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.
- diameter: 16"
- height: 19"
- # of targets on standard ladder: 5 (4 w/ FC, 3 if also want a blank)
- # of feedthroughs: 24 bnc
- radius of inner ring: ~3 7/8"
- radius of middle ring: ~5 3/8"
- radius of outer ring: ~6 1/2"
- FMA entrance apertures: 4 choices mounted between chamber and quadrupole
- close valves before chamber, after chamber, above cryopump, before PPAC
- turn key to bypass so turbo stays open even if ion gauge trips off
- unplug battery for FC suppression (it is on beamstand upstream of chamber)
- turn off monitor HV
- release FMA rotation brake
- crank 1/2 deg (readout is LED and is in degrees)
- check sliding seal
- is seal pressure still ok
- adjust wrenches if bellows upstream of chamber is not straight.
- move any equipment and racks at the focal plane which is not attached
- repeat the previous 3 steps until you are at the desired angle
- set parking brake
- turn on ion gauge if it tripped off
- open cryo valve if pressure is OK
- when pressure is normal, open valves before and after chamber
- close valve above turbo
- turn key to protected and turn alarm on if it was off
- adjust the angles of things inside the chamber (they move with the FMA):
movable FC if any, monitor, target, reset foil
- plug in FC suppression battery
- turn on monitor HV
- open valve in front of PPAC
- turn off monitor HV
- close all valves to chamber: before, after, turbo, cryo
- turn off ion gauge
- alarm off
- turbo off
- unplug battery for FC suppression (on beamstand upstream of chamber)
- nitrogen flow on (valve on beamstand near wall upstream of chamber)
- place hose near vent valve
- open manual vent valve slowly (black needle valve above turbo)
- watch neddle gauge to see when at atmosphere
- turn off nitrogen at wall
- remove lid slowy so you don't create any suction and damage targets
- place lid on its holder with the rubber stoppers
- bring containers for targets over to chamber
- carefully reach into chamber, slide the top target out, put in container
- when sliding targets up and down, do NOT let them drop
- move slowly to avoid disturbing the reset foil
- replace the reset foil if it looks bad
- check big o-ring and lid for hairs, scratches, etc.
- replace chamber lid slowly to prevent rupturing foils
Pumping Out Chamber
- check o-ring and lid, replace lid slowly (if not already done)
- close vent valve
- connect roughing pump fitting on end of hose and hand tighten
- turn on roughing pump, open valve above pump
- slowly open vent valve (now it's a roughing valve). the first sign of
pumping is smoke from the pump exhaust. if the needle gauge does not start
moving soon, you may have to push down on the lid to compress the o-ring.
- at ~2K on the chamber thermocouple gauge turn key to bypass, open turbo
backing valve, open valve above turbo
- close roughing valve
- at ~500 microns turn turbo on
- when turbo light is green, turn switches from on to protected
- when thermocouple pressure =0, try to turn ion gauge on
- open cryo valve when pressure is low enough
- degas ion gauge when ~1e-6
- close valve above turbo (cryo alone is enough)
- turn key to protected, alarm switch on
- plug in FC suppression battery
- turn on monitor HV (make sure windows are covered)
- open beamline valves before and after chamber
Last Updated: May 24, 1996 (D.J. Blumenthal, email@example.com)