[Esr-users] Hall C dipole shms magnet

[Steve Lassiter]

Hi Rolf, 

Actually the SHMS magnets were in the process of being ramped up to their maximum currents and then down to the operating currents. This is the procedure for for reproducing repeatable fields when using current regulation due to hysteresis of the magnets. 
The issue with the warm return valve not opening fast enough can be addressed easily enough by changing valve settings. 

Still collecting data on the event and will report more later. 

Steven 
----- Original Message -----

From: "Rolf Ent" <ent at jlab.org> 
To: "Steve Lassiter" <lassiter at jlab.org> 
Cc: "Dave Kashy" <kashy at jlab.org>, "Cryo" <esr-users at jlab.org>, "Thia Keppel" <keppel at jlab.org>, "Javier Gomez" <gomez at jlab.org>, cperry at jlab.org 
Sent: Tuesday, December 12, 2017 3:10:15 AM 
Subject: Re: Hall C dipole shms magnet 



Hi Steve, 



Seems the issue is really why both the warm return and primary relief 
did not act as supposed at this fast discharge, and the pressure in the 
magnet kept building towards a rupture disk doing its job. 



Was good that we were only at relatively low SHMS momentum settings, 

so not much power stored in the system. 



Good luck! 


Best regards, Rolf 


----- Original Message -----

From: "Steve Lassiter" <lassiter at jlab.org> 
To: "Dave Kashy" <kashy at jlab.org> 
Cc: "Cryo" <esr-users at jlab.org>, "Thia Keppel" <keppel at jlab.org>, "Rolf Ent" <ent at jlab.org>, "Javier Gomez" <gomez at jlab.org>, cperry at jlab.org 
Sent: Monday, December 11, 2017 9:26:43 PM 
Subject: Hall C dipole shms magnet 


Hi 

The Hall C SHMS dipole magnet tripped off this afternoon at about 4 PM. 
The dipole trip caused the rest of the SHMS magnets to trip one after the other probably due to lead flow interlocks. 

The dipole on line data evidence shows that this was a normal fast discharge. 
A fast discharge of this magnet causes some coil heating due to eddy currents and this results in pressure and temperature rise in the coil. 
Helium is usually vented by opening the warm return to keep Helium out of Hall C. 
The warm return did not open fast enough and the pressure rose in the magnet reaching finally 5 atm. 
The primary relief appears not to have opened at all or if it did open, it did not open far enough or long enough to limit the pressure. 
The rupture disc worked as expected and vented the magnet and limited the pressure to 5 Atm. 
When we entered the hall and inspected the SHMS dipole magnet the rupture disc was heavily frosted and still venting at a low rate while the mechanical relief valve was warm to the touch and dry. 

The SHMS dipole was completely isolated and the rupture disc replaced. 
We have set up a low rate ie. few grams per sec. ~ 80 K Helium purge thru the SHMS dipole to measure contamination levels overnight. 

Cheers 

Paul 

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