Transport Modeling of NSTX/NSTX-U discharges

The spherical tokamak (ST) provides critical information required for the optimization of the

design and operation of steady-state compact fusion pilot plants (CFPP). The National

Spherical Torus Experiment Upgrade (NSTX-U) will advance the physics basis by producing

unique non-inductive regimes at low-aspect ratio that operate at large normalized beta,

bootstrap fraction and toroidal field utilization. However, in order to extrapolate the results

obtained on current STs to next-step devices, a better physics understanding of transport,

stability, and non-inductive start-up is required, as well as the development of predictive

capabilities that span aspect ratio. This work describes the results of plasma transport

modeling performed using the OMFIT framework on previous relevant NSTX/NSTX-U

discharges. Simulations are carried out with the TRANSP and TGYRO modules of OMFIT,

and comparisons between calculated and measured plasma quantities indicate the validity of

these predictive tools. To better understand the underlying transport mechanisms, we have

performed linear turbulence mode analysis using the TGLF model and identified conditions

where this model might be applicable for NSTX plasmas.