IMAGING METHODS FOR THE OBSERVATION OF PLASMA DENSITY FLUCTUATIONS
Imaging techniques offer attractive alternatives to small-angle Thomson scattering for scale lengths of density fluctuations causing diffraction in the Raman-Nath regime. This is the case for fluctuations with wavelengths above about 3 mm for tokamak size plasmas, when a CO-2 laser probe beam is used. Four methods ("phase scintillation", phase contrast, wave front shearing and interferometry) are compared, on the basis of their transfer properties. They offer new means of studying density fluctuations of magnitude up to the dimensions of the plasma, such as those associated with turbulence, magnetic islands, convective cells or driven waves. The long wavelength limitations are discussed in detail and are related to those encountered for far-field techniques. An experimental comparison of "phase scintillation" and phase contrast is given, and the criteria relative to the depth of field of imaging instruments in this context are considered.
Bibliographic Reference: WRITE TO CONFEDERATION SUISSE, CENTRE DE RECHERCHES EN PHYSIQUE DES PLASMAS, ECOLE POLYTECHNIQUE FEDERALE DE LAUSANNE (SWITZERLAND), MENTIONING REPORT LRP 278/85, 1985
Record Number: 1989124057200 / Last updated on: 1987-01-01
Available languages: en