Ohmic heating in a magnet coil by eddy currents

The energy dissipation by eddy currents through ohmic losses is addressed, where the effective resistance of a magnetic coil is examined on the basis of the experimental result of heat production. That coil is the single component of a water cooled magnet system that provides the required high magnetic field for operation of the 35 GHz, 100 k W gyrotron under development at INPE. Each pancake coil is wound from an insulated copper tube of 25 m length which has a rectangular cross section (9 x 9 mm2) with a 5 mm-diameter orifice leading the cooling water. It is discussed that, in conventional solenoids the action of eddy currents may be detrimental as the result of a nonuniform current distribution in the conductors which leads to higher ohmic losses. (author)