engleski

E - H mode transitions and hysteresis effects of inductively coupled RF water vapour plasma

Inductively coupled RF water vapour plasma generated in a linear glass tube was studied by means of optical emission spectroscopy. Low pressure water vapour plasma was created by an 8 turn coil with an EM field oscillating at 13.56 MHz. Various total pressures (5-14 Pa) and discharge powers (100-300W) were investigated. Optical spectra in the range from 200 nm to 980 nm were measured by means of a LIBS2000+ spectrometer system from Ocean Optics with spectral resolution 0.1 nm. Spatial resolution was obtained by moving optical fibre along the glass tube. Spectral signatures of O, H, and OH radicals were observed. Typical atomic lines of hydrogen (H at 656 nm, H at 486 nm and H at 434 nm) and oxygen (3p 5P – 3s 5S at 777 nm, 3p 3P –3s 5S at 844 nm, and 3d 5DO – 3p 5P at 926 nm) and the (0, 0) transition of the OH molecular band at 309 nm were the most prominent. Additional oxygen atomic lines could be observed at larger integration times (or higher discharge power), and also traces of H2 Fulcher band (depending on the fibre position). E and H modes of plasma and transitions among them were observed and recognized in optical spatial profiles. Excitation temperatures (between 0.6 and 1.0 eV) of the plasma discharge were estimated from emission spectra by employing the Boltzmann plot method. By observing spectra at given fibre position while changing water vapour pressure and discharge power hysteresis effects were observed. Various sources of hysteresis effects and E-H mode transitions will be discussed.

RF plazma; water vapour; optical emission spectroscopy

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