Millimeter-wave reflectometry for electron density profile and fluctuationmeasurements on NSTX

A millimeter-wave reflectometry system for electron density profile and flu ctuation measurements is being developed and installed on the National Sphe rical Torus Experiment. The initial frequency coverage will be in the bands 12-18, 20-32, and 33-50 GHz, provided by frequency-tunable solid-state sou rces. These frequencies correspond to O-mode cutoff densities ranging from 1.8 x 10(12) to 3.1 x 10(13) cm(-3), which will span both the plasma core ( rho = r/a < 0.8) and edge (rho >0.8) regions. Operated as a broadband swept -frequency (frequency-modulated continuous-wave) reflectometer, the diagnos tic is expected to provide routine (shot-to-shot) time- (less than or equal to 50 mus) and spatially resolved (similar to1 cm) density profiles. The p revious hardware can be easily reconfigured as a fixed-frequency reflectome ter for density fluctuation measurements. The combination of measurements w ould be valuable for studying phenomena such as possible L- to H-mode trans itions and edge-localized modes. (C) 2001 American Institute of Physics.