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An outstanding concern raised over the implementation of liquid metal plasma facing components in fusion reactors is the potential for ejection of liquid metal into the fusion plasma. The influences of Rayleigh–Taylor-like and Kelvin–Helmholtz-like instabilities were experimentally observed and quantified on the thermoelectric-driven liquid-metal plasma-facing structures (TELS) chamber at the University of Illinois at Urbana–Champaign. To probe the stability boundary, plasma currents and velocities were first characterized with a flush probe array. Subsequent observations of lithium ejection under exposure in the TELS chamber exhibited a departure from previous theory based on linear perturbation analysis. The stability boundary is mapped experimentally over the range of plasma impulses of which TELS is capable to deliver, and a new theory based on a modified set of the shallow water equations is presented which accurately predicts the stability of the lithium surface under plasma exposure.

Design and characterization of 2.45 GHz electron cyclotron resonance plasma source with magnetron magnetic field configuration for high flux of hyperthermal neutral beam Rev. Sci. Instrum. 81, 083301 (2010); 10.1063/1.3477998Sheath and potential characteristics in rf magnetron sputtering plasma

An effort to optimize the magnetic field configuration specifically for high-power impulse magnetron sputtering (HiPIMS) was made. Magnetic field configurations with different field strengths, race track widths and race track patterns were designed using COMSOL. Their influence on HiPIMS plasma properties was investigated using a 36 cm diameter copper target. The I-V discharge characteristics were measured. The temporal evolution of electron temperature (T e) and density (n e) was studied employing a triple Langmuir probe, which was also scanned in the whole discharge region to characterize the plasma distribution and transport. Based on the studies, a closed path for electrons to drift along was still essential in HiPIMS in order to efficiently confine electrons and achieve a high pulse current. Very dense plasmas (10 19-10 20 m −3) were generated in front of the race tracks during the pulse, and expanded downstream afterwards. As the magnetic field strength increased from 200 to 800 G, the expansion became faster and less isotropic, i.e. more directional toward the substrate. The electric potential distribution accounted for these effects. Varied race track widths and patterns altered the plasma distribution from the target to the substrate. A spiral-shaped magnetic field design was able to produce superior plasma uniformity on the substrate in addition to improved target utilization.

Liquid metal plasma facing components have shown a potential to supplant solid plasma facing components materials in the high heat flux regions of magnetic confinement fusion reactors due to the reduction or elimination of concerns over melting, wall damage, and erosion. The viability of liquid metal plasma facing components, however, is dependent upon understanding their interaction with the substrates upon which they are mounted. To this end, the wetting of lithium compounds (lithium nitride, oxide, and carbonate) by 200 ℃ liquid lithium at various surface temperature from 230 to 330 ℃ was studied by means of contact angle measurements. Wetting temperatures, defined as the temperature above which the contact angle is less than 90°, were measured. The wetting temperature was 257 ℃ for nitride, 259 ℃ for oxide, and 323 ℃ for carbonate. Surface tensions of solid lithium compounds were calculated from the contact angle measurements. Highlights  Contact angles of liquid lithium and Li 3 N, Li 2 O, Li 2 CO 3 were measured  Liquid lithium wets lithium compounds at relatively low temperatures: Li 3 N at 257 ℃, Li 2 O at 259 ℃, Li 2 CO 3 at 323 ℃ Abbreviations PFC, plasma-facing components; CPS, capillary porous system; LIMIT, liquid metal infused trench;