UV spectral emission evolution during breakdown in a 2.445 GHz ECR hydrogen plasma

Temporal evolution of Ly-alpha and Ly-band emissions during breakdown in a 2.45 GHz ECR plasma generator are reported. A vacuum VUV spectrometer aligned with the axis of the plasma generator and a Langmuir probe reaching into the center of plasma chamber are used to record time resolved signals with 1 μs resolution. Transient peaks of Ly-alpha and Ly-band, simultaneously with electron temperature are observed in the very beginning of breakdown. Results for different incoming powers and magnetic field profiles suggest that such behavior is related to the nature of microwave-plasma coupling and damping of electric field with proceeding ionization. Following the ignition transient the electron temperature and density reach the equilibrium in less than 50 μs. On the other hand, the light emission intensity of Lyman-band decreases and Lyman-alpha increases gradually, reaching steady-state in about 500 μs. Comparison to the data from pulsed ECR ion sources, where species fraction time evolution of extracted beams have been measured, shows that observed saturation time of molecular and atomic emission is in good agreement with the saturation of extracted species fraction.