Electron beam induced fluorescence measurements of the degree of hydrogen dissociation in hydrogen plasmas

The degree of dissociation of hydrogen in a hydrogen plasma has been measured using electron beam induced fluorescence. A 20 kV, 1 mA electron beam excites both the ground state H atom and H2 molecule into atomic hydrogen in an excited state. From the resulting fluorescence the degree of dissociation of hydrogen is determined. In addition, the absolute atomic hydrogen density can be determined if the gas temperature and pressure are known without any additional calibration. To check the consistency of the method the fluorescence from the first four Balmer transitions is measured. It is demonstrated that this technique can be applied in hydrogen and argon–hydrogen plasmas with a pressure of up to 1 mbar and 0.2 mbar, respectively.