Formation of dense plasma on the surface of a stainless steel conductor in superstrong magnetic fields

In experiments on the GIT-12 megaampere generator, the characteristics of conductors made of AISI 321 stainless steel were investigated in the microsecond regime of increasing superstrong magnetic fields. In this regime, a skin explosion of the conductor material takes place with the formation of a dense plasma and its expansion into the interelectrode gap of the vacuum transmission line. The values of the characteristic magnetic field B0 = 100 T are determined, above which there is the effect of nonlinear diffusion of the magnetic field into the conductor, and the critical magnetic field BCT ≅ 260 T, the excess of which leads to the formation of dense plasma on the surface of the massive conductor. A method is proposed for increasing the critical magnetic field on the surface of a conductor up to 1.5 times by choosing the optimal thickness of the conducting surface, and criteria for its determination are given. The effect of increasing the critical magnetic field on the surface of a two-layer sample and creating a pressure in the Mbar range until the moment of formation and expansion of explosion products of an inner conductor with high conductivity has been tested.

Flow separation control on a smooth ledge using an arc discharge in a magnetic field

This paper presents results of experimental study for surface MHD arc actuator as vortex generator in boundary layer of smooth ledge. The study was held at flow velocities 20 to 50 m/s. The pulsed arc discharge was organized in external magnetic field. The amplitude of current was 80 A, while pulse duration was 80 μs. The flow velocity was measured by PIV method. It was founded that the location of the arc breakdown is critically impotent. The arc must be struck just above the separation point. The operation of the actuator in a pulse-periodic mode leads to a shift in the middle position of the flow separation point at frequencies up to 700 Hz and higher. A three-dimensional analysis of the separation region structure behind the MHD actuator shows that the main effect on the flow occurs in the interelectrode gap.

Influence of hydrodynamics of electrolyte flow during electrochemical treatment on the quality of the treated surface

The features of the hydrodynamics of the electrolyte in the interelectrode gap during electrochemical processing of a profile axisymmetric workpiece are considered. The distribution of average flow rates and flow lines is calculated for a specified electrolyte supply. The nature and rate of the electrolyte flow are established. The unevenness of the current density is determined taking into account the change in the electrical conductivity of the electrolyte from heating and gas filling of the interelectrode gap, as well as the quality of the treated surface. Keywords: electrochemical treatment, roughness, electrolyte, electrical conductivity, gas filling. [email protected]

Mechanism of EDM Intensification at Ultrasound Application

This paper considers some theoretical provisions on the impact ultrasonic mechanical vibrations have on the throughput of an electroerosive piercing of small-diameter holes. The approximate estimates confirm the hypothesis that the cumulative jets mechanism makes the greatest contribution to the intensification of a multiphase medium flow in the interelectrode gap. A model is proposed for a periodic localization of the cavitation region in the bottom part of the annular side gap. It allows explaining the occurrence of a multiphase medium flow during hole processing.

Theoretical Modeling for Predicting Material Removal Rate through Interelectrode Gap

In EDM, the thermal energy of the discharge causing material erosion which is supplied by the power source unit as electrical input. The discharge energy may be recognized by the current and voltage pulses on time transient discharge characteristic curve (V-I curve) during machining. However, the plasma resistance is very short for a smaller interelectrode gap in micro-EDM compared to the impedance of the circuit. Hence, direct probe-based measurement of current and voltage pulses may include the voltage drop across the stray impedance which causes variation in its exact value. Here, a modeling-based approach may help to analyze the energy interaction with the interelectrode gap. This article presents a theoretical modeling approach to predict the interelectrode gap based on gap voltage, gap current, and plasma characteristics. Initially, a simplified two-dimensional heat conduction equation (cylindrical form) was studied to understand the asymmetry of heat flow in Gaussian distribution. A numerical analysis of a single discharge pulse was considered by applying some basic assumptions. A numerical model has been developed to predict gap distance and MRR considering gap voltage, gap current, and plasma properties. The predicted model was validated against previously reported data from the literature. Later on, the impact of gap voltage on gap distance, plasma resistance, and material erosion rate was analyzed and discussed briefly.

Variability of Surface Strengthening of Aluminum Cylinders of Internal Combustion Engines

This article discusses the ways of intensification of the oxidation process with the formation of surface properties necessary to increase the service life of one of the parts of an internal combustion engine - a cylinder made of cast aluminum alloy. A brief overview of existing technologies for hardening the aluminum surface is presented. Environmentally friendly options are proposed for using the potential of processes that have accumulated energy within an electrolytic cell by activating the interelectrode gap and forming an oxide with desired properties. The main difference from the existing model approaches of oxide formation lies in the parallel excitation of the main participant in the process, oxygen, in order to dominate it over other, oxygen-containing donors. Ways of using the energy of cavitation phenomena due to acoustic resonance in an electrolytic solution are proposed. Redistribution of the field potential by replacing a flat cathode with a pointed one changed the conductivity conditions in the interelectrode gap as a result of the electroconvective action. The structure of the oxide layer, phase changes, and physical properties confirming the originality of oxide coatings have been investigated.

Simulation of High-Voltage Ion Diode with Wire Cathode at Atmospheric Pressure of Nitrogen

Physic-topological simulation of a high-voltage coaxial ion diode with a wire metal cathode at atmospheric nitrogen pressure in the hydrodynamic drift-diffusion approximation is performed. The reactions of nitrogen ionization by electrons, attachment of electrons to nitrogen molecules with the formation of negative ions, recombination of charged particles with opposite signs of charge, secondary ion-electron emission of the cathode were taken into account. The distribution of potential and density (concentration) of charged particles in the interelectrode gap, the density of ionic and electron currents at the electrodes were calculated within the self-consistent problem with the following parameters: diameter of wire metal cathode 0.01-0.16 mm, diameter of tubular anode 6 or 20 cm, voltage 20-40 kV, gas temperature 300 or 600K. The influence of geometry, voltage and gas temperature on the discharge parameters has been determined. The obtained calculated data on the discharge current are consistent with the experiment. It is shown that two zones are formed in the discharge between the electrode gap – one is with a width of about 1 mm with a strong and rapidly changing electric field near the cathode and the second long zone with the drift of charged particles towards the anode with a smaller but constant field strength. This is a characteristic feature of negative corona discharges. In the cathode zone there is an intensive ionization of nitrogen with the generation of positive ions and electrons. In the second zone, the density of positive ions decreases sharply due to recombination and weak ionization. The reaction of attachment of electrons to nitrogen molecules begins almost near the cathode surface and continues throughout the cathode zone, in the drift zone the concentration of negative ions gradually decreases. Moreover, the role of electronic conductivity is greatly reduced as we approach the anode. Due to the low mobility of negative ions and, accordingly, the high electrical resistance of the drift zone, the voltage drop on this space part represents a significant portion of the discharge voltage (~1.5 kV on the cathode zone and 18.5 kV on the drift space, at the total voltage of 20 kV). The fact that the highest concentration of positive ions is formed near the cathode, and negative – along the entire interelectrode gap, it can be used, respectively, in the processes of ionic nitriding of wire cathode metal materials and for processing materials and biological substances (bacteria, viruses, fungi), sensitive to negative ions, at the location of the carriers of these substances near the anode. To implement the latter, it is advisable to modify the design of the external anode for efficient extraction of nitrogen ions into the environment. It is also advisable to continue research in the direction of increasing the energy efficiency of ion generation by determining the method of the maximum allowable reduction of the voltage drop on the space of drift of charged particles.