Noble gas pumping by the TFTR graphite limiter

Abstract

The TFTR limiter is graphite, lt is possible to decrease the amouut of D trapped in the limiter by making plasma discharges with gas injected only as a prefill. When the limiter is deuterium depleted well enough by this technique for supershots (with RD~0.5-0.6) it pumps noble gases. The effective confinement time Xp* ranges from < 1 s for He down to 0.08 s for Kr. These noble gases escape from the limi[er slowly after the run. The partial pressure of Ar and Ne decay with time-constants of several hours, and the data fbr Ar show evidence of two trapping sites. .,

Plasma-material interactions in current tokamaks and their implications for next step fusion reactors

“…In contrast, fuel balance measurements on plasmas, fuelled with helium showed that the fraction of helium recovered was very close to 100%. Energetically implanted helium is retained in carbon, but at lower concentrations than D and the retained He is thermally released at lower temperatures since it is not chemically bound to the C, i.e., it is less strongly bound than D [714,715]. The weaker binding of helium in carbon is due to the absence of chemical binding, which makes co-deposition ineffective at retaining helium.…”

Measurements of the Production and Transport of Helium Ash in the TFTR Tokamak

“…Although the fusion power in these plasmas ( -5 MW) is modest by reactor standards, the on-axis helium ash source strength is comparable to that expected for ITER. Also, while a reactorrelevant helium pumping scheme needs to be developed, the TFTR bumper limiter pumps helium and other noble gases [8]. These facts enable the study of a prototypical reactor with all the essential elements as they pertain to ash birth, transport, and removal.…”