Measurement of 2/1 intrinsic error field of Joint TEXT tokamak

The amplitude and spatial phase of the intrinsic error field of Joint TEXT (J-TEXT) tokamak were measured by scanning the spatial phase of an externally exerted resonant magnetic perturbation and fitting the mode locking thresholds. For a typical plasma with current of 180 kA, the amplitude of the 2/1 component of the error field at the plasma edge is measured to be 0.31 G, which is about 1.8 × 10−5 relative to the base toroidal field. The measured spatial phase is about 317° in the specified coordinate system (r, θ, φ) of J-TEXT tokamak. An analytical model based on the dynamics of rotating island is developed to verify the measured phase.