Diagnostic Potentials of Diamagnetic Measurements with Two Loops in Tokamaks

Abstract

The magnetic flux through the diamagnetic loop consists of two parts: one is produced by the poloidal current in the plasma and another by the external currents. Separation of these parts is the focus of the study, which is fully analytical. The system is assumed to be axially symmetric. Then the “inductances” in the flux–current relations are expressed via easily tractable integrals. With such precisely defined coefficients, the theoretical possibility of perfect separation by means of two independent simultaneous measurements is demonstrated. The desired result can be obtained with quantities measured by either double-loop method or with a single diamagnetic loop and a correction coil. This conclusion is more optimistic that those in the generally accepted concepts. An additional step is proposed to determine, with the same magnetic data, the poloidal current induced in the vacuum vessel wall. This current can be useful for evaluation of the disruption force on the wall. The proposed algorithms can be used in existing tokamaks with two loops and in the ITER as well.