Recent advances in physics and applications of 3D magnetic fields on the J-TEXT tokamak

This paper summarizes recent experimental and theoretical progress achieved on the J-TEXT tokamak during the past two years, with an emphasis on the physics and applications of three-dimensional (3D) magnetic fields. Key hardware upgrades include a new ICRF system and the advanced 3D magnetic coil systems, consisting of the resonant magnetic perturbation (RMP) coils, the island divertor (ID) coils and the external rotational transform (ERT) coils. And these upgrades enable novel investigations into MHD instabilities, disruptions, transport, and divertor solutions. A major finding is the neoclassical tearing mode (NTM) triggered formation of electron internal transport barrier, where magnetic island nonlinearly interacts with turbulence to suppress transport and steepen core temperature gradients, and reveals a new mechanism for confinement improvement. Furthermore, internal kink mode driven neoclassical toroidal viscosity torque is identified as a key mechanism governing intrinsic rotation. The application of ERT coils successfully creates a Tokamak-Stellarator hybrid configuration, demonstrating complete suppression of NTMs and a 20% increase in stable plasma current. For boundary control, an ID configuration is established, reducing peak heat loads by ∼50% and enabling detachment via supersonic molecular beam injection fuelling. In disruption physics, synergetic control using RMP and O-point aligned electron cyclotron resonance heating efficiently suppresses locked modes and disruption, while low- n magnetic perturbations are capable of runaway electron suppression. Thermal quench timescale, estimated by a unified model with stochastic magnetic field and turbulence, matches experimental observations. Additionally, AI-driven disruption prediction frameworks, incorporating adaptive anomaly detection and cross-machine domain adaptation, are developed, with interpretability analyses linking predictions to physical mechanisms. Studies on turbulence and transport elucidate the role of electrode biasing, turbulence spreading on the edge cooling, density limit, while helium ash removal dynamics are also investigated. The unique up-down symmetric poloidal divertor configuration is measured and modelling to identify the electric field induced drift effect as a key driver for asymmetry, and hence target biasing is designed and experimentally studied for control these asymmetries. These collective advances in heating, 3D field control, stability, and AI forecasting provide critical solutions for managing plasma confinement and mitigating risks in future MCF devices.