Bin-Xiong Yu’s research while affiliated with Spine Institute Northwest and other places

This article concentrates on the field emission (FE) characteristics under the pulsed transient electric field. Experimental measurements are carried out by applying direct current (DC) voltage, millisecond pulse voltage, and microsecond pulse voltage. Additionally, 304 stainless steel, oxygen-free copper and titanium electrodes are utilized to verify the consistency. Compared with the case under DC electric field, three distinctive FE characteristics are observed under pulsed transient electric field: the regular emission, the intense emission, and the annihilation phenomenon. First, the emission starting point implies one strong correlation with the second partial derivative of transient electric field strength with respect to time. Second, the emission current under pulsed electric field is much higher than that under the DC electric field. Moreover, the FE current is deeply associated with the gradient of the electric field during the rising front. Third, the FE current is extinguished though there is still high transient electric field. The mechanism of the three characteristics is still unclear and should be the subject of further investigation.

A method of measuring field emission current under high-voltage (HV) pulse is proposed. The method makes it more convenient to study electron emission under HV pulse. Based on the Kirchhoff law, this method can fundamentally solve the problem, which the emission current is usually covered up by the displacement current. In addition, the method can ensure the safety of oscilloscope and the accuracy of the measurement when the gap gets breakdown. The resolution analysis of this method is carried out. The resolution is positively correlated with the output resistance and negatively correlated with the summation of output capacitance and electrodes capacitance. The resolution, under microsecond and millisecond HV pulse, can achieve $\mu$ A to A class. The measurement platform based on this method contains an energy-storage capacitor, a load resistor, an HV pulse power supply, an electrode cavity, and three resistor–capacitor ( R – C ) voltage dividers.

A novel screw-based probe is put forward to measure the pulse forming line (PFL) voltage in Tesla-type generators. This probe utilizes an existing screw as the key part of the conventional probe. Therefore, no extra hole is needed, which simplifies the design of the PFL. The voltage ratio of this probe is not a constant which varies within the pulsewidth with a deviation of ±5%. By analysis, it is found that this deviation is mainly due to the complicated electromagnetic environment on the outer magnetic core of the Tesla transformer where this probe is assembled. The electromagnetic environment can cause perturbation which adds on the main test waveform when the Tesla transformer is charging. Two solutions are proposed for this question. One is to consider the voltage ratio as a time-dependent variable, rather than a constant any more. The other is to redesign the screw-based probe and assemble it where the electromagnetic environment is weak. Both the methods can decrease the deviation of the voltage ratio to a level smaller than 1% and are applied in practical measurements.

The de-excitation of nitrogen excited states after spark gap discharge was investigated with time-resolved optical emission spectroscopy method. Recombination of ionized particles was experimentally proved less than several tens microseconds. After the recombination process, it was shown that atomic nitrogen in ground state [N( ⁴ S)] and molecular nitrogen in first excited state [N ₂ (A ³ Σ ⁺ _u )] was long-lived particles (metastable state) after gas discharge. Characteristics of decay for N(4S) and [N ₂ (A ³ Σ ⁺ _u )] were studied, and their lifetime and decay of density were estimated in this paper. Peculiar unexponential decay of N ₂ (A ³ Σ ⁺ _u ) showed there was reproduction process of N ₂ (A ³ Σ ⁺ _u ) after gas discharge. N(4S) could be the source for reproduction process under their mechanism of three-body recombination. Low ionization energy and high ionization collision cross section of N2(A3Σ+u ) make it a possible factor limiting the switch recovery. The de-excitation of metastable states opens novel perspectives for understanding the recovery of gas switch.

In this paper, a new match circuit of the capacitive divider is studied. Using the proposed match circuit, the signal measured by the capacitive divider will not be secondarily attenuated near the accelerator, and the secondary attenuation is done at the terminal end of the cable which is located in a shielding room with a good electromagnetic environment. So, the proposed circuit has a better anti-interference capability than the traditional terminal-end match circuit. The result of the theoretic analysis shows that the proposed match circuit is equivalent with the traditional terminal-end match circuit when the parameters of the circuit are well chosen. Rectangular pulse response of the proposed match circuit is tested based on an equivalent circuit. It shows that the proposed match circuit has a good pulse response characteristic for rectangular pulse with a rise time of 5 ns, and the output waveform of the match circuit has a flattop jitter less than 1%. The match circuit proposed in this paper is utilized to measure the diode voltage of the accelerator in our laboratory. It is found that the high-frequency interference on the output waveform measured by the new match circuit is much smaller than that measured by the traditional terminal-end match circuit, which proves that the match circuit proposed in this paper is an effective method for increasing the signal-to-noise ratio of capacitive divider for measurement of nanosecond-range HV pulse.

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 rolled strip pulse-forming line (RSPFL) with a dry structure is researched for the purpose of miniaturization and all-solid state of pulse-forming lines (PFL). The coaxial-output RSPFL consists of a coaxial-output electrode (COE) and a rolled strip line (RSL). The COE is characterized by quasi-coaxial structure, making the output pulse propagate along the axial direction with a small output inductance. The RSL is rolled on the COE, whose transmission characteristics are analyzed theoretically. It shows that the RSL can be regarded as a planar strip line when the rolling radius of the strip line is larger than 60 times of the thickness of the insulation dielectric layer of RSL. CST modeling was carried out to simulate the discharging characteristic of the coaxial-output RSPFL. It shows that the coaxial-output RSPFL can deliver a discharging pulse with a rise time <6 ns when the impedance of the RSL matches that of the COE, which confirms the theoretical analysis. A prototype of the coaxial-output RSPFL was developed. A 49-kV discharging pulse on a matched load was achieved when it was charged to 100 kV. The discharging waveform has a pulse width of 32 ns, with a rise time of 6 ns, which is consistent with the simulation waveform. An energy-storage density of 1.9 J/L was realized in the coaxial-output RSPFL. By the method of multi-stage connection in series, a much higher output voltage is convenient to be obtained.

Research is carried out on the basis of the traditional two-end matched circuit of a capacitive voltage divider with a long measurement cable. Transmission progress in the circuit is analyzed theoretically. A match condition of the circuit is acquired, which requires that the circuit satisfies two conditions: (1) the measurement error should be small for a pulse with a duration of less than twice the delay time of the measurement cable; (2) the initial division ratio and the stable division ratio of the circuit are the same. Two matched methods of the circuit are acquired, including the first-order matched method and the second-order matched method. Numerical simulations are carried out. According to the simulation results, the relative errors of the circuits with a cable of 20 m are less than 1.5%, obtained by using both match methods for measurement of rectangular pulses with rise and fall times of 5 ns. An improved circuit is presented, which is suitable for any situation where the low-voltage capacitance of the capacitive divider is even smaller than the capaictance of the measurement cable. A verification experment is carried out, and the test result confirms the simulation result.