A microwave reflectometer is in operation on TFTR for the measurement of density fluctuations. The system operates in theXmode and comprises three channels with fixed frequencies of 140, 132, and 125 GHz, and one with stepped frequency of 111ndash;123 GHz. All channels use solid state Gunn oscillators and a heterodyne detection scheme. The system is located outside of the TFTR test cell with the power conveyed to the tokamak vessel by lowhyphen;loss corrugated waveguides and remotely controlled parabolic mirrors. Preliminary results indicate that the level of density fluctuations withkperp;thinsp;1 cmminus;1is very small in the central region of Ohmic plasmas (ntilde;/n10minus;3), and that it increases monotonically with minor radius to values of ape;10minus;2atr/a=0.9. This work supported by U.S. Department of Energy Contract No. DEhyphen;AC02hyphen;76hyphen;CHOhyphen;3073.
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