Re: uniform field region

[Jim Stewart <jstewart@jlab.org>]

Hello Yang

Do you agree that 3 parts in 10^4 is appropriately 70mm from the 
effective field boundary which corresponds to the root of the pole in 
the present design?


The arc I drew corresponds to the trajectory of the 12 GeV beam 
particles. You are right that I should expand this to give a bit more 
space for the beam. I propose to increase the hatched region beyond the 
12GeV trajectory by 1cm. This gives 1cm to miss-steer the beam to the 
outside and remain in the "good field" region.

The beam pipe at the entrance of the magnet will probably have an ID of 
about 17mm. Based on this I think 2cm is too much space.  From the inner 
field boundary to the quadrant of the arc defining the beam trajectory 
there is a distance of 88.5mm. If the 70mm line corresponds to 3 parts 
in 10^4 then the maximum tolerance we can give the beam is 18.5mm. 
Clearly 2cm is too much. I am not horribly bound to 1cm clearance and if 
you prefer we can make it 15mm but we cannot make it much larger.

Jim

Guangliang Yang wrote:
> Dear Jim,
>
>    I agree with you that the specification for the field uniformity should
> be changed. The old specification is based on the specification for the
> Mainz tagger which was operated 1 T ( which means it is much easier to get
> high field uniformity). We should make the specification based on our
> calculation. About your drawing, I think we should increase the hatched
> region beyond the 12 GeV electron trajectory by several centimeters, because
> we also need a uniform field for the main beam.  
>
> Cheers
>
> Yang
>  
>
> -----Original Message-----
> From: owner-halld-tagger@jlab.org [mailto:owner-halld-tagger@jlab.org] On
> Behalf Of Jim Stewart
> Sent: 17 February 2009 20:24
> To: tagger list
> Subject: uniform field region
>
> Hello Yang, Franz, and Co.
>
> I am trying to think how to summarize our specification on the field
> uniformity in the clearest most general way. I propose making a drawing like
> what is attached, and then specifying that for any two points inside the
> hatched area that are less than 100 mm apart the difference in field must be
> less than 3 parts in 10^4, and that the uniformity over the whole hatched
> region must be better than 1%.
>
> If I go in from the pole by 70mm my uniformity is only 3 parts in 10^4 and
> not 1 part in 10^4. Do other people agree with this? How far in from the
> effective field boundary should we go and what uniformity does this
> correspond to ?
>
> Jim
>
>