Cold pumping
bruins@indigo.ucdavis.edu
Fri, 2 May 1997 10:08:22 -0700
Dear members since I just recently went thru a cold pumping procedure on
one of our 300 Mhz magnets(9 years since first install) I figure I share my
experience. I decide to use a "Noblegas" Tuned ION pump with a capacity of
30 l. per second. THe initial vacuum on opening the OVC valve was 5* 10
e-4. After four days of pumping the pressure stabilized at 2*10 e-7.
Since no further improvement seemed apparent( due most likely to small
leakage thru the o-rings flanges used in the hookup of pump and valves) I
stopped there. The He boil off rate dropped in half and the ambient
temperature of the probe went from 16 c to near room temperature. One main
advantage of an ion pump, if hooked up correctly , is that it doesnot need
a backing pump once operational pressure a reached. Meaning no lost sleep
due to potentail power failures. All other precautions like leak checking
all connections and safe distance of ion pump from magnet etc should be
followed. Clean, easy and no worries. Paul Bruins