Electron Density Oscillations in CC-RF Oxygen Plasma Investigated by Gaussian Beam Microwave Interferometry
Gaussian beam microwave interferometry (160 GHz, beam waist of 5 mm) is applied to study the electron density in capacitively coupled radio-frequency (RF) oxygen plasma. The microwave interferometry provides immediately the line-integrated electron density without model assumptions. In the considered range of RF power and total pressure, the investigations have shown that the oxygen plasma is dominated by electron density oscillations due to the attachment-induced ionization instability. The frequency of the mostly nonharmonic oscillations ranges between 0.3 and 3 kHz with peak-to-peak line-integrated electron density variations up to 3.5 × 1015 m-2.
The electron density evolution in pulsed 60 MHz capacitively coupled oxygen discharges
The electron density evolution is investigated in a pulsed 60 MHz capacitively coupled low pressure oxygen discharge. A 77 GHz microwave interferometer is used for the time-resolved measurement of the electron density. It is found that, as the duration of the power-off period varies in the range of 0.01–2 ms, the electron density evolution pattern changes significantly. This change is more pronounced at the power-on front, due to the competition between the dissociative-attachment and the ionization processes. A global model is developed to explain the behaviour of electron density evolution under different conditions. The model predicted results agree well with the measured ones. Moreover, it is proposed that, using the measured electron density and a simple global model in the afterglow, the electronegativity and the negative ion lifetime during the power-on phase can be estimated. The value of the electronegativity at various electron densities obtained by this method is found to be consistent with the results measured by the photo-detachment technique in a previous work (Stoffels 1995 Phys. Rev. E 51 2425) under similar discharge conditions.
Research on velocity distribution in semi-dry flue gas desulfurization tower
As an accurate high-quality instantaneous measurement technology, particle image velocimetry (PIV in acronym) has applied widely in single-phase flow and multiphase flow. The velocity distribution in semi-dry FGD tower directly influences gas-solid mix and contact situation. In base of the tower, gas-solid two-phase flow field is more complex, and has the quite tremendous influence to the overall system desulphurization efficiency. This paper utilized PIV to study velocity distribution in Semi-dry flue gas desulfurization tower and obtained velocity distribution.