CO2 laser based two-volume collective scattering instrument for spatially localized turbulence measurements

We describe and demonstrate a two-volume collective scattering system for l ocalized measurements of plasma turbulence. The finite crossfield correlati on length of plasma turbulence combined with spatial variations in the magn etic field direction are used to obtain spatially localized turbulence meas urements at the Wendelstein 7-AS fusion experiment. By comparing with local ized measurements obtained using the single wide beam technique [Truc , Rev . Sci. Instrum. 63, 3716 (1992)] we provide a proof-of-principle demonstrat ion of the two-beam method. An optimized configuration with large toroidal separation of the measurement volumes is predicted to be capable of providi ng spatial resolution better than 5 cm. (C) 2001 American Institute of Phys ics.