sPHENIX discussion of the superconducting solenoid

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

Hello Russ et. al.,

 

Let me type my answers before tomorrow’s meeting.

 

• It looks like the total  force "on  all coils = 1557.798839  -24146.5442  64023.93186 N" are the numbers I should use for the supports that clamp the cryostat inside the Outer HCAL. Is that your understanding? 
• Wuzheng lists these forces as the "force on the coils". Am I correct in saying this is the steady state mutual force between the magnetic field coils and the surrounding iron?

It’s “yes” and “yes” to both of these questions.  As I said yesterday, I found that it’s from my calculations reported (~June 20, 2019)  in the mailing list:

https://lists.bnl.gov/mailman/private/sphenix-magnet-l/2019/000923.htm .

 

• What about transient forces in the aluminum cryostat barrel due to magnet quench? Eddy Current forces?

 

For this, I’ve consulted with Wuzheng Meng and Pasquale Fabbricatore in many emails.  Combining their wisdom and knowledge (with my analytic mind), I have the following determination.

 

This analysis in the 1996 BaBar  ( https://www.c-ad.bnl.gov/kinyip/download/PCSS/Quench%20Protect%20Review.pdf ) is useful and has been used many times by us (including Holger Witte).

On p.24, in the quench from 4811 A, the eddy current in the Al  cylinder can be as high as 251000 A.   It seems high but if you look at the total current originally in the coil (Pasquale first pointed it out to me),

it’s 4810*1067 turns > 5.13E6 A.   So, this is a perturbation of less than 2.51E5/5.136 < 5%.  The eddy current is in the same direction as that in the coil (as the mag field is decreasing the induced current in the mandrel tries to keep
constant the magnetic field in magnet bore).   Since force is proportional to B*I, the magnetic force due to the eddy current is only 5%.   If you like you may add 5% to the static magnetic force in your support estimation.

But I think the above is an over-estimate.  Because if you check the two graphs on p.24 again, it takes ~2 seconds for the current to rise to 251000 A.  By that time, the coil current already drops ~400 A, (400*1067 turns > 400 kA), more than the increased eddy current.    So, the total force is very likely never as big the static case (at time<=0 ) 😊

In fact, in 2017, Holger Witte (https://brookhavenlab.sharepoint.com/:b:/s/sPHENIXMagnet/External/EeIuHdO81R9PhfB1o4Ja1dwBtzXsYeffei2aEj8qmI9vSA?e=iaCcfn) did an eddy current analysis on the return steel and
obtained the same conclusion (that the static magnetic force is the largest compared to any time during the quench).  

Kin

 

From: Feder, Russell <rfeder AT bnl.gov>
Sent: Wednesday, July 22, 2020 10:15 AM
To: Mills, James A <mills AT bnl.gov>; Haggerty, John <haggerty AT bnl.gov>; Yip, Kin <kinyip AT bnl.gov>; Hock, Jonathan <jhock AT bnl.gov>; Ruggiero, Richard <ruggiero AT bnl.gov>; Feder, Russell <rfeder AT bnl.gov>
Subject: Re: Review Magnet Loading

 

Jim, thank you for organizing.

Jon Hock shared some information he has from the full field magnet testing and based on his discussions with Kin and Wuzheng.  

At the meeting on Friday I'd like to try to answer the following questions.

1. It looks like the total  force "on  all coils = 1557.798839  -24146.5442  64023.93186 N" are the numbers I should use for the supports that clamp the cryostat inside the Outer HCAL. Is that your understanding? 
2. Wuzheng lists these forces as the "force on the coils". Am I correct in saying this is the steady state mutual force between the magnetic field coils and the surrounding iron?
3. What about transient forces in the aluminum cryostat barrel due to magnet quench? Eddy Current forces?

Russ

 

---

From: Mills, James A
Sent: Tuesday, July 21, 2020 2:24 PM
To: Mills, James A <mills AT bnl.gov>; Haggerty, John <haggerty AT bnl.gov>; Feder, Russell <rfeder AT bnl.gov>; Yip, Kin <kinyip AT bnl.gov>; Hock, Jonathan <jhock AT bnl.gov>; Ruggiero, Richard <ruggiero AT bnl.gov>
Subject: Review Magnet Loading
When: Friday, July 24, 2020 10:30 AM-12:00 PM.
Where: TEAMS

 

Hi,

 

Can we meet to discuss the forces that are generated by the magnet both internally as well as external forces generated by the magnetic field due to steady state conditions and due to an unexpected quench of the magnet.

 

Thanks guys, please let me know if you can make it.  Also, let me know if you think others should be invited, like Mike Anerella.  I think this will just be a review, but maybe we can converge on a set of meeting minute slides that can be used for future reference on INDICO.

 

Best,

Jim

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