Overview of power and diagnostic upgrades for HIT-SI3 and planned HIT-SIU experiments

The HIT-SI3 device is being upgraded with new switching power amplifiers (SPAs) and capacitor banks for a 70{\%} increase in nameplate power capacity and a 35{\%} increase in stored energy. The additional power injection will enable optimized j/n and longer duration sustainment of high current (\textgreater 100 kA) and high current amplification (\textgreater 3) spheromaks. A new, multi-chord, two-color interferometer is being constructed to measure plasma density in the toroidal midplane. The new system will be able to operate in HIT-SI3's high density regime (n\textunderscore e \textgreater 5 x 10\textasciicircum 19 m\textasciicircum -3) where the previous far-infrared interferometer could not. Additionally, plans for the new HIT-SI-Upgrade (HIT-SIU) are presented. The three, discrete helicity injectors will be replaced with a manifold which has four connections to the spheromak flux conserver. The new injector manifold will test lower density startup, improved plasma-facing insulating coatings, applied perturbation spectra predicted to improve performance, and a geometry compatible with larger, future devices.