On the theory of magnetic diagnostics in stellarators and tokamaks

The main problem of magnetic diagnostics is discussed here: which plasma characteristics can be determined from magnetic measurements in tokamaks and stellarators. The reason is elucidated why diamagnetic measurements are reliable and easily interpretable. Explanation is given of the paradox that the measured diamagnetic signal is always proportional to plasma energy, even in the case when magnetic flux is frozen into the plasma. Diagnostics based on the measurements of poloidal fields outside the plasma is also discussed. The integral nature of measurable signals is shown to be a serious obstacle for estimating plasma pressure and current profiles from magnetic measurements.