Jian-chang Peng’s research while affiliated with Xi'an Jiaotong University and other places

Tesla transformers are widely used in short pulse, repetition pulsed power generators. In this paper, a high repetitive rate intense electron beam accelerator (IEBA) based on high coupling (~1) Tesla transformer, which consists of a primary charging system, coaxial pulse forming line (PFL) charged by Tesla transformer and gas spark switch is described, especially stressed on the high coupling Tesla transformer. By introducing magnetic core to enhance the coupling factor between the primary and secondary windings, the transformer is capable of producing high voltage pulse up to 1.4 MV in approximately 45 µs. A coaxial pulse forming line is closely attached to the transformer that the outer and inner magnetic cores are parts of the PFL's outer and inner conductors respectively. In addition, the parameters of the Tesla transformer and PFL are calculated, including the dimension of the PFL and Tesla transformer. Some experiment results showed that the IEBA is capable of producing electron beams of 300–700 kV/7–13 kA at repetitive rate 100 Hz, with the pulse width 35 ns. The maximal energy efficiency of the Tesla transformer is 83%.

Insulation of a coaxial high-voltage vacuum insulator used in the pulsed power generator TPG700 has been studied in this paper. When output voltage is increased from 700 to 800 kV, breakdown happens in the insulator. With transient simulation, the region of the insulator subject to the highest electric strength is concluded. According to the experimental and simulated results, the breakdown strength has been calculated. An electric-thermal model has been proposed in which factors such as local electric field (E-field) enhancement, imperfection in dielectric, and repetition working state are analyzed. A formula to calculate the effects of these factors is suggested. Moreover, the key structures on the coaxial line which influence the E-field distribution are optimized, and useful advice for designing an insulator of this kind is presented.

A circuit topology which can prevent the series resonant power supply in a Tesla transformer from damage induced by the reversal voltage on the storage capacitor is presented. The circuit is based on current-limiting resistor and auxiliary capacitor which can restrict the over current in the rectifier of series resonant power supply. Moreover, adoption of the auxiliary capacitor can raise the average power output of the power supply due to the increase of initial voltage on the storage capacitor. When reversal voltage on the storage capacitor is zero and the auxiliary capacitor is one quarter of the storage capacitor, analysis shows the average power output can be raised 33%. Computation of charging accuracy and optimization of current-limiting resistance are also discussed.

One of the most widely applied devices for repetitive pulse power generator is high-coupling Tesla transformer. The general designing of the high-coupling Tesla transformer is described in this paper. Because of the requirement of high coupling for Tesla transformer, an open-loop magnetic core is employed. In order to reach high reliability of this high-voltage generator, the windings of Tesla transformer (both primary winding and second winding) are set compactly within the insulating gap of pulse forming line (PFL). The parameters of primary and secondary loops have be well-connectedly designed and suitably adjusted. Moreover, as one of the most important components of the TPG700, a high-coupling Tesla transformer, with open-loop magnetic core applied in it, achieved a high efficiency about 83% after optimization. This Tesla transformer can operate on the range of repetition frequency from 1 to 100 Hz.

The characteristics of laser-induced breakdown in nitrogen at a wavelength of 1064nm were investigated with a 10-ns pulsed laser generator. The threshold field of nitrogen decreases as the pressure increases, and the experimental threshold intensities at the lower pressure were in good agreement with experimental values measured by Striker and Parker in 1982. The delay and jitter decreases while increasing the laser energy or the ratio self-breakdown voltage. Increasing gap field can accelerate the closing rate of switch. Under the conditions of average gap field 35kV/cm, ratio of laser focal length to gap length 0.065 and laser-induced energy a little greater than threshold intensities, experimental results of 25-ns delay and 20-ns jitter of switch were approached. Thus experimental results indicated that, using laser-induced breakdown switch, multi-module high power pulse devices could produce sequential pulses with inter-pulse delays of tens nanosecond.

The design and construction of a repetitive high-current pulsed accelerator-TPG700 is described in this paper. The accelerator consists of a Tesla transformer with 40 ohm build-in coaxial pulse forming line. The triggered high-pressure switch of TPG700 has the capability of conducting current of 17.5kA in 35ns' duration at 100 pps. The transformer was designed to operate at 1.4MV, when its primary capacitors were charged to approximately 1000V. Under the working state of 100pps, the jitter of breakdown of the switch voltages is lower than 1% on average. To enhance the overall efficiency of the pulser, resonant charging technology based on IGBTs was utilized. As the experimental results indicate, the total efficiency of the pulser, when measured on matched dummy load, is close to 75%. The experimental results indicate that in matching case, the output of 700kV, 17kA for 40Ω resistive load is obtained. Moreover, some experiments such as long lifetime cathode testing and high power microwave (HPM) generation using backward oscillator (BWO) have been conducted on TPG700.

A novel approach for producing long pulse is presented. The generator based on this approach consists of a Tesla transformer and a set of pulse forming network (PFN). Tesla transformer is used to charge PFL and PFN in series. When the voltage increases to a certain value, the primary switch will close and the PFL and PFN will discharge rapidly to the load. Therefore, an electric pulse of a certain width is formed on the load. The amplitude of this pulse is dependent only on the charge voltage and the matching state of the load and PFN (PFL). The pulse width is determined by transmission time of PFL and PFN. The rise time is determined by the working state and the impedance of PFN, and independent of the parameters of PFN. The PFN is multi-stage and assembled in series. The direction of main dielectric flux is axial and the time modulation is angular. The single-stage PFN is formed with two-row ceramic capacitors placed between two aperture annular plates. The total series impedance is equal to the sum of every single-stage PFN's impedance. Moreover, a tested generator based on this approach is developed. For this device, PFN of nine stages is in series, and the total impedance is 40Ω. The high voltage of amplitude 295kV, current 7kA and duration ∼110ns is produced at repetition frequency of 10 Hz. And the rise time of voltage waveform is only ∼7ns.