Pulsed radar reflectometry on the LHD

Pulsed radar reflectometry is a suitable reflectometric technique with which to study the effect of strong magnetic shear for the polarization of microwaves in the Large Helical Device. Because pulsed radar reflectometry measures the delay time of the reflected wave, not the phase, X-mode and O-mode polarized waves can be distinguished. At a preliminary stage of X-mode operation it is found that the position of the ergodic edge layer is steady in spite of the increased density in the core region when a neutral beam is injected. If the electron density does not reach the critical cutoff density, the pulsed radar system could be used as a delayometer. The measured delayometer signal is almost in agreement with the numerical calculation under the assumption that polarization of the wave propagated into the plasma is decided at the edge region.