Measurement of fluctuation in plasma is important for studying the improvement in plasma confinement by the formation of the plasma confinement potential. The density fluctuation is observed by microwaves by methods such as interferometry, reflectometry and Fraunhofer diffraction method. We have constructed a new multichannel microwave interferometer to measure the plasma density and fluctuation radial profiles in a single plasma shot. We successfully measured the time-dependent density and line-integrated density fluctuation radial profiles in a single plasma shot using the multichannel microwave interferometer. Thus, we have developed a useful tool for studying the improvement in plasma confinement by the formation of plasma confinement potential.
In this paper, results of spectral measurement in the end-cell of the GAMMA 10/PDX are described. A spectral measurement system consisting of two spectrometers was developed in order to measure the detailed radiation behavior in D-module. Firstly, angular dependence of the V-shaped target plate on the spatial distribution of the Hα radiance was investigated. It is found that the spectral distribution in Hα intensity along the axial direction is affected by the angle of the target plate. Next, in the experiment with H 2 and Ar gas injection, primary 17 line spectra of Ar I were identified and the radiation loss from Ar neutrals was also evaluated from intensity of spectra. A correlation between the power of radiation loss and the electron temperature in D-module are recognized. The correlation between radiation power and electron temperature is also discussed from the view point of radiation cooling.
Low frequency fluctuations of a plasma in the central cell of the GAMMA10 tandem mirror have been observed with electrostatic probes (ESPs) installed at the peripheral region of the plasma. Typical plasma parameters for a hot ion mode operation are ne∼2×1012 cm−3, Ti∼4 keV, Te∼100 eV, B=4 kG, and rp=18 cm. Although the ESP is an effective tool to measure local plasma parameters and fluctuations, it can be damaged with the higher electron temperature. Here, a new visible light detector was introduced, which could measure the plasma fluctuations without contacting the plasma. The obtained results were compared with those of ESPs. It is found that the visible light detector is applicable when the electron temperature becomes much higher in the future experiment.
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