C. Maroli

On the dynamics of weakly ionized gases

Abstract Starting from the Liouville equation and utilizing the multiple time-scale method, we derive the equations which govern the dynamics of a many-species plasma in presence of neutrals and with an arbitrary ionization ratio. The plasma is supposed to be in equilibrium and the collisions between neutral and charged particles are taken to be elastic; thus the temperature of the plasma is quite low, of the order of a few eV. We emphasize the importance of a parameter μ(μ ⋍ ν e,M ω p , where ν e,M is the electron-neutral-molecule elastic collision frequency and where ω p is the electron plasma frequency), such that for μ ⪢ 1 our equations become those of the Lorentz plasma, while for μ ⪡ 1 we have the case of a fully ionized plasma. The domain of applicability of these limiting equations is discussed.

EFFECTS OF INELASTIC COLLISIONS IN LOW-TEMPERATURE, DIFFUSION-DOMINATED DISCHARGES.

A numerical iteration procedure has been used to obtain the solution of an integrodifferential (linear) equation which gives the energy distribution of the electrons of a low-temperature, diffusion-dominated discharge. The equation takes explicitly into account the effects of inelastic electron-neutral collisions. The results presented here have been obtained, as an instance, for helium and neon discharges, in presence of a static and uniform magnetic field.

Bernstein rays in a Tokamak plasma in the electron-cyclotron heating conditions

The authors present results relevant to the ray tracing of Bernstein modes in a rather cold Tokamak, which can help in deciding the damping mechanisms for the energy carried by these waves. Berstein modes are considered as strictly longitudinal waves and their analysis is based on the Vlasov dispersion relation for electrostatic waves, omitting the positive ions dynamics.

Interaction of electromagnetic fields with warm slightly ionized magneto-plasmas

The problem concerning the interaction of electromagnetic fields with a warm, slightly ionized magneto-plasma is analysed by means of the multiple time scales asymptotic technique. Only initial value problems in an infinite plasma are here considered in detail. It is shown how the full set of Vlasov–Maxwell equations, modified through a standard Boltzmann collision integral to take account of the elastic electron-neutral encounters, can be reduced, in the basic limit assumed, to a set of two coupled non-linear integro-difl�erential equations for the dominant terms of the longitudinal fields and of the electron distribution function. Once the initial conditions are specified, the behaviour of the transverse initial field is also described. A particular example has been given for the so-called progressing-wave initial conditions.

Electromagnetic-wave propagation in a weakly ionized plasma — II

SummaryThis work contains the evaluation of the conductivity of a plasma with an arbitrary ionization ratio, in presence of a constant and uniform magnetic field. The calculation method is a generalization of the one employed in the preceding work.RiassuntoIn questo lavoro viene calcolata la conduttività di un plasma con un grado arbitrario di ionizzazione, in presenza di un campo magnetico costante ed uniforme. Il metodo di calcolo è la generalizzazione di quello impiegato nel lavoro precedente.РеэюмеЭта работа содержит вычисление проводимости плаэмы с проиэвольной степенью иониэации при наличии постоянного и однородного магнитного поля. Метод вычисления представляет обобшение метода, испольэованного в предыдушей работе.

Coherent Structures in low Energy Electron Beams in ELTRAP

The experimental investigation of the formation of coherent structures in an electron beam of very low energy produced in a Malmberg‐Penning trap is presented. A rapid development of the structures is observed when, by increasing the emission current of the cathode, a sharp transition to a space charge dominated regime occurs, where a region unaccessible to beam electrons is found around the axis, and is characterized by a sharp density gradient at the edge. The transport of the structures along the beam is studied by varying the strength of the axial magnetic field. A 3D PIC simulation code is used to interpret the results. A modification of the configuration is under way, in which a pulsed electron source is used, and plasma effects in the beam transport, of relevance for X‐ray SASE‐FELs, can be investigated.

Cold plasma resonances outside the WKB approximation

As a detail of a general numerical investigation of the problem of wave propagation in resonance regime the plot of the reflection and transmission coefficients as functions of the parameter mu is given in the two following cases: (i) The so-called magnetic beach configuration, as a simple example of accessible resonance. (ii) The upper-hybrid propagation in a plasma slab as an instance of a non accessible resonance.

Negative conductivity in a neon plasma

Abstract It is shown that electron-molecule inelastic collisions can lead to a negative high-frequency conductivity in a neon plasma.