SLIP – Study of Lithium Infusion in Porous media

February 27, 2009

Innovative materials are created every year as candidates for fusion first-walls and the like. One such material is a porous molybdenum foam specifically proposed to hold a volume of liquid lithium within a fusion experiment. The SLIP experiment was created to examine the wetting behavior of this foam. Its follow-up experiment, SLIP2X, is a plasma source designed to impinge a porous metal target with infused lithium and examine the changes in bulk plasma properties.

Experiments conducted on a number of fusion machines around the world have shown the benefits of deploying lithium plasma facing surfaces (PFCs) in the machines. The list includes TFTR, T11-M, CDX-U, FTU, JT-II and NSTX. Of these machines, TFTR and JT-II have only applied lithium via pellet injection or evaporation. T11-M, CDX-U(early phases) and FTU have utilized a porous metal mesh with liquid lithium wicked into the pores by capillary action. This method restrains the liquid lithium from ejection into the plasma and machine while still maintaining a liquid lithium surface to the plasma. CDX-U has implemented a fully liquid lithium limiter and NSTX will implement a fully liquid lithium divertor.

In order to prevent ejection of the liquid lithium into the machine (as was seen on the Li-DIMES DIII-D experiment), a porous material has been proposed. One such material, fabricated by ULTRAMET was provided to UIUC for examination. Testing was carried out to determine the wetting characteristics of the porous molybdenum mesh and its re-usability. The SLIP experiment was created to examine this and results were recently published in the Journal of Nuclear Materials.

A follow-up experiment has been constructed to diagnose a fusion relevant plasma in contact with a liquid lithium PFC. This experiment has been dubbed “SLIP2X”. It is a magnetized plasma gun with an internal solenoid field similar to a planar spheromak gun (cf. Bellan’s research group at CalTech). The machine pulses energy into the plasma heating it to 10s of eVs at densities above 10^19 m^-3. Probe diagnostics and magnetic diagnostics are utilized to characterize the plasma. SLIP2X is primarily intended for development of diagnostics before implementation on the DEVeX plasma source and as an educational tool.