Plasma density fluctuation measurements from coherent and incoherent microwave reflection

Using the spatial coherency present in a reflected microwave signal (Conway et al 1994 Rev. Sci. Instrum. 65 2920) it is possible to measure a coherent, , and an incoherent, , reflection coefficient (proportional to the radar cross section) from a turbulent plasma cutoff layer. Results acquired with a 17 GHz reflectometer from the STOR-M tokamak edge region give significant and , which suggests two-dimensional structure in the reflection layer. Using a `distorted-mirror' model for the plasma fluctuations, estimates of an effective radial width, , and poloidal correlation length, , can be derived from the reflection coefficients. STOR-M results typically give a of a few millimetres and an of a couple of centimetres.