Retention in Li and Ga

In conjunction with these measurements of hydrogen retention in liquid lithium the release rate of the trapped hydrogen back out of the solution was measured [57]. The recombination rate from the liquid surface was determined to agree well with models that had been developed for solid surfaces [58]. The 

A low-recycling boundary for a magnetically confined plasma may offer benefits from the point of view of confinement, however it presents other problems, for example with respect to fuelling of the confined plasma. While a solid wall in a long pulse device offers effectively 100% recycling from the surface, lithium effectively offers zero. Other flowing liquids may offer the possibility of a recycling coefficient somewhere in between these two extremes. 

Circumstantial evidence was observed in the post-bombardment surface morphology of gallium samples that were exposed to deuterium plasma and then rapidly cooled [20]. Small voids were observed in the sample surface that may have resulted from the coalescence of bubbles during the sample cool down period. Consistent with this view was the fact that the amount of deuterium retained in the samples was independent of the sample exposure conditions. Follow-up experiments are being performed to determine whether gallium samples exposed to deuterium plasma at elevated temperature (around 

400°C) may retain deuterium while hot and release the deuterium as they cool. The results of these measurements will determine whether gallium could provide an opportunity to obtain a midrange recycling condition by simply adjusting the flow speed of a liquid gallium surface exposed to the confined plasma. 

An unresolved issue related to the use of a beryllium, or any solid material, as a first wall is the issue of mixed-materials. Although the properties of beryllium may lend themselves to its use in a particular environment, those properties can change dramatically as material from other locations in the machine is eroded, transported and then deposited on the beryllium plasma facing surfaces. Such mixed-material surfaces can dominate the rate of long-term tritium accumulation within a device and may severely restrict its operational lifetime. 

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