INTRODUCTIONThe set of scient@ objectives for the MARSIS investigation was defined in the context of the objectives of the Mars Express mission [l] and in the more general frame of the current open issues in the study of Mars. The MARSIS primary objective is to map the distribution of water, both liquid and solid, in the upper portions of the crust of Mars. Three secondary objectives are defined for the MARSIS experiment: subsugace geologic probing, sugace characterization, and ionosphere sounding. We can notice that to achieve the global coverage MARSIS has been designed to support both dayside and nightside operations, although performances are maximized during night time, when the ionosphere plasma frequency drops off significantly and the lower frequency bands, which have greater penetration capability, can be used. The MARSIS was designed to work at altitude lower than 800 Km.

The aim of this paper is to report on recent advances made in global gyrokinetic simulations of ion temperature gradient (ITG) modes and other microinstabilities. The nonlinear development and saturation of ITG modes and the role of E × B zonal flows are studied with a global nonlinear δf formulation that retains parallel nonlinearity and thus allows for a check of the energy conservation property as a means of verifying the quality of the numerical simulation. Due to an optimized loading technique, the conservation property is satisfied with an unprecedented quality well into the nonlinear stage. The zonal component of the perturbation evolves to a quasi-steady state with regions of ITG suppression, strongly reduced radial energy flux and steepened effective temperature profiles alternating with regions of higher ITG mode amplitudes, larger radial energy flux and flattened effective temperature profiles. A semi-Lagrangian approach free of statistical noise is proposed as an alternative to the nonlinear δf formulation. An ASDEX-Upgrade experiment with an internal transport barrier is analysed with a global gyrokinetic code that includes trapped electron dynamics. The weakly destabilizing effect of trapped electron dynamics on ITG modes in an axisymmetric bumpy configuration modelling W7-X is shown in global linear simulations that retain the full electron dynamics. Finite β effects on microinstabilities are investigated with a linear global spectral electromagnetic gyrokinetic formulation. The radial global structure of electromagnetic modes shows a resonant behaviour with rational q values.

The interpretation of a measured x-ray spectrum from a carbon plasma induced by subpicosecond laser pulses (Wilhein T et al 1998 J. Opt. Soc. Am. B 15 1235) is re-examined. We calculate a synthetic Lyman spectrum emitted from a plasma layer at a given temperature and density, using a microscopic approach to the lineshape in dense, non-ideal plasmas. Special attention is given to the Stark broadening of the Ly-γ line. Self-absorption is taken into account within a simple model considering one-dimensional radiation transport in a plasma layer. Comparing the synthetic spectrum with the experimental one, we infer a temperature of T = 10 6 K and an electron density of n e = 3×10 21 cm −3 . While the temperature is in agreement with Wilhein et al, the inferred density disagrees by one order of magnitude.

The whole Balmer H(beta) line profiles are studied in detail experimentally in the T-tube discharge for the wide range of plasma parameters. Besides the common one, two additional parameters are introduced to characterize the asymmetry behavior of the experimental Stark profiles with the reference point chosen in the center of the line. The experimental data are analyzed and benchmarked versus the simple theoretical model based on the effects of microfield nonuniformity and electron impact shifts.

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