C. Marmolino

Phase Differences and Gains between Intensity and Velocity in Low-Degree Acoustic Modes Measured by SOHO

Helioseismic instruments aboard SOHO are making possible a more accurate way of investigating the internal structure of the Sun. Making use of the different techniques and characteristics of these instruments, it is possible to measure solar oscillations as variations of the photospheric velocity (GOLF, MDI) or as irradiance and radiance fluctuations (VIRGO, MDI). Among the other advantages of observing solar oscillations simultaneously with different instruments and techniques, the study of velocity and irradiance measurements provides information on nonadiabatic effects in the radiatively cooled solar atmosphere. The thermodynamical properties of the atmosphere determine a phase shift between intensity and velocity (downward positive) oscillations of -90° in the case of an adiabatic atmosphere. Here we compute the phase differences and gains between intensity and velocity acoustic modes measured by SOHO to quantify the nonadiabatic degree of the solar atmosphere. After correcting the observed phase differences of the solar background influence, we find not exactly an adiabactic behavior, but close to it. Finally, we compare our results with three different theoretical models of the solar atmosphere, finding the best agreement with a model that includes turbulent pressure associated with convection and fluctuations of the superadiabatic temperature gradient.

Diagnostics of fast dust particles in tokamak edge plasmas

The use of electrostatic probes as a diagnostic tool of the dust particles in the tokamak edge plasmas is investigated. Probe measurements of electrostatic fluctuations in the scrape-off layer of t ...

The use of RPC in the ARGO-YBJ project

We present the ARGO-YBJ experiment, a full coverage detector placed at high altitude (∼4300 m a.s.l.) that exploits the RPC technique. Results of a test experiment performed at Yanbajing site, with a full coverage RPC carpet of 50 m2 are also presented.

On the role of stochastic heating in experiments with complex plasmas

Stochastic heating of dust particles resulting from dust charge fluctuations is considered in some laboratory situations, where high kinetic temperatures of dust particles have been suggested or could be observed. A particular case, in the conditions of the scrape-off layer in tokamak plasmas, is also considered and it is shown that kinetic energies corresponding to velocities of ≃km/s can be reached in times of order ≃1 ms by micron-size particles interacting with a background of stochastically heated nanosize particles.

Fluctuations in dusty plasmas

Dust charge and density fluctuations can substantially change basic plasma properties—dispersion of low frequency modes, plasma fluctuations—and introduce new effects—attraction of negatively charged dust particles, dust and ion stochastic heating—which cannot be found if dust fluctuations are neglected. The kinetic theory of fluctuations is used to describe these effects, in particular the changes in the spectral densities of the plasma fluctuations in un-magnetized plasmas in the presence of dust.

Plasma fluctuation spectra as a diagnostic tool for submicron dust

It is shown that the measurements of density fluctuation spectra in dusty plasmas can constitute a basis for in situ diagnostic of invisible submicron dust. The self-consistent kinetic theory that includes the charging processes and the natural density fluctuations of the dust particles predicts modifications of the spectra due to the presence of dust. A laboratory experiment was carried out where submicron dust was produced in a gas phase and diagnosed by surface analysis of samples and by measurements of its influence on the plasma density fluctuation spectra. Quantitative comparison of the latter with the theory yields information on dust density, size, and distribution in agreement with the results of the surface analysis. The method can be applied to various plasma environments in laboratory and space.

The effects of acoustic-gravity waves on the K i 7699 line

We examine the effects of acoustic-gravity waves with long and short periods on the solar profile of the K i7699 line using a dynamic model of line formation.First we studied the kinetic equilibrium of the K i atoms in a static atmosphere confirming, with up-to-date atomic data and atmospheric model, that a good fit of the resonance line 7699 is possible only when non-LTE effects are accounted for.Then the static non-LTE line source function and lower-level population are used as input data for calculating the line formation in the presence of waves.The time behaviour of the synthetic profiles corresponding to 300 s and 30 s waves is extensively discussed. The characteristic redshift induced by the 30 s wave is explained within the framework of the S-S line formation model. Long-period waves yield an anticorrelation between the asymmetry at different residual intensities and the line core shift, as observed. The short-period waves with velocity amplitude of about 100 m s−1 (at the base of the photosphere) produce a mean bisector whose lower part has a slope in agreement with the observed one. The efficiency of waves to produce macro and microturbulence is also discussed.

Stochastic Acceleration of Dust Particles in Tokamak Edge Plasmas

Stochastic heating of dust particles resulting from dust charge fluctuations is considered in the conditions of the scrape‐off‐layer (SOL) in tokamak plasmas. It is shown that kinetic energies corresponding to velocities of ≃Km/s can be reached in times of order ≃1 ms by micron‐size dust particles interacting with a background of stochastically heated nano‐size dust particles.

Wave behavior in the solar photosphere: A comparison of theory and observation

We report detailed comparisons between theoretical and empirical eigenfunctions of velocity and intensity for the 5-min modes in the photosphere. The comparison process is accomplished by obtaining synthetic profiles of the Fei λ5434 Å line in the presence of waveforms given by dynamical calculations and then applying a common procedure of reduction both to the observed and to the synthetic data. For the velocity waveforms, our results show a general agreement between theory and observations together with some systematic differences; in particular the theory systematically underestimates the observations in the low photosphere. These systematic differences are stressed by the intensity results since both the computed amplitudes and phases appear to be wrong in the deeper layers.

Observation and Interpretation of Photospheric Line Asymmetry Changes Near Active Regions

Changes in spectral line asymmetries between regions of quiet sun and regions containing varying amounts of magnetic flux were observed. The observed asymmetry changes are used to deduce parameters that describe the local state of convective overshoot. From these parameters we deduce how the local convective energy flux depends on magnetic fields within the observed regions. Observations were obtained during five separate observing runs between July 1983 and February 1987. We observe FeI 5434 and FeI 6302. Fe 5434 is not split in magnetic regions while 6302 is used to map out the longitudinal component of the field. Additionally we obtain a K-line slit jaw image to locate areas of plage. The observations indicate that magnetic fields decrease the flux carried by convective elements deep in the photosphere, but permit the elements to overshoot higher into the photosphere and temperature minimum regions. The quantitative effect on the convective transport depends strongly on the strength of the magnetic field.