Improving a high-power laser based relativistic electron source: the role of laser pulse contrast and gas jet density profile

A relativistic electron source based on high power laser interaction with gas jet targets has been developed at the Institute of Plasma Physics & Lasers of the Hellenic Mediterranean University. Initial measurements were conducted using the “Zeus” 45 TW laser with peak intensities in the range of 1018-1019 W/cm2 interacting with a He pulsed gas jet having a 0.8 mm diameter nozzle. A significant improvement of the electron signal was measured after using an absorber to improve the laser pulse contrast from 10-10 to 10-11. A high stability quasi-monoenergetic electron beam of about 50 MeV was achieved and measured using a magnetic spectrometer for pulsed gas jet backing pressure of 12 bar. Supplementary studies using a 3 mm diameter nozzle for backing pressures in the range of 35 to 40 bar showed electron beam production with energies spread in the range from 50 to 150 MeV. The pulsed jet density profile was determined using interferometric techniques. Particle-in-cell (PIC) simulations, at the above experimentally determined conditions, support our experimental findings.

Evaluation of ambipolar potential barrier in the gas dynamic trap by Doppler spectroscopy

The recently developed Doppler spectroscopy diagnostic has been used to evaluate the height of the ambipolar potential barrier forming in the gas dynamic trap (GDT) plasma between the central cell and the region with a large magnetic expansion ratio beyond the mirror. The diagnostic technique based on the gas jet charge exchange target, allowed to measure the potential profile along the line of sight covering the radial range from the axis to the limiter. The on-axis potential drop was found to be 2.6÷3.1 in units of the central plane electron temperature, which supports the existing theoretical understanding of suppression of electron thermal conductivity in the GDT expander.

Исследование реакции поверхности жидкости на импульсное воздействие наклонной газовой струи при малых числах Рэйнольдса

A mathematical description of the motion of a cavity on the liquid surface under an oblique action of a gas jet is obtained using the well-known expressions for the movement of a gas bubble in a liquid. The boundary of the viscous drag force domination over the form drag force is determined. The impingement of the gas jet on the liquid surface is considered as a dynamic object of the automatic control theory. It is found that the dynamic properties of the two-phase system "gas jet - liquid" are described by the integrator equations. Using a specially designed setup, the transient response of the "gas jet - liquid" system were experimentally obtained for the aerodynamic action at angles of 20º and 50º to the surfaces of liquids with the viscosities of 0.71 and 26.1 Pa•s (Reynolds number Re < 2). The research results are necessary for the analysis of the non-contact aerodynamic method of liquid viscosity measurements.

Experimental Study on the Thermal Effect according to the Distance around a Hydrogen Jet Flame

In this study, the safe distance in the case of a hydrogen vehicle fire was analyzed according to the temperature distribution around a hydrogen gas jet flame formed by the thermally activated pressure relief device operation of a hydrogen storage container. The experiment was conducted while 70 MPa hydrogen gas was released from a 1.8-mm-diameter nozzle to a 1.8- × 1.8 m fire-resistant structure wall for distances of 2 and 4 m between the nozzle output and the wall. To analyze the temperature around the hydrogen gas jet flame, five fire-fighting heat-protective hood test samples, certified by the Korea Fire Institute, and temperature sensors were installed every 1 m from the center of the jet flame in the vertical direction to the direction of the flame. In the experiment, the temperature around the jet flame was measured to observe the safe distance for firefighters. The results show that the safe distances at 70°C or less, which is harmless to firefighters, were 5 m without a heat-protective hood and 3 m with a heat-protective hood. In addition, it was confirmed that the direction of the jet flame and blocking by obstacles affect the safe distance during fire-fighting and rescue activities by firefighters.

Strategy of Compatible Use of Jet and Plunger Pump with Chrome Parts in Oil Well

During oil fields operation, gas is extracted along with oil. In this article it is suggested to use jet pumps for utilization of the associated oil gas, burning of which causes environmental degradation and poses a potential threat to the human body. In order to determine the possibility of simultaneous application of a sucker-rod pump, which is driven by a rocking machine, and a jet pump (ejector) in the oil well, it is necessary to estimate the distribution of pressure along the borehole from the bottomhole to the mouth for two cases: when the well is operated only be the sucker-rod pump and while additional installation of the oil-gas jet pump above its dynamic level. For this purpose, commonly known methods of Poettman-Carpenter and Baksendel were used. In addition, the equations of high-pressure and low-pressure oil-gas jet pumps were obtained for the case, when the working stream of the jet pump is a gas-oil production mixture and the injected stream is a gas from the annulus of the well. The values which are included in the resulting equations are interrelated and can only be found in a certain sequence. Therefore, a special methodology has been developed for the practical usage of these equations in order to calculate the working parameters of a jet pump based on the given independent working parameters of the oil well. Using this methodology, which was implemented in computer programs, many operating parameters were calculated both for the well and for the jet pump itself (pressures, densities of working, injected and mixed flows, flow velocities and other parameters in control sections). According to the results of calculations, graphs were built that indicate a number of regularities during the oil well operation with such a jet pump. The main result of the performed research is a recommendation list on the choice of the oil-gas jet pump location inside the selected oil well and generalization of the principles for choosing the perfect location of such ejectors for other wells. The novelty of the proposed study lays in a systematic approach to rod pump and our patented ejector pump operation in the oil and chrome plating of pump parts. The result of scientific research is a sound method of determining the rational location of the ejector in the oil well and the calculation of its geometry, which will provide a complete selection of petroleum gas released into the annulus of the oil well. To ensure reliable operation of jet and plunger pumps in oil wells, it is proposed to use reinforcement of parts (bushings, plungers, rods, etc.) by electrochemical chromium plating in a flowing electrolyte. This has significantly increased the wear resistance and corrosion resistance of the operational surfaces of these parts and, accordingly, the service life of the pumps. Such measures will contribute to oil production intensification from wells and improve the environmental condition of oil fields.

Numerical Analysis of Particle Trajectories in a Gas–Powder Jet during the Laser-Based Directed Energy Deposition Process

Based on numerical solutions of the equation of motion of a particle in a gas jet modeled by the Reynolds-averaged Navier–Stokes equations, the features of transporting powder particles to the working zone of laser-based directed energy deposition are investigated. The propagation of a gas jet in a confined space in the presence of obstacles in the form of a substrate and a wall of a part is considered. A solution determining the gas-dynamic parameters of the jet is obtained, and the results of calculating its velocity field are presented. The influence of gas-dynamic parameters on the trajectories of the powder particles is analyzed. It is shown that these parameters determine the amount of model material involved in the formation of the geometry of the part.

Modeling of nonstationary gas outflow at breaks of subsea gas pipelines

Numerical modeling of the outflow of an air jet into water with a guillotine rupture of a pipeline by the VOF method using k-ε and k-ω SST turbulence models was carried out. The calculations were carried out in the axisymmetric approximation. The following phases of the outflow process were calculated: the formation of a large gas bubble at the place of the rupture, its growth, the separation of the bubble from the place of rupture, and the formation of a gas jet behind the bubble. It is shown that the rate of bubble detachment in the calculations by the k-ω SST model is higher than that in the calculation by the k-ε model.