Exploring Operation Limits of JT-60SA Cryomagnet Operation: Integrated Commissioning Database Use for Modeling Analysis

Abstract

In the framework of international development on fusion devices, the tokamak JT-60SA was equipped with superconducting magnets within a Europe-Japan collaboration. After a first integrated commissioning (IC) in 2021, another IC was conducted in 2023 reaching magnet energization levels compliant with 1 MA-class plasmas. The Toroidal Field (TF) coil system was loaded at nominal current and the Poloidal Field (PF) at 50% of nominal current. In the 2023 IC various energization pulse patterns were applied on PF coils to gain experience on the magnets control and protection system in operation conditions. Some tailored current pulses were applied to learn about PF coils coupling parameters and protection system, which sensitivity was found to be improved. In this environment, we developed tools and methods to model and predict the magnets behaviour to possibly identify coils limits in operation conditions. First step is with thermo-hydraulic evaluation of PF coil temperature safety margin evaluation along their pulsed current patterns. Second step is a first order analysis of the TF quench detection system sensitivity, found higher than expected to PF transients, and the contribution to possible mitigation measures to avoid spurious false positive detections. Both steps were benchmarked against experimental data collected during 2023 IC to consolidate models prediction capacities. Foreseen applications aim at checking plasma scenarios repetability rate or avoiding pulsed coil current to generate apparent fault signal in absence of real risk (mostly quench). The tools and methods are described and their rationales explained, together with their intrinsic limits and room for improvement.