Measurement of Plasma Density and Magnetic Fluctuations using Microwave Reflectometers and Probes

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(1) A new diagnostic, a microwave reflectometer, is developed in order to measure the electrostatic and electromagnetic fluctuations excited in a magnetized plasma. The reflectometer in the frequency range of 8-18 GHz has calibrated by using a vibrating metal plate and set at the HITOP device. The density fluctuations measured by the reflectometer agree well with that observed by Langmuir probes.(2) Low-Frequency fluctuations related with a radial electric field are investigated in a magnetized plasma produced by the electron cyclotron resonance. When the radial potential profile is controlled by biasing a segmented endplate, flute mode fluctuations are observed to be predominantly excited in a range of positive electric fields, while drift mode fluctuations are observed to persist in the case where the electric field is almost zero. The drift mode fluctuations are stabilized with an increase in the radial electric-field strength.