Plasma boundary position measurements using frequency sweep microwave reflectometer in LHD

In order to measure the plasma boundary position in the high-temperature plasma, the broadband frequency tunable microwave reflectometer system, which has the ability of fast and stable sweeping operation, is applied in the Large Helical Device. When the microwave launches with the extraordinary polarization from the low field side of the magnetic field strength and its frequency is swept from low to high, the microwave of minimum right-hand cut-off frequency is started to reflect at the plasma edge. We can estimate the plasma boundary to measure the change of the reflected power from the cut-off layer. In the plasma experiment, the reflect signal increases according to the sweeping frequency and the information of the plasma edge position can be obtained. (author)