On Error Field Correction in Fusion Reactors

In fusion reactors, errors in the magnetic field, due to inaccuracies and tolerances in both the manufacturing and assembly of magnets, have a critical impact on the device plasma confinement capabilities. This paper presents a methodology to assess the possibility of correcting such "error fields" in ITER using general sets of coils (e.g. ELM coils, or even Toroidal Field and Poloidal Field coils) in addition to subsets of dedicated correction coils. Even though in nominal configuration main field magnets do not produce error fields, due to manufacturing and assembly errors they will actually generate a field map possessing harmonic content suitable for error field correction, if suitably controlled. In the paper, a general procedure able to assess capability of actual magnets to compensate for error fields, and capability of general sets of correction coils to correct error fields, will be presented and assessed to the present design of ITER device.