TFTR microwave reflectometer (abstract)

A microwave reflectometer is in operation on TFTR for the measurement of density fluctuations. The system operates in the X mode and comprises three channels with fixed frequencies of 140, 132, and 125 GHz, and one with stepped frequency of 111–123 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 low-loss corrugated waveguides and remotely controlled parabolic mirrors. Preliminary results indicate that the level of density fluctuations with k⊥ <1 cm−1 is very small in the central region of Ohmic plasmas (ñ/n<10−3), and that it increases monotonically with minor radius to values of ≊10−2 at r/a=0.9. This work supported by U.S. Department of Energy Contract No. DE-AC02-76-CHO-3073.