ricevuto il 31 Maggio 1993; approvato il 24 Gennaio 1994)Summary. --An approach to the calculation of the coplanar symmetric (e, 2e) cross-section which extends the impulsive-approximation (IA) models to relativistic energy is proposed. A relativistic treatment of the kinematical parameters as well as a relativistic description of the initial bound state of the target are introduced in the IA, while the classical treatment of the Coulomb interaction is maintained. A comparison of the predictions of these models with the experimental data on Cu, Ag and Au is presented.PACS 34.80.Dp -Atomic excitation and ionization by electron impact.

Abstmcr-A seriesof experiments in which an electromagnetic pulse (Em) is propagated through a nitrogen plasma are discussed.The pulse has the general characteristics of an EMP. The pulse is observed as it emerges from the plasma as a function of the plasma parameters. As the electron number density increases, it is found that energy is increasingly absorbed from the pulse, a process due to joule heating. In addition, at higher number densities, ringing of the pulse occurs. The nitrogen pressure in these experiments is sufficiently low so that collisions play only a minor role. Also developed is a theoretical model based on the fluid transport equations. This theory predicts that the electrons of the plasma are attaining a temperature of about 15 eV in that part of the system where .the dc magnetic field is about 80 G. More importantly, it is able to predict the output pulse quite well under the conditions that the ambient nitrogen pressure and the electron number density are low. The theory appears to fail as these parameters are increased.

The behavior of a beam plasma system has been modeled with a set of nonlinear rate equations. Solutions of these equations show characteristically different multiple equilibria. The experimental behavior implied by this result is shown to be in agreement with experimental observations.

A highly turbulent beam plasma steady state which completely annihilates the beam has been studied experimentally. A large fraction of the entering beam power appears in a wideband spectrum of longitudinal electrostatic waves. A scaling law relating power spectral density to velocity space particle flux has been derived and applied to this interaction. Its predictions are in excellent agreement with experimental behavior.

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