sPHENIX discussion of the superconducting solenoid

["Yip, Kin" <kinyip AT bnl.gov>]

Hi,

The sPHENIX Magnet cooling has needed a lot of attention from the Cryo group. 
 The cooling
has been interrupted during works in the RHIC (for the diode/cold-snake 
etc.).  

But in addition to that, the Helium loop (from 10 o'clock compressor to the 
Magnet) has suffered from some 
Helium leak to the extent that the Cryo techs need to pump in He from time to 
time.   In one weekend,
as nobody was there to flush in the Helium, the Helium ran out and air was 
sucked into the system.  This 
created some blockage that needed to be dealt with.  

To avoid the above, the Cryo stopped cooling during the weekend.  However, 
recently when the diode/cold-snake work was completed --- including valves 
etc., Roberto noticed that the leak was reduced and (amusingly to me) we 
benefited from cross-leaking (that is, some He leaking back into our He line 
and thus making up for He leaking out).   So, the He leak is considerably 
reduced.   We now have resumed weekend cooling as well !  😊

I attach a plot.  Top shows the temperatures of the Magnet (black) and the 
extension (blue/red) and the bottom plot shows  the insulating vacuum.

The Extension mass is small compared to the Magnet and so it can rise quickly 
to 160-170K or so (red/blue) in the weekend.  
But the average Magnet temperature (black) don't react so violently.   

[ The black data have so large fluctuations because of the vacuum pump (some 
cross-talks between cables) --- I noticed that during a vacuum 
hiccup (that vacuum pump was turned off), the black curve had much much 
smaller fluctuations (just like the red/blue curves) when the pump
was turned off  and reported it back to the Cryo.    The Cryo electrical 
techs haven't found a way to reduce that fluctuation as the cables
in place can't be easily dismantled or moved. ]

The average Magnet temperature is about 90K or so after the weekend cooling 
has been restored.  Let's hope that it remains so.

Kin

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