Sliding Seal FMA Target Chamber


It is impossible to completely describe all the intricacies of this versatile target chamber, but this document should answer some basic questions. To know more you should talk to Cary Davids or Birger Back.
This scattering chamber has a sliding seal which allows the FMA to be rotated with respect to the beam axis from -15 to +45 degrees.
The target height and angle can be adjusted with the aid of stepping motors and shaft encoders on the ends of the rotating feedthroughs. There are 3 concentric rings on the floor of the chamber which rotate. They are also controlled by stepping motors and shaft encoders. Keep in mind that they rotate with the chamber when the FMA rotates so this must taken into account in determining the angle of any detectors on the rings.
The left side of the chamber has a 12"x12" flat opening for access or for attaching large detectors.
A rotating target wheel can be used in place of the standard target ladder.

Getting to Know Your Sliding Seal

There is a bellows upstream of the chamber with one end connected to the seal and the other end fixed to the beamline. The seal is at the front of the chamber so the chamber rotates with the FMA. Two wrenches are connected by a turnbuckle to take up any slack in the metal band and keep it pressed againt the double o-ring seal. A mechanical pump evacuates the volume between the 2 o-rings. It is important to keep tension on the seal and to keep the bellows straight. Otherwise it will leak.
When you rotate the chamber, you must turn the wrenches in the direction which will straighten out the bellows (look at it from above). You'll figure it out by trial and error. Keep an eye on the seal pressure while you turn the wrenches. There is a thermocouple gauge which should be connected somewhere. If you are moving the wrenches correctly, the pressure should not go up much and should come all the way back down to its original base value when you stop moving things.
If you are rotating the FMA to a large angle, you may have to remove and reposition the wrenches. Loosen the turnbuckle, remove the wrenches, put them back on, and tighten the turnbuckle as quickly as possible so the seal does not leak too much.


Rotating FMA

Venting Chamber

Changing Targets

Pumping Out Chamber

Last Updated: May 24, 1996 (D.J. Blumenthal,