Plasma-wall interaction on the SLiC spherical tokamak device with large-area, dynamic liquid lithium free surface

Presentation Abstract Stephen Howard, Alex Mossman, Wade Zawalski, Don Froese (General Fusion) General Fusion is developing a magnetized target fusion system in which a spherical tokamak plasma target is injected by a magnetized Marshall gun into a flux conserver consisting of a liquid lithium vortex. A compression system will then collapse the cavity to compress and heat the target plasma to fusion conditions. We have recently commissioned a subscale experiment called SLiC (Spector Lithium Configuration) as way to de-risk both the engineering and the confinement physics in the situation where a moderately hot magnetized plasma must interact with a large-area free surface of liquid lithium. SLiC is similar in design to the sequence of compact, high-performing spherical tokamak SPECTOR devices that have been in operation at GF since 2016. In the first phase of experiments, ST plasmas were injected into a well-instrumented solid metal flux conserver with an annular liquid lithium puddle on the bottom of the vessel that had an angular coverage of 7 to 28 degrees (spherical polar angle) depending on puddle fill depth. A second phase of experiments, aiming to approach hemispherical coverage of liquid lithium, has extended the angular coverage to 78 degrees (polar angle) starting at the outboard equator going downward. This is done by applying an early current pulse that propels the liquid puddle outward to~coat the flux conserver up to the equator in advance of the plasma formation. Interactions between the plasma and liquid free surface are studied with fast camera video and standard plasma diagnostics and used to validate corresponding MHD-CFD simulations.

Effects on Stable MHD Region of a Magnetized Target Plasma Compression

Presentation Abstract Aaron Froese (General Fusion), Dylan Brennan (Princeton Plasma Physics Laboratory, Princeton University), Sandra Barsky (General Fusion), Alex Wen (University of British Columbia), Meritt Reynolds (General Fusion), Zhirui Wang (Princeton Plasma Physics Laboratory), Michel Laberge (General Fusion) General Fusion is designing a magnetized target fusion reactor to compress a toroidal plasma inside a liquid metal cavity and heat it to fusion conditions. Plasma compression in realistic geometry is modelled as a series of equilibrium states generated by CORSICA. The resistive and ideal MHD stability of each equilibrium is analyzed using the resistive DCON code. We find plasma conditions that are stable to high compression and show how their range is affected by geometry and current density effects. The results are confirmed for representative cases with a time-dependent MHD simulation. Stability is found to be strongly affected by the current density near the plasma edge. Due to the solid central shaft and its effect on plasma elongation, compression reduces the current density near the edge to conserve the q profile. However, this effect can be offset by ramping the shaft current or increasing plasma rotation. At high compression ratios, self-similar compression geometries are ideal MHD unstable for intermediate n, but a longer central shaft and plasma rotation are both stabilizing. This work is supported by a US Dept of Energy INFUSE 2020a Award.