Compact toroid injection into C-2U

Sustainment of an advanced neutral beam-driven FRC for a period in excess of 5 ms is the primary goal of the C-2U [1] machine at Tri Alpha Energy. In addition, a criteria for long-term global sustainment of any magnetically confined fusion reactor is particle refueling. To this end, a magnetized coaxial plasma-gun has been developed [2]. Compact toroids (CT) are to be injected perpendicular to the axial magnetic field of C-2U. To simulate this environment, an experimental test-stand has been constructed. A transverse magnetic field of $B\approx 1 kG$ is established (comparable to the C-2U axial field) and CTs are fired across it. As a minimal requirement, the CT must have energy density greater than that of the magnetic field it is to penetrate, i.e., $\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}\rho v^{2}\ge B^{2}/2\mu_{0} $. This criteria is easily met and indeed the CTs traverse the test-stand field. A preliminary experiment on C-2U shows the CT also capable of penetrating into FRC plasmas and refueling is observed resulting in a 20 $-$ 30{\%} increase in total particle number per single-pulsed CT injection. Results from test-stand and C-2U experiments will be presented. \\[4pt] [1] M. Binderbauer et al., Physics of Plasmas, 22, 056110 (2015) \newline [2] T. Matsumoto et al., Bull. Am. Phys. Soc. 59, UP8.00008 (2014)