Measurements with a high resolution pulsed radar reflectometer

At the RTP Tokamak (RTP = Rijnhuizen Tokamak Project) a four-channel pulsed radar diagnostic is under development. Gaussian shaped pulses, with a full width at half maximum (FWHM) of 500 ps, will be transmitted in the O-mode. The time of flight between transmission and receipt of the pulse, after it has been reflected from the critical density layer, will be measured with a resolution of<70 ps, leading to a spatial resolution of 1 cm. The repetition rate will be 2x106 pulses per second. Since in a pulsed radar system unwanted reflections, e.g. from vacuum breaks, can be separated from reflections from a density layer in the plasma, only one antenna can be used, making the access demands to the tokamak very modest. One of the goals of this system is to study the possibilities of pulsed radar as a JET divertor diagnostic. (author) 6 refs., 3 figs