597,371 research outputs found
GEMPIC: Geometric ElectroMagnetic Particle-In-Cell Methods
We present a novel framework for Finite Element Particle-in-Cell methods
based on the discretization of the underlying Hamiltonian structure of the
Vlasov-Maxwell system. We derive a semi-discrete Poisson bracket, which retains
the defining properties of a bracket, anti-symmetry and the Jacobi identity, as
well as conservation of its Casimir invariants, implying that the semi-discrete
system is still a Hamiltonian system. In order to obtain a fully discrete
Poisson integrator, the semi-discrete bracket is used in conjunction with
Hamiltonian splitting methods for integration in time. Techniques from Finite
Element Exterior Calculus ensure conservation of the divergence of the magnetic
field and Gauss' law as well as stability of the field solver. The resulting
methods are gauge invariant, feature exact charge conservation and show
excellent long-time energy and momentum behaviour. Due to the generality of our
framework, these conservation properties are guaranteed independently of a
particular choice of the Finite Element basis, as long as the corresponding
Finite Element spaces satisfy certain compatibility conditions.Comment: 57 Page
The Energy Conserving Particle-in-Cell Method
A new Particle-in-Cell (PIC) method, that conserves energy exactly, is
presented. The particle equations of motion and the Maxwell's equations are
differenced implicitly in time by the midpoint rule and solved concurrently by
a Jacobian-free Newton Krylov (JFNK) solver. Several tests show that the finite
grid instability is eliminated in energy conserving PIC simulations, and the
method correctly describes the two-stream and Weibel instabilities, conserving
exactly the total energy. The computational time of the energy conserving PIC
method increases linearly with the number of particles, and it is rather
insensitive to the number of grid points and time step. The kinetic enslavement
technique can be effectively used to reduce the problem matrix size and the
number of JFNK solver iterations
Particle-in-cell simulations of rf breakdown
Breakdown voltages of a capacitively coupled radio frequency argon discharge
at 27 MHz are studied. We use a one-dimensional electrostatic PIC code to
investigate the effect of changing the secondary emission properties of the
electrodes on the breakdown voltage, particularly at low pd values. Simulation
results are compared with the available experimental results and a satisfactory
agreement is found.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Load management strategy for Particle-In-Cell simulations in high energy particle acceleration
In the wake of the intense effort made for the experimental CILEX project,
numerical simulation cam- paigns have been carried out in order to finalize the
design of the facility and to identify optimal laser and plasma parameters.
These simulations bring, of course, important insight into the fundamental
physics at play. As a by-product, they also characterize the quality of our
theoretical and numerical models. In this paper, we compare the results given
by different codes and point out algorithmic lim- itations both in terms of
physical accuracy and computational performances. These limitations are illu-
strated in the context of electron laser wakefield acceleration (LWFA). The
main limitation we identify in state-of-the-art Particle-In-Cell (PIC) codes is
computational load imbalance. We propose an innovative algorithm to deal with
this specific issue as well as milestones towards a modern, accurate high-per-
formance PIC code for high energy particle acceleration
Classical Radiation Reaction in Particle-In-Cell Simulations
Under the presence of ultra high intensity lasers or other intense
electromagnetic fields the motion of particles in the ultrarelativistic regime
can be severely affected by radiation reaction. The standard particle-in-cell
(PIC) algorithms do not include radiation reaction effects. Even though this is
a well known mechanism, there is not yet a definite algorithm nor a standard
technique to include radiation reaction in PIC codes. We have compared several
models for the calculation of the radiation reaction force, with the goal of
implementing an algorithm for classical radiation reaction in the Osiris
framework, a state-of-the-art PIC code. The results of the different models are
compared with standard analytical results, and the relevance/advantages of each
model are discussed. Numerical issues relevant to PIC codes such as resolution
requirements, application of radiation reaction to macro particles and
computational cost are also addressed. The Landau and Lifshitz reduced model is
chosen for implementation.Comment: 12 pages, 8 figure
Dynamic acoustic field activated cell separation (DAFACS)
Advances in diagnostics, cell and stem cell technologies drive the development of application-specific tools
for cell and particle separation. Acoustic micro-particle separation offers a promising avenue for highthroughput,
label-free, high recovery, cell and particle separation and isolation in regenerative medicine.
Here, we demonstrate a novel approach utilizing a dynamic acoustic field that is capable of separating an
arbitrary size range of cells. We first demonstrate the method for the separation of particles with different
diameters between 6 and 45 μm and secondly particles of different densities in a heterogeneous medium.
The dynamic acoustic field is then used to separate dorsal root ganglion cells. The shearless, label-free and
low damage characteristics make this method of manipulation particularly suited for biological applications.
Advantages of using a dynamic acoustic field for the separation of cells include its inherent safety and
biocompatibility, the possibility to operate over large distances (centimetres), high purity (ratio of particle
population, up to 100%), and high efficiency (ratio of separated particles over total number of particles to
separate, up to 100%)
Particle-based simulation of ellipse-shaped particle aggregation as a model for vascular network formation
Computational modelling is helpful for elucidating the cellular mechanisms
driving biological morphogenesis. Previous simulation studies of blood vessel
growth based on the Cellular Potts model (CPM) proposed that elongated,
adhesive or mutually attractive endothelial cells suffice for the formation of
blood vessel sprouts and vascular networks. Because each mathematical
representation of a model introduces potential artifacts, it is important that
model results are reproduced using alternative modelling paradigms. Here, we
present a lattice-free, particle-based simulation of the cell elongation model
of vasculogenesis. The new, particle-based simulations confirm the results
obtained from the previous Cellular Potts simulations. Furthermore, our current
findings suggest that the emergence of order is possible with the application
of a high enough attractive force or, alternatively, a longer attraction
radius. The methodology will be applicable to a range of problems in
morphogenesis and noisy particle aggregation in which cell shape is a key
determining factor.Comment: 9 pages, 11 figures, 2 supplementary videos (on Youtube), submitted
to Computational Particle Mechanics, special issue: Jos\'e-Manuel Garcia
Aznar (Ed.) Particle-based simulations on cell and biomolecular mechanic
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