A. Tellini

Computation of the magnetic field in massive conductor systems

Some analytical expressions are reported for the calculation of the magnetic induction and the vector potential in iron-free media due to slab-shaped elements in which a current flows uniformly or linearly distributed in one direction. It is seen that no matter what current distribution functions and conductor geometries are considered, they can be approximated by a series of slabs in which the current distributions are represented by a sum of linear and constant distributions. The algorithms can also be used to calculate the magnetic field in more complicated geometries and to evaluate the self- and mutual-inductance coefficients in systems with massive conductors. >

Magnetic field evaluation for thick annular conductors

The three-dimensional integration of the Biot-Savart law for conductors in annular sector shape, in which only a constant-density theta -directed current flows, is reported. The expressions obtained allow a quick and accurate evaluation of the components of the vector potential of the stationary magnetic field and of the magnetic induction due to this type of conductor, in iron-free media. The relations presented, together with similar expressions that are valid for other shapes of conductor and current distributions, can be useful for evaluating the magnetic fields in complex, linear, iron-free structures when the geometry can be well approximated with a series of current elements of elementary shape, for which the solution of Laplaces equation is known in closed form. >

Analytic expressions for magnetic field from finite curved conductors

Some analytical expressions for the calculation of the magnetic induction and the vector potential in iron-free media due to conductors in annular arc shape with regular cross section are reported. The algorithms derived, together with analogous algorithms reported previously for the calculation of the magnetic fields due to conductors in slab shape, can be used to calculate the magnetic fields in more complicated geometries and may be used to evaluate the self- and the mutual-inductance coefficients in systems with massive conductors.

Some remarks on the current filament modeling of electromagnetic launchers

Current filament models have been widely used for the electromagnetic analysis of induction launchers and electromagnetic devices. Two functions of the eigenvalues of the filament parameter matrix were determined in order to evaluate the errors on the system solution induced by approximate calculations of the matrix parameters and the influence on the solution of a variation of the filament number of the discretization. These functions allow an estimate of the solution convergence and accuracy, avoiding the numerical or analytical integration of the differential equation set of the system. The launcher has been modeled by means of a coordinate system coherent with the moving armature, with the hypothesis of piecewise constant velocity of the armature, in order to have no time-dependent elements in the system matrix. >

Current distribution in rail launchers via an equivalent network simulation approach

An equivalent network approach is presented for the evaluation of the current distribution in the rails of electromagnetic launchers. The massive conductors are simulated by means of a passive network mesh, constituted by resistive and inductive nonlinear and time-varying parameters. The moving plasma-armature is simulated by means of nonlinear active dipoles. The increase of the electrical resistivity due to the ohmically generated heat flux is taken into account in the calculation. Finally, the electric and thermal stresses in the rails are reported. >

Field analysis in axisymmetric actuators

In this paper we present a general methodology for fields analysis of axisymmetric actuators taking into account the presence of moving conductors. The methodology is based on an integral formulation and leads to an equivalent network whose parameters vary with the relative positions of the moving parts of the system. This methodology when applied to axisymmetric systems allows us to obtain accurate results in short time because of the availability of quick formulas for the evaluation of the parameters of the time-varying equivalent network. The methodology has been applied to the analysis of a tubular linear induction motor; numerical results have been compared with experimental data obtained by a prototype.

Thermal and mechanical stress in induction coilguns

The aim of this paper is to define a procedure for the design of induction coilguns in order to obtain thermal and mechanical stress that do not exceed the allowed values in the sleeve. The magnetic vector potential is determined considering a cylindrical sheet current model both for the barrel and the sleeve and solving the related modified Bessel equation. Then the flux, the current density and the propulsive force for each section are determined. By considering the constraints due to mechanical and thermal stress, the maximum muzzle velocity for a one-section launcher is determined. Supposing that the muzzle velocities in the first and in the last section are established, and assuming that all sections, from the second to the last, work with the same mean slip and the same relative velocity, the number of sections and their length are determined. Moreover the surface current density in the barrel is calculated. The design criterion is compared with other criteria, and then used to design an 8 km/s muzzle velocity launcher.

MHD plasma physics in rail accelerators for hydrogen-pellet injection in fusion reactors

The behavior of the electromagnetic and thermal quantities in a plasma arc placed between two conducting rails is analyzed. The plasma hydrogen drives the hydrogen pellets for the refueling of magnetic fusion reactors. Considering the general equations of electromagnetism and of plasma fluid dynamics and assuming steady-state conditions in a frame which is moving at the same rate as the plasma arc armature, a one-dimensional model is deduced. The effects of an applied magnetic field on the behavior of all flow variables are investigated. Results indicate that the adverse effects of plasma arc heating can be reduced by the application of a magnetic-induction field normal to the current path in the armature. At the maximum acceleration pressure (30 bar) applicable to the hydrogen pellet in the proposed one-dimensional model, the arc temperature at the pellet backend falls from 20000 to 14000 K when a magnetic induction of about 5 T is applied. >

Radiated fields in rail launchers operation

In this paper electromagnetic fields radiated from a railgun operating system with a plasma armature are investigated. A small-bore railgun has been fabricated in their laboratory, a capacitor bank (0.12 F-160 V) has been used as energy supply and an experimental setup has been implemented. Experiments have been performed in a remotely operated shielded semi-anechoic chamber in conformity with current standards. The analysis has been conducted in the time domain, using suitable current probes and antennas and an oscilloscope with high bandwidth and high sampling rate. Results were reproducible and a comparison and discussion with previous work are reported.

Frequency-domain formulation for nonlinear method of moments

In this paper a frequency domain formulation of the method of moments taking into account the presence of ferromagnetic materials is presented. By combining the electric field definition, Ohms law and Lorentz gauge inside every volume element into which the system is subdivided, a linear algebraic system of integral equations is obtained. Considering the nonlinear constitutive equation H=H(B) and the magnetization M a nonlinear algebraic system of equations is obtained. The unknowns of these systems are the time Fourier transforms of magnetizations and conduction currents. The solution of these systems for a finite number of harmonics gives the frequency domain solution of the problem. The use of pulse functions as subsection bases allows a quick matrix set up especially when regular volume shapes are selected. Calculated results are compared with results obtained with other methods.