[en] The most significant characteristics of the plasma produced in Thor discharges are described. The results obtained show that the possibility of controlling both the plasma equilibrium and the discharge regime has been fully achieved

[en] Power measurements in mm-wave systems for ECRH are essential during hot tests of gyrotrons and transmission lines. A matched load made of a hollow copper sphere internally coated with a thin layer of absorbing ceramic is proposed. The collimated beam radiating into the sphere from the waveguide is defocussed by an internal scatterer made of good conductor. An appropriate external water circuit provides for cooling and permits calorimetric measurement

[en] The empirical analysis of the electron density evolution during ECRH is given. It is shown that when recycling from the walls is low and the neutral gas injection rate is kept constant, during ECW injection the line density drops mainly as a consequence of a net decrease in the total particle number, whereas profile reshaping occurs only for some conditions. It is also shown that the phenomenon is of resonant nature but not a by-product of plasma heating. By considering the fast time scale on which the particle balance changes and by comparing the profile density evolution during ECRH to that following a step-wise reduction of the gas injection rate, it is inferred that particle confinement is degraded in the presence of EC waves. The consistency of this conclusion with all the experimental evidence is positively verified. (author)

[en] Energy levels of highly excited bound Rydberg states, the position and widths of autoionizing states, and oscillator strengths are calculated for He ³S, ³P^e, ³P^o, ³D^e and ³D^o symmetries up to the N = 5 He⁺ excitation threshold. The calculations are performed with the K-matrix B-spline method with maximum orbital angular momentum l_max = 8. Reliable doubly excited-state parameters up to the n = 20 multiplet below each ionization threshold are presented. One thousand and six hundred newly identified bound and metastable states, seven times those available in literature, fill many gaps, reveal a dozen intruder states, and allow new speculations on propensity rules and radiative decays of triplet Rydberg states

[en] ECRH experiments on the Thor Tokamak aimed at the investigation of r.f. absorption by suprathermal electrons are discussed. At the lowest densities (n-bar_e = 3 x 10¹² cm^-3) the damping of the injected wave is shown to be dominated by a r.f. enhanced suprathermal population in the presence of a bulk with very low optical thickness, so that a rather pure suprathermal interaction regime occurs. At higher density, localization of heating is lost due to refractive effects and multiple reflections. No evidence is found of conversion into electrostatic electron Bernstein waves of the extraordinary mode propagating quasiperpendicularly from the inner side of the torus. (author)

[en] We present a theoretical study of the photoelectron attosecond beating due to interference of two- photon transitions in the presence of autoionizing states. We show that, as a harmonic traverses a resonance, both the phase and frequency of the sideband beating significantly vary with photon energy. Furthermore, the beating between two resonant paths persists even when the pump and probe pulses do not overlap, thus permitting to reconstruct nonholographically coherent metastable wave packets. We characterize these phenomena with an analytical model that accounts for the effect of both intermediate and final resonances on two-photon processes. (paper)

[en] We present a study of radiative continuum-continuum transitions in helium in the presence of doubly-excited states by using the attosecond RABITT technique beyond the Single Active Electron approximation. On the one hand, transition amplitudes between correlated continuum states are calculated both by direct numerical solution of the time-dependent Schrodinger equation as well as with a two-photon perturbative model. The effect of autoionizing states on the sideband phaseshift is thus analyzed. On the other hand, we apply the soft-photon approximation to quantify the effects the IR probe intensity on the sideband non-resonant overtone components.

[en] We investigate theoretically the single ionization of neon by an attosecond XUV pulse, aiming at a better understanding of the outgoing electron wave-packet in the early stages of its detachment. To do so, we integrate the one-electron time-dependent Schrödinger equation numerically. The non-local interaction with the spectator electrons in the time-dependent hamiltonian is accounted for with a configuration-averaged effective Hartree-Fock potential.

[en] Analytical fits for electron density profiles for the FTU tokamak are determined from experimental data

[en] Four gyrotrons at 140 GHz will deliver in total 2 MW of electromagnetic power for 0.5 s, to perform ECRH experiments on the FTU tokamak in Frascati. The waves, at the frequency corresponding to the fundamental electron cyclotron resonance, chosen to exploit the maximum possible electron density, will be launched from the low magnetic field side polarized as the O-mode. The millimeter wave system was designed to achieve the best localization of the absorbed power in order to perform, besides electron and ion heating at high density, detailed studies of energy confinement in tokamaks. The antennas, one for each gyrotron and transmission line, are installed in one port of the FTU vacuum vessel to launch converging microwave beams. The beam waists, with a radius between 18 and 20 mm, are formed in the centre of the chamber and can be moved vertically by tilting the final mirrors. Oblique injection can be achieved at fixed angles by multiple reflections on the vertical walls of the vacuum port. Mechanical stresses due to thermal expansions or movements of the vacuum vessel, which could determine unwanted bends on the waveguide, are released by using sliding joints and rotating mitre bends. (author) 7 refs., 4 figs