sPHENIX discussion of the superconducting solenoid

[Kin Yip <kinyip AT bnl.gov>]

Hi,

I've just got a reply from Pasquale (after his vacation) who confirmed that a 10K pound upward vertical force
should not be a problem for the BaBar coil/internal structure.  I just send it to the list for achival purpose etc.
together with past corresondences and my own deliberation.

Pasquale's reply this morning :

=================================================

Hi Kin,

my apologizes for the late replay. As soon as I was back,
I was really submerged by a number of things to be done asap,
but I gave a look to documents for answering your question.
I think that 45 kN upward directed
should be held by the radial supporting system with no problems
for both tie rods and internal structure.

Best regards

Pasquale

==============================================

( Just in case,  10K pound-force ~ 45 kN . )

Kin

-------- Forwarded Message -------- Subject: Re: box force follow up & again my Fy worry Date: Thu, 18 Aug 2016 14:43:46 -0400 From: Parker, Brett <parker AT bnl.gov> To: Yip, Kin <kinyip AT bnl.gov>

Sounds like everything is ok.  - Brett 

------ Original message------

From: Kin Yip

Date: Thu, Aug 18, 2016 12:09 PM

To: Haggerty, John;Parker, Brett;

Cc: Wanderer, Peter;Cozzolino, John;

Subject:Re: box force follow up & again my Fy worry

Hi,

I am still waiting for Pasquale's reply (usually he's very fast if he's not in vacation) ... But I've discussed it with D. Phillips and Don Lynch
who are familiar with the support of the cold mass (coil + mandrel/cylinder ...).   They tend to think the 10K pound-force upwards shouldn't
be a problem.   The weight of the cold mass is like ~17K pounds (~8000 kg) or so, higher than the 10K pounds and so the upwards force
makes it "lighter".   And then, we have the tie-rods.  We have the axial (z) tie-rods but also the x-y tie-rods (horizontal / vertical tie-rods)
radially.

In the BaBar Solenoid Technical specification (1997):
https://collab.external.bnl.gov/sites/sPHENIX-Magnet/Shared%20Documents/BaBar%20Documents/Technical%20Specification%20for%20the%201.5%20Tesla%20Superconducting%20Solenoid%20for%20the%20BaBar%20Detector.pdf

they mentioned about being able to deal with radial force of 20 tons (5.5.1.3.b) and vertical force 1.6*gravity weight of the cold mass
(5.5.1.5c) etc.  So, it seems that 10K pound force shouldn't be a problem.

If I hear anything from Pasquale, I'll let you know.

Kin

On 08/18/2016 09:57 AM, John Haggerty wrote:

Brett,

Thanks!  A few remarks below.

On 8/17/16 4:55 PM, Parker, Brett wrote:

John, today you were wondering about the difference in having the BaBar
solenoid in a box as opposed to a pure cylinder.



Well here is the simple calculation I suggested doing at the meeting.
Outside the coil (where the field is lower so the box has maximum
impact) there is definitely a variation of Bz as one goes around a
circle at constant radius. So yes there is a "modulation" of the outward
pressure generated in the solenoid coil conductor.



I was surprised to see a 10% variation in this external field; I
suspected that the fractional variation inside the coil is smaller. So
before sending this email I ran the calculation again at R=152mm where
the field is about 1 T… and we indeed see a much smaller fractional
variation (see below).



I really do not see how this variation could hurt the solenoid coil
since this is just a small modulation of the outward pressure. It is not
like the pressure is reversing at any point (it is only pressing with
slightly less force against the outer aluminum support in some places)
so there is no real danger of going out of round. Also consider that
some detectors that I know of have octagonal yoke symmetry with a closer
yoke and much higher fields. A similar effect would occur in such a
detector due to the corners and I don't know of anybody worrying about
it before.





Note that if the box had full four-fold symmetry the net transverse
force should sum to zero.

That sounds very reasonable, and it's excellent to have some quantitative estimates.

What I am wondering about though is the point I brought up in the
meeting… that there seems to be a net vertical force on the coils. For
this Wuzeng's model (from PowerPoint slide but I get similar magnitude
numbers based upon the geometry I got from John C) Wuzeng has:





That is to say the net vertical decentering force is almost as large as
the axial force we are worrying about. I would suggest that someone find
out if the BaBar internal support structure is designed to handle such a
vertical force. My first impression from reading the BaBar design
literature is that they mostly worried about handling the axial
decentering force and there was no mention made of a vertical force
(other than maybe gravity). – Brett

You're right, this vertical force does seem odd.  I don't really get how the symmetry allows a vertical force except for gravity, but maybe the coil axis is somehow "off center" the axis of the flux return.  What I'm wondering is how the vertical force changes with the vertical position of the coil in the steel--maybe we've chosen a "bad position" for the coil?  I don't have the tools in my toolchest to answer that question, but it's the only asymmetry that I can think of that make produce such a force.

The magnitude also does seem a little disturbing.  Although the aluminum coil is a pretty hefty object, I'm not sure I would care to park a truck on top of it (the 5 tons), although I may misunderstand where the force is applied.  Our best resource on the coil design is Pasquale.

Thanks again, it definitely seems a good idea to carefully consider the forces on this coil before the high field test, which is likely to be sort of funny compared to where it's supposed to end up.

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