Confinement Scaling Projections for Local Helicity Injection Plasma Startup on Pegasus-III*

I_p(t) in plasmas produced by Local Helicity Injection (LHI) is described by global helicity conservation and a Taylor relaxation limit that is less restrictive as the device size and B_T is increased. In the helicity-limited regime, the ability to project I_p(t) depends on understanding the dissipation of injected helicity. As no first-principles model presently exists for confinement during LHI (during which stochastic and/or reconnection-driven transport may also occur), modeling to date has assumed resistive dissipation (η∼T_e^-3/2) and utilized tokamak τ_E scalings. Observations of LHI plasmas on Pegasus at B_T < 0.15 T in transport equilibrium were consistent with estimates from neo-Alcator and collisional stochastic models, assuming modest auxiliary heating from reconnection. Modeling considering the expanded helicity drive, increased B_T (< 0.60 T), and n_e in Pegasus-III suggests favorable, distinguishable trends in I_p and T_e amongst the assumed confinement regimes. Recent extensions to an LHI 0D power-balance model incorporate a dynamic estimate of τ_E and self-consistently find I_p(t) and T_e(t) to treat scenarios outside transport equilibrium and assist in design and execution of initial Pegasus-III LHI studies.