The axial propagation of plasma upon radial injection in a current interrupter

The axial propagation of plasma in a current interrupter with radial injection guns has been experimentally studied. In the absence of a generator current passing through the injected plasma, the plasma front with a density of no less than 10¹¹ cm^?3 moves in the axial direction at a velocity of ～(1–1.5)×10⁷ cm/s. At a distance of 20 cm from the injection plane, a plasma density of ～10¹³ cm^?3 is attained 5–6 ms after the current switch on in the guns; at a distance of 50 cm, the plasma density reaches ～(2–5)×10¹² cm^?3.     

Cryogenically pumped laboratory metallurgical installation

The paper is concerned with the laboratory metallurgical installation designed for heat treatment and zone melting of refractory metals without a crucible. A 10kW electron-beam gun serves as a heater. The installation is evacuated from the atmospheric pressure to the ultimate vacuum using cryopumps only. Particular attention is given to hydrogen pumping. Performances of helium adsorption and condensation cryopumps with an efficiency up to 10⁴/s^?1 for hydrogen have been studied experimentally. The consumption of liquid helium was found to be 40–50cm³ h^?1 for adsorption pumps and 7cm³h^?1 for condensation pumps. It is shown that the application of the condensation pump with a surface cooled down to 2.3 K seems to be most efficient.     

Beyond Activated Carbon: Graphite‐Cathode‐Derived Li‐Ion Pseudocapacitors with High Energy and High Power Densities

Supercapacitors have aroused considerable attention due to their high power capability, which enables charge storage/output in minutes or even seconds. However, to achieve a high energy density in a supercapacitor has been a long‐standing challenge. Here, graphite is reported as a high‐energy alternative to the frequently used activated carbon (AC) cathode for supercapacitor application due to its unique Faradaic pseudocapacitive anion intercalation behavior. The graphite cathode manifests both higher gravimetric and volumetric energy density (498 Wh kg^?1 and 431.2 Wh l^?1) than an AC cathode (234 Wh kg^?1 and 83.5 Wh l^?1) with peak power densities of 43.6 kW kg^?1 and 37.75 kW l^?1. A new type of Li‐ion pseudocapacitor (LIpC) is thus proposed and demonstrated with graphite as cathode and prelithiated graphite or Li₄Ti₅O₁₂ (LTO) as anode. The resultant graphite–graphite LIpCs deliver high energy densities of 167–233 Wh kg^?1 at power densities of 0.22–21.0 kW kg^?1 (based on active mass in both electrodes), much higher than 20–146 Wh kg^?1 of AC‐derived Li‐ion capacitors and 23–67 Wh kg^?1 of state‐of‐the‐art metal oxide pseudocapacitors. Excellent rate capability and cycling stability are further demonstrated for LTO‐graphite LIpCs.     

Ion irradiation-induced modifications of diamond nanorods synthesised by microwave plasma chemical vapour deposition

Diamond nanorods (DNRs) synthesised by the high methane content in argon rich microwave plasma chemical vapour deposition (MPCVD) have been implanted with nitrogen ions. The nanorods were characterised by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The DNRs consist of single-crystalline diamond cores of 3–5?nm in diameter and several tens of nanometres in length. For purification from non-diamond contents, hydrogen plasma etching of DNRs was performed. Structural modifications of etched DNRs were studied after irradiating with 50?keV nitrogen ions under the fluence of 5?×?10¹⁴, 1?×?10¹⁵, 5?×?10¹⁵ and 1?×?10¹⁶?ions?cm^?2. Nitrogen-ion implantation changes the carbon–carbon bonding and structural state of the nanocrystalline diamond (NCD). Raman spectroscopy was used to study the structure before and after ion irradiation, indicating the coexistence of diamond and graphite in the samples. The results indicated the increase in graphitic and sp²-related content, at the expense of decrease in diamond crystallinity, for ion implantation dose of 5?×?10^15?cm^?2 and higher. The method proves valuable for the formation of hybrid nanostructures with controlled fractions of sp³–sp² bonding.     

Low-temperature crystallization of thin nickel films under the action of atomic hydrogen

The influence of atomic hydrogen on the electrical properties and structure of thin nickel films obtained by thermal deposition in vacuum on dielectric substrates has been studied. The subsequent treatment of deposited films at 300–310 K in atomic hydrogen at a pressure of ～20 Pa and a density of ～10¹⁹ m^?3 leads to the modification of their structure and electrical properties. A mechanism explaining the observed effect of atomic hydrogen on thin metal films is proposed.     

Generation of gigawatt 10-GHz pulses with stable phase

The generation of microwave pulses in a 10-GHz range has been studied in a nonstationary relativistic backward wave oscillator (BWO) operating at a pulse train repetition rate of up to 300 Hz. Regimes with a stabilized phase of the high-frequency filling of pulses with respect to the accelerating voltage pulse front have been observed at a BWO peak output power of ～1 and 3 GW. In pulse trains with a length of 10–100 s, the average output microwave power reached ～1 kW.     

Efficiency of the plasma-chemical method of preparation of silicon from quartz in an argon-hydrogen flow

A kinetic model of nonequilibrium chemical processes in gas mixtures of Si, O, H, and Ar and a model of the calculation of the main parameters of plasma facilities for the implementation of the plasma-chemical method of the direct preparation of silicon from quartz in argon–hydrogen gas-plasma flows have been formulated. The criteria and general conditions at which the maximal yield of silicon is achieved were determined. The main mode and construction parameters of plasma facilities were determined. It is shown that at the consumed electrical power of a stationary plasmatron of 100 kW the calculated efficiency of the facility (over vapor Si) could be on the order of 10^–2 g/s.     

3D laser ultramicroscopy: A method for nondestructive characterization of micro- and nanoinclusions in high-purity materials for fiber and power optics

This paper describes a 3D laser ultramicroscopy technique and apparatus for the nondestructive characterization of heterophase inclusions in bulk high-purity materials for fiber and power optics. In this technique, the concentration and size of inclusions undetectable by optical microscopy are determined using CCD detection of the light scattered by them in a direction normal to the incident laser beam at wavelengths from 0.63 to 0.98 μm. The detection limit of the technique in terms of inclusion size is n × (10–100) nm, the range of detectable number concentrations is 1–10¹¹ cm^?3, and the scan depth in the sample is ～1 cm. Its performance has been evaluated using test systems. The potential of the technique is illustrated by the dispersion analysis of promising materials for IR fiber-optic applications.     

Plasma density in discharge sustained in inhomogeneous gas flow by high-power radiation in the terahertz frequency range

We have measured the density of plasma (electron concentration) in discharge maintained in inhomogeneous argon flow under the action of high-power pulsed radiation of gyrotron (frequency, 0.67 THz; power 40 kW; pulse duration, 20–30 μs) in a range of background gas pressures in the discharge chamber from 10^–3 to 300 Torr. The electron concentration at low pressures (10^–3 to 7 Torr) was determined using Starkeffect induced broadening of the H_α atomic emission line (656.3 nm) of hydrogen present in discharge as a small impurity in residual gases. The maximum observed Stark broadening of the H_α line corresponded to a plasma density on the order of 2 × 1016 cm^–3, which exceeded the critical value for the given frequency of radiation sustaining the discharge. At background pressures above 7 Torr, the plasma density was estimated from analysis of the spatiotemporal patterns and waveforms of discharge glow in the visible spectral range. These estimations gave electron concentrations on the level of (1–2) × 10¹⁵ cm^–3.     

Study of the velocity distribution in an intense pulsed hydrogen beam

We present the results of measurements of the velocity distributions of particles in a pulsed hydrogen beam obtained from a dissociator with a radio frequency discharge (duration 1.0 ms, repetition rate 1 Hz). It is shown that the hydrogen inside the dissociator is heated up to ～2800 K, so the thermal dissociation of hydrogen molecules is essential. In order to cool the atoms, the gas was let through a pyrex channel 5 mm in diameter. The cooling channel walls being at room temperature and the channel having a length of 50 mm, we have obtained a supersonic beam of hydrogen atoms with a Mach number M_| = 2.7±0.25. When the channel walls were cooled by the flowing liquid nitrogen and the channel was 70 mm long we obtained a beam of cooled atoms with a Mach number M_| = 4.14±0.35. The velocity distribution of atoms depends on the power of the rf discharge inside the dissociator and on the gas consumption per pulse, and varies during the discharge pulse. For a temperature of the cooling channel walls T_ch = 77 K, a gas consumption N = 3.3×10¹⁷ molecules per pulse and a discharge power of 0.23 kW cm^?3, we have obtained an atomic beam with intensity I(0) = (2.8±0.8)×10²⁰ atoms sr^?1 s^?1 and a most probable velocity ν_MP = (1.97±0.07)×10⁵ cm s^?1.     

Properties of SiO2 films formed by oxygen implantation into silicon

Oxygen ions with energies of 5–60 keV were implanted into Si at doses of 10¹⁵–10¹⁸ ions cm^?2 to form SiO₂ layers. Annealing was carried out in nitrogen at 500–1000 °C and in hydrogen at 450 °C. By monitoring the IR transmission spectra, the refractive index, the etching behaviour and the electrical characteristics, it was established that stoichiometric SiO₂ layers can be produced with doses of 10¹⁸ ions cm^?2 on annealing at 700–1000 °C. A voltage-dependent capacitance was obtained only for samples implanted with a dose of 10¹⁸ ions cm^?2 and annealed at 1000 °C in nitrogen and at 450 °C in hydrogen. In the interface state spectrum of such samples, maxima at 0.55 eV and at 0.80 eV below the conduction band were found.     

Behaviour of neutral hydrogen atom density in the presence of a sample holder in a plasma reactor

The behaviour of density of neutral hydrogen atoms in the presence of a sample holder in a MESOX reactor was studied. The MESOX reactor is used for studying interaction of hydrogen atoms with solid state surfaces at extreme conditions. Concentrated solar radiation with power of approximately 6 kW is collimated to a spot with the surface in the order of magnitude 1 cm² thus allowing for independent sample heating above 2000 K. Hydrogen plasma is generated in a MW (microwave) discharge. The H-atom density is measured with a FOCP (Fibre Optics Catalytic Probe). The H-atom density in the empty reactor depends slightly on the pressure and MW power and is about 5 × 10²¹ m⁻³ at a power of 1000 W. The sample holder made from quartz glass was mounted in the centre of the reactor and the H-atom density was measured versus time. The H-atom density in the loaded reactor was decreasing continuously. After a time period in the order of 2 min, the H-atom density was reduced by approximately a factor of 3 in regards to the original value. The results were explained by taking into account a temperature dependence of the recombination coefficient for heterogeneous recombination of H atoms on the quartz surface.     

High‐Performance Asymmetric Supercapacitors Based on Multilayer MnO2/Graphene Oxide Nanoflakes and Hierarchical Porous Carbon with Enhanced Cycling Stability

In this work, MnO₂/GO (graphene oxide) composites with novel multilayer nanoflake structure, and a carbon material derived from Artemia cyst shell with genetic 3D hierarchical porous structure (HPC), are prepared. An asymmetric supercapacitor has been fabricated using MnO₂/GO as positive electrode and HPC as negative electrode material. Because of their unique structures, both MnO₂/GO composites and HPC exhibit excellent electrochemical performances. The optimized asymmetric supercapacitor could be cycled reversibly in the high voltage range of 0–2 V in aqueous electrolyte, which exhibits maximum energy density of 46.7 Wh kg^?1 at a power density of 100 W kg^?1 and remains 18.9 Wh kg^?1 at 2000 W kg^?1. Additionally, such device also shows superior long cycle life along with ～100% capacitance retention after 1000 cycles and ～93% after 4000 cycles.     

The effect of hydrogen annealing on the molybdenum doped ZnO thin film

The electrical characteristics of hydrogen annealing on the molybdenum doped ZnO (MZO) thin film were discussed in the paper. The MZO film was deposited by an radio frequency sputtering, then it was annealed in hydrogen with a microwave plasma chemical vapor deposition system. The resistivity of MZO was decreased from 1.1 × 10^?2 to 9.5 × 10^?3 Ω cm after the hydrogen annealing. Improvements of the electrical properties are both due to the defects repairing through annealing and hydrogen doping effects of the MZO thin film. The higher temperature annealed MZO film shows slightly lower transmittance which is due to the higher carrier concentration.     

Hydrogen-free diamond-like carbon films prepared by microwave electron cyclotron resonance plasma-enhanced direct current magnetron sputtering

Hydrogen-free diamond-like carbon (DLC) films were prepared by means of microwave electron cyclotron resonance plasma enhanced direct current magnetron sputtering. To study the influence of enhanced plasma on film fabrication and properties, the structures as well as mechanical and electrical properties of these films were studied as a function of applied microwave power. Results showed that higher microwave power could induce higher plasma density and electron temperature. The hardness increased from 3.5 GPa to 13 GPa with a variation of microwave power from 0 W to 1000 W. The resistivity showed a drastic increase from 4.5 × 10⁴ Ωcm at 0 W to 1.3 × 10¹⁰ Ωcm at 1000 W. The variation of the intensity ratio I(D)/I(G) and the position of the G-peak of the DLC films with respect to changes in microwave power were also investigated by Raman spectroscopy.     

Correlation between optical emission spectra and the process parameters of a 915 MHz microwave plasma CVD reactor used for depositing polycrystalline diamond coatings

In this paper, the hydrogen and hydrogen-methane mixed plasma have been generated inside a 33 cm diameter quartz bell jar with a low power (9 KW) and lower frequency 915 MHz microwave plasma chemical vapor deposition system. The reactor is being used for growing polycrystalline diamond (PCD) over large area (100 mm). The generated plasma is diagnosed by in situ optical emission spectroscopy method with wave length ranging from 200 to 900 nm. The effects of microwave power, chamber pressure and gas concentration on plasma characteristics have been studied in this work. Within the optical range, Balmer H _α , H _β , C₂swan band and CH lines have been detected at the wavelengths of 655.95, 485.7, 515.82 and 430.17 nm, respectively. It has been observed that for hydrogen plasma, the amount of transition from hydrogen atom inner shell 3 to 2 (H _α ) is almost constant with increasing microwave (MW) power (from 2000 to 2800 W) and pressure (from 15 to 30 Torr) initially, after that it increases with further increase of MW power and pressure, whereas, the transition from 4 to 2 (H _β ) is slowly increased with increasing MW power and pressure. For hydrogen-methane plasma, intensities of C₂ swan band, i.e., the transitions from D³π _g to A³π _μ energy levels, are also increased with the increasing microwave power and reactor pressure. It has been observed that the radicals present in the plasma are affected by variation of different reactor parameters like pressure, MW power, CH₄ concentration, etc.     

Structural and optical characterization of thick and thin polycrystalline diamond films deposited by microwave plasma activated CVD

Preliminary results of growth of thin diamond film in a recently installed 3 kW capacity microwave plasma activated CVD (MW-PACVD) system are being reported. The films were deposited on Si (100) substrate at 850°C using methane and hydrogen mixture at 1·5 kW MW power. The grown polycrystalline films were characterized by micro-Raman, transmission electron microscope (TEM), spectrophotometer and atomic force microscope (AFM). The results were compared with that of a thicker diamond film grown elsewhere in a same make MW-PACVD system at relatively higher power densities. The presence of a sharp Raman peak at 1332 cm^− 1 confirmed the growth of diamond, and transmission spectra showed typical diamond film characteristics in both the samples. Typical twin bands and also a quintuplet twinned crystal were observed in TEM, further it was found that the twinned region in thin sample composed of very fine platelet like structure.     

Effect of magnetic barrier on the plasma parameters in a Trimix-M galatea

The parameters of plasma trapped in a Trimix-M galatea with increased values of the magnetic barrier and the energy of a hydrogen plasma bunch injected in the trap have been determined. For a barrier magnetic field of B _b ～ 0.1 T, the plasma confinement time in the trap is τ_p ≈ 300 μs (which agrees with estimates obtained using formulas describing the classical transfer), the maximum electron density is n _e ～ 5 × 10¹³ cm^?3, and the electron and ion temperatures are T _e ≈ 20 eV and T _i ～ 2T _e, respectively. The energy of trapped plasma is ～110 J, and the ratio of the gaskinetic to magnetic pressure in the plasma is β₀ ～ 0.2.     

Waveguide-surfatron型表面波等离子体源的特性研究

报道了所研制的Waveguide-surfatron型表面波等离子体源的特性,理论计算表明,激发表面波模式为m≥l模,在放电室中电磁场均匀性与等离子体的密度有关。实验结果指出,采用Ar气放电,在气压为10～1000Pa,微波功率800～1000W的范围内可形成大面(体)积(直径为160mm)等离子体,其电子温度为1～4eV,等离子体密度为10     

Nombre de transport et conductivite cationique dans le dioxyde de thorium: ThO2

The cationic transport number for thorium dioxide has been determined using thermal expansion measurements coupled with coulometric titration (“dilato-coulometry”). Polycrystalline ThO₂ was studied in the temperature range 1000–1500° C, under oxygen partial pressures ranging from 1 to 10^?12 atm. In air, t_Th ～ 5 × 10_?7 at 1200° C. Values for total conductivity are compared with data obtained by the Nernst-Einstein relation from the self-diffusion coefficient of Th in ThO₂.