Evaluation of error poloidal field in an iron-cored tokamak

The error field (magnetic induction) conjectured to originate from the connecting conductors and the turnback coil of toroidal field coils and the poloidal field, which is applied to compensate the error field and the electron toroidal drift, are computed with semianalytic expressions. The vertical component of the computed error field agrees roughly with the error vertical field which is evaluated indirectly by determining the optimum value of the applied poloidal field from the standpoint of the tokamak gas breakdown. The computed value of the applied poloidal field produced by simple circular coils agrees satisfactorily with the directly measured one.