Intrinsic non-resonant error field (NREF) amplitude in SPARC

Determine the amplitude of the intrinsic non-resonant error field (NREF) in SPARC tokamak plasmas that remains after cancellation of the dominant mode component by the error field correction coils, since the EF correction modeling conservatively assumes the applied n=1 fields add to this residual non-resonant spectrum but its magnitude is unknown.

Background

Non-resonant components of the error field drive neoclassical toroidal viscosity (NTV) torques that can reduce plasma rotation and limit the effectiveness of error field correction (EFC). In the paper, a simplified torque-balance model is introduced to estimate rotation braking due to residual non-resonant spectra produced when applying n=1 EFC.

Within this framework, the authors adopt a conservative assumption that EFC adds to any pre-existing intrinsic non-resonant error field, but they explicitly state that the magnitude of this intrinsic NREF is unknown. Clarifying this amplitude is important for accurately predicting NTV braking and the maximum correctable error field under realistic EFCC operations.

References

This makes the conservative assumption that the EFC is always adding to the intrinsic NREF, which is left as an unknown.

— SPARC Tokamak Error Field Expectations and Physics-Based Correction Coil Design  (2601.12469 - Logan et al., 18 Jan 2026) in Subsubsection “Non-resonant Rotation Braking” within Section “Nonresonant Error Fields”