No Subject

[Jim Stewart <jstewart@jlab.org>]

Dear Yang

I have started looking over the drawings and documents and have some
questions. I believe the Protvino drawings are the newest set. There is
also a 3D ACAD model which took the Glasgow design and updated it in
parallel to the Protvino work. Then there is a 2005 vintage Glasgow 3D
model which updated the original 2004 Glasgow 3D model. Is this correct or
am I missing other steps?


What are the advantages of having two magnets over one magnet? If the
advantages are only in fabrication and ease of installation, then is it
worth considering giving the company the option to deliver one big magnet
as long as they provide the a clear plan for the assembly given the
constraints of the hall? (It will be a design and build contract so the
manufacturing is their problem.) With the Protvino design we could have
probably easily built it as one magnet if Protvino has a big enough mill.

Now looking at page two (9086-00-00-00 ASSY) of the Protvino drawing set.
Protvino has built an enclosure around the coils. I am assuming this is to
take up the magnetic forces between the coils. Am I correct in assuming
that the force between the coils is equal to the force between the poles,
so according to your calculation you need to account for 150 metric tons
here?  Is what they have done sufficient?

What is the foreseen size of the o-ring between the vacuum chamber and the
pole? The Protvino grove looks funny. I heard a 10mm o-ring is planned.

Drawing 9086-02-02-00 AD - Top pole shoe.
==========================================
What are the little brackets on the side of the pole face which clamp to
the vacuum chamber for? The magnet iron is a big C-clamp which holds the
pole tips in position. It easily can put 20 tons of force on the o-ring. I
assume this is sufficient to compress a rubber o-ring. I simply do not
understand why you need these brackets.  If they are to support the
chamber from vacuum forces then it only makes sense to put them on the
window side of the chamber but they run all around so you clearly has
something else in mind.

There are no lifting fixtures on the pole so I assume it is planned to use
the M30 tapped holes. Should we build a fixture to bolt on here?

The pining system is clearly show which is nice. What is the tolerance
given by the 40H9 spec?

I assume the hole pattern in view B-B is for the pole support structure.
Is this correct?

Has anyone considered making the pole from another material than the
return yoke? Would you gain anything from an small air gap between the
pole and the yoke?


Drawing 9086-03-00-00 AD
=======================
I have not looked this over in detail. What were the arguments for and
against this structure? I like that you have one massive structure to
mount the magnets. You also seem to have a well thought out jack system to
precisely adjust the magnets to each other. What I do not like is that
this is mounted on the floor. Once you have adjusted the magnets to
each other and have mapped the magnet you need to make sure no one can
touch the adjusting screws! Then I see no freedom to move the assembly.
The spec. on settling of teh hall is up to 2 inches with a differential
settlement of half this. I assume this means that the tagger hall can
move up to 25mm relative to the collimator over time. Do we need to move
the magnet stand to accommodate for this?

Drawing 9086-11-00-00 AD
=======================
I am not going to comment on this drawing as Tim will know infinitely more
about it than me.

Drawing 9086-09-00-00 AD
===========================
As far as I can see the purpose of these brackets are to help support the
exit window against he vacuum forces. Do you have a writeup to on the
stress calculation for the vacuum chamber? did you look at how thick the
flange would have to be to make it self supporting? (This is probably a
big number)


Drawing 9086-02-01-00 AD
==========================
The bottom pole piece has big cutouts on the side for bolts to mount it to
the yoke. In the Protvino design you can simply make the top and bottom
mounting the same. If you have the iron up on wood blocks you can put the
bolts in from the bottom.

Drawing 9086-02-00-00 AD
========================
The yoke plates are bolted together but not pinned. Why?
There is a 30x30mm channel for the photon beam. Is it foreseen to have a
flange on the vacuum chamber to mount this? There are no preparations for
survey fixtures on the top of the magnet. What is needed?
How do you pick up and move the individual iron pieces? I see no tapped
holes for lifting eyes.
Will we need leveling fixtures on the magnet iron?

Drawing 9086-00-00-00
======================
The wall if the vacuum chamber is 15mm thick and the lip running around
the pole gives you  an effective 30mm thick steel flange. You could in
principal have a support fin 150mm from the edge. Are you sure you need
the small support brackets to the poles on the window side? The big
brackets to the magnet are probably critical. When you computed the
stress on the magnet and the deflection on the pole did you include the
brackets and the total force on the brackets?

When we measure the field we will have no vacuum. If the poles
move due to the vacuum force then this will change our field in a way we
do not know. Do we need to somehow measure the vacuum forces on the
brackets and then artificially induce this force when we map?



General Questions
======================
What is the manufacturer and model number of the NMR probes you want to
use?

What precision is needed for the current measurement of the magnet?

How big is the JLAB mapping machine and what precision do the hall probes
have?

What iron did you simulate in TOSCA?

Cheers jim