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The electrode erosion and lifetime performance of a compact and repetitively triggered field distortion spark gap switch were studied at a repetitive frequency rate of 30 Hz, a peak current of 8.5 kA, and a working voltage of ±35 kV when the switch was filled with a gas mixture of 30% SF6 and 70% N2 at a pressure of 0.3 MPa. The variations of the time-delay jitter and the self-breakdown voltage were both studied for the whole service lifetime of the spark gap switch. The morphology of both the electrodes and the plate insulator, before and after the service lifetime tests, is also analyzed. The results show that during these tests, the time-delay jitter is basically synchronized with the self-breakdown voltage jitter, and both undergo firstly a process of rapidly decreasing their values, then remaining stable, and finally and gradually increasing after 70 000 pulses. The change in the electrode surface roughness (i.e., surface profile) is caused by erosion and chemical deposits in the switch cavity, which are mainly the two factors that affect the time-delay jitter of the switch. Tip protrusions on the electrode surface, due to electrode erosion, contribute to reducing the time-delay jitter. However, due to chemical reactions, fluorides and sulfides are deposited on the switch components, as well as metal particles caused by electrode erosion sputtering. Slowly, after a large number of shots, all these phenomena affect the self-breakdown performance resulting in an increased self-breakdown voltage jitter, which also causes the time-delay jitter to increase. Although there are a number of reasons that contribute to the deterioration of the performance of the switch, it is fortunate that if a switch suffering a degraded performance is reassembled, with the electrodes mechanically polished and all the components cleaned, the optimal performance of the switch can be restored. If maintenance work is carried out regularly to preserve the condition of the switch’s inner components, the service lifetime of the switch can be prolonged. [ABSTRACT FROM AUTHOR]

This work was stimulated by the assumption that for a gas-filled spark gap closing switch operating at a high repetition frequency, there is an optimal frequency range in which the time-delay jitter reaches a minimum value. The experiments to test this assumption use an electrically triggered, field-distortion spark gap filled with the SF6/N2 gas mixture. The results show that indeed, the time-delay jitter decreases for a range of frequencies for which the filling gas can substantially restore the interelectrode insulation before increasing at a higher operation frequency. The experimental results demonstrate the correctness of the abovepresented assumption: the time-delay jitter of the field-distortion spark gap has its minimum when the unit operates in the repetition frequency range between 20 and 30 Hz. Since the recovery time depends on the gas species and the gap distance, the optimum operation frequency range should also vary depending on the spark–gap distance and the filling gas properties. [ABSTRACT FROM AUTHOR]

This paper describes the development of a small field-distortion spark gap switch. Comprehensive experimental studies made with the switch revealed its self-breakdown characteristics, voltage operating range, time delay and jitter, repetition frequency, and finally the electrode erosion processes and duration of its service lifetime. A series of design improvements were required to be implemented in the switch design. For example, to reduce the structural inductance of the switch and to improve its working characteristics, the main electrode was designed as a circular track structure. Similarly, to increase the operation stability and reduce the self-breakdown probability, the trigger electrode was designed as a disk-like structure. Moreover, to balance the gas pressure in the discharge region and increase the stability during closure, a circular hole was added at the center of the trigger electrode. The compact switch has a small size of only 150 mm $\times42$ mm, a weight of 1.5 kg, and can be successfully operated at a voltage over 110 kV, at a repetition rate between 1 and 50 Hz and having a jitter of less than 4 ns. It was experimentally demonstrated that during normal operation conditions, the switch lifetime exceeds 100 000 shots. [ABSTRACT FROM AUTHOR]

Abstract A compact low jitter high power repetitive long-pulse relativistic electron beam source with novel circuit structure and mechanical structure is presented. Based on Marx type circuit and direct-drive idea, the key technologies such as high energy density pulse forming network, repetitive high voltage pulse generator and low jitter electrical trigger technology are developed. The volume and weight of the pulsed electron beam source are reduced remarkably by using two-capacitor pulse forming modules, alternating superposition structure on both sides and high electric field shielding technology. The key technical parameters of the electron beam source design include a peak output voltage 1 MV with peak current 20 kA. The impulse is 180 ns and has a repetition frequency 1 ∼ 50 Hz, however, the output power and repetition frequency are able to be adjusted within a certain operating range. The machine has a total volume of 2.5 m3 and weighs 2.2 tons, making it much more compact than conventional electron beam sources. The experimental results show that when the e-beam source is operated under a single pulse condition, the output voltage, current, and power are 0.98 MV, 19.6 kA, and 19.2 GW, respectively. When the e-beam source has a continuous operating time of 10 s at a repetition frequency of 30 Hz and an output power of 16.7 GW, the voltage fluctuation range is limited to within ± 1.5%, and the current fluctuation range is limited to within ± 2%. The delay time jitter between the trigger pulse and the output pulse is limited less than 6.5 ns standard mean deviation. Statistical distributions of the delay time jitter and current amplitude variation of the 300 pulses are approximately Gaussian. When the cooling system is working, the electron beam source can work continuously for 100 s under the conditions of an output power of 16.7 GW and repetition frequency of 30 Hz, and the system operation is stable and reliable. [ABSTRACT FROM AUTHOR]