The effect of mode scrambling on pulsed radar reflectometry applied to high shear devices

In this article the effect of mode scrambling on the operation of pulsed radar reflectometers working in the ordinary polarization mode on devices with a high magnetic shear is studied. Mode scrambling occurs when the magnetic field changes considerably on length and/or time scales which are similar to or smaller than those of the probing wave. In this case the polarization of the mode is not conserved during passage through the plasma, and power is transferred from ordinary to extraordinary mode and vice versa. Calculations with a full-wave code are performed for two different high-shear devices: the RFX reversed field pinch and the LHD torsatron. The conclusion of the work is that the density profiles in these devices can excellently be measured by a pulsed radar reflectometer operating in the ordinary mode. (C) 1997 American Institute of Physics.