Hydrodynamic and thermal effects of continuous microwave-sustained plasma in capillary tubes
Résumé
Argon micro-plasmas can be generated at low power (10–100 W) in hollow-core capillaries 100–700 μm in diameter and over a few cm in length using continuous wave (CW) microwave surfatron excitation at 2.45 GHz. Electromagnetic simulations have been performed in order to design the surfatron cavity for optimal discharge ignition and stable plasma CW operation. The plasma characterization was carried out by optical emission spectroscopy on excited species present as impurities in argon. The rotational spectra of OH molecules were used to determine the gas temperature, and Stark broadening of the H β line was used to obtain the electron density. The gas temperature turns out to be in the 500–1200 K range along the plasma column, and the maximum electron density (at the surfatron gap) in the 8 × 1014–5 × 1015 cm−3 range. The electron density was also obtained by a semi-empirical analysis of the power coupled to the plasma along the axial direction and was found to be in good agreement with the Stark measurements. The hydrodynamic and thermal effects of plasma were investigated by the modelling of neutral gas flow and heat transfer which is of interest for the remote control of gas flow properties along the capillary.