Search

The conversion of methane into transportable and storable materials is crucial in the petrochemical sector. In this study, a specially constructed AC‐driven dielectric barrier discharge (DBD) that has charge injector pyramids on one of the electrodes and runs at ambient temperature and pressure was used to evaluate noncatalytic methane conversion. The obtained result was compared with the traditional flat electrode DBD. It was discovered that the product selectivity in direct nonoxidative methane conversion depended on the discharge conditions. Pyramid electrode plasma sources convert methane up to 50% $ \% $ more than flat electrode plasma due to the appearance of more microdischarges. Pyramid electrode plasma generally has a greater production efficiency than flat electrode plasma, while requiring more operational power. The turnkey solutions offered by the sustainable methane coupling method discussed here may be advantageous for the long‐term small‐scale ethylene exploration scenario. [ABSTRACT FROM AUTHOR]

Recently, a bouncing-like mechanism for electron multiplication inside long nano-ruptures during the early stages of nanosecond discharge in liquid water has been proposed in (Bonaventura 2021 Plasma Sources Sci. Technol. 30 065023). This mechanism leads to the formation of electron avalanches within nano-ruptures caused by strong electrostrictive forces. The avalanche propagation is a self-sustaining process: the electrons emitted from the water surface to the cavity support the propagation of the avalanche and the avalanche itself is a source of the parent electrons impinging on the surface of the nano-rupture and causing secondary emission. We analyze the process of the electron secondary emission directly from the simulation results of the electron avalanche propagation. This allow us to perform an in situ study of the secondary emission and related physical processes. We present the results of an extensive parametric study performed using the state-of-the-art simulation toolkit Geant4-DNA for modeling electron-liquid water interactions. It is shown that the typical lifetime of an electron in an avalanche is about 0.1 to 0.2 picoseconds and that the electron experiences about 4 bounces before ending up in liquid water. In addition, it is shown that the secondary electrons are formed in a layer adjacent to the nano-rupture surface that is only a few nanometres thin. The secondary electron velocity distribution at the moment of the electron birth, the velocity space of electrons (re-)emitted from the water, and the velocity space of electrons at the moment of their impact to the cavity surface are analyzed in detail. Electron bouncing and secondary electron generation efficiency are quantified using the secondary emission coefficient, the secondary emission efficiency, and the effective energy consumed to produce new electrons. [ABSTRACT FROM AUTHOR]

The purpose of this work is to study the dielectric charging of polymer fibers with the electron plasma charging effects accompanied by the emergence of waves propagating along the polymer fiber surface. Monitoring of the charge propagation along the single fiber has been performed using dielectric polyhydroxybutyrate (PHB) fibers obtained by the electrospinning (ESP) method under the electron beam inside the scanning electron microscope chamber. The mechanical effect of the electron beam on the polymer fibers has been detected in a time-lapse mode. The influence of the polymer surface irregularities and mechanical defects on the fiber charging has been demonstrated. Plasma mechanism is typical not only for electrophysical phenomena but also for the control of mechanical movement of the fibers by the electron beam and the charge propagation during electron-beam-induced melting and in the presence of hydrodynamic polymer flows. It is assumed that the mechanical effect in the methods using an electron beam (and plasma on the dielectric surface) as an impact source can be determined by the following factors: pressure of the electron beam and the electric field, contribution of the secondary emission, thermal/thermomechanical factors, and dynamic balance or competition between all the forces affecting the sample (electron-beam pressure, gravity pressure, recoil pressure during evaporation, vapor pressure/surface tension, and so on). In addition to purely scientific interest, the above phenomena are also of significant applied interest since the influence of the polymer fiber charging on the separation procedure of aerosols in nonwoven filters is well known, and hence, charging of such polymer fibers is important for some energy storage devices. [ABSTRACT FROM AUTHOR]

In the process of integrating large-scale wind farms into the power system, the harmonic interaction among wind farms causes potential safe and stable operation threats to the power grid. To effectively control the harmonics of the wind power grid-connected system, quantitative analysis of the harmonic interaction is very necessary and meaningful. Therefore, this paper firstly explains the harmonic interaction among wind farms from the perspective of the primary and secondary emission. We use the concept of harmonic impedance to analyze the mechanism of harmonic interaction and proposed a calculation method for quantitative analysis of the harmonic interaction. Using the calculation method, the influence caused by the wind farm self-impedance, the contact impedance, and Static Var Generator to the harmonic interaction are quantitatively analyzed. Finally, taking multiple wind farms in actual operation as a case, the effectiveness of the method is verified by time domain simulation.

Quantum-mechanical transitions arising under optical excitation of globular photonic crystals are analyzed. Possible cases of electron—phonon and electron—photon—phonon coupling initiated by laser pumping are discussed. Spectral characteristics of acoustic waves emitted during electron—phonon transitions in synthetic opal are calculated. The maximum frequency of arising electromagnetic radiation is estimated. The crucial role of free electrons localized within globules in excitation of radiative processes in the crystal is accented. [ABSTRACT FROM AUTHOR]

Measurement of electron energy spectra of dielectrics is a challenge due to charging issues. This article presents experimental results of electron energy spectra of dielectric materials under electron irradiation obtained by transforming the charging process into a spectroscopic tool. The technique was verified on conductive materials in a previous paper. This method is based on capturing the charging transient of the secondary electron emission current. Dielectric materials are irradiated with a single train of pulses of monoenergetic electrons. The evolution of the number of emitted electrons as a function of time is measured. The rate of this evolution coupled to the arising potential on the surface of the material conveys the energy at which the secondary electrons are emitted. The total incident dose used in this method is about 10 pC/mm2, in contrast to the high doses required when other common methods are utilized. The use of low doses ensures a minimal distortion of the pristine state of the dielectric material by avoiding radiation damage, deep charging, defects, aging and other electron induced phenomena in the insulator. This method was applied to obtain the secondary electron energy spectra of the Kapton, Teflon, and Ultem polymers.

The cathode in the magnetron should have good secondary emission property and a certain thermionic property. In this article, ZrH2 was added as an activator to obtain rare earth-doped tungsten matrix impregnated cathode to improve the emission property. Cathodes with ZrH2 (Y15-411-Zr cathode) or without ZrH2 (Y15-411 cathode) were prepared by a spray drying method combined with high-temperature sintering in dry hydrogen atmosphere. The emission properties and emission mechanism have been studied. The results showed that thermionic emission performance and secondary emission performance of Y15-411-Zr cathode are 3.4 times and 1.2 times higher than those of Y15-411 cathode, respectively. With the addition of ZrH2, yttrium was produced during activating process, which contributed to the better emission properties of Y15-411-Zr cathode. Furthermore, the work function of barium and oxygen adsorbed on yttrium oxide and yttrium surface was calculated using the first principle. The results showed that the lowest work function of Ba-O absorbed on Y2O3 and Y is 1.9 and 1.6 eV, respectively. [ABSTRACT FROM AUTHOR]

The test results of the prototype of the secondary-emission probe operating in the mode of self-oscillatory sweep intended for diagnosing nonequilibrium plasma in the presence of epithermal group of electrons are given. Earlier, the method of self-oscillatory probe was tested using an aluminum water-cooled contact surface with formation of a nanoscale thick high-emission oxide coating. The structure of the described probe is peculiar owing to application of refractory tantalum, which is capable of working in the mode of radiation cooling, which simplifies the structure and increases the reliability of the probe. It is shown that, owing to secondary-emission characteristics, oxide-coated tantalum allows under plasma loading obtaining a pronounced N-type current–voltage characteristic with a large excess in the electron-emission current component against the ion saturation current and satisfies all requirements for realization of the method of self-oscillatory probe. [ABSTRACT FROM AUTHOR]