Experimental determination of the helium pumping by beryllium
In 1989 the plasma facing material in JET was changed from graphite to beryllium. This change has dramatically affected the global recycling behaviour of the plasma. An experiment devoted to the measurement of the pumping/release characteristics of He in Be has been carried out in a test bed at JET. The test bed measurements and the data from JET discharges both show that He is pumped by Be and that, for the same wall conditions, the pumping is lower for He than for D. The outgassing observed after implantation indicates the presence of a mobile He population in Be. This is also confirmed by post-pulse outgassing measurements carried out at JET. The characteristic pumping time calculated from the test bed measurements is consistent with the observed He pumping during a JET discharge, taking into account the areas and fluxes involved in each case. The detailed mechanism causing the net retention of He in Be to take place is not clear, but it appears that more than one process is responsible for the pumping/release pattern observed.
Bibliographic Reference: Article: Proceedings of the 18th European Conference on Controlled Fusion and Plasma Physics, Vol. 15C (1991) Part III, pp. 77-80
Record Number: 199210265 / Last updated on: 1994-12-02
Original language: en
Available languages: en