Differential-phase reflectometry for edge profile measurements on Tokamak fusion test reactor

Edge electron density profile measurements, including the scrape-off layer, have been made during ion cyclotron range of frequency (ICRF) heating with the two-frequency differential-phase reflectometer installed on an ICRF antenna on the Tokamak fusion test reactor (TFTR). This system probes the plasma using the extraordinary mode with two signals swept from 90 to 118 GHz, while maintaining a fixed-difference frequency of 125 MHz. The extraordinary mode is used to obtain density profiles in the range of 1×1011–3×1013 cm−3 in high-field (4.5–4.9 T) full-size (R0=2.62 m, a=0.96 m) TFTR plasmas. The reflectometer launcher is located in an ICRF antenna and views the plasma through a small penetration in the center of the Faraday shield. A 26-m-long overmoded waveguide run connects the launcher to the reflectometer microwave electronics. Profile measurements made with this reflectometer system will be presented along with a discussion of the characteristics of this differential phase reflectometer and data analysis.