PROGRESS REPORT - ENEA - Fusione

A1 Magnetic Confinement
A Fusion Programme
probes, due to the impact of μm-sized
dust at a velocity of the order of ten km/s.
This interpretation is supported directly
by electron microscope analysis of the
probe surface, which revealed the
presence of 10 to 100–μm–sized craters,
a typical footprint of the impact ionization
processes (fig. A1.11). A number of
spherically shaped, iron-rich μm-sized
particles was also observed to be
embedded in the probe surface. Neither
craters nor embedded particles were
detected on the surface of the “virgin”
probe. The size, number and distribution
of the observed craters are consistent
with impact ionization processes
Fig. A1.11 – Electron microscope analysis of the probe occurring at an average rate of a few
surface
hundred Hz, which corresponds to
10 4 m -3 density of fast μm–sized dust
particles accelerated at velocities of the order of 10 km/s by ion drag forces associated with plasma
flows in the SOL of FTU.
A1.4 Plasma Theory
Mutual and positive feedbacks between theory and experiments have led to a clear identification of
high-frequency MHD activity (high frequency with respect to that typical of MHD fluctuations) in FTU
as evidence of nonlinear Alfvén mode excitations by a large magnetic island.
Electron-fishbone mode excitations by LH additional power only are explained within a general
theoretical framework, which fully accounts for the various experimental evidence of such modes
and also provides a simple yet relevant model for interpreting the rich nonlinear dynamic behaviour,
observed experimentally.
The theory of propagation and absorption of rf waves in toroidal plasmas has been explored in both
its more basic aspects as well as with detailed applications of practical relevance, such as the
modelling of ICRH experiments in JET and the investigation of burning plasma dynamics issues by
ICRH accelerated minority ion supra-thermal tails.
The investigation of energetic ion dynamics in burning plasmas has been articulated along three
main lines: i) identification of the relevant plasma parameters that make it possible to experimentally
study burning plasma physics issues in sub-ignited regimes; ii) numerical simulation of energetic ion
transport and nonlinear Alfvénic fluctuations in situations of experimental relevance in present-day
experiments; iii) first-principle-based analysis of fundamental processes involved in the collective
excitation of Alfvénic modes and in the fluctuation enhanced energetic ion transport. Item ii) has
been explored with the interpretation of nonlinear Alfvén wave dynamics and energetic ion transport
observed in JT-60U by means of hybrid MHD-gyrokinetic numerical simulations, carried out within
an ongoing collaboration with the Japan Atomic Energy Agency. For item iii) an overview of the
theory of Alfvén waves and energetic particle physics in burning plasmas has been given as a result
of work done within the continuing collaboration with University of California at Irvine (UCI) USA.
Within the same framework of UCI collaboration, recent theoretical work on plasma turbulence and
turbulent transport, or more specifically, on nonlinear equilibria, stability and generation of zonal
structures in toroidal plasmas has been summarised.
Progress Report 2006
16