OPERATION AND PERFORMANCE OF THE LARGE SCALE JET CRYOPUMP SYSTEM

Large scale cryopump systems with a pumping speed of 8 million litres per second each are necessary to provide the pumping requirements of the JET Neutral Injection and the JET Multi-Pellet Injection systems. The first cryopump system has now been operational for more than one year and the performance and operation data are presented. The cryopump system has been operated so far in direct proximity of the extracted particle beam with a total power of up to 32 MW without adverse effect. The compatibility of the system with the Pellet injection requirement of high pulsed gas loads (up to 4 × 10 3 mbl -1 ) and high inventory (up to 5000 bl) has been demonstrated by tests and the related safety aspects have been analysed. The control and instrumentation of the cryopump system performs successfully but the operation of the overall systems showed the need for the decoupling of the system from the main computer and to upgrade the local cryoplant control system.