Intermittent helicity injection for field-reversed configurations control: shear-driven tilt suppression and ion heating

In this study, we present a comprehensive stability analysis of Field-Reversed Configuration (FRC) during formation and sustainment, integrating both experimental and numerical approaches. The formation of bi-directional toroidal flow during spheromaks merging is identified as a key factor in suppressing $n=1$ toroidal mode through the stretching and advection of magnetic field lines. To substantiate experimental findings and assess the efficacy of the innovative "intermittent merging" technique in maintaining plasma stability, we develop a $3$D Hall-MHD model. This technique, involving the periodic merging of new pairs of spheromaks into the FRC, demonstrates the ability to suppress low-n toroidal modes, especially $n=1$, while driving the plasma current, thereby sustaining MHD instabilities for extended periods.