Simultaneous Measurement of an Electron Density Profile and a Density Fluctuation Using Ultrashort-Pulse Reflectometry

An ultrashort-pulse reflectometry using an ordinary mode (O-mode) wave is applied to the GAMMA 10 device. A microwave probing signal is generated by an impulse generator with a pulse width of 65 ps. The signal is transmitted by a pyramidal horn and has a broad frequency spectrum. Different frequency components are reflected at corresponding cutoff layers in the plasrna. The reflected wave is received by an adjacent pyramidal horn and is divided into five frequency channels: 7, 8, 9, 10 and 1 1 GHz. The time-of-flight for each channel is measured using a time-to-amplitude converter. An electron density profile is reconstructed with one-shot data. A radial distribution of density fluctuation is observed simultaneously.