Heterodyne O-mode reflectometer on the JT-60U tokamak

A three-channel heterodyne O-mode reflectometer system has been developed for density fluctuation measurements on the JT-60U tokamak. The system consists of one fixed channel with a frequency of 34 GHz and two selectable frequency channels with frequencies in the range of 34-40 and 48-50 GHz in order to measure the change of fluctuation amplitude, fluctuation coherence, and movement of the cutoff layer during the discharge. The reflectometer system has now become a standard diagnostic for density fluctuation measurements on JT-60U covering both core and edge plasma regions. The capabilities of the system are illustrated for three experimental cases: edge transport barriers in H-mode plasmas, internal transport barriers in reversed shear plasmas, and fast turbulence burst at the onset of multifaceted asymmetric radiation from the edge. (C) 2002 American Institute of Physics.