C. Ferro Fontan

Forward Compton scattering sum rules and j=0 singularities

Abstract A J=0 singularity in the spin averaged forward proton Compton amplitude has been found using continuous moment sum rules. Its residue coincides with the Thomson limit. Values for the Regge parameters of P and P′ were also obtained.

Nonlocal heat transport in plasmas down steep temperature gradients

An analytic solution to the problem of nonlocal heat transport in plasmas by electrons whose range is not short compared to the temperature scale length is presented. The formalism extends the results of Albritton et al. [Phys. Rev. Lett. 57, 1887 (1986)] to an arbitrary ionization state Z. This simple transport scheme is checked against recent experiments in the AURORA device [Phys. Fluids B 1, 741 (1989)]. The agreement, both for the measured cold electron temperature profile and the plasma potential, is very good and comparable to the result of full kinetic calculations.

The plasma state in the surroundings of a multi-cathode-spot vacuum arc

A stationary, two-fluid model with spherical symmetry to describe the region surrounding the electrodes of a multi-cathode-spot vacuum arc is presented. For typical values of arc parameters, there is a weak coupling between ions and electrons and an analytical approximation for the physical quantities of the plasma can be developed. An important feature of this model is the prediction of a voltage profile outside the electrodes which causes an extra acceleration of the ions emerging from the interelectrode plasma.

Generalization of the Glansdorff–Prigogine stability criterion

It will be shown that a mathematical reformulation of the Glansdorff–Prigogine local equilibrium hypothesis makes it possible to associate the Glansdorff–Prigogine stability criterion to the sign of a quadratic form. A comparison with other known results of literature is presented. Moreover, the equivalence between the local potential method of Glansdorff–Prigogine and the Keizer–Lavenda’s generalization of the Onsage–Machlup Lagrangian formulation will be proven.

Energy principles: A non-equilibrium thermodynamic approach

Abstract A formal derivation and generalization of the Sudan-Rosenbluth and other well-known energy principles of plasma physics is obtained from the principle of balance of power of non-equilibrium thermodynamics, by working in the entropy representation. The role of the complex excess power is stressed and clarified in this approach to plasma stability.

MHD stability and fluctuations

Abstract The effect of fluctuations on the stability of magnetohydrodynamic plasma equilibria is studied by the direct Lyapunov method, using the Fokker-Planck equation to model stationary random fluctuations. A fluctuation-dissipation theorem is derived and it is demonstrated that a deterministic stable system is not destabilized by the fluctuations.

On the equivalence of thermodynamical approaches to plasma stability

Abstract Alternative derivations of the expression for the entropy S of a plasma, valid in the neighbourhood of a non-thermodynamic equilibrium state, are summarized and shown to be equivalent. A recent application of the maximum entropy principle with dynamical constraints is used in support of this conclusion which is explicitly verified. A general form of S obtained without coarse-graining arguments and including microscopic information is presented.

Thermodynamical irreversible approach for the stellar pulsation problem

In this paper, the stellar pulsation theory is reformulated following an irreversible thermodynamic approach (Lavenda, Thermodynamics of Irreversible Processes, Denver, New York, 1993). A general stability criterion and a thermodynamic Langrangian for the pulsating star problem are obtained using a variational method (Sicardi and Ferro Fontan, Phys. Lett. 113A (1958) 263; Sicardi et al., J. Math. Phys. 32 (1991) 1350). This formulation, based on the calculation of a free energy excess function, is applied to the adiabatic, non-adiabatic, radial and non-radial cases and, as a result, the already known energy principles are obtained as particular cases of the general stability criterion mentioned above. Eigenvectors and eigenvalues can be calculated in a systematic way from the thermodynamic Lagrangian obtained for the general dissipative case (being independent of the adiabatic one). This allows a better determination of periods and oscillation frequencies.

Cascading process in the flute‐mode turbulence of a plasma

The cascades of ideal invariants in the flute‐mode turbulence are analyzed by considering a statistics based on an elementary three‐mode coupling process. The statistical dynamics of the system is investigated on the basis of the existence of the physically most important (PMI) triad. When finite ion Larmor radius effects are considered, the PMI triad describes the formation of zonal flows.