<i>X</i>-mode broadband reflectometric density profile measurements on DIII-D

A 50–75 GHz, X-mode, broadband reflectometer system is installed and operational on DIII-D. Density profiles have been obtained under a wide range of operating conditions, including Ohmic, L-, and H-mode operation. Good agreement has been found with profiles obtained by Thomson scattering, but only with the use of fast sweeps. Profiles are calculated from the line-integrated phase data using a stable numerical inversion algorithm. Using these techniques, and allowing for the reset time of the tube, density profiles can be measured every 2.5 ms. The system is still under development: By adding an additional 50–75 GHz BWO and mixers, the system will be reconfigured to also act as a correlation reflectometer.