Ilya N. Kosarev

In this paper, we experimentally compare the field emission characteristics of two different cathodes based on polyacrylonitrile fibers (PAN fibers) and carbon nanotube fibers (CNT filaments). The main purpose of the study was to compare the field emission properties of materials for the cathode unit of a cathode luminescent lamp. The current-voltage, current and watt-watt characteristics of the fabricated cathodes were measured. A comparison of the current-voltage characteristics of cathodes made of the two studied materials shows that the minimum field for the occurrence of field emission current for a cathode made of a CNT filament (accelerating voltage in the diode version of measurements is about 625 V) is approximately 3 times lower than for a cathode made of PAN fibers (accelerating voltage is about 1850 V. Accordingly, the current value of about 100 μA for a cathode based on a CNT filament is achieved at an accelerating voltage of about 1300 V, and for a cathode based on PAN fibers, about 2630 V. Structural changes in cathodes were studied using scanning electron microscopy methods. Based on the totality of the results, it was concluded that it is preferable to use a CNT filament as a cathode material. The emission current of a cathode based on a CNT filament, when a constant high voltage is applied, demonstrates an increase during the transition period and reaches a stable value of more than 75 μA, apparently due to the activation of additional emission centers when a high accelerating voltage is applied. The paper also analyzes the factors that determine the efficiency of light sources created on the basis of the materials studied in the work.

Several different types of carbon nanotube fiber cathodes of different diameters (20, 40, 400 μm) were measured for emissive properties. Currents up to 1.5 mA are obtained. Durability properties were qualitatively estimated. Current "saturation" was observed for 20-μm fiber, probably due to resistivity.

The results of the experimental and numerical study of a high-voltage nanosecond discharge developing through a shock wave in air and combustible mixtures were presented for various neutral density jumps across the wave. The discharge uniformity was investigated using ICCD camera images in a shock tube. The results demonstrated that the discharge plasma became more uniform when the ionization wave moved from a high-density region to a low-density region. The radiation intensity emitted by the plasma in the low-density region was higher than that emitted by the plasma in the high-density plasma. The results of a zero-dimensional simulation in the case of quasi-uniform plasma agree well with the measured ratios of the intensities radiated by the plasmas before and after the shock front. A two-dimensional simulation of the development of a steamer intersecting the shock wave showed that the streamer characteristics change drastically during the transition from the high-density region to the low-density region. Streamer penetration into the low-density region was accompanied by the formation of primary and secondary ionization waves.

We study experimentally and numerically the kinetics of ignition in lean and stoichiometric C2H2 : O2 : Ar mixtures after a high-voltage nanosecond discharge. The ignition delay time is measured behind a reflected shock wave with and without the discharge using detection of CH radiation. Generation of the discharge plasma is shown to lead to a decrease in ignition delay time. Discharge processes followed by chain chemical reactions with energy release are simulated during ignition in the C2H2 : O2 : Ar mixtures. The generation of atoms, radicals and excited and charged particles in the discharge phase is numerically simulated. The calculations are based on the measured time-resolved discharge current and electric field. The calculated densities of the active particles produced in the discharge on a nanosecond time scale are employed as input data to simulate plasma-assisted ignition on a microsecond scale. The calculated ignition delay times are compared with the experimental data. It is shown that the effect of the discharge plasma on ignition of the acetylene-containing mixtures is associated with active species production in the discharge phase rather than with gas heating during the discharge and in its afterglow. A sensitivity analysis is made to determine limiting reactions in acetylene autoignition and ignition after the discharge under the conditions studied.

The ignition of acetylene by low-temperature nonequilibrium plasma of a high-voltage nanosecond discharge is experimentally and theoretically studied. The ignition delay time for C₂H₂: O₂ mixtures behind the reflected shock-wave front is measured. It is experimentally shown that discharge initiation leads to a considerable shortening of the ignition delay time. For lean mixtures, this effect is more pronounced. Numerical modeling of discharge and ignition processes under the experimental conditions is carried out. A good agreement between the calculation and experimental results for the ignition delay time is obtained. Analysis of the calculation results shows that the dominant mechanism of the effect of nonequilibrium plasma on ignition is related to the accumulation of atoms and radicals in discharge plasma.