Magnetic Diagnostics For ITER

The measurement and the control of the plasma boundary is one of the fundamental aspects of a magnetically confined plasma. Traditionally, inductive magnetic measurements have been used for discharges of limited duration. For ITER with its projected pulse duration in excess of 1000s with a possible extension to steady state, classical integrators exhibit unacceptable drifts caused by small thermo-electric voltages and the operational amplifier offset current resulting in an erroneous boundary identification by tens of cm. Long term drift compensation schemes have recently been developed based on the intermittent observation of a dummy channel with the same integrator. These schemes have the potential to reduce the drift to < 1 cm for a 1000 s pulse. Therefore the magnetic diagnostic in ITER is based on inductive measurements with voltage loops, saddle loops and pick up coils.