Experimental study of pulsed microwave discharges in nitrogen

Investigations on the breakdown and the maintenance phase in a pulsed N-2 microwave plasma at 2.45 GHz under low pressure (1-10 mbar) have been carried out. The discharge chamber has a cylindrical geometry with a length of 80 mm and a radius of 45 mm. Microwave pulses with a duration of 50-200 mu s and a repetition rate of 10-500 Hz were typical for the experiments. The behaviour of the electric field in the duct has been measured and calculated. The electron number density has been determined using an HCN laser interferometer and a Langmuir probe. The microwave power absorbed in the plasma was obtained measuring the forwardly directed and the reflected time resolved power flux. The vibrational excitation of the N-2 molecules in the plasma was studied with spatial and temporal resolution on the basis of the coherent anti-Stokes Raman scattering (CARS) technique.