SUMMARY OF ALTERNATIVE METHODS OF SUPPORTING THE DETECTOR PACKAGE
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The reference design calls for holding the detector package by means of four
rods, which pass through all detectors and are then supported by a "cage".
Three alternative methods of supporting this cage have been proposed:
A) Cantilevering it from the upstream end-plate of the magnet yoke 
B) Cantilevering it from the downstream end-plate of the magnet yoke 
C) Supporting the cage on rails .

A) MOUNTING OF DETECTOR ASSEMBLY ON UPSTREAM YOKE END-PLATE
  ---------------------------------------------------------

 1) The magnet/yoke assembly has to move on rails out of the target
     position.The weight (~50T) may deform the floor and change the alignment.
     This means that we must be able to check and if necessary adjust the    
     alignment with the magnet/yoke in situ. There are some ideas about how to 
     do this by means of adjustments in the attachment at the upstream yoke 
     endplate

  2)Cryogenics,power supplies and controls for solenoid must also    
     move, but moving cryo and vacuum service connections with the moving
     magnet is not such a big problem. Most cryogenic target assemblies are
     moved in and out of the beam by means of a service hook up to
     boom that swings

  2) The reproducibility of the magnet position has to be checked
     after its returning into the target position, but it can be
     easily accomplished and readjusted if necessary since the
     magnet is outside of the assembly and has ready access for
     both of these operations.


  ADVANTAGES:
  -----------
  1) Free access to the end of beamline.

  2) Detectors aligned right on the beam and this alignment is never
     disturbed.

  3) All cable connections and electronics are fixed throughout set
     up procedures and once set, the electronics is never disturbed.

  4) The fixed cantilever suspension of the detectors is more stable
     and rigid than when it has to be movable.

  5) Easier testing of the detectors with beam without magnetic field.
     Additional monitors could "view" it.

  6) Position monitoring system can be readily set up.

  7) Because we will have to compensate for the sag of the end of the
     cantilevered cage by the positioning mechanism, it is highly
     desirable to be able to see what we are doing with this end.


 DISADVANTAGES:
 --------------
   1) Cantilever is large (more then 1.5 m from endplate to middle of
     detector package). Sag is significant, and will have to be compensated
     for. Sag may change with time

   2) Lack of room in M13 to roll yoke clear of detector package. Will have to
     change shielding if experiment is in M13. Situation for M11 is not known..



B) MOUNTING OF DETECTOR ASSEMBLY ON DOWNSTREAM YOKE END-PLATE
  -----------------------------------------------------------

   1) The detector assembly could be aligned on the beam before the magnet is 
      in place, then rolled back and the magnet/yoke installed.
	
   2) Installation of massive yoke may deform floor and change the             
     alignment.This means that we must be able to check and if necessary adjust 
  
     the alignment with the magnet/yoke in situ. The same ideas about how 
     to do this by means of adjustments in the attachment at the upstream yoke 
     endplate would also work on the downstream endplate.

  3) The detectors complete with all electronics have to move together
     if the connections are to stay undisturbed. This can be accomplished by 
     attaching the platform holding the electronics and gas racks to the 
     downstream endplate and moving everything as a single unit.


 
 ADVANTAGES:
 -----------
  1) Heavy magnet/yoke assembly doesn't move once it has been installed.

  2) Enough room in M13 to (just) remove detector package


 DISADVANTAGES:
 --------------

  1) The very precise position reproducibility of the target/detector
     assembly relative to the beam is jeopardized by the necessity for a moving 
     mechanism .

  2) Cantilever is large (more then 1.5 m from endplate to middle of
     detector package). Sag is significant and must be compensated for .
     Sag may change with time

  3) If we want to check alignment of detector package to beam without the 
     magnet in place, this would be very difficult after magnet installation

C) MOUNTING THE DETECTOR ASSEMBLY ON RAILS
------------------------------------------
1) The detector cage is mounted on wheels which move on rails which pass through
the solenoid without touching it and are supported by stands located at each end
outside the solenoid and inside the yoke. 
2) Auxiliary, temporary rails would need to be put in place whenever it was
desired to remove or install the detector package. In the simplest
implementation, the downstream endplate would be removed before the auxiliary
rails are installed.
3) Alignment would be adjusted by raising or lowering the fixed rails at the
point of support at each end.

 
ADVANTAGES:
-----------


   1) Massive yoke and solenoid, together with cryogenics, power etc stay
      fixed once they have been installed.

    2) No cantilever needed so support can be made mechanically rigid - sag 
       problem much less.

 DISADVANTAGES:
 --------------

 1) Alignment of the detector assembly on the beam must be done inside
     the solenoid but with the two endplates of the yoke removed for access.  
     Solenoid would restrict access to detector package. Unlike the cases where
     the detector package is mounted on the endplates ( A and B 
     above), we have no ideas on how the alignment could be adjusted with 
     complete yoke installed 

  2) The detectors complete with all electronics have to move together
     if the connections are to stay undisturbed. It is hard to see how this 
     could be accomplished, since the cabling would presumably have to come out 
     through a hole in the yoke which stays fixed. At the moment it looks as 
     though it would be necessary to uncable before moving the detector 
     assembly out of the magnet.

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