Speaker
Description
The National Spherical Torus eXperiment (NSTX) has recently undergone a major upgrade to NSTX-U at Princeton Plasma Physics Laboratory (PPPL). To improve plasma performance for NSTX-U, control of the influx of impurity gases and fuel recycling from plasma facing components (PFCs) are critical. On the NSTX fusion device, two lithium oven evaporators (LITERs) were mounted on the upper dome of the vacuum vessel to apply a thin layer of lithium coating downward onto lower divertor, which has resulted in effective deuterium retention and improved energy confinement time. For NSTX-U, it is desirable to have lithium directly coat the upper divertor for double-null plasma operation, and increase the coverage of PFCs in general with lithium. In this paper, the design of a new lithium evaporation system capable of coating NSTX-U PFCs in all directions will be reported. Porous stainless steel (SS) tubes will be used to hold the lithium. Lithium will be loaded into the pores of the SS tube as a liquid at elevated temperature within an argon glovebox. A vacuum heater will be inserted into the lithium-loaded SS tube to heat lithium to more than 600 C for lithium evaporation in the NSTX-U vacuum vessel. With significantly less thermal mass compared to the LITERs, the new lithium evaporator can be heated up and cooled down much faster. The time needed to reach operating temperatures and unwanted lithium evaporation while at temperature will be drastically reduced. The new evaporation system setup and thermal modeling results of the temperature distribution achieved in the porous evaporator will be covered in detail. Safety design considerations and analysis regarding lithium handling during operation will also be included.
| Eligible for student paper award? | No |
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