Confinement Physics on Plasma Injector 3

Achieving energy gain with Magnetized Target Fusion (MTF) requires the plasma to satisfy a set~of goals: particle inventory (10$^{\mathrm{21}}$ ions), magnetic~flux (0.3 Wb) to confine the plasma without MHD instability, and energy confinement time significantly~longer than the compression time.~To study the physics of reactor-scale plasmas, General Fusion (GF) has constructed Plasma Injector 3 (PI3).~The toroidal magnetic field in PI3 is produced by a~pulsed power supply that also provides a low-voltage pulse to compensate resistive losses on a timescale of 10-50 ms.~Once the toroidal field is established, PI3 uses a 50 microsecond pulse of coaxial helicity injection to produce a spherical tokamak plasma with total lifetime of 20 ms, within an aluminum flux conserver of radius 1 m, evap. coated with Li.~Diagnostics include Mirnov probes, visible imaging, interferometers, spectroscopy, Doppler thermometry,~Thomson scattering, AXUV, and FIR polarimetry. The goal is to determine the magnetic profile, stability, and the energy confinement time of the ST plasma during the first 7 ms to evaluate its suitability for compression to fusion conditions by an imploding liquid metal flux conserver. Comparing PI3 data to our SPECTOR devices (vessel radius $=$ 0.2 m) will inform the requirements of the next generation injector for GF's Fusion Demonstration Plant. PI3 is upgrading power supply from 3.5 MJ to 7 MJ by Fall of 2020.