Tailoring tokamak error fields to control plasma instabilities 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 small EFs, even less than 0.1%, can drive a plasma disruption. Meanwhile, the EFs in the tokamak can be favorably used for controlling plasma instabilities, such as edge-localized modes (ELMs). Here we show an optimization that tailors the EFs to maintain an edge 3D response for ELM control with a minimized core 3D response to avoid plasma disruption and unnecessary confinement degradation. We design and demonstrate such an edge-localized 3D response in the KSTAR 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 next-step fusion reactors.

Thermoelectrics for nuclear fusion reactors: opportunities and challenges

“…With the ideal working temperature range of W being 873–1673 K, 8 it was assumed that an average temperature of 1273 K would be the ideal base temperature for normal operations, providing a safe allowance from the upper limit in case of instabilities in the plasma. Recently, there have been a couple of breakthroughs in improving plasma stabilities, such as tailoring the plasma error fields to minimize ELMs with little degradation to the magnetic confinement, 178 negative triangularity shaping of the plasma to suppress ELMs, 179 an AI model to predict “tearing mode” plasma instabilities so that the operating conditions can be adjusted to prevent them from happening, 180 the demonstration of stable tokamak plasmas with line-averaged density approximately 20% above the empirical limit, 181 and the tungsten environment in a steady-state tokamak (WEST) sustaining the plasma for a record-breaking duration of 6 min. 182 Therefore, with the advances in plasma stabilities, less safety allowance may be required so that the fusion reactor may be allowed to operate with the plasma-facing surfaces at higher temperatures for improved conversion efficiencies.…”