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Fluctuation Measurement Using an Ultrashort-Pulse Reflectometry on the GAMMA 10

A. Itakura et al.

Fusion Science and Technology / Volume 47 / Number 1T / January 2005 / Pages 300-302

Technical Paper / Open Magnetic Systems for Plasma Confinement /

Fluctuation of electron density is observed by using a microwave reflectometry in the central cell of GAMMA 10 tandem mirror. An ultrashort-pulse train, whose pulse width is 65 ps, is transmitted into the plasma in the ordinary-wave mode and reflected at the cut-off layer. The reflected wave is detected by the receiving system, and its time-of-flight, i.e., round trip time, is measured. Fluctuation of the time-of-flight is fluctuation of the cutoff layer and it means density fluctuation. The pulse has a broad frequency spectrum, so each frequency component is reflected at different layer corresponding to its frequency. The frequency range of the receiving system is 7 to 11 GHz, and cut-off density ranges 0.61 to 1.5 × 1018 m-3. Density on the central axis of the plasma is about 2 × 1018 m-3. Radial intensity distribution of the fluctuation is observed without any perturbation. Frequency of the fluctuation is around several kHz.

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