sPHENIX discussion of the superconducting solenoid

[Kin Yip <kinyip AT bnl.gov>]

Hi,

As Achim has disclosed earlier, we reached ~4830 A this afternoon and due to the availability of Liquid He, we stayed for ~40 minutes. They actually watched that the gas-cooled lead voltage stabilized, stopping to go up, before they started the slow discharge.   Carl and the Cryo group have been discussing about optimizing the lead flow rate from 0.27 g/s to 0.33 g/s as the max.  (at 5000 A).   Brian van Kuik told me that the max. they reached was ~0.31 g/s.

This morning, when we tried to ramped to 2 A/s to 4000 A, the pet page etc. suddenly all disappeared in front of us (in 912 or my office or anywhere).  The C-AD control file system crashed !   When did this happen last time ?!    One felt like everything was against us, at that point.   At that time, the power supply/magnet was ramping up and after the file system crash, we could only observe from Zeynep's quench-detection system (PXIe) screen  or  Pablo's power supply touch-screen :-)   Around 2500 A, Carl's phase-locked-loop (PLL) was lost which causing Zeynep's PXIe to issue a fast-discharge (for quench protection) --- which had not happened since we started testing in 912.   Maybe, the loss of PLL was due to the control system failure or maybe not ??!   ( Depending on who you ask ... )   We couldn't ramp (even John Morris discouraged from there doing so) as there was no Logging (slow
logging or fast logging) to monitor etc.

Luckily, shortly before 1 pm, the control system was back to operation.   After testing a bit at 100 A, we started ramping at 2 A/s to 4000 A and then 2 A/s in 200 A step (or 230 A for the last step).    

As mentioned, we reached ~4830 A and stayed there for ~40 minutes and did the slow-discharge, to avoid the Liquid Helium tank being empty.  The slow-discharge is slow and the calculator that I created said that it'd take ~6102 seconds to go from 4830 A to 0.   It's slower at the end :-)    Just like BaBar, people don't want to wait for it to slowly go to 0.  So, at below 1000 A (or ~966 A or so), we did a fast discharge.  This saved
waiting for another almost 40 minutes.

I attached the 2018-2-13.gif for today's current and Magnetic field.  Our Opera calculation/simulation assuming 1010 steel, for this Return Flux
(Steel Box), predicts a magnetic field of 1.37 T at 4596 A.     At ~4830 A, we got ~1.34 T whereas at 4600 A, we got ~1.275 T.  Almost 7% lower than
expectation.   I guess the probe was probably not exactly at the center and the 40+ years old steel is far from what we expected (rusty too).

A surveyer today was also there trying to measure any sidewards expansion and I heard that he got only 0.002 inch (within their error/uncertainty)
between 0 and 4000 A.   Jon Hock came to my office to make me plot his linear pots and there we also saw the maximum of 0.002 inches between 0
and 4830 A.   All smaller than the engineers have been worried about.

Kin

PS:
I've read Monday Memo and heard about the "new" Day-to-Day Appreciation and Recognition more than once.   I'm trying to fill out the "Group Food Celebration Recognition Form",  https://sbms.bnl.gov/SBMSearch/subjarea/55/5509e011.pdf ,

to see whether it'd work :-)  

On 02/13/2018 02:57 PM, Franz, Achim wrote:

Great news

Magnet is at 4830A = 105% operating point

Sent from my iPhone

Achim Franz

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