Chapter 4: Laser-Aided Plasma Diagnostics

Laser-aided diagnostics are widely applied in the field of high-temperature plasma diagnostics for a large variety of measurements. Incoherent Thomson scattering is used for highly localized measurements of the electron temperature and density in the plasma. Coherent Thomson scattering yields information on the fast ion population in the plasma and/or depending on the geometry and wavelength chosen electron density fluctuations. Interferometry and polarimetry are often combined in a single diagnostics setup to measure the electron density and the component of the magnetic field parallel to the laser chord. Density fluctuations can be measured by means of phase contrast imaging, scattering, and various other laser-aided techniques. This paper is primarily focused on laser diagnostics utilized in the mainstream magnetic confinement research (tokamaks and stellarators with some examples from other devices if applicable). In the paper a brief tutorial introduction in each of the techniques is given, followed by a description of some typical implementations on magnetic confinement devices and some examples of recent experimental results. For each of the techniques the potential application to the ITER tokamak is also discussed. The paper is not meant as a comprehensive and exhaustive review giving a proper tribute to all the work that has been done in this field over the years.