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The Space Plasma Environment Research Facility (SPERF) in Harbin, China, is a user facility dedicated to studying space plasma physics on ground. Magnetic forces are critical to the reliable operation of a magnetic system. A dipole magnet plays a central role in the system and its force conditions are extremely complicated. So, the magnetic force of the dipole magnet is studied in this article. The magnetic system is first introduced. Then, the virtual work principle is presented to evaluate the force analytically. Not dedicated to the complex analytical computation, the qualitative analysis is done based on the breaking of the symmetry of the system from the perspective of the dipole. To validate the qualitative results and solve the force precisely, the finite-element analysis in ANSYS Maxwell is performed. The force results are analyzed and regular patterns are obtained. The influence of the spatial position and the eddy current are studied. In a complex system, the dipole forces from different source magnets compete to dominate as the time proceeds. The methods for analyzing the magnetic forces can easily be extended to other electromagnetic systems.

An innovative, hybrid, inductively coupled, dual-antenna 13.56-MHz radio frequency source of dense low-temperature plasma was developed and experimentally investigated. The electrical and plasma properties of the conventional single-coil inductively coupled plasma source and the upgraded dual-antenna configuration were comparatively studied. As compared to the conventional setup, the dual antenna hybrid scheme maintains the low-temperature plasma with significantly higher electron densities reaching to $1.85\times 10^{12}$ cm−3 at a low electron temperature of 1.7 eV over a large area, and much faster transits to a steady-state plasma. It was also found that the dual-coil system heats electrons more effectively and produces a synergistic effect on the enhancement of power transfer efficiency to the discharge. Significant advantages warrant the efficient employment of this system in many techniques requiring cost effective, convenient, and efficient systems for low electron temperature high-density plasma-based applications.

This is the final draft, after peer-review, of a manuscript published in IEEE Transactions on Plasma Science. The published version is available online at http://dx.doi.org/10.1109/TPS.2017.2783954

An integrated microcontroller-based data acquisition and robotic actuation suite comprising digital electronics, microcontrollers, custom-made hardware, and accessorial software for diagnostics, and characterization of electric propulsion thrusters in a large vacuum space environment simulator is designed, built, and tested. The components of the characterization suite have been aggregated into modular add-on units for rapid rearrangement and easy customization to suit various applications. The modules include a force calibration system for accurate thrust measurements in various thrust stands, and spatially resolved measurements in a multiprobe array comprising Langmuir and Faraday probes for plume diagnostics of plasma thrusters. Plume and thrust characteristics of a miniaturized Hall-type thruster were successfully measured in situ, enabling users to vary process controls and efficiently optimize the thruster performance. The system revealed a further potential for real-time flight mission diagnostics and control.

The recombination of photogenerated charge carriers hinder the application of photocatalyst. In this study, ternary piezoelectric photocatalyst consisting of ZnO, ZnS and MoS2 nanostructures has been synthesized by a two-step hydrothermal method, which exhibits excellent piezo-photocatalytic efficiency while degrading methylene blue (MB). The piezo-photocatalytic degradation efficiency of MB is ~2.5 times of that without piezoelectricity. Moreover, the ZnO/ZnS/MoS2 nanocomposites exhibit good piezo-photocatalytic stability; after 5 cycles, the efficiency remains at ~80% of the initial value. This mechanism can be attributed to the coupling effect of piezoelectricity, photocatalysis and dual heterojunctions, as verified by ESR and diagrammed by band energy structure.

Nitrogen-doped porous carbon (NPC) was prepared by directly carbonizing zeolite ZSM-39 containing a structure-directing agent, tetramethylammonium chloride (TMACl), which also acted as a source of C and N for NPC. The cage-like pore of zeolite ZSM-39 acted as an ideal space for immobilizing the C and N species. The obtained NPCs have a high N content up to 18.14%. The quaternary N of template TMACl was transformed into pyridinic and pyrrolic/pyridonic N during the carbonization. NPCs were suitable for selective adsorption of CO2 because of their unique ultra-micropores and abundant basic sites. The adsorption selectivity of CO2 over N2 was more than 12.1 (molar ratio). The CO2 adsorption capacity of the unit surface area for a NPC-723 sample was calculated as 26.6 μmol m−2 at 0.93 bar and 273 K, which is one of the highest values among carbon adsorbents. Its excellent selectivity makes the NPC a good candidate for separating low concentrations of CO2 in the purification of gas mixtures.

The performance of atmospheric pressure dielectric barrier discharge (DBD) driven by dual-frequency sources of 200 kHz/13.56 MHz has been investigated numerically here in a one-dimensional fluid model. By varying the ratio of dual frequency excitation amplitudes, strong nonlinear coupling in the discharge is observed, with the electron density rising significantly due to the synergistic effect governing the ionization process. Moreover, it is shown that the phase shift between the dual frequencies also has an influence on the electron temperature and density. As to different high frequency components, the modulation of the electron temperature and density induced by the phase-shift also varies significantly. Those results then demonstrated the possibility of applying amplitude and/or phase modulations in a wide operation window to optimize the plasma parameters in dual-frequency DBDs with fixed frequencies.The performance of atmospheric pressure dielectric barrier discharge (DBD) driven by dual-frequency sources of 200 kHz/13.56 MHz has been investigated numerically here in a one-dimensional fluid model. By varying the ratio of dual frequency excitation amplitudes, strong nonlinear coupling in the discharge is observed, with the electron density rising significantly due to the synergistic effect governing the ionization process. Moreover, it is shown that the phase shift between the dual frequencies also has an influence on the electron temperature and density. As to different high frequency components, the modulation of the electron temperature and density induced by the phase-shift also varies significantly. Those results then demonstrated the possibility of applying amplitude and/or phase modulations in a wide operation window to optimize the plasma parameters in dual-frequency DBDs with fixed frequencies.

In the giga-Hz (GHz) regime, not only does an advanced electromagnetic platform need a stealth function to shield itself from radar detection, similar to the “invisible” cloak in the visible light regime, but also an enhanced transmission function to communicate with others. To satisfy the seemingly contradictory requirements, we here propose a multi-functional mode of plasma cloaking, invisible to radar detection but signal-enhanced in communication bands. Such a synergistic effect is achieved by combining a “detour” layer of cloaking and an enhancement layer of communication. Thus, with such a design we can successfully apply an ideal “cloak” to the low frequency detecting regime (in the P-band) and improve signal transmission capabilities in a higher frequency communication regime (in the L-band) at the same time. Furthermore, the tunability and limitations of the multi-functional system are discussed, and the principles of designing inner and outer plasma layers are acquired.

In this work involving an atmospheric dielectric barrier discharge system, the feasibility of independence control of key plasma parameters through strategic modulation of applied dual-frequency excitation sources is demonstrated. In this paper, a one-dimensional fluid model with semi-kinetic method has been used to investigate the discharge properties of atmospheric dielectric barrier discharge by using 200 kHz/13.56 MHz excitations. Bearing good consistency and coherence with experimental results, the electrical characteristics and typical electron dynamics are studied numerically. It is revealed that the application of the high frequency excitation can restrain the increment of the low frequency current component and is effective in preventing the discharge from transitioning to a filamentary mode. This method then suggests and enables possible approaches to obtain discharges with good stability in described DBD systems.

The dielectric barrier discharge (DBD) is a promising technology to generate high density and uniform cold plasmas in atmospheric pressure gases. The effective independent tuning of key plasma parameters is quite important for both application-focused and fundamental studies. In this paper, based on a one-dimensional fluid model with semi-kinetics treatment, numerical studies of ionization asymmetry effects on the properties modulation of atmospheric DBD sustained by tailored voltage waveforms are reported. The driving voltage waveform is characterized by an asymmetric-slope fundamental sinusoidal radio frequency signal superimposing one or more harmonics, and the effects of the number of harmonics, phase shift, as well as the fluctuation of harmonics on the sheath dynamics, impact ionization of electrons and key plasma parameters are investigated. The results have shown that the electron density can exhibit a substantial increase due to the effective electron heating by a spatially asymmetric sheath structure. The strategic modulation of harmonics number and phase shift is capable of raising the electron density significantly (e.g., nearly three times in this case), but without a significant increase in the gas temperature. Moreover, by tailoring the fluctuation of harmonics with a steeper slope, a more profound efficiency in electron impact ionization can be achieved, and thus enhancing the electron density effectively. This method then enables a novel alternative approach to realize the independent control of the key plasma parameters under atmospheric pressure.

Plasma ionization, excitation, mode transitions and associated electron heating mechanisms in atmospheric pressure dielectric barrier discharges (DBD) driven by dual radio frequency sources are investigated in this paper. The electrons are found to be heated mainly by the high frequency component in the plasma bulk when discharged in α mode. On the contrary, the low frequency component is primarily responsible for heating in the sheath which is caused by intense motion in the sheath. It was also found that variation of the lower frequency component ratio could effectively modulate the electron energy distribution as determined from time averaged EEDF. The results above have demonstrated that the independent control of plasma parameters via non-linear synergistic effect between the dual frequency sources can be achieved through reasonable selection of processing parameters.

Dielectric barrier discharges (DBDs) provide a promising technology of generating non-equilibrium cold plasmas in atmospheric pressure gases. For both application-focused and fundamental studies, it is important to explore the strategy and the mechanism for enabling effective independent tuning of key plasma parameters in a DBD system. In this paper, we report numerical studies of effects of dual-frequency excitation on atmospheric DBDs, and modulation as well as separate tuning mechanism, with emphasis on dual-frequency coupling to the key plasma parameters and discharge evolution. With an appropriately applied low frequency to the original high frequency, the numerical calculation demonstrates that a strong nonlinear coupling between two frequencies governs the process of ionization and energy deposition into plasma, and thus raises the electron density significantly (e.g., three times in this case) in comparisons with a single frequency driven DBD system. Nevertheless, the gas temperature, which is mainly determined by the high frequency discharge, barely changes. This method then enables a possible approach of controlling both averaged electron density and gas temperature independently.