Abstract
We have upgraded the multi-channel microwave reflectometer system which uses a frequency comb as a source and measure the distribution of the density fluctuation caused by magneto-hydro dynamics instability. The previous multi-channel system was composed of the Ka-band, and the U-band system has been developed. Currently, the U-band system has eight frequency channels, which are 43.0, 45.0, 47.0, 49.0, 51.0, 53.0, 55.0, and 57.0 GHz, in U-band. Before the installation to the Large Helical Device (LHD), several tests for understanding the system characteristics, which are the phase responsibility, the linearity of output signal, and others, have been carried out. The in situ calibration in LHD has been done for the cross reference. In the neutral beam injected plasma experiments, we can observe the density fluctuation of the interchange mode and obtain the radial distribution of fluctuation amplitude.
Highlights
Helical Device reflectometer system in the U-band microwave range for measuring plasma regions at higher density
The microwave reflectometer system has been applied to the LHD plasma experiment with the condition that the magnetic field strength of the axis is -1.375 T and the magnetic axis position is 3.60 m
In the shot number 129946, the plasma was initiated by ECH from t = 3.0 s to t = 3.5 s and the additional heating of NBI was injected with almost constant power from t = 3.5 s to t =
Summary
Helical Device reflectometer system in the U-band microwave range for measuring plasma regions at higher density. The microwave frequency comb reflectometer system in U-band shown in Figure 1 is explained below. In the U-band the number of comb components is around 20, when SG frequency is 1 GHz. multi-frequency (a) hi jklmno pqrstuvwx
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