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Based on the gas discharge theory involving distorted E-field enhancement, a physical model is proposed to estimate the switching delay for gas-insulated trigatron spark gaps with a trigger pin inside the main electrode. Two discovered breakdown modes, i.e., fast-breakdown mode (FBM) and slow-breakdown mode (SBM), can be unified in this model. Raether criterion can distinguish these two modes. If the main E-field and enhanced E-field near the trigger pin tip are great enough, FBM forms easily. Otherwise, if streamer development needs to rely on the second ionization process and relevant distorted E-field enhancement, the breakdown of the main gap would turn into SBM. The enhanced E-field near the trigger pin tip may affect the threshold main E-field of FBM. The distorted E-field enhancement may affect the switching delay length of SBM. [ABSTRACT FROM AUTHOR]

Compressed air is used in spark gap switches as an insulating gas. Triggered by nanosecond pulsed voltage, the streamer bridges the electrode gap in the switch. During the streamer-arc transition, the spatial distribution of the arc changes drastically. The nitrogen and oxygen in the compressed air will react with each other under high temperatures. Damaging effects in the switch are caused by arc reaction. In this paper, by adjusting the parameters of the high-energy pulse discharge circuit, the arc is produced with different current waveform in the spark gap switch, while the gaseous product is analyzed. The results show that, when current pulse-width remains constant, the amount of transferred charge is approximately linear with the production of nitrogen oxides. The proportion of NO is higher when the current pulse-width is shorter. The concentration of nitrogen oxides is determined by the chemical reaction, which relies on the dynamic change of the impulse arc. During the arcing time, there is the collision dissociation reaction in the local thermodynamic equilibrium (LTE) plasma, leading to the production of gas atoms and excitation molecules. In the boundary of the arc channel, the nitrogen oxides formation reactions mainly occur in the arc quenching period. According to the characteristics of the high-current arc, a simplified analysis of chemical kinetics on the reactions of nitrogen and oxygen is implemented to expound the effect of pulsed arc on the gas composition. [ABSTRACT FROM AUTHOR]

Starting from the updated requirements of an advanced laser system, a switch–trigger system for a 2.0-MJ pulsed power supply (PPS) module is developed. This paper discusses the design, construction, and testing of this switch–trigger system. The two-electrode construction for the spark gap switch is selected because of its superiority in terms of long working life, high peak currents, and fast rise time of currents. The trigger generator based on resonant charging of a pulse transformer is constructed. A magnetic isolator and a pressure controller are the auxiliary equipment of this system. In the section based on mathematical principles, the equations of the lifetime and stability of this spark gap switch with graphite electrodes are given. These expressions can be regarded as the design basis of the same type of switch. As for the trigger generator, the analysis states that an appropriate ratio can be obtained when using the resonant charging based on a core-type pulse transformer. The charging time is dependent on the leakage inductance and the capacitance of the primary and secondary capacitors. Extensive testing proves the operating parameters of the switches and the trigger generator. The measured discharge current waveform of the 2.0-MJ capacitive PPS module is demonstrated to be over 500 kA peak current and 500 \mus pulse width. The life test proves that the switch–trigger system can support more than 200 kC transfer charge. By replacing the electrodes, the lifetime of this switch can be extended furthrer. [ABSTRACT FROM PUBLISHER]

The development of a three-electrode trigatron gap with the trigger electrode inside the main electrode is discussed in this paper. Two models of the operation mechanism are proposed to explain the breakdown in the trigatron gap. In addition, a mathematical model was proposed to calculate the breakdown time based on the theoretical analysis. The influence of different parameters on the breakdown time is discussed. Some characteristics in dry air have been experimentally determined such as the influence of the air pressure and the influence of the undervoltage ratio on the spark gap operation. The experimental results show that the operating voltage range between 0.5 and 0.7 might be reasonable. Then, the experimental results and analysis demonstrate that there are three regions divided by two inflection points, and the corresponding values of the undervoltage ratio are threshold values presenting different breakdown processes. [ABSTRACT FROM PUBLISHER]

The limited lifetime in a high current is the main drawback of spark-gap switches. Electrode replacement is an easily suggested method to extend the lifetime. In order to perform electrode replacement, thermal damage caused by heating effect should be prevented at the static electrical contact interfaces between the electrodes and the holders. Based on the Holm model, the Hertz formula, and the heat conduction theory, a mathematical model of the contact temperature rise is proposed in this paper. This mathematical model can prove quantitatively that the pulse-current integral (action integral), material physical properties, and mechanical characteristics of spark-gap switches are key parameters affecting the temperature rise. The action integral is determined by the electrical parameters. Material physical properties include the thermal conductivity, the specific heat, the density, the electrical resistivity, the elasticity modulus, and the Poisson ratio. Mechanical characteristics of spark-gap switches include the contact radius/area, the contact force, and the contact surface roughness. The implementation of electrode replacement depends on the reasonable configuration of these key parameters. The experiments in a 1.2-MJ power supply module give that the phenomenona correspond with our analysis. Based on the analysis in this paper, an electrode holder structure is proposed as a practical solution for extending the useful lifetime of spark-gap switches with graphite electrodes. [ABSTRACT FROM PUBLISHER]

Working characteristics of a three-electrode trigatron spark gap is discussed in this paper. Breakdown probability is proven to fit a Weibull distribution. For an engineering application, the lower limit of undervoltage ratio depends on breakdown probability, and the upper limit of undervoltage ratio depends on self-breakdown probability. Some characteristics have been determined experimentally, such as the influence of the air pressure and the influence of the undervoltage ratio on spark gap operation. Curve fitting and quasi-data mining are good methods for research on triggering characteristic in the paper. Therefore, a maximum operation range curve and a boundary line of expected delay time could be determined by application requirements, theory calculation, experimental data and curve fitting. On this basis, optimization operation range could be obtained, which represents a preferable performance of breakdown with expected delay time. It may provide guidance for engineering application. [ABSTRACT FROM AUTHOR]

Electrode replacement is an effective method to extend the useful lifetime of the spark gap switch with graphite electrodes. In order to perform electrode replacement, suppressing temperature rise and preventing static welding/erosion should be considered for the static electrical contact interface between the electrode and the holder. In this paper, a mathematical model of contact temperature rise is proposed based on the Holm model and heat-conduction equations. This mathematical model can quantitatively prove that some material properties of the metal holder and some mechanical characteristics of the spark gap switch are key parameters affecting temperature rise. Material properties of the metal holder include thermal conductivity, specific heat, density, electrical resistivity, elasticity modulus, and the Poisson ratio. Mechanical characteristics of the spark gap switch include contact radius/area, contact pressure, and contact surface roughness. Optimum configuration of these key parameters reduces temperature rise and prevents static welding/erosion. [ABSTRACT FROM AUTHOR]