Jingming Gao

An improved rolled strip pulse forming line

The rolled strip pulse forming line (RSPFL) has advantages of compactness, portability, and long pulse achievability which could well meet the requirements of industrial application of the pulse power technology. In this paper, an improved RSPFL with an additional insulator between the grounded conductors is investigated numerically and experimentally. Results demonstrate that the jitter on the flat-top of the output voltage waveform is reduced to 3.8% due to the improved structure. Theoretical analysis shows that the electromagnetic coupling between the conductors of the RSPFL strongly influences the output voltage waveform. Therefore, the new structure was designed to minimize the detrimental effect of the electromagnetic coupling. Simulation results show that the electromagnetic coupling can be efficiently reduced in the improved RSPFL. Experimental results illustrate that the improved RSPFL, with dimensions and weight of Φ 290 × 250 mm and 16 kg, when used as a simple pulse forming line, could generate a well shaped quasi-square pulse with output power of hundreds of MW and pulse duration of 250 ns. Importantly, the improved RSPFL was successfully used as a Blumlein pulse forming line, and a 10.8 kV, 260 ns quasi-square pulse was obtained on a 2 Ω dummy load. Experiments show reasonable agreement with numerical analysis.

Investigation on a High Power, Low Impedance, and Long Pulse Generator Based on Magnetic Switches

Magnetic switches could improve the stability, reliability, repetition rate, and life of pulsed power systems, based on which, a high power, low impedance, and long pulse generator has been investigated numerically and experimentally. The generator accomplishes the power compression and the pulse forming at a relatively low voltage level, consisting of a core-type pulse transformer, a two-stage magnetic compression unit, a low impedance pulse forming network, and magnetic type main switches. A full circuit model was developed using PSPICE software to analyze key factors that influence output characteristics of the generator. Key subsystems were manufactured and experimental research was carried out on the whole system. Preliminary results achieved with a dummy load of 2.5 Ω show that the output pulse power is about 2.0 GW and the pulsewidth is about 170 ns, which are in reasonable agreement with the numerical analysis.

Study on a Solid-State Pulse Generator Based on Magnetic Switch for Food Treatments by Pulsed Electric Field (PEF)

In the present paper, a solid-state pulse generator based on magnetic switch is investigated both numerically and experimentally. The generator have potential advantage of high repetitive rate achievability and long life time reliability, which is proper to be used for food treatments by pulsed electric field (PEF). Specially, the pulse generator is designed and the total weight and volume is expected to be 90kg and 0.20m3, approximately. Circuit of the generator is simulated using the P-Spice software. Influence of the impedance of a dummy load is analyzed. The peak voltage over 20kV and pulse duration of 1 s-2.5 s can be achieved on the dummy load. The expected maximum frequency is up to 1kHz. As important parameters, characteristics of the cores used for establishing the magnetic switch were measured at the actual working frequency. Additionally, the magnetic switch with winding number of 30turns and volume of 6000cm3 was tested on an equivalent experimental platform. Typical current with peak amplitude over 520A, duration of 1.52 s was obtained with dummy load of 45 Importantly, the short-circuit termination was also tested for possible flashover in the treatment chamber. Experimental results show reasonable agreement with the numerical analysis.

An Adjustable Magnetic Switch

In this paper, an adjustable magnetic switch (AMS) based on splice winding is investigated numerically and experimentally. The proposed AMS has advantage of high power level, high repetitive rate capability, long lifetime achievability, and electrical parameters tunability, which meets the growing requirements of the military and industrial application of pulsed power technology. Adjustment of the electrical parameters of magnetic switch is achieved by altering the number of windings via the modification of the joint points between the AMS and the main circuit. Specifically, basic principle of the AMS is analyzed based on characteristics of the magnetic switch. Detailed design considerations are described for achieving modification of the windings number ranging from 1 to M (positive integer larger than 1), which is limited by the insulation density, easily and reliably. In order to verify the design, two typical electrical parameters of an AMS are numerically calculated and simulated by the circuit simulation software. Accordingly, a test experiment platform was setup in our laboratory and the primary experimental study demonstrates that the AMS can successfully alter the electrical parameters with results similar to the calculation. A typical (1 - cos ωt) pulse with rise times of 4 and 5 μs, a peak voltage of approximately 20 kV, and a peak current of over 1.0 kA was achieved on the capacitor load. The experimental results show reasonable agreement with the theoretical and numerical analyses.

Experimental study the electric characteristics of the deionized water and its mixture with ethylene glycol in tens microsecond regime and its application

As it is known that the breakdown electric characteristics of deionized water in the pulsed forming line (PFL) depends on the charging time of voltage. In the constructing of the high-current repetitively pulsed accelerator, the PFL usually is charged by the capacitors through the pulse transformer, in order to realize the repetition operation, the semiconductor switches such as thyristors generally be used in the primary circuit of the pulse transformer, the charging time of voltage is prolonged to tens of microsecond because of the application of thyristors, if the deionized water is used as the medium of PFL, how about the breakdown characteristic of deionized water in the PFL in the region of tens microsecond? How about the breakdown characteristic of deionized water under the repetitive operation? A testing device has been set up to investigate the electric characteristics in tens of microsecond regime, the experimental results shown that the time dependent relation of the breakdown electric of the deionized water is weakened, the exponential relation with the effective time of the charging time of voltage is near to −1/6. A high-current repetitively pulsed accelerator is built using the deionized water filled PFL and the semiconductor switches, the experimental results shown that the electric characteristic of deionized water does not to be deteriorated obviously under the 20Hz repetitive operation. The conclusions can be made that the deionized water and its mixture with the ethylene glycol is suitable to construct the compact repetitive high-current accelerator controlled by the semiconductors.

Hydrodynamic Loading of Ceramic Components Due to Pulsed Discharge in Water

Pulsed discharge in water produces transient pressure waves. For one kind of high-current electron accelerators composed of a water pulse-forming line and a ceramic-insulated vacuum diode, the mechanical stability of the water-vacuum interface should be taken into account during operations. In this paper, by combining empirical formulas of a plasma-driven water-shock theory with a self-consistent underwater explosive approach, a finite element model was introduced to investigate the shock-wave behaviors. The pressure-time history and ceramic mechanical response to pressure waves were presented. In order to get the pressure profile and verify the calculation models, the arc pressure test, including ldquopoint-planerdquo electrode system, was carried out based on a ten-stage Marx generator. Peak pressures of shock waves were measured by the piezoelectric sensor, and related results have a close approximation to the predictions. The relationship between peak pressure and shock-wave energy under nanosecond time-scale pulsed-discharge condition was also obtained in the experiment. These results may be helpful for the estimation of a water shock when designing structural components of pulsed-power machines.

Experiments of a 100 kV-level pulse generator based on metal-oxide varistor

This paper introduces the development and experiments of a 100 kV-level pulse generator based on a metal-oxide varistor (MOV). MOV has a high energy handling capacity and nonlinear voltage-current (V-I) characteristics, which makes it useful for high voltage pulse shaping. Circuit simulations based on the measured voltage-current characteristics of MOV verified the shaping concept and showed that a circuit containing a two-section pulse forming network (PFN) will result in better defined square pulse than a simple L-C discharging circuit. A reduced-scale experiment was carried out and the result agreed well with simulation prediction. Then a 100 kV-level pulse generator with multiple MOVs in a stack and a two-section pulse forming network (PFN) was experimented. A pulse with a voltage amplitude of 90 kV, rise time of about 50 ns, pulse width of 500 ns, and flat top of about 400 ns was obtained with a water dummy load of 50 Ω. The results reveal that the combination of PFN and MOV is a practical way to generate high voltage pulses with better flat top waveforms, and the load voltage is stable even if the loads impedance varies. Such pulse generator can be applied in many fields such as surface treatment, corona plasma generation, industrial dedusting, and medical disinfection.

Development of a test platform for high voltage ceramic capacitors based on magnetic compression

The capabilities of long lifetime, fast charging and discharging of high voltage ceramic capacitors are important for their application in pulsed power facilities. This paper presents a rep-rate platform for testing capacitors at several tens kilovolts with charging and discharging time in microsecond region. The platform consists of a high voltage power supply, a primary unit, a core-type pulse transformer, a magnetic compression network, a core reset power supply and a test cell. A circuit model is presented to optimize the electrical parameters of the platform. Then, the test platform is built and experimented. One pseudo-Spark Switch (PSS) is used as a control switch in the primary unit for pulse charging and another PSS is used for discharging the under-tested capacitors in the test cell. Test results of the platform with dummy load and test cell are presented to verify the design and capabilities of the platform.

A gigawatt level repetitive rate adjustable magnetic pulse compressor.

In this paper, a gigawatt level repetitive rate adjustable magnetic pulse compressor is investigated both numerically and experimentally. The device has advantages of high power level, high repetitive rate achievability, and long lifetime reliability. Importantly, dominate parameters including the saturation time, the peak voltage, and even the compression ratio can be potentially adjusted continuously and reliably, which significantly expands the applicable area of the device and generators based on it. Specifically, a two-stage adjustable magnetic pulse compressor, utilized for charging the pulse forming network of a high power pulse generator, is designed with different compression ratios of 25 and 18 through an optimized design process. Equivalent circuit analysis shows that the modification of compression ratio can be achieved by just changing the turn number of the winding. At the same time, increasing inductance of the grounded inductor will decrease the peak voltage and delay the charging process. Based on these analyses, an adjustable compressor was built and studied experimentally in both the single shot mode and repetitive rate mode. Pulses with peak voltage of 60 kV and energy per pulse of 360 J were obtained in the experiment. The rise times of the pulses were compressed from 25 μs to 1 μs and from 18 μs to 1 μs, respectively, at repetitive rate of 20 Hz with good repeatability. Experimental results show reasonable agreement with analyses.

Preliminary experimental results on water breakdown in tens nanoseconds region

Deionized water is a good dielectric material. In this paper, preliminary investigations are carried out on water breakdown in tens nanoseconds region via a switch with “point-plane” electrodes. The switch is set up on the output port of a wave erection Marx generator, which can deliver a minus high voltage pulse with an amplitude of 0∼300 kV, and a pulse width of 40∼50 ns to a matched load. According to the experimental results, the breakdown electric field is calculated to be about 1.2 MV/cm by Martins formula. A circuit model for the whole system is built utilizing PSpice software, and the simulation results agree with the experimental ones basically.