Electron kinetic effects on interferometry and polarimetry in high temperature fusion plasmas

At anticipated high electron temperatures in ITER, the effects of electron thermal motion on phase measurements made by the toroidal interferometer/polarimeter (TIP) and poloidal polarimeter (PoPola) diagnostics will be significant and must be precisely treated or the measurement accuracy will fail to meet the specified requirements for ITER operation. We calculate electron thermal corrections to the interferometric phase and polarization state of an electromagnetic wave propagating along tangential and poloidal chords (Faraday and Cotton–Mouton polarimetry) and incorporate them into the Stokes vector equation for evolution of polarization. Although these corrections are small at electron temperatures Te ! 1 keV, they become sizable at Te ! 10 keV. The precision of the previous lowest order linear in the τ = Te/mec model may be insufficient; we present a more precise model with τ 2-order corrections to satisfy the high accuracy required for ITER TIP and PoPola diagnostics. Proper treatment of temperature effects will ensure more accurate interpretation of interferometric and polarimetric measurements in fusion devices like ITER and DEMO. The use of precise analytic expressions is especially important for burning plasmas where various interferometric techniques will be used for direct real time feedback control of device operations with time resolution ∼1 ms to regulate the rate of the thermonuclear burn and monitor/control the safety factor profile.