[Esr-users] Hall C dipole shms magnet

[Paul Brindza]

Greetings

There are two issues with SHMS dipole ( and other shms magnets) that we  
have identified that we can certainly address now.

First :

The warm return valve fast open settings were just too conservative. Too 
slow and not enough valve stroke to be effective.
We choose these settings to try to minimize system disruptions.
We will revisit and revise.

Second:

The lead flow interlocks are just way too sensitive.
All the Hall C magnets enjoy having burn out resistant current leads and 
we are not taking advantage of this fact.
Lead flow interlocks really should be on slow discharge instead of fast 
discharge and the thresholds should be reexamined and adjusted for more 
transient tolerance.

The final problem that needs some testing is the function of the dipole 
mechanical relief valve.
This is the only mechanical relief on SHMS to ever open ( just once) 
during magnet training.
It alone enjoys a one time demonstration that it can limit the pressure 
at 4 atm.
There is nothing in the pressure rise curve from yesterday to suggest 
that the pressure rise was too fast or conditions too severe for the 
mechanical relief have been able to handle it.
Indeed, the warm return valve should have been able to cope.
The event yesterday was a "normal" fast dump  based on temperature and 
pressure profiles.
The pressure curve looks like the mechanical valve did not open.
The valve was warm and dry when we entered the hall while the rupture 
disc and its line were heavily frosted and still venting.
We did find evidence in Hall C that the mechanical valve may have opened 
even though there is no evidence in the pressure curve that was recorded 
or its temperature or appearance.

I would like to remove the valve and test its function as soon as possible.

WE started a very slow ~ 1 gm/sec purge using He gas at about 240 K last 
night back thru the warm return to try to measure contamination in the 
dipole.
The dipole is 35-40 degrees and very slowly warming.
The magnet exhaust temperature is about 80K in the dipole warm return 
line so if we have significant N2 contamination it should show up unless 
it is too dilute to measure.
We will need a Hall  access today to trouble shoot the warm up system.
We could not get LN2 into the Cool down/warm up system after 12 hours.
That is why the flow thru the dipole was kept very small.

Cheers


Paul Brindza


On 12/12/2017 3:10 AM, Rolf Ent wrote:
> 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
>
> ------------------------------------------------------------------------
> *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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