2,714 research outputs found
Mixed-state dynamics in one-dimensional quantum lattice systems: a time-dependent superoperator renormalization algorithm
We present an algorithm to study mixed-state dynamics in one-dimensional
quantum lattice systems. The algorithm can be used, e.g., to construct thermal
states or to simulate real time evolutions given by a generic master equation.
Its two main ingredients are (i) a superoperator renormalization scheme to
efficiently describe the state of the system and (ii) the time evolving block
decimation (TEBD) technique to efficiently update the state during a time
evolution. The computational cost of a simulation increases significantly with
the amount of correlations between subsystems but it otherwise depends only
linearly in the system size. We present simulations involving quantum spins and
fermions in one spatial dimension.Comment: See also F. Verstraete et al. cond-mat/040642
Target Design for XUV Probing of Radiative Shock Experiments
Radiative shocks are strong shocks characterized by plasma at a high
temperature emitting an important fraction of its energy as radiation.
Radiative shocks are commonly found in many astrophysical systems and are
templates of radiative hydrodynamic flows, which can be studied experimentally
using high-power lasers. This is not only important in the context of
laboratory astrophysics but also to benchmark numerical studies. We present
details on the design of experiments on radiative shocks in xenon gas performed
at the kJ scale PALS laser facility. It includes technical specifications for
the tube targets design and numerical studies with the 1-D radiative
hydrodynamics code MULTI. Emphasis is given to the technical feasibility of an
XUV imaging diagnostic with a 21 nm (~58 eV) probing beam, which allows to
probe simultaneously the post-shock and the precursor region ahead of the
shock. The novel design of the target together with the improved X-ray optics
and XUV source allow to show both the dense post-shock structure and the
precursor of the radiative shock.Comment: 12 pages, 4 figure
Experimental Studies of Magnetically Driven Plasma Jets
We present experimental results on the formation of supersonic, radiatively
cooled jets driven by pressure due to the toroidal magnetic field generated by
the 1.5 MA, 250 ns current from the MAGPIE generator. The morphology of the jet
produced in the experiments is relevant to astrophysical jet scenarios in which
a jet on the axis of a magnetic cavity is collimated by a toroidal magnetic
field as it expands into the ambient medium. The jets in the experiments have
similar Mach number, plasma beta and cooling parameter to those in protostellar
jets. Additionally the Reynolds, magnetic Reynolds and Peclet numbers are much
larger than unity, allowing the experiments to be scaled to astrophysical
flows. The experimental configuration allows for the generation of episodic
magnetic cavities, suggesting that periodic fluctuations near the source may be
responsible for some of the variability observed in astrophysical jets.
Preliminary measurements of kinetic, magnetic and Poynting energy of the jets
in our experiments are presented and discussed, together with estimates of
their temperature and trapped toroidal magnetic field.Comment: 7 pages, 6 figures, accepted for publication in Astrophysics & Space
Scienc
Formation of Episodic Magnetically Driven Radiatively Cooled Plasma Jets in the Laboratory
We report on experiments in which magnetically driven radiatively cooled
plasma jets were produced by a 1 MA, 250 ns current pulse on the MAGPIE pulsed
power facility. The jets were driven by the pressure of a toroidal magnetic
field in a ''magnetic tower'' jet configuration. This scenario is characterized
by the formation of a magnetically collimated plasma jet on the axis of a
magnetic ''bubble'', confined by the ambient medium. The use of a radial
metallic foil instead of the radial wire arrays employed in our previous work
allows for the generation of episodic magnetic tower outflows which emerge
periodically on timescales of ~30 ns. The subsequent magnetic bubbles propagate
with velocities reaching ~300 km/s and interact with previous eruptions leading
to the formation of shocks.Comment: 6 pages, 5 figures. Accepted for publication in Astrophysics & Space
Scienc
Numerical study of jets produced by conical wire arrays on the Magpie pulsed power generator
The aim of this work is to model the jets produced by conical wire arrays on
the MAGPIE generator, and to design and test new setups to strengthen the link
between laboratory and astrophysical jets. We performed the modelling with
direct three-dimensional magneto-hydro-dynamic numerical simulations using the
code GORGON. We applied our code to the typical MAGPIE setup and we
successfully reproduced the experiments. We found that a minimum resolution of
approximately 100 is required to retrieve the unstable character of the jet. We
investigated the effect of changing the number of wires and found that arrays
with less wires produce more unstable jets, and that this effect has magnetic
origin. Finally, we studied the behaviour of the conical array together with a
conical shield on top of it to reduce the presence of unwanted low density
plasma flows. The resulting jet is shorter and less dense.Comment: Accepted for publication in Astrophysics & Space Science. HEDLA 2010
conference procedings. Final pubblication will be available on Springe
An Experimental Platform for Pulsed-Power Driven Magnetic Reconnection
We describe a versatile pulsed-power driven platform for magnetic
reconnection experiments, based on exploding wire arrays driven in parallel
[Suttle, L. G. et al. PRL, 116, 225001]. This platform produces inherently
magnetised plasma flows for the duration of the generator current pulse (250
ns), resulting in a long-lasting reconnection layer. The layer exists for long
enough to allow evolution of complex processes such as plasmoid formation and
movement to be diagnosed by a suite of high spatial and temporal resolution
laser-based diagnostics. We can access a wide range of magnetic reconnection
regimes by changing the wire material or moving the electrodes inside the wire
arrays. We present results with aluminium and carbon wires, in which the
parameters of the inflows and the layer which forms are significantly
different. By moving the electrodes inside the wire arrays, we change how
strongly the inflows are driven. This enables us to study both symmetric
reconnection in a range of different regimes, and asymmetric reconnection.Comment: 14 pages, 9 figures. Version revised to include referee's comments.
Submitted to Physics of Plasma
Formation and Structure of a Current Sheet in Pulsed-Power Driven Magnetic Reconnection Experiments
We describe magnetic reconnection experiments using a new, pulsed-power
driven experimental platform in which the inflows are super-sonic but
sub-Alfv\'enic.The intrinsically magnetised plasma flows are long lasting,
producing a well-defined reconnection layer that persists over many
hydrodynamic time scales.The layer is diagnosed using a suite of high
resolution laser based diagnostics which provide measurements of the electron
density, reconnecting magnetic field, inflow and outflow velocities and the
electron and ion temperatures.Using these measurements we observe a balance
between the power flow into and out of the layer, and we find that the heating
rates for the electrons and ions are significantly in excess of the classical
predictions. The formation of plasmoids is observed in laser interferometry and
optical self-emission, and the magnetic O-point structure of these plasmoids is
confirmed using magnetic probes.Comment: 14 pages, 12 figures. Accepted for publication in Physics of Plasma
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