Electron density profile measurement using an ultrashort-pulsed radar reflectometer on large helical device

Abstract

We have installed a six channel ultrashort-pulsed radar reflectometer system on the large helical device and performed electron density profile measurements. The delay time of the reflected pulses from each cutoff layer in the plasma is measured by a time-of-flight measurement technique in order to avoid the mixture of radiation effects and spurious reflections. The electron density profile is reconstructed using an Abel inversion method from the profile of the delay time as a function of the probing frequency. The reconstructed density profile is compared with the profile measured with the far-infrared (FIR) interferometer. It is found that the arrival time of each reflected pulse differs from the estimated time measured with the FIR interferometer.