Plasma diagnostic method using the transmission attenuation of microwaves at three frequencies

The plasma frequency and the electron collision frequency can be deduced with the plasma diagnostic method which utilizes the transmission attenuation of microwaves at three frequencies in a non-magnetized plasma. Then the electron density can be obtained from the plasma frequency. The measurement system consists of a sweep oscillator, a pair of broad-band horns, and a scalar network, etc. The plasma produced by an electric discharge of helium with the pressure range 100~700 Pa in a closed cavity is diagnosed by this way at three frequencies of 6.2, 6.8 and 7.4 GHz. As a comparison, the Langmuir double probe method is used at the same time. The results indicate that the electron collision frequencies got by these two methods are coincident. The electron densities got by the attenuation of