A method to produce lithium pellets for fueling and ELM pacing in NSTX-U

•A new method for delivering lithium to the lithium granular injector has been developed.•Frequencies up to 1.5 kHz achieved.•Droplet/pellet sizes down to 0.6 mm in diameter have been achieved.•Aim is for ELM control and pacing.•This has the potential for replenishing lithium coating during a plasma discharge.

A device for producing small, high frequency spherical droplets or pellets for lithium or other liquid metals has been developed and could aid in the controlled excitation or pacing of edge-localized plasma modes (ELMs). The Liquid Lithium/metal Pellet Injector (LLPI) could also be used to replenish lithium coatings of plasma-facing components (PFCs) during a plasma discharge. With NSTX-U having longer pulse lengths (up to 5 s), it is desirable to be able to inject lithium during the discharge to maintain the beneficial effects. Using a nozzle injector design and a surrogate to lithium, Wood's metal, the LLPI has achieved droplet diameters between 0.6 mm < ddrop < 1 mm in diameter and frequencies up to 1.5 kHz with argon gas driving the formation. This paper presents the LLPI being developed with initial results mainly using Wood's metal and some lithium, using high pressure argon to force the liquid lithium through the nozzle.