The most notable difference with this vacuum system is the reduction of the 18" long KF40 bellows to a more reasonable 6 inch long (2 inch diameter) bellows mounted for an almost straight run to the chamber. This is accompolished by a bracket that mounts the diffusion pump as close to the chamber as possible. A significant improvement in vacuum quality has been noticed, both in absolute pressure and pump down time. Pressures as low as 9E-7 have been reached, and from a cold start it takes approximately 1 hour to reach the high E-6 Torr range.
An improvement that increases time efficeincy is the addition of a manifold of valves on the chamber pumping port to allow a second mechanical pump to rough out the chamber. This is useful when wanting to make quick changes to targets or ion source filaments which requires bringing the chamber up to atmosphere. The operator simply isolates the diffusion pump from the chamber, brings the chamber up to atmosphere, performs required work, then using the second mechanical (roughing) pump, roughs out the chamber to 1E-3 torr, isolates the roughing pump, and finally reconnects the diffusion pump. This eliminates the 40 minute cool down time and 60 minute warm up time of the diffusion pump. This will prove to be useful feature once the cyclotron is put into "production" lab use.
Pressure is monitored in the foreline with a standard thermocouple gauge, pressure at the cold trap is monitored with an ion gauge, cyclotron chamber pressure is monitored with both a thermocouple gauge and an ion gauge. All pressure units have outputs that are monitored by the DAQ/Control system and are used in the operation and safety of the vacuum system.
Anyone viewing this page that has worked on reasonably high vacuum systems will sympathize with us in the task of looking for minute vacuum leak(s). One of our visiting scientists, Dan Hoffman, is skilled in vacuum leak hunting. Using an Alcatel leak detector Stuart and Dan spent many hours locating and fixing a pesky leak. It was found, the joint re-welded, and succesfully retested. The vacuum system is pretty well understood and satisfactory.
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