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Papers by Claudio Chiuderi

Highlights of Astronomy, 1980

From the Contents: Resistive and Collisionless Magnetic Reconnection.- Rotating MHD Winds.- Parti... more From the Contents: Resistive and Collisionless Magnetic Reconnection.- Rotating MHD Winds.- Particle Acceleration.-Turbulence, Statistics and Structures: An Introduction.- Radio Astronomical Diagnostics.- Spectroscopic Diagnostics of Astrophysical Plasmas.- Hot Plasmas in Space: X-Ray Diagnostics Instrumentation.

ABSTRACT The heating of high temperature plasmas by MHD waves is one of the most interesting and ... more ABSTRACT The heating of high temperature plasmas by MHD waves is one of the most interesting and challenging problems of plasma physics especially when the energy is injected into the system at length scales much larger than the dissipative ones. It has been conjectured that in 2-D MHD systems the possibility exist of establishing a state in which energy is dissipated at a rate that is independent of the ohmic resistivity and that the time needed to reach such a state is finite and independent of resistivity as well. We study the nonlinear interaction of long-wavelength, small amplitude perturbations with an inhomogeneous magnetic field showing that energy is transferred to the fluctuations from the background equilibrium. In the case of an isolated system, the free energy initially stored in the equilibrium would decrease and the field would tend to become homogeneous. To model the process of energy injection into the system, we force the large scale field to maintain its initial profile. In these circumstances, we prove that it is actually possible after a finite time, independent of the dissipative mechanism, to generate a well developed 2-D MHD turbulent state where the dissipation rate does not depend on the Lundquist number, at least for values of the order of a few thousands. To our knowledge, this is the first time in which the existence of the conjectured resistivity independent dissipation has been explicitly demonstrated.

International Astronomical Union Colloquium

The amount of heat required to maintain the chromosphere and corona can be found from an estimate... more The amount of heat required to maintain the chromosphere and corona can be found from an estimate of the losses. The two processes that transport energy from the corona into interstellar space are electromagnetic radiation and the solar wind. In the Inner corona thermal conduction constitutes the dominant means of energy loss, but convection by the solar wind gradually takes over in the outer corona.

Astron Astrophys, 1982

The observations of X-ray emission from late type main sequence and giant stars show that a coron... more The observations of X-ray emission from late type main sequence and giant stars show that a coronal heating due to acoustic waves is unlikely. As suggested by Vaiana and Rosner, the conversion of magnetic into thermal energy may be responsible for the X-ray emission from such a kind of stars. The proposed ingredients in our analysis are the differential rotation and dynamo action which are able to generate a magnetic activity at the star's surface which in turn gives rise to the observed X-ray emission. We assume that the interaction of rotation with convection, in stars possessing outer convective envelopes, is the dominant mechanism for generating differential rotation and dynamo action, and that the stressing of the coronal magnetic flux tubes by the surface turbulence, converting magnetic into thermal energy, determine the level of X-ray emission. Therefore we compute a series of models of luminosity class III giant stars, and determine the surface X-ray flux. Comparing these results with those concerning the late type main sequence star models, previously computed by the same authors, and with observations, it appears that the proposed mechanism is plausible.

A brief introduction to Plasma Physics is presented, focusing on ionized gases, the plasma consti... more A brief introduction to Plasma Physics is presented, focusing on ionized gases, the plasma constituting the greatest part of the visible (baryonic) Universe. Basic plasma features such as ionization degree and the condition of quasi-neutrality are discussed. A heuristic derivation of fundamental plasma parameters, such as plasma frequency and Debye length are given. Finally, the different possible approaches to the physical description of plasma dynamics are introduced.

Annales De Physique, 1980

Magnetic Reconnection in the Solar Atmosphere, 1997

Nasa Conference Publication, 1985

Small Scale Motions on the Sun, 1979

Proceedings of the International Astronomical Union, 1997

Radiophysics and Quantum Electronics, 1994

The propagation and dissipation properties of magnetohydrodynamic waves in a nonuniform,, highlyc... more The propagation and dissipation properties of magnetohydrodynamic waves in a nonuniform,, highlyconducting plasma, is investigated with a normal mode approach. The interaction between the pertur-bm~,ion and the non-uniform supporting medium is analyzed as the main mechanism able to produce the small scale spatial structure necessary to dissipate e]fieiently the wave energy. Two fundamental classes of modes are found, characterized by their resistive or ideal asymptotic behavior, the damping rates are shown to be orders of magnitude larger than those obtained when the plasma is perfectly homogeneous, and an application to the problem, of solar coronal heating is discussed