Pumping
and Cooling INGRID - Special Procedure
There is a general document on vacuum procedures here. Please read it if you are not familiar with vacuum techniques.
INGRID is a large cryostat with an integrated
closed cycle cooler. A more complete procedure is given here for pumping
and cooling the camera.
Use this procedure if the cryostat has
not been vented to atmosphere.
Connect the required pipework as described
above.
Open the vacuum pump valve.
Connect the pump to the power, the trap heater supply
to the cryostat connector using the special 26 pin converter plug, and
the vacuum gauge meter to the cryostat gauge head.
Power up the vacuum pump and watch the pump pressure.
This will reduce quickly to around 1 10-4 millibar or better.
At this time and with great care,
very
slowly open the cryostat vacuum valve while monitoring the pump pressure.
If the pump pressure suddenly drops the close the cryostat valve and wait
until the pump pressure drops further. Normally the pump pressure will
rise as the gas begins to flow from the cryostat, then recover and begin
to fall again as the valve reaches the open position.
Monitor the pump pressure until it drops into the 10-3
millibar regime again. At this point you can be sure that the pump down
will proceed normally. If a cryostat gauge is fitted it is normal to see
a one magnitude or greater pressure difference between the pump and
cryostat.
Before leaving the system, start a trap heater
cycle by cycling the power to the trap power supply. This begins a twenty-minute
heat cycle of the cold gas trap that will rejuvenate the traps’ capacity
to absorb gas when cold.
Dependent on the state of the vacuum when starting,
the pump down time will be much longer than a CCD cryostat. At least 48
hours should be allowed. This cryostat is designed to be cold and autonomous
for periods of 6 months. It is essential therefore that the initial vacuum
be of very good quality.
There is an example of an INGRID cooldown for information purposes
here.