During a time passed after 9th EML Symposium. the principal topics of electromagnetic acceleration have been under development in Ukraine mainly due to activity of small initiative groups of scientists, There were the nest problems of interests: 1) some details of high current sliding contact operation and problem of contact pair choice-the role of different imperfect resistance between armature and both rails was shown there by simulation; 2) the search of analytical solutions for current density distribution in the contact zone of railgun-for the critical zone disposed on the trailing corner of armature the good approximation have been found in the model of quasisteady motion; 3) analysis of electromagnetic process and energy conversion in the rotating pulsed generator of increased density of energy, as with iron-free rotor-the ways of flux leakage reduction at the magnetic compression were analyzed there: 4) applicability of coilgun for military air-defense mission-there the goal of application was estimated and efficiency of the flying target defeat was calculated, The paper presents some details of results obtained in these topics.

During the time since the 9th EML Symposium, the principal topics of electromagnetic acceleration have been under development in the Ukraine mainly due to the activity of small groups of scientists. There problems of interest are: (1) some details of high current sliding contact operation and problem of contact pair choice-the role of different imperfect resistance between armature and both rails was shown by simulation; (2) the search of analytical solutions for current density distribution in the contact zone of a railgun-for the critical zone disposed on the trailing corner of armature the good approximation has been found in the model of quasisteady motion; (3) analysis of electromagnetic process and energy conversion in the rotating pulsed generator of increased density of energy, as with iron-free rotor-the ways of flux leakage reduction at the magnetic compression were analyzed; and (4) the applicability of a coilgun for military air-defense mission-the goal of application was estimated and efficiency of the flying target defeat was calculated. The paper presents some details of results obtained in these topics.

At a high enough velocity of moving body in electromagnetic rail accelerator (1.5...2.0 km/s and more) a relaxation time for a field is much less than a time of body replacement along the rails. The calculation expressions and algorithm for a building of 2D magnetic field and current density distribution are obtained with a using of the Green's functions method in the approximation of stationary diffusion for the area in the neighborhood of the angle point of contact at the rectangular form of moving electrode's cross section. The integral equation with integrated nuclei has been obtained for a magnetic field on the contact border of media. The algorithm of its solution has been realized and pictures of the field distribution at different ratio of electrical conductivity coefficients for contacting media have been built.

Summary form only given. Two models of rotating machines for pulsed power generation based on the magnetic flux compression have been considered in the frame of FEM computation system containing up to 2800 knots, that was enough to get a numerical solution for one half of cross section of machine applying the symmetry condition and equality of stator bore diameters of both models. The laminated steel core for both rotor and stator has been assumed for traditional model of generator. The alternative model has contained the laminated steel outer core of stator and laminated non-magnetic steel (or titanium) core of rotor (air-core rotor). The level of initial (exciting) magnetic field can be essentially different for both generators in view of difference in the magnetic circuit design. The calculation model has enabled a combination of field analysis and circuit calculation as parallel processes. The highest parameters obtained for the pulses generated by each generator were taken into consideration for a comparison. Numerical experiments have been performed for the models with total output energy since 100 kJ up to 1 MJ. At the work on saturated part of the magnetization curve the generator with iron-core rotor displays the increase of pulse duration in ratio to the period of rotation, since the generator with non-magnetic rotor's core saves the initial pulse shape. Leaving the problem of mechanical strength, the results of electromagnetic simulation have allowed to consider that the compression generator with air-core rotor is able in the limit to develop both the same and much more magnitude of volume density of output energy, using more light non-magnetic materials for the rotor design. That gives the foundation to believe that this machine can be used as the perspective source of repetitive pulses with improved mass and volume density for energy production in the final stage of pulsed systems.

Computer simulation of electrical discharges in the high-pressure chambers of electrothermal launcher pulsed power supply systems containing homopolar generators (HPGs), storage inductors (SIs) and two-stage opening switches with mechanical and explosive circuit breakers has been carried out at the chamber radii of (0.02-0.1) m and various values of the gap spacing (0.1-0.8) m. Space-time dependences of pressure and temperature in the chambers as well as energy losses in the circuit elements are calculated. Up to 40 per cent of the HPG energy is shown to be delivered to the plasma load. Taking it into account, the volume and the mass of a transportable power supply providing the energy input to the load at the level of 5 MJ and consisting of two 6.5 MJ HPGs connected in parallel, a 9 MJ SI, a rotating mechanical circuit breaker as well as an explosive one operating due to the current conducting thin metal cylinder destruction by annular cumulative jets are evaluated. Simulation results of the medium heating and pressure oscillations in the chamber operating at the currents of 200-300 kA through each HPG and energies of 100-300 kJ per shot are presented.

The paper contains the further consideration of the idea to use the rotating pulsed generator with iron-free rotor which was discussed briefly in the poster presented on the IEEE Pulsed Power Conference 1997 and in the poster of 8th EML 1997, both not published. The estimations made previously with application of both mathematic simulation and measurements on the small laboratory model have yielded low coefficient of total inductance variation (on the level 10-15 instead of 300-400 and more for completely iron machines). Now the modeling of a bigger sample of generator is done with the following dimensions: rotor diameter 0.25 m, active length 0.425 m and rotation frequency 6000 rpm. The results have enabled the possibility to reach the value of this coefficient near 120 at the increased density of initial magnetic energy for excitation in the space occupied by the rotor, equal to 1.6 MJ/m/sup 3/, and increased volume of the excitation field. The output energy in the ohmic load of the generator considered is equal to 2.14 MJ, what is near 34% of peak total magnetic energy.

The current transfer between an armature and electrodes in a rail accelerator is considered in the paper using the analytical model based on the solution of the magnetic field diffusion and energy equations written in the integral form, with a one-parametrical approximation of the sought functions. The system of algebraic equations is received for definition a critical speed of a projectile, which corresponds to beginning of the contact surface of an armature evaporation. The influence of the main physical factor as the conductivity of contacting materials on a critical speed has been studied. Computation of a critical speed has been spent in a wide range of problem criteria. The comparison of results with known experimental data has shown, that the offered method has acceptable accuracy. It was possible to formulate on this basis the main principle for the selection of contact pair materials: to reduce the influence of high-speed skin-effect, the coefficients of conductivity for contacting materials must differ strongly, irrespective of what materials are used on the armature and the electrode. To simplify the technical realization of such a principle, it may be recommended to use an armature of graphite when the electrodes are made of a good conducting material.

Energy dissipation which accompanies the individual action of laser beams or electrical sparks on the surface of solid is able to cause several effects: local electromagnetic field generation; some portion of material melting; its transition into gas or plasma state; and diffusion of heat inwards to a solid medium with corresponding thermal tensions in materials appearance. As a result, part of material, being in a solid state before the pulsed action, can be separated from the main mass of body. This process is repetitive in technological devices. Analytical expressions for the components of the thermomechanical tensions tensor are given, and analysis of local destruction of media is carried out in this paper for two different situations: solid or porous media. It is shown in the theory developed that, under a pulsed action, the local destruction of a solid medium takes place at the achievement of the some critical value by the definite combination of tensions tensor components. The Mieses' criterion is offered as corresponding to this process. In this connection, the second invariant of the tensions tensor must be calculated in the space of interaction to search the co-ordinates of the destruction area. The process of pulsed influence is fast-alternating, and the type of destruction which is typical for the fragile materials, can also be developed in unfragile materials.

A brief description of Ukranian research in the area of electromagnetic acceleration and related energy sources is given. Some important historical facts regarding the development of this field in Ukraine are mentioned. The analysis covers the railgun, solenoid gun and coilgun. The theoretical background of this research and simulation tools are described briefly. Capacitive and inductive storage techniques, macrobody accelerators and research on rotating magnetic flux compression pulsed current generators are discussed.