sPHENIX discussion of the superconducting solenoid

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

Hi,

 

This is a follow-up to my email (about “force inversion due to current change”) : 

https://lists.bnl.gov/mailman/private/sphenix-magnet-l/2016/000360.html

 

Basically I’ve done what I’ve said I’d do.

 

I’ve made use (or hijacked) Wuzheng’s models of BaBar (2D) and sPHENIX (3D) in Opera.  I’ve

calculated the net axial forces on the entire coil while I change currents and shift the coil position

(3 cm with respect to the return yoke).

 

The BaBar (2D) model was made up just a couple weeks ago when Wuzheng had a little time.  Though

he’s just made his best estimate of the dimensions etc., it may not be perfect.    Comparatively, Wuzheng’s sPHENIX (3D) has been well established/used for some time.  

 

Opera-2D is very fast to get result whereas the 3D would take something like 5 hours to get a point.

 

In the plot, the blue and red points are the forces at various currents for the BaBar model.  The blue

points are for the case that the coil is shifted 3 cm away from the return yoke center whereas the red points

are the points when coil is centered with respect to the return yoke.

 

The green points are the case for the sPHENIX model when the coil is centered with respect to the return yoke.

( I didn’t do as many points as in the BaBar case as much time is needed and I think the trend is clear. )

 

You can see that the forces for the BaBar (centered) change signs at very higher current  but the sign of

the force remain the same after it’s shifted by 3 cm, presumably due saturation for the steel at very high field.   Though the effect may be a bit too large than reality, it shows qualitatively what BaBar has done to avoid sign changes.

 

For the sPHENIX model, you can see that even without any shift, the net axial forces don’t change signs.

From Wuzheng, I understand this is because our field is smaller (and the caps are further apart) which cause

less or possibly no saturation.

 

I’ve sent the plot to Wuzheng today and he seems to think that what I’ve done is correct.   I’ll try to explain

this in futuer meetings ….

 

Kin

 

From: Meng, Wuzheng
Sent: Tuesday, March 15, 2016 5:39 PM
To: Yip, Kin <kinyip AT bnl.gov>
Subject: Re: plot (results)

 

Kin, 

 

I believe that what you have done are correct and very useful studies. 

 

The 3 cm shift gives much more effect in Babar case than sPhenix case, my understanding (presently) is that sPhenix has much larger Air-Gap in its magnetic circuit (between steel tips = 6 meter) compare with the Gap in Babar case (between

steel tips = 4.04 meter if I remember correctly). 3 cm shift is equivalent to 1/200 of the gap in sPhenix, but only 1/133 in Babar case.

 

Another possibility is my Babar magnet 2d model was not accurate; as I told you --- I had difficulties to find exact dimensions on Q2 shielding in forward end; steel plugs shape in backward end, …etc. Hope you and Achim can find errors and correct them 

in the future. In their documents, those Ansys plots are not consistent with those drawings (as built).  

 

Wuzheng

 

On Mar 15, 2016, at 4:34 PM, Kin Yip <kinyip AT bnl.gov> wrote:

Hi,

I show you all the calclations that I've done on this plot, BaBar (centered), BaBar (3 cm shifted) and sPHENIX (centered).

I've multiplied 1E-5 to get to N for those results from Opera-2D.  

The forces for the BaBar ( 3 cm shifted ) seem much larger than what Babar found experimentally (or theoretically).

I also attach the "lp" files for babar (centered) and babar (3 cm shifted) so that you can see the forces, currents ....

Any comments ?

Kin

 

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