[Shms_users] 3rd-Arm Clearance in Hall-C at 12 GeV

[Howard Fenker (w)]

SHMS Colleagues,

If you are imagining an experiment in Hall-C that will use a detector 
system
other than the HMS or SHMS, you should be aware that the floor space with
an unobstructed view of the experimental target will be more limited 
than it
has been in the pre-12GeV era.  See the figures posted HERE 
<https://hallcweb.jlab.org/doc-private/ShowDocument?docid=691>. 
(Username 12gev,
Password makeshms )

File #1 shows, in two shades of green,  the "large" scattering angles 
which are not
shadowed by components of the SHMS when it is 'parked' at its most 
forward angle.
Thanks go to Charles Perdrisat, whose suggestion led to a redesign of 
the SHMS
structure in order to extend this region down to as low as about 50 
degrees.
(Previously, the minimum scattering angle was about 90 degrees.)  The 
largest
possible scattering angle has not been determined.

File #2 shows the range of "low" scattering angles between the 
spectrometers:
from about 5 degrees to about 30 degrees.  Note, however, that placing a 
large
apparatus between the two  spectrometers could be difficult or impossible
because of the heights of the HMS and SHMS.

The angles mentioned above should not be taken as specifications, or even
promises. This is a work in progress and we will do the best we can. The 
designs
will be frozen very soon, however. If you are planning an experiment which
will be impacted by this, you should discuss it with me promptly.

Best regards,
     Howard Fenker
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