Re: Ring size meeting

["Daniel S. Carman" <carman@jlab.org>]

Elke,

We have been talking to the same people this afternoon.  I too
am now coming to an understanding of why the change from 1200 mm
to 1178 mm was made.  

It seems that different folks in the group have been assuming 1200 mm 
and others 1178 mm.  My sense of the decreased O.D. was that this would
adversely affect the real estate needed for the layout of the signal
traces and appropriate definition of the ground planes.  Kim has indicated 
that the real estate available in the current model (with an O.D. of 1178 mm) 
seems to be sufficient for board layout from the standpoint of signal
traces.  However we have not yet talked about the available of board
space for sufficient and appropriate definitions of ground.

Chuck has indicated that at 1178 mm, we have plenty of room for the cables 
and connectors.  Our design goal has been to leave at least 1 cm of 
clearance between the FDC cables and the I.D. of the BCAL.  With the current 
design, this goal should be easily met (especially now given the mods to
the cables choice and removal of jackets, etc). 

However, the prototypes that have been designed and constructed for the 
cathodes and wire frames have all been based on an O.D. of 1200 mm.  There 
should be no serious impact on the mechanical strengths or deflections 
between the 1200 and 1178 mm designs.  If there are no strong reasons to 
design to 1200 mm, then 1178 mm has the clear advantages that the model and 
circuit boards designs are already using this number and there is less
material between the FDC active area and the BCAL.  

From what we understand from David's Monte Carlo studies, there is very 
little impact on the performance of GlueX if we were to increase the O.D. 
to 1200 mm and also take the opportunity to slightly increase the I.D. to
increase the active area of the chambers.  Anyway, we will have final
arguments presented Monday morning by the folks involved and make the most 
sensible decision on a final number taking everything that we have into 
consideration.


				Regards,

					Daniel


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*                                                                    *
* Dr. Daniel S. Carman                   e-mail : carman@jlab.org    *  
* Staff Scientist                        office : (757)-269-5586     *
* Jefferson Laboratory                   web: www.jlab.org/~carman   *  
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