Analysis of the expected resolution of the electron-cyclotron emission crossed-sightline magnetic field diagnostic

The local value of the magnetic field B(r) inside the plasma in magnetic fusion experiments is a quantity of considerable interest. Given information about plasma density and temperature it can be used to calculate the poloidal magnetic field, or given a zero current device (or the current profile) the local value of beta. The time history B(r,t) can be used to infer the level of magnetic fluctuations in the plasma. The poloidal magnetic field and the level of magnetic fluctuations are particularly interesting quantities, since they are difficult to measure, and are both important for understanding particle and energy transport in magnetic fusion experiments. In fact, to date, no measurement of the local value of the total magnetic field or its time variation has been made in a high temperature plasma. Previous measurements have been confined to relatively cold plasmas where probes could be used, or have inadequate resolution to distinguish the value of the field with plasma present from its vacuum value. It has been recently suggested that crossed-sightline correlation of electron-cyclotron emission might be used to infer B(r _x,t) at the crossing point r_x in the plasma of the two sightlines. The equations and techniques necessary to simulate this proposed diagnostic are developed below, and the results of a numerical simulation of the diagnostic resolution for both TEXT and CIT are presented.