Spatial-spectral structure of superluminosity in a high-pressure gas discharge

The spatial-spectral characteristics of superluminosity of a high-pressure N ₂ ⁺ laser have been studied both theoretically and experimentally. The observed characteristics are explained by using the concepts on emission of a thermal source that is limited in time and space.     

Mitigation of tokamak disruptions using high-pressure gas injection

High-pressure gas-jet injection of neon and argon is shown to be a simple and robust method to mitigate the deleterious effects of disruptions on the DIII-D tokamak. The gas jet penetrates to the central plasma at its sonic velocity. The deposited species dissipates >95% of the plasma by radiation and substantially reduces mechanical stresses on the vessel caused by poloidal halo currents. The gas-jet species-charge distribution can include >50% fraction neutral species which inhibits runaway electrons. The favorable scaling of this technique to burning fusion plasmas is discussed.     

Laser spark ignition of a jet diffusion flame

In this work we report preliminary results on the laser ignition of a jet diffusion flame with jet flow rates ranging from 35 (Re=1086) to 103 cm³/s (Re=3197). The laser spark energy of about 4 mJ was used for all the tests. The relative amounts of fuel and air concentrations at the laser focus have been estimated using a variant of laser-induced breakdown spectroscopy. The ignition and the flame blow out times were measured using the time-resolved OH emission. Ignition times in the range from 3 to about 10 ms were observed depending on the experimental conditions and they increased towards the rich as well as the lean sides. The early time and late-time OH emissions indicate that chemical reactions during the initial stage of the blast wave expansion are not immediately responsible for the ignition. The ultimate fate of an ignition depends on the reactions at later times which determines whether the gas could undergo a transition from hot plasma to a propagating flame.     

Effect of fuel injection location on a plasma jet assisted combustion with a backward-facing step

Non-reacting and reacting experiments on the ignition by a plasma jet (PJ) torch were performed to understand the correlation between fuel injection location and combustion characteristics in unheated Mach 2 airflow. Fuel was injected through three sonic injectors in the recirculation region behind a backward-facing step: a parallel injector at 2 mm from the bottom wall and two normal injectors at 2 and 9 mm from the step wall. In order to mitigate the combustion pressure interaction with nozzle, an isolator was installed between the nozzle and combustor. The combustion performance of normal injection was little affected by the difference of fuel injection locations. Moreover, normally injected fuel was escaped not to be held in the recirculation region despite of low fuel injection rates. This led to lower combustion performance relative to the parallel injection which provided fuel not to leave the recirculation region. In this case, the role of the recirculation region was to fully hold fuel, and the PJ torch provided hot gases as a heat source and acted as a flame-holder to ignite fuel–air mixtures. In a low temperature inflow condition, combustible regions were constrained around the bottom wall where embedded with the PJ torch. When thermal choking occurred in the combustor, it induced shock train both in the combustor and isolator. Under this unstable condition, the combustion performance of the normal injection was lower than that of the parallel injection. This is because the normal injection led most fuel into low temperature incoming air-stream.     

Optical diagnostics and direct injection of liquid fuel sprays

The research described here addresses the problem of a paucity of high quality data on the full field structure of high pressure liquid fuel sprays for gasoline direct injection, GDI, engines. The paper describes the application of phase Doppler anemometry, PDA, and single-shot laser sheet Mie imaging to the study of GDI sprays and discusses the methodologies adopted for the experimental systems and the optimisation of the techniques. Experimental data is presented which defines the spray structure in terms of PDA vector and scalar fields and single-shot CCD digital images. The work demonstrates the essential complementary nature of the single point and planar optical diagnostics for spray studies.     

Effects of the injector geometry on a sonic jet into a supersonic crossflow

Large-eddy simulation of a sonic injection from circular and elliptic injectors into a supersonic crossflow has been performed.The effects of injector geometry on various fundamental mechanisms dictating the intricate flow phenomena including shock/jet interaction,jet shear layer vortices and their evolution,jet penetration properties and the relevant turbulence behaviors have been studied systematically.As a jet issuing transversely into a supersonic crossflow,salient three-dimensional shock and vortical structures,such as bow,separation and barrel shocks,Mach disk,horseshoe vortex,jet shear layer vortices and vortex pairs,are induced.The shock structures exhibit considerable deformations in the circular injection,while their fluctuation becomes smaller in the elliptic injection.The jet shear layer vortices are generated at the jet periphery and their evolution characteristics are analyzed through tracing the centroid of these coherent structures.It is found that the jet from the elliptic injector spreads rapidly in the spanwise direction but suffers a reduction in the transverse penetration compared to the circular injection case.The turbulent fluctuations are amplified because of the jet/crossflow interaction.The vertical Reynolds normal stress is enhanced in the downstream of the jet because of the upwash velocity induced by the counter-rotating vortex pair.     

Spin injection in the multiple quantum-well LED structure with the Fe/AlOx injector

A spin-injection/-detection device has been fabricated based on the multiple quantum well light emitting diode (LED) structure. It is found that only a broad electroluminescence (EL) peak of a full width at half maximum of 8.6 nm appears at the wavelength of 801 nm in EL spectra with a circular luminescence polarization degree of 18%, despite PL spectra always show three well resolved peaks. The kinetic energy gained by injected electrons and holes in their drift along opposite directions broadens the EL pe...     

Periodic injector with a porous pellet mold for introducing fuel into plasmas

A ten-barrel pneumatic injector for periodic introduction of fuel pellets into steady-state thermonuclear experiments has been developed. Solid hydrogen pellets with diameters of 2.7 mm and lengths of 3 to 4 mm are formed in each barrel at a rate of 0.1–0.2 Hz with periodic pulsed heating of a porous insert, which is continuously filled with hydrogen and cooled with liquid helium, and accelerated to 1–1.2 km/s. Zh. Tekh. Fiz. 69, 35–39 (May 1999)     

Interaction of shock waves with a jet wake during gas injection into supersonic stream

In the present paper, we report the results of an experimental study of the interaction region of a planar compression shock produced by a wedge in stream with the wake formed behind a cocurrent gas jet (H₂, air, or Ar) injected into the flow. Depending on the gas jet parameters, three modes of interaction could be distinguished: a strong interaction, observed when the flow velocity in the wake was subsonic; a moderate interaction, observed when a subsonic flow region, bounded by a shock of almost conical shape, formed in the vicinity of the compression shock; and a neutral interaction. Three-dimensional non-stationary Euler equations were solved to numerically examine the interaction of an axisymmetric jet with an oblique shock wave. The obtained interaction regimes were found to be in a reasonable agreement with experimental data.     

Short-pulse laser interferometric measurement of absolute gas densities from a cooled gas jet

We report on the use of a novel technique to measure the gas density from a pulsed gas jet. Deuterium gas is fully ionized with an intense picosecond laser, and the resulting electron density is measured by interferometric probing with a second picosecond pulse. We have applied this technique to characterize a cryogenically cooled, high-density gas jet.     

ITER����ϵͳ��͸�ṹ���

介绍了作为ITER气体加料系统关键技术之一的管道穿透结构的设计工作进展,给出了偏滤器窗口延伸部分和低温冷屏以及上窗口延伸部分和环向真空封闭法兰的管道穿透结构设计和初步分析结果。     

ITER送气系统穿透结构设计

介绍了作为ITER气体加料系统关键技术之一的管道穿透结构的设计工作进展,给出了偏滤器窗口延伸部分和低温冷屏以及上窗口延伸部分和环向真空封闭法兰的管道穿透结构设计和初步分析结果。     

Some parameters of a spark channel with preionization of the gas

Spark discharges in a preionized gas gap were studied. Preionization was produced by breaking down the spark gap directly before the main discharge, which was used to ignite fuel gas mixtures. The resulting experimental and computed data are compared with theoretical data and with results obtained in an investigation of spark discharge parameters.It is shown that, as in the case of self-breakdown, the volume energy density in discharges in a preionized gas remains constant in order of magnitude (10¹⁹ eV/cm³).The studies were carried out in order to obtain certain spark characteristics for the purpose of increasing the thermal efficiency of discharges in igniting fuel mixtures.The authors are grateful to Doctor of Engineering Sciences Professor I. V. poroikov for his advice.     

The jet over a stretching wall with suction or injection

The steady laminar wall jet over a stretching surface in the presence of lateral suction or injection is considered. Similarity solutions absent in previous publications are found in some new ranges of parameters in the governing equation. The accuracy and reliability of the solutions have been checked through detailed convergence study and compared with the solutions from the numerical method and analytic method, and excellent agreement has been found. This gives the strongest evidence that those solutions...     

Spin-polarized injection into a p-type GaAs layer from a Co2 MnAl injector

Electric luminescence and its circular polarization in a Co2 MnAl injector-based light emitting diode (LED) has been detected at the transition of e-A0 C , where injected spin-polarized electrons recombine with bound holes at carbon acceptors. A spin polarization degree of 24.6% is obtained at 77 K after spin-polarized electrons traverse a distance of 300 nm before they recombine with holes bound at neutral carbon acceptors in a p + -GaAs layer. The large volume of the p + -GaAs layer can facilitate the detection of weak electric luminescence (EL) from e-A 0C emission without being quenched at higher bias as in quantum wells. Moreover, unlike the interband electric luminescence in the p+ -GaAs layer, where the spin polarization of injected electrons is destroyed by a very effective electron-hole exchange scattering (BAP mechanism), the spin polarization of injected electrons seems to survive during their recombination with holes bound at carbon acceptors.     

Method for analyzing the gas jet impinging on a liquid surface

The impingement of a gas jet on a liquid surface in the stable-state regime is analyzed theoretically. We consider the case of the perpendicular jet action. It is found that for describing analytically the processes occurring in this case, it is necessary to employ the balance equation for forces at the interface and not the balance equation for pressures at the lowest point of cavity, which was used in most available publications. Recommendations for experimental studies of a gas jet impinging on a liquid surface are formulated. We report on the results of experiments confirming the correctness of our theoretical analysis and making it possible to determine the empirical value of the shape factor. The experiments were carried out with air and epoxy resin. The cavity formed on the liquid surface had radius R₀ = 1–8 mm and depth h = 0.2–12.5 mm.     

The modification of anode material for direct borohydride fuel cell

The direct borohydride fuel cell (DBFC) is a promising device that converts chemical energy into electricity by electrochemical reactions. This type of power source is technically more simple than traditional fuel cells, because it does not require any hydrogen container and noble metals. Hydrogen evolution during hydrolysis can be inhibited by modification of anode materials. Extensive studies are focused on various specific electrocatalysts and their impact on oxidation and hydrolysis of borohydride. The aim of the study is to determine the effect of anode material composition using borohydride as a fuel. In order to enhance the utilization of borohydride fuel, AB₅-type alloy (LaMnNi_3.55Al_0.30Mn_0.40Co_0.75) was modified by adding Si or two kinds of carbon materials using the ball milling method. The most proper electrolyte was selected. The physical and electrochemical properties of anode materials were evaluated by scanning electron microscopy (SEM), cyclic voltammetry, chronopotentiometric measurements and electrochemical impedance spectroscopy. Studies showed that graphite was the best additive to anode material due to its density, compact structure and improvement of conductivity.

     

Threshold for a cumulative resonant microwave streamer discharge in a high-pressure gas

Results are reported from experiments aimed at investigating how the structure of a microwave streamer discharge depends on the gas pressure. The formation of a bright core in the streamer channel is shown to be of a threshold nature: in discharges initiated in the field of a standing electromagnetic wave of an open two-mirror cavity, a bright core forms in air and hydrogen in the pressure ranges p ₀≥540±50 torr and p ₀≥740±70 torr, respectively. Estimates are presented, according to which the appearance of a bright core can be attributed to the onset of a local microwave pinch effect.     

Stabilization and onset of oscillation of an edge-flame in the near-wake of a fuel injector

The stabilization of an edge-flame in the near-wake of a fuel injector is discussed within the context of a diffusive-thermal model, but with a realistically computed flow. Although the boundary layer approximation can be used to describe the mixing process in the wake region, the velocity field in the immediate vicinity of the injector satisfies the full Navier-Stokes equations. The stabilization of the edge-flame and its dynamics are affected not only by diffusive-thermal effects, but also by the acceleration experienced by the fuel and oxidizer entrained into the mixing layer. The present calculations confirm an earlier prediction that edge-flame oscillations can be triggered by heat losses alone. Moreover, it is shown that when the intensity of the losses is excessive, oscillations can occur even when the Lewis numbers are less than one. New results are also obtained when examining the flame response to variations in Lewis numbers. For Lewis numbers that are not too large, there exists a minimum value of the Damkhler number D below which the edge-flame cannot be stabilized. The response curve, describing the standoff distance as a function of D is multi-valued and the turning point, which also coincides with the marginal stability state, identifies extinction or blowoff conditions. For D above this value, the edge-flame is steady and stable. For relatively large values of the Lewis number the response curve is monotonic. There is, however, a restricted range of states where the flame undergoes spontaneous oscillations with the edge-flame moving back and forth along the stoichiometric surface dragging behind it the trailing diffusion flame.