Use of ferrofluidic seals in the design of tritium compatible pumps

The present design of the ITER mechanical forevacuum system foresees the use of Roots pumps with pumping speeds of 4200 and 1200 m 3 /h. Commercial Roots pumps on the market are not tritium compatible. They require one or more of the following modifications: i) replacement of elastomer O-rings by metal seals, ii) minimisation or elimination of leaks along the rotating shafts and iii) only use of tritium compatible materials. This paper presents the possible application of ferrofluidic seals to avoid gas flows between the pumping and the oil filled volumes. Tests were performed with ferrofluidic seals for different rotational shaft speeds up to 1500 rpm and for various pressure differences up to 100 kPa. The results with the ferrofluidic seal were very encouraging showing very small leak rates under Roots pump relevant conditions. To verify the performance of ferrofluidic seals under realistic conditions a tritium compatible Roots pump having a pumping speed of 250 m 3 /h and using ferrofluidic and metal seals is being constructed.