Constantino Ferro Fontan

Soliton decay of nonlinear Alfvén waves: Numerical studies

The derivative nonlinear Schrodinger equation is numerically solved for arbitrary initial conditions by an extension of the Ablowitz–Ladik scheme [Stud. Appl. Math 57, 1 (1977)]. The numerical nonlinear difference code, which takes advantage of the inverse scattering method, simulates the original differential equation reproducing common features, like solitons and an infinite set of constants of motion. The long‐time behavior is analyzed in terms of the sign of one of the constants of motion. The formation of a soliton train is seen whenever the constant has a negative value. This fact is the global expression of the Mj≂lhus local criterion to distinguish between modulationally stable and unstable cases.

Solitons in a magnetized relativistic electron-positron plasma

Abstract Nonlinear equations for the interaction of the Langmuir wave field and the transverse electromagnetic field in the pulsar magnetosphere are derived. These equations take into account the modulational instability of plasma waves and its decay into two transversal waves.

Ionization state and bound level populations in hot, dense plasmas☆

Abstract The ionization state and bound level populations in hot, dense plasmas are studied in the average atom approximation. Bound level energies are fixed self-consistently with the complete set of population numbers, using pre-existent Hartree-Fock calculations. We present a pressure- ionization scheme that gradually merges bound electrons into the continuum. To solve the nonlinear algebraic system of equations of the model, we have derived an efficient iterative algorithm. Results are shown for aluminum and iron.

Bifurcation of solutions of a field‐reversed cylindrical model

It is shown that the self‐consistent solutions of Vlasov steady states for the double delta distribution model of cylindrical field‐reversed configurations, generated by large ion orbits, have bifurcations within a definite interval of values for the total number of ions. The conjugate states have the same number of particles and the same radius of confinement but different azimuthal canonical momentum, orbit patterns, and magnetic fields. It is also shown that the states with a lower canonical momentum have a smaller energy content.

Comments on a time-dependent ionization algorithm

Abstract In a recent paper published by this journal, Magill used a three-fractions model to compute time-dependent ionization kinetics in plasmas. We comment on his time-step control procedure and present an alternative simple algorithm for the integration of the complete system of rate equations, which is implicit and conservative, and uses a variable number of the fractional densities allowed at any time. Only the ground state of the ionization stages are considered.

Large orbit plasma stability theory

A new analysis of the low frequency flute modes for the large ion orbit migma configuration is reported. Results are given for the triple delta distribution function of ions. The theory for the m = 1 mode shows an important reduction of the instability gap, when compared with conventional small Larmor radius treatments. The Migma IV experiment, which did not experience flute instability, was well within the unstable density range of thermal plasma calculations, and partially overlaps or lies below the unstable gap of the new theory. The second part of the paper considers microinstabilities. An explanation of the stabilization, by a negative bias potential, of the Harris instability observed in Migma IV is suggested. A localized unstable radial mode driven by ion counterstreaming at the center is discussed. Single particle orbit behavior for finite p2 has been studied to ascertain losses that may arise due to stochasticity. Results indicate accurate conservation of the adiabatic invariant for orbits with axial energy up to 25% of the total kinetic energy. Finally, some stability problems of the high density diamagnetic migma regime are outlined.

Soliton interactions in pulsar magnetospheres

Abstract The modulational instability of Langmuir waves and their interaction with Alfven waves is described by a nonlinear Schrodinger equation with a self-consistent field. We show that this equation may be derived from a lagrangian density which allows us to study soliton interactions. Moreover, we analyze one-dimensional self-similar collapse of solitons in the presence of an external source of plasmons.