2,685 research outputs found
Generalised relativistic Ohm's laws, extended gauge transformations and magnetic linking
Generalisations of the relativistic ideal Ohm's law are presented that
include specific dynamical features of the current carrying particles in a
plasma. Cases of interest for space and laboratory plasmas are identified where
these generalisations allow for the definition of generalised electromagnetic
fields that transform under a Lorentz boost in the same way as the real
electromagnetic fields and that obey the same set of homogeneous Maxwell's
equations
Lagrangian coherent structures and plasma transport processes
A dynamical system framework is used to describe transport processes in
plasmas embedded in a magnetic field. For periodic systems with one degree of
freedom the Poincar\'e map provides a splitting of the phase space into regions
where particles have different kinds of motion: periodic, quasi-periodic or
chaotic. The boundaries of these regions are transport barriers; i.e., a
trajectory cannot cross such boundaries during the whole evolution of the
system. Lagrangian Coherent Structure (LCS) generalize this method to systems
with the most general time dependence, splitting the phase space into regions
with different qualitative behaviours. This leads to the definition of
finite-time transport barriers, i.e. trajectories cannot cross the barrier for
a finite amount of time. This methodology can be used to identify fast
recirculating regions in the dynamical system and to characterize the transport
between them
Coherent transport structures in magnetized plasmas II: Numerical results
In a pair of linked articles (called Article I and II respectively) we apply
the concept of Lagrangian Coherent Structures borrowed from the study of
Dynamical Systems to magnetic field configurations in order to separate regions
where field lines have different kind of behavior. In the present article,
article II, by means of a numerical procedure we investigate the Lagrangian
Coherent Structures in the case of a two-dimensional magnetic configuration
with two island chains that are generated by magnetic reconnection and evolve
nonlinearly in time. The comparison with previous results, obtained by assuming
a fixed magnetic field configuration, allows us to explore the dependence of
transport barriers on the particle velocity
Coherent transport structures in magnetized plasmas, I : Theory
In a pair of linked articles (called Article I and II respectively) we apply
the concept of Lagrangian Coherent Structures (LCSs) borrowed from the study of
Dynamical Systems to magnetic field configurations in order to separate regions
where field lines have different kind of behaviour. In the present article,
article I, after recalling the definition and the properties of the LCSs, we
show how this conceptual framework can be applied to the study of particle
transport in a magnetized plasma. Futhermore we introduce a simplified model
that allows us to consider explicitly the case where the magnetic configuration
evolves in time on timescales comparable to the particle transit time through
the configuration. In contrast with previous works on this topic, this analysis
requires that a system that is aperiodic in time be investigated. In this case
the Poincar\'e map technique cannot be applied and LCSs remain the only viable
tool
Radiation Reaction Effects on Electron Nonlinear Dynamics and Ion Acceleration in Laser-solid Interaction
Radiation Reaction (RR) effects in the interaction of an ultra-intense laser
pulse with a thin plasma foil are investigated analytically and by
two-dimensional (2D3P) Particle-In-Cell (PIC) simulations. It is found that the
radiation reaction force leads to a significant electron cooling and to an
increased spatial bunching of both electrons and ions. A fully relativistic
kinetic equation including RR effects is discussed and it is shown that RR
leads to a contraction of the available phase space volume. The results of our
PIC simulations are in qualitative agreement with the predictions of the
kinetic theory
Neutrino oscillation studies with laser-driven beam dump facilities
A new mechanism is suggested for efficient proton acceleration in the GeV
energy range; applications to non-conventional high intensity proton drivers
and, hence, to low-energy (10-200 MeV) neutrino sources are discussed. In
particular we investigate possible uses to explore subdominant oscillations at the atmospheric scale and their CP conjugate.
We emphasize the opportunity to develop these facilities in conjunction with
projects for inertial confined nuclear fusion and neutron spallation sources.Comment: 30 pages, 9 figures, minor changes, version to appear in
Nucl.Instrum.Meth.
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