He3 Recirculation and Purification System for a Cyclotron Ion Source

Abstract

A He³ circulation system for a cyclotron has been built which will recover the gas and purify it continuously. This is accomplished by modifying a mechanical vacuum pump to meet the following special requirements: intake and exhaust sealed for both pressure and vacuum; small volume on the exhaust side; minimum oil volume. This pump, which is used instead of the cyclotron forevac pump during He³ operation, recovers the gas and forces it through a liquid nitrogen‐cooled charcoal trap and on to the ion source. The system is completely interlocked to ensure He³ safety in the event of operator or electrical failure. With a flow rate of 6 cc per minute, the normal He³ loss over a period of 200 hours operation was less than 3 cc per hour after an initial charge of 1000 cc NTP. With trap reactivation periods of 50 hours, no change in ion yield was observed. External beams of approximately 100 μa of doubly charged particles were obtained.