Millimeter Wave Imaging and Visualization of Plasma Waves and Instabilities

Summary form only given. The microwave and millimeter wave region of the electromagnetic spectrum is ideally suited for the determination of plasma parameters such as electron density and temperature as well as more subtle phenomena such as collective waves and instabilities through exploitation of the frequency dependent properties of this dielectric medium. This spectral region is witnessing intensive activity through the recent microwave and millimeter wave technology advances which have made possible the development of novel imaging and visualization diagnostics for hot plasmas. These include imaging scattering systems and imaging interferometer/polarimeter systems as well as electron cyclotron emission imaging (ECEI) systems and microwave imaging reflectometry (MIR) systems. For example, a novel 2-D ECEI on the TEXTOR tokamak provides 2-D images with high spatial resolution [128 pixels covering 8 cm (radial) x 16 cm (vertical)], and high temporal resolution (up to ~5 microsec) which have revealed the details of 2-D images of the electron temperature fluctuations during the precursor phase and the crash time of m=1 (sawtooth) oscillations, with a level of detail that is not accessible through conventional methods (1-D ECE and/or tomography). Also on TEXTOR, a 16-channel MIR system, that can measure multiple poloidal wavenumbers up to ~3 cm^-1, has been designed and installed for plasma experiments. These and other imaging diagnostics implementations will be described.