Laser-triggered Vacuum Switch Research Articles

Experimental Study on the Initial Current Characteristics of Laser-Triggered Vacuum Switch During Trigger Process

The trigger characteristics of the laser-triggered vacuum switch (LTVS) are significantly affected by the parameters of the laser-produced initial current. In this paper, a low operating voltage is applied across LTVS, and the trigger experiments are carried out under different laser energy and operating voltage. The initial current is obtained by measuring the voltage drop across a 25 Ω resistor. The influence of laser energy and operating voltage on the trigger characteristics can be characterized by the parameters of the initial current, such as the current peak value, the number of charges released, the rate of rise, and the delay time. The experimental results show that an increase in laser energy can increase the current peak value, the number of charges released, and the rate of rise, and can decrease the delay time. These results show that an increase in laser energy helps the LTVS trigger process. The external electric field is much smaller than the laser electric field. Hence, only the current peak value is affected by the operating voltage, and the impact on the other current parameters is weak.

Study on the trigger characteristics of triple-gap laser-triggered vacuum switch

Multi-gap series connection is an effective way to improve the insulation capacity of laser-triggered vacuum switch. In this paper, a triple-gap laser-triggered vacuum switch (TLTVS) is built using a detachable vacuum chamber. The TLTVS consists of a laser-triggered gap and two self-breakdown gaps. The trigger characteristics of the TLTVS are obtained under different laser energy and operating voltages through experiments. Then a simplified model for the trigger delay time is established to reveal the effect mechanism of laser energy and operating voltage. The experimental results show that the trigger delay time and the jitter time can be reduced by increasing laser energy and operating voltage, but their influence mechanisms are different. The laser energy directly affects the trigger characteristics and the discharge channel impedance of the laser-triggered gap. The latter can link the trigger process of the laser-triggered gap and that of self-breakdown gaps. The laser energy indirectly affects the trigger characteristics of self-breakdown gaps through its effect on the discharge channel impedance of the laser-triggered gap. The operating voltage mainly impacts the field current density flowing through the self-breakdown gap, which in turn affects the trigger characteristics.

Research on Current-Rise Rate During Closing Process of Laser-Triggered Vacuum Switch

The plasma development characteristics of laser-triggered vacuum switch (LTVS) have an effect on the current-rise rate when a pulsed-power system releases energy to the load. The current-rise rate is an important performance parameter for the evaluation of LTVS. In this article, the plasma impedance parameters during LTVS closing process are analyzed theoretically. The mathematical expressions of current are obtained with the equivalent circuit. Furthermore, LTVS closing experiments are carried out under different laser energy, operating voltage, gap distance, and electrode structure. Theoretical analysis and experimental results show that the current-rise rate is determined by the plasma time-varying resistance and time-varying inductance under certain external circuit conditions. The high current-rise rate can be obtained by enhancing laser energy, increasing operating voltage, shortening gap distance, or using axial magnetic field (AMF) electrodes. Remarkably, increasing laser energy or using AMF electrodes will lead to a sharp current fluctuation, resulting in overvoltage during closing process.

Calculation and analysis of plasma impedance during closing process of laser‐triggered vacuum switch

The plasma characteristics of laser‐triggered vacuum switch (LTVS) have significant effects on the output characteristics of a pulsed power system during closing process. The plasma impedance can link the microscopic properties of plasma and the macroscopic electrical parameters effectively. In this paper, the mathematic representations of plasma impedance are calculated theoretically with the equivalent circuit. External circuit inductance and resistance are calculated by means of ANSYS software and discharge time constant, respectively. Furthermore, the current and voltage experimental waveforms during closing process are analyzed by fitting piecewise linear functions in MATLAB. The plasma impedance can be calculated based on the above conditions. The calculation results show that the plasma resistance reduces with time exponentially, which is caused by an exponential increase in electron density during closing process. In addition, the plasma inductance shows an overall trend of decreasing over time, but there are fluctuations.

Modelling the initial plasma dynamics in a laser triggered vacuum switch

The numerical simulations of the initial plasma dynamics induced by 1064 nm laser irradiation on a KCl-Ti mixture target in a laser-triggered vacuum switch are performed. The simulation results showed that laser irradiance strongly affects the dynamics of the initial plasma. With higher laser fluence, the plasma plume will have higher temperatures and densities, and the shock front will also move faster. During the laser ablation, the plasma shielding is a non-negligible process. As the degree of ionization increases, the absorption coefficient of the plume increases and the it begins to absorb the laser energy. The temperature and velocity of the plume increase dramatically as it absorbs laser energy. When laser fluence gets higher, the plasma shielding starts with a shorter time and a larger proportion of the laser energy is absorbed by the plume.

Research on the conduction process of laser triggered vacuum switch

In this paper, the conduction process of the Laser Triggered Vacuum Switch (LTVS) is studied. First, the velocity, density, and temperature of the initial plasma in the LTVS are simulated using COMSOL Multiphysics software. It is found that the generation and development of the initial plasma are at the ns level. Second, the pre-breakdown current test circuit of the LTVS is established. It is found that when the applied voltage at both ends of the switch is 60 V, the multi-rod LTVS is successfully conducted, and then, the current becomes the conduction current and the voltage applied at both ends of the switch decreases significantly. Finally, the images of the LTVS vacuum arc are taken. With the increase in laser energy, the more abundant the initial plasma is, the lower the required gap voltage is. When the current increases to a certain value, the vacuum arc appears in multiple discharge channels, which makes the arc have a diffusion morphology. It is found that the current withstand capacity of a single channel is about 50 kA. As the multi-rod LTVS has three channels, its current withstand capacity can reach 150 kA.

Research on the triggering process of a laser-triggered vacuum switch

The laser-triggered vacuum switch (LTVS) is a type of high-voltage closing switch with broad application prospects in pulsed-power technology. Research into the triggering process of the LTVS is not only helpful to understand the triggering mechanism of the LTVS but also beneficial to the optimization of the LTVS. In this paper, the triggering process and the delay time of a LTVS with a Ti–KCl mixture target was analyzed theoretically. A numerical simulation was performed to describe the laser-target ablation process and the expansion dynamics of the initial plasma. The simulation results were compared with the experimental results. It is clear that the triggering process and delay time strongly depend on the laser intensity. As the laser intensity rises, the velocity of initial plasma increases, resulting in a shorter delay time of the LTVS. Increasing the gap voltage can also shorten the delay time.

Closing performances of double‐gap laser‐triggered vacuum switch

To develop high-voltage-pulsed power switches with better performances, a multi-gap laser-triggered vacuum switch is proposed in this study. Based on established test prototype for double-gap laser-triggered vacuum switch, closing processes of double-gap laser-triggered vacuum switch are discussed combined with laser-produced plasma. Closing performances of double-gap laser-triggered vacuum switch under different gap polarity configurations, operating voltages, laser energies and laser split ratios are investigated. Closing time delay characteristics of double-gap laser-triggered vacuum switch and single-gap laser-triggered vacuum switch are compared later. The test results prove that, affected by the imbalanced developed initial plasma between gaps, double-gap laser-triggered vacuum switch with two positive gaps and 1:1 laser split ratio presents best closing performances than other switches. With the rise of laser energy, closing delay time and jitter time of double-gap laser-triggered vacuum switch both decrease, while the influences from increasing voltages are weak. Closing delay time of P–P type double-gap laser-triggered vacuum switch can be controlled within 103 ± 1.5 ns under 90 mJ laser energy, and it is about 10 ns longer than single-gap laser-triggered vacuum switch. For some direct current applications with changing voltage directions, P–N type double-gap laser-triggered vacuum switch with 1:1 laser split ratio shows more stable closing performances. In addition, closing performances of double-gap laser-triggered vacuum switch can be further improved by optimizing the developments of initial plasma in series gaps.

Influence of Electrode Configurations on the Interruption Capacity of Laser Triggered Vacuum Switch

The electrode configurations have an important effect on the interruption performances of laser triggered vacuum switch (LTVS), but few works pay attention to it so far. The objective of this article is to study the interruption capacity of LTVS with different electrode configurations. The 3-D simulation models of axial magnetic field (AMF) electrode and transverse magnetic field (TMF) electrode are built up, and the magnetic field distributions are calculated and compared. The test platform is set up based on a detachable vacuum chamber. The interruption capacity of LTVS with different electrode structures, electrode spacings, and polarity configurations is studied and analyzed. The test results prove that, compared to the AMF electrode, the interruption capacity of LTVS under the TMF electrode is obviously better, but it is more susceptible to the electrode spacing, and gradually decreases with the increase of electrode spacing. Influence of polarity configuration on the interruption capacity of LTVS is closely related to the target material. The LTVS with KCl + Ti under the positive polarity configuration shows better interruption capacity than negative polarity configuration. The works in this article provide references for the design of LTVS products.

Influences of Target Configurations on the Trigger Characteristics of Laser-Triggered Vacuum Switch

Working performances of laser-triggered vacuum switch (LTVS) mainly rely on the interactions of laser with target materials. Influences from target configuration, which is one of key factors in the interactions, are neglected so far. The trigger performances of LTVS with different target configurations are studied in this paper. Relevant influence factors about target configurations are discussed briefly based on theoretical analysis about the trigger process. The test prototype is established based on detachable vacuum chamber. The trigger characteristics of LTVS with different target structures, target depths, and laser focal positions are compared. The relationships between target configurations and trigger performances of LTVS are analyzed and discussed. The preferred targets in LTVS are suggested while considering its lifetime. The test results prove that the conical target shows the best trigger performances compared to other targets. Due to the enlarged laser irradiated area and shortened plasma moving distance, the delay time of LTVS reduces with the decrease in conical target angle and the increase in target depth, while the delay time is controlled within 32 ns. Benefited from laser reflection and plasma collision, the trigger performances of conical targets can be enhanced by focusing laser on the target side surface. In particular, the 90° conical target with 1.5 mm depth is suggested to be employed in LTVS products.

Study on the trigger mechanism of a laser triggered vacuum switch

According to the preliminary study, the laser triggered vacuum switch (LTVS) might be an advanced high-voltage, high-intensity pulse switch. It will have the advantages of short trigger conduction time and good isolation from the main circuit. The study of the trigger mechanism of LTVS is not only conducive to both the optimization and the miniaturization, and also beneficial to promoting its practical process. In this paper, the LTVS which has a composite trigger electrode made of potassium chloride and titanium is studied. The material loss on the focal spot of the trigger before and after the triggering process is compared by X-ray spectroscopy. Based on the result, the composition of the plasma mass generated by LTVS is analyzed. The trigger mechanism of LTVS is proposed for laser ablation and vaporization according to the physical phenomenon and the analysis. The research about the trigger mechanism of the LTVS is of great guiding significance for its optimization and application.

Study on Trigger Lifetime of Target Electrode on Laser-Triggered Vacuum Switch

The trigger lifetime of the target electrode has a great effect on the triggering characteristics of the laser-triggered vacuum switch. In this paper, the relevant experimental research shows that when the main voltage is 1 kV and the laser energy is 10 mJ, a irradiation point on the target electrode can work continuously 18 000 times. By comparing two laser energy of 10 and 3 mJ, it is found that the KCl/Ti loss ratio of the high-energy laser pulse is much larger than that of the lower energy laser pulse, which will worsen the conduction performance more rapidly, therefore, it is necessary to adjust the mixing ratio of KCl and Ti in accordance with the energy of the pulsed laser to increase the conduction reliability of the switch and the lifetime of the target electrode. In the pulsed-arc spectroscopy experiments, the laser pulse energy has little effect on the intensity of the arc spectrum, however, the intensity of the arc spectrum increases obviously with the increase of the main gap voltage of the switch and the enhancement effect of voltage on different linear lines is different, which means that the density and number of different plasmas are not increased uniformly.

Study of Laser-Triggered Vacuum Switch with a Six-gap Rod

In this paper, the triggered polar material structure of the Laser Triggered Vacuum Switch (LTVS) was redesigned and the shape of the main electrode was improved. At last, we know that when the gap length of the LTVS is 12mm and the withstand voltage is 30kV, the LTVS is successfully conducted with 5kV gap voltage and 10mJ laser whose wavelength is 1064nm. Meanwhile, jitter time of the switch is approximately 2ns and the conduction time is approximately 20ns. By comparing the gap voltage, capacitance value, laser power and laser wavelength, the implications of such improvements on the jitter time and conduction time of the switch are discussed.

Ablation characteristics of hybrid target materials for laser triggered vacuum switches

The key difference of laser triggered vacuum switch (LTVS) and electrical triggered vacuum switch (ETVS) is the different triggered way, because the initial plasmas were generated by laser irradiation target material of LTVS, which generates different impact on the triggered characteristics of LTVS with different target materials. There are three laser wavelength (1064nm, 532nm and 266nm) which are tested the triggered characteristics of target materials, with decreased conduction time delay under the condition of increasing laser energy.

The Effect of Laser Energy on the Initial Plasma Characteristics of Laser-Triggered Vacuum Switch

With the development of pulsed-power technology, more and more applications require high-voltage and heavy-current pulse switches. Laser-triggered vacuum switch combines laser technology, vacuum switch technology, and three-electrode trigger switch technology, and has the advantages of heavy current capability, good isolation from the main circuit, and short delay time. In this paper, the 1-D thermal conduction model was developed to analyze the influence of laser energy on the velocity of initial plasma. The relationship between the ablation area and the laser energy was derived. The theoretical analysis can be verified by the relationship between the trigger delay time and laser energy and the initial plasma microcurrent curve in the experiments.

Research on the Prebreakdown Current of the Laser-Triggered Vacuum Switch

The prebreakdown current flowing in a laser-triggered vacuum switch (LTVS), investigated in this paper, is below the threshold voltage, where the switch becomes conducting. The laser irradiates in a short time the sintered KCl and Ti target of the vacuum switch and produces an initial plasma. The prebreakdown currents are measured in two different electrode geometries (planar and multirod) at both polarities and analyzed with respect to the ion and electron interactions with the electrodes. It is found that the peak value of the prebreakdown current increases with the applied voltage across the LTVS until 60 to 80 V, where it turns instantly into the conducting state. The multirod and planar LTVSs show different prebreakdown currents at different polarities, which is related to the condition of becoming conducting.

The effect of laser wavelength on the delay time of laser triggered vacuum switch.

The study on the influence of laser wavelength on the initial plasma properties of laser-triggered vacuum switch (LTVS) is not only beneficial to understanding the trigger mechanism but also to optimizing its design for miniaturization and generalization. In this paper, the one-dimensional heat conduction model of the target was developed and then the effect of laser wavelength on the depth of laser ablation and the quantity of initial plasma were investigated experimentally and theoretically with the laser absorption rate. The theoretical analysis was in good agreement with experimental measurement of the delay time of the LTVS. It is clear that the shorter the wavelength, the shorter the delay time will be after the LTVS is triggered.

Design and investigation of a multichannel laser-triggered vacuum switch.

A laser-triggered vacuum switch (LTVS) is an advanced closing switch with nanosecond delay and jitter. In order to enhance hold-off voltage and extend the service lifetime of an LTVS, we designed a multichannel laser-triggered vacuum switch (MLTVS) utilizing a cone-shaped target electrode placed on the cathode platform. The fabrication and testing of the MLTVS is described in this paper. Experimental results show that the working voltage of the MLTVS with a gap distance of 12 mm is from 30 V to 20 kV. The threshold energy for triggering the switch is 0.4 mJ corresponding to a peak power density of 27.9 MW/cm(2). The triggering lifetime of a spot can reach up to 18,000 shots. In addition, the relationship between triggering lifetime and target materials is analyzed using a field emission scanning electron microscope. A hypothesis of the vacuum gap's triggering mechanism is discussed based on the measured results.

Research on the Time-Delay Characteristics of the Laser-Triggered Vacuum Switch

The basic structure and work mechanism of laser-triggered vacuum switch (LTVS) are introduced briefly in this paper, and the processes of primary plasma production and expansion are analyzed as well. A series of experiments has been carried out with different gap voltages, laser wavelengths, laser energies, polarity configuration modes, switch structures, focal lengths, and laser waveforms. The switch structure is modified to improve the heavy-current capability of the switch, and the gap distance is increased to improve the voltage capacity. The special design of the trigger structure can reduce the dependence on the laser energy of the switch and the time delay. A new laser waveform of LTVS multiple wave crests could further decrease the laser energy, and it is the research basis of laser trigger miniaturization and its application in the LTVS.

Research on the Interaction of Primary Plasma and Main Electrode for Laser Triggered Vacuum Switch

Research on the Interaction of Primary Plasma and Main Electrode for Laser Triggered Vacuum Switch