Re:

["Guangliang Yang" <y.guangliang@physics.gla.ac.uk>]

Dear Jim,

 

      Please see my following answers (in blue) to your questions.

 

 

Cheers

 

Yang

 

 

----- Original Message -----

From: "Jim Stewart" <jstewart@jlab.org>

To: <halld-tagger@jlab.org>

Sent: Friday, April 18, 2008 11:30 PM

> 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.

 

The advantages of having two dipoles are the cheap cost, ease of installation and fabrication etc.

 

 

>
> 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?
>

 

The magnetic force applied to the coils is only around 1 tonne and the magnetic force applied to the pole shoes is around 150 tonnes when the magnet is operating at 1.5 T.

 

> 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.

 

Yes, Franz and I both agree that we should have a 10 mm O-ring.

>
> 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.

 

We need these brackets to compress the O-ring uniformly. We also need these brackets to support the vacuum chamber (on the window side).

 

>
> 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?

 

Yes, you are right there is no such lifting fixtures in the current design.  And we need them, you can add anything you think is reasonable..

>
> 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?

 

They will be used to support the coils.

>
> 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?

 

We don't intend to specify the materials for the tagger yokes. The manufacturer can choose what ever they want as along as they can meet the specifications.  For the pole shoes, we require soft steel AISI 1006 or equivalent.

 

By introducing a small gap, you can get better magnetic filed uniformity.

>
>
> 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?
>

 

The reason we need a strong support is that no relative motion among
the tagger assembly components is allowed (precision alignment, vacuum seals, etc),
although movement of the entire assembly as a unit is acceptable (it can be realigned as a
unit if necessary).

 

The tiny change of distance from the hall to the collimator is not a big issue, but if this affects the alignment, we probably need to adjust the magnets assembly.

 

 

 

> 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)
>

 

Yes, these brackets are used to support the vacuum box. We still need a FEA calculation to optimize the rib structure for stiffening the vacuum box.  

>
> 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.

 

We should try to avoid this kind big cutout, because it will affect the field uniformity. 

Because the big strongback support will block the access from the bottom side, how to mount the bottom pole shoes and return yoke on the bottom yoke is a problem. If we can get large crane, then probably we can preassemble them together, then put them on the support structure as a whole unit. 

 

>
> 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?

 

Yes, there should be a flange on the vacuum chamber to mount the photon pipe.  The protvino people made a mistake, they should put a flange on the vacuum chamber.

We have a plan to use position pins on the pole shoes and on the floor to align the magnet. ( please look at Jim Kellies presentation for the tagger review).  I will provide the co-ordinates for these position pins.

Of cause we need tapped holes for lifting.

>
> 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?
>

 

We will need these brackets to compress the O-ring uniformly.  If the vacuum box is stiff enough, the magnet itself will provide the forces to compress the O-ring. But the thin window is ~10 meters long, it is not easy to achieve self-supporting for the vacuum chamber.  Any way, we need a good FEA calculation for the vacuum chamber. If we can find a way to make the chamber stiff enough, then we will not need these complicated brackets any more. 

 

 

>
> General Questions
> ======================
> What is the manufacturer and model number of the NMR probes you want to
> use?
Metrolab,  PT2025 NMR TESLAMETER.

 

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

 

For operating at 1.5 T, the conductor current need to be 143 A. We need at least 10 ppm precision.

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

 

I never see this machine before. The precision is not a problem for us. you can easily achieve a precision of  0.01%.

 

>
> What iron did you simulate in TOSCA?

Tosca default(AISI 1006), I also used AISI 1010.

 

 

 

 

 

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