Application of far-infrared and millimeter wave techniques in plasma diagnostics in Hefei tokamaks

In magnetically confined fusion plasmas, confining magnetic field and electron densities determine the plasma dielectric properties. Electromagnetic waves either generated in the plasmas or being launched into and reflected from the plasmas carry the information of plasma properties. The passive reception of the electromagnetic waves emitted from plasma or the actively launched probing waves into plasmas provide effective diagnostic tools to measure both spatially and temporally resolved plasma properties, such as plasma equilibrium profiles of electron temperature profile, electron density profile, and plasma transport related fluctuations of electron temperature and density, as well as the electron velocity distribution function and the internal poloidal magnetic field. In fusion devices, the characteristic cut-off frequencies and resonant frequencies in plasmas are in infrared to millimeter wave ranges (/spl lambda/: 0.3mm-30mm). Various microwave and infrared systems have been developed for plasma diagnostics purposes. Heterodyne radiometry, interferometer, polarimeter, reflectometry, millimeter transmission and absorption analysis and RDAR techniques are widely used in fusion devices. We present here an overview of the practices of infrared and millimeter techniques, systems developed on Hefei tokamaks (HT-6B, HT-6M, HT-7, HT-7U) for plasma diagnostics.