Benchmarking of spherical tokamak power plant design in PROCESS and SARAS

Uncertainty in systems codes can be analyzed based on the assumptions in the models used, and their combinations of input parameters before optimization. In this paper we compare the PROCESS and SARAS codes across a range of spherical tokamak designs that have been identified as possible pilot plant and commercial designs on the Indian-DEMO programme. Overall both codes produce partially similar results though differences in the calculation and treatment of the edge safety factor lead to discrepancies in the calculation of other key parameters with differences of $\approx \pm 20\text{\%}$. Mainly with plasma current, $\beta$ components and subsequently confinement time calculations. Bootstrap current fraction calculations were shown to be unreliable and out of the regime of future power plants, highlighting the need for new surrogate models closer to power plant conditions . Using Monte Carlo based uncertainty quantification focusing on the epistemic uncertainty of the inboard toroidal field coil leg we see reasonable agreement in stress quantification between the two codes. The pessimistic uncertainty assumption still shows room for performance recovery in a reduced toroidal field strength scenario.