field reading was missing for a large fraction of the current ramp.  The highest B-field
detected today is ~5507 G at ~2000 A


Some other things to note:

--- Pablo didn't say anything to me but apparently he's fixed the Power Supply Current reading !  Bravo !

--- A. Meier came to measure magnetic field at our roped 5 Gauss line.  All were like 1 or 2 G or so, except at Pablo's rack for power supply control (which apparently
generates some minor magnetic field).  But that area was roped off by power supply safety yellow tape anyway.

--- The survey group also

--- Strain gauge readings were screwed (some minutes after the fast discharge) ... and we're trying to see how to recover it ...

--- Last Friday and over the weekend, with conversations among Zepnep, Winston, Al Marusic and myself, we have realized that there was some synchronization problem
for the quenech signals and other voltage tap signals etc.   This hampers our "analysis".   I hope Winston may work on it with Al.



The cryo group is trying to repair the system and depending on how it goes, we may or may not have another run this Thursday.

Kin

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