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The influence of SF6-admixtures to N2 on electrodeless streamer inception at the surface of a dielectric solid (epoxy resin) is investigated for different SF6/N2 ratios and gas pressures, with focus on the lower pressure region (below 1 bar) which is only sparsely discussed in literature. For this purpose, we use a special set-up with cylindrical electrodes embedded out of axis in a cylindrical epoxy rod. The influence of the dielectric surface on streamer development is analyzed by estimating the ionization rate. Ionization rates obtained from experimental measurements seem to be higher than those available for discharges in bulk gas under similar conditions. The main influence on the inception voltage, however, seems to come from the change in the field distribution due to the presence of the dielectric solid. Furthermore, it turns out that the streamer inception voltage increases with gas pressure for a constant SF6/N2 ratio, increases rapidly as a function of the SF6/N2 ratio at small amounts of SF6 (∼ 5%), and increases at lower rates for higher amounts. The total duration of the discharge decreases almost by a factor of 10, i.e., from tens of nanoseconds to several nanoseconds for pure nitrogen and 5% SF6-admixture, respectively. Overall, it is shown, that the major inception parameters (critical voltage, rise and fall times, current shapes) of streamer discharges on a gas-solid dielectric interface change considerably starting already with a small (5%) admixture of SF6 to nitrogen. [ABSTRACT FROM PUBLISHER]

When charged particles impact the surface of a solid material, they can be backscattered from that surface or cause secondary electrons to be emitted. The ratio of the number of emitted electrons (secondary and backscattered) to the incident electrons number is known as the total electron emission yield. Knowledge of this total electron emission yield (TEEY) is highly required in various modern technologies, and several experimental techniques were developed with the purpose of its determination. However, experimental data, obtained with different methods are not in good agreement and sometimes are even contradictive. The purpose of this paper is to review the existing experimental methods of investigating electron emission (EE) from dielectric surfaces, as well as to analyze their accuracy and reliability. The focus is on the processes of the emission from thick layers of insulators which is the case for modern high voltage technologies. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]

The area of pulsed-power technology covers a broad range of powers (up to 1014 W), voltages (up to 106-107 V), currents (as high as 106 A or higher) and pulse durations (below 10-8 s). State of the art systems have voltages up to a few hundred kilovolts at pulse lengths down to the nanosecond range. Special applications require extreme field strengths in the range of 1 GV/m. The design of a compact source, meeting the above requirement aims for 1 MV, 1 ns pulses. In this paper, we present a novel compact TLT (Transmission Line Transformer). The TLT consists of 10 coaxial transmission lines which are connected in parallel at the input and in series at the output. To verify the theoretical analysis a model of the transmission line transformer has been simulated by a time domain electromagnetic field solver. An optimized transmission line transformer has been built and first measurements have been performed. The equivalent circuit model and the simulations agree with the experimental results. The effect of secondary mode suppression by means of ferrite has been investigated. Both simulations and experiments showed that ferromagnetic cores around each individual transmissions line in our design can be omitted. [ABSTRACT FROM AUTHOR]

Breakdown strength in uniform electric fields of N 2 O mixtures with CO 2 , N 2 , and O 2 is measured under AC voltage stress, 300 kPa pressure, and electrode separation of 5 mm. The obtained results show the best synergism of 115% for N 2 O/CO 2 30/70 mixture. For high electric strength of mixtures, a high fraction of N 2 O is beneficial, but is limited by the oxidizing power. Considering this limit, a N 2 O/CO 2 49.1/50.9 mixture can be used with the electric strength 135% of synthetic air and 45% of SF 6 , respectively. [ABSTRACT FROM AUTHOR]

Fast and repetitive switching in high-power circuits is a challenging task where the ultimate solutions still have to be found. We proposed a new approach. Supercritical fluids (SCFs) combine favorable properties of liquids - insulation strength, thermal behavior, and gases - self healing, high fluidity, and absence of vapor bubbles. That's why we start investigating the subject of plasma switches in SC media. First results indicate excellent switch recovery and very high insulation strength. We present the design of a SCF insulated switch (SC switch). Breakdown strength of the SCF is investigated and found to be high in comparison with most of the solid insulating media. The dielectric recovery inside the SC N2 switch is tested under a repetitive 30 kV, 200 ns pulse voltage at repetition rate up to 5 kHz. The recovery breakdown voltage across the SC switch achieves 80 % within 200 μs. The current interruption capability of SC N2 is investigated experimentally in a synthetic circuit generating a high-frequency arc of several hundreds of amperes and a transient recovery voltage of hundreds of volts. The results show that a SC N2 switch with fixed electrodes and an inter-electrode distance of mm range can successfully interrupt this current at approximately 2 ms after arc initiation. [ABSTRACT FROM PUBLISHER]