Status of Alignment of MEGHA and the target ladders  (DLW)
****************************************************

The ring for mounting the strip detector array and a second target
ladder mechanism have been added to the MEGHA chamber.

These were aligned as follows:-

1) The telescope was aligned to a bulleye target up stream of the
collimator housing. The line was checked with a small aperture in the
entrance to the beam pipe of the centre module. This was central to a
few thou.

2) The new MOUNTING RING FOR THE STRIP DETECTOR ARRAY was set to the
correct distance into the chamber using a set of jigs and centred with
a small aperture at the centre of the mounting disc. It was set so that
the centre line across the chamber was horizontal. The ring MUST NOT be
moved. The alignment procedures are not trivial.

The centre of the mounting disc is 1.5 thou low & 3 thou to the left
(looking from the back of the chamber) It is hortizontal to within 6
thou in 10 inches.

The position of the target centre relative to the disc was checked and
is within .3 mm of the correct position (along the direction of thhe
beam line). Remember that the target centre is on the upstream side of
the target frame.

It was checked that the array with all its mounts in place did not foul
with any part of the target chamber and that the target ladder would
move through the array withoout hitting any detectors.

3) A SECOND TARGET LADDER assembly was added to the chamber at centre
of the movable section. This was aligned so that it moved vertically (
ie. the centre of each target frame was at the same position relative
to the telescope line.  The ladder was aligned so that the plane of the
targets are perpendular to the beams axis. The position of each target
frame was found and marked on the drive mechanism. The wiper on the
drive mechanism should be set in the centre of the marked line.

4) The ORIGINAL TARGET LADDER position was checked and found to drive
vertically but isa few thou off the telescope axis.  Again the target
centres were found and marked on the drive mechanism.

5) The following measurements where taken with a special ladder
asssembly, which consists of a standard boss and target frame with a
solid brass "target' with three 1/16 holes accurately set along the
centre axis. One hole is at the top of the ladder one in the middle and
the third at the bottom. THIS LADDER ASSEMBLY SHOULD NOT BE  DISMANTLED
AS IT IS THE STANDARD FOR FUTURE REFERENCE.  There are two other bosses
available and four target ladders. Direction are looking from the rear
of the chamber towards the switching magnet

Uncertainty in all these numbers is of the order of +- 1 to 2 thou

Original target position
------------------------
	Top		Right		7 thou
	Middle		Right 		2 thou
	Bottom		Left		5 thou

New target position
------------------------
	Top		Right		22 thou
	Middle		Right 		18 thou
	Bottom		Left		14 thou

Other alignment numbers

Entrance to the centre module 
-----------------------------
	Horizontal	Right 		9 to 10 thou
	Vertical 	within 1 to 2 thou of telescope axis

Collimation system
------------------
Measured with chamber closed
Collimator position	Horizontal	Right 		10 thou
			vertical	High 		 6 thou 

Anti Scatter position	Horizontal	Right 		12 thou
			vertical	High 		 6 thou 

The distance between the collimator and antiscatter slit is 99 +- 1 mm.
The anti scatter slit is located in the same position as for the dec 96
run. The collimator is approximately at the exit of the collimator
housing Box. (the small chamber in fromt of MEGHA.

It is clear from rotating the collimators that the holes are NOT in the
centre of the blanks. New ones are required to be made or we need to
recover some of the ones sent to Strasbourg.

Target Positions
-----------------
NOTE 
The target centre for the MEGHA modules and the strip detecotrs is on
the upstream side of the target ladder. The ladders should be mounted
on the boss with the rounded edge in the cornewr of the boss -- the
targets should be mounted on the other side.

6) At present we have only one motor controller and the lead has to be
interchanged between the two motors. IF YOU NEED TO CHANGE TO DRIVES
YOU MUST SWITCH OF THE CONTROLLER AND WAIT 30 SECONDS BEFORE REMOVING
THE CABLE OTHERWISE YOU WILL DAMAGE THE MOTOR.