Advances in the FTU collective Thomson scattering system.

The new collective Thomson scattering diagnostic installed on the Frascati Tokamak Upgrade device started its first operations in 2014. The ongoing experiments investigate the presence of signals synchronous with rotating tearing mode islands, possibly due to parametric decay processes, and phenomena affecting electron cyclotron beam absorption or scattering measurements. The radiometric system, diagnostic layout, and data acquisition system were improved accordingly. The present status and near-term developments of the diagnostic are presented.

Theory of light-ion acceleration driven by a strong charge separation.

A theoretical model of the quasistatic electric field, formed at the rear surface of a thin solid target irradiated by a ultraintense subpicosecond laser pulse, due to the appearance of a cloud of ultrarelativistic bound electrons, is developed. It allows one to correctly describe the spatial profile of the accelerating field and to predict the maximum energies and the energy spectra of the accelerated ions. The agreement of the theoretical expectations with the experimental data looks satisfactory in a wide range of conditions. Previsions of regimes achievable in the future are given.

Observation of the effects of dust particles on plasma fluctuation spectra.

Charged dust particles are theoretically expected to modify the amplitude and spectrum of plasma fluctuations, and this can eventually provide novel diagnostic tools. Direct experimental evidence of the effects of dust particles on the fluctuations of a low collisionality plasma is reported, in agreement with the expectations of kinetic theory.

Electron hole generation and propagation in an inhomogeneous collisionless plasma.

The generation of "trains" of electron holes in phase space due to an external electrostatic disturbance is investigated by using a Vlasov-Ampere code with open boundary conditions. Electron holes are produced mostly during the initial phase of the wave-plasma interaction, with a given drift velocity which is maintained until they exit the integration box, even in the presence of plasma inhomogeneities. They present macroscopic features, a dipolar electrostatic field and an electron density perturbation, which can be exploited for diagnostic purposes. Their equilibrium is intrinsically kinetic, in that they are accompanied by a stationary hole in the electron distribution function.

Charge separation effects in solid targets and ion acceleration with a two-temperature electron distribution.

The electrostatic field at the solid-vacuum interface generated by two electron populations with different thermal energies, each following a Boltzmann distribution, is analytically derived from the Poisson equation and studied in terms of plasma parameters. In particular, the effect of the pressure of each of the two populations on the amplitude of the electric field and on its spatial extension is described. In order to evaluate the cold electron temperature, an analytical model for the Ohmic heating of the background electron population by laser generated fast electrons is developed and the consequences on ion detachment, ionization, and acceleration processes in laser-solid experiments are discussed. The efficiency of ion acceleration is shown to be controlled by the heating rate of the background electrons.

Hydrodynamic approach to the interaction of a relativistic ultrashort laser pulse with an underdense plasma.

The interaction of an ultrashort, high peak power laser pulse with an underdense plasma is investigated within a physical model based on the three-dimensional cold hydrodynamic approach, which allows one to study the dynamics of the laser pulse and of the generated wakefields self-consistently, in the fully relativistic, strongly nonlinear regime. Our model is developed with the aim of describing very short laser pulses (with l(0)

Induced plasma nonuniformities and wave vector cascade in the strong wave-plasma interaction

The interaction of finite amplitude electrostatic waves with an unmagnetized electron-ion plasma is studied by means of a one-dimensional kinetic code that solves the Vlasov equations for the plasma species coupled with the Poisson equation for the self-consistent electric field. An external force acts upon the charged particles, in the form of the sum of several counterpropagating electrostatic waves, characterized by a unique frequency and a broad wave-vector spectrum, which form a standing wave pattern. The interplay between several nonlinear aspects of the interaction, such as the wavebreaking, the particle trapping, the electron heating, the production of ion beams, and the principal role of the wave-induced plasma density nonuniformities as the trigger of the above processes are investigated.

Relativistic solitons in magnetized plasmas

The results of analytical and numerical investigations on the properties of one-dimensional (nondrifting) solitons of relativistic amplitude, in the presence of an externally imposed uniform magnetic field B0, are presented and compared with those of the unmagnetized plasma theory (Esirkepov et al., Pis'ma Zh. Eksp. Teor. Fiz. 68, 33 (1998) [JETP Lett. 68, 36 (1998)]). The presence of a uniform longitudinal magnetic field, the intensity of which corresponds to an electron cyclotron frequency Omega(e)=eB(0)/m(e)c that is a non-negligible fraction of the laser frequency omega(0), has important consequences on the properties of relativistically intense solitons. The region of the parameter space (omega(0),Omega(e)) where magnetized solitons exist is determined analytically, and new conditions of breaking due to the total density depletion are given. It is shown that stable high energy magnetized solitons can be produced.