ИСТИНА

Capillary nanosecond discharge at moderate pressures (20 Torr) in N2:O2 mixtures was used to study strongly non-equilibrium plasma at high electric fields and high specific deposited energy. The discharge developed in the form of the fast ionization wave (FIW) in quartz capillary with inner diameter 1.5 mm and length 80 mm. The capillary was inserted into the break in the coaxial cable at the distance 30 m from the high-voltage generator (FID FPG 10-MKS20 HV, FID GmbH). Pulses of 20 kV amplitude on the electrode, 30 ns FWHM and 4 ns rise time were repeated with a frequency of a few Hz to accumulate the signal; gas flow rate provided change of the gas in the capillary between two pulses. Custom made calibrated back current shunts where used to measure current, voltage in the cable and energy stored in plasma. Capacitive detector provided data to measure longitudinal electric field. Electric field was also measured from optical emission spectroscopy. For emission spectroscopy measurements, the Acton spectrometer (SP-7500i, 600 I/mm grating, Princeton Instrument) was combined with Pi-Max4 (Princeton Instruments) ICCD camera or with UV and IR photomultipliers (Hamamatsu). ICCD imaging was performed with the help of Pi-Max4 ICCD. Measurements of oxygen atoms in the discharge and near afterglow (t<100 ns) were carried out with the help of actinometry technique, using Ar gas (about 5%) as actinometer. Two-photon absorption laser induced fluorescence (TALIF) was used to measure O-atoms density in the late afterglow (t<1000 ns). Measurements of rotational and vibrational temperatures of molecular nitrogen were made in the discharge and in the afterglow. Measured specific deposited energy in the discharge was as high as 0.5-1.5 eV/molecule, the electric field on the stage of maximum energy deposition was in the range of 200-300 Td. High quenching of electronically excited species by electrons was observed in early afterglow (tens of ns). Dissociation degree of oxygen in the discharge reached tens of percent, increasing to 100% at microseconds due to reactions between O2 and electronically excited nitrogen. Heating of the gas up to a few thousand K was observed at the time scale less than VT- relaxation due to energy release in collisions with electronically excited species.