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The discharge mode characteristics of cathodes may strongly influence the discharge stability and performance of electrostatic thrusters. In this article, discharge characteristics and mode transition phenomenon of the ring-cusp magnetically confined plasma bridge neutralizer (RCM-PBN) were experimentally studied using argon as the working gas. The dependences of anode current and oscillation amplitude on anode voltage, argon flow rate, heater power, and cathode-to-anode distance were investigated. Plasma properties were measured and plasma plume images were taken under different discharge modes. Two distinct discharge modes were observed during the experiments: high oscillation mode and low oscillation mode. In the high oscillation mode, the plasma plume appears dim, the anode current is low, and the oscillation level is more than 2%. While in the low oscillation mode, a spot-like structure close to the orifice is observed. The plume becomes brighter, the anode current increases, and the oscillation level decreases below 2%. The RCM-PBN was found to transition into the low oscillation mode by increasing anode voltage, flow rate, heater power and by decreasing the cathode-to-anode distance. [ABSTRACT FROM AUTHOR]

The Blumlein pulse forming network (PFN) has widely been used in pulsed power technology to generate square waves with short pulse widths. In this paper, we developed a repetitive frequency square wave generator based on Blumlein PFN and pseudospark switch (PSS). A Blumlein PFN with unequal capacitances has been proposed, and the PFN parameters have been optimized for better output waveforms. A single-gap PSS with a withstand voltage of 40 kV and a repetitive frequency of 100 Hz has been designed to switch the Blumlein PFN. The experiment results show that the square wave generator can output pulses with a voltage of 26 kV, a rise time of 25 ns, and a pulse width of 90 ns on a matched load of 11 Ω. It has operated steadily for 10 h with a repetitive frequency of 100 Hz, and the jitter remains at around 1 ns after 1.05 × 106 shots. [ABSTRACT FROM AUTHOR]

With the development of technology, low-temperature plasma plays an increasingly important role in industrial applications. The industrial application of low-temperature plasma has the following requirements for plasma, high electron energy, low macroscopic temperature, and uniformity. Low-temperature plasma driven by nanosecond pulses reflects more significant advantages in these aspects compared to direct current plasma and alternating current plasma. In this paper, a simple topology is proposed, which is based on the pseudospark switch and the diode opening switch. A pulse generator is developed, which can eventually output pulses with an amplitude of 106 kV, a rise time of 15.5 ns, a pulse width of 46 ns, and a maximum repetition rate of 1 kHz on a 260 Ω resistive load. The pulse generator can successfully drive needle-plate discharge plasma in ambient air. It has excellent parameters, stability, compactness, and a long lifetime. The proposed topology may be helpful for nanosecond pulse generators with amplitude ranging from tens to hundreds of kilovolts, which could be widely used in industry. [ABSTRACT FROM AUTHOR]

Different surface planes of various types of titanium dioxide (TiO2) crystals have diverse catalysis effects on the splitting of H2O and H2 and the electronic structures of the formed hydroxylated TiO2 vary significantly. A series of sixteen types of hydroxylated TiO2 surfaces containing two types of hydroxyls (OH1 and OH2) on four kinds of low index surfaces [(001), (100), (101), and (110)] of two types of crystals [anatase (A) and rutile (R)] are studied using first-principles density functional theory calculations. The catalyzed splitting of H2O and H2 on the eight low index surfaces is compared using Gibbs free energy. The geometries and electronic structures including the total and partial density of states and the charge density distribution of the sixteen hydroxylated surfaces are systematically described. The electronic structures of R-101, R-001, A-110, A-100, and A-001 surfaces are more significantly influenced by hydroxylation than other surfaces and the effects of OH2 are larger than those of OH1. In particular, the band gap values decrease and a new electronic energy state appears in R-001-OH2 and A-100-OH2. A new electronic state appears in the middle of the bands of R-101 and A-110 surfaces upon hydroxylation. The electron spin balance at the edge of the conduction band minimum of A-001-OH2 is disturbed. This research can provide theoretical guidance for experimental researchers to design surface hydroxylated TiO2 materials with tunable electronic structures and high catalytic performance. [ABSTRACT FROM AUTHOR]

In recent years, several novel avalanche transistor-based power synthesis topologies have been proposed to improve the output performance of pulse generators based on avalanche transistors. The most promising is the topology based on avalanche transistors Marx Bank Circuits (MBCs) and linear transformer driver (LTD). However, it suffers from the same problems as other semiconductor switch-based LTD generators. The greater the number of LTD modules, the higher the requirements for synchronization and drive capability of the trigger system. This paper proposes a new self-triggering topology for pulse generators based on avalanche transistors MBCs and LTD, which significantly simplifies the entire generator's requirement for trigger system synchronization and driving capability. First, the circuit topology and its operation principle are introduced. Then, three prototypes with one trigger LTD module and three self-triggering LTD modules are developed. The output characteristics are experimentally investigated. The results verify the feasibility of the proposed topology. Finally, the output amplitude and the rise time are 3.35 kV/3.7 ns, 4.12 kV/3.7 ns, and 4.88 kV/4.0 ns on a 25 Ω resistive load, respectively. All generators can operate at 1 kHz. The topology proposed in the article maximally simplifies the requirements for synchronization and drive capability of the trigger system for generators based on avalanche transistor MBCs and LTD. [ABSTRACT FROM AUTHOR]

The plasma bridge neutralizer (PBN) based on a tungsten filament is a promising technique of a thermionic DC electron source where a hot filament is immersed in an inert gas flow and electrons are "bridged" from a small orifice to the ion beam. PBNs have been widely used in space propulsion and industrial applications due to their relatively simple structure and low power consumption. However, they have well-known disadvantages, namely, low emission current density and short lifetime. In this article, we propose a novel ring-cusp magnetically confined PBN (RCM-PBN) to address these issues. In the RCM-PBN, electrons are confined by a ring-cusp magnetic field, which improves the ionization efficiency and reduces the discharge chamber wall losses. Electrical insulation of the orifice plate from the chamber wall prevents a large number of electrons from being collected by the orifice plate, which greatly improves the extracted electron current. The effects of different operating parameters on the extracted electron current were studied through experiments. It was found that the increase in the extracted electron current with the extraction voltage was related to the anode spot formation. Analysis of the gas utilization factor and electron extraction cost shows that the optimal operating condition was obtained at an argon mass flow rate of 1.2 SCCM and a heater power of 45 W. At its optimum, a stable electron current of 1.1 A was extracted from the RCM-PBN with a gas utilization factor of 12.8 and an electron extraction cost of 143 W/A. [ABSTRACT FROM AUTHOR]

In this article, we show the feasibility of improving the performance of a high voltage and high repetition avalanche transistor pulse generator by applying a two-phase immersion cooling technique. The forced air cooling, single-phase immersion cooling, and two-phase immersion cooling techniques were applied to a 60-stage subnanosecond pulse generator. The experimental results indicate that the two-phase immersion cooling technique can effectively control the temperature rising of the avalanche transistor and, thus, reduce the time base jitter and voltage amplitude jitter. Five types of dielectric fluid with different boiling temperatures were comparatively studied. The FC-72 was finally adopted for the balanced performance on voltage amplitude and repetition rate. The two-phase immersion cooling technique could reduce the thermal resistance between the case and ambient and increase the maximum power from 330 to 876 mW. With this cooling method, the surface temperature of the transistor can be effectively controlled below 62 °C. The pulse generator could achieve outstanding performance with a voltage of 2350 V and a rise time of 180 ps. It can work stably at 200 kHz for more than 30 min, and the burst repetition rate could be 260 kHz within 1 min. This article offers new perspectives in the design of high repetitive avalanche transistorized subnanosecond generators. [ABSTRACT FROM AUTHOR]

This paper studied the plasma plume evolution process of a capillary discharge based pulsed plasma thruster. Time-resolved imaging and optical emission spectroscopy were applied to investigate the plume morphology and plasma species characteristics. It showed that ionized particles (mainly C II and F II) were accelerated early in the pulse and neutral particles (mainly C I and F I) later. An optical time-of-flight (OTOF) method was developed using a photodiode array combined with narrow bandpass filters. The equivalent streaming velocity of the plasma plume was evaluated with the OTOF technique. Measurements of individual species showed that both the ionized and the neutral species could be effectively accelerated by gasdynamic forces, and the ionized particles could reach a higher velocity. A Doppler shift measurement of the plasma plume was also performed to compare it with the findings from the OTOF method. The plasma plume streaming velocity of a thruster with a discharge energy of 5 J was measured and found to be (25.34 ± 0.17) km/s (OTOF) and (22.36 ± 4.02) km/s (Doppler shift). In addition, differences between the operation processes of the capillary discharge based pulsed plasma thruster and the electromagnetic pulsed plasma thruster were analyzed. [ABSTRACT FROM AUTHOR]

Low-temperature plasma technology is widely used in various industrial fields, which require the plasma to be of large volume, diffuse, and stable. Furthermore, previous studies have shown that better plasma performance has been obtained by using generators with a high voltage, a high repetition rate, a fast rise time, and a short pulse duration. In this paper, a novel topology is proposed for such generators, which is based on magnetic switches and diode opening switches. A prototype is developed, and its output characteristics are investigated by varying essential parameters, such as the load resistance and the power supply voltage. The experimental results show that it can generate pulses with a voltage of 30.6 kV, a rise time of 7.1 ns, a pulse duration of 8.2 ns, and a maximum repetition rate of 12 kHz on a 300 Ω resistive load. The prototype has been successfully used to drive uniform plasma in ambient air. In the proposed topology, a diode is added to make the magnetic cores independent of each other, significantly simplifying the design calculation. It may help develop nanosecond solid-state generators. [ABSTRACT FROM AUTHOR]

In this paper, a 60-stage Marx circuit with the two-phase immersion cooling technique is presented. The performance parameters of the pulse generator with phase change immersion cooling and forced air cooling are compared. The results show that the maximum repetition rate is increased from 80 to 260 kHz, the pulse drift is significantly reduced from 900 to 200 ps, and the temperature rise of transistors is controlled effectively to enhance the stability of the amplitude. We also studied the influence of temperature on the turn-on and turn-off processes of the transistors to show the importance of heat management under high repetition conditions. Finally, a pulse generator is developed with the repetition rate of 200 kHz, the rise time of 180 ps, and the amplitude of 2350 V on a matched 50 Ω resistive load, which can work for more than 30 min. [ABSTRACT FROM AUTHOR]