This section explains why and when the coldhead has to be regenerated.

As we now know the cryopump is a capturing device. If there's any  contaminants in the system they will concentrate in the coldhead and in particular the displacer. Therefore the displacer which is filled with activated charcoal has to be regenerated from time to time. This is all to make sure that any impurities in the helium are taken out of the system before they start to cause any problems. Eventually the displacer could freeze up!

When the coldhead is going to be regenerated it is very important to disconnect the coldhead (flexlines) from the rest of the system before warm-up. This way is prevented that any contaminants start to migrate through the system. To do a decent regeneration, we warm the coldhead up, then pump using the coldtrap , to finally clean the system. Before putting it back into the system the coldhead has to be filled with helium again.

Regenerating:    

• Swith off compressor
• Take flexlines off, (remember, disconnecting: first supply-flexline, then return-flexline)
• Let coldhead warm up. (Will be easier for molecules to leave the charcoal)
• Connect maintenance manifold with the heater to the coldhead return
• Connect helium bottle to the manifold.
• Connect the other maintenance manifold to the coldhead supply.
• Power up the heater and open helium bottle
• Open supply manifold so the 'warm' helium will flow through the coldhead.

• Leave this for an hour.
• Close supply manifold and close helium bottle.
• Connect the vacuum port to the supply manifold.
• Pump down to 10 ^-6  
• Close pump valve and switch off. Then take off vacuum port.
• Now fill the coldhead with pure helium:
• Open vent valve on supply manifold en let the helium flush through the coldhead.
• Operate the coldhead-displacer (connect compressor electrical lead) a couple of times to open and close the valves.
• Close the vent valve and let the pressure rise to 150 Psi, then close bottle.

This should ensure that all contaminants are removed and the coldhead is filled with 'clean' helium, ready to be reinstalled in the system.

Its is recommended that every time the close cycle cooler system is switched off for a longer period, that the coldhead is to be regenerated. With a minimum of once every year.

Last Updated 28/04/2002, Michiel van der Hoeven