Pseudospark Switch Research Articles

Experimental Research of ZnO Surface Flashover Trigger Device of Pseudo-Spark Switch

Pseudo-spark switch (PSS) is one of the most widely used discharge switches for pulse power technology. It has many special characteristics such as reliability in a wide voltage range, small delay time, as well as small delay jitter. In this paper, the measuring method for the initial plasma of ZnO surface flashover triggering device of PSS is studied and the results of the measurement show that the electron emission charge is mainly influenced by trigger voltage, gas pressure and DC bias voltage. When the bias voltage increases from 2 kV to 6 kV with the gap distance fixed at 3 mm, the electron emission charge changes from 2 μC to about 6 μC. When the gap distance changes from 3 mm to 5 mm with the bias voltage fixed at 2 kV, the electron emission charge increases from 1.5 μC to 2.5 μC. When the gap distance is 4 mm, the hold-off voltage of PSS is 45 kV at gas pressure of 2 Pa, the minimum operating voltage is less than 1 kV. So, the operating scope is from 2.22% to 99% of its self-breakdown voltage. The discharging delay time decreases from 450 ns to 150 ns when the trigger pulse voltage is 1 kV and the discharging voltage is changed from 1 kV to 12 kV. When the trigger pulse voltage is 6 kV, the discharging delay time is less than 100 ns and changes from 100 ns to 50 ns, and the delay jitters are less than 30 ns.

A high-repetition rate pulsed electron accelerator

A new electron beam accelerator with beam ejection into the atmosphere has been recently developed for radiation technology application. The high-voltage nanosecond pulse generator of the accelerator is based on a low-inductance pulse transformer. A cold cathode thyratron is used as a primary switcher. The diode consists of a cathode, which provides a high delay time in the plasma formation. The electron beam current pulse duration at half height is 75 ns. The kinetic energy of the electron beam is 450 keV. A cooling system is used for the anode, which makes it possible to extract an electron beam with the current density of 12 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> into the atmosphere. The accelerator is capable to operate in a long-term-repetition rate producing up to 40 pulses per second, which is possible due to the use of a built-in system of regeneration and cooling of the transformer oil. The results of shot-to-shot variation of the beam parameters in the repetitive mode are presented.

High-Current Stages in a Low-Pressure Glow Discharge With Hollow Cathode

This paper presents an interpretation of the dense and superdense glow discharge stages in pseudospark switch geometry. The discharge is treated as a self-organizing system that is able to rearrange itself to provide the current requested by external electric circuit. The principal discharge regions in the glow stages are the hollow-cathode plasma, the positive column plasma, and the double electric layer that separates these plasma regions. A model that allows some quantitative estimates when applied to the hollow-cathode plasma is developed, in which a generalized secondary emission coefficient that considers an external emission current is introduced. The abrupt transition from dense glow stage to superdense glow stage occurs because of microexplosions at the cathode surface and appearing the metal vapor plasma. In terms of the model, this means an abrupt increase in the secondary emission coefficient. The comparison with the experiment is made for discharges in hydrogen and xenon at a current up to several kiloamperes and at a current rise time from several microseconds to hundreds of nanoseconds. The physical reasons for the current quenching effect that manifests itself at a decreased gas pressure are also discussed.

辉光放电触发双级赝火花开关

辉光放电触发双级赝火花开关

Development of High Power Vacuum Tubes for Accelerators and Plasma Heating

High pulsed power magnetrons and klystrons for medical and industrial accelerators, and high CW power klystrons and gyrotrons for plasma heating in tokamak, are being developed at CEERI. S-band 2.0MW pulsed tunable magnetrons of centre frequency 2856MHz and 2998 MHz were developed, and S-band 2.6MW pulsed tunable magnetron is being developed for medical LINAC, and 3MW pulsed tunable magnetron is being developed for industrial accelerator. S-band (2856MHz), 5MW pulsed klystron was developed for particle accelerator, and S-band 6MW pulsed klystron is under development for 10MeV industrial accelerator. 350MHz, 100kW (CW) klystron is being developed for proton accelerator, and C-band 250kW (CW) klystron is being developed for plasma heating. 42GHz, 200kW (CW/Long pulse) gyrotron is under development for plasma heating. Plasma filled tubes are also being developed for switching. 25kV/1kA and 40kV/3kA thyratrons were developed for high voltage high current switching in pulse modulators for magnetrons and klystrons. 25kV/3kA Pseudospark switch of current rise time of 1kA/|a-sec and pulse repetition rate of 500Hz is being developed. Plasma assisted high power microwave device is also being investigated.

Carbon-Nanotube-Triggered Pseudospark Switch

Pseudospark switches are fast-closing low-pressure gas discharge switches with a hollow-cathode geometry. They can be triggered optically or by electron injection, where electrons emitted from a cold cathode emitter are accelerated in the electric field and initiate breakdown. The efficiency of charge carrier accumulation in the hollow-cathode structure determines the performance of the switch operation. The advantages of such switches include high hold-off voltage, high conduction current, fast current rise time, low delay and jitter time, and long lifetime. In this paper, the operating characteristics of a pseudospark switch, triggered by a carbon-nanotube (CNT)-coated electron emitter, are presented. The electron emitter is fabricated by coating randomly oriented CNTs on silicon substrate using chemical vapor deposition method. Field emission characteristics of CNTs are determined and then used as part of the trigger electrode which is integrated into an in-house constructed pseudospark switch. The operating characteristics of the switch are tested under different background pressures and different trigger voltages. Delay and jitter time under different working conditions are analyzed. Hold-off voltage and current rise time are also presented.

Magnesium-Based Photocathodes for Back-Lighted Thyratrons

Pseudospark switches have been successfully employed in a variety of pulsed power applications including high-power electron beam sources, high-power microwaves, and transient plasma ignition for pulsed detonation engines. For applications such as these, advances that improve and simplify triggering are important. Here, magnesium was investigated as a photocathode candidate for optically triggered pseudospark switches, also called back-lighted thyratrons (BLTs). A Mg foil on the back surface of a copper BLT cathode reduced trigger delay and jitter by one order of magnitude when a 5 ns, 3 mJ light pulse at 266-nm wavelength was incident at the back of the cathode at a constant switch voltage of 4.1 kV. Delays less than 150 ns were obtained. An increased photoemission due to the lower work function of magnesium is considered as the main reason for the improvement in trigger delay and jitter for the BLT system. Mg-based cathodes are promising for development of compact optical triggering units with low optical energy sources for BLTs.

辉光放电触发赝火花开关的时延及抖动特性

辉光放电触发赝火花开关的时延及抖动特性

赝火花开关辉光放电腔的粒子模拟与实验研究

赝火花开关辉光放电腔的粒子模拟与实验研究

Application of TPI-thyratrons in a double-pulse mode power modulator with inductive-resistive load

A double pulse modulator is described that is capable of generating two pulses of 200 ns duration at peak currents up to 10 kA with the delay between pulses as short as 2 μs. The TPI1-10k/50 tetrode and the TPI5-10k/50 pentode cold cathode thyratrons, which can be operated at voltages up to 50 kV, have been used as switching elements. A voltage hold-off recovery time of less than 1 μs has been demonstrated at an operating current of 7 kA and a reverse voltage hold-off of 24 kV. Unlike common gaseous switches, TPI thyratrons can operate for over 20,000 h at hundreds of kHz. These devices are serious competitors to both conventional hydrogen hot cathode thyratrons and to high-power solid-state switches. TPI thyratrons are particularly advantageous in burst mode operation where direct and reverse voltages in the range of tens of kV, currents up to 10 kA, nanosecond jitter and risetimes of 1-5 ns are required.

Characterization of high power Pseudospark Plasma Switch (PSS)

The Pseudospark switch is able to control high voltage and high current discharges and operates at low pressure like Thyratron but much simpler in construction and does not suffer in electrodes wear. This switch is bipolar and has 100 % reverse current capability, much faster than Thyratron and has applications in pulse power modulators, linear accelerators, laser systems etc. Such switch has been developed at CEERI Pilani and tested in a demountable setup. For this switch, as a cold cathode based ferroelectric trigger source has also been developed and characterized. High dielectric material has been opted for such a source. The hold off voltage can be doubled if the gap of the electrodes is stacked to two single stage gaps. Such stack of two single stage switches has also been fabricated in a demountable setup. Switching behavior has been observed up to 23 kV and 7 kA in single stage. High voltage conditioning and characterization is still in progress. The paper includes the introduction with working principle, description of the demountable set up, simulation by TriComp, AMaze and OOPIC Pro (Without Comparison among them), and switching behavior.

赝火花开关放电的蒙特卡罗粒子模拟

赝火花开关放电的蒙特卡罗粒子模拟

Gas-discharge laser on a self-terminating thallium transition

We report an experimental study of the performance parameters of a gas discharge pumped thallium vapour laser operating on the 7s2S1/2 - 6p2P3/2o self-terminating transition at 535 nm. The switch we used, a TPI3-10k/25 cold-cathode thyratron, ensures a rise time of the load voltage pulse less than 15 ns. The laser output power is shown to increase in proportion to the energy stored in the discharge capacitor (up to the maximum voltage of the thyratron). The optimal pump pulse repetition rate for He(Ne)—Tl mixtures is ∼1.75 kHz. Even small hydrogen additions reduce the lasing energy and average output power. The addition of bismuth vapour increases the optimal pulse repetition rate (up to 3 kHz) and average output power. The factors responsible for the lower lasing efficiency in comparison with the copper vapour laser are analysed.

Quantum Efficiency Measurements of Photocathode Candidates for Back-Lighted Thyratrons

Light-activated pseudospark switches, also called back-lighted thyratrons (BLTs), are low pressure, high voltage (typ. 10-50 kV), high current (typ. 1-100 kA) glow-mode switches. It is of interest to develop BLTs with reliable and practical optical triggering systems for applications of compact pulsed power. This paper reports the results of research into photocathode materials for BLTs to enhance switching performance and provide optimal cathode conditions for optical triggering. Effective photocathode materials have many specific qualities, the most important being low work function, high quantum yield, and long lifetime at typical BLT operation pressures of 1.3-133 Pa (0.01-1 Torr). Photoemission measurements were conducted with 266 nm, 5 ns laser pulses in a pressure range from 4 × 10-5- 13.3 Pa (3 × 10-7 to 0.1 Torr) using helium as the background gas. Quantum efficiencies up to 1.5 × 10-5, 1.4 × 10-5, and 1.2 × 10-5 were measured for magnesium, copper, and molybdenum samples, respectively. An increase in gas pressure 4 × 10-5- 13.3 Pa (3 × 10-7 to 0.1 Torr) corresponded to an increase in quantum efficiency (QE) of 13% for magnesium and copper; the same increase in pressure corresponded to a quantum efficiency decrease of 10% for molybdenum. Square root of quantum efficiency shows a linear dependence on the square root of the sample surface's electric field due to the Schottky effect. 2D electrostatic simulation of the electric field distribution in a typical compact BLT shows that the field strengths are up to hundreds of kV/cm near the surfaces of the electrodes when a voltage potential of 30 kV is applied between the electrodes. This indicates that higher photoelectron yields can be expected when the tested photocathodes are implemented into BLTs.

SN-series Pseudospark Switches, Operating Completely without Permanent Heating. New Prospects of Application in Pulsed Power

Since 1990th a process of exclusion of gas-discharge and vacuum devices (GDDs and VDs) from Pulsed Power systems has been conditioned by two major factors – unsufficient service time and necessaty to supply filament circuits of GDDs and VDs. And the process was inspite of a number of positive features of GDDs. In the report a design and longterm test results of TDI-type pseudospark switches (PSSs) are presented. The PSSs are a great extent free of the mentioned shortcomings, in particular, the devices are capable of operating without filament, providing a wide number of perspective applications of the tubes in Pulsed Power

Pulsed Power Application of TDI-Type Pseudospark Switches

The module of pulsed power electrohydraulic installation equipped with a technological tank having 2 working electrodes, storing energy up to 3 kJ at average power of 10 kW was constructed and tested. As power switching elements pseudospark switches of TDI-type were used. During the tests organic materials (flax straw) were processed. In the paper various factors, affecting PSS electrodes erosion, are considered. Valuable recommendations on providing the best service time of the switches are summarized. The major object of the investigations is the development of technological system capable of providing a continuous production process with power consumption up to hundreds of kWh with large volumes (up to several tons) processed materials transportation. The process continuity substantially reduces cost of processing, simplifies design, and improves operational characteristics of the device and finally increases competitiveness of the production.

Application of Unheated Cathode Thyratrons for High-Voltage High Current Pulse Series Formation

The circuit of modulator, serving to supply inductive-resistive load in double-pulse mode with currents up to 10 kA and pulse duration of 300 ns, is described. As switching components unheated cathode thyratrons (pseudospark switches) TPI1-10k/50 and TPI5-10k/50 with anode voltage up to 50 kV have been used. The results of tests, confirming possibility of the thyratron reverse dielectric strength recovery within some microseconds after switching of 10 kA forward anode current, are presented.

Pseudospark switch development for pulse power modulators

The Pseudospark switch is able to control high voltage and high current discharges and operates at low pressure like thyratron but much simpler in construction and does not suffer in electrodes wear. This switch is bipolar and has 100 % reverse current capability, much faster than thyratron and has applications in pulse power modulators, linear accelerators, laser systems etc. Such switch has been developed at CEERI Pilani and tested in a demountable setup. Switching behavior has been observed at 22 kV and 7 kA in hydrogen atmosphere (13 Pa). Electrodes shaping and high voltage gap has been simulated in ESTAT and designed accordingly. For this switch, as a cold cathode, a ferroelectric trigger source has also been developed and characterized. High dielectric material has been opted for such a source. The hold off voltage can be doubled if the gap of the electrodes is stacked to two single stage gaps. Such stack of two single stage switches has also been fabricated in a demountable setup. Switching behavior has been observed up to 40 kV and 2.9 kA. High voltage conditioning and characterization is still in progress. In this paper design of the electrodes, ferroelectric source, description of the demountable set up, fabrication, processing of the Pseudospark switch and switching behavior have been presented and discussed.

A Novel Crowbar Impulse Current Circuit for Testing the Switch-Type SPD

A crowbar impulse current circuit for testing the switch-type surge protective device (SPD) is presented. The crowbar circuit consists of a computer control circuit, a trigger voltage pulse generator, a main discharging switch, and a crowbar pseudospark switch. The active trigger technology was studied in the crowbar impulse current circuit. The circuit monitors the main discharging current and generates a trigger signal at a proper time for the crowbar pseudospark switch operation. The trigger characteristics of the main discharge switch and the crowbar pseudospark switch were investigated. By monitoring the preset applied capacitor voltage, the gap distance of the main discharging switch could be adjusted to ensure a discharging delay time less than 2 μs. Equipped with a surface flashover trigger device made of high relative perimittivity dielectric material BaTiO3 (∊r = 3460), the discharge delay time of the crowbar pseudospark switch is less than 85 ns, and the minimum operating voltage is less than 1% of its self-breakdown voltage. With a storage capacitor of 9 μF, an inductor of 18 μH and a crowbar pseudospark switch, a load of 30 mω and an applied capacitor voltage of 40 kV, an impulse current waveform of maximum 25 kA was generated with a rise time and time to half peak value of 17.2 μs and 336 μs respectively.

Multi-gap Pseudospark Switches for High Voltage Applications

The long-term goal of the described experiments is to construct multi-gap pseudospark switches, which can handle reliably the specifications of the pulse forming network (PFN) for the injection/extraction kicker magnet system of the future heavy ion synchrotron accelerator complex SIS100/300 at the Gesellschaft fuer Schwerionenforschung (GSI). The PFN requires an high-voltage switch, that can handle an hold-off voltage up to 70 kV, peak currents up to 6 kA and pulse durations up to 7 mus. In this paper most of the reported experimental data have been obtained by using a two-gap prototype pseudospark switch with total hold-off voltage up to 30 kV. There are two major problems correlated with the development of such multi-gap systems. The first one concerns efficient and reliable triggering of switch for the overall switch lifetime. Two trigger systems have been studied, the so-called high-dielectric trigger (HDT), which already has proven its long term capability, and second, a novel system, based upon the electron emission from carbon nanotubes (CNT). The CNT- trigger still suffers from an insufficient small lifetime of 104 discharges. The second critical part concerns the instant breakdown initiation in the individual gaps, separated by a drift space. In the experiments with this prototype an active pre-ionization of the drift space was nor foreseen. For both trigger systems the measured delay and jitter in the first gap vary from 50 to 60 ns and 15 to 30 ns, respectively; corresponding the second gap has a delay and a jitter of up to 200 and 45 ns, respectively.