Tritium retention and conditioning of graphite limiters in TFTR

The attainment of high confinement auxiliary heated plasmas in TFTR requires careful conditioning of the graphite limiters. In addition to the usual techniques of glow discharge and pulse discharge cleaning, the authors have found it necessary to use multiple low density ohmic discharges to thoroughly degas the limiter. Further conditioning is achieved by high power auxiliary heated plasmas. The result of the conditioning is a limiter with low recycling (R approx. = 0.5) and a large capacity of pumping hydrogenic atoms. Limiter conditioning has also been found to assist hydrogen isotope exchange. The retention of hydrogen isotopes in the limiter has been studied. Present estimates of the retention yield an in-vessel tritium inventory of 1.8-3.0 g after the equivalent D-T fueling of 600 full-power plasmas. (author). 13 refs, 4 figs, 1 tab