-------- Original Message --------
Subject: Re: status
Date: Thu, 17 May 2001 11:27:18 -0700
From: John Macdonald 
Reply-To: john.macdonald@triumf.ca
Organization: TRIUMF
To: nathan.rodning@ualberta.ca
CC: drgill@triumf.ca, Carl Gagliardi ,Robert
Tribble ,Vladimir Selivanov
,Glen Marshall
,Jean-Michel Poutissou ,Michael
Barnes 
References: <3B035997.5F57C531@phys.ualberta.ca>
<3B0407EE.CFDC3FA3@triumf.ca> <3B040A7D.EF8575ED@phys.ualberta.ca>

Hi,

According to the email Dave received from Frank Davies of Oxford, the
issue of
whether or not our magnet was built to "cold-ship" standards or not is
directly
linked to the issue of what forces it can tolerate when mounted in the
iron.  In
other words, if our magnet were not "cold-shippable", it may also be
incapable of
withstanding the forces in the iron without some significant
modification. The
Oxford email is quoted below.

         John

------------------------
Hello Dave,

It's good to hear from you again after so long. I'm glad the magnet is
still
giving good service.

I have been struggling to confirm the build standard of the suspension
system within the magnet, which is what will determine whether the
forces
are a problem. If, as I recall, it was manufactured in 1986 it will be
to
our 'Cold ship' standard. which means that the suspension is robust
enough
to withstand transport loads without additional transit brackets that
needed
to be removed during installation. The loads this suspension system will
handle correspond to more than 1g acceleration, which is a few tonnes in
any
direction.

In practice it is advisable to try to keep the forces on the magnet to
no
more than about a tonne in any direction, because the suspension is
slightly
elastic and excessive force may result in one vessel touching another
internally resulting in high Helium boil-off. The force of 685 pounds
you
mention is certainly no problem, because vertical is the strongest
direction.

Many MRI systems were encased in iron shields, and force is certainly an
issue to be aware of. When systems were being set up like this for the
first
time the usual practice was to measure the gradients of the magnetic
field
starting at a very low value of centre field. An NMR-based device is
ideal,
but a good quality Hall-effect gaussmeter should be good enough
measuring at
+/- 20cm from the centre in each of the 3 prinicpal axes. By providing
some
means of adjusting the magnet position it is possible to reduce the
field
gradient, which directly translates to a reduction in force. Repeating
this
adjustment at progressively higher fields results in the magnet being
finally well centred in its shield, which also gives the minimum
disturbance
to the field homogeneity. Once the magnet was set up on the first ramp
it
was operated normally with no special measures on subsequent ramps.

Your Opera 3d model should be adequate to estimate the sensitivity of
the
force to position. It should also be able to predict the effect on the
magnetic field homogeneity quite accurately, and we use this to adjust
the
amounts of iron in different parts of a shield to make sure we can still
achieve the high specs we need for MRI. Finally, of course, it will also
help you to predict what the new field/current ratio is, since lots of
iron
will boost the central field considerably, especially at low currents.

I hope these few notes help you in your project. If you have any more
questions, I'll be happy to do my best to answer them.

Best regards,

Frank

Frank Davies                  Director of Research
Oxford
Magnet Technology Ltd.
Wharf Road, Eynsham, Witney, Oxon. OX8 1BP England
Tel: +44 (0) 1865 850220    Fax: +44 (0) 1865 850176  Email:
Frank.Davies@omt.co.uk

----------------------------


Nathan Rodning wrote:

> Hi All-
>         I don't doubt the honesty of the cryomag people, I guess that we were
> just surprised when we saw this portion of the manual which had pictures
> that looked like our magnet, and cautions about the shipping flanges
> inside!
>
>         In any case, when the magnet gets warm and is opened (hopefully within
> a week) it should be interesting to see inside.  Of course, it may look
> good as new inside, in which case we'll be scratching our collective
> head!
>
>                         nate
>
> "David R. Gill" wrote:
> >
> > Hi Nate,
> >  The words in the manual are generic to many models
> > manufactured by Oxford. We were assured that those words
> > to which you refer regarding the supports for travel do
> > not apply to our magnet model. They shipped it to us
> > cold, which they claimed was a standard procedure that
> > they employed many times for such magnets. I do not know
> > of any reason that we should doubt the honesty of the
> > Cryomag people.
> >  If however we now decide that we do not believe their
> > assurances re moving the magnet cold then we will have
> > to accept putting in extra supports for the move back
> > to M13 where we will have to disassemble again to remove
> > these supports before cooling down. All of this will be
> > very time consuming so I believe that we should check
> > on the veracity of the Cryomag statements before going
> > to this procedure.
> >
> >       Dave
> >
> > *****************************************************
> > David R. Gill (drgill@triumf.ca)   (604) 221-3219
> > TRIUMF                              Fax  222-1074
> > 4004 Wesbrook Mall, Vancouver, BC      V6T 2A3
>
> --
> Nathan Rodning, Associate Chair
> Professor of Physics
> University of Alberta
> Edmonton, Alberta   T6G 2J1
> Canada
> (780) 492-3518  /  Fax:  (780) 492-0714
> http://www.thehungersite.com/

--

John Macdonald              phone :  (604) 222-7348  (direct line)
TRIUMF                                       (604) 222-1047 (switchbrd)
4004 Wesbrook Mall            fax :  (604) 222-1074
Vancouver, BC                  email :  john.macdonald@triumf.ca
Canada, V6T 2A3                            jam@triumf.ca

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