Magnetic field reconstruction in toroidal geometry

Information on magnetic fields in the whole plasma volume are estimated, in RFX-mod, from the solutions of a Newcomb-type equation solved con- sistently with experimental boundary conditions in toroidal geometry, [zt]. The solutions, the complex harmonics of the (Fourier decomposed) magnetic fluxes, are the output of the eigenfunction routine [notafc]. This outputs are routinely used for every magnetic reconstruction, as e.g. in SHEq or FLiT. We show here how to compute the magnetic field component profiles start- ing from the magnetic fluxes, using eigenfunction and the toroidal (non- diagonal) geometry in which the fluxes are computed. Because of the curvi- linear metrics, the derivative of the magnetic fluxes are related to the con- travariant magnetic field components, which are not the measureble ones. In order to compare the reconstructed fields with experimental measurements, one needs to go back to the components in an ortho-normal coordinate system: we choose the machine coordinates (r m ;? m ;? ) with a normalized vector basis. This is done in section 2 of this note, while in section 3 some comparison with ISIS magnetic measurements are shown.