sPHENIX discussion of the superconducting solenoid

["Mills, James A" <mills AT bnl.gov>]

Hi Wuzheng,

 

Thank you for your comprehensive and insightful answers to my questions.  I appreciate it very much and am learning a great deal from our correspondence.  I think that your response to eddy current effects due to a change in pole thickness assures us that using the thicker pole tip in your calculations is a more conservative estimate on TPC end-wheel forces due to a quench.  I suspect that Kin and John may want to further explore the field quality of the central region of the detector if we use a thinner pole tip, but I will leave that to them for further discussions.  However, this is great, news.

 

I suspect then that if we use the 600 N force on each face of the end wheel, any variation in the distribution of the pressure probably will not affect the results too much.  Though, I will ask John Cozzolino, our TPC mechanical engineer to perform an analysis of the wheel if all of the force is located at the center (inner-most) ring.  This would bound our problem for us (I think), and give us a conservative value for the maximum deflection of the wheel and its potential effect on the TPC gems and electric field.  He has already done a wonderful job analyzing the wheel due to a uniform end pressure of 130 pounds (600 N) and has calculated a maximum deflection of 0.0016 inches.  If we place the 130 pound force at the inner ring I think that this would be our worse-case scenario for deflection. 

 

In fact, since I started writing this email to you John has already redone his analysis.  His results show a maximum deflection of 0.0041 inches and a maximum stress of less than 1,000 psi.   Both values are very low.  Now that we have this information we can talk with Tom Hemmick about the overall effects to the TPC and decide if we need to look at it more closely.  So I would suggest for now that we can hold off on looking at the force distribution more closely.

 

Thank you again Wuzheng.  I appreciate your efforts very much in helping us understand the magnet response more fully.  Have a wonderful weekend.

 

With best regards,

Jim

 

 

From: Meng, Wuzheng
Sent: Friday, October 12, 2018 10:50 AM
To: Mills, James A <mills AT bnl.gov>; Yip, Kin <kinyip AT bnl.gov>; Haggerty, John <haggerty AT bnl.gov>
Cc: sphenix-magnet-l AT lists.bnl.gov
Subject: RE: Forces on the wheels (of TPC)

 

Hi Jim,

 

In my analysis, the thickness of pole tip is still 30 cm. All my information about the magnet parts are old (before 2015, I guess).  I remember that Kin has done some studies about changing the thickness of pole tip to thinner case, to see if the force (?) on the pole tip changes. I don’t remember details. Kin may remind me.  From my view, if the pole tip is thinner, then the force (the pulling force) on the wheels will be slightly smaller. This is because of the degree of saturation (in steel) is slightly higher, but not much.

 

About the force magnitude, near time=0, it gives 905 N; I think it is not real. If you imagine, during t </= 0, f(t)=1, which means the full operation current; at t > 0, the current drops.

The eddy current is produced by dB/dt (or dφi/dt, here φ is the flux linkage). At the point  t=0, this first derivative does not exist, or it is undefined, based upon the definition of the derivatives, the derivative (at certain point) exists only if you get the same value of the slop when you approach to this point from the left and from the right.

 

In my Excel file, I did not break down the force into parts; I only gave out the total forces on each entire wheel. According to present setting, I am able to get forces on separate parts: forces on Ring 1, 2, 3, 4 (separately), and forces on 12 bars (totally). If you think this will be helpful, I can do it.

 

Please comment.

Wuzheng

 

 

 

From: sPHENIX-magnet-l <sphenix-magnet-l-bounces AT lists.bnl.gov> On Behalf Of Mills, James A
Sent: Friday, October 12, 2018 9:02 AM
To: Yip, Kin <kinyip AT bnl.gov>; Haggerty, John <haggerty AT bnl.gov>
Cc: sphenix-magnet-l AT lists.bnl.gov
Subject: Re: [Sphenix-magnet-l] Forces on the wheels (of TPC)

 

Hi Kin,

 

I am back to work and finally getting a chance to look at Wuzheng’s analysis.  This looks good, but I do have a question and am not sure how it affects his results.  Do you know what value he is using for the pole tip thickness?  If you recall we had been proposing a change, to go with a 7.5-8” design thickness.  The poles in Wuzheng’s model appear to be the original 12” thick versions.  At least from my old eyes, that it how it appears, though I may not be correct and we should verify this.  Does this have an effect on the quench calculations?

 

Also, is the calculated force uniformly distributed across the face of each end wheel?  And, the question of using 600N versus 905N is a good one.  I suspect we should examine both forces.  What do you think?

 

Thanks,

Jim

 

From: sPHENIX-magnet-l <sphenix-magnet-l-bounces AT lists.bnl.gov> On Behalf Of Yip, Kin
Sent: Wednesday, October 10, 2018 9:29 PM
To: Haggerty, John <haggerty AT bnl.gov>
Cc: sphenix-magnet-l AT lists.bnl.gov
Subject: [Sphenix-magnet-l] Forces on the wheels (of TPC)

 

Hi John,

 

Please find here:

https://collab.external.bnl.gov/sites/sPHENIX-Magnet/Shared%20Documents/Dr.%20Meng%20Wuzheng's%20calculations/2018-10-10%20Wheel_eddy_curr_force.pptx

 

Wuzheng’s calculation of the forces on the two wheels here.   Are those hundreds of tons manageable  ??

 

{ By the way, Wuzheng doesn’t charge us the time that the Opera has taken to calculate, many days 😊  }

 

Kin

 

From: Meng, Wuzheng
Sent: Wednesday, October 10, 2018 9:24 PM
To: Yip, Kin <kinyip AT bnl.gov>
Subject: RE: Modified power point file

 

Hi,

 

Thanks for your time!

 

Wuzheng

 

From: Yip, Kin
Sent: Wednesday, October 10, 2018 9:22 PM
To: Meng, Wuzheng <meng AT bnl.gov>
Subject: RE: Modified power point file

 

Hi,

 

Looks good !  Thanks !  … I’ll send it to the sPHENIX Magnet mailing list …

 

Kin

 

From: Meng, Wuzheng
Sent: Wednesday, October 10, 2018 8:08 PM
To: Yip, Kin <kinyip AT bnl.gov>
Subject: Modified power point file

 

Kin,

I modified page 4 and 6. I keep the same file name.

How is the new one?

Wuzheng