Nikola T. Nesic

Microcontroller based system for electrical breakdown time delay measurement in gas-filled devices

This paper presents realization of a digital embedded system for measuring electrical breakdown time delay. The proposed system consists of three major parts: dc voltage supply, analog subsystem, and a digital subsystem. Any dc power source with the range from 100 to 1000 V can be used in this application. The analog subsystem should provide fast and accurate voltage switching on the testing device as well as transform the signals that represent the voltage pulse on the device and the device breakdown into the form suitable for detection by a digital subsystem. The insulated gate bipolar transistor IRG4PH40KD driven by TC429 MOSFET driver is used for high voltage switching on the device. The aim of a digital subsystem is to detect the signals from the analog subsystem and to measure the elapsed time between their occurrences. Moreover, the digital subsystem controls various parameters that influence time delay and provides fast data storage for a large number of measured data. For this propose, we used the PIC18F4550 microcontroller with a full-speed compatible universal serial bus (USB) engine. Operation of this system is verified on different commercial and custom made gas devices with different structure and breakdown mechanisms. The electrical breakdown time delay measurements have been carried out as a function of several parameters, which dominantly influence electrical breakdown time delay. The obtained results have been verified using statistical methods, and they show good agreement with the theory. The proposed system shows good repeatability, sensitivity, and stability for measuring the electrical breakdown time delay.

The influence of additional electrons on memory effect in nitrogen at low pressures

Memory effect in nitrogen based on experimental data of electrical breakdown time delay as a function of afterglow period in the presence of additional electrons has been investigated. The additional electrons were supplied as a result of extraction from the auxiliary electrode pair or nitrogen irradiation with the radioactive source 226 Ra of low activity. The results show that these electrons have an important role in the recombination of positive ions formed in mutual metastable molecules’ collisions and collisions between metastable and highly vibrationally excited molecules in the early afterglow. As a consequence of the ion‐electron recombination N( 4 S) atoms are formed which, as well as N( 4 S) atoms formed in previous discharge, have a significant influence on the memory effect in late afterglow. The presence of N( 4 S) atoms in the late afterglow is tracked by monitoring the secondary emission which they induce via catalytic recombination on the cathode of a nitrogen-filled tube. Also, it has been shown that the contribution of secondary electrons which originate from N( 4 S) atoms and Compton electrons when the radioactive source is and isn’t present can be distinguished.

Analysis of low-pressure dc breakdown in nitrogen between two spherical iron electrodes

The influence of afterglow period τ, voltage increase rate k, and electrode gap d on breakdown voltage Ub for a nitrogen-filled tube with spherical electrodes of diameter D⪢d and p=6.5mbar has been investigated. The data for the breakdown voltage were obtained for the case when there is a presence of N(S4) atoms, which release secondary electrons via recombination on the cathode. By fitting the experimental data of breakdown voltage mean values as a function of the voltage increase rate, the static breakdown voltages for afterglow periods of 15 and 100 s were estimated. The electrical field as a function of the electrode gap using breakdown voltage mean values was also determined. It is shown that experimental results of the breakdown voltage mean value as a function of pd in the interval of d from 0.82 to 1.62 mm can be very well described with Paschen’s law, valid for the case of parallel-plate electrodes.

Investigation of post-discharge processes in nitrogen at low pressure

The processes which are a consequence of neutral active particles presence in post-discharge nitrogen-filled tube at 13.3 mbar pressure have been analyzed. The analysis has been performed based on the experimental data of electrical breakdown time delay as a function of afterglow period τ. The most significant parameters such as applied voltage, discharge current, time, and exposure to radiation have been varied. It has been shown that the increase in applied voltage and discharge time, as well as exposure to UV radiation, leads to the decrease of the mean value of electrical breakdown time delay t¯d. This decrease occurs for τ>70u2009ms, when N(S4) atoms play a dominant role in breakdown initiation. The increase in discharge current leads to the decrease of t¯d values for τ≤70u2009ms, when positive ions dominantly induce breakdown. The most important reactions which lead to formation of positive ions and neutral active particles are also presented in the paper.

Modelling of time delay of electrical breakdown for nitrogen-filled tubes at pressures of 6.6 and 13.3 mbar in the increase region of the memory curve

Experimentally measured electrical breakdown time delay data versus the afterglow period (representing memory curves) for nitrogen-filled tubes at pressures of 6.6 and 13.3u2009mbar have been shown. The influence of N(4S) nitrogen atoms on secondary electron emission from the cathode (the SEE process) in late afterglow has been discussed. N(4S) atom concentration decay over relaxation time τ, N(4S)(τ), has been analysed by a numerical model and two analytical models. N(4S) decay analytical models are combined with different yield models that describe the SEE process by N(4S) and these combinations are employed to fit the experimental data. It has been shown that in late afterglow solving of very simple analytical equations instead of numerical solving of partial differential equations for N(4S)(τ) fitting can be used and that the combination of the first and the second order of the SEE process by N(4S) in yield modelling should be used in the case of 13.3u2009mbar pressure.

Electrical breakdown time delay in nitrogen filled tube with small inter electrode gap

The processes which are responsible for breakdown initiation in nitrogen-filled tube at 6.6×102 Pa (6.6 mbar) and inter electrode gap 0.1 mm have been investigated. These processes have been monitored based on experimental data of electrical breakdown time delay td as a function of relaxation time τ. It was shown that, for τ<; 300 ms, the dominant role in breakdown initiation is taken by positive ions, while in the 300 ms<; τ<;150 s interval N(4S) nitrogen atoms in ground state initiate breakdown. For τ>150 s breakdown is initiated by cosmic rays. Also, it was shown that the increase in applied voltage and glow current, as well as presence of external radiation, lead to the decrease of td value.

Kinetics of positive ions and electrically neutral active particles in afterglow in neon at low pressure

Kinetics of positive ions and electrically neutral active particles formed during breakdown and successive discharge in neon-filled tube at 6.6 millibars pressure had been analyzed. This analysis was performed on the basis of mean value of electrical breakdown time delay t¯d dependence on afterglow period τ (memory curve). It was shown that positive ions are present in the 1μsu2009 u20093u2009s, breakdown is initiated by cosmic rays and natural radioactivity. The increase of discharge current leads to ...