Vacuum cryopump systems supplied by cryogenerators and using heatpipes for heat transfer

Abstract

Vacuum cryosystems providing large pumping speeds have been specially constructed to be installed inside cyclotron vacuum chambers, like AGOR (KVI lab at Groningen) or SPIRAL (GANIL-Caen). In such systems, the refrigeration power is supplied by cryogenerators located a few metres away from the cryopanel, and efficiently transferred through dual heatpipes that form closed loops where condensing and vapourising cryofluids are self contained. By using the phase changing properties of fluids, heatpipes allow important heat transfer over several metres and under almost constant temperature. Since liquid and vapour coexist in the heatpipe, the conditions of pressure and temperature of the fluid must remain between its triple point and its critical point. The chosen fluid must therefore have its properties in agreement with the temperature range at which we want to transfer the cooling power. Hence, liquid/gaseous nitrogen is used for the loop assigned to the 80 K shielding and liquid/gaseous hydrogen for the 20 K cryopanel loop. Natural convection of a cold gas under moderate pressure has also been successfully experienced inside the heatpipe loop. By using pure helium in a natural convection mode and with only modest masses of gas, very promising results were obtained. Some examples of this original conception will be described. Results and performances for cooldown and steady state operation will be given.