High-pressure Spark-gap Switches Research Articles

Energy transfer efficiency of nano-seconds pulsed power generator for nonthermal plasma processing technique

Development of a high voltage nano-seconds pulsed power generator (NS-PG) is attracting attentions from plant manufacturing makers since it enables higher energy efficiencies of plasma processing: such as pollution control, ozone generation and so on. The pulsed power system developed in this study consisted of a pulsed charging circuit, the NS-PG, and a load. The NS-PG consisted of a high-pressure spark gap switch (SGS) as a low inductance self-closing switch, a triaxial Blumlein line as a pulse-forming line, and a voltage transmission line from the Blumlein line to load. The SGS was filled with SF6 gas, and the output voltage of the generator is regulated by varying the pressure of SF6. The pulse duration of output voltage is 5 ns. In this study, energy transfer efficiency from NS-PG to load is investigated for both positive and negative voltage polarities. In addition, experiments were carried out using a low inductance resistor and a discharge reactor as connected load. The results showed maximum energy transfer efficiency was 85.2% in case of a low inductance resistive load, and 56.7% in case of a discharge reactor. Further efficiency can be achieved by impedance matching the discharge reactor to the NS-PG.

Empirical analysis of high pressure SF6 gas breakdown strength in a spark gap switch

It is difficult to predict or measure the breakdown strength of SF6 gas in the high pressure range. Therefore, it is hard to find reference data of the high pressure SF6 gas breakdown strength. This paper attempts to provide empirically a novel criterion for the estimation of SF6 gas breakdown strength in a spark gap switch. For this purpose, J.C. Martin's breakdown field strength of non-uniform gap in air and Kuffel et al's breakdown field strength by exploiting streamer criterion of uniform field in SF6 gas are adopted. The research is made for the empirical method of predicting the high pressure SF6 breakdown strength and compared results have been ascertained with several experimental data from different investigators in a wide range of pd (pressure times distance) and field enhancement factor (FEF). For further confirmation of the empirical approach, we have designed and developed a high pressure spark gap switch to be closely coupled to a high voltage PFN-Marx system. The designed spark gap switch operates above 1 MV. Our tests have verified the prediction of the breakdown strength of the SF6 filled spark gap switch in a pd range of 0.27-1.62 MPa . cm (2.7 to 16.2 bar.cm).

An Efficient, Repetitive Nanosecond Pulsed Power Generator with Ten Synchronized Spark Gap Switches

This paper describes an efficient, repetitive nanosecond pulsed power generator using a Transmission-Line-Transformer (TLT) based multiple-switch technology. Within this setup, a 10-stage TLT and ten high-pressure spark-gap switches are adopted. At the input side, ten spark-gap switches are interconnected in series via the TLT, so that all the spark-gap switches can be synchronized automatically. At the output side, all the stages of the TLT are connected in parallel, thus a low output impedance (5 Ω) is obtained, and a large output current is realized by adding the currents through all the switches. Experimental results show that 10 spark-gap switches can be synchronized within about 10 ns. The system has been successfully demonstrated at repetition rates up to 300 pps (Pulses Per Second). Pulses with a rise-time of about 11 ns, a pulse width of about 55 ns, an energy of 9-24 J per pulse, a peak power of 300-810 MW, a peak voltage of 40-77 kV, and a peak current of 6-11 kA have been achieved with an energy conversion efficiency of 93-98%.

Gas-filled metal-ceramic high-pressure spark-gap switches

The results of the upgrading of P-48 and P-49 spark-gap switches that allowed us to improve their electric performances are presented. The design and performance data of РИМ 100/35 and РИМ 200/50 gas-filled metal-ceramic spark-gap switches are described. When used in the circuit of the Marx generator of the APCA accelerator operating at a voltage-rise time of 5–6 μs, they ensure a pulsed breakdown voltage of 120 and 150 kV, respectively. In such devices as МИРА, ДИНА, etc., operating at a voltage-rise time of 0.5–1 μs, the breakdown voltage of these spark-gap switches can be increased up to 130 kV (for РИМ 100/35) and 220 kV (for РИМ 200/50). The intrinsic switch time is <0.5 ns. Some practical recommendations for the metal-ceramic spark-gap switch design are provided.

A novel HV double pulse modulator

A high-voltage double pulse modulator has been developed which is capable of generating two discrete rectangular pulses with a variable interpulse delay. It is comprised of two Blumlein pulse forming networks connected in series, and discharged independently using high-pressure spark gap switches. Each voltage pulse is 120 ns in duration with a risetime of approximately 15 ns. The maximum output voltage is 350 kV of either polarity, and the output impedance is 200 Omega .

The operation of repetitive high-pressure spark gap switches

Two parallel experiments have been undertaken to investigate the mechanisms which govern the recovery of spark gap switches in repetitive applications. Measurement of the neutral gas density is accomplished using a laser Schlieren technique which enables spatial and temporal cooling of the gas to be observed. The rate of rise of voltage recovery is recorded using a double-pulse modulator system which determines the breakdown voltage of the gas at specific time intervals after breakdown by the first pulse. A continuous sweep voltage is applied to the switch in order to establish the influence of ions on the recovery characteristics. Results are presented for SF6/bin and air which show that voltage recovery is not solely governed by recovery of neutral gas density. There is a significant influence from the residual ion population created by the previous discharge. This influence is dominant for several hundred milliseconds after breakdown. The application of a suitable sweep voltage effectively minimizes the ion population, which results in significantly improved voltage recovery characteristics.

High repetition rate, fast current rise, pseudo-spark switch

A pseudo-spark switch triggered by a pulsed low-current gas discharge has been developed. It switches medium voltages and currents of typically less than 20 kV and 10 kA, respectively. The switch works at high repetition rates of up to 100 kHz and fast rates of current rise of up to 5*1011 A s-1. At positive charging voltage, the jitter may be much smaller than 1 ns. This pseudo-spark switch has been successfully tested by running a discharge-heated longitudinal copper vapour laser and a transverse Blumlein N2 laser, replacing a hydrogen thyratron and a high-pressure spark gap switch, respectively.

High repetition rate LC oscillator

LC oscillators have been built which can produce multikilowatt RF pulses in the megahertz frequency range with repetition rates of tens of kilohertz. The L and C for these oscillators can be determined from the frequency requirement and the high-Q requirements. The high repetition rates are achieved using a high-pressure spark-gap switch together with a dc to ac inverter power supply. Closely spaced antenna elements can be used to increase the number of cycles in the radiated waveforms (radiated Q).