Projections of spheromak configurations sustained with steady, inductive magnetic helicity injection (SIHI) toward high Lundquist number*

The spheromak plasma configuration offers a potential pathway toward compact and simple magnetic fusion energy systems without the toroidal field coils (TFCs) or central solenoid (CS) characteristic of tokamaks. Due to the usage of large magnetic field-normalized plasma currents, spheromaks offer the potential for ohmic ignition provided sufficient energy confinement is achieved. For a spheromak system to operate continuously, both an equilibrium field coil (EFC) set and some method for plasma current drive are needed. Steady, Inductive Helicity Injection (SIHI) is actively being developed to efficiently sustain spheromak plasma currents while directly driving non-axisymmetric dynamics needed for MHD dynamo current drive. Based on recent data from both the HIT-SI3 and HIT-SIU experiments and supporting computational works, projections of SIHI-driven spheromak configurations toward high Lundquist number will be presented. These scaling laws are used to support the envisioned design point for a next-generation Proof-Of-Concept (POC) device that aims to demonstrate the highest core triple product and core ion and electron temperatures for the spheromak concept to-date with pulse lengths of ~ 50 - 100 ms.