Design of a coil to correct magnetic field errors on the DIII-D tokamak

Careful measurements have been made of the error fields created by the 19 field-shaping coils on DIII-D. Spectral analysis has yielded a better understanding of the source of the toroidal and poloidal field errors existing on the tokamak. With this new information, a much better error-field correction coil (C-coil) has been designed which should be able to nearly eliminate the m=2, n=1 component of the error field without introducing other toroidal modes. By dividing the C-coil into segments which can be connected in different configurations, one will be able to program the phase and amplitude of a variety of perturbation fields for experimentation. Alternatively, the coil can be configured and programmed to provide the maximum reduction of error fields for routine plasma operations, enabling a wider stable operating parameter space for the tokamak. Details for the C-coil design and its harmonic spectrum are presented.<>