Density fluctuation measurements using a frequency hopping reflectometer in JT-60U

Oyama, Naoyuki; Takenaga, Hidenobu; Suzuki, Takahiro; Sakamoto, Yoshiteru; Isayama, Akihiko; JT-60 Team

In JT-60U, the frequency hopping reflectometer has been developed to evaluate the poloidal rotation velocity as a Doppler reflectometer and the radial correlation of density fluctuations in plasmas. The system can measure the radial profile of density fluctuations or the profile of radial correlation at two spatial points by combining the fixed frequency reflectometer within 250 ms. The radial profiles of the poloidal rotation velocity evaluated from the Doppler-shifted frequency spectrum in density fluctuations show a positive radial electric field in co-rotating plasma and a negative radial electric field in counter-rotating plasma. The density fluctuation measurement at the internal transport barrier using a correlation reflectometer revealed that the long-range correlation was increased when the internal transport barrier was degraded with the central heating by electron cyclotron wave.