An annular pulse forming line based on coaxial transmission lines.

The miniaturization, lightweight, and solidification of pulse forming lines (PFLs) are of prime significance during the evolution of pulsed power technology. In this paper, an all-solid-state annular pulse forming line (APFL) based on film-insulated coaxial transmission lines is developed to generate fast-rise time quasi-square pulses. First, a coiled coaxial transmission line (CCTL) comprised of multilayer polypropylene films with outstanding insulating properties is constructed. It can withstand direct current voltages up to 200 kV, with a cross section diameter of 7.4 mm. In addition, in order to turn the pulse transmission direction from circumferential to axial, a compact insulated terminal with a 90° bend structure is designed for CCTL. Although single terminal inductance can slow down the rising edge of the output pulse, their parallel connection in an APFL can weaken such an effect. The APFL, with a characteristic impedance of 2.95 Ω and a transmission time of 13 ns, is composed of three CCTLs with six terminals, which can run over 100 thousand times under the pulse voltage of 75 kV. Finally, 15 series APFL modules are employed to assemble a multi-stage PFL for the Tesla-type pulse generator. When charged to a voltage of 1 MV, the mixed PFL consisting of a coaxial line and the multi-stage PFL outputs quasi-square pulses with a voltage amplitude, rise time, and width of 510 kV, 4 ns, and 41.5 ns, respectively, and the fluctuation of the flat top is about 6%.

Investigation into Layer Number Effect on Breakdown Strength of Multi-Layer Polymer Films.

The layer number effect on electric breakdown strength (EBD) of multi-layer polymer films is investigated using 10-µm polypropylene (PP) films under a dc condition. The layer number, n, of the films during the test is as large as 120. It is observed that the relation between EBD and n conforms to a minus power law, i.e., EBD(n) = E1'n-a, where the power exponent, a, is 0.27, E1' is a constant. By reviewing the experimental data in references, it is found that the power law holds true for different types of polymers in different test conditions, but the value of a varies from 0.072 to 0.5. The variation of a is explained in perspective of the discontinuous structures within films and those between films. A small value of a means a good purity level of the film, which is due to the decrease of the size of the inter-layer defects. A large value of a means a poor purity level of the films, which is due to the increase of the amount of intra-layer defects. Both factors influence the value of a, leading to the variation of a.

A 100 kV, 50 Hz repetitive high-voltage pulse lifetime test platform.

The pulse lifetime characteristics of solid materials have been widely concerned in the field of pulse power technology. In this paper, a repetitive high-voltage pulse lifetime test platform for the pulse lifetime test of insulation materials is set up. The platform contains a closed magnetic-core transformer and a sample cavity. The transformer insulated by transformer oil was stably operated at the 100 kV/50 Hz mode with maximum rise time of 45 µs. The sample cavity insulated by SF6 gas includes a gas switch with an amplitude jitter less than 3% at the 50 Hz mode. The platform has advantages of high efficiency and reliability. First, it can generate three kinds of different pulses simultaneously, which satisfied the insulation test requirements under different pulse conditions. The first kind of the generated pulse is a sinusoidal pulse with an amplitude of 100 kV when the gas switch keeps open. The second one is a unipolar microsecond pulse when the gas switch closes. The last one is a nanosecond pulse generated by secondary capacitor discharge. Second, long-time operation of the platform including the pulse transformer is realized. The platform was stably operated for more than 20 × 106 pulses at the 50 Hz/100 kV mode for pulse lifetime tests of solid pulse forming lines and other solid materials.

5-GW Tesla-type pulse generator based on a mixed pulse-forming line.

To shorten the length of the pulse-forming line (PFL) and generate pulses with good flat-top quality, a 5-GW Tesla-type pulse generator based on a mixed PFL is developed in this paper to produce intense electron beams and generate high-power microwaves (HPMs). The mixed PFL is composed of a coaxial PFL and a multistage series annular PFL, which, in turn, consists of 18 coaxial-output capacitor-loaded annular PFL modules in series. The generator can produce quasi-square electrical pulses with a width of 43 ns and a peak power of 5 GW on a matched load. In experiments where it is used to drive a relative backward-wave oscillator to generate HPMs, the results show that the HPM frequency is 16.15 GHz and the power is 1.06 GW with an efficiency of 25% when the voltage of the diode is 620 kV and the beam current is 6.9 kA.

A quasi-coaxial HV rolled pulse forming line.

A quasi-coaxial high-voltage (HV) rolled pulse forming line (rolled PFL) is researched in this paper. The PFL is rolled n circles on a support cylinder simultaneously by two layers of copper foil electrodes and two layers of insulation dielectrics. The first circle of the two electrodes are elicited in opposite directions along the axis, acting as the quasi-coaxial output structure of the PFL, and the left n - 1 circles of the PFL form a complete rolled strip line of n - 1 circles. The rolled PFL is convenient to realize HV insulation and is able to output a pulse with good quality. Characteristic parameters of the PFL are designed theoretically. Besides, the pulse discharge process of the PFL is simulated by computer simulation technology (CST) modeling, and the simulation result verifies the correctness of theory design. Furthermore, a rolled PFL with a characteristic impedance of 4.4 Ω is developed. The test characteristic impedance of the developed PFL by the incident pulse method confirms to the theory design. The discharge voltage waveform with a full width at half maximum of 57 ns of the PFL is acquired, which has a rise time of 6.8 ns. The HV test of the rolled PFL is carried out, and a discharge current pulse with an amplitude of 7 kA is acquired when the PFL is charged to 70 kV. It is calculated that the developed PFL has an energy storage density of 2.5 J/l. A Tesla generator based on 13 stages of rolled PFLs is designed, which is expected to output a 450 kV pulse with a duration of 100 ns on a 40-Ω match load. The discharge waveform of the generator is simulated by the CST software. The simulative output pulse has a rise time of 5 ns, with a flattop jitter less than 5%.

A coaxial-output capacitor-loaded annular pulse forming line.

A coaxial-output capacitor-loaded annular pulse forming line (PFL) is developed in order to reduce the flat top fluctuation amplitude of the forming quasi-square pulse and improve the quality of the pulse waveform produced by a Tesla-pulse forming network (PFN) type pulse generator. A single module composed of three involute dual-plate PFNs is designed, with a characteristic impedance of 2.44 Ω, an electrical length of 15 ns, and a sustaining voltage of 60 kV. The three involute dual-plate PFNs connected in parallel have the same impedance and electrical length. Due to the existed small inductance and capacitance per unit length in each involute dual-plate PFN, the upper cut-off frequency of the PFN is increased. As a result, the entire annular PFL has better high-frequency response capability. Meanwhile, the three dual-plate PFNs discharge in parallel, which is much closer to the coaxial output. The series connecting inductance between adjacent two modules is significantly reduced when the annular PFL modules are connected in series. The pulse waveform distortion is reduced when the pulse transfers along the modules. Finally, the shielding electrode structure is applied on both sides of the module. The electromagnetic field is restricted in the module when a single module discharges, and the electromagnetic coupling between the multi-stage annular PFLs is eliminated. Based on the principle of impedance matching between the multi-stage annular PFL and the coaxial PFL, the structural optimization design of a mixed PFL in a Tesla type pulse generator is completed with the transient field-circuit co-simulation method. The multi-stage annular PFL consists of 18 stage annular PFL modules in series, with the characteristic impedance of 44 Ω, the electrical length of 15 ns, and the sustaining voltage of 1 MV. The mixed PFL can generate quasi-square electrical pulses with a pulse width of 43 ns, and the fluctuation ratio of the pulse flat top is less than 8% when the pulse rise time is about 5 ns.

A novel structure of transmission line pulse transformer with mutually coupled windings.

A novel structure of transmission line transformer (TLT) with mutually coupled windings is described in this paper. All transmission lines except the first stage of the transformer are wound on a common ferrite core for the TLT with this structure. A referral method was introduced to analyze the TLT with this structure, and an analytic expression of the step response was derived. It is shown that a TLT with this structure has a significantly slower droop rate than a TLT with other winding structures and the number of ferrite cores needed is largely reduced. A four-stage TLT with this structure was developed, whose input and output impedance were 4.2 Ω and 67.7 Ω, respectively. A frequency response test of the TLT was carried out. The test results showed that pulse response time of the TLT is several nanoseconds. The TLT described in this paper has the potential to be used as a rectangle pulse transformer with very fast response time.

A high-impedance attenuator for measurement of high-voltage nanosecond-range pulses.

A novel kind of high-impedance cable attenuator for measurement of high-voltage ns-range pulses is investigated in this paper. The input and output ports of the proposed attenuator were both high-impedance ports, and good pulse response characteristics of the proposed attenuator were obtained with pulse response time less than 1 ns. According to the requirement of measurement, two attenuators with lengths at 14 m and 0.7 m were developed with response time of 1 ns and 20 ns, and the attenuation coefficient of 96 and 33.5, respectively. The attenuator with the length of 14 m was used as a secondary-stage attenuator of a capacitive divider to measure the high-voltage pulses at several hundred ns range. The waveform was improved by the proposed attenuator in contrast to the result only measured by the same capacitive divider and a long cable line directly. The 0.7 m attenuator was also used as a secondary-stage attenuator of a standard resistant divider for an accurate measurement of high-voltage pulses at 100 ns range. The proposed cable attenuator can be used to substitute the traditional secondary-stage attenuators for the measurement of high-voltage pulses.