Tailoring error field of tokamak to control plasma instability and transport

Abstract A tokamak relies on the axisymmetric magnetic fields to confine fusion plasmas and aims to deliver sustainable and clean energy. However, misalignments arise inevitably in the tokamak construction, leading to small asymmetries in the magnetic field known as error fields (EFs). The EFs have been a major concern in the tokamak approaches because a small level EFs, even less than 0.1 %, can drive a plasma disruption. Contrary to conventional wisdom, we report that the EFs in a tokamak can be favorably used for controlling plasma instabilities, such as edge-localized modes (ELMs), while maintaining a hot fusion plasma at a temperature of 100 million kelvin. A novel optimization tailors the EFs to maintain an edge 3D response for ELM control with a minimized core 3D response to avoid plasma disruption and unnecessary degradation. We design and demonstrate such an edge-localized 3D response at the Korean Superconducting Tokamak Advanced Research facility, benefiting from its unique flexibility to change many degrees of freedom in the 3D coil space for the various fusion plasma regimes. This favorable control of the tokamak EF represents a notable advance for designing intrinsically 3D tokamaks to optimize stability and confinement for the next-step fusion reactors.