Design And Research On The Triggering Mechanism Of Laser Triggered Vacuum Switch

Laser Triggered Vacuum Switch(LTVS) is an advanced pulsed power device with high voltage and current. Compared with other switches, LTVS has a lot of advantages such as rapid dielectric recovery, wide range of applied voltage, nanosecond delay and jitter. In addition, it can isolate the switch with the trigger system and be triggered repeated conveniently because of laser triggering. In order to improve the triggered characteristics,reduce the threshold energy for triggering the switch and extend the service lifetime of the switch, this paper designed a Multirod Laser Triggered Vacuum Switch(MLTVS) with a long gap distance. The fabrication and testing of the MLTVS are described in this paper.Firstly, the paper analyzes the theoretical basis for the design of a LTVS, containing the mechanism and factors on the breakdown of the vacuum switch, the generic features of vacuum arc and trigger mechanism. Based on the theoretical basis, a Nd: YAG laser is considered due to the good physical and chemical properties. The main electrode chooses the T shape multi-rod system which is made of Cu Cr and the insulation shell is glass. This paper uses a cone-shaped target electrode which is made by dry compression of equal amounts of powdered KCl and Ti and placed on the cathode platform. The target electrode is made by dry compression of equal amounts of powdered KCl and Ti and placed on the cathode platform. Therefore, we completed the design of MLTVS and realized considerable reduction in size of laser.Secondly, the optical platform and experimental circuit are set up to research the triggered characteristics of MLTVS at the 1064 nm wavelength. Experimental results show that the minimum delay time is 17 ns and the threshold energy for triggering the switch is0.4 m J. The working voltage of the MLTVS with a gap distance of 12 mm is from 30 V to20 k V. Triggering lifetime of a spot can reach up to 18000 shots. In addition, it is beneficial to form the cathode spots in the positive mode, which can make the switch work steadily and reduce the delay time. Delay and jitter time decrease by increasing the laser energy and have less dependence on the operating voltage.Finally, in order to explore the triggering mechanism, the paper researches and analyzes the influence of energy density, defocus, power density and polarization on the working performances of MLTVS and detects the arc pulse and laser-induced breakdownspectroscopy. It is considered that the vacuum gap's triggering mechanism is contributions of laser ablation and thermal ion emission based on the experimental results. In addition,the triggering lifetime and the relationship between it and the types and contents of target materials are analyzed. The weight percentages of KCl decrease as the test number increases and drop close to zero. The variation of Ti shows the opposite. This indicates that the initial plasmas mainly consist of K+ and Cl-. Considering that KCl cannot effectively absorb the light energy and convert it into heat energy at 1064 nm. It is likely that Ti absorbs the light energy and converts light energy into heat energy. Then heat energy is transferred from Ti to KCl resulting in the ionization of KCl. Initial plasmas are generated and the switch is closed.