Information on collective scattering spatial resolution using a two-sample-volume cross-correlation technique

The spatial resolution of small-angle collective scattering systems is often ambiguous due to the extended length of the scattering volume. By examining two sample volumes at the same wave vector (or scattering angle) that lie along the incident beam, and by varying the separation between these two volumes, one can examine their cross-correlation through use of simple digital signal processing techniques. As the separation between the two volumes is increased, the signals are observed to decorrelate. Application of this technique on the DIII-D and TEXT tokamaks shows that when the volumes are located at the plasma edge and core, the two signals are decorrelated indicating that fluctuations in the plasma core can be resolved