There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Polymer materials, such as polymethylmethacrylate (PMMA), are widely used as insulators in vacuum. The insulating performance of a high-voltage vacuum system is mainly limited by surface flashover of the insulators rather than bulk breakdown. Non-thermal plasmas are an efficient method to modify the chemical and physical properties of polymer material surfaces, and enhance the surface insulating performance. In this letter, an atmospheric-pressure dielectric barrier discharge is used to treat the PMMA surface to improve the surface flashover strength in vacuum. Experimental results indicate that the plasma treatment method using Ar and CF4 (10:1) as the working gas can etch the PMMA surface, introduce fluoride groups to the surface, and then alter the surface characteristics of the PMMA. The increase in the surface roughness can introduce physical traps that can capture free electrons, and the fluorination can enhance the charge capturing ability. The increase in the surface roughness and the introduction of the fluoride groups can enhance the PMMA hydrophobic ability, improve the charge capturing ability, decrease the secondary electron emission yield, increase the surface resistance, and improve the surface flashover voltage in vacuum.

Enhanced surface flashover strength in vacuum of polymethylmethacrylate by surface modification using atmospheric-pressure dielectric barrier discharge

This paper reviews the last twenty years of work concerning surface flashover of insulators in vacuum. It complements an earlier review paper [H.C. Miller, Flashover of Insulators in Vacuum, IEEE Trans. Electr .Insul., Vol. 28, pp. 512-527, 1993]. The surface flashover voltage of insulators in vacuum depends upon many parameters, such as material, geometry, surface finish, and attachments to electrodes, but also on the applied voltage waveform, duration, single pulse or repetitive, and on the process history of the insulator, operating environment, and previous applications of voltage. Suggestions are made for choosing the material, geometry, and processing when selecting an insulator for a particular application. Some specific techniques for improving the holdoff voltage of insulators are recommended.

Flashover of insulators in vacuum: the last twenty years

With theoretical prediction and experimental validation, we propose a novel approach to significantly enhance the conversion efficiency of thermoacoustic (TA) imaging by using an ultrashort microwave pulse. The implementation of the ultrashort microwave pulse leads to orders of magnitude enhancement in excitation efficiency and spatial resolution, compared to that from existing TA imaging techniques. This allows high-resolution ($\ensuremath{\sim}100$ micron resolution) TA imaging to be acquired noninvasively. The present work represents a major breakthrough in the conversion efficiency of the TA effect and the resolution of TA imaging, which can potentially be used for clinical imaging.

Ultrashort microwave-induced thermoacoustic imaging: a breakthrough in excitation efficiency and spatial resolution.

A compact high power pulsed modulator based on spiral water Blumlein line, which consists of primary storage capacitors, a Tesla transformer, a spiral Blumlein line of water dielectric, and a field-emission diode, is described. The experimental results showed that the diode voltage is more than 500kV, the electron beam current of diode is about 32kA, and the pulse duration is about 180ns. The distributions for electrical field in the spiral water Blumlein line were obtained by the simulations. In addition, the process of the charging a spiral Blumlein line was simulated through the PSPICE software to get the wave form of charging voltage of pulse forming line, the diode voltage, and diode current of modulator. The theoretical and simulated results are in agreement. This accelerator is very compact and works stably and reliably.

A compact high power pulsed modulator based on spiral Blumlein line.

This paper discusses the development and testing of a low-jitter, high-voltage, high-current, and triggered spark-gap switch, designed as part of an intense electron-beam accelerator (IEBA). The voltage/pressure (V/p) curve of the switch was measured for N2 when the gas pressure is 0.10-0.25 MPa with the main gap spacing of 10 mm. In addition, the operating ranges, delay time, and jitter of the switch were measured during the single trigger experiment when the gas pressures were 0.10, 0.15, 0.20, and 0.25 MPa and the trigger voltage was 80 kV. The experimental results showed that the operating ranges of the switch were 25%-94%, 38%-86%, 40%-88%, and 44%-88% of the switch's self-breakdown voltage, and these results also identified a suitable operating condition for the application of the switch on the IEBA. When the gas pressure was 0.25 MPa, the operating voltage was 40 kV, which was about 88% of the self-breakdown voltage, the delay time was 50 ns, and jitter was 1.28 ns. At last, the repetition rate of the switch was measured when the switch was used as the trigger switch of the IEBA. The pulse repetition rate (PRR) is 10 Hz at the operating voltage of 20 kV and peak currents of 40 kA. The PRR is 5 Hz at the operating voltage of up to 40 kV and the peak currents of up to 80 kA. The switch works steadily and reliably.

Research of a High-Current Repetitive Triggered Spark-Gap Switch and its Application

A compact high-voltage nanosecond pulse generator, based on a pulse transformer with a closed magnetic core, is presented in this paper. The pulse generator consists of a miniaturized pulse transformer, a curled parallel strip pulse forming line (PFL), a spark gap, and a matched load. The innovative design is characterized by the compact structure of the transformer and the curled strip PFL. A new structure of transformer windings was designed to keep good insulation and decrease distributed capacitance between turns of windings. A three-copper-strip structure was adopted to avoid asymmetric coupling of the curled strip PFL. When the 31 microF primary capacitor is charged to 2 kV, the pulse transformer can charge the PFL to 165 kV, and the 3.5 ohm matched load can deliver a high-voltage pulse with a duration of 9 ns, amplitude of 84 kV, and rise time of 5.1 ns. When the load is changed to 50 ohms, the output peak voltage of the generator can be 165 kV, the full width at half maximum is 68 ns, and the rise time is 6.5 ns.

A compact high-voltage pulse generator based on pulse transformer with closed magnetic core

A new kind of miniature high-voltage pulse transformer based on closed magnetic core is developed, and its output characteristics are analyzed in this paper. The amplitude of the output high-voltage pulse of the transformer is 210 kV, the step-up ratio is 1:105, and the effective coupling coefficient is 0.984. The time-domain and frequency responses of the transformer have also been analyzed in detail by circuit theory. The experimental results show that the pulse transformer can respond well to square voltage pulse with a pulsewidth ranging from 5 to 100 ?s and a frequency band ranging from 100 Hz to 500 kHz. With these characteristics, the small pulse transformer with very low cost can be used for applications of dielectric barrier discharge and high-voltage nanosecond-pulse generator.

Output Characteristics of a Kind of High-Voltage Pulse Transformer With Closed Magnetic Core

https://aip.scitation.org/doi/pdf/10.1016/j.mre.2018.07.002

Xinbing Cheng

Papers

A compact high power pulsed modulator based on spiral Blumlein line.

Research of a High-Current Repetitive Triggered Spark-Gap Switch and its Application

A compact high-voltage pulse generator based on pulse transformer with closed magnetic core

Output Characteristics of a Kind of High-Voltage Pulse Transformer With Closed Magnetic Core

Compact intense electron-beam accelerators based on high energy density liquid pulse forming lines