To save this undefined to your undefined account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your undefined account.
Find out more about saving content to .
To save this article to your Kindle, first ensure firstname.lastname@example.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
The prospects of using extreme relativistic laser-matter interactions for laboratory
astrophysics are discussed. Laser-driven process simulation of matter
dynamics at ultra-high energy density is proposed for the studies of astrophysical compact
objects and the early universe.
Magnetic field generation in the Universe is still an open problem. Possible mechanisms
involve the Weibel instability, due to anisotropic phase-space distributions, as well as
the Biermann battery, due to misaligned density and temperature gradients. These
mechanisms can be reproduced in scaled laboratory experiments. In this contribution we
estimate the relative importance of these two processes and explore the laser-energy
requirements for producing Weibel dominated shocks.
Cosmic rays are accelerated in astrophysical plasmas which collide at supersonic speeds
where shock waves are formed, and along with other instabilities, they compete for the
dissipation and acceleration mechanisms. The diffusive acceleration mechanism plays a
leading role in the explanation of very high energy cosmic rays observed. In this
mechanism, particles are repeatedly gaining energy in multiple crossings of an
astrophysical shock discontinuity, due to collisions with upstream and downstream magnetic
scattering centers, resulting in a power-law spectrum extending up to very high energies.
Relativistic jets and their shocks in Active Galactic Nuclei (AGN) is a prominent source
for particle acceleration. Especially, relativistic single or multiple shocks have been
theorized and observed along the jets of AGN and are claimed to be responsible for
accelerating even the highest-energy cosmic rays observed. In this paper we will report
and discuss the cosmic ray acceleration efficiency and properties of single or multiple
shocks in the limit of relativistic plasmas in AGN jet environments.
A two-dimensional numerical study of the expansion of a dense plasma through a more
rarefied one is reported. The electrostatic ion-acoustic shock, which is generated during
the expansion, accelerates the electrons of the rarefied plasma inducing a superthermal
population which reduces electron thermal anisotropy. The Weibel instability is therefore
not triggered and no self-generated magnetic fields are observed, in contrast with
published theoretical results dealing with plasma expansion into vacuum.
Using powerful lasers, we are now able to produce in laboratory relevant regimes of
density, temperature and velocity to create a diagnosable exact scaled model of magnetic
cataclysmic variables accretion column. We present here preliminary results of a numerical
modeling of these astrophysical objects which will allow us to precise the experimental
setup of future experiments.
CNES, ESA and NASA have invested in helioseismic and asteroseismic disciplines for 2
decades with SoHO (1995–2015), COROT (2006–2013), KEPLER (2009–2014), PICARD (2010–2013)
and SDO (2010–2015). These missions focus on the stellar internal dynamics and their
influence of neighboring planets. Progress along this path requires that the microscopic
physics is well under control, but several seismic probes indicate some discrepancies
which justify new investigations of the energy transport in radiative zones of the Sun and
massive stars, despite strong efforts dedicated to reaction rates, screening, equation of
state and opacity coefficients between 1990 and 2000. We describe here how the OPAC
consortium tackles the complex problem of photon absorption by matter both theoretically
and experimentally, by using high energy laser facilities. These studies might be also
useful for other disciplines like fusion for energy and X-ray spectroscopy astronomy.
We discuss the role of Configuration Interaction (CI) and the influence of the number of
configurations taken into account in the calculations of nickel and iron spectral
opacities provided by the OPAC international collaboration, including statistical
approaches (SCO, CASSANDRA, STA), detailed accounting (OPAS, LEDCOP, OP, HULLAC-v9) or
hybrid method (SCO-RCG). Opacity calculations are presented for a temperature T of 27.3 eV
and a density of 3.4 mg/cm3, conditions relevant for pulsating stellar
We report laboratory measurements of the Zeeman response of lines in the 0-0 Wing-Ford
band of the F-X system (λ ~ 1 μm) of FeH, measured
in magnetic fields 0.3 – 0.5 Tesla. New Landé factors are used to deduce the magnetic
field in sunspots from Stokes V profiles recorded at the solar telescope THEMIS. The
magnetic field deduced from atomic lines (Ti, Fe) is slightly higher than that found from
The influence of a magnetic field on the broadening of spectral lines and transition
arrays in complex spectra is investigated. The anomalous absorption or emission Zeeman
pattern is a superposition of many profiles with different relative strengths, shifts,
widths, asymmetries and sharpnesses. The σ and π
profiles can be described statistically, using the moments of the Zeeman components. We
present two statistical modellings: the first one provides a diagnostic of the magnetic
field and the second one can be used to include the effect of a magnetic field on
simulated atomic spectra in an approximate way.
The optical spectra of L- and T-type dwarfs exhibit a continuum dominated by the far
wings of the absorption profiles of the Na 3s-3p and K 4s-4p doublets perturbed by
molecular hydrogen and helium. We examine the K resonance line wing and core with a
unified line profile theory and compare to laboratory experiments and observations of the
cool brown dwarf ϵ Indi Ba,b.
Stark broadening theories and calculations have been extensively developed for about 50
years. The theory can now be considered as mature for many applications, especially for
accurate spectroscopic diagnostics and modelling. This requires the knowledge of numerous
collisional line profiles, especially for very low abundant atoms and ions which are used
as probes for modern spectroscopic diagnostics in astrophysics. Nowadays, the access to
such data via an on line database becomes essential. STARK-B (http://stark-b.obspm.fr) is a collaborative project between the Astronomical
Observatory of Belgrade and the Laboratoire d’Étude du Rayonnement et de la matière en
Astrophysique (LERMA). It is a database of calculated widths and shifts of isolated lines
of atoms and ions due to electron and ion collisions (impacts). It is devoted to modelling
and spectroscopic diagnostics of stellar atmospheres and envelopes, laboratory plasmas,
laser equipments and technological plasmas. Hence, the domain of temperatures and
densities covered by the tables is wide and depends on the ionization degree of the
considered ion. The STARK-B database is a part of VAMDC (Virtual Atomic and Molecular Data
Centre, http://www.vamdc.eu), which is an European Union funded collaboration
between groups involved in the generation and use of atomic and molecular data. VAMDC aims
to build a secure, documented, flexible and interoperable e-science environment-based
interface to existing atomic and molecular data.
Energy in the solar system is constantly being converted from one form to another. Often
these processes take the form of dramatic events such as solar eruptions or geomagnetic
storms with important societal impacts. Understanding energy conversion and magnetic
storms is one of the grand challenges facing science and poses a great cultural and
scientific puzzle. We plan to use a new modelling approach based on combining state of the
art supercomputers with state of the art numerical methods that allow us to capture the
key aspect in energy conversion: the interplay of small and large scales. At the core of
energy conversion is the ability of macroscopic systems to store and process vast amounts
of energy while at the same time requiring microscopic processes at the moment the energy
is released. To describe and predict how energy can be stored for long periods and why it
is then suddenly released, a complete description down to the level of tracking the
trajectory of single particles is needed.
We review the main results of our previous works, in which we have investigated the
development of the Kelvin-Helmholtz (KH) instability in the transitional regime from
sub-magnetosonic to super-magnetosonic by varying the solar wind velocity, in conditions
typical of those observed at the Earth’s magnetopause flanks. In super-magnetosonic
regimes, we show that the vortices produced by the development of the KH instability act
as an obstacle in the plasma flow and may generate quasi-perpendicular magnetosonic shock
structures extending well outside the region of velocity shear.
Results are presented from studies of the process of plasma acceleration along the
current sheet width under different experimental conditions. The behavior of the neutral
component is included in the analysis.
The aim of this work is the analysis of the different transport regimes related to the
propagation in the solar wind of solar energetic particles (SEPs) generated by impulsive
events like solar flares. A numerical implementation of a Lévy random walk for parallel
particle transport is developed, which allows obtaining superdiffusive transport. The
comparison between the flows measured by satellites and fluxes extracted from the
numerical simulation, will contribute to a deeper understanding of the mechanisms
underlying the presence of superdiffusive regimes of SEP transport in interplanetary
It can be argued that all astrophysical jets, from lowly sub-stellar objects such as
young brown dwarfs to massive black holes at the centre of AGN, are generated by the same
basic physical mechanism. While the nature of that mechanism is still debated, jets from
young stars may represent our best chance of deciphering it. There are several reasons for
this statement. First of all they are nearby, thus affording us not only high spatial
resolution studies of the “central engine” but also time-resolved analysis of their
kinematics. Moreover as they radiate emission lines, spectroscopy can reveal radial
velocities, temperature, density, ion fraction, etc., along their flow. This wealth of
data is a challenge to the theorist/computational simulator but also a highly effective
means of discriminating between models. In addition, the observations tightly constrain
laboratory experiments. Here, I briefly review what is known about conditions in jets from
young stars as a guide to experiments, their generation including their link with
accretion disks, and their evolution from the earliest proto-stellar to pre-main sequence
We investigate the launching process of jets from accretion disks by means of
axisymmetric MHD simulations. Here, we present results of numerical MHD simulations
investigating how magnetic diffusivity and numerical resolution may affect the
ejection-to-accretion fraction and the asymptotic outflow structure.
Outflows and jets are intimately related to the formation of stars, and play a central
role in redistributing mass, energy and angular momentum within the core, disk and parent
cloud. The interplay between magnetic field and rotation is widely thought to be
responsible for launching and collimating these outflows. Shear induced by differential
rotation along initially poloidal field lines results in an azimuthal component of the
magnetic field being generated; the magnetic pressure gradient then accelerates the
plasma, and inflates bipolar magnetic cavities within the circumstellar matter. However,
the resulting winding of the magnetic field can be potentially disrupted by
magneto-hydrodynamic instabilities. To better understand the role of magnetic fields in
shaping these ouflows, a series of experiments on pulsed-power z-pinch machines have been
developed. In this talk I will present results related to the formation of jets in young
stellar objects and in the laboratory, and draw a parallel between the two systems.