Pulsed radar reflectometry on the LHD

Pulsed radar reflectometry is a suitable reflectometric technique with whic h to study the effect of strong magnetic shear for the polarization of micr owaves in the Large Helical Device. Because pulsed radar reflectometry meas ures 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 ope ration 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 i njected. If the electron density does not reach the critical cutoff density , the pulsed radar system could be used as a delayometer. The measured dela yometer 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. (C) 2001 American Institute of Physics.