Core correlation reflectometer at the JT-60U tokamak

Core correlation reflectometer has been newly installed on the JT-60U tokamak. The target of this reflectometer is to measure the fluctuation of the electron density and its correlation in the core region, especially in the internal transport barrier, region of high-performance-reversed shear plasma. The reflectometer consists of four channels, two of which operate in fixed frequency and the other two channels are tunable. The tunable channels can step through five frequencies in each 60 ms. The fluctuation correlation is determined from the correlation between fixed and variable frequency channels and the radial profile of the correlations can be measured every 60 ms in a discharge. The polarization of the launched wave is the extraordinary mode, X mode, in order to obtain a high space resolution and to access the high-field side of the magnetic axis. (C) 1999 American Institute of Physics. [S0034-6748(99)04511-6].