PICsar: Particle in cell pulsar magnetosphere simulator
NASA Astrophysics Data System (ADS)
Belyaev, Mikhail A.
2016-07-01
PICsar simulates the magnetosphere of an aligned axisymmetric pulsar and can be used to simulate other arbitrary electromagnetics problems in axisymmetry. Written in Fortran, this special relativistic, electromagnetic, charge conservative particle in cell code features stretchable body-fitted coordinates that follow the surface of a sphere, simplifying the application of boundary conditions in the case of the aligned pulsar; a radiation absorbing outer boundary, which allows a steady state to be set up dynamically and maintained indefinitely from transient initial conditions; and algorithms for injection of charged particles into the simulation domain. PICsar is parallelized using MPI and has been used on research problems with ~1000 CPUs.
NASA Astrophysics Data System (ADS)
Han, Daoru; Wang, Pu; He, Xiaoming; Lin, Tao; Wang, Joseph
2016-09-01
Motivated by the need to handle complex boundary conditions efficiently and accurately in particle-in-cell (PIC) simulations, this paper presents a three-dimensional (3D) linear immersed finite element (IFE) method with non-homogeneous flux jump conditions for solving electrostatic field involving complex boundary conditions using structured meshes independent of the interface. This method treats an object boundary as part of the simulation domain and solves the electric field at the boundary as an interface problem. In order to resolve charging on a dielectric surface, a new 3D linear IFE basis function is designed for each interface element to capture the electric field jump on the interface. Numerical experiments are provided to demonstrate the optimal convergence rates in L2 and H1 norms of the IFE solution. This new IFE method is integrated into a PIC method for simulations involving charging of a complex dielectric surface in a plasma. A numerical study of plasma-surface interactions at the lunar terminator is presented to demonstrate the applicability of the new method.
Electromagnetic ''particle-in-cell'' plasma simulation
Langdon, A.B.
1985-04-22
''PIC'' simulation tracks particles through electromagnetic fields calculated self-consistently from the charge and current densities of the particles themselves, external sources, and boundaries. Already used extensively in plasma physics, such simulations have become useful in the design of accelerators and their r.f. sources. 5 refs.
Concurrent Algorithm For Particle-In-Cell Simulations
NASA Technical Reports Server (NTRS)
Liewer, Paulett C.; Decyk, Viktor K.
1990-01-01
Separate decompositions used for particle-motion and field calculations. General Concurrent Particle-in-Cell (GCPIC) algorithm used to implement motions of individual plasma particles (ions and electrons) under influence of particle-in-cell (PIC) computer codes on concurrent processors. Simulates motions of individual plasma particles under influence of electromagnetic fields generated by particles themselves. Performed to study variety of nonlinear problems in plasma physics, including magnetic and inertial fusion, plasmas in outer space, propagation of electron and ion beams, free-electron lasers, and particle accelerators.
Global particle-in-cell simulations of Alfvenic modes
Mishchenko, A.; Koenies, A.; Hatzky, R.
2008-11-01
Global linear gyro-kinetic particle-in-cell (PIC) simulations of electromagnetic modes in pinch and tokamak geometries are reported. The Toroidal Alfven Eigenmode and the Kinetic Ballooning Mode have been simulated. All plasma species have been treated kinetically (i.e. no hybrid fluid-kinetic or reduced-kinetic model has been applied). The main intention of the paper is to demonstrate that the global Alfven modes can be treated with the gyro-kinetic PIC method.
Accelerating particle-in-cell simulations using multilevel Monte Carlo
NASA Astrophysics Data System (ADS)
Ricketson, Lee
2015-11-01
Particle-in-cell (PIC) simulations have been an important tool in understanding plasmas since the dawn of the digital computer. Much more recently, the multilevel Monte Carlo (MLMC) method has accelerated particle-based simulations of a variety of systems described by stochastic differential equations (SDEs), from financial portfolios to porous media flow. The fundamental idea of MLMC is to perform correlated particle simulations using a hierarchy of different time steps, and to use these correlations for variance reduction on the fine-step result. This framework is directly applicable to the Langevin formulation of Coulomb collisions, as demonstrated in previous work, but in order to apply to PIC simulations of realistic scenarios, MLMC must be generalized to incorporate self-consistent evolution of the electromagnetic fields. We present such a generalization, with rigorous results concerning its accuracy and efficiency. We present examples of the method in the collisionless, electrostatic context, and discuss applications and extensions for the future.
Wavenumber spectrum of whistler turbulence: Particle-in-cell simulation
Saito, S.; Gary, S. Peter; Narita, Y.
2010-12-15
The forward cascade of decaying whistler turbulence is studied in low beta plasma to understand essential properties of the energy spectrum at electron scales, by using a two-dimensional electromagnetic particle-in-cell (PIC) simulation. This simulation demonstrates turbulence in which the energy cascade rate is greater than the dissipation rate at the electron inertial length. The PIC simulation shows that the magnetic energy spectrum of forward-cascaded whistler turbulence at electron inertial scales is anisotropic and develops a very steep power-law spectrum which is consistent with recent solar wind observations. A comparison of the simulated spectrum with that predicted by a phenomenological turbulence scaling model suggests that the energy cascade at the electron inertial scale depends on both magnetic fluctuations and electron velocity fluctuations, as well as on the whistler dispersion relation. Thus, not only kinetic Alfven turbulence but also whistler turbulence may explain recent solar wind observations of very steep magnetic spectra at short scales.
Oblique electron fire hose instability: Particle-in-cell simulations
NASA Astrophysics Data System (ADS)
Hellinger, Petr; Trávníček, Pavel M.; Decyk, Victor K.; Schriver, David
2014-01-01
Nonlinear properties of the oblique resonant electron fire hose instability are investigated using two-dimensional particle-in-cell simulations in the Darwin approximation for weak initial growth rates. The weak electron fire hose instability has a self-destructive nonlinear behavior; it destabilizes a nonpropagating branch which only exists for a sufficiently strong temperature anisotropy. The nonlinear evolution leads to generation of nonpropagating waves which in turn scatter electrons and reduce their temperature anisotropy. As the temperature anisotropy is being reduced, the nonpropagating branch disappears and the generated standing waves are transformed to propagating whistler waves which are rapidly damped. Consequently, the oblique electron fire hose efficiently reduces the electron temperature anisotropy.
Particle-in-cell simulations of Hall plasma thrusters
NASA Astrophysics Data System (ADS)
Miranda, Rodrigo; Ferreira, Jose Leonardo; Martins, Alexandre
2016-07-01
Hall plasma thrusters can be modelled using particle-in-cell (PIC) simulations. In these simulations, the plasma is described by a set of equations which represent a coupled system of charged particles and electromagnetic fields. The fields are computed using a spatial grid (i.e., a discretization in space), whereas the particles can move continuously in space. Briefly, the particle and fields dynamics are computed as follows. First, forces due to electric and magnetic fields are employed to calculate the velocities and positions of particles. Next, the velocities and positions of particles are used to compute the charge and current densities at discrete positions in space. Finally, these densities are used to solve the electromagnetic field equations in the grid, which are interpolated at the position of the particles to obtain the acting forces, and restart this cycle. We will present numerical simulations using software for PIC simulations to study turbulence, wave and instabilities that arise in Hall plasma thrusters. We have sucessfully reproduced a numerical simulation of a SPT-100 Hall thruster using a two-dimensional (2D) model. In addition, we are developing a 2D model of a cylindrical Hall thruster. The results of these simulations will contribute to improve the performance of plasma thrusters to be used in Cubesats satellites currenty in development at the Plasma Laboratory at University of Brasília.
Particle-in-cell simulations for fast ignition
NASA Astrophysics Data System (ADS)
Ren, C.; Tonge, J.; Li, G.; Fiuza, F.; Fonseca, R. A.; May, J.; Mori, W. B.; Silva, L. O.; Wang, T. L.; Yan, R.
2008-07-01
The hole-boring scheme in fast ignition is studied via largee-scale, two-dimensional particle-in-cell simulations in two steps. First, laser channeling in millimeter-scale underdense plasmas is simulated. The results show a highly nonlinear and dynamic process involving longitudinal plasma buildup, laser hosing, channel bifurcation and self-correction, and electron heating to relativistic temperatures. The channeling speed is much less than the linear group velocity of the laser. Low-intensity channeling pulses are preferred to minimize the required laser energy. The channel is also shown to significantly increase the transmission of an ignition pulse. In the second step, the interactions of the ignition pulse and a hundred-critical-density plasma are simulated to study hot electron generation and transport. The results show that at ultra-high intensities, I > 5 × 1019W/cm2, most of the electrons transporting energy through 50μm of 100 times critical density plasma are in a relatively low energy range. The fraction of laser power that transits the dense plasma and is deposited into a dense core increases with laser intensity. Overall these results show the promise of using ultra-high-intensity ignition pulses in the hole-boring scheme.
Particle-in-cell Simulation of Langmuir Probes
NASA Astrophysics Data System (ADS)
Iza, Felipe
2005-10-01
Ion kinetics in the sheath and pre-sheath of planar and cylindrical probes has been studied by means of 1-dimensional (1d3v) particle-in-cell Monte Carlo collision simulations. Collisionless and collisional regimes are considered and simulation results (floating potentials and the ion saturation currents) are compared with available theories. As pressure increases, the ion velocity at the sheath edge decreases below the Bohm velocity (uB). For planar probes, this velocity is ˜ uB(1+5λDe/λi) where λDe is the Debye length at the sheath edge and λi the ion mean free path. Although ionization can be neglected in the sheath region, it plays a key role in determining the voltage across the presheath. For planar probes and Maxwellian electrons, this voltage increases rapidly for electron temperatures below ˜2eV. For cylindrical probes, however, the voltage across the presheath can be drastically reduced by the geometrical increase of current density as ions approach the probe. At low pressure, simulation results lie between the Laframboise and the ABR theories. As pressure increases, however, collisions and ionization in the presheath becomes critical in determining the ion flux to the probe at a given bias voltage.
NASA Astrophysics Data System (ADS)
Shon, J. W.; Bateson, W. B.; Hewett, D. W.; Tabak, M.; Baldis, H. A.
1997-11-01
Ultrahigh intensity lasers can ignite ICF capsules with a total energy of a few tens of kilo joules of laser light, and can possibly lead to high gain with as little as 100 kJ(M. Tabak, J. Hammer, M. E. Glinsky, W. L. Kruer, S. C. Wilks and R. J. Mason, Phys. Plasmas, 1, (1994), 1626.). The energy deposition by relativistic electrons, produced in the high-intensity laser-plasma interactions, is a critical issue for the fuel ignition. A new plasma/fluid transport algorithm called GaPH method(W. B. Bateson and D. W. Hewett, J. Comput. Phys., submitted.) is applied to simulate the propagation of suprathermal electrons and their interactions with background plasma. A field solver using Darwin approximation(D. W. Hewett, J. Comput. Phys., 38, (1980), 378.) provides all components of electromagnetic fields. The initial investigation is focused at hot electron transport to the high density core and the characterization of localized energy deposition. The penetration of energetic electrons depends on the formation of charge-neutralising return current, which is a strong function of the electrical conductivity of the background plasma. *Work performed under the auspices of the U.S. DOE by the LLNL under contract no. W-7405-ENG-48.
Classical radiation reaction in particle-in-cell simulations
NASA Astrophysics Data System (ADS)
Vranic, M.; Martins, J. L.; Fonseca, R. A.; Silva, L. O.
2016-07-01
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. For parameters of interest where the classical description of the electron motion is applicable, all the models considered are shown to give comparable results. The Landau and Lifshitz reduced model is chosen for implementation as one of the candidates with the minimal overhead and no additional memory requirements.
Object-Oriented Parallel Particle-in-Cell Code for Beam Dynamics Simulation in Linear Accelerators
Qiang, J.; Ryne, R.D.; Habib, S.; Decky, V.
1999-11-13
In this paper, we present an object-oriented three-dimensional parallel particle-in-cell code for beam dynamics simulation in linear accelerators. A two-dimensional parallel domain decomposition approach is employed within a message passing programming paradigm along with a dynamic load balancing. Implementing object-oriented software design provides the code with better maintainability, reusability, and extensibility compared with conventional structure based code. This also helps to encapsulate the details of communications syntax. Performance tests on SGI/Cray T3E-900 and SGI Origin 2000 machines show good scalability of the object-oriented code. Some important features of this code also include employing symplectic integration with linear maps of external focusing elements and using z as the independent variable, typical in accelerators. A successful application was done to simulate beam transport through three superconducting sections in the APT linac design.
Benchmarking of particle-in-cell simulations with Monte Carlo collisions using LXcat data
NASA Astrophysics Data System (ADS)
Turner, M. M.; Hanzlikova, N.; Eremin, D.; Mussenbrock, T.; Derzsi, A.; Donko, Z.
2011-10-01
As a direct solution of the Boltzmann equation, particle-in-cell simulation potentially yields highly accurate descriptions of low-temperature plasma. However, this accuracy is realised only with correct implementation and appropriately chosen numerical parameters. Particle-in-cell simulation is a computationally intensive procedure. Consequently, efficient implementations that take full advantage of the resources of modern computer hardware are highly desirable. Such hardware typically offers some degree of parallelisation, such as is found in multicored processors and graphical processing units. Implementations exploiting these facilities can be orders of magnitude faster than traditional serialized approaches. However, parallelisation introduces a great increase in algorithmic complexity, and thereby intensifies concerns about correct implementation. In this report we describe a suite of benchmark calculations for particle-in-cell simulations, making use of LXcat cross section data. These bench marks have three aims: (1) to demonstrate correct implementation (2) to facilitate performance comparisons of different implementations and (3) to provide a baseline for other simulation methods. We will discuss the benchmarks, which include measurements of plasma kinetic properties, transport coefficients and discharge simulations, together with the results obtained from a variety of particle-in-cell implementations.
Implementations of mesh refinement schemes for particle-in-cell plasma simulations
Vay, J.-L.; Colella, P.; Friedman, A.; Grote, D.P.; McCorquodale, P.; Serafini, D.B.
2003-10-20
Plasma simulations are often rendered challenging by the disparity of scales in time and in space which must be resolved. When these disparities are in distinctive zones of the simulation region, a method which has proven to be effective in other areas (e.g. fluid dynamics simulations) is the mesh refinement technique. We briefly discuss the challenges posed by coupling this technique with plasma Particle-In-Cell simulations and present two implementations in more detail, with examples.
Global gyrokinetic particle-in-cell simulations of internal kink instabilities
Mishchenko, Alexey; Zocco, Alessandro
2012-12-15
Internal kink instabilities have been studied in straight tokamak geometry employing an electromagnetic gyrokinetic particle-in-cell (PIC) code. The ideal-MHD internal kink mode and the collisionless m=1 tearing mode have been successfully simulated with the PIC code. Diamagnetic effects on the internal kink modes have also been investigated.
NASA Astrophysics Data System (ADS)
Lucca Fabris, Andrea; Young, Christopher; Manente, Marco; Pavarin, Daniele; Cappelli, Mark
2014-10-01
This work aims to provide new insight into the physical mechanisms occurring in the discharge channel and acceleration region of a cusped field plasma thruster through a combined experimental and computational approach. Simulations are performed using the 3D particle-in-cell code F3MPIC, comprised of a PIC core coupled with a finite element electrostatic field solver over an unstructured mesh of tetrahedra. The cusped field structure is also included to resolve magnetized particle dynamics. We perform simulations with two ionization schemes: one where constant particle source rates are assigned to certain regions, and a more rigorous approach based on Monte Carlo collision events. The simulation results reveal correlations between the particle density distributions, electrostatic potential, and magnetic field topology inside the thruster discharge channel that are confirmed through experiments. Laser induced fluorescence measurements have resolved xenon ion velocities at several points near the thruster exit plane. Faraday and floating emissive probe measurements indicate this velocity field is correlated with the measured ion beam current profile and electrostatic potential field. This work sponsored by the U.S.A.F. Office of Scientific Research, with Dr. Mitat Birkan as program manager. F3MPIC developed under the European Union FP7 HPH.com project. C.V.Y. acknowledges the DOE NNSA SSGF fellowship under Contract DE-FC52-08NA28752.
Application of adaptive mesh refinement to particle-in-cell simulations of plasmas and beams
Vay, J.-L.; Colella, P.; Kwan, J.W.; McCorquodale, P.; Serafini, D.B.; Friedman, A.; Grote, D.P.; Westenskow, G.; Adam, J.-C.; Heron, A.; Haber, I.
2003-11-04
Plasma simulations are often rendered challenging by the disparity of scales in time and in space which must be resolved. When these disparities are in distinctive zones of the simulation domain, a method which has proven to be effective in other areas (e.g. fluid dynamics simulations) is the mesh refinement technique. We briefly discuss the challenges posed by coupling this technique with plasma Particle-In-Cell simulations, and present examples of application in Heavy Ion Fusion and related fields which illustrate the effectiveness of the approach. We also report on the status of a collaboration under way at Lawrence Berkeley National Laboratory between the Applied Numerical Algorithms Group (ANAG) and the Heavy Ion Fusion group to upgrade ANAG's mesh refinement library Chombo to include the tools needed by Particle-In-Cell simulation codes.
Particle-in-cell simulations of plasma accelerators and electron-neutral collisions
Bruhwiler, David L.; Giacone, Rodolfo E.; Cary, John R.; Verboncoeur, John P.; Mardahl, Peter; Esarey, Eric; Leemans, W.P.; Shadwick, B.A.
2001-10-01
We present 2-D simulations of both beam-driven and laser-driven plasma wakefield accelerators, using the object-oriented particle-in-cell code XOOPIC, which is time explicit, fully electromagnetic, and capable of running on massively parallel supercomputers. Simulations of laser-driven wakefields with low ({approx}10{sup 16} W/cm{sup 2}) and high ({approx}10{sup 18} W/cm{sup 2}) peak intensity laser pulses are conducted in slab geometry, showing agreement with theory and fluid simulations. Simulations of the E-157 beam wakefield experiment at the Stanford Linear Accelerator Center, in which a 30 GeV electron beam passes through 1 m of preionized lithium plasma, are conducted in cylindrical geometry, obtaining good agreement with previous work. We briefly describe some of the more significant modifications of XOOPIC required by this work, and summarize the issues relevant to modeling relativistic electron-neutral collisions in a particle-in-cell code.
Particle-in-cell simulations of whistler turbulence: A review (Invited)
NASA Astrophysics Data System (ADS)
Gary, S. P.; Chang, O.; Hughes, R. S.; Wang, J.
2013-12-01
Measurements of broadband magnetic fluctuations in the solar wind at wavelengths shorter than the ion inertial length indicate that the primary constituent of such turbulence is kinetic Alfven waves at frequencies well below the proton cyclotron frequency. Nevertheless, it is possible that much higher frequency whistler fluctuations also contribute to this short-wavelength turbulence. To better understand such potential contributions to solar wind turbulence, we have carried out a series of three-dimensional (3D) particle-in-cell (PIC) simulations of whistler turbulence in a collisionless, homogeneous, magnetized plasma [Chang et al., 2011, 2013; Gary et al., 2012]. We here review the properties of these simulations, which address turbulence driven by both an initial ensemble of whistler waves and by the whistler anisotropy instability. Our results include the consequences due to both forward and inverse cascades, to variations in the amplitudes of the initial fluctuations and to variations in βe. We describe the magnetic fluctuation spectral properties as well as dissipation on the electrons, which are heated primarily in directions parallel and antiparallel to the background magnetic field. Magnetic fluctuation energy spectra exhibit a break to steeper slopes which scales as the inverse electron inertial length. The simulation results are consistent with the interpretation that the forward cascade is due to nonlinear three-wave interactions. Chang, O., S. P. Gary, and J. Wang (2011), Whistler turbulence forward cascade: Three-dimensional particle-in-cell simulations, Geophys. Res. Lett., 38, L22102. Chang, O., S. P. Gary, and J. Wang (2013), Whistler turbulence at variable electron beta: Three-dimensional particle-in-cell simulations, J. Geophys. Res., 118, 2824. Gary, S. P., O. Chang, and J. Wang (2012), Forward cascade of whistler turbulence: Three-dimensional particle-in-cell simulations, Ap. J., 755, 142.
Verification of particle-in-cell simulations against exact solutions of kinetic equations
NASA Astrophysics Data System (ADS)
Turner, Miles
2015-09-01
Demonstrating correctness of computer simulations (or verification) has become a matter of increasing concern in recent years. The strongest type of verification is a demonstration that the simulation converges to an exact solution of the mathematical model that is supposed to be solved. Of course, this is possible only if such an exact solution is available. In this paper, we are interested in kinetic simulation using the particle-in-cell method, and consequently a relevant exact solution must be a solution of a kinetic equation. While we know of no such solutions that exercise all the features of a typical particle-in-cell simulation, in this paper we show that the mathematical literature contains several such solutions that involve a large fraction of the functionality of such a code, and which collectively exercise essentially all of the code functionality. These solutions include the plane diode, the neutron criticality problem, and the calculation of ion energy distribution functions in oscillating fields. In each of theses cases, we can show the the particle-in-cell simulation converges to the exact solution in the expected way. These demonstrations are strong evidence of correct implementation. Work supported by Science Foundation Ireland under grant 08/SRC/I1411.
Wang, Huihui; Meng, Lin; Liu, Dagang; Liu, Laqun
2013-12-15
A particle-in-cell/Monte Carlo code is developed to rescale the microwave breakdown theory which is put forward by Vyskrebentsev and Raizer. The results of simulations show that there is a distinct error in this theory when the high energy tail of electron energy distribution function increases. A rescaling factor is proposed to modify this theory, and the change rule of the rescaling factor is presented.
John A. Krommes
2007-10-09
The present state of the theory of fluctuations in gyrokinetic GK plasmas and especially its application to sampling noise in GK particle-in-cell PIC simulations is reviewed. Topics addressed include the Δf method, the fluctuation-dissipation theorem for both classical and GK many-body plasmas, the Klimontovich formalism, sampling noise in PIC simulations, statistical closure for partial differential equations, the theoretical foundations of spectral balance in the presence of arbitrary noise sources, and the derivation of Kadomtsev-type equations from the general formalism.
Particle-in-Cell Simulations of Ponderomotive Particle Acceleration in a Plasma
Startsev, E.A.; McKinstrie, C.J.
2003-06-17
(B204)In previous publications the ponderomotive acceleration of electrons by an idealized (one-dimensional) circularly polarized laser pulse in a plasma was studied analytically. Acceleration gradients of order 100 GeV/m were predicted. To verify the predictions of the theoretical model, a two-dimensional relativistic particle-in-cell code was developed. Simulations of the interaction of a preaccelerated electron bunch with a realistic (two-dimensional)laser pulse in a plasma are presented and analyzed. The simulation results validate the theoretical model and show that significant ponderomotive acceleration is possible.
Enhanced stopping of macro-particles in particle-in-cell simulations
May, J.; Tonge, J.; Ellis, I.; Mori, W. B.; Fiuza, F.; Fonseca, R. A.; Silva, L. O.
2014-05-15
We derive an equation for energy transfer from relativistic charged particles to a cold background plasma appropriate for finite-size particles that are used in particle-in-cell simulation codes. Expressions for one-, two-, and three-dimensional particles are presented, with special attention given to the two-dimensional case. This energy transfer is due to the electric field of the wake set up in the background plasma by the relativistic particle. The enhanced stopping is dependent on the q{sup 2}/m, where q is the charge and m is the mass of the relativistic particle, and therefore simulation macro-particles with large charge but identical q/m will stop more rapidly. The stopping power also depends on the effective particle shape of the macro-particle. These conclusions are verified in particle-in-cell simulations. We present 2D simulations of test particles, relaxation of high-energy tails, and integrated fast ignition simulations showing that the enhanced drag on macro-particles may adversely affect the results of these simulations in a wide range of high-energy density plasma scenarios. We also describe a particle splitting algorithm which can potentially overcome this problem and show its effect in controlling the stopping of macro-particles.
A GeneralizedWeight-Based Particle-In-Cell Simulation Scheme
W.W. Lee, T.G. Jenkins and S. Ethier
2010-02-02
A generalized weight-based particle simulation scheme suitable for simulating magnetized plasmas, where the zeroth-order inhomogeneity is important, is presented. The scheme is an extension of the perturbative simulation schemes developed earlier for particle-in-cell (PIC) simulations. The new scheme is designed to simulate both the perturbed distribution (δf) and the full distribution (full-F) within the same code. The development is based on the concept of multiscale expansion, which separates the scale lengths of the background inhomogeneity from those associated with the perturbed distributions. The potential advantage for such an arrangement is to minimize the particle noise by using δf in the linear stage stage of the simulation, while retaining the flexibility of a full-F capability in the fully nonlinear stage of the development when signals associated with plasma turbulence are at a much higher level than those from the intrinsic particle noise.
Levko, D.; Gurovich, V. Tz.; Krasik, Ya. E.
2012-06-15
The conductivity of the discharge gap during the nanosecond high-voltage pulsed discharge in nitrogen and sulfur hexafluoride is studied using particle-in-cell numerical simulations. It is shown that the conductivity in different locations of the cathode-anode gap is not uniform and that the conductivity is determined by both the runaway and the plasma electrons. In addition, it is shown that runaway electrons generated prior to the virtual cathode formation pre-ionize the discharge gap, which makes it conductive.
Global particle-in-cell simulations of plasma pressure effects on Alfvenic modes
Mishchenko, Alexey; Koenies, Axel; Hatzky, Roman
2011-01-15
Global linear gyrokinetic particle-in-cell simulations of electromagnetic modes in realistic tokamak geometry are reported. The effect of plasma pressure on Alfvenic modes is studied. It is shown that the fast-particle pressure can considerably affect the shear Alfven wave continuum structure and hence the toroidicity-induced gap in the continuum. It is also found that the energetic ions can substantially reduce the growth rate of the ballooning modes (and perhaps completely stabilize them in a certain parameter range). Ballooning modes are found to be the dominant instabilities if the bulk-plasma pressure gradient is large enough.
Sheath and presheath in ion-ion plasmas via particle-in-cell simulation
Meige, A.; Leray, G.; Raimbault, J.-L.; Chabert, P.
2008-02-11
A full particle-in-cell simulation is developed to investigate electron-free plasmas constituted of positive and negative ions under the influence of a dc bias voltage. It is shown that high-voltage sheaths following the classical Child-law sheaths form within a few microseconds (which corresponds to the ion transit time) after the dc voltage is applied. It is also shown that there exists the equivalent of a Bohm criterion where a presheath accelerates the ions collected at one of the electrodes up to the sound speed before they enter the sheath. From an applied perspective, this leads to smaller sheaths than one would expect.
Philippov, Alexander A.; Spitkovsky, Anatoly
2014-04-20
We perform ''first-principles'' relativistic particle-in-cell simulations of aligned pulsar magnetosphere. We allow free escape of particles from the surface of a neutron star and continuously populate the magnetosphere with neutral pair plasma to imitate pair production. As pair plasma supply increases, we observe the transition from a charge-separated ''electrosphere'' solution with trapped plasma and no spin-down to a solution close to the ideal force-free magnetosphere with electromagnetically dominated pulsar wind. We calculate the magnetospheric structure, current distribution, and spin-down power of the neutron star. We also discuss particle acceleration in the equatorial current sheet.
Acceleration of a Particle-in-Cell Code for Space Plasma Simulations with OpenACC
NASA Astrophysics Data System (ADS)
Peng, Ivy Bo; Markidis, Stefano; Vaivads, Andris; Vencels, Juris; Deca, Jan; Lapenta, Giovanni; Hart, Alistair; Laure, Erwin
2015-04-01
We simulate space plasmas with the Particle-in-cell (PIC) method that uses computational particles to mimic electrons and protons in solar wind and in Earth magnetosphere. The magnetic and electric fields are computed by solving the Maxwell's equations on a computational grid. In each PIC simulation step, there are four major phases: interpolation of fields to particles, updating the location and velocity of each particle, interpolation of particles to grids and solving the Maxwell's equations on the grid. We use the iPIC3D code, which was implemented in C++, using both MPI and OpenMP, for our case study. By November 2014, heterogeneous systems using hardware accelerators such as Graphics Processing Unit (GPUs) and the Many Integrated Core (MIC) coprocessors for high performance computing continue growth in the top 500 most powerful supercomputers world wide. Scientific applications for numerical simulations need to adapt to using accelerators to achieve portability and scalability in the coming exascale systems. In our work, we conduct a case study of using OpenACC to offload the computation intensive parts: particle mover and interpolation of particles to grids, in a massively parallel Particle-in-Cell simulation code, iPIC3D, to multi-GPU systems. We use MPI for inter-node communication for halo exchange and communicating particles. We identify the most promising parts suitable for GPUs accelerator by profiling using CrayPAT. We implemented manual deep copy to address the challenges of porting C++ classes to GPU. We document the necessary changes in the exiting algorithms to adapt for GPU computation. We present the challenges and findings as well as our methodology for porting a Particle-in-Cell code to multi-GPU systems using OpenACC. In this work, we will present the challenges, findings and our methodology of porting a Particle-in-Cell code for space applications as follows: We profile the iPIC3D code by Cray Performance Analysis Tool (CrayPAT) and identify
Quasilinear theory and particle-in-cell simulation of proton cyclotron instability
Seough, Jungjoon E-mail: yoonp@umd.edu; Yoon, Peter H. E-mail: yoonp@umd.edu; Hwang, Junga E-mail: yoonp@umd.edu
2014-06-15
The electromagnetic ion (proton) cyclotron instability is important for regulating the excessive development of perpendicular temperature anisotropy in the solar wind, for instance, when it is compressed in the vicinity of the Earth's magnetosheath environment. A recent letter [Seough et al., Phys. Rev. Lett. 110, 071103 (2013)] successfully employed the quasilinear kinetic theory to explain the observed temperature anisotropy upper bound. The present paper rigorously examines the reliability of the quasilinear theory by making a direct comparison against results from the particle-in-cell simulation method. It is found that the quasilinear approach is indeed a valid first-cut theoretical tool in the study of proton cyclotron instability.
Particle-in-cell simulations on spontaneous thermal magnetic field fluctuations
Simões, F. J. R. Jr.; Pavan, J.; Gaelzer, R.; Ziebell, L. F.; Yoon, P. H.
2013-10-15
In this paper an electromagnetic particle code is used to investigate the spontaneous thermal emission. Specifically we perform particle-in-cell simulations employing a non-relativistic isotropic Maxwellian particle distribution to show that thermal fluctuations are related to the origin of spontaneous magnetic field fluctuation. These thermal fluctuations can become seed for further amplification mechanisms and thus be considered at the origin of the cosmological magnetic field, at microgauss levels. Our numerical results are in accordance with theoretical results presented in the literature.
Numerical thermalization in particle-in-cell simulations with Monte-Carlo collisions
Lai, P. Y.; Lin, T. Y.; Lin-Liu, Y. R.; Chen, S. H.
2014-12-15
Numerical thermalization in collisional one-dimensional (1D) electrostatic (ES) particle-in-cell (PIC) simulations was investigated. Two collision models, the pitch-angle scattering of electrons by the stationary ion background and large-angle collisions between the electrons and the neutral background, were included in the PIC simulation using Monte-Carlo methods. The numerical results show that the thermalization times in both models were considerably reduced by the additional Monte-Carlo collisions as demonstrated by comparisons with Turner's previous simulation results based on a head-on collision model [M. M. Turner, Phys. Plasmas 13, 033506 (2006)]. However, the breakdown of Dawson's scaling law in the collisional 1D ES PIC simulation is more complicated than that was observed by Turner, and the revised scaling law of the numerical thermalization time with numerical parameters are derived on the basis of the simulation results obtained in this study.
Numerical thermalization in particle-in-cell simulations with Monte-Carlo collisions
NASA Astrophysics Data System (ADS)
Lai, P. Y.; Lin, T. Y.; Lin-Liu, Y. R.; Chen, S. H.
2014-12-01
Numerical thermalization in collisional one-dimensional (1D) electrostatic (ES) particle-in-cell (PIC) simulations was investigated. Two collision models, the pitch-angle scattering of electrons by the stationary ion background and large-angle collisions between the electrons and the neutral background, were included in the PIC simulation using Monte-Carlo methods. The numerical results show that the thermalization times in both models were considerably reduced by the additional Monte-Carlo collisions as demonstrated by comparisons with Turner's previous simulation results based on a head-on collision model [M. M. Turner, Phys. Plasmas 13, 033506 (2006)]. However, the breakdown of Dawson's scaling law in the collisional 1D ES PIC simulation is more complicated than that was observed by Turner, and the revised scaling law of the numerical thermalization time with numerical parameters are derived on the basis of the simulation results obtained in this study.
Quasisteady and steady states in global gyrokinetic particle-in-cell simulations
Jolliet, S.; McMillan, B. F.; Vernay, T.; Villard, L.; Bottino, A.; Angelino, P.
2009-05-15
Collisionless delta-f gyrokinetic particle-in-cell simulations suffer from the entropy paradox, in which the entropy grows linearly in time while low-order moments are saturated. As a consequence, these simulations do not reach a steady state and are unsuited to make quantitative predictions. A solution to this issue is the introduction of artificial dissipation. The notion of steady state in gyrokinetic simulations is studied by deriving an evolution equation for the fluctuation entropy and applying it to the global collisionless particle-in-cell code ORB5 [S. Jolliet et al., Comput. Phys. Commun. 177, 409 (2007)]. It is shown that a recently implemented noise-control algorithm [B. F. McMillan et al., Phys. Plasmas 15, 052308 (2008)] based on a W-stat provides the necessary dissipation to reach a steady state. The two interesting situations of decaying and driven turbulence are considered. In addition, it is shown that a separate heating algorithm, not based on a W-stat, does not lead to a statistical steady state.
Particle-In-Cell simulations of high pressure plasmas using graphics processing units
NASA Astrophysics Data System (ADS)
Gebhardt, Markus; Atteln, Frank; Brinkmann, Ralf Peter; Mussenbrock, Thomas; Mertmann, Philipp; Awakowicz, Peter
2009-10-01
Particle-In-Cell (PIC) simulations are widely used to understand the fundamental phenomena in low-temperature plasmas. Particularly plasmas at very low gas pressures are studied using PIC methods. The inherent drawback of these methods is that they are very time consuming -- certain stability conditions has to be satisfied. This holds even more for the PIC simulation of high pressure plasmas due to the very high collision rates. The simulations take up to very much time to run on standard computers and require the help of computer clusters or super computers. Recent advances in the field of graphics processing units (GPUs) provides every personal computer with a highly parallel multi processor architecture for very little money. This architecture is freely programmable and can be used to implement a wide class of problems. In this paper we present the concepts of a fully parallel PIC simulation of high pressure plasmas using the benefits of GPU programming.
Electron-Anode Interactions in Particle-in-Cell Simulations of Applied-B Ion Diodes
Bailey, J.E.; Cuneo, M.D.; Johnson, D.J.; Mehlhorn, T.A.; Pointon, T.D.; Renk, T.J.; Stygar, W.A.; Vesey, R.A.
1998-11-12
Particle-in-cell simulations of applied-B ion diodes using the QUICKSILVER code have been augmented with Monte Carlo calculations of electron-anode interactions (reflection and energy deposition). Extraction diode simulations demonstrate a link between the instability evolution and increased electron loss and anode heating. Simulations of radial and extraction ion diodes show spatial non-uniformity in the predicted electron loss profile leading to hot spots on the anode that rapidly exceed the 350-450 {degree}C range, known to be sufficient for plasma formation on electron-bombarded surfaces. Thermal resorption calculations indicate complete resorption of contaminants with 15-20 kcal/mole binding energies in high-dose regions of the anode during the power pulse. Comparisons of parasitic ion emission simulations and experiment show agreement in some aspects; but also highlight the need for better ion source, plasma, and neutral gas models.
Model and particle-in-cell simulation of ion energy distribution in collisionless sheath
Zhou, Zhuwen; Kong, Bo; Luo, Yuee; Chen, Deliang; Wang, Yuansheng
2015-06-15
In this paper, we propose a self-consistent theoretical model, which is described by the ion energy distributions (IEDs) in collisionless sheaths, and the analytical results for different combined dc/radio frequency (rf) capacitive coupled plasma discharge cases, including sheath voltage errors analysis, are compared with the results of numerical simulations using a one-dimensional plane-parallel particle-in-cell (PIC) simulation. The IEDs in collisionless sheaths are performed on combination of dc/rf voltage sources electrodes discharge using argon as the process gas. The incident ions on the grounded electrode are separated, according to their different radio frequencies, and dc voltages on a separated electrode, the IEDs, and widths of energy in sheath and the plasma sheath thickness are discussed. The IEDs, the IED widths, and sheath voltages by the theoretical model are investigated and show good agreement with PIC simulations.
Relativistic Particle-In-Cell Simulations of Particle Accleration in Relativistic Jets
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Hardee, P.; Mizuno, Y.; Medvedev, M.; Hartmann, D. H.; Fishman, J. F.
2008-01-01
Highly accelerated particles are observed in astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), microquasars, and Gamma-Ray Bursts (GRBs). Particle-In-Cell (PIC) simulations of relativistic electron-ion and electron-positron jets injected into a stationary medium show that efficient acceleration occurs downstream in the jet. In collisionless relativistic shocks particle acceleration is due to plasma waves and their associated instabilities, e.g., the Buneman instability, other two-stream instabilities, and the Weibel (filamentation) instability. Simulations show that the Weibel instability is responsible for generating and amplifying highly non-uniform, small-scale magnetic fields. The instability depends on strength and direction of the magnetic field. Particles in relativistic jets may be accelerated in a complicated dynamics of relativistic jets with magnetic field. We present results of our recent PIC simulations.
Particle in cell simulation of laser-accelerated proton beams for radiation therapy.
Fourkal, E; Shahine, B; Ding, M; Li, J S; Tajima, T; Ma, C M
2002-12-01
In this article we present the results of particle in cell (PIC) simulations of laser plasma interaction for proton acceleration for radiation therapy treatments. We show that under optimal interaction conditions protons can be accelerated up to relativistic energies of 300 MeV by a petawatt laser field. The proton acceleration is due to the dragging Coulomb force arising from charge separation induced by the ponderomotive pressure (light pressure) of high-intensity laser. The proton energy and phase space distribution functions obtained from the PIC simulations are used in the calculations of dose distributions using the GEANT Monte Carlo simulation code. Because of the broad energy and angular spectra of the protons, a compact particle selection and beam collimation system will be needed to generate small beams of polyenergetic protons for intensity modulated proton therapy. PMID:12512712
NASA Astrophysics Data System (ADS)
Tsiklauri, D.; Thurgood, J. O.
2015-12-01
first co-author Jonathan O. Thurgood (QMUL) The simulation of three-wave interaction based plasma emission, an underlying mechanism for type III solar radio bursts, is a challenging task requiring fully-kinetic, multi-dimensional models. This paper aims to resolve a contradiction in past attempts, whereby some authors report that no such processes occur and others draw conflicting conclusions, by using 2D, fully kinetic, particle-in-cell simulations of relaxing electron beams. Here we present the results of particle-in-cell simulations which for different physical parameters permit or prohibit the plasma emission. We show that the possibility of plasma emission is contingent upon the frequency of the initial electrostatic waves generated by the bump-in-tail instability, and that these waves may be prohibited from participating in the necessary three-wave interactions due to the frequency beat requirements. We caution against simulating astrophysical radio bursts using unrealistically dense beams (a common approach which reduces run time), as the resulting non-Langmuir characteristics of the initial wave modes significantly suppresses the emission. Comparison of our results indicates that, contrary to the suggestions of previous authors, a plasma emission mechanism based on two counter-propagating beams is unnecessary in astrophysical context. Finally, we also consider the action of the Weibel instability, which generates an electromagnetic beam mode. As this provides a stronger contribution to electromagnetic energy than the emission, we stress that evidence of plasma emission in simulations must disentangle the two contributions and not simply interpret changes in total electromagnetic energy as the evidence of plasma emission. In summary, we present the first self-consistent demonstration of fundamental and harmonic plasma emission from a single-beam system via fully kinetic numerical simulation. Pre-print can be found at http://astro.qmul.ac.uk/~tsiklauri/jtdt1
Particle-in-Cell laser-plasma simulation on Xeon Phi coprocessors
NASA Astrophysics Data System (ADS)
Surmin, I. A.; Bastrakov, S. I.; Efimenko, E. S.; Gonoskov, A. A.; Korzhimanov, A. V.; Meyerov, I. B.
2016-05-01
This paper concerns the development of a high-performance implementation of the Particle-in-Cell method for plasma simulation on Intel Xeon Phi coprocessors. We discuss the suitability of the method for Xeon Phi architecture and present our experience in the porting and optimization of the existing parallel Particle-in-Cell code PICADOR. Direct porting without code modification gives performance on Xeon Phi close to that of an 8-core CPU on a benchmark problem with 50 particles per cell. We demonstrate step-by-step optimization techniques, such as improving data locality, enhancing parallelization efficiency and vectorization leading to an overall 4.2 × speedup on CPU and 7.5 × on Xeon Phi compared to the baseline version. The optimized version achieves 16.9 ns per particle update on an Intel Xeon E5-2660 CPU and 9.3 ns per particle update on an Intel Xeon Phi 5110P. For a real problem of laser ion acceleration in targets with surface grating, where a large number of macroparticles per cell is required, the speedup of Xeon Phi compared to CPU is 1.6 ×.
Load management strategy for Particle-In-Cell simulations in high energy particle acceleration
NASA Astrophysics Data System (ADS)
Beck, A.; Frederiksen, J. T.; Dérouillat, J.
2016-09-01
In the wake of the intense effort made for the experimental CILEX project, numerical simulation campaigns 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 limitations both in terms of physical accuracy and computational performances. These limitations are illustrated 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-performance PIC code for high energy particle acceleration.
Particle-in-cell simulations of ion-acoustic waves with application to Saturn's magnetosphere
Koen, Etienne J.; Collier, Andrew B.; Hellberg, Manfred A.; Maharaj, Shimul K.
2014-07-15
Using a particle-in-cell simulation, the dispersion and growth rate of the ion-acoustic mode are investigated for a plasma containing two ion and two electron components. The electron velocities are modelled by a combination of two kappa distributions, as found in Saturn's magnetosphere. The ion components consist of adiabatic ions and an ultra-low density ion beam to drive a very weak instability, thereby ensuring observable waves. The ion-acoustic mode is explored for a range of parameter values such as κ, temperature ratio, and density ratio of the two electron components. The phase speed, frequency range, and growth rate of the mode are investigated. Simulations of double-kappa two-temperature plasmas typical of the three regions of Saturn's magnetosphere are also presented and analysed.
Plasma electron hole kinematics. II. Hole tracking Particle-In-Cell simulation
NASA Astrophysics Data System (ADS)
Zhou, C.; Hutchinson, I. H.
2016-08-01
The kinematics of a 1-D electron hole is studied using a novel Particle-In-Cell simulation code. A hole tracking technique enables us to follow the trajectory of a fast-moving solitary hole and study quantitatively hole acceleration and coupling to ions. We observe a transient at the initial stage of hole formation when the hole accelerates to several times the cold-ion sound speed. Artificially imposing slow ion speed changes on a fully formed hole causes its velocity to change even when the ion stream speed in the hole frame greatly exceeds the ion thermal speed, so there are no reflected ions. The behavior that we observe in numerical simulations agrees very well with our analytic theory of hole momentum conservation and the effects of "jetting."
Particle in cell simulation of a radiofrequency plasma jet expanding in vacuum
Charles, C. Hawkins, R.; Boswell, R. W.
2015-03-02
The effect of a pressure gradient (∼133 Pa–0.133 Pa) on electron and ion energy distributions in a radiofrequency (rf at 13.56 MHz) argon plasma jet is studied using a 1D-3v Particle In Cell (PIC) simulation. The PIC domain is three times that of the 0.018 m long plasma cavity and the total simulation time is 1 ms. Ion heating and acceleration up to a drift velocity about 2000 m s{sup −1} are measured along the jet's main expansion axis. Elastic and charge exchange ion-neutral collisions histograms computed at equilibrium during 0.74 ms show that charge exchange collisions act as the main neutral heating mechanism.
Three-dimensional particle-in-cell simulations of laser channeling in fast ignition
Li, G.; Yan, R.; Ren, C.; Tonge, J.; Mori, W. B.
2011-04-15
Three-dimensional particle-in-cell simulations with an underdense plasma length up to 540 {mu}m are presented to show that laser channeling in 3D is qualitatively similar to that shown in previous 2D simulations [Li et al., Phys. Rev. Lett. 100, 125002 (2008)], but quantitative differences exist. Due to a larger laser ponderomotive force resulting from self-focusing and easier channel formation in 3D, the channeling speed in 3D is larger compared to 2D. Laser hosing and channel bending are also observed in 3D. Decoupling of the laser and plasma is observed when the electrons are heated to relativistic temperatures during the channeling process.
Particle-in-cell simulations for virtual cathode oscillator including foil ablation effects
NASA Astrophysics Data System (ADS)
Singh, Gursharn; Chaturvedi, S.
2011-06-01
We have performed two- and three-dimensional, relativistic, electromagnetic, particle-in-cell simulations of an axially extracted virtual cathode oscillator (vircator). The simulations include, for the first time, self-consistent dynamics of the anode foil under the influence of the intense electron beam. This yields the variation of microwave output power as a function of time, including the role of anode ablation and anode-cathode gap closure. These simulations have been done using locally developed particle-in-cell (PIC) codes. The codes have been validated using two vircator designs available from the literature. The simulations reported in the present paper take account of foil ablation due to the intense electron flux, the resulting plasma expansion and shorting of the anode-cathode gap. The variation in anode transparency due to plasma formation is automatically taken into account. We find that damage is generally higher near the axis. Also, at all radial positions, there is little damage in the early stages, followed by a period of rapid erosion, followed in turn by low damage rates. A physical explanation has been given for these trends. As a result of gap closure due to plasma formation from the foil, the output microwave power initially increases, reaches a near-flat-top and then decreases steadily, reaching a minimum around 230 ns. This is consistent with a typical plasma expansion velocity of ˜2 cm/μs reported in the literature. We also find a significant variation in the dominant output frequency, from 6.3 to 7.6 GHz. This variation is small as long as the plasma density is small, up to ˜40 ns. As the AK gap starts filling with plasma, there is a steady increase in this frequency.
Discrete Particle Noise in Particle-in-Cell Simulations of Plasma Microturbulence
Nevins, W M; Dimits, A; Hammett, G
2005-05-24
Recent gyrokinetic simulations of electron temperature gradient (ETG) turbulence with flux-tube continuum codes vs. the global particle-in-cell (PIC) code GTC yielded different results despite similar plasma parameters. Differences between the simulations results were attributed to insufficient phase-space resolution and novel physics associated with toroidicity and/or global simulations. We have reproduced the results of the global PIC code using the flux-tube PIC code PG3EQ, thereby eliminating global effects as the cause of the discrepancy. We show that the late-time decay of ETG turbulence and the steady-state heat transport observed in these PIC simulations results from discrete particle noise. Discrete particle noise is a numerical artifact, so both these PG3EQ simulations and the previous GTC simulations have nothing to say about steady-state ETG turbulence and the associated anomalous heat transport. In the course of this work we develop three diagnostics which can help to determine if a particular PIC simulation has become dominated by discrete particle noise.
Half-Cell RF Gun Simulations with the Electromagnetic Particle-in-Cell Code VORPAL
Paul, K.; Dimitrov, D. A.; Busby, R.; Bruhwiler, D. L.; Smithe, D.; Cary, J. R.; Kewisch, J.; Kayran, D.; Calaga, R.; Ben-Zvi, I.
2009-01-22
We have simulated Brookhaven National Laboratory's half-cell superconducting RF gun design for a proposed high-current ERL using the three-dimensional, electromagnetic particle-in-cell code VORPAL. VORPAL computes the fully self-consistent electromagnetic fields produced by the electron bunches, meaning that it accurately models space-charge effects as well as bunch-to-bunch beam loading effects and the effects of higher-order cavity modes, though these are beyond the scope of this paper. We compare results from VORPAL to the well-established space-charge code PARMELA, using RF fields produced by SUPERFISH, as a benchmarking exercise in which the two codes should agree well.
Whistler turbulence forward vs. inverse cascade. Three-dimensional particle-in-cell simulations
Chang, Ouliang; Gary, S. Peter; Wang, Joseph
2015-02-12
In this study, we present the results of the first fully three-dimensional particle-in-cell simulations of decaying whistler turbulence in a magnetized, homogeneous, collisionless plasma in which both forward cascades to shorter wavelengths, and inverse cascades to longer wavelengths are allowed to proceed. For the electron beta βe = 0.10 initial value considered here, the early-time rate of inverse cascade is very much smaller than the rate of forward cascade, so that at late times the fluctuation energy in the regime of the inverse cascade is much weaker than that in the forward cascade regime. Similarly, the wavevector anisotropy in themore » inverse cascade regime is much weaker than that in the forward cascade regime.« less
Half-Cell RF Gun Simulations with the Electromagnetic Particle-in-Cell Code VORPAL
NASA Astrophysics Data System (ADS)
Paul, K.; Dimitrov, D. A.; Busby, R.; Bruhwiler, D. L.; Smithe, D.; Cary, J. R.; Kewisch, J.; Kayran, D.; Calaga, R.; Ben-Zvi, I.
2009-01-01
We have simulated Brookhaven National Laboratory's half-cell superconducting RF gun design for a proposed high-current ERL using the three-dimensional, electromagnetic particle-in-cell code VORPAL. VORPAL computes the fully self-consistent electromagnetic fields produced by the electron bunches, meaning that it accurately models space-charge effects as well as bunch-to-bunch beam loading effects and the effects of higher-order cavity modes, though these are beyond the scope of this paper. We compare results from VORPAL to the well-established space-charge code PARMELA, using RF fields produced by SUPERFISH, as a benchmarking exercise in which the two codes should agree well.
Whistler turbulence forward vs. inverse cascade. Three-dimensional particle-in-cell simulations
Chang, Ouliang; Gary, S. Peter; Wang, Joseph
2015-02-12
In this study, we present the results of the first fully three-dimensional particle-in-cell simulations of decaying whistler turbulence in a magnetized, homogeneous, collisionless plasma in which both forward cascades to shorter wavelengths, and inverse cascades to longer wavelengths are allowed to proceed. For the electron beta β_{e} = 0.10 initial value considered here, the early-time rate of inverse cascade is very much smaller than the rate of forward cascade, so that at late times the fluctuation energy in the regime of the inverse cascade is much weaker than that in the forward cascade regime. Similarly, the wavevector anisotropy in the inverse cascade regime is much weaker than that in the forward cascade regime.
Particle-in-cell simulations of electron energization in laser-driven magnetic reconnection
NASA Astrophysics Data System (ADS)
Lu, San; Lu, Quanming; Guo, Fan; Sheng, Zhengming; Wang, Huanyu; Wang, Shui
2016-01-01
Electrons can be energized during laser-driven magnetic reconnection, and the energized electrons form three super-Alfvénic electron jets in the outflow region (Lu et al 2014 New J. Phys. 16 083021). In this paper, by performing two-dimensional particle-in-cell simulations, we find that the electrons can also be significantly energized before magnetic reconnection occurs. When two plasma bubbles with toroidal magnetic fields expand and squeeze each other, the electrons in the magnetic ribbons are energized through betatron acceleration due to the enhancement of the magnetic field, and an electron temperature anisotropy {T}{{e}\\perp }\\gt {T}{{e}| | } develops. Meanwhile, some electrons are trapped and bounced repeatedly between the two expanding/approaching bubbles and get energized through a Fermi-like process. The energization before magnetic reconnection is more significant (or important) than that during magnetic reconnection.
New Particle-in-Cell Code for Numerical Simulation of Coherent Synchrotron Radiation
Balsa Terzic, Rui Li
2010-05-01
We present a first look at the new code for self-consistent, 2D simulations of beam dynamics affected by the coherent synchrotron radiation. The code is of the particle-in-cell variety: the beam bunch is sampled by point-charge particles, which are deposited on the grid; the corresponding forces on the grid are then computed using retarded potentials according to causality, and interpolated so as to advance the particles in time. The retarded potentials are evaluated by integrating over the 2D path history of the bunch, with the charge and current density at the retarded time obtained from interpolation of the particle distributions recorded at discrete timesteps. The code is benchmarked against analytical results obtained for a rigid-line bunch. We also outline the features and applications which are currently being developed.
Chang, Ouliang; Gary, S. Peter; Wang, Joseph E-mail: pgary@lanl.gov
2015-02-20
We present the results of the first fully three-dimensional particle-in-cell simulations of decaying whistler turbulence in a magnetized, homogeneous, collisionless plasma in which both forward cascades to shorter wavelengths, and inverse cascades to longer wavelengths are allowed to proceed. For the electron beta β {sub e} = 0.10 initial value considered here, the early-time rate of inverse cascade is very much smaller than the rate of forward cascade, so that at late times the fluctuation energy in the regime of the inverse cascade is much weaker than that in the forward cascade regime. Similarly, the wavevector anisotropy in the inverse cascade regime is much weaker than that in the forward cascade regime.
NASA Astrophysics Data System (ADS)
Chen, Guangye; Chacon, Luis
2015-11-01
We discuss a new, conservative, fully implicit 2D3V Vlasov-Darwin particle-in-cell algorithm in curvilinear geometry for non-radiative, electromagnetic kinetic plasma simulations. Unlike standard explicit PIC schemes, fully implicit PIC algorithms are unconditionally stable and allow exact discrete energy and charge conservation. Here, we extend these algorithms to curvilinear geometry. The algorithm retains its exact conservation properties in curvilinear grids. The nonlinear iteration is effectively accelerated with a fluid preconditioner for weakly to modestly magnetized plasmas, which allows efficient use of large timesteps, O (√{mi/me}c/veT) larger than the explicit CFL. In this presentation, we will introduce the main algorithmic components of the approach, and demonstrate the accuracy and efficiency properties of the algorithm with various numerical experiments in 1D (slow shock) and 2D (island coalescense).
NASA Astrophysics Data System (ADS)
Chacon, Luis; Chen, Guangye
2015-11-01
We discuss a new, implicit 2D-3V particle-in-cell (PIC) algorithm for non-radiative, electromagnetic kinetic plasma simulations, based on the Vlasov-Darwin model. The Vlasov-Darwin model avoids radiative noise issues, but is elliptic and renders explicit time integration unconditionally unstable. Absolutely stable, fully implicit, charge and energy conserving PIC algorithms for both electrostatic and electromagnetic regimes have been recently developed in 1D. In this study, we build on these recent successes to develop a multi-D, fully implicit PIC algorithm for the Vlasov-Darwin model. The algorithm conserves global energy, local charge, and particle canonical-momentum exactly. The nonlinear iteration is effectively accelerated with a fluid preconditioner, allowing the efficient use of large timesteps compared to the explicit CFL. We demonstrate the potential of the approach with various numerical examples in 2D-3V.
Wavelet-based Poisson Solver for use in Particle-In-CellSimulations
Terzic, B.; Mihalcea, D.; Bohn, C.L.; Pogorelov, I.V.
2005-05-13
We report on a successful implementation of a wavelet based Poisson solver for use in 3D particle-in-cell (PIC) simulations. One new aspect of our algorithm is its ability to treat the general(inhomogeneous) Dirichlet boundary conditions (BCs). The solver harnesses advantages afforded by the wavelet formulation, such as sparsity of operators and data sets, existence of effective preconditioners, and the ability simultaneously to remove numerical noise and further compress relevant data sets. Having tested our method as a stand-alone solver on two model problems, we merged it into IMPACT-T to obtain a fully functional serial PIC code. We present and discuss preliminary results of application of the new code to the modeling of the Fermilab/NICADD and AES/JLab photoinjectors.
Two Dimensional Particle-In-Cell Code for Simulation of Quantum Plasmas
NASA Astrophysics Data System (ADS)
Decyk, V. K.; Tonge, J.; Dauger, D. E.
2002-11-01
We have developed a two dimensional code for simulating quantum plasmas (1). This unique code propagates many quantum particles forward in time self-consistently using the semi-classical approximation. Because of this it can model the statistical properties of interacting quantum particles. We are currently testing this code using small numbers of particles with model problems which we can use to verify the accuracy of the code. The goal is to model from first principles the statistical properties of plasmas where quantum mechanics plays a role such as hot high density plasmas found in stellar interiors (2). (1) D. Dauger, Semiclassical Modeling of Quantum-Mechanical Multiparticle Systems using Parallel Particle-In-Cell Methods, PHD Thesis (2) M. Opher et. al. , Nuclear reaction rates and energy in stellar plasmas: The effect of highly damped modes, Physics of Plasma, 8, No. 5, p. 2454 Sponsored by NSF
Particle-in-cell simulations of particle energization from low Mach number fast mode shocks
NASA Astrophysics Data System (ADS)
Park, Jaehong; Workman, Jared; Blackman, Eric; Ren, Chuang; Siller, Robert
2012-10-01
Low Mach number, high plasma beta, fast mode shocks likely occur in the outflows from reconnection sites associated with solar flares. These shocks are sites of particle energization with observable consequences, but there has been much less work on understanding the underlying physics compared to that of Mach number shocks. To make progress, we have simulated a low Mach number/high beta shock using 2D particle-in-cell simulations with a ``moving wall'' method and studied the shock structure and particle acceleration processes therein [Park et. al (2012), Phys. Plasmas, 19, 062904]. The moving wall method can control the shock speed in the simulation frame to allow smaller simulation boxes and longer simulation times. We found that the modified two-stream instability in the shock transition region is responsible for shock sustenance via turbulent dissipation and entropy creation throughout the downstream region long after the initial shock formation. Particle tracking and the particle energy distributions show that both electrons and ions participate in shock-drift-acceleration (SDA). The simulation combined with a theoretical analysis reveals a two-temperature Maxwellian distribution for the electron energy distribution via SDA.
On energy and momentum conservation in particle-in-cell plasma simulation
NASA Astrophysics Data System (ADS)
Brackbill, J. U.
2016-07-01
Particle-in-cell (PIC) plasma simulations are a productive and valued tool for the study of nonlinear plasma phenomena, yet there are basic questions about the simulation methods themselves that remain unanswered. Here we study energy and momentum conservation by PIC. We employ both analysis and simulations of one-dimensional, electrostatic plasmas to understand why PIC simulations are either energy or momentum conserving but not both, what role a numerical stability plays in non-conservation, and how errors in conservation scale with the numerical parameters. Conserving both momentum and energy make it possible to model problems such as Jeans'-type equilibria. Avoiding numerical instability is useful, but so is being able to identify when its effect on the results may be important. Designing simulations to achieve the best possible accuracy with the least expenditure of effort requires results on the scaling of error with the numerical parameters. Our results identify the central role of Gauss' law in conservation of both momentum and energy, and the significant differences in numerical stability and error scaling between energy-conserving and momentum-conserving simulations.
NASA Astrophysics Data System (ADS)
Feng, Bing
Electron cloud instabilities have been observed in many circular accelerators around the world and raised concerns of future accelerators and possible upgrades. In this thesis, the electron cloud instabilities are studied with the quasi-static particle-in-cell (PIC) code QuickPIC. Modeling in three-dimensions the long timescale propagation of beam in electron clouds in circular accelerators requires faster and more efficient simulation codes. Thousands of processors are easily available for parallel computations. However, it is not straightforward to increase the effective speed of the simulation by running the same problem size on an increasingly number of processors because there is a limit to domain size in the decomposition of the two-dimensional part of the code. A pipelining algorithm applied on the fully parallelized particle-in-cell code QuickPIC is implemented to overcome this limit. The pipelining algorithm uses multiple groups of processors and optimizes the job allocation on the processors in parallel computing. With this novel algorithm, it is possible to use on the order of 102 processors, and to expand the scale and the speed of the simulation with QuickPIC by a similar factor. In addition to the efficiency improvement with the pipelining algorithm, the fidelity of QuickPIC is enhanced by adding two physics models, the beam space charge effect and the dispersion effect. Simulation of two specific circular machines is performed with the enhanced QuickPIC. First, the proposed upgrade to the Fermilab Main Injector is studied with an eye upon guiding the design of the upgrade and code validation. Moderate emittance growth is observed for the upgrade of increasing the bunch population by 5 times. But the simulation also shows that increasing the beam energy from 8GeV to 20GeV or above can effectively limit the emittance growth. Then the enhanced QuickPIC is used to simulate the electron cloud effect on electron beam in the Cornell Energy Recovery Linac
Two- and three-dimensional particle-in-cell simulations of ExB discharges
NASA Astrophysics Data System (ADS)
Carlsson, Johan; Kaganovich, Igor; Khrabrov, Alexander; Raitses, Yevgeny; Smolyakov, Andrei
2015-09-01
The Large-Scale Plasma (LSP) Particle-In-Cell with Monte-Carlo Collisions (PIC-MCC) code has been used to simulate several crossed-field (ExB) discharges in two and three dimensions. Two-dimensional (2D) simulations of a cold-cathode electric discharge with power-electronics applications and a Penning discharge will be presented. Three-dimensional (3D) simulation results of a cylindrical Hall thruster with scaled plasma parameters will also be shown and compared to experiment [Ellison2012]. To enable the 2D and 3D ExB discharge simulations, several improvements to the LSP code were made, including implementation of a new electrostatic field solver, external-circuit model and models for particle injection and secondary-electron emission. To ensure the correctness of the collision models used (and particularly important for the cold-cathode-discharge simulations), validation and code benchmarking was done with the LSP and EDIPIC codes in 1D for a glow discharge. Results and conclusions will be presented. Work funded by AFOSR and ARPA-E.
Two- and three-dimensional particle-in-cell simulations of ExB discharges
NASA Astrophysics Data System (ADS)
Carlsson, Johan; Kaganovich, Igor D.; Khrabrov, Alexander V.; Raitses, Yevgeny; Smolyakov, Andrei
2015-11-01
The Large-Scale Plasma (LSP) Particle-In-Cell with Monte-Carlo Collisions (PIC-MCC) code has been used to simulate several crossed-field (ExB) discharges in two and three dimensions. Two-dimensional (2D) simulations of a cold-cathode electric discharge with power-electronics applications and a Penning discharge will be presented. Three-dimensional (3D) simulation results of a cylindrical Hall thruster with scaled plasma parameters will also be shown and compared to experiment [Ellison2012]. To enable the 2D and 3D ExB discharge simulations, several improvements to the LSP code were made, including implementation of a new electrostatic field solver, external-circuit model and models for particle injection and secondary-electron emission. To ensure the correctness of the collision models used (and particularly important for the cold-cathode-discharge simulations), validation and code benchmarking was done with the LSP and EDIPIC codes in 1D for a glow discharge. Results and conclusions will be presented. L. Ellison, Y. Raitses and N. J. Fisch, ``Cross-field electron transport induced by a rotating spoke in a cylindrical Hall thruster,'' Physics of Plasmas 19, 013503 (2012). Research supported by the U.S. Air Force Office of Scientific Research.
Kinetic properties of the particle-in-cell simulation of a Lorentz plasma
NASA Astrophysics Data System (ADS)
Lin-Liu, Y. R.; Lin, T. Y.; Chen, S. H.
2010-11-01
The phenomenon of numerical thermalization in the standard particle-in-cell (PIC) simulation of Vlasov plasmas has been extensively studied at the early stage of its development [1] and was considered well understood. However, it was recently reported [2] that the well-established scaling law for the thermalization time could be compromised by the presence of an additional stochastic force acting on the particles, which is used to simulate collisional processes in a weakly ionized gas. In the present work, we are interested in the problem of electron-ion collisions in a fully ionized plasma. We investigate the thermal relaxation phenomenon in the PIC simulation of a Lorentz plasma in one dimension [3]. The pitch-angle scattering of the electrons by the stationary ion background is modeled by a Monte-Carlo algorithm. The numerical results obtained indicate that the thermal relaxation time is proportional to ND (the number of particles per Debye length), and not ND^2 as in the standard PIC simulations. Our results appear to complement those found by the previous study [2]. [4pt] [1] C. K. Birdsall and A. B. Langdon, Plasma Physics via Computer Simulation (McGraw-Hill, New York, 1985). [0pt] [2] M. M. Turner, Phys. of Plasmas 13, 033506 (2006). [0pt] [3] R. Shanny, J. M. Dawson, and J. M. Greene, Phys. of Fluids 10, 1281 (1967).
Electron and ion heating by whistler turbulence: Three-dimensional particle-in-cell simulations
Hughes, R. Scott; Gary, S. Peter; Wang, Joseph
2014-12-17
Three-dimensional particle-in-cell simulations of decaying whistler turbulence are carried out on a collisionless, homogeneous, magnetized, electron-ion plasma model. In addition, the simulations use an initial ensemble of relatively long wavelength whistler modes with a broad range of initial propagation directions with an initial electron beta βe = 0.05. The computations follow the temporal evolution of the fluctuations as they cascade into broadband turbulent spectra at shorter wavelengths. Three simulations correspond to successively larger simulation boxes and successively longer wavelengths of the initial fluctuations. The computations confirm previous results showing electron heating is preferentially parallel to the background magnetic field Bo,more » and ion heating is preferentially perpendicular to Bo. The new results here are that larger simulation boxes and longer initial whistler wavelengths yield weaker overall dissipation, consistent with linear dispersion theory predictions of decreased damping, stronger ion heating, consistent with a stronger ion Landau resonance, and weaker electron heating.« less
Electron and ion heating by whistler turbulence: Three-dimensional particle-in-cell simulations
Hughes, R. Scott; Gary, S. Peter; Wang, Joseph
2014-12-17
Three-dimensional particle-in-cell simulations of decaying whistler turbulence are carried out on a collisionless, homogeneous, magnetized, electron-ion plasma model. In addition, the simulations use an initial ensemble of relatively long wavelength whistler modes with a broad range of initial propagation directions with an initial electron beta β_{e} = 0.05. The computations follow the temporal evolution of the fluctuations as they cascade into broadband turbulent spectra at shorter wavelengths. Three simulations correspond to successively larger simulation boxes and successively longer wavelengths of the initial fluctuations. The computations confirm previous results showing electron heating is preferentially parallel to the background magnetic field B_{o}, and ion heating is preferentially perpendicular to B_{o}. The new results here are that larger simulation boxes and longer initial whistler wavelengths yield weaker overall dissipation, consistent with linear dispersion theory predictions of decreased damping, stronger ion heating, consistent with a stronger ion Landau resonance, and weaker electron heating.
Energy dissipation by whistler turbulence: Three-dimensional particle-in-cell simulations
Chang, Ouliang; Peter Gary, S.; Wang, Joseph
2014-05-15
Three-dimensional particle-in-cell simulations of whistler turbulence are carried out on a collisionless, homogeneous, magnetized plasma model. The simulations use an initial ensemble of relatively long wavelength whistler modes and follow the temporal evolution of the fluctuations as they cascade into a broadband, anisotropic, turbulent spectrum at shorter wavelengths. For relatively small levels of the initial fluctuation energy ϵ{sub e}, linear collisionless damping provides most of the dissipation of the turbulence. But as ϵ{sub e} and the total dissipation increase, linear damping becomes less important and, especially at β{sub e} ≪ 1, nonlinear processes become stronger. The PDFs and kurtoses of the magnetic field increments in the simulations suggest that intermittency in whistler turbulence generally increases with increasing ϵ{sub e} and β{sub e}. Correlation coefficient calculations imply that the current structure dissipation also increases with increasing ϵ{sub e} and β{sub e}, and that the nonlinear dissipation processes in these simulations are primarily associated with regions of localized current structures.
3D Particle-In-Cell (PIC) simulations of plasma sheath formation above lunar craters
NASA Astrophysics Data System (ADS)
Likhanskii, A.; Poppe, A. R.; Piquette, M.; Amyx, K.; Messmer, P.; Horanyi, M.
2010-12-01
Comprehensive investigation of plasma sheath formation and consequent dust levitation on lunar surface is important for interpretation of results of future lunar missions (such as LADEE and ARTEMIS). Until recently, most of such studies were done in experimental laboratories at reduced scales. Due to the complexity and nonlinearity of the problem, only simplified theories, describing this effect, were developed. However, recent progress in high-performance kinetic plasma simulations allowed tackling the problem of plasma sheath formation numerically. In this poster we will present the simulation results of plasma sheath formation above the lunar craters in presence of solar wind and photoelectron emission. These results were obtained using 3D Particle-In-Cell (PIC) code VORPAL. In the simulations we considered plasma sheath formation for normal, 45 and 90 degree incidence solar wind. Sample distribution of electric field in plasma sheath is shown in Figure 1. In the second part of the poster, we will present results of simulations of the LASP (Laboratory for Atmospheric and Space Physics at University of Colorado) experiments on study of plasma sheath formation above hemispherical isolated dimple. Figure 1. Electric field distribution in the plasma sheath above the lunar crater
Particle-in-Cell Simulations of Atmospheric Pressure He/2%H2O Discharges
NASA Astrophysics Data System (ADS)
Kawamura, E.; Lieberman, M. A.; Lichtenberg, A. J.; Graves, D. B.; Gopalakrishnan, R.
2015-09-01
Atmospheric pressure micro-discharges in contact with liquid surfaces are of increasing interest, especially in the bio-medical field. We conduct 1D3v particle-in-cell (PIC) simulations of a voltage-driven 1 mm width atmospheric pressure He/2% H2O plasma discharge in series with an 0.5 mm width liquid H2O layer and a 1mm width quartz dielectric layer. A previously developed two-temperature hybrid global model of atmospheric pressure He/H2O discharges was used to determine the most important species and collisional reactions to use in the PIC simulations. We found that H13O6+, H5O3-, and electrons were the most prominent charged species, while most of the metastable helium He* was quenched via Penning ionization. The ion-induced secondary emission coefficient γi was assumed to be 0.15 at all surfaces. A series of simulations were conducted at 27.12 MHz with Jrf ~ 800-2200 A/m2. The H2O rotational and vibrational excitation losses were so high that electrons reached the walls at thermal temperatures. We also simulated a much lower frequency case of 50 kHz with Vrf = 10 kV. In this case, the discharge ran in a pure time-varying γ-mode. This work was supported by the Department of Energy Office of Fusion Energy Science Contract DE-SC0001939.
NASA Astrophysics Data System (ADS)
Baraka, S. M.; Ben-Jaffel, L. B.
2014-12-01
We use particle-in-cell PIC 3D Electromagnetic, relativistic global code to address large-scale problems in magnetosphere electrodynamics. Terrestrial bow shock is simulated as an example. 3D Magnetohydrodynamics model ,MHD GUMICS in CCMC project, have been used in parallel with PIC under same scaled Solar wind (SW) and IMF conditions. We report new results from the coupling between the two models. Further investigations are required for confirmations of these results. In both codes the Earth's bow shock position is found at ~14.8 RE along the Sun-Earth line, and ~29 RE on the dusk side which is consistent with past in situ observation. Both simulations reproduce the theoretical jump conditions at the shock. However, PIC code density and temperature distributions are inflated and slightly shifted sunward when compared to MHD results. Reflected ions upstream of the bow shock may cause this sunward shift for density and temperature. Distribution of reflected ions and electrons are shown in the foreshock region, within the transition of the shock and in the downstream. The current version of PIC code can be run under modest computing facilities and resources. Additionally, existing MHD simulations should be useful to calibrate scaled properties of plasma resulting from PIC simulations for comparison with observations. Similarities and drawbacks of the results obtained by the two models are listed. The ultimate goal of using these different models in a complimentary manner rather than competitive is to better understand the macrostructure of the magnetosphere
Extended magnetohydrodynamics with embedded particle-in-cell simulation of Ganymede's magnetosphere
NASA Astrophysics Data System (ADS)
Tóth, Gábor; Jia, Xianzhe; Markidis, Stefano; Peng, Ivy Bo; Chen, Yuxi; Daldorff, Lars K. S.; Tenishev, Valeriy M.; Borovikov, Dmitry; Haiducek, John D.; Gombosi, Tamas I.; Glocer, Alex; Dorelli, John C.
2016-02-01
We have recently developed a new modeling capability to embed the implicit particle-in-cell (PIC) model iPIC3D into the Block-Adaptive-Tree-Solarwind-Roe-Upwind-Scheme magnetohydrodynamic (MHD) model. The MHD with embedded PIC domains (MHD-EPIC) algorithm is a two-way coupled kinetic-fluid model. As one of the very first applications of the MHD-EPIC algorithm, we simulate the interaction between Jupiter's magnetospheric plasma and Ganymede's magnetosphere. We compare the MHD-EPIC simulations with pure Hall MHD simulations and compare both model results with Galileo observations to assess the importance of kinetic effects in controlling the configuration and dynamics of Ganymede's magnetosphere. We find that the Hall MHD and MHD-EPIC solutions are qualitatively similar, but there are significant quantitative differences. In particular, the density and pressure inside the magnetosphere show different distributions. For our baseline grid resolution the PIC solution is more dynamic than the Hall MHD simulation and it compares significantly better with the Galileo magnetic measurements than the Hall MHD solution. The power spectra of the observed and simulated magnetic field fluctuations agree extremely well for the MHD-EPIC model. The MHD-EPIC simulation also produced a few flux transfer events (FTEs) that have magnetic signatures very similar to an observed event. The simulation shows that the FTEs often exhibit complex 3-D structures with their orientations changing substantially between the equatorial plane and the Galileo trajectory, which explains the magnetic signatures observed during the magnetopause crossings. The computational cost of the MHD-EPIC simulation was only about 4 times more than that of the Hall MHD simulation.
Three-dimensional particle-in-cell simulation on gain saturation effect of microchannel plate
NASA Astrophysics Data System (ADS)
Wang, Qiangqiang; Yuan, Zheng; Cao, Zhurong; Deng, Bo; Chen, Tao; Deng, Keli
2016-07-01
We present here the results of the simulation work, using the three-dimensional particle-in-cell method, on the performance of the lead glass microchannel plate under saturated state. We calculated the electron cascade process with different DC bias voltages under both self-consistent condition and non-self-consistent condition. The comparative results have demonstrated that the strong self-consistent field can suppress the cascade process and make the microchannel plate saturated. The simulation results were also compared to the experimental data and good agreement was obtained. The simulation results also show that the electron multiplication process in the channel is accompanied by the buildup process of positive charges in the channel wall. Though the interactions among the secondary electron cloud in the channel, the positive charges in the channel wall, and the external acceleration field can make the electron-surface collision more frequent, the collision energy will be inevitably reduced, thus the electron gain will also be reduced.
Three-dimensional particle-in-cell simulation on gain saturation effect of microchannel plate.
Wang, Qiangqiang; Yuan, Zheng; Cao, Zhurong; Deng, Bo; Chen, Tao; Deng, Keli
2016-07-01
We present here the results of the simulation work, using the three-dimensional particle-in-cell method, on the performance of the lead glass microchannel plate under saturated state. We calculated the electron cascade process with different DC bias voltages under both self-consistent condition and non-self-consistent condition. The comparative results have demonstrated that the strong self-consistent field can suppress the cascade process and make the microchannel plate saturated. The simulation results were also compared to the experimental data and good agreement was obtained. The simulation results also show that the electron multiplication process in the channel is accompanied by the buildup process of positive charges in the channel wall. Though the interactions among the secondary electron cloud in the channel, the positive charges in the channel wall, and the external acceleration field can make the electron-surface collision more frequent, the collision energy will be inevitably reduced, thus the electron gain will also be reduced. PMID:27475552
Particle-in-cell simulations of electron beam control using an inductive current divider
Swanekamp, S. B.; Angus, J. R.; Cooperstein, G.; Ottinger, P. F.; Richardson, A. S.; Schumer, J. W.; Weber, B. V.
2015-11-18
Kinetic, time-dependent, electromagnetic, particle-in-cell simulations of the inductive current divider are presented. The inductive current divider is a passive method for controlling the trajectory of an intense, hollow electron beam using a vacuum structure that inductively splits the beam’s return current. The current divider concept was proposed and studied theoretically in a previous publication [Phys. Plasmas 22, 023107 (2015)] A central post carries a portion of the return current (I1) while the outer conductor carries the remainder (I2) with the injected beam current given by Ib=I1+I2. The simulations are in agreement with the theory which predicts that the total forcemore » on the beam trajectory is proportional to (I2-I1) and the force on the beam envelope is proportional to Ib. For a fixed central post, the beam trajectory is controlled by varying the outer conductor radius which changes the inductance in the return-current path. The simulations show that the beam emittance is approximately constant as the beam propagates through the current divider to the target. As a result, independent control over both the current density and the beam angle at the target is possible by choosing the appropriate return-current geometry.« less
Particle-in-cell simulations of electron beam control using an inductive current divider
Swanekamp, S. B.; Angus, J. R.; Cooperstein, G.; Ottinger, P. F.; Richardson, A. S.; Schumer, J. W.; Weber, B. V.
2015-11-18
Kinetic, time-dependent, electromagnetic, particle-in-cell simulations of the inductive current divider are presented. The inductive current divider is a passive method for controlling the trajectory of an intense, hollow electron beam using a vacuum structure that inductively splits the beam’s return current. The current divider concept was proposed and studied theoretically in a previous publication [Phys. Plasmas 22, 023107 (2015)] A central post carries a portion of the return current (I_{1}) while the outer conductor carries the remainder (I_{2}) with the injected beam current given by I_{b}=I_{1}+I_{2}. The simulations are in agreement with the theory which predicts that the total force on the beam trajectory is proportional to (I_{2}-I_{1}) and the force on the beam envelope is proportional to I_{b}. For a fixed central post, the beam trajectory is controlled by varying the outer conductor radius which changes the inductance in the return-current path. The simulations show that the beam emittance is approximately constant as the beam propagates through the current divider to the target. As a result, independent control over both the current density and the beam angle at the target is possible by choosing the appropriate return-current geometry.
Three-dimensional particle-in-cell simulations of 300 GHz reflex klystrons
Jeon, S. G.; Jin, Y. S.; Kim, J. I.; Kim, G. J.; Shon, C. H.
2007-03-01
Three-dimensional (3D) particle-in-cell simulations of 300 GHz reflex klystrons are presented. 300 GHz electromagnetic wave generation in a resonant cavity is analyzed by using a 3D simulation model in which all the geometric parameters (such as the grid thickness, repeller shape, beam radius, etc.) are described. When an electron beam of an energy of 1.0 keV and a net current of 8.9 mA is used, the maximum electronic efficiency of energy transfer is observed when the gap transit angle is 0.7{pi} rad, and the efficiency saturates when the beam current is over 10 mA. Space charge forces produce a shift in the optimum repeller voltage. It is also shown that the effect of the beam temperature is not critical, even though the bunching wavelength of the electron beam is several times smaller than that in conventional vacuum electron devices. Our simulation results show that a microfabricated 300 GHz reflex klystron can directly generate electromagnetic waves with output power levels of several tens of milliwatts.
Miyake, Yohei; Usui, Hideyuki; Kojima, Hirotsugu; Omura, Yoshiharu
2008-12-31
We applied the electromagnetic Particle-In-Cell simulation to the analysis of receiving antenna characteristics in space plasma environment. In the analysis, we set up external waves in a simulation region and receive them with a numerical antenna model placed in the simulation region. Using this method, we evaluated the effective length of electric field antennas used for plasma wave investigations conducted by scientific spacecraft. We particularly focused on the effective length of an electric field instrument called MEFISTO for a future mission to Mercury: BepiColombo. We first confirmed that the effective length of the MEFISTO-type antenna is basically longer than that of a simple dipole antenna for both electrostatic and electromagnetic plasma waves. By applying the principle of a voltmeter, the effective length of the MEFISTO-type antenna is predicted to become identical to the separation between two sensor-conductor's midpoints. However, the numerical result revealed that the actual effective length becomes shorter than the prediction, which is caused by the shorting-out effect due to the presence of a center boom conductor between the two sensor conductors. Since the above effect is difficult to treat theoretically, the present numerical method is a powerful tool for further quantitative evaluation of the antenna characteristics.
NASA Astrophysics Data System (ADS)
Majzoobi, Alireza
The first magnetron as a vacuum-tube device, capable of generating microwaves, was invented in 1913. This thesis research focuses on numerical simulation-based analysis of magnetron performance. The particle-in-cell (PIC) based MAGIC software tool has been utilized to study the A6 and the Rising-Sun magnetron structures, and to obtain the optimized geometry for optimizing the device performance. The A6 magnetron is the more traditional structure and has been studied more often. The Rising-Sun geometry, consists of two alternating groups of short and long vanes in angular orientation, and was created to achieve mode stability. The effect of endcaps, changes in lengths of the cathode, the location of cathodes with respect to the anode block, and use of transparent cathodes have been probed to gauge the performance of the A6 magnetron with diffraction output. The simulations have been carried out with different types of endcaps. The results of this thesis research demonstrate peak output power in excess of 1GW, with efficiencies on the order of 66% for magnetic (B)-fields in the range of 0.4T - 0.42T. In addition, particle-in-cell simulations have been performed to provide a numerical evaluation of the efficiency, output power and leakage currents for a 12-cavitiy, Rising-Sun magnetron with diffraction output with transparent cathodes. The results demonstrate peak output power in excess of 2GW, with efficiencies on the order of 68% for B-fields in the 0.42T - 0.46T range. While slightly better performance for longer cathode length has been recorded. The results show the efficiency in excess of 70% and peak output power on the order of 2.1GW for an 18 cm cathode length at 0.45T magnetic field and 400 kV applied voltage. All results of this thesis conform to the definite advantage of having endcaps. Furthermore, the role of secondary electron emission (SEE) on the output performance of the12-cavity, 12-cathodes Rising-Sun magnetron has been probed. The results indicate
NASA Astrophysics Data System (ADS)
Shaw, J. L.; Lemos, N.; Marsh, K. A.; Tsung, F. S.; Mori, W. B.; Joshi, C.
2016-03-01
Many current laser wakefield acceleration (LWFA) experiments are carried out in a regime where the laser pulse length is on the order of or longer than the wake wavelength and where ionization injection is employed to inject electrons into the wake. In these experiments, the electrons can gain a significant amount of energy from the direct laser acceleration (DLA) mechanism as well as the usual LWFA mechanism. Particle-in-cell (PIC) codes are frequently used to discern the relative contribution of these two mechanisms. However, if the longitudinal resolution used in the PIC simulations is inadequate, it can produce numerical heating that can overestimate the transverse motion, which is important in determining the energy gain due to DLA. We have therefore carried out a systematic study of this LWFA regime by varying the longitudinal resolution of PIC simulations and then examining the energy gain characteristics of both the highest-energy electrons and the bulk electrons. By calculating the contribution of DLA to the final energies of the electrons produced from the LWFA, we find that even at the highest longitudinal resolutions, DLA contributes a significant portion of the energy gained by the highest-energy electrons and also contributes to accelerating the bulk of the charge in the electron beam produced by the LWFA.
Gyrokinetic and kinetic particle-in-cell simulations of guide-field reconnection
NASA Astrophysics Data System (ADS)
Munoz Sepulveda, Patricio Alejandro; Büchner, Jörg; Kilian, Patrick; Told, Daniel; Jenko, Frank
2016-07-01
Fully kinetic Particle-in-Cell (PIC) simulations of (strong) guide-field reconnection can be computationally very demanding, due to the intrinsic stability and accuracy conditions required by this numerical method. One convenient approach to circumvent this issue is using gyrokinetic theory, an approximation of the Vlasov-Maxwell equations for strongly magnetized plasmas that eliminates the fast gyromotion, and thus reduces the computational cost. Although previous works have started to compare the features of reconnection between both approaches, a complete understanding of the differences is far from being complete. This knowledge is essential to discern the limitations of the gyrokinetic simulations of magnetic reconnection when applied to scenarios with moderate guide fields, such as the Solar corona, in contrast to most of the fusion/laboratory plasmas. We extend a previous work by our group, focused in the differences in the macroscopic flows, by analyzing the heating processes and non-thermal features developed by reconnection between both plasma approximations. We relate these processes by identifying some high-frequency cross-streaming instabilities appearing only in the fully kinetic approach. We characterize the effects of these phenonema such as anisotropic electron heating, beam formation and turbulence under different parameter regimes. And finally, we identify the conditions under which these instabilities tends to become negligible in the fully kinetic model, and thus a comparison with gyrokinetic theory becomes more reliable.
Particle-in-cell Simulations of Raman Laser Amplification in Preformed Plasmas
Daniel S. Clark; Nathaniel J. Fisch
2003-06-27
Two critical issues in the amplification of laser pulses by backward Raman scattering in plasma slabs are the saturation mechanism of the amplification effect (which determines the maximum attainable output intensity of a Raman amplifier) and the optimal plasma density for amplification. Previous investigations [V.M. Malkin, et al., Phys. Rev. Lett., 82 (22):4448-4451, 1999] identified forward Raman scattering and modulational instabilities of the amplifying seed as the likely saturation mechanisms and lead to an estimated unfocused output intensities of 10{sup 17}W/cm{sup 2}. The optimal density for amplification is determined by the competing constraints of minimizing the plasma density so as to minimize the growth rate of the instabilities leading to saturation but also maintaining the plasma sufficiently dense that the driven Langmuir wave responsible for backscattering does not break prematurely. Here, particle-in-cell code are simulations presented which verify that saturation of backward Raman amplification does occur at intensities of {approx}10{sup 17}W/cm{sup 2} by forward Raman scattering and modulational instabilities. The optimal density for amplification in a plasma with the representative temperature of T(sub)e = 200 eV is also shown in these simulations to be intermediate between the cold plasma wave-breaking density and the density limit found by assuming a water bag electron distribution function.
NASA Astrophysics Data System (ADS)
Toth, G.; Daldorff, L. K. S.; Jia, X.; Gombosi, T. I.; Lapenta, G.
2014-12-01
We have recently developed a new modeling capability to embed theimplicit Particle-in-Cell (PIC) model iPIC3D into the BATS-R-USmagnetohydrodynamic model. The PIC domain can cover the regions wherekinetic effects are most important, such as reconnection sites. TheBATS-R-US code, on the other hand, can efficiently handle the rest ofthe computational domain where the MHD or Hall MHD description issufficient. As one of the very first applications of the MHD-EPICalgorithm (Daldorff et al. 2014, JCP, 268, 236) we simulate theinteraction between Jupiter's magnetospheric plasma with Ganymede'smagnetosphere, where the separation of kinetic and global scalesappears less severe than for the Earth's magnetosphere. Because theexternal Jovian magnetic field remains in an anti-parallel orientationwith respect to Ganymede's intrinsic magnetic field, magneticreconnection is believed to be the major process that couples the twomagnetospheres. As the PIC model is able to describe self-consistentlythe electron behavior, our coupled MHD-EPIC model is well suited forinvestigating the nature of magnetic reconnection in thisreconnection-driven mini-magnetosphere. We will compare the MHD-EPICsimulations with pure Hall MHD simulations and compare both modelresults with Galileo plasma and magnetic field measurements to assess therelative importance of ion and electron kinetics in controlling theconfiguration and dynamics of Ganymede's magnetosphere.
Multidimensional, fully implicit, exactly conserving electromagnetic particle-in-cell simulations
NASA Astrophysics Data System (ADS)
Chacon, Luis
2015-09-01
We discuss a new, conservative, fully implicit 2D-3V particle-in-cell algorithm for non-radiative, electromagnetic kinetic plasma simulations, based on the Vlasov-Darwin model. Unlike earlier linearly implicit PIC schemes and standard explicit PIC schemes, fully implicit PIC algorithms are unconditionally stable and allow exact discrete energy and charge conservation. This has been demonstrated in 1D electrostatic and electromagnetic contexts. In this study, we build on these recent algorithms to develop an implicit, orbit-averaged, time-space-centered finite difference scheme for the Darwin field and particle orbit equations for multiple species in multiple dimensions. The Vlasov-Darwin model is very attractive for PIC simulations because it avoids radiative noise issues in non-radiative electromagnetic regimes. The algorithm conserves global energy, local charge, and particle canonical-momentum exactly, even with grid packing. The nonlinear iteration is effectively accelerated with a fluid preconditioner, which allows efficient use of large timesteps, O(√{mi/me}c/veT) larger than the explicit CFL. In this presentation, we will introduce the main algorithmic components of the approach, and demonstrate the accuracy and efficiency properties of the algorithm with various numerical experiments in 1D and 2D. Support from the LANL LDRD program and the DOE-SC ASCR office.
Global Explicit Particle-in-cell Simulations of the Nonstationary Bow Shock and Magnetosphere
NASA Astrophysics Data System (ADS)
Yang, Zhongwei; Huang, Can; Liu, Ying D.; Parks, George K.; Wang, Rui; Lu, Quanming; Hu, Huidong
2016-07-01
We carry out two-dimensional global particle-in-cell simulations of the interaction between the solar wind and a dipole field to study the formation of the bow shock and magnetosphere. A self-reforming bow shock ahead of a dipole field is presented by using relatively high temporal-spatial resolutions. We find that (1) the bow shock and the magnetosphere are formed and reach a quasi-stable state after several ion cyclotron periods, and (2) under the B z southward solar wind condition, the bow shock undergoes a self-reformation for low β i and high M A . Simultaneously, a magnetic reconnection in the magnetotail is found. For high β i and low M A , the shock becomes quasi-stationary, and the magnetotail reconnection disappears. In addition, (3) the magnetopause deflects the magnetosheath plasmas. The sheath particles injected at the quasi-perpendicular region of the bow shock can be convected downstream of an oblique shock region. A fraction of these sheath particles can leak out from the magnetosheath at the wings of the bow shock. Hence, the downstream situation is more complicated than that for a planar shock produced in local simulations.
Kinetic structures of quasi-perpendicular shocks in global particle-in-cell simulations
Peng, Ivy Bo Markidis, Stefano; Laure, Erwin; Johlander, Andreas; Vaivads, Andris; Khotyaintsev, Yuri; Henri, Pierre; Lapenta, Giovanni
2015-09-15
We carried out global Particle-in-Cell simulations of the interaction between the solar wind and a magnetosphere to study the kinetic collisionless physics in super-critical quasi-perpendicular shocks. After an initial simulation transient, a collisionless bow shock forms as a result of the interaction of the solar wind and a planet magnetic dipole. The shock ramp has a thickness of approximately one ion skin depth and is followed by a trailing wave train in the shock downstream. At the downstream edge of the bow shock, whistler waves propagate along the magnetic field lines and the presence of electron cyclotron waves has been identified. A small part of the solar wind ion population is specularly reflected by the shock while a larger part is deflected and heated by the shock. Solar wind ions and electrons are heated in the perpendicular directions. Ions are accelerated in the perpendicular direction in the trailing wave train region. This work is an initial effort to study the electron and ion kinetic effects developed near the bow shock in a realistic magnetic field configuration.
Deca, J; Divin, A; Lapenta, G; Lembège, B; Markidis, S; Horányi, M
2014-04-18
We present the first three-dimensional fully kinetic and electromagnetic simulations of the solar wind interaction with lunar crustal magnetic anomalies (LMAs). Using the implicit particle-in-cell code iPic3D, we confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface forming a mini-magnetosphere, as suggested by spacecraft observations and theory. In contrast to earlier magnetohydrodynamics and hybrid simulations, the fully kinetic nature of iPic3D allows us to investigate the space charge effects and in particular the electron dynamics dominating the near-surface lunar plasma environment. We describe for the first time the interaction of a dipole model centered just below the lunar surface under plasma conditions such that only the electron population is magnetized. The fully kinetic treatment identifies electromagnetic modes that alter the magnetic field at scales determined by the electron physics. Driven by strong pressure anisotropies, the mini-magnetosphere is unstable over time, leading to only temporal shielding of the surface underneath. Future human exploration as well as lunar science in general therefore hinges on a better understanding of LMAs. PMID:24785022
Particle-in-Cell (PIC) simulation of CW industrial heating magnetron.
Andreev, Andrey D; Hendricks, Kyle J
2010-01-01
Modern CW industrial heating magnetrons are capable for producing as high as 300 kW of continuous-wave microwave power at frequencies around 900 MHz and are sold commercially [Wynn et al., 2004]. However, to utilize these magnetrons in some specific research and scientific applications being of interest for the Air Force, the necessary adaptation and redesign are required. It means that the detailed knowledge of principles of their operation and full understanding of how the changes of the design parameters affect their operational characteristics are necessary. We have developed and tested computer model of a 10-vane high-power strapped magnetron, which geometrical dimensions and design parameters are close to those of the California Tube Laboratory's commercially produced CWM-75/100L tube. The computer model is built by using the 3-D Improved Concurrent Electromagnetic Particle-in-Cell (ICEPIC) code. Simulations of the strapped magnetron operation are performed and the following operational characteristics are obtained during the simulation: frequency and mode of magnetron oscillations, output microwave power and efficiency of magnetron operation, anode current and anode-cathode voltage dynamics. The developed computer model of a non-relativistic high-power strapped magnetron may be used by the industrial magnetron community for designing following generations of the CW industrial heating high-power magnetrons. PMID:21721323
Particle-in-cell simulations of electron beam control using an inductive current divider
NASA Astrophysics Data System (ADS)
Swanekamp, S. B.; Angus, J. R.; Cooperstein, G.; Ottinger, P. F.; Richardson, A. S.; Schumer, J. W.; Weber, B. V.
2015-11-01
Kinetic, time-dependent, electromagnetic, particle-in-cell simulations of the inductive current divider are presented. The inductive current divider is a passive method for controlling the trajectory of an intense, hollow electron beam using a vacuum structure that inductively splits the beam's return current. The current divider concept was proposed and studied theoretically in a previous publication [Swanekamp et al., Phys. Plasmas 22, 023107 (2015)]. A central post carries a portion of the return current (I1), while the outer conductor carries the remainder (I2) with the injected beam current given by Ib = I1 + I2. The simulations are in agreement with the theory which predicts that the total force on the beam trajectory is proportional to (I2-I1) and the force on the beam envelope is proportional to Ib. Independent control over both the current density and the beam angle at the target is possible by choosing the appropriate current-divider geometry. The root-mean-square (RMS) beam emittance (ɛRMS) varies as the beam propagates through the current divider to the target. For applications where control of the beam trajectory is desired and the current density at the target is similar to the current density at the entrance foil, there is a modest 20% increase in ɛRMS at the target. For other applications where the beam is pinched to a current density ˜5 times larger at the target, ɛRMS is 2-3 times larger at the target.
Shock Injection Problem and Beyond in Hybrid/Particle-in-Cell Simulations
NASA Astrophysics Data System (ADS)
Hoshino, Masahiro
Collisionless shocks are a rich repository of nonlinear plasma instabilities and the self-regulated system of plasma waves, and provide not only quick thermalization but also nonthermal particle acceleration. One of the most widely accepted models of the nonthermal particle acceleration is the diffusive shock acceleration (DSA), which was established in the late seventies. In order that DSA operates effectively, however, the pre-acceleration of particles - the acceleration from the thermal into the suprathermal energies - is needed, namely, the so-called "shock injection problem" remains elusive. The transition from the thermal energies, the suprathermal energies, and the high energy nothermal particles are not well understood yet. With the recent advance of supper computer technology, kinetic plasma modeling by hybrid/particle-in-cell simulations are widely used for understanding the shock dynamics and the particle acceleration mechanisms etc. The modern computer capability is not enough to demonstrate DAS or other strong particle acceleration processes yet, but a great progress is now obtained. In this review talk, we discuss several important progresses: the pre-acceleration at the shock front as the particle injection problem, the turbulent wave generation in the shock transition/upstream as the particle scatterers of DAS, and the magnetic field amplification and so on. We will also give a perspective of the shock acceleration in the future simulation study.
The Plasma Simulation Code: A modern particle-in-cell code with patch-based load-balancing
NASA Astrophysics Data System (ADS)
Germaschewski, Kai; Fox, William; Abbott, Stephen; Ahmadi, Narges; Maynard, Kristofor; Wang, Liang; Ruhl, Hartmut; Bhattacharjee, Amitava
2016-08-01
This work describes the Plasma Simulation Code (PSC), an explicit, electromagnetic particle-in-cell code with support for different order particle shape functions. We review the basic components of the particle-in-cell method as well as the computational architecture of the PSC code that allows support for modular algorithms and data structure in the code. We then describe and analyze in detail a distinguishing feature of PSC: patch-based load balancing using space-filling curves which is shown to lead to major efficiency gains over unbalanced methods and a previously used simpler balancing method.
Monte Carlo particle-in-cell methods for the simulation of the Vlasov-Maxwell gyrokinetic equations
NASA Astrophysics Data System (ADS)
Bottino, A.; Sonnendrücker, E.
2015-10-01
> The particle-in-cell (PIC) algorithm is the most popular method for the discretisation of the general 6D Vlasov-Maxwell problem and it is widely used also for the simulation of the 5D gyrokinetic equations. The method consists of coupling a particle-based algorithm for the Vlasov equation with a grid-based method for the computation of the self-consistent electromagnetic fields. In this review we derive a Monte Carlo PIC finite-element model starting from a gyrokinetic discrete Lagrangian. The variations of the Lagrangian are used to obtain the time-continuous equations of motion for the particles and the finite-element approximation of the field equations. The Noether theorem for the semi-discretised system implies a certain number of conservation properties for the final set of equations. Moreover, the PIC method can be interpreted as a probabilistic Monte Carlo like method, consisting of calculating integrals of the continuous distribution function using a finite set of discrete markers. The nonlinear interactions along with numerical errors introduce random effects after some time. Therefore, the same tools for error analysis and error reduction used in Monte Carlo numerical methods can be applied to PIC simulations.
Particle in cell simulations of tearing modes in reversed-field-pinch-like plasma
Svidzinski, Vladmir; Li, Hui; Albright, Brian
2008-01-01
Particle in cell (PIC) simulations of tearing modes in two-dimensional plane geometry in a force free reversed field pinch (RFP) like plasma equilibrium are performed to study possible kinetic effects on these modes in RFPs. Linear tearing modes are compared in the PIC and two fluid models. The results showed that the growth rates and the profiles of magnetic field components in the two models are very similar, indicating that the kinetic effects on the tearing modes are weak such that the two fluid approximation is rather accurate for modeling these instabilities in RFPs. During the nonlinear evolution of the tearing mode in this geometry small scale secondary instabilities located near the internal layer of the primary tearing instability are excited. These secondary instabilities appear to be driven by the nonlinearly induced local pressure gradient in the regions of unfavorable curvature of the nonlinearly evolved magnetic field. They could also appear in a realistic RFP geometry and play a role during sawtooth crashes in these machines.
NASA Astrophysics Data System (ADS)
Toth, Gabor; Gombosi, Tamas; Jia, Xianzhe; Welling, Daniel; Chen, Yuxi; Haiducek, John; Jordanova, Vania; Peng, Ivy Bo; Markidis, Stefano; Lapenta, Giovanni
2016-04-01
We have recently developed a new modeling capability to embed the implicit Particle-in-Cell (PIC) model iPIC3D into the BATS-R-US extended magnetohydrodynamic model. The PIC domain can cover the regions where kinetic effects are most important, such as reconnection sites. The BATS-R-US code with its block-adaptive grid can efficiently handle the rest of the computational domain where the MHD or Hall MHD description is sufficient. The current implementation of the MHD-EPIC model allows two-way coupled simulations in two and three dimensions with multiple embedded PIC regions. The MHD and PIC grids can have different grid resolutions and grid structures. The MHD variables and the moments of the PIC distribution functions are interpolated and message passed in an efficient manner through the Space Weather Modeling Framework (SWMF). Both BATS-R-US and iPIC3D are massively parallel codes fully integrated into, run by and coupled through the SWMF. We have successfully applied the MHD-EPIC code to model Ganymede's and Mercury's magnetospheres. We compared our results with Galileo and MESSENGER magnetic observations, respectively, and found good overall agreement. We will report our progress on modeling the Earth magnetosphere with MHD-EPIC with the goal of providing direct comparison with and global context for the MMS observations.
Particle-in-cell simulation study of a lower-hybrid shock
NASA Astrophysics Data System (ADS)
Dieckmann, M. E.; Sarri, G.; Doria, D.; Ynnerman, A.; Borghesi, M.
2016-06-01
The expansion of a magnetized high-pressure plasma into a low-pressure ambient medium is examined with particle-in-cell simulations. The magnetic field points perpendicular to the plasma's expansion direction and binary collisions between particles are absent. The expanding plasma steepens into a quasi-electrostatic shock that is sustained by the lower-hybrid (LH) wave. The ambipolar electric field points in the expansion direction and it induces together with the background magnetic field a fast E cross B drift of electrons. The drifting electrons modify the background magnetic field, resulting in its pile-up by the LH shock. The magnetic pressure gradient force accelerates the ambient ions ahead of the LH shock, reducing the relative velocity between the ambient plasma and the LH shock to about the phase speed of the shocked LH wave, transforming the LH shock into a nonlinear LH wave. The oscillations of the electrostatic potential have a larger amplitude and wavelength in the magnetized plasma than in an unmagnetized one with otherwise identical conditions. The energy loss to the drifting electrons leads to a noticeable slowdown of the LH shock compared to that in an unmagnetized plasma.
Electron Debye scale Kelvin-Helmholtz instability: Electrostatic particle-in-cell simulations
Lee, Sang-Yun; Lee, Ensang Kim, Khan-Hyuk; Lee, Dong-Hun; Seon, Jongho; Jin, Ho
2015-12-15
In this paper, we investigated the electron Debye scale Kelvin-Helmholtz (KH) instability using two-dimensional electrostatic particle-in-cell simulations. We introduced a velocity shear layer with a thickness comparable to the electron Debye length and examined the generation of the KH instability. The KH instability occurs in a similar manner as observed in the KH instabilities in fluid or ion scales producing surface waves and rolled-up vortices. The strength and growth rate of the electron Debye scale KH instability is affected by the structure of the velocity shear layer. The strength depends on the magnitude of the velocity and the growth rate on the velocity gradient of the shear layer. However, the development of the electron Debye scale KH instability is mainly determined by the electric field generated by charge separation. Significant mixing of electrons occurs across the shear layer, and a fraction of electrons can penetrate deeply into the opposite side fairly far from the vortices across the shear layer.
Particle-in-Cell Simulation of a Micro ECR Plasma Thruster
NASA Astrophysics Data System (ADS)
Ueno, Keisuke; Mori, Daisuke; Takao, Yoshinori; Eriguchi, Koji; Ono, Kouichi
2015-09-01
Downsizing spacecrafts has recently been focused on to decrease mission costs and to increase launch rates, and missions with small satellites would bring a great advantage of reducing their risks. Such a concept supports a new approach to developing precise, reliable, and low-cost micropropulsion systems. We have developed a new type of electromagnetic micro plasma thruster using electron cyclotron resonance (ECR) discharges. The microthruster consists of a microwave antenna and a quartz microplasma chamber 4.15 mm in inner diameter surrounded by two permanent magnet rings. The plasma is generated by 4-GHz microwaves of < 10 W with a propellant gas of Xe, where the ions are accelerated through divergent magnetic fields and the resulting ambipolar electric fields generated. To investigate plasma characteristics of the thruster, we simulated the plasma density, electrostatic potential, and ion velocity in the exhaust area by the particle-in-cell (PIC) method with a Monte Carlo calculation for particle collisions, where the electrostatic field and the ion velocity were obtained by solving the Poisson equation and the equation of motion, respectively. The numerical results showed that the ions generated in the plasma are well confined by the applied magnetic fields and diffuse out of the discharge tube, then being accelerated by a potential drop of ~7 V through divergent magnetic fields from < 1000 to > 3000 m/s (< 0 . 7 to > 6 eV) in the axial direction.
Different Choices of the Form Factor in Particle-in-Cell Simulations
NASA Astrophysics Data System (ADS)
Kilian, P.; Ganse, U.; Spanier, F.
2013-04-01
Numerical simulations have proven a valuable tool to study plasma behavior, especially for conditions in astrophysical scenarios and which are not readily accessible under laboratory conditions. Whenever single particle behavior becomes important or the development of non-thermal components is of interest fluid descriptions have to be replaced by more accurate but also more expensive kinetic descriptions. A very popular such method is the Particle-in-Cell method. Conceptually this method combines the integration of motion if individual elementary particles with field quantities that are restricted to a spatial grid. Both the analytic derivation of the method as well as the computational feasibility require the use of phase space samples instead of the more readily envisioned individual elementary particles. Each macroparticle represents an ensemble of particles of one species that are close to each other in phase space and carries the total charge and mass of the ensemble. Unlike the elementary particles the macroparticle does not necessarily have a vanishing spatial extent. Different choices of the form factor, that is spatial distribution of the particle quantities within the macroparticle, are investigated. Included are the standard choices NGP, CIC and TSC as well as new schemes of higher order.
Kato, Tsunehiko N.; Takabe, Hideaki
2010-03-15
A two-dimensional electromagnetic particle-in-cell simulation with the realistic ion-to-electron mass ratio of 1836 is carried out to investigate the electrostatic collisionless shocks in relatively high-speed (approx3000 km s{sup -1}) plasma flows and also the influence of both electrostatic and electromagnetic instabilities, which can develop around the shocks, on the shock dynamics. It is shown that the electrostatic ion-ion instability can develop in front of the shocks, where the plasma is under counterstreaming condition, with highly oblique wave vectors as was shown previously. The electrostatic potential generated by the electrostatic ion-ion instability propagating obliquely to the shock surface becomes comparable with the shock potential and finally the shock structure is destroyed. It is also shown that in front of the shock the beam-Weibel instability gradually grows as well, consequently suggesting that the magnetic field generated by the beam-Weibel instability becomes important in long-term evolution of the shock and the Weibel-mediated shock forms long after the electrostatic shock vanished. It is also observed that the secondary electrostatic shock forms in the reflected ions in front of the primary electrostatic shock.
NASA Astrophysics Data System (ADS)
Cartwright, Keith
2015-09-01
Numerical error estimation is a key component in verification, validation, and uncertainty quantification. For ParticleIn-Cell (PIC) plasma simulations, error estimation is complicated due to the presence of stochastic noise and multiple convergence parameters (grid size, time step, macro particle weight). In this talk, we will discuss recent developments for the Stochastic Richardson Extrapolation Based Error Quantification method (StREEQ). This method at its core is a multi-regression technique, where nine regression models and multiple bootstrap samples propagate uncertainties due to the fit and the stochasticity of the underlying data for an appropriate error model with unknown convergence rates. Recently, automation of the convergence parameter domain selection has been implemented; this enables efficient error estimation for large data sets, including analysis of multiple quantities of interest and time dependent data. This method is demonstrated for verification of both steady and time-periodic electron diodes, as well as validation of radiation generated plasma in an end-radiated cylinder. In collaboration with Gregg Radtke, Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DOE's National Nuclear Security Administration under Contract DE-AC04-94AL85000.
Beta dependence of electron heating in decaying whistler turbulence: Particle-in-cell simulations
Saito, S.; Peter Gary, S.
2012-01-15
Two-dimensional particle-in-cell simulations have been carried out to study electron beta dependence of decaying whistler turbulence and electron heating in a homogeneous, collisionless magnetized plasma. Initially, applied whistler fluctuations at relatively long wavelengths cascade their energy into shorter wavelengths. This cascade leads to whistler turbulence with anisotropic wavenumber spectra which are broader in directions perpendicular to the background magnetic field than in the parallel direction. Comparing the development of whistler turbulence at different electron beta values, it is found that both the wavenumber spectrum anisotropy and electron heating anisotropy decrease with increasing electron beta. This indicates that higher electron beta reduces the perpendicular energy cascade of whistler turbulence. Fluctuation energy dissipation by electron Landau damping responsible for the electron parallel heating becomes weaker at higher electron beta, which leads to more isotropic heating. It suggests that electron kinetic processes are important in determining the properties of whistler turbulence. This kinetic property is applied to discuss the generation of suprathermal strahl electron distributions in the solar wind.
Particle-in-Cell Simulation of Collisionless Driven Reconnection with Open Boundaries
NASA Technical Reports Server (NTRS)
Kimas, Alex; Hesse, Michael; Zenitani, Seiji; Kuznetsova, Maria
2010-01-01
First results are discussed from an ongoing study of driven collisionless reconnection using a 2 1/2-dimensional electromagnetic particle-in-cell simulation model with open inflow and outflow boundaries. An extended electron diffusion region (EEDR) is defined as that region surrounding a reconnecting neutral line in which the out-of-plane nonideal electric field is positive. It is shown that the boundaries of this region in the directions of the outflow jets are at the positions where the electrons make the transition from unfrozen meandering motion in the current sheet to outward drifting with the magnetic field in the outflow jets; a turning length scale is defined to mark these positions, The initial width of the EEDR in the inflow directions is comparable to the electron bounce width. Later. as shoulders develop to form a two-scale structure. thc EEDR width expands to the ion bounce width scale. The inner portion of the EEDR or the electron diffusion region proper remains at the electron bounce width. Two methods are introduced for predicting the reconnection electric field using the dimensions of the EEDR. These results are interpreted as further evidence that the EEDR is the region that is relevant to understanding the electron role in the neutral line vicinity.
Comparison of dust charging between orbital-motion-limited theory and particle-in-cell simulations
Delzanno, Gian Luca Tang, Xian-Zhu
2015-11-15
The Orbital-Motion-Limited (OML) theory has been modified to predict the dust charge and the results were contrasted with the Whipple approximation [X. Z. Tang and G. L. Delzanno, Phys. Plasmas 21, 123708 (2014)]. To further establish its regime of applicability, in this paper, the OML predictions (for a non-electron-emitting, spherical dust grain at rest in a collisionless, unmagnetized plasma) are compared with particle-in-cell simulations that retain the absorption radius effect. It is found that for large dust grain radius r{sub d} relative to the plasma Debye length λ{sub D}, the revised OML theory remains a very good approximation as, for the parameters considered (r{sub d}/λ{sub D} ≤ 10, equal electron and ion temperatures), it yields the dust charge to within 20% accuracy. This is a substantial improvement over the Whipple approximation. The dust collected currents and energy fluxes, which remain the same in the revised and standard OML theories, are accurate to within 15%–30%.
Open Boundary Particle-in-Cell Simulation of Dipolarization Front Propagation
NASA Technical Reports Server (NTRS)
Klimas, Alex; Hwang, Kyoung-Joo; Vinas, Adolfo F.; Goldstein, Melvyn L.
2014-01-01
First results are presented from an ongoing open boundary 2-1/2D particle-in-cell simulation study of dipolarization front (DF) propagation in Earth's magnetotail. At this stage, this study is focused on the compression, or pileup, region preceding the DF current sheet. We find that the earthward acceleration of the plasma in this region is in general agreement with a recent DF force balance model. A gyrophase bunched reflected ion population at the leading edge of the pileup region is reflected by a normal electric field in the pileup region itself, rather than through an interaction with the current sheet. We discuss plasma wave activity at the leading edge of the pileup region that may be driven by gradients, or by reflected ions, or both; the mode has not been identified. The waves oscillate near but above the ion cyclotron frequency with wavelength several ion inertial lengths. We show that the waves oscillate primarily in the perpendicular magnetic field components, do not propagate along the background magnetic field, are right handed elliptically (close to circularly) polarized, exist in a region of high electron and ion beta, and are stationary in the plasma frame moving earthward. We discuss the possibility that the waves are present in plasma sheet data, but have not, thus far, been discovered.
Particle-in-cell simulation of large amplitude ion-acoustic solitons
Sharma, Sarveshwar Sengupta, Sudip; Sen, Abhijit
2015-02-15
The propagation of large amplitude ion-acoustic solitons is studied in the laboratory frame (x, t) using a 1-D particle-in-cell code that evolves the ion dynamics by treating them as particles but assumes the electrons to follow the usual Boltzmann distribution. It is observed that for very low Mach numbers the simulation results closely match the Korteweg-de Vries soliton solutions, obtained in the wave frame, and which propagate without distortion. The collision of two such profiles is observed to exhibit the usual solitonic behaviour. As the Mach number is increased, the given profile initially evolves and then settles down to the exact solution of the full non-linear Poisson equation, which then subsequently propagates without distortion. The fractional change in amplitude is found to increase linearly with Mach number. It is further observed that initial profiles satisfying k{sup 2}λ{sub de}{sup 2}<1 break up into a series of solitons.
Masson-Laborde, P. E.; Casanova, M.; Loiseau, P.; Rozmus, W.; Peng, Z.; Pesme, D.; Hueller, S.; Chapman, T.; Bychenkov, V. Yu.
2010-09-15
In the following work, we analyze one-dimensional (1D) and two-dimensional (2D) full particle-in-cell simulations of stimulated Raman scattering (SRS) and study the evolution of Langmuir waves (LWs) in the kinetic regime. It is found that SRS reflectivity becomes random due to a nonlinear frequency shift and that the transverse modulations of LWs are induced by (i) the Weibel instability due to the current of trapped particles and (ii) the trapped particle modulational instability (TPMI) [H. Rose, Phys. Plasmas 12, 12318 (2005)]. Comparisons between 1D and 2D cases indicate that the nonlinear frequency shift is responsible for the first saturation of SRS. After this transient interval of first saturation, 2D effects become important: a strong side-scattering of the light, caused by these transverse modulations of the LW and the presence of a nonlinear frequency shift, is observed together with a strong transverse diffusion. This leads to an increase of the Landau damping rate of the LW, contributing to the limiting of Raman backscattering. A model is developed that reproduces the transverse evolution of the magnetic field due to trapped particles. Based on a simple 1D hydrodynamic model, the growth rate for the Weibel instability of the transverse electrostatic mode and magnetic field is estimated and found to be close to the TPMI growth rate [H. Rose et al., Phys. Plasmas 15, 042311 (2008)].
Particle-In-Cell Simulations on Electric Field Antenna Characteristics in the Spacecraft Environment
NASA Astrophysics Data System (ADS)
Miyake, Y.; Usui, H.; Kojima, H.; Omura, Y.; Matsumoto, H.
2006-12-01
The Solar Terrestrial Physics (STP) group in Japan has organized a new magnetospheric mission named SCOPE whose objective is to investigate the scale-coupling process of plasma dynamics in the Terrestrial magnetosphere. For the sophisticated electric field measurements planned in the SCOPE mission, we have to investigate the antenna characteristics which are essential for the precise calibration of observed data. Particularly, (1) realistic antenna geometries including spacecraft body and (2) inhomogeneous plasma environment created by plasma-spacecraft interactions should be taken into consideration in the antenna analysis for application to the scientific mission. However, the analysis of the antenna impedance is very complex because the plasma is a dispersive and anisotropic medium, and thus it is too difficult to consider the realistic plasma environment near the spacecraft by the theoretical approaches. In the present study, we apply the Particle-In-Cell simulations to the antenna analysis, which enables us to treat the antenna model including a spacecraft body and analyze the effects of photoelectron emission on antenna characteristics. The present antenna model consists of perfect conducting antennas and spacecraft body, and the photoelectron emission from the sunlit surfaces is also modeled. Using these models, we first performed the electrostatic simulations and examined the photoelectron environment around the spacecraft. Next, the antenna impedance under the obtained photoelectron environment was examined by the electromagnetic simulations. Impedance values obtained in photoelectron environment were much different from those in free space, and they were analogous to the impedance characteristics of an equivalent electric circuit consisting of a resistance and capacitance connected in parallel. The validity of the obtained values has been examined by the comparison with the measurements by the scientific spacecraft.
Particle-in-cell simulation of spacecraft/plasma interactions in the vicinity of Enceladus
NASA Astrophysics Data System (ADS)
Yaroshenko, V. V.; Miloch, W. J.; Lühr, H.
2015-09-01
The Cassini Langmuir Probe of the Radio and Plasma Wave Science instrument has measured an electron depletion in a region extending at least 50 satellite radii away from Saturn's small but geologically active icy moon Enceladus. The maximal imbalance between the electron and ion densities was observed in the dust loaded plume and to date is attributed to the electron attachment to abundant dust grains. We report the results from a three dimensional particle-in-cell simulation of a plasma structure formed around a charged spacecraft in the conditions relevant inside the Enceladus torus and in the moon's plume. In addition to the plasma population the plume simulation includes singly charged nanograins detected by the Cassini Plasma Spectrometer. The accompanied spacecraft plasma perturbations can significantly modify an ambient plasma at the Cassini Langmuir probe positions and thus impact the plasma measurements. Our modeling reveals a domination of water group ions over the electron population due to the formation of a conventional plasma sheath at the ram-oriented probe positions in the Enceladus torus and in the plume regions with low dust density (nd0
Colliding Two Shocks: 1-D full Particle-in-Cell Simulation
NASA Astrophysics Data System (ADS)
Nakanotani, Masaru; Hada, T.; Matsukiyo, Shuichi; Mazelle, Christian
2016-07-01
Shock-shock interactions occur on various places in space and the interaction can produce high energy particles. A coronal mass ejection driven shock can collide with the Earth's bow shock [Hietala et al., 2011]. This study reported that ions are accelerated by the first Fermi acceleration between the two shocks before the collision. An electron acceleration through an interplanetary shock-Earth's bow shock interaction was also reported [Terasawa et al., 1997]. Shock-shock interactions can occur in astrophysical phenomena as well as in the heliosphere. For example, a young supernova shock can collide with the wind termination shock of a massive star if they are close to each other [Bykov et al., 2013]. Although hybrid simulations (ions and electrons treated as super-particles and mass-less fluid, respectively) were carried out to understand the kinetic nature of a shock-shock interaction [Cargill et al., 1986], hybrid simulations cannot resolve electron dynamics and non-thermal electrons. We, therefore, use one-dimensional full particle-in-cell (PIC) simulations to investigate a shock-shock interaction in which two shocks collide head-on. In a case of quasi-perpendicular shocks, electrons are accelerated by the mirror reflection between the two shocks before the collision (Fermi acceleration). On the other hand, because ions cannot go back upstream, the electron acceleration mechanism does not occur for ions. In a case of quasi-parallel shocks, ions can go back upstream and are accelerated at the shocks. The accelerated ions have great effect on the shock structure.
Lagrangian MHD Particle-in-Cell simulations of coronal interplanetary shocks driven by observations
NASA Astrophysics Data System (ADS)
Lapenta, Giovanni; Bacchini, Fabio; Bemporad, Alessandro; Susino, Roberto; Olshevskyi, Vyacheslav
2016-04-01
In this work, we compare the spatial distribution of the plasma parameters along the June 11, 1999 CME-driven shock front with the results obtained from a CME-like event simulated with the FLIPMHD3D code, based on the FLIP-MHD Particle-in-Cell (PiC) method. The observational data are retrieved from the combination of white-light (WL) coronagraphic data (for the upstream values) and the application of the Rankine-Hugoniot (RH) equations (for the downstream values). The comparison shows a higher compression ratio X and Alfvénic Mach number MA at the shock nose, and a stronger magnetic field deflection d towards the flanks, in agreement with observations. Then, we compare the spatial distribution of MA with the profiles obtained from the solutions of the shock adiabatic equation relating MA, X, and the angle between the upstream magnetic field and the shock front normal for the special cases of parallel and perpendicular shock, and with a semi-empirical expression for a generically oblique shock. The semi-empirical curve approximates the actual values of MA very well, if the effects of a non-negligible shock thickness and plasma-to magnetic pressure ratio are taken into account throughout the computation. Moreover, the simulated shock turns out to be supercritical at the nose and sub-critical at the flanks. Finally, we develop a new 1D Lagrangian ideal MHD method based on the GrAALE code, to simulate the ion-electron temperature decoupling due to the shock transit. Two models are used, a simple solar wind model and a variable-gamma model. Both produce results in agreement with observations, the second one being capable of introducing the physics responsible for the additional electron heating due to secondary effects (collisions, Alfvén waves, etc.). Work supported by the European Commission under the SWIFF project (swiff.eu)
NASA Astrophysics Data System (ADS)
Thurgood, J. O.; Tsiklauri, D.
2015-12-01
Aims: The simulation of three-wave interaction based plasma emission, thought to be the underlying mechanism for Type III solar radio bursts, is a challenging task requiring fully-kinetic, multi-dimensional models. This paper aims to resolve a contradiction in past attempts, whereby some studies indicate that no such processes occur. Methods: We self-consistently simulate three-wave based plasma emission through all stages by using 2D, fully kinetic, electromagnetic particle-in-cell simulations of relaxing electron beams using the EPOCH2D code. Results: Here we present the results of two simulations; Run 1 (nb/n0 = 0.0057, vb/ Δvb = vb/Ve = 16) and Run 2 (nb/n0 = 0.05, vb/ Δvb = vb/Ve = 8), which we find to permit and prohibit plasma emission respectively. We show that the possibility of plasma emission is contingent upon the frequency of the initial electrostatic waves generated by the bump-in-tail instability, and that these waves may be prohibited from participating in the necessary three-wave interactions due to frequency conservation requirements. In resolving this apparent contradiction through a comprehensive analysis, in this paper we present the first self-consistent demonstration of fundamental and harmonic plasma emission from a single-beam system via fully kinetic numerical simulation. We caution against simulating astrophysical radio bursts using unrealistically dense beams (a common approach which reduces run time), as the resulting non-Langmuir characteristics of the initial wave modes significantly suppresses emission. Comparison of our results also indicates that, contrary to the suggestions of previous authors, an alternative plasma emission mechanism based on two counter-propagating beams is unnecessary in an astrophysical context. Finally, we also consider the action of the Weibel instability which generates an electromagnetic beam mode. As this provides a stronger contribution to electromagnetic energy than the emission, we stress that
Revealing the sub-structures of the magnetic reconnection separatrix via particle-in-cell simulation
Zhou, M.; Deng, X. H.; Pang, Y.; Xu, X. J.; Yao, M.; Huang, S. Y.; Yuan, Z. G.; Li, H. M.; Wang, D. D.; Wang, Y. H.
2012-07-15
Magnetic separatrix is an important boundary layer separating the inflow and outflow regions in magnetic reconnection. In this article, we investigate the sub-structures of the separatrix region by using two-and-half dimensional electromagnetic particle-in-cell simulation. The separatrix region can be divided into two sub-regions in terms of the ion and electron frozen-in conditions. Far from the neutral sheet, ions and electrons are magnetized in magnetic fields. Approaching the neutral sheet, ion frozen-in condition is broken in a narrow region ({approx}c/{omega}{sub pi}) at the edge of a density cavity, while electrons are frozen-in to magnetic fields. In this region, electric field E{sub z} is around zero, and the convective term -(v{sub i} Multiplication-Sign B) is balanced by the Hall term in the generalized Ohm's law because ions carry the perpendicular current. Inside the density cavity, both ion and electron frozen-in conditions are broken. The region consists of two sub-ion or electron-scale layers, which contain intense electric fields. Formation of the two sub-layers is due to the complex electron flow pattern around the separatrix region. In the layer, E{sub z} is balanced by a combination of Hall term and the divergence of electron pressure tensor, with the Hall term being dominant. Our preliminary simulation result shows that the separatrix region in guide field reconnection also contains two sub-regions: the inner region and the outer region. However, the inner region contains only one current layer in contrast with the case without guide field.
Particle-in-Cell WARP simulation studies of positron plasmas in micro-Penning-Malmberg traps
NASA Astrophysics Data System (ADS)
Narimannezhad, Alireza; Weber, Marc H.; Lynn, Kelvin G.
2013-10-01
The charged particles storage capacity of microtraps with large length to radius aspect ratios and radii of the order of tens of microns was explored using particle-in-cell WARP code. The new design of the trap consisted of an array of microtraps with substantially lower end electrodes potential than conventional Penning-Malmberg traps, which makes this trap quite portable. It was shown that each microtrap with 50 μm radius immersed in a 7 T uniform, axial magnetic field, stored positrons with a density (1.6E11 cm-3) even higher than that in conventional Penning-Malmberg traps (~ 1E11 cm-3) while the confinement voltage was only 10 V. The trapped density scaled as r-2 down to 3 μm radius. It was presented in this work how to evaluate and lower the numerical noise by controlling the modeling parameters so the simulated plasma can evolve toward computational equilibrium. The local equilibrium distribution was attained in time scales of the simulation for plasmas initialized with a uniform density and Boltzmann energy distribution. The charge clouds developed the expected radial soft edge density distribution and rigid rotation evolved to some extent. To reach global equilibrium (i.e. rigid rotation) longer runs are required. The plasma confinement time and its thermalization were independent of the length. We would like to thank program managers Dr. William Beck and Dr. Parvez Uppal of the ARL who provide funding under contract W9113M-09-C-0075, and program manager Dr. Scott Coombe of the ONR who provide finding under award #N00014-10-1-0543.
Particle-in-cell simulations of the critical ionization velocity effect in finite size clouds
Moghaddam-Taaheri, E.; Lu, G.; Nishikawa, K.I.
1994-04-01
The critical ionization velocity (CIV) mechanism in a finite size cloud is studied with a series of electrostatic particle-in-cell simulations. It is observed that an initial seed ionization, produced by non-CIV mechanisms, generates a cross-field ion beam which excites a modified beam-plasma instability (MBPI) with frequency in the range of the lower hybrid frequency. The excited waves accelerate electrons along the magnetic field up to the ion drift energy that exceeds the ionization energy of the neutral atoms. The heated electrons in turn enhance the ion beam by electron-neutral impact ionization, which established a positive feedback loop in maintaining the CIV process. It is also found that the efficiency of the CIV mechanism depends on the finite size of the gas cloud in the following ways: (1) Along the ambient magnetic field the finite size of the cloud, L{parallel}, restricts the growth of the fastest growing mode, with a wavelength {lambda}{sub m{parallel}}, of the MBPI. (2) Momentum coupling between the cloud and the ambient plasma via the Alfven waves occurs as a result of the finite size of the cloud in the direction perpendicular to both the ambient magnetic field and the neutral drift. (3) The transverse charge separation field across the cloud was found to result in the modulation of the beam velocity which reduces the parallel heating of electrons and increases the transverse acceleration of electrons. (4) Some energetic electrons are lost from the cloud along the magnetic field at a rate characterized by the acoustic velocity, instead of the electron thermal velocity. It is also shown that a factor of 4 increase in the ambient plasma density, increases the CIV ionization yield by almost 2 orders of magnitude at the end of a typical run. The simulation results are used to interpret various chemical release experiments in space. 68 refs., 22 figs., 4 tabs.
Particle-in-cell simulations of electron beam control using an inductive current divider
Swanekamp, S. B.; Angus, J. R.; Cooperstein, G.; Ottinger, P. F.; Richardson, A. S.; Schumer, J. W.; Weber, B. V.
2015-11-15
Kinetic, time-dependent, electromagnetic, particle-in-cell simulations of the inductive current divider are presented. The inductive current divider is a passive method for controlling the trajectory of an intense, hollow electron beam using a vacuum structure that inductively splits the beam's return current. The current divider concept was proposed and studied theoretically in a previous publication [Swanekamp et al., Phys. Plasmas 22, 023107 (2015)]. A central post carries a portion of the return current (I{sub 1}), while the outer conductor carries the remainder (I{sub 2}) with the injected beam current given by I{sub b} = I{sub 1} + I{sub 2}. The simulations are in agreement with the theory which predicts that the total force on the beam trajectory is proportional to (I{sub 2}−I{sub 1}) and the force on the beam envelope is proportional to I{sub b}. Independent control over both the current density and the beam angle at the target is possible by choosing the appropriate current-divider geometry. The root-mean-square (RMS) beam emittance (ε{sub RMS}) varies as the beam propagates through the current divider to the target. For applications where control of the beam trajectory is desired and the current density at the target is similar to the current density at the entrance foil, there is a modest 20% increase in ε{sub RMS} at the target. For other applications where the beam is pinched to a current density ∼5 times larger at the target, ε{sub RMS} is 2–3 times larger at the target.
Wang, Liang Germaschewski, K.; Hakim, Ammar H.; Bhattacharjee, A.
2015-01-15
We introduce an extensible multi-fluid moment model in the context of collisionless magnetic reconnection. This model evolves full Maxwell equations and simultaneously moments of the Vlasov-Maxwell equation for each species in the plasma. Effects like electron inertia and pressure gradient are self-consistently embedded in the resulting multi-fluid moment equations, without the need to explicitly solving a generalized Ohm's law. Two limits of the multi-fluid moment model are discussed, namely, the five-moment limit that evolves a scalar pressures for each species and the ten-moment limit that evolves the full anisotropic, non-gyrotropic pressure tensor for each species. We first demonstrate analytically and numerically that the five-moment model reduces to the widely used Hall magnetohydrodynamics (Hall MHD) model under the assumptions of vanishing electron inertia, infinite speed of light, and quasi-neutrality. Then, we compare ten-moment and fully kinetic particle-in-cell (PIC) simulations of a large scale Harris sheet reconnection problem, where the ten-moment equations are closed with a local linear collisionless approximation for the heat flux. The ten-moment simulation gives reasonable agreement with the PIC results regarding the structures and magnitudes of the electron flows, the polarities and magnitudes of elements of the electron pressure tensor, and the decomposition of the generalized Ohm's law. Possible ways to improve the simple local closure towards a nonlocal fully three-dimensional closure are also discussed.
NASA Astrophysics Data System (ADS)
Wang, Liang; Hakim, Ammar H.; Bhattacharjee, A.; Germaschewski, K.
2015-01-01
We introduce an extensible multi-fluid moment model in the context of collisionless magnetic reconnection. This model evolves full Maxwell equations and simultaneously moments of the Vlasov-Maxwell equation for each species in the plasma. Effects like electron inertia and pressure gradient are self-consistently embedded in the resulting multi-fluid moment equations, without the need to explicitly solving a generalized Ohm's law. Two limits of the multi-fluid moment model are discussed, namely, the five-moment limit that evolves a scalar pressures for each species and the ten-moment limit that evolves the full anisotropic, non-gyrotropic pressure tensor for each species. We first demonstrate analytically and numerically that the five-moment model reduces to the widely used Hall magnetohydrodynamics (Hall MHD) model under the assumptions of vanishing electron inertia, infinite speed of light, and quasi-neutrality. Then, we compare ten-moment and fully kinetic particle-in-cell (PIC) simulations of a large scale Harris sheet reconnection problem, where the ten-moment equations are closed with a local linear collisionless approximation for the heat flux. The ten-moment simulation gives reasonable agreement with the PIC results regarding the structures and magnitudes of the electron flows, the polarities and magnitudes of elements of the electron pressure tensor, and the decomposition of the generalized Ohm's law. Possible ways to improve the simple local closure towards a nonlocal fully three-dimensional closure are also discussed.
NASA Astrophysics Data System (ADS)
Toth, G.; Jia, X.; Chen, Y.; Markidis, S.; Peng, B.; Daldorff, L. K. S.; Tenishev, V.; Borovikov, D.; Haiducek, J. D.; Gombosi, T. I.; Glocer, A.; Dorelli, J.; Lapenta, G.
2015-12-01
We have recently developed a new modeling capability to embed the implicit Particle-in-Cell (PIC) model iPIC3D into the BATS-R-US magnetohydrodynamic model. The PIC domain can cover the regions where kinetic effects are most important, such as reconnection sites. The BATS-R-US code, on the other hand, can efficiently handle the rest of the computational domain where the MHD or Hall MHD description is sufficient with its block-adaptive grid. The current implementation of the MHD-EPIC model allows two-way coupled simulations in two and three dimensions with multiple embedded PIC regions. The MHD and PIC grids can have different grid resolutions. The MHD variables and the moments of the PIC distribution functions are interpolated and message passed in an efficient manner through the Space Weather Modeling Framework (SWMF). Both BATS-R-US and iPIC3D are massively parallel codes fully integrated into, run by and coupled through the SWMF. We have successfully applied the MHD-EPIC code to model Ganymede's magnetosphere. Using four PIC regions we have in effect performed a fully kinetic simulation of the moon's mini-magnetosphere with a grid resolution that is about 5 times finer than the ion inertial length. The Hall MHD model provides proper boundary conditions for the four PIC regions and connects them with each other and with the inner and outer outer boundary conditions of the much larger MHD domain. We compare our results with Galileo magnetic observations and find good overall agreement with both Hall MHD and MHD-EPIC simulations. The power spectrum for the small scale fluctuations, however, agrees with the data much better for the MHD-EPIC simulation than for Hall MHD. In the MHD-EPIC simulation, unlike in the pure Hall MHD results, we also find signatures of flux transfer events (FTEs) that agree very well with the observed FTE signatures both in terms of shape and amplitudes. We will also highlight our ongoing efforts to model the magnetospheres of Mercury and
Particle in Cell Simulations of the Pulsar Y-Point -- Nature of the Accelerating Electric Field
NASA Astrophysics Data System (ADS)
Belyaev, Mikhail
2016-06-01
Over the last decade, satellite observations have yielded a wealth of data on pulsed high-energy emission from pulsars. Several different models have been advanced to fit this data, all of which “paint” the emitting region onto a different portion of the magnetosphere.In the last few years, particle in cell simulations of pulsar magnetospheres have reached the point where they are able to self-consistently model particle acceleration and dissipation. One of the key findings of these simulations is that the region of the current sheet in and around the Y-point provides the highest rate of dissipation of Poynting flux (Belyaev 2015a). On the basis of this physical evidence, it is quite plausible that this region should be associated with the pulsed high energy emission from pulsars. We present high resolution PIC simulations of an axisymmetric pulsar magnetosphere, which are run using PICsar (Belyaev 2015b). These simulations focus on the particle dynamics and electric fields in and around the Y-point region. We run two types of simulations -- first, a force-free magnetosphere and second, a magnetosphere with a gap between the return current layer and the outflowing plasma in the polar wind zone. The latter setup is motivated by studies of pair production with general relativity (Philippov et al. 2015, Belyaev & Parfrey (in preparation)). In both cases, we find that the Y-point and the current sheet in its direct vicinity act like an “electric particle filter” outwardly accelerating particles of one sign of charge while returning the other sign of charge back to the pulsar. We argue that this is a natural behavior of the plasma as it tries to adjust to a solution that is as close to force-free as possible. As a consequence, a large E dot J develops in the vicinity of the Y-point leading to dissipation of Poynting flux. Our work is relevant for explaining the plasma physical mechanisms underlying pulsed high energy emission from pulsars.
NASA Astrophysics Data System (ADS)
Melzani, Mickaël; Walder, Rolf; Folini, Doris; Winisdoerffer, Christophe; Favre, Jean M.
2014-10-01
Magnetic reconnection is a leading mechanism for magnetic energy conversion and high-energy non-thermal particle production in a variety of high-energy astrophysical objects, including ones with relativistic ion-electron plasmas (e.g., microquasars or AGNs), a regime where first principle studies are scarce. We present 2D particle-in-cell (PIC) simulations of low β ion-electron plasmas under relativistic conditions, i.e., with inflow magnetic energy exceeding the plasma restmass energy. We identify outstanding properties: (i) For relativistic inflow magnetizations (here 10 ≤ σe ≤ 360), the reconnection outflows are dominated by thermal agitation instead of bulk kinetic energy. (ii) At high inflow electron magnetization (σe ≥ 80), the reconnection electric field is sustained more by bulk inertia than by thermal inertia. It challenges the thermal-inertia paradigm and its implications. (iii) The inflows feature sharp transitions at the entrance of the diffusion zones. These are not shocks but results from particle ballistic motions, all bouncing at the same location, provided that the thermal velocity in the inflow is far lower than the inflow E × B bulk velocity. (iv) Island centers are magnetically isolated from the rest of the flow and can present a density depletion at their center. (v) The reconnection rates are slightly higher than in non-relativistic studies. They are best normalized by the inflow relativistic Alfvén speed projected in the outflow direction, which then leads to rates in a close range (0.14-0.25), thus allowing for an easy estimation of the reconnection electric field.
Ab Initio Pulsar Magnetosphere: Three-dimensional Particle-in-cell Simulations of Oblique Pulsars
NASA Astrophysics Data System (ADS)
Philippov, Alexander A.; Spitkovsky, Anatoly; Cerutti, Benoit
2015-03-01
We present “first-principles” relativistic particle-in-cell simulations of the oblique pulsar magnetosphere with pair formation. The magnetosphere starts to form with particles extracted from the surface of the neutron star. These particles are accelerated by surface electric fields and emit photons capable of producing electron-positron pairs. We inject secondary pairs at the locations of primary energetic particles whose energy exceeds the threshold for pair formation. We find solutions that are close to the ideal force-free magnetosphere with the Y-point and current sheet. Solutions with obliquities ≤40° do not show pair production in the open field line region because the local current density along the magnetic field is below the Goldreich-Julian value. The bulk outflow in these solutions is charge-separated, and pair formation happens in the current sheet and return current layer only. Solutions with higher inclinations show pair production in the open field line region, with high multiplicity of the bulk flow and the size of the pair-producing region increasing with inclination. We observe the spin-down of the star to be comparable to MHD model predictions. The magnetic dissipation in the current sheet ranges between 20% for the aligned rotator and 3% for the orthogonal rotator. Our results suggest that for low obliquity neutron stars with suppressed pair formation at the light cylinder, the presence of phenomena related to pair activity in the bulk of the polar region, e.g., radio emission, may crucially depend on the physics beyond our simplified model, such as the effects of curved spacetime or multipolar surface fields.
Development of 1D Particle-in-Cell Code and Simulation of Plasma-Wall Interactions
NASA Astrophysics Data System (ADS)
Rose, Laura P.
This thesis discusses the development of a 1D particle-in-cell (PIC) code and the analysis of plasma-wall interactions. The 1D code (Plasma and Wall Simulation -- PAWS) is a kinetic simulation of plasma done by treating both electrons and ions as particles. The goal of this thesis is to study near wall plasma interaction to better understand the mechanism that occurs in this region. The main focus of this investigation is the effects that secondary electrons have on the sheath profile. The 1D code is modeled using the PIC method. Treating both the electrons and ions as macroparticles the field is solved on each node and weighted to each macro particle. A pre-ionized plasma was loaded into the domain and the velocities of particles were sampled from the Maxwellian distribution. An important part of this code is the boundary conditions at the wall. If a particle hits the wall a secondary electron may be produced based on the incident energy. To study the sheath profile the simulations were run for various cases. Varying background neutral gas densities were run with the 2D code and compared to experimental values. Different wall materials were simulated to show their effects of SEE. In addition different SEE yields were run, including one study with very high SEE yields to show the presence of a space charge limited sheath. Wall roughness was also studied with the 1D code using random angles of incidence. In addition to the 1D code, an external 2D code was also used to investigate wall roughness without secondary electrons. The roughness profiles where created upon investigation of wall roughness inside Hall Thrusters based off of studies done on lifetime erosion of the inner and outer walls of these devices. The 2D code, Starfish[33], is a general 2D axisymmetric/Cartesian code for modeling a wide a range of plasma and rarefied gas problems. These results show that higher SEE yield produces a smaller sheath profile and that wall roughness produces a lower SEE yield
Particle-In-Cell simulations on spacecraft charging mitigation by plasma injection
NASA Astrophysics Data System (ADS)
Usui, Hideyuki; Imasato, Koujirou; Kuninaka, Hitoshi
By performing three-dimensional Particle-In-Cell simulations, we have been investigating the time-dependent process of spacecraft charging mitigation by plasma injection. We particularly focus on the differential charging occurring between solar panel and spacecraft conducting part of spacecraft in the polar environment. In the presence of aurora electron beam, the absolute charging of spacecraft becomes the order of KeV as the worst case and the differential charging between the conducting surface of the spacecraft and the dielectric material on the solar panel can become several hundreds volts. To mitigate the charging, active plasma release from a plasma contactor onboard the spacecraft is proposed as one of the effective methods. In order to understand the charging mitigation process we started to examine the transient plasma process in terms of electron/ion flux to the spacecraft surface and the corresponding potential variation by performing 3D PIC simulations. In the simulation space, we set a spacecraft consisting of conducting body and dielectric film on the solar panels. This spacecraft system is immersed in isothermal magnetized plasma environment. We assume the aurora beam energy is around 100 eV. We started a simulation with no plasma emission from the body in order for the spacecraft to achieve a floating potential. Then, we start emitting plasma from the spacecraft surface from one side of the spacecraft. Due to the aurora current, the conducting part of the spacecraft was negatively charged around -50 V while the dielectric surface of the solar panel is about -30 V because of ion flux impinging at the ram side. In this case, approximately 20V differential charging occurs at the dielectric surface. In such a situation, we started emitting electrons from the spacecraft surface. Because of negative charge emission, the spacecraft potential increases and approaches to the plasma potential. This implies the absolute charging of spacecraft has been
NASA Astrophysics Data System (ADS)
Deca, Jan; Divin, Andrey; Lapenta, Giovanni; Lembège, Bertrand; Markidis, Stefano; Horányi, Mihály
2014-05-01
We present the first three-dimensional fully kinetic and electromagnetic simulations of the solar wind interaction with lunar crustal magnetic anomalies (LMAs). Using the implicit particle-in-cell code iPic3D, we confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface forming a mini-magnetosphere, as suggested by spacecraft observations and theory. In contrast to earlier MHD and hybrid simulations, the fully kinetic nature of iPic3D allows to investigate the space charge effects and in particular the electron dynamics dominating the near-surface lunar plasma environment. We describe the general picture of the interaction of a dipole model centred just below the lunar surface under various solar wind and plasma conditions and focus on the kinetic effects. It is shown that the configuration is dominated by electron motion, because the LMA scale size is small with respect to the gyroradius of the solar wind ions. Driven by strong pressure anisotropies, the mini-magnetosphere is also unstable over time, leading to only temporal shielding of the surface underneath. Our work opens new frontiers of research toward a deeper understanding of LMAs and is ideally suited to be compared with field or particle observations from spacecraft such as Kaguya (SELENE), Lunar Prospector or ARTEMIS. The ability to evaluate the implications for future lunar exploration as well as lunar science in general hinges on a better understanding of LMAs. This research has received funding from the European Commission's FP7 Program with the grant agreement SWIFF (project 2633430, swiff.eu) and EHEROES (project 284461, www.eheroes.eu). The simulations were conducted on the computational resources provided by the PRACE Tier-0 project 2011050747 (Curie supercomputer). This research was supported by the Swedish National Space Board, Grant No. 136/11. JD has received support through the HPC-Europa2 visitor programme (project HPC08SSG85) and
Gyrokinetic particle-in-cell simulations of Alfvén eigenmodes in presence of continuum effects
Mishchenko, Alexey Könies, Axel; Hatzky, Roman
2014-05-15
First-principle gyrokinetic particle-in-cell simulations of a global Toroidal Alfvén Eigenmode (TAE) are undertaken in the presence of a strong coupling with the continuum. Effects of the bulk plasma temperature on the interplay between the TAE and Kinetic Alfvén Waves (KAWs) are investigated. A global TAE-KAW structure is identified which appears to be more unstable with respect to the fast ions than a simple (fluid-like) TAE mode.
NASA Astrophysics Data System (ADS)
Moon, Haksu; Teixeira, Fernando L.; Omelchenko, Yuri A.
2015-09-01
We describe a charge-conserving scatter-gather algorithm for particle-in-cell simulations on unstructured grids. Charge conservation is obtained from first principles, i.e., without the need for any post-processing or correction steps. This algorithm recovers, at a fundamental level, the scatter-gather algorithms presented recently by Campos-Pinto et al. (2014) (to first-order) and by Squire et al. (2012), but it is derived here in a streamlined fashion from a geometric viewpoint. Some ingredients reflecting this viewpoint are (1) the use of (discrete) differential forms of various degrees to represent fields, currents, and charged particles and provide localization rules for the degrees of freedom thereof on the various grid elements (nodes, edges, facets), (2) use of Whitney forms as basic interpolants from discrete differential forms to continuum space, and (3) use of a Galerkin formula for the discrete Hodge star operators (i.e., "mass matrices" incorporating the metric datum of the grid) applicable to generally irregular, unstructured grids. The expressions obtained for the scatter charges and scatter currents are very concise and do not involve numerical quadrature rules. Appropriate fractional areas within each grid element are identified that represent scatter charges and scatter currents within the element, and a simple geometric representation for the (exact) charge conservation mechanism is obtained by such identification. The field update is based on the coupled first-order Maxwell's curl equations to avoid spurious modes with secular growth (otherwise present in formulations that discretize the second-order wave equation). Examples are provided to verify preservation of discrete Gauss' law for all times.
Particle-In-Cell/Monte Carlo Simulation of Ion Back Bombardment in Photoinjectors
Qiang, Ji; Corlett, John; Staples, John
2009-03-02
In this paper, we report on studies of ion back bombardment in high average current dc and rf photoinjectors using a particle-in-cell/Monte Carlo method. Using H{sub 2} ion as an example, we observed that the ion density and energy deposition on the photocathode in rf guns are order of magnitude lower than that in a dc gun. A higher rf frequency helps mitigate the ion back bombardment of the cathode in rf guns.
NASA Astrophysics Data System (ADS)
Daldorff, L. K. S.; Toth, G.; Borovikov, D.; Gombosi, T. I.; Lapenta, G.
2014-12-01
With the new modeling capability in the Space Weather Modeling Framework (SWMF) of embedding an implicit Particle-in-Cell (PIC) model iPIC3D into the BATS-R-US magnetohydrodynamics model (Daldorff et al. 2014, JCP, 268, 236) we are ready to locally handle the full physics of the reconnection and its implications on the full system where globally, away from the reconnection region, a magnetohydrodynamic description is satisfactory. As magnetic reconnection is one of the main drivers in magnetospheric and heliospheric plasma dynamics, the self-consistent description of the electron dynamics in the coupled MHD-EPIC model is well suited for investigating the nature of these systems. We will compare the new embedded MHD-EPIC model with pure MHD and Hall MHD simulations of the Earth's magnetosphere.
Huang, C.; An, W.; Decyk, V.K.; Lu, W.; Mori, W.B.; Tsung, F.S.; Tzoufras, M.; Morshed, S.; Antomsen, T.; Feng, B.; Katsouleas, T; Fonseca, R.A.; Martins, S.F.; Vieira, J.; Silva, L.O.; Geddes, C.G.R.; Cormier-Michel, E; Vay, J.-L.; Esarey, E.; Leemans, W.P.; Bruhwiler, D.L.; Cowan, B.; Cary, J.R.; Paul, K.
2009-05-01
The concept and designs of plasma-based advanced accelerators for high energy physics and photon science are modeled in the SciDAC COMPASS project with a suite of Particle-In-Cell codes and simulation techniques including the full electromagnetic model, the envelope model, the boosted frame approach and the quasi-static model. In this paper, we report the progress of the development of these models and techniques and present recent results achieved with large-scale parallel PIC simulations. The simulation needs for modeling the plasma-based advanced accelerator at the energy frontier is discussed and a path towards this goal is outlined.
Lorentz boosted frame simulation technique in Particle-in-cell methods
NASA Astrophysics Data System (ADS)
Yu, Peicheng
In this dissertation, we systematically explore the use of a simulation method for modeling laser wakefield acceleration (LWFA) using the particle-in-cell (PIC) method, called the Lorentz boosted frame technique. In the lab frame the plasma length is typically four orders of magnitude larger than the laser pulse length. Using this technique, simulations are performed in a Lorentz boosted frame in which the plasma length, which is Lorentz contracted, and the laser length, which is Lorentz expanded, are now comparable. This technique has the potential to reduce the computational needs of a LWFA simulation by more than four orders of magnitude, and is useful if there is no or negligible reflection of the laser in the lab frame. To realize the potential of Lorentz boosted frame simulations for LWFA, the first obstacle to overcome is a robust and violent numerical instability, called the Numerical Cerenkov Instability (NCI), that leads to unphysical energy exchange between relativistically drifting particles and their radiation. This leads to unphysical noise that dwarfs the real physical processes. In this dissertation, we first present a theoretical analysis of this instability, and show that the NCI comes from the unphysical coupling of the electromagnetic (EM) modes and Langmuir modes (both main and aliasing) of the relativistically drifting plasma. We then discuss the methods to eliminate them. However, the use of FFTs can lead to parallel scalability issues when there are many more cells along the drifting direction than in the transverse direction(s). We then describe an algorithm that has the potential to address this issue by using a higher order finite difference operator for the derivative in the plasma drifting direction, while using the standard second order operators in the transverse direction(s). The NCI for this algorithm is analyzed, and it is shown that the NCI can be eliminated using the same strategies that were used for the hybrid FFT
Lorentz boosted frame simulation technique in Particle-in-cell methods
NASA Astrophysics Data System (ADS)
Yu, Peicheng
In this dissertation, we systematically explore the use of a simulation method for modeling laser wakefield acceleration (LWFA) using the particle-in-cell (PIC) method, called the Lorentz boosted frame technique. In the lab frame the plasma length is typically four orders of magnitude larger than the laser pulse length. Using this technique, simulations are performed in a Lorentz boosted frame in which the plasma length, which is Lorentz contracted, and the laser length, which is Lorentz expanded, are now comparable. This technique has the potential to reduce the computational needs of a LWFA simulation by more than four orders of magnitude, and is useful if there is no or negligible reflection of the laser in the lab frame. To realize the potential of Lorentz boosted frame simulations for LWFA, the first obstacle to overcome is a robust and violent numerical instability, called the Numerical Cerenkov Instability (NCI), that leads to unphysical energy exchange between relativistically drifting particles and their radiation. This leads to unphysical noise that dwarfs the real physical processes. In this dissertation, we first present a theoretical analysis of this instability, and show that the NCI comes from the unphysical coupling of the electromagnetic (EM) modes and Langmuir modes (both main and aliasing) of the relativistically drifting plasma. We then discuss the methods to eliminate them. However, the use of FFTs can lead to parallel scalability issues when there are many more cells along the drifting direction than in the transverse direction(s). We then describe an algorithm that has the potential to address this issue by using a higher order finite difference operator for the derivative in the plasma drifting direction, while using the standard second order operators in the transverse direction(s). The NCI for this algorithm is analyzed, and it is shown that the NCI can be eliminated using the same strategies that were used for the hybrid FFT
Particle-in-cell simulations of the critical ionization velocity effect in finite size clouds
NASA Technical Reports Server (NTRS)
Moghaddam-Taaheri, E.; Lu, G.; Goertz, C. K.; Nishikawa, K. - I.
1994-01-01
The critical ionization velocity (CIV) mechanism in a finite size cloud is studied with a series of electrostatic particle-in-cell simulations. It is observed that an initial seed ionization, produced by non-CIV mechanisms, generates a cross-field ion beam which excites a modified beam-plasma instability (MBPI) with frequency in the range of the lower hybrid frequency. The excited waves accelerate electrons along the magnetic field up to the ion drift energy that exceeds the ionization energy of the neutral atoms. The heated electrons in turn enhance the ion beam by electron-neutral impact ionization, which establishes a positive feedback loop in maintaining the CIV process. It is also found that the efficiency of the CIV mechanism depends on the finite size of the gas cloud in the following ways: (1) Along the ambient magnetic field the finite size of the cloud, L (sub parallel), restricts the growth of the fastest growing mode, with a wavelength lambda (sub m parallel), of the MBPI. The parallel electron heating at wave saturation scales approximately as (L (sub parallel)/lambda (sub m parallel)) (exp 1/2); (2) Momentum coupling between the cloud and the ambient plasma via the Alfven waves occurs as a result of the finite size of the cloud in the direction perpendicular to both the ambient magnetic field and the neutral drift. This reduces exponentially with time the relative drift between the ambient plasma and the neutrals. The timescale is inversely proportional to the Alfven velocity. (3) The transvers e charge separation field across the cloud was found to result in the modulation of the beam velocity which reduces the parallel heating of electrons and increases the transverse acceleration of electrons. (4) Some energetic electrons are lost from the cloud along the magnetic field at a rate characterized by the acoustic velocity, instead of the electron thermal velocity. The loss of energetic electrons from the cloud seems to be larger in the direction of
NASA Astrophysics Data System (ADS)
Tejero-del-Caz, A.; Fernández Palop, J. I.; Díaz-Cabrera, J. M.; Ballesteros, J.
2016-02-01
A particle-in-cell (PIC) simulation of the plasma sheath around a cylindrical Langmuir probe has been developed to evaluate the ion current collected by the probe. The simulation includes the positive ion thermal motion and has been optimized by solely describing the positive ion motion. A transition from the prediction of the radial model to the orbital-motion-limited model is observed. The transition is explained as an effect of the positive ion thermal motion and the radial model is recovered when the positive ion to electron temperature ratio is decreased. The behaviour of this transition strongly depends on the dimensionless probe radius.
Benchmarking Particle-in-Cell drift wave simulations with Eulerian simulations in a flux-tube
NASA Astrophysics Data System (ADS)
Chen, Yang; Parker, Scott; Wan, Weigang; Bravenec, Ronald; Wang, Eric; Candy, Jeff
2012-10-01
We present the implementation of a flux-tube option in the global turbulence code GEM.footnotetextY. Chen and S. E. Parker, J. Comp. Phys. 220, 839 (2007) This is necessary for benchmarking purposes because of the immense complexity involved in comparing global simulations. The global GEM assumes the magnetic equilibrium to be completely given. Our initial flux-tube implementation simply selects a radial location as the center of the flux-tube and a radial size of the flux-tube, sets all equilibrium quantities (B, ∇B, T, ∇T, the Jacobian etc.) to be equal to their values at the center of the flux-tube, and retains only a linear radial profile of the safety factor needed for boundary conditions. We found good agreement between GEM and GYRO/GS2 for the mode frequency/growth rate in the case of adiabatic electrons, but a difference of ˜15% in the growth rates when kinetic electrons are included. Our goal is to understand the origin of this moderate disagreement. An alternative local geometry model based on a local solution of the Grad-Shafranov equationfootnotetextJ. Candy, Plasma Phys. Control. Fusion 51, 105009 (2009) has been implemented and new benchmarking results from this model will be presented.
Birdsall, C.K. . Dept. of Electrical Engineering and Computer Sciences)
1991-04-01
Many-particle (meaning 100's) charged-particle plasma simulations using spatial meshes for the electromagnetic field solutions, particle-in-cell (PIC) merged with Monte Carlo collision (MCC) calculations, are coming into wide use for application to partially ionized gases. This paper emphasizes the development of PIC computer experiments since the 1950's starting with one-dimensional (1-D) charged-sheet models, the addition of the mesh, and fast direct Poisson equation solvers for 2-D and 3-D. The finite-size particle-in-mesh (finite {Delta}{chi}, {Delta}t) theory of Langdon is presented in part to display the effects of too small {lambda}{sub D}/{Delta}{chi}, even for Maxwellian velocity distributions, as a caution, for example, when some ions are cooled to background gas temperatures by charge exchange. Early work on adding collisions to 1-D charge-sheet models by Burger and Shanny et al. are presented, with many of the elements of current Monte Carlo codes. Bounded plasma modeling is presented with electrode charges and external R, L, C, and V(t), I(t) sources now in use on fast desktop computers as real-time computer experiments, complementing analytic modeling and laboratory experiments. This paper reports that the addition of Monte Carlo collisions (usually done with irregular timesteps) to PIC (usually done with uniform {Delta}t's) is displayed as a developing art, relying on experimental total cross sections and approximate analytical differential cross sections to produce changes in charged-particle speed and direction due to collisions with neutrals, so far including elastic, excitation, ionization, charge exchange, and attachment processes.
NASA Astrophysics Data System (ADS)
Dubinov, Alexander E.
2000-11-01
The earliest stage of a non-completed sliding on a dielectric surface discharge, which is of an avalanche form, is studied by a two-dimensional particle-in-cell computer simulation with the use of a well known self-consistent electromagnetic code `KARAT'. The influence of a dielectric constant on the discharge dynamics is investigated. A return current of secondary electrons is discovered. It is obtained that the dielectric constant increases, approaches the ionization front velocity, decreases, and that there is a growth of an electric field near a cathode.
Pan, K. Q.; Zheng, C. Y. Cao, L. H.; He, X. T.; Wu, Dong; Liu, Z. J.
2015-11-02
Synchrotron radiation is strongly enhanced by the resonant excitation of surface plasma waves (SPWs). Two-dimensional particle-in-cell simulations show that energy conversion efficiency from laser to radiation in the case of SPWs excitation is about 18.7%, which is improved by more than 2 orders of magnitude compared with that of no SPWs excitation. Besides the high energy conversion efficiency, the frequency spectrum and the angular distribution of the radiation are also improved in the case of SPWs excitation because of the quasi-static magnet field induced by surface plasma waves excitation.
Vay, J.-L.; Adam, J.-C.; Heron, A.
2003-09-24
We present an extension of the Berenger Perfectly Matched Layer with additional terms and tunable coefficients which introduce some asymmetry in the absorption rate. We show that the discretized version of the new PML offers superior absorption rates than the discretized standard PML under a plane wave analysis. Taking advantage of the high rates of absorption of the new PML, we have devised a new strategy for introducing the technique of Mesh Refinement into electromagnetic Particle-In-Cell plasma simulations. We present the details of the algorithm as well as a 2-D example of its application to laser-plasma interaction in the context of fast ignition.
NASA Astrophysics Data System (ADS)
Bao, Rong; Wang, Hongguang; Li, Yongdong; Liu, Chunliang
2016-07-01
The output power fluctuations caused by weights of macro particles used in particle-in-cell (PIC) simulations of a backward wave oscillator and a travelling wave tube are statistically analyzed. It is found that the velocities of electrons passed a specific slow-wave structure form a specific electron velocity distribution. The electron velocity distribution obtained in PIC simulation with a relative small weight of macro particles is considered as an initial distribution. By analyzing this initial distribution with a statistical method, the estimations of the output power fluctuations caused by different weights of macro particles are obtained. The statistical method is verified by comparing the estimations with the simulation results. The fluctuations become stronger with increasing weight of macro particles, which can also be determined reversely from estimations of the output power fluctuations. With the weights of macro particles optimized by the statistical method, the output power fluctuations in PIC simulations are relatively small and acceptable.
Jolliet, S.; McMillan, B. F.; Vernay, T.; Villard, L.; Hatzky, R.; Bottino, A.; Angelino, P.
2009-07-15
In this paper, the influence of the parallel nonlinearity on zonal flows and heat transport in global particle-in-cell ion-temperature-gradient simulations is studied. Although this term is in theory orders of magnitude smaller than the others, several authors [L. Villard, P. Angelino, A. Bottino et al., Plasma Phys. Contr. Fusion 46, B51 (2004); L. Villard, S. J. Allfrey, A. Bottino et al., Nucl. Fusion 44, 172 (2004); J. C. Kniep, J. N. G. Leboeuf, and V. C. Decyck, Comput. Phys. Commun. 164, 98 (2004); J. Candy, R. E. Waltz, S. E. Parker et al., Phys. Plasmas 13, 074501 (2006)] found different results on its role. The study is performed using the global gyrokinetic particle-in-cell codes TORB (theta-pinch) [R. Hatzky, T. M. Tran, A. Koenies et al., Phys. Plasmas 9, 898 (2002)] and ORB5 (tokamak geometry) [S. Jolliet, A. Bottino, P. Angelino et al., Comput. Phys. Commun. 177, 409 (2007)]. In particular, it is demonstrated that the parallel nonlinearity, while important for energy conservation, affects the zonal electric field only if the simulation is noise dominated. When a proper convergence is reached, the influence of parallel nonlinearity on the zonal electric field, if any, is shown to be small for both the cases of decaying and driven turbulence.
Particle-in-cell simulations with charge-conserving current deposition on graphic processing units
NASA Astrophysics Data System (ADS)
Ren, Chuang; Kong, Xianglong; Huang, Michael; Decyk, Viktor; Mori, Warren
2011-10-01
Recently using CUDA, we have developed an electromagnetic Particle-in-Cell (PIC) code with charge-conserving current deposition for Nvidia graphic processing units (GPU's) (Kong et al., Journal of Computational Physics 230, 1676 (2011). On a Tesla M2050 (Fermi) card, the GPU PIC code can achieve a one-particle-step process time of 1.2 - 3.2 ns in 2D and 2.3 - 7.2 ns in 3D, depending on plasma temperatures. In this talk we will discuss novel algorithms for GPU-PIC including charge-conserving current deposition scheme with few branching and parallel particle sorting. These algorithms have made efficient use of the GPU shared memory. We will also discuss how to replace the computation kernels of existing parallel CPU codes while keeping their parallel structures. This work was supported by U.S. Department of Energy under Grant Nos. DE-FG02-06ER54879 and DE-FC02-04ER54789 and by NSF under Grant Nos. PHY-0903797 and CCF-0747324.
Particle-in-cell simulation of stationary processes in a relativistic carcinotron
NASA Astrophysics Data System (ADS)
Pegel', I. V.
1996-12-01
A one-dimensional nonstationary model of relativistic carcinotrons, combines the particle-in-cell method in the description of an electron beam with a single-wave approximation in the description of the dynamics of an electromagnetic field. The influence of the intrinsic space charge of the beam is taken into account in the quasistatic approximation. A procedure is developed for computational experiment with a carcinotron in the axisymmetric approximation on the basis of the entirely electromagnetic code KARAT. The computations support the main known laws for a relativistic carcinotron. The effect the space charge has on inertial electronbeam bunching is examined. Mechanisms by which the space charge affects the carcinotron generation efficiency are demonstrated. The space charge may cause anomalously accelerated electrons in the beam and a reverse electron current to appear, increasing the impedance of the coaxial magnetically insulated diode that feeds the device. The carcinotron power and frequency are studied as functions of the strength of the guiding magnetic field. Cyclotron suppression of generation is confirmed. Calculation in combination with an electronic diode shows that generation at a higher frequency can be excited in the cyclotron “dip”.
Two-dimensional particle-in-cell simulations of transport in a magnetized electronegative plasma
Kawamura, E.; Lichtenberg, A. J.; Lieberman, M. A.
2010-11-15
Particle transport in a uniformly magnetized electronegative plasma is studied in two-dimensional (2D) geometry with insulating (dielectric) boundaries. A 2D particle-in-cell (PIC) code is employed, with the results compared to analytic one-dimensional models that approximate the end losses as volume losses. A modified oxygen reaction set is used to scale to the low densities used in PIC codes and also to approximately model other gases. The principal study is the limiting of the transverse electron flow due to strong electron magnetization. The plasma in the PIC calculation is maintained by axial currents that vary across the transverse dimension. For a cosine current profile nearly uniform electron temperature is obtained, which at the B-fields studied (600-1200 G) give a small but significant fraction (0.25 or less) of electron to negative ion transverse loss. For a more transverse-confined current, and approximating the higher mass and attachment reaction rate of iodine, the fraction of electron to negative ion transverse loss can be made very small. The models which have been constructed reasonably approximate the PIC results and indicate that the cross-field transport is nearly classical.
Numerical simulation of quantum systems using the Particle-In-Cell method
NASA Astrophysics Data System (ADS)
Dirkmann, Sven; Youssef, Ziad; Hemke, Torben; Mussenbrock, Thomas
2014-10-01
The Particle-In-Cell (PIC) method is a very powerful method for studying the dynamics of plasmas. It has been primarily developed for tracking the charged particle trajectories subject to selfconsistent and external electromagnetic fields. Exploiting the power of modern computers, one is able to track the classical paths of tens of millions of particles at the same time. In the late 1980th, it was Dawson (and later Dauger) who had the idea to apply the PIC method to the classical part in the semiclassical approach to quantum systems via path integral methods. One could estimate that if a thousands of classical paths are sufficient to describe the dynamics of one quantum particle, then millions classical paths could describe the dynamics of a quantum particle system. A PIC code in the frame of a semiclassical approach would therefore enable the investigation of a number of quantum phenomena, e.g., optical properties, electrical properties, and, ultimately, chemical reactions. In this contribution we explain the use of the PIC code yapic (developed by the authors) in the frame of the path integral method and discuss the numerical results for simple quantum phenomena, i.e., the quantum harmonic oscillator and quantum tunneling. This work is supported by the German Research Foundation in the frame of FOR 2093.
Fully implicit Particle-in-cell algorithms for multiscale plasma simulation
Chacon, Luis
2015-07-16
The outline of the paper is as follows: Particle-in-cell (PIC) methods for fully ionized collisionless plasmas, explicit vs. implicit PIC, 1D ES implicit PIC (charge and energy conservation, moment-based acceleration), and generalization to Multi-D EM PIC: Vlasov-Darwin model (review and motivation for Darwin model, conservation properties (energy, charge, and canonical momenta), and numerical benchmarks). The author demonstrates a fully implicit, fully nonlinear, multidimensional PIC formulation that features exact local charge conservation (via a novel particle mover strategy), exact global energy conservation (no particle self-heating or self-cooling), adaptive particle orbit integrator to control errors in momentum conservation, and canonical momenta (EM-PIC only, reduced dimensionality). The approach is free of numerical instabilities: ω_{pe}Δt >> 1, and Δx >> λ_{D}. It requires many fewer dofs (vs. explicit PIC) for comparable accuracy in challenging problems. Significant CPU gains (vs explicit PIC) have been demonstrated. The method has much potential for efficiency gains vs. explicit in long-time-scale applications. Moment-based acceleration is effective in minimizing N_{FE}, leading to an optimal algorithm.
NASA Astrophysics Data System (ADS)
Zhu, Danni; Zhang, Jun; Zhong, Huihuang; Cai, Dan
2016-03-01
The expansion of cathode plasma in magnetically insulated coaxial diode (MICD) is investigated in theory and particle-in-cell (PIC) simulation. The temperature and density of the cathode plasma are about several eV and 1013-1016 cm-3, respectively, and its expansion velocity is of the level of few cm/μs. Through hydrodynamic theory analysis, expressions of expansion velocities in axial and radial directions are obtained. The characteristics of cathode plasma expansion have been simulated through scaled-down PIC models. Simulation results indicate that the expansion velocity is dominated by the ratio of plasma density other than the static electric field. The electric field counteracts the plasma expansion reverse of it. The axial guiding magnetic field only reduces the radial transport coefficients by a correction factor, but not the axial ones. Both the outward and inward radial expansions of a MICD are suppressed by the much stronger guiding magnetic field and even cease.
López, Rodrigo A.; Muñoz, Víctor; Viñas, Adolfo F.; Valdivia, Juan A.
2015-09-15
We use a particle-in-cell simulation to study the propagation of localized structures in a magnetized electron-positron plasma with relativistic finite temperature. We use as initial condition for the simulation an envelope soliton solution of the nonlinear Schrödinger equation, derived from the relativistic two fluid equations in the strongly magnetized limit. This envelope soliton turns out not to be a stable solution for the simulation and splits in two localized structures propagating in opposite directions. However, these two localized structures exhibit a soliton-like behavior, as they keep their profile after they collide with each other due to the periodic boundary conditions. We also observe the formation of localized structures in the evolution of a spatially uniform circularly polarized Alfvén wave. In both cases, the localized structures propagate with an amplitude independent velocity.
Particle-In-Cell simulation of laser irradiated two-component microspheres in 2 and 3 dimensions
NASA Astrophysics Data System (ADS)
Pauw, Viktoria; Ostermayr, Tobias M.; Bamberg, Karl-Ulrich; Böhl, Patrick; Deutschmann, Fabian; Kiefer, Daniel; Klier, Constantin; Moschüring, Nils; Ruhl, Hartmut
2016-09-01
We examine proton acceleration from spherical carbon-hydrogen targets irradiated by a relativistic laser pulse. Particle-In-Cell (PIC) simulations are carried out in 2 and 3 dimensions (2D and 3D) to compare fast proton spectra. We find very different final kinetic energies in 2D and 3D simulations. We show that they are caused by the different Coulomb fields in 2D and 3D. We propose a correction scheme for the proton energies to test this hypothesis. In the case of sub-focus diameter targets comparison of corrected 2D energies with 3D results show good agreement. This demonstrates that caution is required when modeling experiments with simulations of reduced dimensionality.
The Convergence of Particle-in-Cell Schemes for Cosmological Dark Matter Simulations
NASA Astrophysics Data System (ADS)
Myers, Andrew; Colella, Phillip; Van Straalen, Brian
2016-01-01
Particle methods are a ubiquitous tool for solving the Vlasov-Poisson equation in comoving coordinates, which is used to model the gravitational evolution of dark matter (DM) in an expanding universe. However, these methods are known to produce poor results on idealized test problems, particularly at late times, after the particle trajectories have crossed. To investigate this, we have performed a series of one- and two-dimensional “Zel’dovich pancake” calculations using the popular particle-in-cell (PIC) method. We find that PIC can indeed converge on these problems provided that the following modifications are made. The first modification is to regularize the singular initial distribution function by introducing a small but finite artificial velocity dispersion. This process is analogous to artificial viscosity in compressible gas dynamics, and, as with artificial viscosity, the amount of regularization can be tailored so that its effect outside of a well-defined region—in this case, the high-density caustics—is small. The second modification is the introduction of a particle remapping procedure that periodically reexpresses the DM distribution function using a new set of particles. We describe a remapping algorithm that is third-order accurate and adaptive in phase space. This procedure prevents the accumulation of numerical errors in integrating the particle trajectories from growing large enough to significantly degrade the solution. Once both of these changes are made, PIC converges at second order on the Zel’dovich pancake problem, even at late times, after many caustics have formed. Furthermore, the resulting scheme does not suffer from the unphysical, small-scale “clumping” phenomenon known to occur on the pancake problem when the perturbation wavevector is not aligned with one of the Cartesian coordinate axes.
Ohira, Yutaka; Takahara, Fumio; Reville, Brian; Kirk, John G.
2009-06-10
In supernova remnants, the nonlinear amplification of magnetic fields upstream of collisionless shocks is essential for the acceleration of cosmic rays to the energy of the 'knee' at 10{sup 15.5} eV. A nonresonant instability driven by the cosmic ray current is thought to be responsible for this effect. We perform two-dimensional, particle-in-cell simulations of this instability. We observe an initial growth of circularly polarized nonpropagating magnetic waves as predicted in linear theory. It is demonstrated that in some cases the magnetic energy density in the growing waves can grow to at least 10 times its initial value. We find no evidence of competing modes, nor of significant modification by thermal effects. At late times, we observe saturation of the instability in the simulation, but the mechanism responsible is an artifact of the periodic boundary conditions and has no counterpart in the supernova-shock scenario.
Niknam, A. R. Roozbahani, H.; Komaizi, D.; Hashemzadeh, M.
2014-09-15
The nonlinear evolution of low frequency Buneman instability in an unmagnetized current-driven plasma with q-nonextensive electron velocity distribution is investigated using particle in cell simulation. Simulation results show that the generation of electron phase space holes and the counter-streaming current induced in the plasma strongly depend on the q-parameter. It is found that by increasing the nonextensive parameter, the distribution of electron density becomes highly peaked. This density steepening or grating-like pattern occurs at the saturation time. In addition, a generalized dispersion relation is obtained using the kinetic theory. Analysis of the dispersion relation and the temporal evolution of the electric field energy density reveal that the growth rate of instability increases by increasing the q-parameter. Finally, the results of Maxwellian and q-nonextensive velocity distributions have been compared and discussed.
Heinrich, Jonathon R.; Cooke, David L.
2013-09-15
Electron trapping, electron heating, space-charge wings, wake eddies, and current collection by a positive probe in E×B drifting plasma were studied in three-dimensional electromagnetic particle-in-cell simulations. In these simulations, electrons and ions were magnetized with respect to the probe and the plasma was underdense (ω{sub pe}<ω{sub ce}). A large drift velocity (Mach 4.5 with respect to the ion acoustic speed) between the plasma and probe was created with background electric and magnetic fields. Four distinct regions developed in the presences of the positive probe: a quasi-trapped electron region, an electron-depletion wing, an ion-rich wing, and a wake region. We report on the observations of strong electron heating mechanisms, space-charge wings, ion cyclotron charge-density eddies in the wake, electron acceleration due to a magnetic presheath, and the current-voltage relationship.
NASA Astrophysics Data System (ADS)
Cook, J. W. S.; Dendy, R. O.; Chapman, S. C.
2013-06-01
Ion cyclotron emission (ICE) is the only collective radiative instability, driven by confined fusion-born alpha-particles, observed from deuterium-tritium (DT) plasmas in both JET and TFTR. Using first principles particle-in-cell simulations of the magnetoacoustic cyclotron instability (MCI), we elucidate some of the fully kinetic nonlinear processes that may underlie observations of ICE from fusion products in these large tokamaks. We find that the MCI is intrinsically self-limiting on very fast timescales, which may help explain the observed correlation between linear theory and observed ICE intensity. The simulations elaborate the nature of the excited electric and magnetic fluctuations, from first principles, confirming the dominant role of fast Alfvénic and electrostatic components which is assumed ab initio in analytical treatments.
Xiao, Jianyuan; Liu, Jian; Qin, Hong; Yu, Zhi; Xiang, Nong
2015-09-15
In this paper, the nonlinear mode conversion of extraordinary waves in nonuniform magnetized plasmas is studied using the variational symplectic particle-in-cell simulation. The accuracy of the nonlinear simulation is guaranteed by the long-term accuracy and conservativeness of the symplectic algorithm. The spectra of the electromagnetic wave, the evolution of the wave reflectivity, the energy deposition profile, and the parameter-dependent properties of radio-frequency waves during the nonlinear mode conversion are investigated. It is illustrated that nonlinear effects significantly modify the physics of the radio-frequency injection in magnetized plasmas. The evolutions of the radio-frequency wave reflectivity and the energy deposition are observed, as well as the self-interaction of the Bernstein waves and mode excitations. Even for waves with small magnitude, nonlinear effects can also become important after continuous wave injections, which are common in the realistic radio-frequency wave heating and current drive experiments.
Dipp, T.M. |
1993-12-01
The generation of radiation via photoelectrons induced off of a conducting surface was explored using Particle-In-Cell (PIC) code computer simulations. Using the MAGIC PIC code, the simulations were performed in one dimension to handle the diverse scale lengths of the particles and fields in the problem. The simulations involved monoenergetic, nonrelativistic photoelectrons emitted normal to the illuminated conducting surface. A sinusoidal, 100% modulated, 6.3263 ns pulse train, as well as unmodulated emission, were used to explore the behavior of the particles, fields, and generated radiation. A special postprocessor was written to convert the PIC code simulated electron sheath into far-field radiation parameters by means of rigorous retarded time calculations. The results of the small-spot PIC simulations were used to generate various graphs showing resonance and nonresonance radiation quantities such as radiated lobe patterns, frequency, and power. A database of PIC simulation results was created and, using a nonlinear curve-fitting program, compared with theoretical scaling laws. Overall, the small-spot behavior predicted by the theoretical scaling laws was generally observed in the PIC simulation data, providing confidence in both the theoretical scaling laws and the PIC simulations.
Chen, Guangye; Chacon, Luis; Knoll, Dana Alan; Barnes, Daniel C
2015-07-31
A multi-rate PIC formulation was developed that employs large timesteps for slow field evolution, and small (adaptive) timesteps for particle orbit integrations. Implementation is based on a JFNK solver with nonlinear elimination and moment preconditioning. The approach is free of numerical instabilities (ω_{pe}Δt >>1, and Δx >> λ_{D}), and requires many fewer dofs (vs. explicit PIC) for comparable accuracy in challenging problems. Significant gains (vs. conventional explicit PIC) may be possible for large scale simulations. The paper is organized as follows: Vlasov-Maxwell Particle-in-cell (PIC) methods for plasmas; Explicit, semi-implicit, and implicit time integrations; Implicit PIC formulation (Jacobian-Free Newton-Krylov (JFNK) with nonlinear elimination allows different treatments of disparate scales, discrete conservation properties (energy, charge, canonical momentum, etc.)); Some numerical examples; and Summary.
NASA Astrophysics Data System (ADS)
Mitchell, Robert A.; Schumacher, Douglass W.; Chowdhury, Enam A.
2015-11-01
We present our results of a fundamental simulation of a periodic grating structure formation on a copper target during the femtosecond-pulse laser damage process, and compare our results to recent experiment. The particle-in-cell (PIC) method is used to model the initial laser heating of the electrons, a two-temperature model (TTM) is used to model the thermalization of the material, and a modified PIC method is employed to model the atomic transport leading to a damage crater morphology consistent with experimental grating structure formation. This laser-induced periodic surface structure (LIPSS) is shown to be directly related to the formation of surface plasmon polaritons (SPP) and their interference with the incident laser pulse.
Particle-in-cell simulations of multi-MeV pulsed X-ray induced air plasmas at low pressures
NASA Astrophysics Data System (ADS)
Ribière, M.; Cessenat, O.; d'Almeida, T.; de Gaufridy de Dortan, F.; Maulois, M.; Delbos, C.; Garrigues, A.; Azaïs, B.
2016-03-01
A full kinetic modelling of the charge particles dynamics generated upon the irradiation of an air-filled cavity by a multi-MeV pulsed x-ray is performed. From the calculated radiative source generated by the ASTERIX generator, we calculated the electromagnetic fields generated by x-ray induced air plasmas in a metallic cavity at different pressures. Simulations are carried out based on a Particle-In-Cell interpolation method which uses 3D Maxwell-Vlasov calculations of the constitutive charged species densities of air plasmas at different pressures at equilibrium. The resulting electromagnetic fields within the cavity are calculated for different electron densities up to 4 × 1010 cm-3. For each air pressure, we show electronic plasma waves formation followed by Landau damping. As electron density increases, the calculations exhibit space-charged neutralization and return current formation.
NASA Technical Reports Server (NTRS)
Thiemann, H.; Schunk, R. W.
1990-01-01
The interaction between satellite solar arrays and the LEO plasma is presently studied with particle-in-cell simulations in which an electrical potential was suddenly applied to the solar cell interconnector. The consequent temporal response was followed for the real O(+)-electron mass ratio in the cases of 100- and 250-V solar cells, various solar cell thicknesses, and solar cells with secondary electron emission. Larger applied potentials and thinner solar cells lead to greater initial polarization surface charges, and therefore longer discharging and shielding times. When secondary electron emission from the cover glass is brought to bear, however, the potential structure is nearly planar, allowing constant interaction between plasma electrons and cover glass; a large fraction of the resulting secondary electrons is collected by the interconnector, constituting an order-of-magnitude increase in collected current.
NASA Astrophysics Data System (ADS)
Shukla, Chandrasekhar; Das, Amita; Patel, Kartik
2016-08-01
We carry out particle-in-cell simulations to study the instabilities associated with a 2-D sheared electron flow configuration against a neutralizing background of ions. Both weak and strong relativistic flow velocities are considered. In the weakly relativistic case, we observe the development of electromagnetic Kelvin-Helmholtz instability with similar characteristics as that predicted by the electron Magnetohydrodynamic (EMHD) model. On the contrary, in a strong relativistic case, the compressibility effects of electron fluid dominate and introduce upper hybrid electrostatic oscillations transverse to the flow which are very distinct from EMHD fluid behavior. In the nonlinear regime, both weak and strong relativistic cases lead to turbulence with broad power law spectrum.
NASA Astrophysics Data System (ADS)
Hofmann, I.; Boine-Frankenheim, O.
2014-12-01
The numerical noise inherent to particle-in-cell (PIC) simulation of 3d anisotropic high intensity bunched beams in periodic focusing is compared with the analytical model by Struckmeier [Part. Accel. 45, 229 (1994)]. The latter assumes that entropy growth can be related to Markov type stochastic processes due to temperature anisotropy and the artificial "collisions" caused by using macro-particles and calculating the space charge effect. The PIC simulations are carried out with the tracewin code widely used for high intensity beam simulation. The resulting noise can lead to growth of the six-dimensional rms emittance. The logarithm of the latter is shown to qualify as rms-based entropy. We confirm the dependence of this growth on the bunch temperature anisotropy as predicted by Struckmeier. However, we also find a grid and focusing dependent component of noise not predicted by Struckmeier. Although commonalities exist with well-established models for collision effects in PIC-simulation of extended plasmas, a distinctive feature is the presence of a periodic focusing potential, wherein the beam one-component plasma extends only over relatively few Debye lengths. Our findings are applied in particular to noise in high current linac beam simulation, where they help for optimization of the balance between the number of simulation particles and the grid resolution.
NASA Astrophysics Data System (ADS)
Innocenti, Maria Elena; Beck, Arnaud; Markidis, Stefano; Lapenta, Giovanni
2013-10-01
Particle in Cell (PIC) simulations of plasmas are not bound anymore by the stability constraints of explicit algorithms. Semi implicit and fully implicit methods allow to use larger grid spacings and time steps. Adaptive Mesh Refinement (AMR) techniques permit to locally change the simulation resolution. The code proposed in Innocenti et al., 2013 and Beck et al., 2013 is however the first to combine the advantages of both. The use of the Implicit Moment Method allows to taylor the resolution used in each level to the physical scales of interest and to use high Refinement Factors (RF) between the levels. The Multi Level Multi Domain (MLMD) structure, where all levels are simulated as complete domains, conjugates algorithmic and practical advantages. The different levels evolve according to the local dynamics and achieve optimal level interlocking. Also, the capabilities of the Object Oriented programming model are fully exploited. The MLMD algorithm is demonstrated with magnetic reconnection and collisionless shocks simulations with very high RFs between the levels. Notable computational gains are achieved with respect to simulations performed on the entire domain with the higher resolution. Beck A. et al. (2013). submitted. Innocenti M. E. et al. (2013). JCP, 238(0):115-140.
Fully kinetic particle-in-cell simulations of a deuterium gas puff z pinch.
Welch, D R; Rose, D V; Clark, R E; Mostrom, C B; Stygar, W A; Leeper, R J
2009-12-18
We present the first fully kinetic, collisional, and electromagnetic simulations of the complete time evolution of a deuterium gas puff z pinch. Recent experiments with 15-MA current pinches have suggested that the dominant neutron-production mechanism is thermonuclear. We observe distinct differences between the kinetic and magnetohydrodynamic simulations in the pinch evolution with the kinetic simulations producing both thermonuclear and beam-target neutrons. The kinetic approach demonstrated in this Letter represents a viable alternative for performing future plasma physics calculations. PMID:20366259
On efficiency of collisions` simulation via particles-in-cells technique
Ovchenkov, P.A.; Sigov, Yu.S.
1995-12-31
Macro-particle technique is widely used to simulate kinetic processes in plasmas and plasma-like media. The common feature of various versions of this technique is tracing phase particles trajectories and detection of macro-characteristics system under modelling as average by particles band. The method is rather costly from the point of view of computer resources needed (as compared with flid calculations) but it permits to simulate complex kinetic processes in cases whet their precise theoretical description is impossible. In particular, the PIC technique allows to simulate spatial-nonuniform (SNU) non-equilibrium systems with self-consistent fields. The pair collisions between macro-particles are often used to model collisions in the frame of particle simulation technique. In so doing the SNU problems are not eliminated. By {open_quotes}pair collisions{close_quotes} we mean the collisions` simulation techniques witch is characterize by use of a collision act between two macro-particles. Such a method is commonly used in molecular dynamic technique. The collision can be treated as either determinate (solid sphere technique) or probabilistic one. There with, as the second interaction agent can be used both the same particle and a hypotetic {open_quotes}average{close_quotes} particle with properties derived from averaging over particles` ensemble. In the first case the technique must include the procedure of choice of pairs for collisions, the second one must include some averaging procedure. In this paper we propose one more method of pair collisions.
NASA Astrophysics Data System (ADS)
Hughes, R. Scott; Wang, Joseph; Decyk, Viktor K.; Gary, S. Peter
2016-04-01
This paper investigates how the physics of the whistler anisotropy instability (WAI) is affected by variations in the electron thermal velocity vte, referred to here in terms of the ratio v̂ t e=vt e/c , where c is the speed of light. The WAI is driven by the electron condition RT>1 , where RT=Te ⊥/Te ∥ is the temperature anisotropy ratio and ⊥/∥ signify directions perpendicular/parallel to the background magnetic field B0 . While a typical value of v̂ t e in the solar wind is ˜0.005 , electromagnetic (EM) particle-in-cell (PIC) simulations often use a value near 0.1 in order to maximize the computational time step. In this study, a two-dimensional (2D) Darwin particle-in-cell (DPIC) code, MDPIC2, is used. The time step in the DPIC model is not affected by the choice of v̂ t e , making DPIC suited for this study. A series of simulations are carried out under the condition that the electron βe is held fixed, while v̂ t e is varied over the range 0.1 ≥v̂ t e≥0.025 . The results show that, with βe held fixed, the linear dispersion properties and the nonlinear saturation amplitude and pitch angle scattering rates associated with the WAI are insensitive to the value of v̂ t e . A supplementary investigation is conducted which characterizes how the WAI model is affected at various values of v̂ t e by noise associated with the limited number of particles in a typical PIC simulation. It is found that the evolution of the WAI is more strongly influenced by electrostatic noise as v̂ t e is decreased. The electrostatic noise level is inversely proportional to the number of particles per computational cell ( Nc ); this implies that the number of particles required to remove nonphysical effects from the PIC simulation increases as v̂ t e decreases. It is concluded that PIC simulations of this instability which use an artificially large value of v̂ t e accurately reproduce the response of a cooler plasma as long as a realistic value of βe is used
Kwok, Dixon T. K.; Wu, Shuilin; Liu, Xiangmei; Fu, Ricky K. Y.; Chu, Paul K.
2008-03-01
A multiple-grid-particle-in-cell numerical method has been developed. This method uses grids of different cell sizes and details are needed in only one part of the simulation region and not others. Hence, there are fewer nodes in the simulation thereby reduced computational time without sacrificing details. In the multiple-grid system, a phenomenon is identified to arise at the interface between two grids and a half-cell weighting method is utilized to solve the weighting issue at the boundary. It is shown that the expression of the change of momentum has no weighting function. This method is employed to numerically simulate the plasma immersion ion implantation process into a nickel titanium rod measuring 50 mm long and 4.8 mm in diameter used in orthopaedic surgery. To conduct more uniform implantation, the NiTi rod is elevated on the sample stage by a metal rod. The nitrogen implantation fluences and depth profiles are simulated and compared to experimental values determined by x-ray photoelectron spectroscopy.
Qi, Xin; Xu, Yan-xia; Duan, Wen-shan E-mail: lyang@impcas.ac.cn; Zhang, Ling-yu; Yang, Lei E-mail: lyang@impcas.ac.cn
2014-08-15
The head-on collision of two ion acoustic solitary waves in plasmas composed of hot electrons and cold ions has been studied by using the Poincare-Lighthill-Kuo (PLK) perturbation method and one-dimensional Particle-in-Cell (PIC) simulation. Then the phase lags of ion acoustic solitary waves (IASWs) obtained from the two approaches have been compared and discussed. It has been found that: if the amplitudes of both the colliding IASWs are small enough, the phase lags obtained from PLK method are in good agreement with those obtained from PIC simulation. As the amplitudes of IASWs increase, the phase lags from PIC simulation become smaller than the analytical ones from PLK method. Besides, the PIC simulation shows the phase lag of an IASW involved in collision depends not only on the characteristics of the wave it collides with but also on itself, which disagrees with the prediction of the PLK method. Finally, the application scopes of the PLK method in studying both the single IASW and the head-on collisions of IASWs have been studied and discussed, and the latter turns out to be more strict.
Fully 3D Particle-in-Cell Simulation of Double Post-Hole Convolute on PTS Facility
NASA Astrophysics Data System (ADS)
Zhao, Hailong; Dong, Ye; Zhou, Haijing; Zou, Wenkang; Institute of Fluid Physics Collaboration; Institute of Applied Physics; Computational Mathematics Collaboration
2015-11-01
In order to get better understand of energy transforming and converging process during High Energy Density Physics (HEDP) experiments, fully 3D particle-in-cell (PIC) simulation code NEPTUNE3D was used to provide numerical approach towards parameters which could hardly be acquired through diagnostics. Cubic region (34cm × 34cm × 18cm) including the double post-hole convolute (DPHC) on the primary test stand (PTS) facility was chosen to perform a series of fully 3D PIC simulations, calculating ability of codes were tested and preliminary simulation results about DPHC on PTS facility were discussed. Taking advantages of 3D simulation codes and large-scale parallel computation, massive data (~ 250GB) could be acquired in less than 5 hours and clear process of current transforming and electron emission in DPHC were demonstrated with the help of visualization tools. Cold-chamber tests were performed during which only cathode electron emission was considered without temperature rise or ion emission, current loss efficiency was estimated to be 0.46% ~ 0.48% by comparisons between output magnetic field profiles with or without electron emission. Project supported by the National Natural Science Foundation of China (Grant No. 11205145, 11305015, 11475155).
NASA Astrophysics Data System (ADS)
Doss, C. E.; Cassak, P. A.; Swisdak, M.
2016-08-01
We investigate magnetic reconnection in systems simultaneously containing asymmetric (anti-parallel) magnetic fields, asymmetric plasma densities and temperatures, and arbitrary in-plane bulk flow of plasma in the upstream regions. Such configurations are common in the high-latitudes of Earth's magnetopause and in tokamaks. We investigate the convection speed of the X-line, the scaling of the reconnection rate, and the condition for which the flow suppresses reconnection as a function of upstream flow speeds. We use two-dimensional particle-in-cell simulations to capture the mixing of plasma in the outflow regions better than is possible in fluid modeling. We perform simulations with asymmetric magnetic fields, simulations with asymmetric densities, and simulations with magnetopause-like parameters where both are asymmetric. For flow speeds below the predicted cutoff velocity, we find good scaling agreement with the theory presented in Doss et al. [J. Geophys. Res. 120, 7748 (2015)]. Applications to planetary magnetospheres, tokamaks, and the solar wind are discussed.
Quasi-One-Dimensional Particle-in-Cell Simulation of Magnetic Nozzles
NASA Technical Reports Server (NTRS)
Ebersohn, Frans H.; Sheehan, J. P.; Gallimore, Alec D.; Shebalin, John V.
2015-01-01
A method for the quasi-one-dimensional simulation of magnetic nozzles is presented and simulations of a magnetic nozzle are performed. The effects of the density variation due to plasma expansion and the magnetic field forces on ion acceleration are investigated. Magnetic field forces acting on the electrons are found to be responsible for the formation of potential structures which accelerate ions. The effects of the plasma density variation alone are found to only weakly affect ion acceleration. Strongly diverging magnetic fields drive more rapid potential drops.
Foust, F. R.; Bell, T. F.; Spasojevic, M.; Inan, U. S.
2011-06-15
We present results showing the measured Landau damping rate using a high-order discontinuous Galerkin particle-in-cell (DG-PIC) [G. B. Jacobs and J. S. Hesthaven, J. Comput. Phys. 214, 96 (2006)] method. We show that typical damping rates measured in particle-in-cell (PIC) simulations can differ significantly from the linearized Landau damping coefficient and propose a simple numerical method to solve the plasma dispersion function exactly for moderate to high damping rates. Simulation results show a high degree of agreement between the high-order PIC results and this calculated theoretical damping rate.
NASA Astrophysics Data System (ADS)
Main, Daniel; Caplinger, James; Kim, Tony; Sotnikov, Vladimir
2014-10-01
The propagation of electromagnetic (EM) waves can be influenced by the presence of plasma turbulence. It is known that vortex density structures can develop on nonlinear stage of an interchange instability in Earth's ionosphere and can affect radio communication channels. These density structures play an important role in the refraction and scattering of EM waves in Earth's ionosphere and also in laser diagnostic scattering experiments. We will use a numerical solution of nonlinear equations which govern the development of interchange instability to define a spatial dependence of density irregularities which can be used to analyze scattering of high frequency EM waves. This solution contains both large scale vortex density structures coexisting with short scale density perturbations. Next we will initialize a PIC simulation with the density distribution from the fluid simulation to calculate the scattering cross-section and compare the results with an analytic solution obtained using numerically calculated density spectra.
Martins, S. F.; Fonseca, R. A.; Vieira, J.; Silva, L. O.
2010-05-15
The development of new laser systems at the 10 Petawatt range will push laser wakefield accelerators to novel regimes, for which theoretical scalings predict the possibility to accelerate electron bunches up to tens of GeVs in meter-scale plasmas. Numerical simulations will play a crucial role in testing, probing, and optimizing the physical parameters and the setup of future experiments. Fully kinetic simulations are computationally very demanding, pushing the limits of today's supercomputers. In this paper, the recent developments in the OSIRIS framework [R. A. Fonseca et al., Lect. Notes Comput. Sci. 2331, 342 (2002)] are described, in particular the boosted frame scheme, which leads to a dramatic change in the computational resources required to model laser wakefield accelerators. Results from one-to-one modeling of the next generation of laser systems are discussed, including the confirmation of electron bunch acceleration to the energy frontier.
Abdul, R. F. Mace, R. L.
2015-10-15
Electrostatic Bernstein waves that propagate exactly perpendicularly to a static magnetic field in an electron-ion plasma are investigated using one-and-two-halves dimensional particle-in-cell simulations. An ion-to-electron mass ratio of m{sub i}/m{sub e} = 100 is used, allowing sufficient separation of the electron and ion time scales while still accounting for the ion dynamics without resorting to exceptionally long simulation run times. As a consequence of the mass ratio used, both the high frequency electron Bernstein wave and the lower frequency ion Bernstein wave are resolved within a single simulation run. The simulations presented here use isotropic three-dimensional kappa velocity distributions as well as the widely used Maxwellian velocity distribution, and the results from using each of these velocity distributions are analysed and compared. The behaviour of the Bernstein waves is found to be significantly dependent on the spectral index, κ, of the kappa distribution in all frequency domains of the Bernstein waves. In both the Maxwellian and kappa cases, spectral analysis of the electric field (wave) intensities, as a function of ω and k, show very good agreement between the simulation results and the linear dispersion relation for Bernstein waves. This agreement serves to validate the simulation techniques used, as well as the theory of Bernstein waves in plasmas with a kappa velocity distribution. The intensity of the field fluctuations in the simulations containing an abundance of superthermal particles, i.e., where the plasma has a kappa velocity distribution with a low kappa index, is slightly higher compared to the simulations of plasmas with higher kappa values. The plasmas with low kappa values also exhibit a broader region in frequency space of high intensity field fluctuations.
3-D Particl-in-Cell Simulations of Transport Driven Currents
NASA Astrophysics Data System (ADS)
Tsung, F. S.; Dawson, J. M.
1997-11-01
In the advanced tokamak regime, transport phenomena can account for a signficant fraction of the toroidal current, possibly over that driven directly by the ohmic heating electric fields. Although bootstrap theory accounts for contributions of the collisional modification of banana orbits on the toroidal currents, the corresponding transport theory does not accurately predict the transport of particles and heat in present-day tokamak experiments. Furthermore, in our previous simulations in 21/2-D, currents were spontaneously generated in both the cylindrical and the toroidal geometries, contrary to neoclassical predictions. In these calculations, it was believed that the driving mechanism is the preferential loss of particles whose initial velocity is opposite to that of the plasma current. Because the preferential loss mechanism assumes the conservation of toroidal angular momentum, we have extended these simulations to three dimensions to study the effects of toroidal assymetries. A parallel, 3-D electromagnetic PIC code running on the IBM SP, with a localized field-solver has been developed to investigate the effects of perturbations parallel to the field lines, and direct comparisons has been made between the 21/2-D and 3-D simulations, and we have found good agreements between the 2 1/2-D calculations and the 3-D results. We will present these results at the meeting.
Three-Dimensional Particle-in-Cell Simulations of Laser WakefieldExperiments
Tsung, F.S.; Antonsen, T.; Bruhwiler, D.L.; Cary, J.R.; Decyk,V.K.; Esarey, E.; Geddes, C.G.R.; Huang, C.; Hakim, A.; Katsouleas, T.; Lu, W.; Messmer, P.; Mori, W.B.; Tzoufras, M.; Vieira, J.
2007-06-01
Plasma accelerator methods offer the potential to reduce thesize of moderate and high energy accelerators by factors of 1000. In thepast few years great advances have been made in the production of lowemittance, high quality (i.e., monoenergetic) electron beams withenergies between .1 and 1 GeV using ultra-fast (<50 femtoseconds),high power (>10TW) lasers. The most noticeable of these advances werethe experimental results presented in the "Dream Beam" issue of Natureand in a recent issues of Physical Review Letters, Nature, and NaturePhysics. The experimental progress have been made due to advances inlasers, diagnostics, plasma sources, and the knowledge of how to controlof this highly nonlinear acceleration process. And this experimentalprogress has occurred simultaneously with and been in part due toadvances in modeling capabilities. Using a hierarchy of particlein-cell(PIC) codes OSIRIS, VORPAL, and QuickPIC, we have performed numerous fullscale 3D simulations using parameters quoted from the Nature and NaturePhysics articles. Our simulations have predicted results, providedagreement between simulations and experiments (within the shot-to-shotvariations of the experiments), and provided insight into the complicatedphysics of the experiments. Most importantly, as our confidence in thefidelity of our methods increases we can now guide the planning of newexperiments, and probe parameters that are not yet available. Therebyproviding a "road map" for generating high quality, high-charge 10 to 100GeV electron beams for use in high-energy physics and lightsources.
NASA Astrophysics Data System (ADS)
Sewell, Stephen
This thesis introduces a software framework that effectively utilizes low-cost commercially available Graphic Processing Units (GPUs) to simulate complex scientific plasma phenomena that are modeled using the Particle-In-Cell (PIC) paradigm. The software framework that was developed conforms to the Compute Unified Device Architecture (CUDA), a standard for general purpose graphic processing that was introduced by NVIDIA Corporation. This framework has been verified for correctness and applied to advance the state of understanding of the electromagnetic aspects of the development of the Aurora Borealis and Aurora Australis. For each phase of the PIC methodology, this research has identified one or more methods to exploit the problem's natural parallelism and effectively map it for execution on the graphic processing unit and its host processor. The sources of overhead that can reduce the effectiveness of parallelization for each of these methods have also been identified. One of the novel aspects of this research was the utilization of particle sorting during the grid interpolation phase. The final representation resulted in simulations that executed about 38 times faster than simulations that were run on a single-core general-purpose processing system. The scalability of this framework to larger problem sizes and future generation systems has also been investigated.
NASA Technical Reports Server (NTRS)
Chap, Andrew; Tarditi, Alfonso G.; Scott, John H.
2013-01-01
A Particle-in-cell simulation model has been developed to study the physics of the Traveling Wave Direct Energy Converter (TWDEC) applied to the conversion of charged fusion products into electricity. In this model the availability of a beam of collimated fusion products is assumed; the simulation is focused on the conversion of the beam kinetic energy into alternating current (AC) electric power. The model is electrostatic, as the electro-dynamics of the relatively slow ions can be treated in the quasistatic approximation. A two-dimensional, axisymmetric (radial-axial coordinates) geometry is considered. Ion beam particles are injected on one end and travel along the axis through ring-shaped electrodes with externally applied time-varying voltages, thus modulating the beam by forming a sinusoidal pattern in the beam density. Further downstream, the modulated beam passes through another set of ring electrodes, now electrically oating. The modulated beam induces a time alternating potential di erence between adjacent electrodes. Power can be drawn from the electrodes by connecting a resistive load. As energy is dissipated in the load, a corresponding drop in beam energy is measured. The simulation encapsulates the TWDEC process by reproducing the time-dependent transfer of energy and the particle deceleration due to the electric eld phase time variations.
Study of self-consistent particle flows in a plasma blob with particle-in-cell simulations
Hasegawa, Hiroki Ishiguro, Seiji
2015-10-15
The self-consistent particle flows in a filamentary coherent structure along the magnetic field line in scrape-off layer (SOL) plasma (plasma blob) have been investigated by means of a three-dimensional electrostatic particle-in-cell simulation code. The presence of the spiral current system composed of the diamagnetic and parallel currents in a blob is confirmed by the particle simulation without any assumed sheath boundary models. Furthermore, the observation of the electron and ion parallel velocity distributions in a blob shows that those distributions are far from Maxwellian due to modification with the sheath formation and that the electron temperature on the higher potential side in a blob is higher than that on the lower potential side. Also, it is found that the ions on the higher potential side are accelerated more intensively along the magnetic field line than those on the lower potential side near the edge. This study indicates that particle simulations are able to provide an exact current closure to analysis of blob dynamics and will bring more accurate prediction of plasma transport in the SOL without any empirical assumptions.
Riconda, C.; Weber, S.; Tikhonchuk, V. T.; Adam, J.-C.; Heron, A.
2006-08-15
Two-dimensional particle-in-cell simulations of laser-plasma interaction using a plane-wave geometry show strong bursty stimulated Brillouin backscattering, rapid filamentation, and subsequent plasma cavitation. It is shown that the cavitation is not induced by self-focusing. The electromagnetic fields below the plasma frequency that are excited are related to transient soliton-like structures. At the origin of these solitons is a three-wave decay process exciting new modes in the plasma. The cavitation is responsible for a strong local reduction of the reflectivity and goes along with an efficient but transient heating of the electrons. Once heating ceases, transmission starts to increase. Local as well as global average reflectivities attain a very low value due to strong plasma density variations brought about by the cavitation process. On the one hand, the simulations confirm the existence of a new mechanism of cavity and soliton formation in nonrelativistic laser-plasma interaction in two dimensions, which was shown to exist in one-dimensional simulations [S. Weber, C. Riconda, and V. T. Tikhonchuk, Phys. Rev. Lett. 94, 055005 (2005)]. On the other hand, new aspects are introduced inherently related to the additional degree of freedom.
Fu, Xiangrong; Cowee, Misa M; Friedel, Reinhard H; Funsten, Herbert O; Gary, S Peter; Hospodarsky, George B; Kletzing, Craig; Kurth, William; Larsen, Brian A; Liu, Kaijun; MacDonald, Elizabeth A; Min, Kyungguk; Reeves, Geoffrey D; Skoug, Ruth M; Winske, Dan
2014-01-01
Magnetospheric banded chorus is enhanced whistler waves with frequencies ωr<Ωe, where Ωe is the electron cyclotron frequency, and a characteristic spectral gap at ωr≃Ωe/2. This paper uses spacecraft observations and two-dimensional particle-in-cell simulations in a magnetized, homogeneous, collisionless plasma to test the hypothesis that banded chorus is due to local linear growth of two branches of the whistler anisotropy instability excited by two distinct, anisotropic electron components of significantly different temperatures. The electron densities and temperatures are derived from Helium, Oxygen, Proton, and Electron instrument measurements on the Van Allen Probes A satellite during a banded chorus event on 1 November 2012. The observations are consistent with a three-component electron model consisting of a cold (a few tens of eV) population, a warm (a few hundred eV) anisotropic population, and a hot (a few keV) anisotropic population. The simulations use plasma and field parameters as measured from the satellite during this event except for two numbers: the anisotropies of the warm and the hot electron components are enhanced over the measured values in order to obtain relatively rapid instability growth. The simulations show that the warm component drives the quasi-electrostatic upper band chorus and that the hot component drives the electromagnetic lower band chorus; the gap at ∼Ωe/2 is a natural consequence of the growth of two whistler modes with different properties. PMID:26167433
NASA Astrophysics Data System (ADS)
Kwan, Thomas; Huang, Chengkun; Carlsten, Bruce
2012-10-01
Understanding CSR effects in a bunch compressor requires accurate and self-consistent dynamical simulations accounting for the realistic beam shape and parameters, transient dynamics and possibly a material boundary. We first extend the well-known 1D CSR model into two dimensions and develop a simple numerical algorithm based on the Lienard-Wiechert formula for the electric field of a stiff beam. This numerical model includes the 2D spatial dependence of the field in the bending plane and is accurate for arbitrary beam energy. It also removes the singularity in space charge field presented in a 1D model. Good agreement is obtained with 1D CSR analytic [1] result for FEL related beam parameters but deviations are also found for low-energy or large spot size beams and off-axis fields. We also employ fully electromagnetic Particle-In-Cell (PIC) simulations for self-consistent CSR modeling. The relatively large numerical phase error and anisotropy in a standard PIC algorithm is improved with a high order Finite Difference Time Domain scheme. Detail self-consistent PIC simulations of the CSR fields and beam dynamics will be presented and discussed.
NASA Astrophysics Data System (ADS)
Yu, Peicheng; Xu, Xinlu; Davidson, Asher; Tableman, Adam; Dalichaouch, Thamine; Li, Fei; Meyers, Michael D.; An, Weiming; Tsung, Frank S.; Decyk, Viktor K.; Fiuza, Frederico; Vieira, Jorge; Fonseca, Ricardo A.; Lu, Wei; Silva, Luis O.; Mori, Warren B.
2016-07-01
When modeling laser wakefield acceleration (LWFA) using the particle-in-cell (PIC) algorithm in a Lorentz boosted frame, the plasma is drifting relativistically at βb c towards the laser, which can lead to a computational speedup of ∼ γb2 = (1 - βb2)-1. Meanwhile, when LWFA is modeled in the quasi-3D geometry in which the electromagnetic fields and current are decomposed into a limited number of azimuthal harmonics, speedups are achieved by modeling three dimensional (3D) problems with the computational loads on the order of two dimensional r - z simulations. Here, we describe a method to combine the speedups from the Lorentz boosted frame and quasi-3D algorithms. The key to the combination is the use of a hybrid Yee-FFT solver in the quasi-3D geometry that significantly mitigates the Numerical Cerenkov Instability (NCI) which inevitably arises in a Lorentz boosted frame due to the unphysical coupling of Langmuir modes and EM modes of the relativistically drifting plasma in these simulations. In addition, based on the space-time distribution of the LWFA data in the lab and boosted frame, we propose to use a moving window to follow the drifting plasma, instead of following the laser driver as is done in the LWFA lab frame simulations, in order to further reduce the computational loads. We describe the details of how the NCI is mitigated for the quasi-3D geometry, the setups for simulations which combine the Lorentz boosted frame, quasi-3D geometry, and the use of a moving window, and compare the results from these simulations against their corresponding lab frame cases. Good agreement is obtained among these sample simulations, particularly when there is no self-trapping, which demonstrates it is possible to combine the Lorentz boosted frame and the quasi-3D algorithms when modeling LWFA. We also discuss the preliminary speedups achieved in these sample simulations.
NASA Astrophysics Data System (ADS)
Kakad, A.; Kakad, B. A.; Omura, Y.
2014-12-01
In recent spacecraft observations, coherent electrostatic solitary wave (ESWs) structures are observed in various regions of the Earth's magnetosphere. Over the years, many researchers have attempted to model these observations in terms of electron/ion acoustic solitary waves by using nonlinear fluid theory/simulations. The ESW structures predicted by fluid models can be inadequate due to its inability in handling kinetic effects. To provide clear view on the application of the fluid and kinetic treatments in modeling the ESWs, we perform both fluid and particle-in-cell (PIC) simulations of ion acoustic solitary waves (IASWs) and estimate the quantitative differences in their characteristics like speed, amplitude, and width. It is noted that a long time evolution of Gaussian type perturbations in the equilibrium electron and ion densities generated the nonlinear IASW structures in both fluid and PIC simulations. The IASW structures represent vortices of trapped electrons in PIC simulations. We find that the number of trapped electrons in the wave potential is higher for the large amplitude IASW, which are generated by large-amplitude initial density perturbation (IDP). The present fluid and PIC simulation results are in close agreement for small amplitude IDPs, whereas for large IDPs they show discrepancy in the amplitude, width, and speed of the IASW, which is attributed to negligence of kinetic effects in the former approach. The speed of IASW in the fluid simulations increases with the increase of IASW amplitude, while the reverse tendency is seen in the PIC simulation. The present study suggests that the fluid treatment is appropriate to model the IASW observations when the magnitude of phase velocity of IASW is less than the ion acoustic (IA) speed obtained from their linear dispersion relation, whereas when it exceeds IA speed, it is necessary to include the kinetic effects in the model.
Velocity-Shear Driven Magnetic Reconnection in Particle-In-Cell Simulations
NASA Astrophysics Data System (ADS)
Black, Carrie; Antiochos, Spiro; DeVore, Rick; Karpen, Judy; Germaschewski, Kai
2012-10-01
In the standard model for coronal mass ejections (CME) and/or solar flares, the free energy for the event resides in the strongly sheared magnetic field of a filament channel. The pre-eruption force balance consists of an upward force due to the magnetic pressure of the sheared field balanced by a downward tension due to overlying un-sheared field. Magnetic reconnection is widely believed to be the mechanism that disrupts this force balance, leading to explosive eruption. For understanding CME/flare initiation, therefore, it is critical to model the onset of reconnection that is driven by the buildup of magnetic shear. In MHD simulations, the application of a magnetic field shear is a trivial matter. However, kinetic effects are important in the diffusion region and thus, it is important to examine this process with PIC simulations as well. The implementation of such a driver in PIC methods is nontrivial: it must be done in a self-consistent manner that avoids the generation of waves that destroy the applied shear. In this work, we discuss methods for applying a velocity shear perpendicular to the plane of reconnection within a 2.5D, aperiodic, PIC system. We also discuss the implementation of boundary conditions that allow a net electric current to flow through the walls.
Particle-in-cell plasma simulation codes on the connection machine
NASA Astrophysics Data System (ADS)
Walker, D. W.
Methods for implementing three-dimensional, electromagnetic, relativistic PIC plasma simulation codes on the Connection Machine (CM-2) are discussed. The gather and scatter phases of the PIC algorithm involve indirect indexing of data, which results in a large amount of communication on the CM-2. Different data decompositions are described that seek to reduce the amount of communication while maintaining good load balance. These methods require the particles to be spatially sorted at the start of each time step, which introduced another form of overhead. The different methods are implemented in CM FORTRAN on the CM-2 and compared. It was found that the general router is slow in performing the communication in the gather and scatter steps, which precludes an efficient CM FORTRAN implementation. An alternative method that uses PARIS calls and the NEWS communication network to pipeline data along the axes of the VP set is suggested as a more efficient algorithm.
Particle-In-Cell (PIC) simulation of long-anode magnetron
NASA Astrophysics Data System (ADS)
Verma, Rajendra Kumar; Maurya, Shivendra; Singh, Vindhyavasini Prasad
2016-03-01
Long Anode Magnetron (LAM) is a design scheme adopted to attain greater thermal stability and higher power levels for the conventional magnetrons. So a LAM for 5MW Power level at 2.858 GHz was `Virtual Prototyped' using Admittance Matching field theory (AMT) andthen a PIC Study (Beam-wave interaction) was conducted using CST Particle Studio (CST-PS) which is explained in this paper. The convincing results thus obtained were - hot resonant frequency of 2.834 GHz. Output power of 5 MW at beam voltage of 58kV and applied magnetic field of 2200 Gauss with an overall efficiency of 45%. The simulated parameters values on comparison with the E2V LAM tube (M5028) were in good agreement which validates the feasibility of the design approach.
Particle-in-cell/accelerator code for space-charge dominated beam simulation
2012-05-08
Warp is a multidimensional discrete-particle beam simulation program designed to be applicable where the beam space-charge is non-negligible or dominant. It is being developed in a collaboration among LLNL, LBNL and the University of Maryland. It was originally designed and optimized for heave ion fusion accelerator physics studies, but has received use in a broader range of applications, including for example laser wakefield accelerators, e-cloud studies in high enery accelerators, particle traps and other areas. At present it incorporates 3-D, axisymmetric (r,z) planar (x-z) and transverse slice (x,y) descriptions, with both electrostatic and electro-magnetic fields, and a beam envelope model. The code is guilt atop the Python interpreter language.
Particle-in-cell/accelerator code for space-charge dominated beam simulation
Energy Science and Technology Software Center (ESTSC)
2012-05-08
Warp is a multidimensional discrete-particle beam simulation program designed to be applicable where the beam space-charge is non-negligible or dominant. It is being developed in a collaboration among LLNL, LBNL and the University of Maryland. It was originally designed and optimized for heave ion fusion accelerator physics studies, but has received use in a broader range of applications, including for example laser wakefield accelerators, e-cloud studies in high enery accelerators, particle traps and other areas.more » At present it incorporates 3-D, axisymmetric (r,z) planar (x-z) and transverse slice (x,y) descriptions, with both electrostatic and electro-magnetic fields, and a beam envelope model. The code is guilt atop the Python interpreter language.« less
NASA Astrophysics Data System (ADS)
Blackman, Eric; Park, Jaehong; Ren, Chuang; Workman, Jared
2012-10-01
Low Mach/high beta fast mode shocks can occur in the magnetic reconnection outflows of solar flares. These shocks, which occur above flare loop tops, may provide electron energization responsible for some of the hard X-rays detected by YOHKO and the RHESSE, and radio emission. There has been a dearth of work on understanding the microphysics of these low Mach number shocks. We present new 2D particle-in-cell simulations of low Mach/high beta shocks for the general quasi-perpendicular geometry of field and shock normal to compare with the results for the purely perpendicular case considered in Park et. al. (2012)[Phys.Plasmas 19,062904]. Our aim is to study shock structure and particle acceleration. We find that the modified-two-stream instability sustains the shock and accounts for the entropy creation downstream. We observe the electron Whistler instability in the transition region due to the temperature anisotropy. To have enough simulation electrons above the threshold energy for shock-drift-acceleration (SDA), we inject a two-temperature Maxwellian distribution represented by two separate species, which is approximated to a kappa distribution with κ=10. From particle tracking and the particle energy distribution, we find copious high-energy electrons experiencing SDA.
Ratcliffe, H. Brady, C. S.; Che Rozenan, M. B.; Nakariakov, V. M.
2014-12-15
Quasilinear theory has long been used to treat the problem of a weak electron beam interacting with plasma and generating Langmuir waves. Its extension to weak-turbulence theory treats resonant interactions of these Langmuir waves with other plasma wave modes, in particular, ion-sound waves. These are strongly damped in plasma of equal ion and electron temperatures, as sometimes seen in, for example, the solar corona and wind. Weak turbulence theory is derived in the weak damping limit, with a term describing ion-sound wave damping then added. In this paper, we use the EPOCH particle-in-cell code to numerically test weak turbulence theory for a range of electron-ion temperature ratios. We find that in the cold ion limit, the results agree well, but for increasing ion temperature the three-wave resonance becomes broadened in proportion to the ion-sound wave damping rate. Additionally, we establish lower limits on the number of simulation particles needed to accurately reproduce the electron and wave distributions in their saturated states and to reproduce their intermediate states and time evolution. These results should be taken into consideration in, for example, simulations of plasma wave generation in the solar corona of Type III solar radio bursts from the corona to the solar wind and in weak turbulence investigations of ion-acoustic lines in the ionosphere.
Lo, F. S.; Lee, T. H.; Lu, P. S.; Ragan-Kelley, B.; Minnich, A.; Lin, M. C.; Verboncoeur, J. P.
2014-02-15
A thermionic energy converter (TEC) is a static device that converts heat directly into electricity by boiling electrons off a hot emitter surface across a small inter-electrode gap to a cooler collector surface. The main challenge in TECs is overcoming the space charge limit, which limits the current transmitted across a gap of a given voltage and width. We have verified the feasibility of studying and developing a TEC using a bounded finite-difference time-domain particle-in-cell plasma simulation code, OOPD1, developed by Plasma Theory and Simulation Group, formerly at UC Berkeley and now at Michigan State University. In this preliminary work, a TEC has been modeled kinetically using OOPD1, and the accuracy has been verified by comparing with an analytically solvable case, giving good agreement. With further improvement of the code, one will be able to quickly and cheaply analyze space charge effects, and seek designs that mitigate the space charge effect, allowing TECs to become more efficient and cost-effective.
NASA Astrophysics Data System (ADS)
Kawamura, E.; Lieberman, M. A.; Lichtenberg, A. J.; Chabert, P.; Lazzaroni, C.
2014-06-01
Atmospheric pressure radio-frequency (rf) capacitive micro-discharges are of interest due to emerging applications, especially in the bio-medical field. A previous global model did not consider high-power phenomena such as sheath multiplication, thus limiting its applicability to the lower power range. To overcome this, we use one-dimensional particle-in-cell (PIC) simulations of atmospheric He/0.1% N2 capacitive discharges over a wide range of currents and frequencies to guide the development of a more general global model which is also valid at higher powers. The new model includes sheath multiplication and two classes of electrons: the higher temperature ‘hot’ electrons associated with the sheaths, and the cooler ‘warm’ electrons associated with the bulk. The electric field and the electron power balance are solved analytically to determine the time-varying hot and warm temperatures and the effective rate coefficients. The particle balance equations are integrated numerically to determine the species densities. The model and PIC results are compared, showing reasonable agreement over the range of currents and frequencies studied. They indicate a transition from an α mode at low power characterized by relatively high electron temperature Te with a near uniform profile to a γ mode at high power with a Te profile strongly depressed in the bulk plasma. The transition is accompanied by an increase in density and a decrease in sheath widths. The current and frequency scalings of the model are confirmed by the PIC simulations.
NASA Astrophysics Data System (ADS)
Camporeale, Enrico
2014-05-01
Whistler wave chorus are believed to play a crucial role in the radiation belt dynamics, possibly being responsible for the loss and acceleration of energetic electrons. For this reason, the mechanisms related to the formation and propagation of whistlers in the radiation belt have been intensively investigated during the last decade. It is now generally acknowledged, via observational and simulation studies, that the whistler waves generated close to the magnetic equator through linear temperature anisotropy instabilities undergo an amplitude amplification that is essentially regulated by nonlinear mechanisms. In this work we focus on the wave-particle interaction between electrons and whistler chorus by employing two-dimensional fully-kinetic Particle-in-Cell simulations. The magnetic field is assumed to form a magnetic bottle that captures the particle bouncing motions and mimics the Earth's magnetic dipole. The code employs a semi-implicit time stepping algorithm that, in this context, is shown to be important in order to achieve accurate results with realistic parameters. We analyze and discuss the pitch-angle/energy scattering of energetic particles and comment on the applicability of the quasi-linear diffusion paradigm.
NASA Astrophysics Data System (ADS)
Riquelme, Mario A.; Quataert, Eliot; Verscharen, Daniel
2015-02-01
We use particle-in-cell simulations to study the nonlinear evolution of ion velocity space instabilities in an idealized problem in which a background velocity shear continuously amplifies the magnetic field. We simulate the astrophysically relevant regime where the shear timescale is long compared to the ion cyclotron period, and the plasma beta is β ~ 1-100. The background field amplification in our calculation is meant to mimic processes such as turbulent fluctuations or MHD-scale instabilities. The field amplification continuously drives a pressure anisotropy with p > p ∥ and the plasma becomes unstable to the mirror and ion cyclotron instabilities. In all cases, the nonlinear state is dominated by the mirror instability, not the ion cyclotron instability, and the plasma pressure anisotropy saturates near the threshold for the linear mirror instability. The magnetic field fluctuations initially undergo exponential growth but saturate in a secular phase in which the fluctuations grow on the same timescale as the background magnetic field (with δB ~ 0.3 langBrang in the secular phase). At early times, the ion magnetic moment is well-conserved but once the fluctuation amplitudes exceed δB ~ 0.1 langBrang, the magnetic moment is no longer conserved but instead changes on a timescale comparable to that of the mean magnetic field. We discuss the implications of our results for low-collisionality astrophysical plasmas, including the near-Earth solar wind and low-luminosity accretion disks around black holes.
Riquelme, Mario A.; Quataert, Eliot; Verscharen, Daniel E-mail: eliot@berkeley.edu
2015-02-10
We use particle-in-cell simulations to study the nonlinear evolution of ion velocity space instabilities in an idealized problem in which a background velocity shear continuously amplifies the magnetic field. We simulate the astrophysically relevant regime where the shear timescale is long compared to the ion cyclotron period, and the plasma beta is β ∼ 1-100. The background field amplification in our calculation is meant to mimic processes such as turbulent fluctuations or MHD-scale instabilities. The field amplification continuously drives a pressure anisotropy with p > p {sub ∥} and the plasma becomes unstable to the mirror and ion cyclotron instabilities. In all cases, the nonlinear state is dominated by the mirror instability, not the ion cyclotron instability, and the plasma pressure anisotropy saturates near the threshold for the linear mirror instability. The magnetic field fluctuations initially undergo exponential growth but saturate in a secular phase in which the fluctuations grow on the same timescale as the background magnetic field (with δB ∼ 0.3 (B) in the secular phase). At early times, the ion magnetic moment is well-conserved but once the fluctuation amplitudes exceed δB ∼ 0.1 (B), the magnetic moment is no longer conserved but instead changes on a timescale comparable to that of the mean magnetic field. We discuss the implications of our results for low-collisionality astrophysical plasmas, including the near-Earth solar wind and low-luminosity accretion disks around black holes.
Verification of high voltage rf capacitive sheath models with particle-in-cell simulations
NASA Astrophysics Data System (ADS)
Wang, Ying; Lieberman, Michael; Verboncoeur, John
2009-10-01
Collisionless and collisional high voltage rf capacitive sheath models were developed in the late 1980's [1]. Given the external parameters of a single-frequency capacitively coupled discharge, plasma parameters including sheath width, electron and ion temperature, plasma density, power, and ion bombarding energy can be estimated. One-dimensional electrostatic PIC codes XPDP1 [2] and OOPD1 [3] are used to investigate plasma behaviors within rf sheaths and bulk plasma. Electron-neutral collisions only are considered for collisionless sheaths, while ion-neutral collisions are taken into account for collisional sheaths. The collisionless sheath model is verified very well by PIC simulations for the rf current-driven and voltage-driven cases. Results will be reported for collisional sheaths also. [1] M. A. Lieberman, IEEE Trans. Plasma Sci. 16 (1988) 638; 17 (1989) 338 [2] J. P. Verboncoeur, M. V. Alves, V. Vahedi, and C. K. Birdsall, J. Comp. Phys. 104 (1993) 321 [3] J. P. Verboncoeur, A. B. Langdon and N. T. Gladd, Comp. Phys. Comm. 87 (1995) 199
NASA Astrophysics Data System (ADS)
Gudmundsson, J. T.; Lieberman, M. A.; Wang, Ying; Verboncoeur, J. P.
2009-10-01
The oopd1 particle-in-cell Monte Carlo (PIC-MC) code is used to simulate a capacitively coupled discharge in oxygen. oopd1 is a one-dimensional object-oriented PIC-MC code [1] in which the model system has one spatial dimension and three velocity components. It contains models for planar, cylindrical, and spherical geometries and replaces the XPDx1 series [2], which is not object-oriented. The revised oxygen model includes, in addition to electrons, the oxygen molecule in ground state, the oxygen atom in ground state, the negative ion O^-, and the positive ions O^+ and O2^+. The cross sections for the collisions among the oxygen species have been significantly revised from earlier work using the xpdp1 code [3]. Here we explore the electron energy distribution function (EEDF), the ion energy distribution function (IEDF) and the density profiles for various pressures and driving frequencies. In particular we investigate the influence of the O^+ ion on the IEDF, we explore the influence of multiple driving frequencies, and we do comparisons to the previous xpdx1 codes. [1] J. P. Verboncoeur, A. B. Langdon, and N. T. Gladd, Comp. Phys. Comm. 87 (1995) 199 [2] J. P. Verboncoeur, M. V. Alves, V. Vahedi, and C. K. Birdsall, J. Comp. Physics 104 (1993) 321 [2] V. Vahedi and M. Surendra, Comp. Phys. Comm. 87 (1995) 179
NASA Astrophysics Data System (ADS)
Lafleur, T.; Baalrud, S. D.; Chabert, P.
2016-05-01
Using a 1D particle-in-cell simulation with perpendicular electric, E0, and magnetic, B0, fields, and modelling the azimuthal direction (i.e., the E0 × B0 direction), we study the cross-field electron transport in Hall effect thrusters (HETs). For low plasma densities, the electron transport is found to be well described by classical electron-neutral collision theory, but at sufficiently high densities (representative of typical HETs), a strong instability is observed to significantly enhance the electron mobility, even in the absence of electron-neutral collisions. This instability is associated with correlated high-frequency (of the order of MHz) and short-wavelength (of the order of mm) fluctuations in both the electric field and the plasma density, which are shown to be the cause of the anomalous transport. Saturation of the instability is observed to occur due to a combination of ion-wave trapping in the E0 × B0 direction, and convection in the E0 direction.
Oudini, N.; Raimbault, J.-L.; Chabert, P.; Aanesland, A.; Meige, A.
2013-04-15
A one-dimensional electronegative plasma situated between two symmetrical parallel electrodes under DC bias is studied by Particle-In-Cell simulation with Monte Carlo Collisions. By varying the electronegativity {alpha}{identical_to}n{sub -}/n{sub e} from the limit of electron-ion plasmas (negative ion free) to ion-ion plasmas (electron free), the sheaths formation, the negative ion flux flowing towards the electrodes, and the particle velocities at the sheath edges are investigated. Depending on {alpha}, it is shown that the electronegative plasma behavior can be described by four regimes. In the lowest regime of {alpha}, i.e., {alpha} < 50, negative ions are confined by two positive sheaths within the plasma, while in the higher regimes of {alpha}, a negative sheath is formed and the negative ion flux can be extracted from the bulk plasma. In the two intermediate regimes of {alpha}, i.e., 50 < {alpha} < 10{sup 5}, both the electron and the negative ion fluxes are involved in the neutralization of the positive ions flux that leaves the plasma. In particular, we show that the velocity of the negative ions entering the negative sheath is affected by the presence of the electrons, and is not given by the modified Bohm velocity generally accepted for electronegative plasmas. For extremely high electronegativity, i.e., {alpha} > 10{sup 5}, the presence of electrons in the plasma is marginal and the electronegative plasma can be considered as an ion-ion plasma (electron free).
NASA Astrophysics Data System (ADS)
Usui, Hideyuki; Imasato, Koujiro; Kuninaka, Hitoshi
2008-12-01
We focus on the mitigation process of absolute and differential charging of spacecraft in the polar environment by plasma release from the spacecraft surface. In the presence of aurora electron beam, the absolute charging of spacecraft sometimes becomes the order of KeV at the worst case and the differential charging between the conducting surface of the spacecraft and the dielectric material on the solar panel can become several hundred volts. To avoid the discharge due to the differential charging at the solar panel, plasma release from a plasma contactor onboard the spacecraft is proposed as one of the effective methods. In the current study, we performed three-dimensional Particle-In-Cell simulations to examine the situation of spacecraft charging and its mitigation process by plasma release from the spacecraft surface. To mitigate the absolute charging, we showed the electron release is effective. The released electrons are accelerated away from the spacecraft by the intense electric field induced in the ion sheath at the spacecraft surface. As to the mitigation of differential voltage at the solar panel surface, we showed that ion release in addition to electrons from the contactor is effective. The released ions can neutralize the charges locally accumulated on the dielectric surface. Their dynamics including gyromotion with respect to the geomagnetic field and acceleration along the geomagnetic field can perturb the field and plasma environment in the spacecraft region.
NASA Astrophysics Data System (ADS)
Camporeale, E.; Zimbardo, G.
2015-12-01
We study the wave-particle interactions between lower band chorus whistlers and an anisotropic tenuous population of relativistic electrons. We present the first direct comparison of first-principle particle-in-cell (PIC) simulations with a quasi-linear diffusion code. In the PIC approach, the waves are self-consistently generated by the temperature anisotropy instability that quickly saturates and relaxes the system toward marginal stability. We show that the quasi-linear diffusion and PIC results have significant quantitative mismatch in regions of energy/pitch angle where the resonance condition is not satisfied. Moreover, for pitch angles close to the loss cone the diffusion code overestimates the scattering, particularly at low energies. This suggests that higher-order nonlinear theories should be taken in consideration in order to capture non-resonant interactions, resonance broadening, and to account for scattering at angles close to 90 degree. Finally, we show that pitch angle diffusion is enhanced during the linear wave growth phase, and it rapidly saturates well before a single bounce period. We discuss how the saturation is related to the fact that the domain in which the particles pitch angle diffuse is bounded, and to the well-known problem of 90 degree diffusion barrier.
Lemke, R.W.; Genoni, T.C.; Spencer, T.A.
1999-08-02
This work is an attempt to elucidate effects that may limit efficiency in magnetrons operated at relativistic voltages (V {approximately} 500 kV). Three-dimensional particle-in-cell simulation is used to investigate the behavior of 14 and 22 cavity, cylindrical, rising-sun magnetrons. Power is extracted radially through a single iris located at the end of every other cavity. Numerical results show that in general output power and efficiency increase approximately linearly with increasing iris width (decreasing vacuum Q) until the total Q becomes too low for stable oscillation in the n-mode to be maintained. Beyond this point mode competition and/or switching occur and efficiency decreases. Results reveal that the minimum value of Q (maximum efficiency) that can be achieved prior to the onset of mode competition is significantly affected by the magnitude of the 0-space-harmonic of the {pi}-mode, a unique characteristic of rising-suns, and by the magnitude of the electron current density (space-charge effects). By minimizing these effects, up to 3.7 GW output power has been produced at an efficiency of 40%.
NASA Technical Reports Server (NTRS)
Poppe, A. R.; Halekas, J. S.; Delory, G. T.; Farrell, W. M.
2012-01-01
As the solar wind is incident upon the lunar surface, it will occasionally encounter lunar crustal remanent magnetic fields. These magnetic fields are small-scale, highly non-dipolar, have strengths up to hundreds of nanotesla, and typically interact with the solar wind in a kinetic fashion. Simulations, theoretical analyses, and spacecraft observations have shown that crustal fields can reflect solar wind protons via a combination of magnetic and electrostatic reflection; however, analyses of surface properties have suggested that protons may still access the lunar surface in the cusp regions of crustal magnetic fields. In this first report from a planned series of studies, we use a 1 1/2-dimensional, electrostatic particle-in-cell code to model the self-consistent interaction between the solar wind, the cusp regions of lunar crustal remanent magnetic fields, and the lunar surface. We describe the self-consistent electrostatic environment within crustal cusp regions and discuss the implications of this work for the role that crustal fields may play regulating space weathering of the lunar surface via proton bombardment.
Lu, San; Lu, Quanming; Huang, Can; Wang, Shui; Dong, Quanli; Zhu, Jianqiang; Sheng, Zhengming; Zhang, Jie
2013-11-15
Recently, magnetic reconnection has been realized in high-energy-density laser-produced plasmas. Plasma bubbles with self-generated magnetic fields are created by focusing laser beams to small-scale spots on a foil. The bubbles expand into each other, which may then drive magnetic reconnection. The reconnection experiment in laser-produced plasmas has also been conducted at Shenguang-II (SG-II) laser facility, and the existence of a plasmoid was identified in the experiment [Dong et al., Phys. Rev. Lett. 108, 215001 (2012)]. In this paper, by performing two-dimensional (2-D) particle-in-cell simulations, we investigate such a process of magnetic reconnection based on the experiment on SG-II facility, and a possible explanation for the formation of the plasmoid is proposed. The results show that before magnetic reconnection occurs, the bubbles squeeze strongly each other and a very thin current sheet is formed. The current sheet is unstable to the tearing mode instability, and we can then observe the formation of plasmoid(s) in such a multiple X-lines reconnection.
NASA Astrophysics Data System (ADS)
Wang, Yue; Wang, Jianguo; Chen, Zaigao; Cheng, Guoxin; Wang, Pan
2016-08-01
To overcome the staircase error in the traditional particle-in-cell (PIC) method, a three dimensional (3D) simple conformal (SC) symplectic PIC method is presented in this paper. The SC symplectic finite integration technique (FIT) scheme is used to advance the electromagnetic fields without reduction of the time step. Particles are emitted from conformal boundaries with the charge conserving emission scheme and moved by using the relativistic Newton-Lorentz force equation. The symplectic formulas of auxiliary-differential equation, complex frequency shifted perfectly matched layer (ADE-CFS-PML) are given for truncating the open boundaries, numerical results show that the maximum relative error of truncation is less than 90 dB. Based on the surface equivalence theorem, the computing algorithms of conformal signals' injection are given, numerical results show that the algorithms can give the right mode patterns and the errors of cutoff frequencies could be as low as 0.1%. To verify the conformal algorithms, a magnetically insulated line oscillator is simulated, and the results are compared to those provided by using the 2.5D UNIPIC code, which show that they agree well. The results also show that the high order symplectic integration method can suppress the numerical Cherenkov radiation.
Gibbons, M.R.
1995-06-01
This dissertation describes a new algorithm for simulating low frequency, kinetic phenomena in plasmas. DArwin Direct Implicit Particle-in-Cell (DADIPIC), as its name implies, is a combination of the Darwin and direct implicit methods. One of the difficulties in simulating plasmas lies in the enormous disparity between the fundamental scale lengths of a plasma and the scale lengths of the phenomena of interest. The objective is to create models which can ignore the fundamental constraints without eliminating relevant plasma properties. Over the past twenty years several PIC methods have been investigated for overcoming the constraints on explicit electrodynamic PIC. These models eliminate selected high frequency plasma phenomena while retaining kinetic phenomena at low frequency. This dissertation shows that the combination of Darwin and Direct Implicit allows them to operate better than they have been shown to operate in the past. Through the Darwin method the hyperbolic Maxwell`s equations are reformulated into a set of elliptic equations. Propagating light waves do not exist in the formulation so the Courant constraint on the time step is eliminated. The Direct Implicit method is applied only to the electrostatic field with the result that electrostatic plasma oscillations do not have to be resolved for stability. With the elimination of these constraints spatial and temporal discretization can be much larger than that possible with explicit, electrodynamic PIC. The code functions in a two dimensional Cartesian region and has been implemented with all components of the particle velocities, the E-field, and the B-field. Internal structures, conductors or dielectrics, may be placed in the simulation region, can be set at desired potentials, and driven with specified currents.
Muñoz, P. A. Kilian, P.; Büchner, J.; Told, D.; Jenko, F.
2015-08-15
In this work, we compare gyrokinetic (GK) with fully kinetic Particle-in-Cell (PIC) simulations of magnetic reconnection in the limit of strong guide field. In particular, we analyze the limits of applicability of the GK plasma model compared to a fully kinetic description of force free current sheets for finite guide fields (b{sub g}). Here, we report the first part of an extended comparison, focusing on the macroscopic effects of the electron flows. For a low beta plasma (β{sub i} = 0.01), it is shown that both plasma models develop magnetic reconnection with similar features in the secondary magnetic islands if a sufficiently high guide field (b{sub g} ≳ 30) is imposed in the kinetic PIC simulations. Outside of these regions, in the separatrices close to the X points, the convergence between both plasma descriptions is less restrictive (b{sub g} ≳ 5). Kinetic PIC simulations using guide fields b{sub g} ≲ 30 reveal secondary magnetic islands with a core magnetic field and less energetic flows inside of them in comparison to the GK or kinetic PIC runs with stronger guide fields. We find that these processes are mostly due to an initial shear flow absent in the GK initialization and negligible in the kinetic PIC high guide field regime, in addition to fast outflows on the order of the ion thermal speed that violate the GK ordering. Since secondary magnetic islands appear after the reconnection peak time, a kinetic PIC/GK comparison is more accurate in the linear phase of magnetic reconnection. For a high beta plasma (β{sub i} = 1.0) where reconnection rates and fluctuations levels are reduced, similar processes happen in the secondary magnetic islands in the fully kinetic description, but requiring much lower guide fields (b{sub g} ≲ 3)
Fu, Xiangrong; Cowee, Misa M.; Friedel, Reinhard H.; Funsten, Herbert O.; Gary, S. Peter; Hospodarsky, George B.; Kletzing, Craig; Kurth, William; Larsen, Brian A.; Liu, Kaijun; MacDonald, Elizabeth A.; Reeves, Geoffrey D.; Skoug, Ruth M.; Winske, Dan
2014-10-22
Magnetospheric banded chorus is enhanced whistler waves with frequencies ω_{r} < Ω_{e}, where Ω_{e} is the electron cyclotron frequency, and a characteristic spectral gap at ω_{r} ≃ Ω_{e}/2. This paper uses spacecraft observations and two-dimensional particle-in-cell simulations in a magnetized, homogeneous, collisionless plasma to test the hypothesis that banded chorus is due to local linear growth of two branches of the whistler anisotropy instability excited by two distinct, anisotropic electron components of significantly different temperatures. The electron densities and temperatures are derived from Helium, Oxygen, Proton, and Electron instrument measurements on the Van Allen Probes A satellite during a banded chorus event on 1 November 2012. The observations are consistent with a three-component electron model consisting of a cold (a few tens of eV) population, a warm (a few hundred eV) anisotropic population, and a hot (a few keV) anisotropic population. The simulations use plasma and field parameters as measured from the satellite during this event except for two numbers: the anisotropies of the warm and the hot electron components are enhanced over the measured values in order to obtain relatively rapid instability growth. The simulations show that the warm component drives the quasi-electrostatic upper band chorus and that the hot component drives the electromagnetic lower band chorus; the gap at ~Ω_{e}/2 is a natural consequence of the growth of two whistler modes with different properties.
Fu, Xiangrong; Cowee, Misa M.; Friedel, Reinhard H.; Funsten, Herbert O.; Gary, S. Peter; Hospodarsky, George B.; Kletzing, Craig; Kurth, William; Larsen, Brian A.; Liu, Kaijun; et al
2014-10-22
Magnetospheric banded chorus is enhanced whistler waves with frequencies ωr < Ωe, where Ωe is the electron cyclotron frequency, and a characteristic spectral gap at ωr ≃ Ωe/2. This paper uses spacecraft observations and two-dimensional particle-in-cell simulations in a magnetized, homogeneous, collisionless plasma to test the hypothesis that banded chorus is due to local linear growth of two branches of the whistler anisotropy instability excited by two distinct, anisotropic electron components of significantly different temperatures. The electron densities and temperatures are derived from Helium, Oxygen, Proton, and Electron instrument measurements on the Van Allen Probes A satellite during a bandedmore » chorus event on 1 November 2012. The observations are consistent with a three-component electron model consisting of a cold (a few tens of eV) population, a warm (a few hundred eV) anisotropic population, and a hot (a few keV) anisotropic population. The simulations use plasma and field parameters as measured from the satellite during this event except for two numbers: the anisotropies of the warm and the hot electron components are enhanced over the measured values in order to obtain relatively rapid instability growth. The simulations show that the warm component drives the quasi-electrostatic upper band chorus and that the hot component drives the electromagnetic lower band chorus; the gap at ~Ωe/2 is a natural consequence of the growth of two whistler modes with different properties.« less
NASA Technical Reports Server (NTRS)
Wang, J.; Biasca, R.; Liewer, P. C.
1996-01-01
Although the existence of the critical ionization velocity (CIV) is known from laboratory experiments, no agreement has been reached as to whether CIV exists in the natural space environment. In this paper we move towards more realistic models of CIV and present the first fully three-dimensional, electromagnetic particle-in-cell Monte-Carlo collision (PIC-MCC) simulations of typical space-based CIV experiments. In our model, the released neutral gas is taken to be a spherical cloud traveling across a magnetized ambient plasma. Simulations are performed for neutral clouds with various sizes and densities. The effects of the cloud parameters on ionization yield, wave energy growth, electron heating, momentum coupling, and the three-dimensional structure of the newly ionized plasma are discussed. The simulations suggest that the quantitative characteristics of momentum transfers among the ion beam, neutral cloud, and plasma waves is the key indicator of whether CIV can occur in space. The missing factors in space-based CIV experiments may be the conditions necessary for a continuous enhancement of the beam ion momentum. For a typical shaped charge release experiment, favorable CIV conditions may exist only in a very narrow, intermediate spatial region some distance from the release point due to the effects of the cloud density and size. When CIV does occur, the newly ionized plasma from the cloud forms a very complex structure due to the combined forces from the geomagnetic field, the motion induced emf, and the polarization. Hence the detection of CIV also critically depends on the sensor location.
NASA Astrophysics Data System (ADS)
Muñoz, P. A.; Told, D.; Kilian, P.; Büchner, J.; Jenko, F.
2015-08-01
In this work, we compare gyrokinetic (GK) with fully kinetic Particle-in-Cell (PIC) simulations of magnetic reconnection in the limit of strong guide field. In particular, we analyze the limits of applicability of the GK plasma model compared to a fully kinetic description of force free current sheets for finite guide fields (bg). Here, we report the first part of an extended comparison, focusing on the macroscopic effects of the electron flows. For a low beta plasma (βi = 0.01), it is shown that both plasma models develop magnetic reconnection with similar features in the secondary magnetic islands if a sufficiently high guide field (bg ≳ 30) is imposed in the kinetic PIC simulations. Outside of these regions, in the separatrices close to the X points, the convergence between both plasma descriptions is less restrictive (bg ≳ 5). Kinetic PIC simulations using guide fields bg ≲ 30 reveal secondary magnetic islands with a core magnetic field and less energetic flows inside of them in comparison to the GK or kinetic PIC runs with stronger guide fields. We find that these processes are mostly due to an initial shear flow absent in the GK initialization and negligible in the kinetic PIC high guide field regime, in addition to fast outflows on the order of the ion thermal speed that violate the GK ordering. Since secondary magnetic islands appear after the reconnection peak time, a kinetic PIC/GK comparison is more accurate in the linear phase of magnetic reconnection. For a high beta plasma (βi = 1.0) where reconnection rates and fluctuations levels are reduced, similar processes happen in the secondary magnetic islands in the fully kinetic description, but requiring much lower guide fields (bg ≲ 3).
Particle-in-cell simulation of multipactor discharge on a dielectric in a parallel-plate waveguide
NASA Astrophysics Data System (ADS)
Sakharov, A. S.; Ivanov, V. A.; Konyzhev, M. E.
2016-06-01
An original 2D3V (two-dimensional in coordinate space and three-dimensional in velocity space) particle-in-cell code has been developed for simulation of multipactor discharge on a dielectric in a parallelplate metal waveguide with allowance for secondary electron emission (SEE) from the dielectric surface and waveguide walls, finite temperature of secondary electrons, electron space charge, and elastic and inelastic scattering of electrons from the dielectric and metal surfaces. The code allows one to simulate all stages of the multipactor discharge, from the onset of the electron avalanche to saturation. It is shown that the threshold for the excitation of a single-surface multipactor on a dielectric placed in a low-profile waveguide with absorbing walls increases as compared to that in the case of an unbounded dielectric surface due to escape of electrons onto the waveguide walls. It is found that, depending on the microwave field amplitude and the SEE characteristics of the waveguide walls, the multipactor may operate in two modes. In the first mode, which takes place at relatively low microwave amplitudes, a single-surface multipactor develops only on the dielectric, the surface of which acquires a positively potential with respect to the waveguide walls. In the second mode, which occurs at sufficiently high microwave intensities, a single-surface multipactor on the dielectric and a two-surface multipactor between the waveguide walls operate simultaneously. In this case, both the dielectric surface and the interwall space acquire a negative potential. It is shown that electron scattering from the dielectric surface and waveguide walls results in the appearance of high-energy tails in the electron distribution function.
Fubiani, G. Boeuf, J. P.
2014-07-15
Previously reported 2D Particle-In-Cell Monte Carlo Collisions (PIC-MCC) simulations of negative ion sources under conditions similar to those of the ITER neutral beam injection system have shown that the presence of the magnetic filter tends to generate asymmetry in the plasma properties in the extraction region. In this paper, we show that these conclusions are confirmed by 3D PIC-MCC simulations and we provide quantitative comparisons between the 2D and 3D model predictions.
NASA Astrophysics Data System (ADS)
Hughes, R. S.; Gary, S. P.; Wang, J.
2015-12-01
Three-dimensional particle-in-cell simulations are utilized in order to model the forward cascade of an initially narrowband, isotropic spectrum of relatively long wavelength magnetosonic-whistler fluctuations in a collisionless, homogeneous, magnetized, electron-proton plasma. The intention of the investigation is to gain insight into the details of interaction between the electromagnetic fluctuations, the proton population, and the electron population. In particular, the manner in which each population is heated while the fluctuation energy dissipates is of interest. The results show that electrons are preferentially heated in the direction parallel to the background magnetic field, while ions are preferentially heated perpendicular to the background field. These behaviors appear to be universal with respect to the plasma βe and the initial fluctuation amplitudes. In order to better understand how such heating scales at variable plasma parameters two parametric studies have been carried out. The first study holds β(t=0) fixed at βe = βi = 0.25, and varies the initial fluctuation energy density ɛ0 = Σ δB2/B02 = 0.025, 0.05, 0.1, 0.25, 0.5, while the second study holds ɛ0(t=0) fixed at ɛ0 = 0.1 and varies βe = βi = 0.05, 0.1, 0.25, 0.5, 1.0. The investigations show that the ion heating rates scale approximately linearly with ɛ0, while they have a far weaker scaling with βe.
NASA Astrophysics Data System (ADS)
Liu, Hui; Chen, Peng-Bo; Zhao, Yin-Jian; Yu, Da-Ren
2015-08-01
Magnetic mirror used as an efficient tool to confine plasma has been widely adopted in many different areas especially in recent cusped field thrusters. In order to check the influence of magnetic mirror effect on the plasma distribution in a cusped field thruster, three different radii of the discharge channel (6 mm, 4 mm, and 2 mm) in a cusped field thruster are investigated by using Particle-in-Cell Plus Monte Carlo (PIC-MCC) simulated method, under the condition of a fixed axial length of the discharge channel and the same operating parameters. It is found that magnetic cusps inside the small radius discharge channel cannot confine electrons very well. Thus, the electric field is hard to establish. With the reduction of the discharge channel’s diameter, more electrons will escape from cusps to the centerline area near the anode due to a lower magnetic mirror ratio. Meanwhile, the leak width of the cusped magnetic field will increase at the cusp. By increasing the magnetic field strength in a small radius model of a cusped field thruster, the negative effect caused by the weak magnetic mirror effect can be partially compensated. Therefore, according to engineering design, the increase of magnetic field strength can contribute to obtaining a good performance, when the radial distance between the magnets and the inner surface of the discharge channel is relatively big. Project supported by the National Natural Science Foundation of China (Grant No. 51006028) and the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No. 51121004).
Fu, X. R. Cowee, M. M.; Winske, D.; Liu, K.; Peter Gary, S.
2014-04-15
The velocity space scattering of an anisotropic electron beam (T{sub ⊥b}/T{sub ∥b}>1) flowing along a background magnetic field B{sub 0} through a cold plasma is investigated using both linear theory and 2D particle-in-cell simulations. Here, ⊥ and ∥ represent the directions perpendicular and parallel to B{sub 0}, respectively. In this scenario, we find that two primary instabilities contribute to the scattering in electron pitch angle: an electrostatic electron beam instability and a predominantly parallel-propagating electromagnetic whistler anisotropy instability. Our results show that at relative beam densities n{sub b}/n{sub e}≤0.05 and beam temperature anisotropies T{sub b⊥}/T{sub b∥}≤25, the electrostatic beam instability grows much faster than the whistler instabilities for a reasonably fast hot beam. The enhanced fluctuating fields from the beam instability scatter the beam electrons, slowing their average speed and increasing their parallel temperature, thereby increasing their pitch angles. In an inhomogeneous magnetic field, such as the geomagnetic field, this could result in beam electrons scattered out of the loss cone. After saturation of the electrostatic instability, the parallel-propagating whistler anisotropy instability shows appreciable growth, provided that the beam density and late-time anisotropy are sufficiently large. Although the whistler anisotropy instability acts to pitch-angle scatter the electrons, reducing perpendicular energy in favor of parallel energy, these changes are weak compared to the pitch-angle increases resulting from the deceleration of the beam due to the electrostatic instability.
NASA Astrophysics Data System (ADS)
Deca, J.; Lapenta, G.; Divin, A. V.; Lembege, B.; Markidis, S.
2013-12-01
Unlike the Earth and Mercury, our Moon has no global magnetic field and is therefore not shielded from the impinging solar wind by a magnetosphere. However, lunar magnetic field measurements made by the Apollo missions provided direct evidence that the Moon has regions of small-scale crustal magnetic fields, ranging up to a few 100km in scale size with surface magnetic field strengths up to hundreds of nanoTeslas. More recently, the Lunar Prospector spacecraft has provided high-resolution observations allowing to construct magnetic field maps of the entire Moon, confirming the earlier results from Apollo, but also showing that the lunar plasma environment is much richer than earlier believed. Typically the small-scale magnetic fields are non-dipolar and rather tiny compared to the lunar radius and mainly clustered on the far side of the moon. Using iPic3D we present the first 3D fully kinetic and electromagnetic Particle-in-Cell simulations of the solar wind interaction with lunar magnetic anomalies. We study the behaviour of a dipole model with variable surface magnetic field strength under changing solar wind conditions and confirm that lunar crustal magnetic fields may indeed be strong enough to stand off the solar wind and form a mini-magnetosphere, as suggested by MHD and hybrid simulations and spacecraft observations. 3D-PIC simulations reveal to be very helpful to analyze the diversion/braking of the particle flux and the characteristics of the resulting particles accumulation. The particle flux to the surface is significantly reduced at the magnetic anomaly, surrounded by a region of enhanced density due to the magnetic mirror effect. Second, the ability of iPic3D to resolve all plasma components (heavy ions, protons and electrons) allows to discuss in detail the electron physics leading to the highly non-adiabatic interactions expected as well as the implications for solar wind shielding of the lunar surface, depending on the scale size (solar wind protons
NASA Astrophysics Data System (ADS)
Min, Kyungguk; Liu, Kaijun
2016-01-01
Linear dispersion theory and electromagnetic particle-in-cell (PIC) simulations are used to investigate linear growth and nonlinear saturation of the proton velocity ring-driven instabilities, namely, ion Bernstein instability and Alfvén-cyclotron instability, which lead to fast magnetosonic waves and electromagnetic ion cyclotron waves in the inner magnetosphere, respectively. The proton velocity distribution is assumed to consist of 10% of a ring distribution and 90% of a low-temperature Maxwellian background. Here two cases with ring speeds vr/vA=1 and 2 (vA is the Alfvén speed) are examined in detail. For the two cases, linear theory predicts that the maximum growth rate γm of the Bernstein instability is 0.16Ωp and 0.19Ωp, respectively, and γm of the Alfvén-cyclotron instability is 0.045Ωp and 0.15Ωp, respectively, where Ωp is the proton cyclotron frequency. Two-dimensional PIC simulations are carried out for the two cases to examine the instability development and the corresponding evolution of the particle distributions. Initially, Bernstein waves develop and saturate with strong electrostatic fluctuations. Subsequently, electromagnetic Alfvén-cyclotron waves grow and saturate. Despite their smaller growth rate, the saturation levels of the Alfvén-cyclotron waves for both cases are larger than those of the Bernstein waves. Resonant interactions with the Bernstein waves lead to scattering of ring protons predominantly along the perpendicular velocity component (toward both decreasing and, at a lesser extent, increasing speeds) without substantial change of either the parallel temperature or the temperature anisotropy. Consequently, the Alfvén-cyclotron instability can still grow. Furthermore, the free energy resulting from the pitch angle scattering by the Alfvén-cyclotron waves is larger than the free energy resulting from the perpendicular energy scattering, thereby leading to the larger saturation level of the Alfvén-cyclotron waves.
NASA Astrophysics Data System (ADS)
Innocenti, M. E.; Goldman, M. V.; Newman, D. L.; Markidis, S.; Lapenta, G.
2015-12-01
The long term evolution of large domain Particle In Cell simulations of collisionless magnetic reconnection is investigated following observations that show two possible outcomes for collisionless reconnection: towards a Petschek-like configuration (Gosling 2007) or towards multiple X points (Eriksson et al. 2014). In the simulations presented here and described in [Innocenti2015*], a mixed scenario develops. At earlier time, plasmoids are emitted, disrupting the formation of Petschek-like structures. Later, an almost stationary monster plasmoid forms, preventing the emission of other plasmoids. A situation reminding of Petschek's switch-off then ensues. Switch-off is obtained through a slow shock / rotational discontinuity (SS/RD) compound structure, with the rotation discontinuity downstreamthe slow shock. Two external slow shocks located in correspondence of the separatrices reduce the in plane tangential component of the magnetic field, but not to zero. Two transitions reminding of rotational discontinuities in the internal part of the exhausts then perform the final switch-off. Both the slow shocks and the rotational discontinuities are characterized as such through the analysis of their Rankine-Hugoniot jump conditions. A moderate guide field is used to suppress the development of the firehose instability in the exhaust that prevented switch off in [Liu2012]. Compound SS/RD structures, with the RD located downstream the SS, have been observed in both the solar wind and the magnetosphere in Wind and Geotail data respectively [Whang1998, Whang2004]. Ion trajectiories across the SS/RD structure are followed and the kinetic origin of the SS/RD structure is investigated. * Innocenti, Goldman, Newman, Markidis, Lapenta, Evidence of magnetic field switch-off in collisionless magnetic reconnection, accepted in Astrophysical Journal Letters, 2015 Acknowledgements: NERSC, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of
Zharkova, Valentina V.; Khabarova, Olga V. E-mail: habarova@izmiran.ru
2012-06-10
In this paper, we apply an assumption of the reconnecting heliospheric current sheet (HCS) for explanation of some contradictory results in the experimental detection of the sector boundaries (SBs) from the interplanetary magnetic field and electron pitch-angle measurements. Trajectories, densities, velocity, and pitch-angle distributions of particles accelerated by a super-Dreicer electric field are investigated with 2.5D full kinetic particle-in-cell approach in the HCS assumed to undergo a slow magnetic reconnection process with magnetic field configurations deduced from the solar wind observations. This approach reveals that during motion in a current sheet both kinds of particles, electrons and protons, are to be separated, either fully or partially, with respect to its midplane that can lead to their ejection to the opposite semiplanes that was also observed during the HCS crossings. This separation is found to form Hall's currents and polarization electric field across the current sheet, which distribution over the current sheets allows us to reproduce the magnitudes and temporal profiles of proton and ion velocities measured across the SB (current sheet midplane). This separation process, in turn, divides both kinds of particles on 'transit' and 'bounced' ones depending on a side of the current sheet where they enter it and where they are supposed to be ejected. The transit and bounced protons reproduce rather closely the measured distributions of proton/ion densities about the current sheet midplane with a larger maximum occurring at the heliospheric SB to be formed by the bounced protons and the other two smaller maximums on both sides from the central one to be formed by 'transit' protons. The observed electron distributions of density and energy before and after sector boundary crossings are found to fit the simulated ones for electrons accelerated in a current sheet revealing a sharp increase of density from one side from the HCS boundary and a
Walker, D.W.
1992-07-01
The hierarchical spatial decomposition method is a promising approach to decomposing the particles and computational grid in parallel particle-in-cell application codes, since it is able to maintain approximate dynamic load balance while keeping communication costs low. In this paper we investigate issues in implementing a hierarchical spatial decomposition on a hypercube multiprocessor. Particular attention is focused on the communication needed to update guard ring data, and on the load balancing method. The hierarchical approach is compared with other dynamic load balancing schemes.
NASA Astrophysics Data System (ADS)
Liu, M.; Huang, Z.; Fuks, M. I.; Jiang, W.; Schamiloglu, E.; Liu, C.
2016-05-01
We report on the performance of a 12-cavity rising-sun relativistic magnetron with diffraction output (12-cavity rising-sun RMDO). Particle-in-cell simulations show an electronic efficiency of 70% for a gigawatt output power 12-cavity rising-sun RMDO with a transparent cathode operating in the π mode for an applied voltage of U ˜400 kV ±50 kV. When the RMDO is driven by the "F" transparent cathode, which is a coaxial transparent cathode, the axial leakage current can be reduced by about 50%.
Qiang, J.; Leitner, D.; Todd, D.S.; Ryne, R.D.
2005-03-15
The superconducting ECR ion source VENUS serves as the prototype injector ion source for the Rare Isotope Accelerator (RIA) driver linac. The RIA driver linac requires a great variety of high charge state ion beams with up to an order of magnitude higher intensity than currently achievable with conventional ECR ion sources. In order to design the beam line optics of the low energy beam line for the RIA front end for the wide parameter range required for the RIA driver accelerator, reliable simulations of the ion beam extraction from the ECR ion source through the ion mass analyzing system are essential. The RIA low energy beam transport line must be able to transport intense beams (up to 10 mA) of light and heavy ions at 30 keV.For this purpose, LBNL is developing the parallel 3D particle-in-cell code IMPACT to simulate the ion beam transport from the ECR extraction aperture through the analyzing section of the low energy transport system. IMPACT, a parallel, particle-in-cell code, is currently used to model the superconducting RF linac section of RIA and is being modified in order to simulate DC beams from the ECR ion source extraction. By using the high performance of parallel supercomputing we will be able to account consistently for the changing space charge in the extraction region and the analyzing section. A progress report and early results in the modeling of the VENUS source will be presented.
NASA Astrophysics Data System (ADS)
Qiang, J.; Leitner, D.; Todd, D. S.; Ryne, R. D.
2005-03-01
The superconducting ECR ion source VENUS serves as the prototype injector ion source for the Rare Isotope Accelerator (RIA) driver linac. The RIA driver linac requires a great variety of high charge state ion beams with up to an order of magnitude higher intensity than currently achievable with conventional ECR ion sources. In order to design the beam line optics of the low energy beam line for the RIA front end for the wide parameter range required for the RIA driver accelerator, reliable simulations of the ion beam extraction from the ECR ion source through the ion mass analyzing system are essential. The RIA low energy beam transport line must be able to transport intense beams (up to 10 mA) of light and heavy ions at 30 keV. For this purpose, LBNL is developing the parallel 3D particle-in-cell code IMPACT to simulate the ion beam transport from the ECR extraction aperture through the analyzing section of the low energy transport system. IMPACT, a parallel, particle-in-cell code, is currently used to model the superconducting RF linac section of RIA and is being modified in order to simulate DC beams from the ECR ion source extraction. By using the high performance of parallel supercomputing we will be able to account consistently for the changing space charge in the extraction region and the analyzing section. A progress report and early results in the modeling of the VENUS source will be presented.
Skjaeraasen, Olaf; Melatos, A.; Spitkovsky, A.; /KIPAC, Menlo Park
2005-08-15
A 2.5-dimensional particle-in-cell code is used to investigate the propagation of a large-amplitude, superluminal, nearly transverse electromagnetic (TEM) wave in a relativistically streaming electron-positron plasma with and without a shock. In the freestreaming, unshocked case, the analytic TEM dispersion relation is verified, and the streaming is shown to stabilize the wave against parametric instabilities. In the confined, shocked case, the wave induces strong, coherent particle oscillations, heats the plasma, and modifies the shock density profile via ponderomotive effects. The wave decays over {approx}> 10{sup 2} skin depths; the decay length scale depends primarily on the ratio between the wave frequency and the effective plasma frequency, and on the wave amplitude. The results are applied to the termination shock of the Crab pulsar wind, where the decay length-scale ({approx}> 0.05''?) might be comparable to the thickness of filamentary, variable substructure observed in the optical and X-ray wisps and knots.
NASA Astrophysics Data System (ADS)
Dendy, Richard; Cook, James; Chapman, Sandra
2009-11-01
Suprathermal ion cyclotron emission (ICE) was the first collective radiative instability, driven by fusion products, observed on JET and TFTR. Strong emission occurs at sequential cyclotron harmonics of the energetic ion population at the outer mid-plane. Its intensity scales linearly with fusion reactivity, including its time evolution during a discharge. The emission mechanism is probably the magnetoacoustic cyclotron instability (MCI), involving resonance between: fast Alfv'en waves; cyclotron harmonic waves supported by the energetic particle population and by the background thermal plasma; and a subset of the centrally born fusion products, just inside the trapped-passing boundary, whose drift orbits make large radial excursions. The linear growth rate of the MCI has been intensively studied analytically, and yields good agreement with several key observational features of ICE. To address outstanding issues in the nonlinear ICE regime, we have developed a particle-in-cell code which self-consistently evolves electron and multi-species ion macroparticles and the electromagnetic field. We focus on the growth rate of the MCI, as it evolves from the linear into the nonlinear regime for JET-like parameters.
Yoon, E. S.; Chang, C. S.
2014-03-15
An approximate two-dimensional solver of the nonlinear Fokker-Planck-Landau collision operator has been developed using the assumption that the particle probability distribution function is independent of gyroangle in the limit of strong magnetic field. The isotropic one-dimensional scheme developed for nonlinear Fokker-Planck-Landau equation by Buet and Cordier [J. Comput. Phys. 179, 43 (2002)] and for linear Fokker-Planck-Landau equation by Chang and Cooper [J. Comput. Phys. 6, 1 (1970)] have been modified and extended to two-dimensional nonlinear equation. In addition, a method is suggested to apply the new velocity-grid based collision solver to Lagrangian particle-in-cell simulation by adjusting the weights of marker particles and is applied to a five dimensional particle-in-cell code to calculate the neoclassical ion thermal conductivity in a tokamak plasma. Error verifications show practical aspects of the present scheme for both grid-based and particle-based kinetic codes.
Camporeale, Enrico; Zimbardo, Gaetano
2015-09-15
We present a self-consistent Particle-in-Cell simulation of the resonant interactions between anisotropic energetic electrons and a population of whistler waves, with parameters relevant to the Earth's radiation belt. By tracking PIC particles and comparing with test-particle simulations, we emphasize the importance of including nonlinear effects and time evolution in the modeling of wave-particle interactions, which are excluded in the resonant limit of quasi-linear theory routinely used in radiation belt studies. In particular, we show that pitch angle diffusion is enhanced during the linear growth phase, and it rapidly saturates well before a single bounce period. This calls into question the widely used bounce average performed in most radiation belt diffusion calculations. Furthermore, we discuss how the saturation is related to the fact that the domain in which the particles pitch angle diffuses is bounded, and to the well-known problem of 90° diffusion barrier.
NASA Astrophysics Data System (ADS)
Qin, Hong; Liu, Jian; Xiao, Jianyuan; Zhang, Ruili; He, Yang; Wang, Yulei; Sun, Yajuan; Burby, Joshua W.; Ellison, Leland; Zhou, Yao
2016-01-01
Particle-in-cell (PIC) simulation is the most important numerical tool in plasma physics. However, its long-term accuracy has not been established. To overcome this difficulty, we developed a canonical symplectic PIC method for the Vlasov-Maxwell system by discretising its canonical Poisson bracket. A fast local algorithm to solve the symplectic implicit time advance is discovered without root searching or global matrix inversion, enabling applications of the proposed method to very large-scale plasma simulations with many, e.g. 109, degrees of freedom. The long-term accuracy and fidelity of the algorithm enables us to numerically confirm Mouhot and Villani’s theory and conjecture on nonlinear Landau damping over several orders of magnitude using the PIC method, and to calculate the nonlinear evolution of the reflectivity during the mode conversion process from extraordinary waves to Bernstein waves.
Qin, Hong; Liu, Jian; Xiao, Jianyuan; Zhang, Ruili; He, Yang; Wang, Yulei; Sun, Yajuan; Burby, Joshua W.; Ellison, Leland; Zhou, Yao
2015-12-14
Particle-in-cell (PIC) simulation is the most important numerical tool in plasma physics. However, its long-term accuracy has not been established. To overcome this difficulty, we developed a canonical symplectic PIC method for the Vlasov-Maxwell system by discretising its canonical Poisson bracket. A fast local algorithm to solve the symplectic implicit time advance is discovered without root searching or global matrix inversion, enabling applications of the proposed method to very large-scale plasma simulations with many, e.g. 10(9), degrees of freedom. The long-term accuracy and fidelity of the algorithm enables us to numerically confirm Mouhot and Villani's theory and conjecture on nonlinear Landau damping over several orders of magnitude using the PIC method, and to calculate the nonlinear evolution of the reflectivity during the mode conversion process from extraordinary waves to Bernstein waves.
López, Rodrigo A. Muñoz, Víctor; Viñas, Adolfo F.; Alejandro Valdivia, J.
2014-03-15
Parametric decays of a left-handed circularly polarized Alfvén wave propagating along a constant background magnetic field in a relativistic thermal electron-positron plasma are studied by means of a one dimensional relativistic particle-in-cell simulation. Relativistic effects are included in the Lorentz equation for the momentum of the particles and in their thermal motion, by considering a Maxwell-Jüttner velocity distribution function for the initial condition. In the linear stage of the simulation, we find many instabilities that match the predictions of relativistic fluid theory. In general, the growth rates of the instabilities increase as the pump wave amplitude is increased, and decrease with a raise in the plasma temperatures. We have confirmed that for very high temperatures the Alfvén branch is suppressed, consistent with analytical calculations.
Qiang, J.
2009-10-17
In this paper, we report on study of ion back bombardment in a high average current radio-frequency (RF) photo-gun using a particle-in-cell/Monte Carlo simulation method. Using this method, we systematically studied effects of gas pressure, RF frequency, RF initial phase, electric field profile, magnetic field, laser repetition rate, different ion species on ion particle line density distribution, kinetic energy spectrum, and ion power line density distribution back bombardment onto the photocathode. Those simulation results suggested that effects of ion back bombardment could increase linearly with the background gas pressure and laser repetition rate. The RF frequency has significantly affected the ion motion inside the gun so that the ion power deposition on the photocathode in an RF gun can be several orders of magnitude lower than that in a DC gun. The ion back bombardment can be minimized by appropriately choosing the electric field profile and the initial phase.
NASA Astrophysics Data System (ADS)
Camporeale, Enrico; Zimbardo, Gaetano
2015-09-01
We present a self-consistent Particle-in-Cell simulation of the resonant interactions between anisotropic energetic electrons and a population of whistler waves, with parameters relevant to the Earth's radiation belt. By tracking PIC particles and comparing with test-particle simulations, we emphasize the importance of including nonlinear effects and time evolution in the modeling of wave-particle interactions, which are excluded in the resonant limit of quasi-linear theory routinely used in radiation belt studies. In particular, we show that pitch angle diffusion is enhanced during the linear growth phase, and it rapidly saturates well before a single bounce period. This calls into question the widely used bounce average performed in most radiation belt diffusion calculations. Furthermore, we discuss how the saturation is related to the fact that the domain in which the particles pitch angle diffuses is bounded, and to the well-known problem of 90° diffusion barrier.
NASA Astrophysics Data System (ADS)
Grant, Edwin J.; Posada, Chrystian M.; Castaño, Carlos H.; Lee, Hyoung K.
2011-03-01
A novel x-ray source based on carbon nanotubes (CNTs) field emitters is being developed as an alternative for medical imaging diagnostic technologies. The design is based on an array of millions of micro sized x-ray sources similar to the way pixels are arranged in flat panel displays. The trajectory and focusing characteristics of the field emitted electrons, as well as the x-ray generation characteristics of each one of the proposed micro-sized x-ray tubes are simulated. The electron field emission is simulated using the OOPIC PRO particle-in-cell code. The x-ray generation is analyzed with the MCNPX Monte Carlo code. MCNPX is used to optimize both the bremsstrahlung radiation energy spectra and to verify the angular distribution for 0.25-12 μm thick molybdenum, rhodium and tungsten targets. Also, different extracting, accelerating and focusing voltages, as well as different focusing structures and geometries of the micro cells are simulated using the OOPIC Pro particle-in-cell code. The electron trajectories, beam spot sizes, I-V curves, bremsstrahlung radiation energy spectra, and angular distribution are all analyzed for a given cell. The simulation results show that micro x-ray cells can be used to generate suitable electron currents using CNT field emitters and strike a thin tungsten target to produce an adequate bremsstrahlung spectrum. The shape and trajectory of the electron beam was modified using focusing structures in the microcell. Further modifications to the electron beam are possible and can help design a better x-ray transmission source.
NASA Astrophysics Data System (ADS)
Ngirmang, Gregory K.; Orban, Chris; Feister, Scott; Morrison, John T.; Frische, Kyle D.; Chowdhury, Enam A.; Roquemore, W. M.
2016-04-01
We present 3D Particle-in-Cell (PIC) modeling of an ultra-intense laser experiment by the Extreme Light group at the Air Force Research Laboratory using the Large Scale Plasma (LSP) PIC code. This is the first time PIC simulations have been performed in 3D for this experiment which involves an ultra-intense, short-pulse (30 fs) laser interacting with a water jet target at normal incidence. The laser-energy-to-ejected-electron-energy conversion efficiency observed in 2D(3v) simulations were comparable to the conversion efficiencies seen in the 3D simulations, but the angular distribution of ejected electrons in the 2D(3v) simulations displayed interesting differences with the 3D simulations' angular distribution; the observed differences between the 2D(3v) and 3D simulations were more noticeable for the simulations with higher intensity laser pulses. An analytic plane-wave model is discussed which provides some explanation for the angular distribution and energies of ejected electrons in the 2D(3v) simulations. We also performed a 3D simulation with circularly polarized light and found a significantly higher conversion efficiency and peak electron energy, which is promising for future experiments.
NASA Astrophysics Data System (ADS)
Shi, Feng; Wang, Dezhen; Ren, Chunsheng
2008-06-01
Atmospheric pressure discharge nonequilibrium plasmas have been applied to plasma processing with modern technology. Simulations of discharge in pure Ar and pure He gases at one atmospheric pressure by a high voltage trapezoidal nanosecond pulse have been performed using a one-dimensional particle-in-cell Monte Carlo collision (PIC-MCC) model coupled with a renormalization and weighting procedure (mapping algorithm). Numerical results show that the characteristics of discharge in both inert gases are very similar. There exist the effects of local reverse field and double-peak distributions of charged particles' density. The electron and ion energy distribution functions are also observed, and the discharge is concluded in the view of ionization avalanche in number. Furthermore, the independence of total current density is a function of time, but not of position.
Zhang, Jie; Yang, Yang; Xu, Yan-Xia; Qi, Xin E-mail: duanws@nwnu.edu.cn; Duan, Wen-shan E-mail: duanws@nwnu.edu.cn; Yang, Lei
2014-10-15
The application scope of the Poincare-Lighthill-Kuo (PLK) method is suggested by using the Particle-in-cell (PIC) numerical method to study head-on collision of two solitary waves. Comparisons between the numerical results from PIC simulations and the analytical ones from the PLK method indicate that the both are in good agreement with each other. The dependence of the phase shifts after the head-on collision on both amplitudes of two solitary waves is given from our PIC method. It is found that the phase shifts depended on the amplitude of both waves. The maximum amplitude during the colliding process is approximately equal to the sum of both amplitudes for the small amplitude solitary waves.
Self-consistent Nonlinear Analysis and 3D Particle-In-Cell Simulation of a W-band Gyro-TWT
NASA Astrophysics Data System (ADS)
Tang, Yong; Luo, Yong; Xu, Yong; Yan, Ran
2014-10-01
The self-consistent nonlinear analysis and CST 3D particle-in-cell (PIC) simulation of a W-band gyrotron traveling wave tube (gyro-TWT) are presented in this paper. Both the simulation results of the two codes are excellent agreement with each other. The gyro-TWT loaded with periodic lossy dielectric in the circuit for suppressing potential spurious oscillations. It is driven by a 70kV, 10A gyrating electron beam with velocity ratio of 1.0. PIC simulation results are: the maximum peak output power of 198kW, statured gain of 62.3dB and efficiency of 28.3% at 92.5GHz. Only the operating mode TE 01 is observed in the CST 3D simulation and the potential competing backward wave oscillations are effectively suppressed. The CST simulation also predicts that the device works stably under the condition of the beam current lower than 14A and B 0 /B g lower than 1.05. The simulated bandwidth with peak power greater than 100kW is 6.8GHz without axial velocity spread, and 4.1GHz with 6% axial velocity spread.
Chowdhury, J.; Wan, Weigang; Chen, Yang; Parker, Scott E.; Groebner, Richard J.; Holland, C.; Howard, N. T.
2014-11-15
The δ f particle-in-cell code GEM is used to study the transport “shortfall” problem of gyrokinetic simulations. In local simulations, the GEM results confirm the previously reported simulation results of DIII-D [Holland et al., Phys. Plasmas 16, 052301 (2009)] and Alcator C-Mod [Howard et al., Nucl. Fusion 53, 123011 (2013)] tokamaks with the continuum code GYRO. Namely, for DIII-D the simulations closely predict the ion heat flux at the core, while substantially underpredict transport towards the edge; while for Alcator C-Mod, the simulations show agreement with the experimental values of ion heat flux, at least within the range of experimental error. Global simulations are carried out for DIII-D L-mode plasmas to study the effect of edge turbulence on the outer core ion heat transport. The edge turbulence enhances the outer core ion heat transport through turbulence spreading. However, this edge turbulence spreading effect is not enough to explain the transport underprediction.
The semi-implicit, adaptive Multi-Level Multi-Domain method for Particle In Cell plasma simulations
NASA Astrophysics Data System (ADS)
Innocenti, Maria Elena; Markidis, Stefano; Lapenta, Giovanni
2015-11-01
The Multi Level Multi Domain (MLMD) method (Innocenti (2013), Beck (2014)) is a fully kinetic, semi-implicit PIC method which simulates a domain as a collection of sub-domains where increasingly higher resolution is used. The aim is to reduce the computational costs of PIC simulations: simulations which are computationally challenging even with a traditional semi-implicit PIC code, e.g., realistic mass ratio simulations, become feasible with moderate computational resources. We present two sets of realistic mass ratio simulations: magnetic reconnection and Lower Hybrid Drift Instability (LHDI). MLMD reconnection simulations are discussed in Innocenti (2015). In the MLMD LHDI simulations, we show how the MLMD method cheaply extends the range of simulatedwavenumbers with respect to traditional simulations. We simulate the three LHDI stages (fast and slow LHDI branch, kink instability), which are well separated in wavenumber at realistic mass ratio. The coupling observed by Norgren (2012) between the magnetic field and perpendicular electric field LHDI oscillations in the magnetotail is investigated in these different stages. NERSC, Contract N. DE-AC02-05CH11231, PRACE SuperMUC, contract N. 2013091928, FWO, grant N. 12O5215N.
NASA Astrophysics Data System (ADS)
Voitcu, Gabriel; Echim, Marius
2016-05-01
In this paper we use three-dimensional electromagnetic particle-in-cell simulations to investigate the interaction of a small Larmor radius plasma cloud/jet with a transverse nonuniform magnetic field typical to a tangential discontinuity in a parallel geometry. The simulation setup corresponds to an idealized, yet relevant, magnetospheric configuration likely to be observed at the magnetopause during northward orientation of the interplanetary magnetic field. The numerical simulations are adapted to study the kinetic effects and their role on the transport and entry of localized plasma jets similar to those identified inside the Earth's magnetosheath propagating toward the magnetopause. The simulations reveal the formation of a perpendicular polarization electric field inside the main bulk of the plasma cloud that enables its forward transport and entry across the transverse magnetic field. The jet is able to penetrate the transition region when the height of the magnetic barrier does not exceed a certain critical threshold. Otherwise, the forward transport along the injection direction is stopped before full penetration of the magnetopause. Moreover, the jet is pushed back and simultaneously deflected in the perpendicular plane to the magnetic field. Our simulations evidence physical processes advocated previously by the theoretical model of impulsive penetration and revealed in laboratory experiments.
Park, Jaehong; Ren Chuang; Workman, Jared C.; Blackman, Eric G.
2013-03-10
Low Mach number, high beta fast mode shocks can occur in the magnetic reconnection outflows of solar flares. These shocks, which occur above flare loop tops, may provide the electron energization responsible for some of the observed hard X-rays and contemporaneous radio emission. Here we present new two-dimensional particle-in-cell simulations of low Mach number/high beta quasi-perpendicular shocks. The simulations show that electrons above a certain energy threshold experience shock-drift-acceleration. The transition energy between the thermal and non-thermal spectrum and the spectral index from the simulations are consistent with some of the X-ray spectra from RHESSI in the energy regime of E {approx}< 40 {approx} 100 keV. Plasma instabilities associated with the shock structure such as the modified-two-stream and the electron whistler instabilities are identified using numerical solutions of the kinetic dispersion relations. We also show that the results from PIC simulations with reduced ion/electron mass ratio can be scaled to those with the realistic mass ratio.
NASA Astrophysics Data System (ADS)
Dargent, J.; Aunai, N.; Belmont, G.; Dorville, N.; Lavraud, B.; Hesse, M.
2016-06-01
Tangential current sheets are ubiquitous in space plasmas and yet hard to describe with a kinetic equilibrium. In this paper, we use a semi-analytical model, the BAS model, which provides a steady ion distribution function for a tangential asymmetric current sheet and we prove that an ion kinetic equilibrium produced by this model remains steady in a fully kinetic particle-in-cell simulation even if the electron distribution function does not satisfy the time independent Vlasov equation. We then apply this equilibrium to look at the dependence of magnetic reconnection simulations on their initial conditions. We show that, as the current sheet evolves from a symmetric to an asymmetric upstream plasma, the reconnection rate is impacted and the X line and the electron flow stagnation point separate from one another and start to drift. For the simulated systems, we investigate the overall evolution of the reconnection process via the classical signatures discussed in the literature and searched in the Magnetospheric MultiScale data. We show that they seem robust and do not depend on the specific details of the internal structure of the initial current sheet.
NASA Astrophysics Data System (ADS)
Lasinski, Barbara F.; Langdon, A. Bruce; Hatchett, Stephen P.; Key, Michael H.; Tabak, Max
1999-05-01
Zohar (two-dimensions, particle-in-cell) [C. K. Birdsall and A. B. Langdon, Plasma Physics via Computer Simulation (McGraw-Hill, New York, 1985)] simulations of ultra intense laser beams boring into overdense plasmas whose parameters are guided by the fast-ignitor concept and radiography applications are presented. Complex low frequency magnetic field structures, narrow channel formation, and beam deflection are all evident. Particle tracking diagnostics elucidate the nature of the currents that produce and interact with these static magnetic fields which are larger than 109 G for simulations at 1021W/cm2 in a 50nc plasma. Tracking electron orbits provides a more complete understanding of the hot electron generation as the short pulse, high intensity laser penetrates overdense plasma. Particles which constitute the current in the narrow channel are partially confined by the low frequency magnetic field. In contrast, the return current particles on the outside of the channel are defocused by the high magnetic field and move away from the channel.
Lasinski, B.F.; Langdon, A.B.; Hatchett, S.P.; Key, M.H.; Tabak, M.
1999-05-01
Zohar (two-dimensions, particle-in-cell) [C. K. Birdsall and A. B. Langdon, {ital Plasma Physics via Computer Simulation} (McGraw{endash}Hill, New York, 1985)] simulations of ultra intense laser beams boring into overdense plasmas whose parameters are guided by the fast-ignitor concept and radiography applications are presented. Complex low frequency magnetic field structures, narrow channel formation, and beam deflection are all evident. Particle tracking diagnostics elucidate the nature of the currents that produce and interact with these static magnetic fields which are larger than 10{sup 9} G for simulations at 10{sup 21} W/cm{sup 2} in a 50n{sub c} plasma. Tracking electron orbits provides a more complete understanding of the hot electron generation as the short pulse, high intensity laser penetrates overdense plasma. Particles which constitute the current in the narrow channel are partially confined by the low frequency magnetic field. In contrast, the return current particles on the outside of the channel are defocused by the high magnetic field and move away from the channel.
Kato, Tsunehiko N.; Takabe, Hideaki
2010-09-20
A two-dimensional particle-in-cell simulation is performed to investigate weakly magnetized perpendicular shocks with a magnetization parameter of {sigma} = 6 x 10{sup -5}, which is equivalent to a high Alfven Mach number M{sub A} of {approx}130. It is shown that current filaments form in the foot region of the shock due to the ion-beam-Weibel instability (or the ion filamentation instability) and that they generate a strong magnetic field there. In the downstream region, these current filaments also generate a tangled magnetic field that is typically 15 times stronger than the upstream magnetic field. The thermal energies of electrons and ions in the downstream region are not in equipartition and their temperature ratio is T{sub e}/T{sub i} {approx} 0.3-0.4. Efficient electron acceleration was not observed in our simulation, although a fraction of the ions are accelerated slightly on reflection at the shock. The simulation results agree very well with the Rankine-Hugoniot relations. It is also shown that electrons and ions are heated in the foot region by the Buneman instability (for electrons) and the ion-acoustic instability (for both electrons and ions). However, the growth rate of the Buneman instability is significantly reduced due to the relatively high temperature of the reflected ions. For the same reason, ion-ion streaming instability does not grow in the foot region.
NASA Astrophysics Data System (ADS)
Main, D. S.; Caplinger, J.; Kim, T. C.; Sotnikov, V. I.
2014-12-01
The propagation of electromagnetic (EM) waves can be influenced by the presence of plasma turbulence. It is known that Flute-type density irregularities can develop during the nonlinear stage of an interchange instability in Earth's ionosphere and can affect radio communication channels. These density structures play an important role in the refraction and scattering of EM waves in Earth's ionosphere and also in laser diagnostic scattering experiments. To generate Flute-type density irregularities, we will use previously obtained numerical solution of nonlinear fluid equations involving the electrostatic potential and density. The solutions to these fluid equations govern the development of an interchange instability and results in the spatial dependence of density irregularities which can be used to analyze scattering of high frequency EM waves. This solution contains both large scale vortex density structures coexisting with short scale density perturbations. Next we will initialize a PIC simulation with the density structure from the fluid simulation to calculate the scattering cross-section and compare the results with an analytic solution obtained using numerically calculated density spectra. Because the linear and non-linear stages are well separated in time, we will compare the effect of scattering from density irregularities which form in both the linear and non-linear stages.
NASA Astrophysics Data System (ADS)
Lapenta, G.; Sanna, L.; Goldman, M. V.; Newman, D. L.; Markidis, S.
2014-12-01
A perduring challenge in the study of reconnection it has long been the failing attempts to reconcile the large scale MHD view based on the Petschek model with the small scale view based on kinetic theory. The first is based on the existence of standing switch off slow shocks (SSS) that eliminate the horizontal (the x component in the usual GSM coordinates) reconnecting magnetic field component forming vertical magnetic field lines. The second is based on nested diffusion regions where the magnetic field lines become decoupled first from ions and then from electrons. The kinetic picture when observed superficially does seem to have seem resemblance to the Petschek topology, despite the nested boxes being more of a Sweet-Parker concept. Nevertheless, the question has always been: if expanded to sufficiently large scales, does the kinetic description eventually lead tot the formation os SSS? The question remains answered. Recently a first negative answer has been proposed in Ref. [1]. The proposed answer is in essence that SSS are made impossible by the presence of a firehose instability in the reconnection exhaust and by the formation of a plateau in the firehose parameter at a value of 0.25 corresponding to the condition where nonlinear slow and intermediate wave become degenerate. We report a new series of simulations where we demonstrate that this is not the case in general. While for the specific case used in Ref [1], we indeed re-obtain the same conclusions reached by the authors. But our study demonstrates that case to be very peculiar and not representative of the more general kinetic answer. We will report direct evidence of the presence of extended SSS (over regions of hundreds of ion inertial lengths) in fully kinetic simulations for parameters typical of the magntotail and of the solar wind. Our results indicate that SSS are the natural extension of kinetic reconnection to large scales. The simulations required for the study are heroic and were conducted
Saito, S.; Umeda, T.
2011-07-20
Shock drift acceleration is one of the important mechanisms for electron acceleration associated with magnetic mirror reflection along the magnetic field in a quasi-perpendicular collisionless shock. We study the influence of a rippled shock surface in the in-plane magnetic field on the magnetic mirror reflection of electrons. Simulation results show that the number of reflected electrons reduces after generation of the rippled shock surface. Electric and magnetic wavenumber spectra of the generated fluctuations in the shock transition region indicate the existence of kinetic Alfven turbulence. The kinetic Alfven turbulence decreases the electron pitch angle by parallel scattering, which reduces the magnetic mirror force acting on the electrons. These results suggest that the shock-generated kinetic Alfven turbulence suppresses the magnetic mirror reflection of electrons during the shock drift acceleration.
NASA Astrophysics Data System (ADS)
Innocenti, M.; Beck, A.; Lapenta, G.; Markidis, S.
2012-12-01
The kinetic simulation of intrinsically multi scale processes such as magnetic reconnection events with realistic mass ratios is a daunting task for explicit Particle In Cell (PIC) codes, which require to use resolutions of the order of the electron Debye length even when simulating dramatically bigger domains. As an example, a simulation of reconnection in the magnetotail, with domain sizes of the order of 20 di x 10 di (˜ 7.2 106 m x 3.6 106 m, with di being the ion skin depth) and a resolution of λD,e= 687 m, with λD,e the electron Debye length, requires the astounding number of 10500 x 5240 cells. Higher grid spacings can be used if the simulation is performed with an implicit PIC code, which substitutes a much less strict accuracy constraint to the stability constraint of explicit PIC codes. The same reconnection problem as before can be simulated, with an implicit PIC code resolving the scale of interest of de /2 instead of the electron Debye length (de is the electron skin depth), with the much more manageable number of 1920 x 958 cells. However, an even smaller number of cells can be used if, instead of using the same, high resolution on the entire domain, the domain to simulate is divided into subdomains each resolved with a grid spacing related to the physical scale of interest in the specific subdomain. In the case of reconnection, the division which immediately springs to mind is between electron diffusion region, ion diffusion region and outer region, where resolutions respectively of the order of fractions of the electron skin depth, of the ion skin depth and bigger can be used. We present here a new Multi Level Multi Domain (MLMD) Implicit Moment Method (IMM) Particle In Cell (PIC) code, Parsek2D-MLMD, able to perform simulations of magnetic reconnection where the expensive high resolutions are used only when needed, while the rest of the domain is simulated with grid spacings chosen according to the local scales of interest. The major difference
NASA Astrophysics Data System (ADS)
Brambilla, Gabriele; Kalapotharakos, Constantions; Timokhin, Andrey; Kust Harding, Alice; Kazanas, Demosthenes
2016-04-01
Accelerated charged particles flowing in the magnetosphere produce pulsar gamma-ray emission. Pair creation processes produce an electron-positron plasma that populates the magnetosphere, in which the plasma is very close to force-free. However, it is unknown how and where the plasma departs from the ideal force-free condition, which consequently inhibits the understanding of the emission generation. We found that a dissipative magnetosphere outside the light cylinder effectively reproduces many aspects of the young gamma-ray pulsar emission as seen by the Fermi Gamma-ray Space Telescope, and through particle-in-cell simulations (PIC), we started explaining this configuration self-consistently. These findings show that, together, a magnetic field structure close to force-free and the assumption of gamma-ray curvature radiation as the emission mechanism are strongly compatible with the observations. Two main issues from the previously used models that our work addresses are the inability to explain luminosity, spectra, and light curve features at the same time and the inconsistency of the electrodynamics. Moreover, using the PIC simulations, we explore the effects of different pair multiplicities on the magnetosphere configurations and the locations of the accelerating regions. Our work aims for a self-consistent modeling of the magnetosphere, connecting the microphysics of the pair-plasma to the global magnetosphere macroscopic quantities. This direction will lead to a greater understanding of pulsar emission at all wavelengths, as well as to concrete insights into the physics of the magnetosphere.
NASA Astrophysics Data System (ADS)
Wang, Hong-Yu; Sun, Peng; Jiang, Wei; Zhou, Jie; Xie, Bai-Song
2015-06-01
An implicit electrostatic particle-in-cell/Monte Carlo (PIC/MC) algorithm is developed for the magnetized discharging device simulation. The inductive driving force can be considered. The direct implicit PIC algorithm (DIPIC) and energy conservation scheme are applied together and the grid heating can be eliminated in most cases. A tensor-susceptibility Poisson equation is constructed. Its discrete form is made up by a hybrid scheme in one-dimensional (1D) and two-dimensional (2D) cylindrical systems. A semi-coarsening multigrid method is used to solve the discrete system. The algorithm is applied to simulate the cylindrical magnetized target fusion (MTF) pre-ionization process and get qualitatively correct results. The potential application of the algorithm is discussed briefly. Project supported by the National Natural Science Foundation of China (Grant Nos. 11275007, 11105057, 11175023, and 11275039). One of the author (Wang H Y) is supported by Program for Liaoning Excellent Talents in University (Grant No. LJQ2012098).
NASA Astrophysics Data System (ADS)
Gildea, Stephen Robert
Cusped-field plasma thrusters are an electric propulsion concept being investigated by several laboratories in the United States and Europe. This technology was implemented as a low-power prototype in 2007 to ascertain if durability and performance improvements over comparable Hall thruster designs could be provided by the distinct magnetic topologies inherent to these devices. The first device tested at low-powers was eventually designated the "diverging cusped-field thruster" (DCFT) and demonstrated performance capabilities similar to state-of-the-art Hall thrusters. The research presented herein is a continuation of these initial studies, geared toward identifying significant operational characteristics of the thruster using experiments and numerical simulations. After a review of hybrid, fluid, and particle-in-cell Hall thruster models, experimental contributions from this work are presented. Anode current waveform measurements provide the first evidence of the distinct time-dependent characteristics of the two main modes of DCFT operation. The previously named "high-current" mode exhibits oscillation amplitudes several factors larger than mean current values, while magnitudes in "low-current" mode are at least a full order smaller. Results from a long-duration test, exceeding 200 hours of high-current mode operation, demonstrate lifetime-limiting erosion rates about 50% lower than those observed in comparable Hall thrusters. Concurrently, the plasma thruster particle-in-cell (PTpic) simulator was developed by upgrading numerous aspects of a preexisting Hall thruster model. Improvements in performance and accuracy have been achieved through modifications of the particle moving and electrostatic potential solving algorithms. Data from simulations representing both modes of operation are presented. In both cases, despite being unable to predict the correct location of the main potential drop in the thruster chamber, the model successfully reproduces the hollow
Fan, Yu; Zou, Ying; Sun, Jizhong; Wang, Dezhen; Stirner, Thomas
2013-10-15
The influence of an applied magnetic field on plasma-related devices has a wide range of applications. Its effects on a plasma have been studied for years; however, there are still many issues that are not understood well. This paper reports a detailed kinetic study with the two-dimension-in-space and three-dimension-in-velocity particle-in-cell plus Monte Carlo collision method on the role of E×B drift in a capacitive argon discharge, similar to the experiment of You et al.[Thin Solid Films 519, 6981 (2011)]. The parameters chosen in the present study for the external magnetic field are in a range common to many applications. Two basic configurations of the magnetic field are analyzed in detail: the magnetic field direction parallel to the electrode with or without a gradient. With an extensive parametric study, we give detailed influences of the drift on the collective behaviors of the plasma along a two-dimensional domain, which cannot be represented by a 1 spatial and 3 velocity dimensions model. By analyzing the results of the simulations, the occurring collisionless heating mechanism is explained well.
Choi, E. J.; Min, K.; Choi, C. R.; Nishikawa, K.-I.
2014-07-15
We report the results of a 3D particle-in-cell simulation carried out to study the early-stage evolution of the shock formed when an unmagnetized relativistic jet interacts with an ambient electron-ion plasma. Full-shock structures associated with the interaction are observed in the ambient frame. When open boundaries are employed in the direction of the jet, the forward shock is seen as a hybrid structure consisting of an electrostatic shock combined with a double layer, while the reverse shock is seen as a double layer. The ambient ions show two distinct features across the forward shock: a population penetrating into the shocked region from the precursor region and an accelerated population escaping from the shocked region into the precursor region. This behavior is a signature of a combination of an electrostatic shock and a double layer. Jet electrons are seen to be electrostatically trapped between the forward and reverse shock structures showing a ring-like distribution in a phase-space plot, while ambient electrons are thermalized and become essentially isotropic in the shocked region. The magnetic energy density grows to a few percent of the jet kinetic energy density at both the forward and the reverse shock transition layers in a rather short time scale. We see little disturbance of the jet ions over this time scale.
NASA Astrophysics Data System (ADS)
Martins, S. F.; Fonseca, R. A.; Lu, W.; Mori, W. B.; Silva, L. O.
2010-04-01
Plasma-based acceleration offers compact accelerators with potential applications for high-energy physics and photon sources. The past five years have seen an explosion of experimental results with monoenergetic electron beams up to 1GeV on a centimetre-scale, using plasma waves driven by intense lasers. The next decade will see tremendous increases in laser power and energy, permitting beam energies beyond 10GeV. Leveraging on the Lorentz transformations to bring the laser and plasma spatial scales together, we have reduced the computational time for modelling laser-plasma accelerators by several orders of magnitude, including all the relevant physics. This scheme enables the first one-to-one particle-in-cell simulations of the next generation of accelerators at the energy frontier. Our results demonstrate that, for a given laser energy, choices in laser and plasma parameters strongly affect the output electron beam energy, charge and quality, and that all of these parameters can be optimized.
NASA Astrophysics Data System (ADS)
Gao, Liang; Sun, Jizhong; Feng, Chunlei; Bai, Jing; Ding, Hongbin
2012-01-01
A particle-in-cell plus Monte Carlo collisions method has been employed to investigate the nitrogen discharge driven by a nanosecond pulse power source. To assess whether the production of the metastable state N2(A3 Σu+) can be efficiently enhanced in a nanosecond pulsed discharge, the evolutions of metastable state N2(A3 Σu+) density and electron energy distribution function have been examined in detail. The simulation results indicate that the ultra short pulse can modulate the electron energy effectively: during the early pulse-on time, high energy electrons give rise to quick electron avalanche and rapid growth of the metastable state N2(A3 Σu+) density. It is estimated that for a single pulse with amplitude of -9 kV and pulse width 30 ns, the metastable state N2(A3 Σu+) density can achieve a value in the order of 109 cm-3. The N2(A3 Σu+) density at such a value could be easily detected by laser-based experimental methods.
Rekaa, V. L.; Chapman, S. C.; Dendy, R. O.
2014-08-10
Supernova remnant and heliopause termination shock plasmas may contain significant populations of minority heavy ions, with relative number densities n{sub α}/n{sub i} up to 50%. Preliminary kinetic simulations of collisionless shocks in these environments showed that the reformation cycle and acceleration mechanisms at quasi-perpendicular shocks can depend on the value of n{sub α}/n{sub i} . Shock reformation unfolds on ion spatio-temporal scales, requiring fully kinetic simulations of particle dynamics, together with the self-consistent electric and magnetic fields. This paper presents the first set of particle-in-cell simulations for two ion species, protons (n{sub p} ) and α-particles (n{sub α}), with differing mass and charge-to-mass ratios, that spans the entire range of n{sub α}/n{sub i} from 0% to 100%. The interplay between the differing gyro length scales and timescales of the ion species is crucial to the time-evolving phenomenology of the shocks, the downstream turbulence, and the particle acceleration at different n{sub α}/n{sub i} . We show how the overall energization changes with n{sub α}/n{sub i} , and relate this to the processes individual ions undergo in the shock region and in the downstream turbulence, and to the power spectra of magnetic field fluctuations. The crossover between shocks dominated by the respective ion species happens when n{sub α}/n{sub i} = 25%, and minority ion energization is strongest in this regime. Energization of the majority ion species scales with injection energy. The power spectrum of the downstream turbulence includes peaks at sequential ion cyclotron harmonics, suggestive of ion ring-beam collective instability.
Tsiklauri, D.
2012-08-15
The process of particle acceleration by left-hand, circularly polarised inertial Alfven waves (IAW) in a transversely inhomogeneous plasma is studied using 3D particle-in-cell simulation. A cylindrical tube with, transverse to the background magnetic field, inhomogeneity scale of the order of ion inertial length is considered on which IAWs with frequency 0.3{omega}{sub ci} are launched that are allowed to develop three wavelength. As a result time-varying parallel electric fields are generated in the density gradient regions which accelerate electrons in the parallel to magnetic field direction. Driven perpendicular electric field of IAWs also heats ions in the transverse direction. Such numerical setup is relevant for solar flaring loops and earth auroral zone. This first, 3D, fully kinetic simulation demonstrates electron acceleration efficiency in the density inhomogeneity regions, along the magnetic field, of the order of 45% and ion heating, in the transverse to the magnetic field direction, of 75%. The latter is a factor of two times higher than the previous 2.5D analogous study and is in accordance with solar flare particle acceleration observations. We find that the generated parallel electric field is localised in the density inhomogeneity region and rotates in the same direction and with the same angular frequency as the initially launched IAW. Our numerical simulations seem also to suggest that the 'knee' often found in the solar flare electron spectra can alternatively be interpreted as the Landau damping (Cerenkov resonance effect) of IAWs due to the wave-particle interactions.
Scisciò, M.; Palumbo, L.; D'Humières, E.; Fourmaux, S.; Kieffer, J. C.; Antici, P.
2014-12-15
In this paper, we report on bi-dimensional Particle-In-Cell simulations performed in order to reproduce the laser-driven proton acceleration obtained when a commercial 200 TW Ti:Sa Laser hits a solid target. The laser-to prepulse contrast was enhanced using plasma mirrors yielding to a main-to-prepulse contrast of ∼10{sup 12}. We varied the pulse duration from 30 fs to 500 fs and the target thickness from 30 nm to several tens of μm. The on-target laser energy was up to 1.8 J leading to an intensity in excess of 10{sup 20 }W cm{sup −2}. A comparison between numerical and existing experimental data [S. Fourmaux et al., Phys. Plasmas 20, 013110 (2013)] is performed, showing a good agreement between experimental results and simulations which confirms that for ultra-thin targets there is an optimum expansion regime. This regime depends on the target thickness and on the laser intensity: if the target is too expanded, the laser travels through the target without being able to deposit its energy within the target. If the target is not sufficiently expanded, the laser energy is reflected by the target. It is important to note that maximum proton energies are reached at longer pulse durations (in the 100 fs regime) than what is currently the best compression pulse length for this type of lasers (typically 20–30 fs). This duration, around 50–100 fs, can be considered a minimum energy transfer time between hot electrons to ions during the considered acceleration process.
Conformal Electromagnetic Particle in Cell: A Review
Meierbachtol, Collin S.; Greenwood, Andrew D.; Verboncoeur, John P.; Shanker, Balasubramaniam
2015-10-26
We review conformal (or body-fitted) electromagnetic particle-in-cell (EM-PIC) numerical solution schemes. Included is a chronological history of relevant particle physics algorithms often employed in these conformal simulations. We also provide brief mathematical descriptions of particle-tracking algorithms and current weighting schemes, along with a brief summary of major time-dependent electromagnetic solution methods. Several research areas are also highlighted for recommended future development of new conformal EM-PIC methods.
NASA Astrophysics Data System (ADS)
Deca, Jan; Divin, Andrey; Lapenta, Giovanni; Lembège, Bertrand; Markidis, Stefano; Horányi, Mihály
2015-04-01
We present three-dimensional fully kinetic and electromagnetic simulations of the solar wind interaction with lunar crustal magnetic anomalies (LMAs). Using the implicit particle-in-cell code iPic3D, we confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface forming a mini-magnetosphere, as suggested by spacecraft observations and theory. In contrast to earlier MHD and hybrid simulations, the fully kinetic nature of iPic3D allows to investigate the space charge effects and in particular the electron dynamics dominating the near-surface lunar plasma environment. We describe the general picture of the interaction of a dipole model centered just below the lunar surface under various solar wind and plasma conditions, and focus afterwards on the ion and electron kinetic behavior of the system. It is shown that the configuration is dominated by electron motion, because the LMA scale size is small with respect to the gyroradius of the solar wind ions. We identify a population of backstreaming ions, the deflection of magnetized electrons via the ExB-drift motion and the subsequent formation of a halo region of elevated density around the dipole source. Finally, it is shown that the presence and efficiency of the latter mechanisms are heavily impacted by the upstream plasma conditions and, on their turn, influence the overall structure and evolution of the LMA system. Our work opens new frontiers of research toward a deeper understanding of LMAs and is ideally suited to be compared with field or particle observations from spacecraft such as Kaguya (SELENE), Lunar Prospector or ARTEMIS. The ability to evaluate the implications for future lunar exploration as well as lunar science in general hinges on a better understanding of LMAs. This research has received funding from the European Commission's FP7 Program with the grant agreement SWIFF (project 2633430, swiff.eu) and EHEROES (project 284461, www.eheroes.eu). The
NASA Astrophysics Data System (ADS)
Deca, J.; Divin, A. V.; Lapenta, G.; Lembege, B.; Markidis, S.; Horanyi, M.
2014-12-01
We present three-dimensional fully kinetic and electromagnetic simulations of the solar wind interaction with lunar crustal magnetic anomalies (LMAs). Using the implicit particle-in-cell code iPic3D, we confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface forming a mini-magnetosphere, as suggested by spacecraft observations and theory. In contrast to earlier MHD and hybrid simulations, the fully kinetic nature of iPic3D allows to investigate the space charge effects and in particular the electron dynamics dominating the near-surface lunar plasma environment. We describe the general picture of the interaction of a dipole model centered just below the lunar surface under various solar wind and plasma conditions, and focus afterwards on the ion and electron kinetic behavior of the system. It is shown that the configuration is dominated by electron motion, because the LMA scale size is small with respect to the gyroradius of the solar wind ions. The dominant LMA interaction mechanism is also highly dependent on the solar wind and IMF conditions. Driven by strong pressure anisotropies, the mini-magnetosphere is also unstable over time, leading to only temporal shielding of the surface underneath. Our work opens new frontiers of research toward a deeper understanding of LMAs and is ideally suited to be compared with field or particle observations from spacecraft such as Kaguya (SELENE), Lunar Prospector or ARTEMIS. The ability to evaluate the implications for future lunar exploration as well as lunar science in general hinges on a better understanding of LMAs. This research has received funding from the European Commission's FP7 Program with the grant agreement SWIFF (project 2633430, swiff.eu) and EHEROES (project 284461, www.eheroes.eu). The simulations were conducted on the computational resources provided by the PRACE Tier-0 project 2011050747 (Curie) and 2013091928 (SuperMUC). This research was supported
NASA Astrophysics Data System (ADS)
Zhang, Ya; Wang, Hong-yu; Jiang, Wei; Bogaerts, Annemie
2015-08-01
The plasma behavior in a parallel-plate dielectric barrier discharge (DBD) is simulated by a two-dimensional particle-in-cell/Monte Carlo collision model, comparing for the first time an unpacked (empty) DBD with a packed bed DBD, i.e., a DBD filled with dielectric spheres in the gas gap. The calculations are performed in air, at atmospheric pressure. The discharge is powered by a pulse with a voltage amplitude of -20 kV. When comparing the packed and unpacked DBD reactors with the same dielectric barriers, it is clear that the presence of the dielectric packing leads to a transition in discharge behavior from a combination of negative streamers and unlimited surface streamers on the bottom dielectric surface to a combination of predominant positive streamers and limited surface discharges on the dielectric surfaces of the beads and plates. Furthermore, in the packed bed DBD, the electric field is locally enhanced inside the dielectric material, near the contact points between the beads and the plates, and therefore also in the plasma between the packing beads and between a bead and the dielectric wall, leading to values of 4× {10}8 V m-1, which is much higher than the electric field in the empty DBD reactor, i.e., in the order of 2× {10}7 V m-1, thus resulting in stronger and faster development of the plasma, and also in a higher electron density. The locally enhanced electric field and the electron density in the case of a packed bed DBD are also examined and discussed for three different dielectric constants, i.e., {ɛ }r=22 (ZrO2), {ɛ }r=9 (Al2O3) and {ɛ }r=4 (SiO2). The enhanced electric field is stronger and the electron density is higher for a larger dielectric constant, because the dielectric material is more effectively polarized. These simulations are very important, because of the increasing interest in packed bed DBDs for environmental applications.
Tsiklauri, David
2011-05-15
High-resolution (sub-Debye length grid size and 10 000 particle species per cell), 1.5D particle-in-cell, relativistic, fully electromagnetic simulations are used to model electromagnetic wave emission generation in the context of solar type III radio bursts. The model studies generation of electromagnetic waves by a super-thermal, hot beam of electrons injected into a plasma thread that contains uniform longitudinal magnetic field and a parabolic density gradient. In effect, a single magnetic line connecting Sun to Earth is considered, for which five cases are studied. (i) We find that the physical system without a beam is stable and only low amplitude level electromagnetic drift waves (noise) are excited. (ii) The beam injection direction is controlled by setting either longitudinal or oblique electron initial drift speed, i.e., by setting the beam pitch angle (the angle between the beam velocity vector and the direction of background magnetic field). In the case of zero pitch angle, i.e., when v-vector{sub b{center_dot}}E-vector{sub perpendicular}=0, the beam excites only electrostatic, standing waves, oscillating at local plasma frequency, in the beam injection spatial location, and only low level electromagnetic drift wave noise is also generated. (iii) In the case of oblique beam pitch angles, i.e., when v-vector{sub b{center_dot}}E-vector{sub perpendicular}=0, again electrostatic waves with same properties are excited. However, now the beam also generates the electromagnetic waves with the properties commensurate to type III radio bursts. The latter is evidenced by the wavelet analysis of transverse electric field component, which shows that as the beam moves to the regions of lower density and hence lower plasma frequency, frequency of the electromagnetic waves drops accordingly. (iv) When the density gradient is removed, an electron beam with an oblique pitch angle still generates the electromagnetic radiation. However, in the latter case no frequency
Mehdian, H. Kargarian, A.; Hajisharifi, K.
2015-06-15
In this paper, the effect of an external inhomogeneous magnetic field on the high intensity laser absorption rate in a sub-critical plasma has been investigated by employing a relativistic electromagnetic 1.5 dimensional particle-in-cell code. Relying on the effective nonlinear phenomena such as phase-mixing and scattering, this study shows that in a finite-size plasma the laser absorption increases with inhomogeneity of the magnetic field (i.e., reduction of characteristic length of inhomogeneous magnetic field, λ{sub p}) before exiting a considerable amount of laser energy from the plasma due to scattering process. On the other hand, the presence of the external inhomogeneous magnetic field causes the maximum absorption of laser to occur at a shorter time. Moreover, study of the kinetic results associated with the distribution function of plasma particles shows that, in a special range of the plasma density and the characteristic length of inhomogeneous magnetic field, a considerable amount of laser energy is transferred to the particles producing a population of electrons with kinetic energy along the laser direction.
NASA Astrophysics Data System (ADS)
Miyagawa, Y.; Tanaka, M.; Ikeyama, M.; Nakao, S.; Choi, J.; Miyagawa, S.
2006-01-01
The plasma behavior inside of a PET bottle has been simulated under the condition of plasma immersed ion implantation and deposition (PIII&D) using the simulation software "PEGASUS". The software uses the "PIC-MCCM" module for the plasma analysis and the "DSMCM" module for the gas flow field analysis. DSMCM gives densities, velocities, fluxes, temperatures and pressures of each neutral species such as the fed gas species and radicals. By coupling PIC-MCCM with DSMCM simulation, the plasma behavior in the flowing Ar gas and N2 gas has been simulated. The gas was injected from the tip of the gas inlet which was inserted into the center of the bottle. The base gas pressure was 1-50 Pa and a positive pulse voltage (maximum voltage = 0.1-1 kV) was applied to the center rod. A two-dimensional cylindrical coordinate system was used. Time evolution of the spacial distribution was obtained for densities of electrons, N2+ ions, N2∗ radicals and N atoms in N2 gas, and Ar+ ions, Ar∗ and Ar∗(4s) radicals in Ar gas. Time evolution of the particle flux and the energy flux of electrons and ions on the target surface was also obtained.
Fully implicit particle-in-cell algorithm.
NASA Astrophysics Data System (ADS)
Kim, Hyung; Chacon, Luis
2005-10-01
Most current particle-in-cell (PIC) algorithms employ an explicit approach. Explicit PIC approaches are not only time-step limited for numerical stability, but also grid-intensive due to the so-called finite-grid instability.ootnotetextC. Birdsall and A. Langdon, Plasma physics via computer simulation, McGraw-Hill, New York, 1985 As a result, explicit PIC methods are very hardware-intensive, and become prohibitive for system scale simulations even with modern supercomputers. To avoid such stringent time-step and grid-size requirements, the implicit moment method PIC approach (IM-PIC) was developed.ootnotetextJ. Brackbill and D. Forslund, J. Comput. Phys. 46, 271 (1982). IM-PIC advances the required moments (density, current) using Chapman-Enskop-based fluid equations, and then advances the particles with such moments. While being able to employ much larger time steps and grid spacings than explicit PIC methods, IM-PIC is limited in that the time-advanced moments and the particle moments are inconsistent, resulting in lack of energy conservation. To remedy this, we propose here a fully implicit, fully nonlinear PIC approach (FI-PIC) where the particles and the moments are converged simultaneously using Newton-Krylov techniques. This guarantees the consistency of moments and particles upon convergence. We will demonstrate the feasibility of the concept using a purely electrostatic Vlasov-Poisson model, and will show its effectiveness with several fully kinetic examples.
NASA Astrophysics Data System (ADS)
Kurilenkov, Yu. K.; Tarakanov, V. P.; Gus'kov, S. Yu.
2010-12-01
Results of particle-in-sell simulations of ion acceleration by using the KARAT code in a cylindrical geometry in the problem formulation corresponding to an actual experiment with a low-energy vacuum discharge with a hollow cathode are presented. The fundamental role of the formed virtual cathode is analyzed. The space-time dynamics of potential wells related to the formation of the virtual cathode is discussed. Quasi-steady potential wells (with a depth of ˜80% of the applied voltage) cause acceleration of deuterium ions to energies about the electron beam energy (˜50 keV). In the well, a quasi-isotropic velocity distribution function of fast ions forms. The results obtained are compared with available data on inertial electrostatic confinement fusion (IECF). In particular, similar correlations between the structure of potential wells and the neutron yield, as well as the scaling of the fusion power density, which increases with decreasing virtual cathode radius and increasing potential well depth, are considered. The chosen electrode configuration and potential well parameters provide power densities of nuclear DD fusion in a nanosecond vacuum discharge noticeably higher than those achieved in other similar IECF systems.
GPU acceleration of particle-in-cell methods
NASA Astrophysics Data System (ADS)
Cowan, Benjamin; Cary, John; Meiser, Dominic
2015-11-01
Graphics processing units (GPUs) have become key components in many supercomputing systems, as they can provide more computations relative to their cost and power consumption than conventional processors. However, to take full advantage of this capability, they require a strict programming model which involves single-instruction multiple-data execution as well as significant constraints on memory accesses. To bring the full power of GPUs to bear on plasma physics problems, we must adapt the computational methods to this new programming model. We have developed a GPU implementation of the particle-in-cell (PIC) method, one of the mainstays of plasma physics simulation. This framework is highly general and enables advanced PIC features such as high order particles and absorbing boundary conditions. The main elements of the PIC loop, including field interpolation and particle deposition, are designed to optimize memory access. We describe the performance of these algorithms and discuss some of the methods used. Work supported by DARPA contract W31P4Q-15-C-0061 (SBIR).
A Parallelized 3D Particle-In-Cell Method With Magnetostatic Field Solver And Its Applications
NASA Astrophysics Data System (ADS)
Hsu, Kuo-Hsien; Chen, Yen-Sen; Wu, Men-Zan Bill; Wu, Jong-Shinn
2008-10-01
A parallelized 3D self-consistent electrostatic particle-in-cell finite element (PIC-FEM) code using an unstructured tetrahedral mesh was developed. For simulating some applications with external permanent magnet set, the distribution of the magnetostatic field usually also need to be considered and determined accurately. In this paper, we will firstly present the development of a 3D magnetostatic field solver with an unstructured mesh for the flexibility of modeling objects with complex geometry. The vector Poisson equation for magnetostatic field is formulated using the Galerkin nodal finite element method and the resulting matrix is solved by parallel conjugate gradient method. A parallel adaptive mesh refinement module is coupled to this solver for better resolution. Completed solver is then verified by simulating a permanent magnet array with results comparable to previous experimental observations and simulations. By taking the advantage of the same unstructured grid format of this solver, the developed PIC-FEM code could directly and easily read the magnetostatic field for particle simulation. In the upcoming conference, magnetron is simulated and presented for demonstrating the capability of this code.
Propagation of numerical noise in particle-in-cell tracking
NASA Astrophysics Data System (ADS)
Kesting, Frederik; Franchetti, Giuliano
2015-11-01
Particle-in-cell (PIC) is the most used algorithm to perform self-consistent tracking of intense charged particle beams. It is based on depositing macroparticles on a grid, and subsequently solving on it the Poisson equation. It is well known that PIC algorithms occupy intrinsic limitations as they introduce numerical noise. Although not significant for short-term tracking, this becomes important in simulations for circular machines over millions of turns as it may induce artificial diffusion of the beam. In this work, we present a modeling of numerical noise induced by PIC algorithms, and discuss its influence on particle dynamics. The combined effect of particle tracking and noise created by PIC algorithms leads to correlated or decorrelated numerical noise. For decorrelated numerical noise we derive a scaling law for the simulation parameters, allowing an estimate of artificial emittance growth. Lastly, the effect of correlated numerical noise is discussed, and a mitigation strategy is proposed.
Elements of Regolith Simulant's Cost Structure
NASA Technical Reports Server (NTRS)
Rickman, Douglas L.
2009-01-01
The cost of lunar regolith simulants is much higher than many users anticipate. After all, it is nothing more than broken rock. This class will discuss the elements which make up the cost structure for simulants. It will also consider which elements can be avoided under certain circumstances and which elements might be altered by the application of additional research and development.
NASA Astrophysics Data System (ADS)
Benstâali, W.; Harrache, Z.; Belasri, A.
2012-06-01
Plasma display panels (PDPs) are one of the leading technologies in the flat panels market. However, they are facing intense competition. Different fluid models, both one-dimensional (1D) and 2D, have been used to analyze the energy balance in PDP cells in order to find out how the xenon excitation part can be improved to optimize the luminous efficiency. The aim of this work is to present a 1D particle-in-cell with Monte Carlo collision (PIC-MCC) model for PDPs. The discharge takes place in a Xe10-Ne gas mixture at 560 Torr. The applied voltage is 381 V. We show at first that this model reproduces the electric characteristics of a single PDP discharge pulse. Then, we calculate the energy deposited by charged particles in each collision. The total energy is about 19 μJ cm-2, and the energy used in xenon excitation is of the order of 12.5% compared to the total energy deposited in the discharge. The effect of xenon content in a Xe-Ne mixture is also analyzed. The energies deposited in xenon excitation and ionization are more important when the xenon percentage has been increased from 1 to 30%. The applied voltage increases the energy deposited in xenon excitation.
Mo, Yongpeng; Shi, Zongqian; Jia, Shenli; Wang, Lijun
2015-02-15
The inter-contact region of vacuum circuit breakers is filled with residual plasma at the moment when the current is zero after the burning of metal vapor arc. The residual plasma forms an ion sheath in front of the post-arc cathode. The sheath then expands towards the post-arc anode under the influence of a transient recovery voltage. In this study, a one-dimensional particle-in-cell model is developed to investigate the post-arc sheath expansion. The influence of ion and electron temperatures on the decrease in local plasma density at the post-arc cathode side and post-arc anode side is discussed. When the decay in the local plasma density develops from the cathode and anode sides into the high-density region and merges, the overall plasma density in the inter-contact region begins to decrease. Meanwhile, the ion sheath begins to expand faster. Furthermore, the theory of ion rarefaction wave only explains quantitatively the decrease in the overall plasma density at relatively low ion temperatures. With the increase of ion temperature to certain extent, another possible reason for the decrease in the overall plasma density is proposed and results from the more active thermal diffusion of plasma.
Nuclear Thermal Rocket Element Environmental Simulator (NTREES)
NASA Technical Reports Server (NTRS)
Schoenfeld, Michael
2009-01-01
A detailed description of the Nuclear Thermal Rocket Element Environmental Simulator (NTREES) is presented. The contents include: 1) Design Requirements; 2) NTREES Layout; 3) Data Acquisition and Control System Schematics; 4) NTREES System Schematic; and 5) NTREES Setup.
A Radiation Transport Coupled Particle-In-Cell Model for Hg-Ar Discharges
NASA Astrophysics Data System (ADS)
Lee, Hae June; Verboncoeur, J. P.; Smith, H. B.; Parker, G. J.; Birdsall, C. K.
2000-10-01
We simulate a radial slice of the fluorescent lamp discharge in the positive column with a radiation transport coupled particle-in-cell (RT-PIC) code. In this model, the radiative and meta stable excited states of Hg-Ar mixture and their collisions as well as radiation transport are simulated by the fluid equations. The motions of electrons and ions and collisions with neutral or excited states are simulated by the conventional particle-in-cell method. We consider radiation transport of excited states using the Holstein equation[1] including the time varying nonuniform background gas density. The background gas density is calculated from the temperature profile by solving the heat transfer equation. The motion of charged particles are simulated by using the 1-D cylindrical particle-in-cell code, XPDC1[2]. Separate time scales are used for the charged particles, the excited states, and the neutral gas, respectively, and parallel processing can be used for the expensive calculation including radiation transport. This work was supported in part by General Electric Company contract GE-20000181. [1] T. Holstein, Phys. Rev. 72, 1213 (1947). [2] J. P. Verboncoeur, M. V. Alves, V. Vahedi, and C. K. Birdsall, Journal of Computational Physics 104(2), 321, (1993).
Improved modeling of relativistic collisions and collisional ionization in particle-in-cell codes
Perez, F.; Gremillet, L.; Decoster, A.; Drouin, M.; Lefebvre, E.
2012-08-15
An improved Monte Carlo collisional scheme modeling both elastic and inelastic interactions has been implemented into the particle-in-cell code CALDER[E. Lefebvre et al., Nucl. Fusion 43, 629 (2003)]. Based on the technique proposed by Nanbu and Yonemura [J. Comput. Phys. 145, 639 (1998)] allowing to handle arbitrarily weighted macro-particles, this binary collision scheme uses a more compact and accurate relativistic formulation than the algorithm recently worked out by Sentoku and Kemp [J. Comput. Phys. 227, 6846 (2008)]. Our scheme is validated through several test cases, demonstrating, in particular, its capability of modeling the electrical resistivity and stopping power of a solid-density plasma over a broad parameter range. A relativistic collisional ionization scheme is developed within the same framework, and tested in several physical scenarios. Finally, our scheme is applied in a set of integrated particle-in-cell simulations of laser-driven fast electron transport.
DEMOCRITUS: An adaptive particle in cell (PIC) code for object-plasma interactions
NASA Astrophysics Data System (ADS)
Lapenta, Giovanni
2011-06-01
A new method for the simulation of plasma materials interactions is presented. The method is based on the particle in cell technique for the description of the plasma and on the immersed boundary method for the description of the interactions between materials and plasma particles. A technique to adapt the local number of particles and grid adaptation are used to reduce the truncation error and the noise of the simulations, to increase the accuracy per unit cost. In the present work, the computational method is verified against known results. Finally, the simulation method is applied to a number of specific examples of practical scientific and engineering interest.
Element fracture technique for hypervelocity impact simulation
NASA Astrophysics Data System (ADS)
Zhang, Xiao-tian; Li, Xiao-gang; Liu, Tao; Jia, Guang-hui
2015-05-01
Hypervelocity impact dynamics is the theoretical support of spacecraft shielding against space debris. The numerical simulation has become an important approach for obtaining the ballistic limits of the spacecraft shields. Currently, the most widely used algorithm for hypervelocity impact is the smoothed particle hydrodynamics (SPH). Although the finite element method (FEM) is widely used in fracture mechanics and low-velocity impacts, the standard FEM can hardly simulate the debris cloud generated by hypervelocity impact. This paper presents a successful application of the node-separation technique for hypervelocity impact debris cloud simulation. The node-separation technique assigns individual/coincident nodes for the adjacent elements, and it applies constraints to the coincident node sets in the modeling step. In the explicit iteration, the cracks are generated by releasing the constrained node sets that meet the fracture criterion. Additionally, the distorted elements are identified from two aspects - self-piercing and phase change - and are deleted so that the constitutive computation can continue. FEM with the node-separation technique is used for thin-wall hypervelocity impact simulations. The internal structures of the debris cloud in the simulation output are compared with that in the test X-ray graphs under different material fracture criteria. It shows that the pressure criterion is more appropriate for hypervelocity impact. The internal structures of the debris cloud are also simulated and compared under different thickness-to-diameter ratios (t/D). The simulation outputs show the same spall pattern with the tests. Finally, the triple-plate impact case is simulated with node-separation FEM.
Elements of a theory of simulation
Rasmussen, S.; Barrett, C.L. |
1995-06-01
Artificial Life and the more general area of Complex Systems does not have a unified theoretical framework although most theoretical work in these areas is based on simulation. This is primarily due to am insufficient representational power of the classical mathematical frameworks for the description of discrete dynamical systems of interacting objects with often complex internal states. Unlike computation or the numerical analysis of differential equations, simulation does not have a well established conceptual and mathematical foundation. Simulation is an arguable unique union of modeling and computation. However, simulation also qualifies as a separate species of system representation with its own motivations, characteristics, and implications. This work outlines how simulation can be rooted in mathematics and shows which properties some of the elements of such a mathematical framework has. The properties of simulation are described and analyzed in terms of properties of dynamical systems. It is shown how and why a simulation produces emergent behavior and why the analysis of the dynamics of the system being simulated always is an analysis of emergent phenomena. Indeed, the single fundamental class of properties of the natural world that simulation will open to new understanding, is that which occurs only in the dynamics produced by the interactions of the components of complex systems. Simulation offers a synthetic, formal framework for the experimental mathematics of representation and analysis of complex dynamical systems. A notion of a universal simulator and the definition of simulatabuity is proposed. This allows a description of conditions under which simulations can distribute update functions over system components, thereby determining simulatability. The connection between the notion of simulatability and the notion of computability is defined and the concepts are distinguished.
An Integrated Radiation Transport Particle-in-Cell Method
NASA Astrophysics Data System (ADS)
Lee, H. J.; Verboncoeur, J. P.; Smith, H. B.; Parker, G. J.; Birdsall, C. K.
2000-10-01
The study of radiation transport is important to understand the basic physics and to calculate the efficiency in a lamp discharge or laser induced plasma. Many models neglect radiation transport effects in evolving the steady state. In this study, we established a basic model to calculate radiation transport, including the effects of nonuniform ground state density and atomic collisions in one dimensional cylindrical and planar geometries. We coupled radiation transport with the self-consistent kinetic particle-in-cell codes, XPDP1 and XPDC1[1]. We treat electrons and ions with a particle-in-cell method, and the neutral ground and excited states with a fluid model to calculate radiation transport and atomic collisions. The steady state result of this model compares well with the solution of Holstein equation[2]. [1] J. P. Verboncoeur, M. V. Alves, V. Vahedi, and C. K. Birdsall, Journal of Computational Physics 104, 321 (1993). [2] T. Holstein, Phys. Rev. 72, 1213 (1947).
On the use of particle-in-cell methods for the study of magnetically-confined fusion plasmas
Procassini, R.J. California Univ., Berkeley, CA . Electronics Research Lab.)
1991-06-12
The applicability of electrostatic particle-in-cell (PIC) methods for the simulation of magnetically-confined fusion plasmas is investigated. The aspects of the PIC methodology which allow one to accurately model the representative charge separations found in hot fusion plasmas with far fewer simulation particles are discussed. The number of simulation particles required to resolve the collective effects of interest (such as the ambipolar potential) above the statistical fluctuations is also analyzed. 8 refs., 1 fig.
Particle-In-Cell modeling of Fast Ignition experiments on the Titan Laser
NASA Astrophysics Data System (ADS)
Link, Anthony; Akli, K. U.; Beg, F.; Chen, C. D.; Davies, J. R.; Freeman, R. R.; Kemp, G. E.; Li, K.; McLean, H. S.; Morace, A.; Patel, P. K.; Schumacher, D. W.; Sorokovikova, A. V.; Stephens, R.; Streeter, M. J. V.; Wertepny, D.; Westhover, B.
2012-10-01
We report on particle-in-cell-modeling (PIC) of fast ignition experiments conducted on the Titan laser. The Titan laser was used to irradiate multilayer planar targets at intensities greater than 10^20 Wcm-2 to diagnose the laser to electron coupling, electron beam divergence, and energy spectrum of the hot electrons at relativistic intensities. Hot electron beam properties were inferred through buried fluors, escaping electrons and bremsstrahlung measurements. The PIC simulations of the experiment were conducted in two stages: a high resolution laser plasma interaction (LPI) simulation using measured on shot laser parameters but with a subscale target; and a lower resolution transport simulation containing the full scale multilayer target. The transport simulation utilized the electron source based on the output of the LPI simulation and included necessary models to simulate the experimental diagnostics. Comparison of the predicted electron source properties and the experimental data will be presented.
Simulation of rotor blade element turbulence
NASA Technical Reports Server (NTRS)
Mcfarland, R. E.; Duisenberg, Ken
1995-01-01
A piloted, motion-based simulation of Sikorsky's Black Hawk helicopter was used as a platform for the investigation of rotorcraft responses to vertical turbulence. By using an innovative temporal and geometrical distribution algorithm that preserved the statistical characteristics of the turbulence over the rotor disc, stochastic velocity components were applied at each of twenty blade-element stations. This model was implemented on NASA Ames' Vertical Motion Simulator (VMS), and ten test pilots were used to establish that the model created realistic cues. The objectives of this research included the establishment of a simulation-technology basis for future investigation into real-time turbulence modeling. This goal was achieved; our extensive additions to the rotor model added less than a 10 percent computational overhead. Using a VAX 9000 computer the entire simulation required a cycle time of less than 12 msec. Pilot opinion during this simulation was generally quite favorable. For low speed flight the consensus was that SORBET (acronym for title) was better than the conventional body-fixed model, which was used for comparison purposes, and was determined to be too violent (like a washboard). For high speed flight the pilots could not identify differences between these models. These opinions were something of a surprise because only the vertical turbulence component on the rotor system was implemented in SORBET. Because of the finite-element distribution of the inputs, induced outputs were observed in all translational and rotational axes. Extensive post-simulation spectral analyses of the SORBET model suggest that proper rotorcraft turbulence modeling requires that vertical atmospheric disturbances not be superimposed at the vehicle center of gravity but, rather, be input into the rotor system, where the rotor-to-body transfer function severely attenuates high frequency rotorcraft responses.
Fully explicit nonlinear optics model in a particle-in-cell framework
Gordon, D.F. Helle, M.H.; Peñano, J.R.
2013-10-01
A numerical technique which incorporates the nonlinear optics of anisotropic crystals into a particle-in-cell framework is described. The model is useful for simulating interactions between crystals, ultra-short laser pulses, intense relativistic electron bunches, plasmas, or any combination thereof. The frequency content of the incident and scattered radiation is limited only by the resolution of the spatial and temporal grid. A numerical stability analysis indicates that the Courant condition is more stringent than in the vacuum case. Numerical experiments are carried out illustrating the electro-optic effect, soliton propagation, and the generation of fields in a crystal by a relativistic electron bunch.
NASA Astrophysics Data System (ADS)
Kempf, Andreas; Kilian, Patrick; Ganse, Urs; Schreiner, Cedric; Spanier, Felix
2015-03-01
A three-dimensional, parallelized implementation of the electromagnetic relativistic moment implicit particle-in-cell method in Cartesian geometry (Noguchi et al., 2007) is presented. Particular care was taken to keep the C++11 codebase simple, concise, and approachable. GMRES is used as a field solver and during the Newton-Krylov iteration of the particle pusher. Drifting Maxwellian problem setups are available while more complex simulations can be implemented easily. Several test runs are described and the code's numerical and computational performance is examined. Weak scaling on the SuperMUC system is discussed and found suitable for large-scale production runs.
Finite Element Simulation of Smart Structures
NASA Technical Reports Server (NTRS)
Cui, Y. Lawrence; Panahandeh, M.
1996-01-01
Finite element equations representing the behavior of piezoelectric materials when bounded to a typical structure and used as sensors and actuators were developed. Emphasis was placed on generating sensor output equations of piezoelectric sensors and responses of a typical structure bonded with piezoelectric sensors and actuators on the basis of finite element formulation. The model can predict not only structural responses due to both mechanical and electrical loading but also electrical potential due to mechanical or thermal effects. The resulted finite element equations were then used for simple control design and performance evaluation. In the control algorithm, voltages coming out from piezoelectric sensors, which are proportional to strains at sensing locations, are taken as input. The voltages applied to the piezoelectric actuators are used as output. The feasibility of integrating control algorithm with the element routine developed herein and FEAP was demonstrated. In particular, optimal independent modal space control was implemented in a software package on the basis of finite element formulation. A rudimentary finite element-control algorithm package was also developed to evaluate the performance of candidate control laws. A few numerical simulations using the software package developed herein were given. The integrated software package will provide a design tool to address issues such as how adaptive smart systems will scale to a full size aircraft, the amount of piezoelectric materials and the powers needed to actuate it for desired performance. It will also provide a viable new structural control design concept for practical applications in large flexible structures such as aerospace vehicles and aircraft.
Nuclear Thermal Rocket Element Environmental Simulator (NTREES)
Emrich, William J. Jr.
2008-01-21
To support a potential future development of a nuclear thermal rocket engine, a state-of-the-art non nuclear experimental test setup has been constructed to evaluate the performance characteristics of candidate fuel element materials and geometries in representative environments. The test device simulates the environmental conditions (minus the radiation) to which nuclear rocket fuel components could be subjected during reactor operation. Test articles mounted in the simulator are inductively heated in such a manner as to accurately reproduce the temperatures and heat fluxes normally expected to occur as a result of nuclear fission while at the same time being exposed to flowing hydrogen. This project is referred to as the Nuclear Thermal Rocket Element Environment Simulator or NTREES. The NTREES device is located at the Marshall Space flight Center in a laboratory which has been modified to accommodate the high powers required to heat the test articles to the required temperatures and to handle the gaseous hydrogen flow required for the tests. Other modifications to the laboratory include the installation of a nitrogen gas supply system and a cooling water supply system. During the design and construction of the facility, every effort was made to comply with all pertinent regulations to provide assurance that the facility could be operated in a safe and efficient manner. The NTREES system can currently supply up to 50 kW of inductive heating to the fuel test articles, although the facility has been sized to eventually allow test article heating levels of up to several megawatts.
Nuclear Thermal Rocket Element Environmental Simulator (NTREES)
NASA Technical Reports Server (NTRS)
Emrich, William J., Jr.
2008-01-01
To support the eventual development of a nuclear thermal rocket engine, a state-of-the-art experimental test setup has been constructed to evaluate the performance characteristics of candidate fuel element materials and geometries in representative environments. The test device simulates the environmental conditions (minus the radiation) to which nuclear rocket fuel components will be subjected during reactor operation. Test articles mounted in the simulator are inductively heated in such a manner as to accurately reproduce the temperatures and heat fluxes normally expected to occur as a result of nuclear fission while at the same time being exposed to flowing hydrogen. This project is referred to as the Nuclear Thermal Rocket Element Environment Simulator or NTREES. The NTREES device is located at the Marshall Space flight Center in a laboratory which has been modified to accommodate the high powers required to heat the test articles to the required temperatures and to handle the gaseous hydrogen flow required for the tests. Other modifications to the laboratory include the installation of a nitrogen gas supply system and a cooling water supply system. During the design and construction of the facility, every effort was made to comply with all pertinent regulations to provide assurance that the facility could be operated in a safe and efficient manner. The NTREES system can currently supply up to 50 kW of inductive heating to the fuel test articles, although the facility has been sized to eventually allow test article heating levels of up to several megawatts.
Convected element method for simulation of angiogenesis.
Pindera, Maciej Z; Ding, Hui; Chen, Zhijian
2008-10-01
We describe a novel Convected Element Method (CEM) for simulation of formation of functional blood vessels induced by tumor-generated growth factors in a process called angiogenesis. Angiogenesis is typically modeled by a convection-diffusion-reaction equation defined on a continuous domain. A difficulty arises when a continuum approach is used to represent the formation of discrete blood vessel structures. CEM solves this difficulty by using a hybrid continuous/discrete solution method allowing lattice-free tracking of blood vessel tips that trace out paths that subsequently are used to define compact vessel elements. In contrast to more conventional angiogenesis modeling, the new branches form evolving grids that are capable of simulating transport of biological and chemical factors such as nutrition and anti-angiogenic agents. The method is demonstrated on expository vessel growth and tumor response simulations for a selected set of conditions, and include effects of nutrient delivery and inhibition of vessel branching. Initial results show that CEM can predict qualitatively the development of biologically reasonable and fully functional vascular structures. Research is being carried out to generalize the approach which will allow quantitative predictions. PMID:18365201
Simulation of Rotor Blade Element Turbulence
NASA Technical Reports Server (NTRS)
McFarland, R. E.; Duisenberg, Ken
1996-01-01
A turbulence model has been developed for blade-element helicopter simulation. This model, called Simulation of Rotor Blade Element Turbulence (SORBET), uses an innovative temporal and geometrical distribution algorithm that preserves the statistical characteristics of the turbulence spectra over the rotor disc, while providing velocity components in real time to each of five blade-element stations along each of four blades. An initial investigation of SORBET has been performed using a piloted, motion-based simulation of the Sikorsky UH60A Black Hawk. Although only the vertical component of stochastic turbulence was used in this investigation, vertical turbulence components induce vehicle responses in all translational and rotational degrees of freedom of the helicopter. The single-degree-of-freedom configuration of SORBET was compared to a conventional full 6-degrees-of-freedom baseline configuration, where translational velocity inputs are superimposed at the vehicle center of gravity, and rotational velocity inputs are created from filters that approximate the immersion rate into the turbulent field. For high-speed flight the vehicle responses were satisfactory for both models. Test pilots could not distinguish differences between the baseline configuration and SORBET. In low-speed flight the baseline configuration received criticism for its high frequency content, whereas the SORBET model elicited favorable pilot opinion. For this helicopter, which has fully articulated blades, results from SORBET show that vehicle responses to turbulent blade-station disturbances are severely attenuated. This is corroborated by in-flight observation of the rotor tip path plane as compared to vehicle responses.
photon-plasma: A modern high-order particle-in-cell code
Haugbølle, Troels; Frederiksen, Jacob Trier; Nordlund, Åke
2013-06-15
We present the photon-plasma code, a modern high order charge conserving particle-in-cell code for simulating relativistic plasmas. The code is using a high order implicit field solver and a novel high order charge conserving interpolation scheme for particle-to-cell interpolation and charge deposition. It includes powerful diagnostics tools with on-the-fly particle tracking, synthetic spectra integration, 2D volume slicing, and a new method to correctly account for radiative cooling in the simulations. A robust technique for imposing (time-dependent) particle and field fluxes on the boundaries is also presented. Using a hybrid OpenMP and MPI approach, the code scales efficiently from 8 to more than 250.000 cores with almost linear weak scaling on a range of architectures. The code is tested with the classical benchmarks particle heating, cold beam instability, and two-stream instability. We also present particle-in-cell simulations of the Kelvin-Helmholtz instability, and new results on radiative collisionless shocks.
Load-balancing techniques for a parallel electromagnetic particle-in-cell code
PLIMPTON,STEVEN J.; SEIDEL,DAVID B.; PASIK,MICHAEL F.; COATS,REBECCA S.
2000-01-01
QUICKSILVER is a 3-d electromagnetic particle-in-cell simulation code developed and used at Sandia to model relativistic charged particle transport. It models the time-response of electromagnetic fields and low-density-plasmas in a self-consistent manner: the fields push the plasma particles and the plasma current modifies the fields. Through an LDRD project a new parallel version of QUICKSILVER was created to enable large-scale plasma simulations to be run on massively-parallel distributed-memory supercomputers with thousands of processors, such as the Intel Tflops and DEC CPlant machines at Sandia. The new parallel code implements nearly all the features of the original serial QUICKSILVER and can be run on any platform which supports the message-passing interface (MPI) standard as well as on single-processor workstations. This report describes basic strategies useful for parallelizing and load-balancing particle-in-cell codes, outlines the parallel algorithms used in this implementation, and provides a summary of the modifications made to QUICKSILVER. It also highlights a series of benchmark simulations which have been run with the new code that illustrate its performance and parallel efficiency. These calculations have up to a billion grid cells and particles and were run on thousands of processors. This report also serves as a user manual for people wishing to run parallel QUICKSILVER.
NASA Astrophysics Data System (ADS)
Rose, D. V.; Welch, D. R.; Genoni, T. C.; Mehlhorn, T. A.; Campbell, R. B.
2008-03-01
Particle-based numerical simulations are required to study the dynamics and evolution of inhomogeneous nonequilibrium multispecies strongly coupled plasmas. Molecular dynamics (MD) and particle-in-cell (PIC) techniques and been compared previously [K. Y. Sanbonmatsu, et al., J. Phys. IV (France) 10, Pr5-259 (2000)], with the PIC methodology demonstrating the capability of improved accuracy over the MD simulations at high resolution. However, the PIC simulations were significantly slower, limiting their utility. Here we explore several schemes to improve the computational speed of such calculations including non-iterative, implicit EM field solvers and subgrid models. The simulations are compared directly with the results of Sanbonmatsu, et al., and a new theoretical analysis of the hypernetted chain model where all inter-species correlations are retained [V. Schwarz, et al., Contrib. Plasma Phys. 47, 324 (2007)].
Gatsonis, Nikolaos A. Spirkin, Anton
2009-06-01
The mathematical formulation and computational implementation of a three-dimensional particle-in-cell methodology on unstructured Delaunay-Voronoi tetrahedral grids is presented. The method allows simulation of plasmas in complex domains and incorporates the duality of the Delaunay-Voronoi in all aspects of the particle-in-cell cycle. Charge assignment and field interpolation weighting schemes of zero- and first-order are formulated based on the theory of long-range constraints. Electric potential and fields are derived from a finite-volume formulation of Gauss' law using the Voronoi-Delaunay dual. Boundary conditions and the algorithms for injection, particle loading, particle motion, and particle tracking are implemented for unstructured Delaunay grids. Error and sensitivity analysis examines the effects of particles/cell, grid scaling, and timestep on the numerical heating, the slowing-down time, and the deflection times. The problem of current collection by cylindrical Langmuir probes in collisionless plasmas is used for validation. Numerical results compare favorably with previous numerical and analytical solutions for a wide range of probe radius to Debye length ratios, probe potentials, and electron to ion temperature ratios. The versatility of the methodology is demonstrated with the simulation of a complex plasma microsensor, a directional micro-retarding potential analyzer that includes a low transparency micro-grid.
The use of electromagnetic particle-in-cell codes in accelerator applications
Eppley, K.
1988-12-01
The techniques developed for the numerical simulation of plasmas have numerous applications relevant to accelerators. The operation of many accelerator components involves transients, interactions between beams and rf fields, and internal plasma oscillations. These effects produce non-linear behavior which can be represented accurately by particle in cell (PIC) simulations. We will give a very brief overview of the algorithms used in PIC Codes. We will examine the range of parameters over which they are useful. We will discuss the factors which determine whether a two or three dimensional simulation is most appropriate. PIC codes have been applied to a wide variety of diverse problems, spanning many of the systems in a linear accelerator. We will present a number of practical examples of the application of these codes to areas such as guns, bunchers, rf sources, beam transport, emittance growth and final focus. 8 refs., 8 figs., 2 tabs.
Finite element simulation of pipe dynamic response
Slagis, G.C.; Litton, R.W.
1996-12-01
Nonlinear finite element dynamic analyses of the response of a pipe span to controlled-displacement, sinusoidal vibration have been performed. The objective of this preliminary study is to compare strain and acceleration response data to those generated by Beaney in the Berkeley Nuclear Laboratories experiments. Results for an unpressurized, 5 Hz, carbon steel pipe are in good agreement with the experiments. Hence, it appears that analytical simulation will be useful to assess seismic margins. Recommendations for additional studies are provided. The analyses confirm the test results--dynamic response is greatly attenuated by material plasticity. Analytical strains and accelerations are about 30% higher than test data. There are several possible explanations for the differences. To assess the effect of frequency on response, the length of the pipe span was increased. Analysis of the longer, 2 Hz, pipe span shows significantly greater cyclic strains than the 5 Hz span at the same input excitation levels.
A parallel particle-in-cell model for beam-beam interaction in high energy ring colliders
NASA Astrophysics Data System (ADS)
Qiang, Ji; Furman, Miguel A.; Ryne, Robert D.
2004-07-01
In this paper we present a self-consistent simulation model of colliding beams in high energy ring colliders. The model, which is based on a particle-in-cell method, uses a new developed shifted effective Green function algorithm for the efficient calculation of the beam-beam interaction with arbitrary separation and large aspect ratio. The model uses transfer maps to treat the external focusing elements and a stochastic map to treat radiation damping and quantum excitation of the beams. In the parallel implementation we studied various strategies to deal with the particular nature of the colliding beam system - a system in which there can be significant particle movement between beam-beam collisions. We chose a particle-field decomposition approach instead of the conventional domain decomposition or particle decomposition approach. The particle-field approach leads to good load balance, reduced communication cost, and shows the best scalability on an IBM SP3 among the three parallel implementations we studied. A performance test of the beam-beam model on a Cray T3E, IBM SP3, and a PC cluster is presented. As an application, we studied the flip-flop instability in an electron-positron collider.
Finite Element Aircraft Simulation of Turbulence
NASA Technical Reports Server (NTRS)
McFarland, R. E.
1997-01-01
A turbulence model has been developed for realtime aircraft simulation that accommodates stochastic turbulence and distributed discrete gusts as a function of the terrain. This model is applicable to conventional aircraft, V/STOL aircraft, and disc rotor model helicopter simulations. Vehicle angular activity in response to turbulence is computed from geometrical and temporal relationships rather than by using the conventional continuum approximations that assume uniform gust immersion and low frequency responses. By using techniques similar to those recently developed for blade-element rotor models, the angular-rate filters of conventional turbulence models are not required. The model produces rotational rates as well as air mass translational velocities in response to both stochastic and deterministic disturbances, where the discrete gusts and turbulence magnitudes may be correlated with significant terrain features or ship models. Assuming isotropy, a two-dimensional vertical turbulence field is created. A novel Gaussian interpolation technique is used to distribute vertical turbulence on the wing span or lateral rotor disc, and this distribution is used to compute roll responses. Air mass velocities are applied at significant centers of pressure in the computation of the aircraft's pitch and roll responses.
Computing quasi-linear diffusion coefficients using the delta-f particle-in-cell method
Austin, T. M.; Smithe, D. N.; Ranjbar, V.
2009-11-26
Linear wave codes AORSA and TORIC couple to the bounce-averaged nonlinear Fokker-Planck code CQL3D through quasi-linear diffusion coefficients. Both linear wave codes rely on the quasi-local approximation that includes only first-order parallel and perpendicular gradient variations of cyclotron frequency and ignores field line curvature along with temperature and density gradient effects. The delta-f particle-in-cell (DFPIC) method has been successfully used for simulating ion-cyclotron fast wave behavior. This method also permits particle behavior such as multiple pass resonance, banana orbits, and superadiabaticity. We present new work on generating quasi-linear diffusion coefficients using the DFPIC method that will permit the electromagnetic particle-in-cell (EMPIC) code, VORPAL, to couple to CQL3D and to compare to AORSA and TORIC. A new multiple weight delta-f approach will be presented that converts velocity derivatives to action derivatives and yields a full tensor quasi-linear diffusion coefficient.
Particle-in-Cell Modeling of Laser-Plasma Interactions in Three Dimensions
NASA Astrophysics Data System (ADS)
Wen, H.; Maximov, A. V.; Yan, R.; Li, J.; Ren, C.; Myatt, J. F.
2014-10-01
In the direct-drive method of inertial confinement fusion, the laser-plasma interactions (LPI's) near quarter-critical density are very important for laser absorption and fast-electron generation. Three-dimensional simulations with the particle-in-cell (PIC) code OSIRIS have allowed us to study different parametric instabilities including two-plasmon decay, stimulated Raman scattering, and stimulated Brillouin scattering. These instabilities may coexist and interact in the region near quarter-critical density. The spectra of forward-going and backward-going scattered light and fast electrons in two-dimensional and three-dimensional PIC simulations have been studied. Characteristics of LPI driven by a plane-wave laser and by an incoherent laser beam are compared. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.
Balancing Particle and Mesh Computation in a Particle-In-Cell Code
Worley, Patrick H; D'Azevedo, Eduardo; Hager, Robert; Ku, Seung-Hoe; Yoon, Eisung; Chang, C. S.
2016-01-01
The XGC1 plasma microturbulence particle-in-cell simulation code has both particle-based and mesh-based computational kernels that dominate performance. Both of these are subject to load imbalances that can degrade performance and that evolve during a simulation. Each separately can be addressed adequately, but optimizing just for one can introduce significant load imbalances in the other, degrading overall performance. A technique has been developed based on Golden Section Search that minimizes wallclock time given prior information on wallclock time, and on current particle distribution and mesh cost per cell, and also adapts to evolution in load imbalance in both particle and mesh work. In problems of interest this doubled the performance on full system runs on the XK7 at the Oak Ridge Leadership Computing Facility compared to load balancing only one of the kernels.
On the numerical dispersion and the spectral fidelity of the Particle-In-Cell method
NASA Astrophysics Data System (ADS)
Huang, Chengkun; Meyers, M. D.; Zeng, Y.; Yi, S.; Albright, B. J.
2015-11-01
The Particle-In-Cell (PIC) method is widely used in plasma modeling. However, the PIC method exhibits grid type numerical instabilities, including the finite grid instability and the numerical Cherenkov instability that can render unphysical simulation results or disrupt the simulation. A faithful numerical dispersion of the electromagnetic PIC algorithm is obtained and analyzed to obtain the insight about the numerical instabilities inherent in such a computation model. Using this dispersion, we investigate how the finite grid instability arises from the interaction of the numerical modes admitted in the system and their aliases. Compared with the gridless model, we show that the lack of spectral fidelity relative to the real system due to the aliasing effect is a major cause of the numerical instabilities in the PIC model. Work supported by the U.S. Department of Energy through the LDRD program at Los Alamos National Laboratory.
Candel, A.; Kabel, A.; Lee, L.; Li, Z.; Limborg, C.; Ng, C.; Prudencio, E.; Schussman, G.; Uplenchwar, R.; Ko, K.; /SLAC
2009-06-19
Over the past years, SLAC's Advanced Computations Department (ACD), under SciDAC sponsorship, has developed a suite of 3D (2D) parallel higher-order finite element (FE) codes, T3P (T2P) and Pic3P (Pic2P), aimed at accurate, large-scale simulation of wakefields and particle-field interactions in radio-frequency (RF) cavities of complex shape. The codes are built on the FE infrastructure that supports SLAC's frequency domain codes, Omega3P and S3P, to utilize conformal tetrahedral (triangular)meshes, higher-order basis functions and quadratic geometry approximation. For time integration, they adopt an unconditionally stable implicit scheme. Pic3P (Pic2P) extends T3P (T2P) to treat charged-particle dynamics self-consistently using the PIC (particle-in-cell) approach, the first such implementation on a conformal, unstructured grid using Whitney basis functions. Examples from applications to the International Linear Collider (ILC), Positron Electron Project-II (PEP-II), Linac Coherent Light Source (LCLS) and other accelerators will be presented to compare the accuracy and computational efficiency of these codes versus their counterparts using structured grids.
Beam Dynamics in an Electron Lens with the Warp Particle-in-cell Code
Stancari, Giulio; Moens, Vince; Redaelli, Stefano
2014-07-01
Electron lenses are a mature technique for beam manipulation in colliders and storage rings. In an electron lens, a pulsed, magnetically confined electron beam with a given current-density profile interacts with the circulating beam to obtain the desired effect. Electron lenses were used in the Fermilab Tevatron collider for beam-beam compensation, for abort-gap clearing, and for halo scraping. They will be used in RHIC at BNL for head-on beam-beam compensation, and their application to the Large Hadron Collider for halo control is under development. At Fermilab, electron lenses will be implemented as lattice elements for nonlinear integrable optics. The design of electron lenses requires tools to calculate the kicks and wakefields experienced by the circulating beam. We use the Warp particle-in-cell code to study generation, transport, and evolution of the electron beam. For the first time, a fully 3-dimensional code is used for this purpose.
A 2D Particle in Cell model for ion extraction and focusing in electrostatic accelerators
Veltri, P. Serianni, G.; Cavenago, M.
2014-02-15
Negative ions are fundamental to produce intense and high energy neutral beams used to heat the plasma in fusion devices. The processes regulating the ion extraction involve the formation of a sheath on a scale comparable to the Debye length of the plasma. On the other hand, the ion acceleration as a beam is obtained on distances greater than λ{sub D}. The paper presents a model for both the phases of ion extraction and acceleration of the ions and its implementation in a numerical code. The space charge of particles is deposited following usual Particle in Cell codes technique, while the field is solved with finite element methods. Some hypotheses on the beam plasma transition are described, allowing to model both regions at the same time. The code was tested with the geometry of the NIO1 negative ions source, and the results are compared with existing ray tracing codes and discussed.
Boundary element and finite element coupling for aeroacoustics simulations
NASA Astrophysics Data System (ADS)
Balin, Nolwenn; Casenave, Fabien; Dubois, François; Duceau, Eric; Duprey, Stefan; Terrasse, Isabelle
2015-08-01
We consider the scattering of acoustic perturbations in the presence of a flow. We suppose that the space can be split into a zone where the flow is uniform and a zone where the flow is potential. In the first zone, we apply a Prandtl-Glauert transformation to recover the Helmholtz equation. The well-known setting of boundary element method for the Helmholtz equation is available. In the second zone, the flow quantities are space dependent, we have to consider a local resolution, namely the finite element method. Herein, we carry out the coupling of these two methods and present various applications and validation test cases. The source term is given through the decomposition of an incident acoustic field on a section of the computational domain's boundary. Validations against analytic, another numerical method and measurements on different test cases are presented.
Adaptable Particle-in-Cell Algorithms for Graphical Processing Units
NASA Astrophysics Data System (ADS)
Decyk, Viktor; Singh, Tajendra
2010-11-01
Emerging computer architectures consist of an increasing number of shared memory computing cores in a chip, often with vector (SIMD) co-processors. Future exascale high performance systems will consist of a hierarchy of such nodes, which will require different algorithms at different levels. Since no one knows exactly how the future will evolve, we have begun development of an adaptable Particle-in-Cell (PIC) code, whose parameters can match different hardware configurations. The data structures reflect three levels of parallelism, contiguous vectors and non-contiguous blocks of vectors, which can share memory, and groups of blocks which do not. Particles are kept ordered at each time step, and the size of a sorting cell is an adjustable parameter. We have implemented a simple 2D electrostatic skeleton code whose inner loop (containing 6 subroutines) runs entirely on the NVIDIA Tesla C1060. We obtained speedups of about 16-25 compared to a 2.66 GHz Intel i7 (Nehalem), depending on the plasma temperature, with an asymptotic limit of 40 for a frozen plasma. We expect speedups of about 70 for an 2D electromagnetic code and about 100 for a 3D electromagnetic code, which have higher computational intensities (more flops/memory access).
Second order gyrokinetic theory for particle-in-cell codes
NASA Astrophysics Data System (ADS)
Tronko, Natalia; Bottino, Alberto; Sonnendrücker, Eric
2016-08-01
The main idea of the gyrokinetic dynamical reduction consists in a systematical removal of the fast scale motion (the gyromotion) from the dynamics of the plasma, resulting in a considerable simplification and a significant gain of computational time. The gyrokinetic Maxwell-Vlasov equations are nowadays implemented in for modeling (both laboratory and astrophysical) strongly magnetized plasmas. Different versions of the reduced set of equations exist, depending on the construction of the gyrokinetic reduction procedure and the approximations performed in the derivation. The purpose of this article is to explicitly show the connection between the general second order gyrokinetic Maxwell-Vlasov system issued from the modern gyrokinetic theory and the model currently implemented in the global electromagnetic Particle-in-Cell code ORB5. Necessary information about the modern gyrokinetic formalism is given together with the consistent derivation of the gyrokinetic Maxwell-Vlasov equations from first principles. The variational formulation of the dynamics is used to obtain the corresponding energy conservation law, which in turn is used for the verification of energy conservation diagnostics currently implemented in ORB5. This work fits within the context of the code verification project VeriGyro currently run at IPP Max-Planck Institut in collaboration with others European institutions.
A particle-in-cell approach to obliquely propagating electrostatic waves
Koen, Etienne J.; Collier, Andrew B.; Maharaj, Shimul K.
2014-09-15
The electron-acoustic and beam-driven modes associated with electron beams have previously been identified and studied numerically. These modes are associated with Broadband Electrostatic Noise found in the Earth's auroral and polar cusp regions. Using a 1-D spatial Particle-in-Cell simulation, the electron-acoustic instability is studied for a magnetized plasma, which includes cool ions, cool electrons and a hot, drifting electron beam. Both the weakly and strongly magnetized regimes with varying wave propagation angle, θ, with respect to the magnetic field are studied. The amplitude and frequency of the electron-acoustic mode are found to decrease with increasing θ. The amplitude of the electron-acoustic mode is found to significantly grow at intermediate wavenumber ranges. It reaches a saturation level at the point, where a plateau forms in the hot electron velocity distribution after which the amplitude of the electron-acoustic mode decays.
Laser-plasma interactions with a Fourier-Bessel particle-in-cell method
NASA Astrophysics Data System (ADS)
Andriyash, Igor A.; Lehe, Remi; Lifschitz, Agustin
2016-03-01
A new spectral particle-in-cell (PIC) method for plasma modeling is presented and discussed. In the proposed scheme, the Fourier-Bessel transform is used to translate the Maxwell equations to the quasi-cylindrical spectral domain. In this domain, the equations are solved analytically in time, and the spatial derivatives are approximated with high accuracy. In contrast to the finite-difference time domain (FDTD) methods, that are used commonly in PIC, the developed method does not produce numerical dispersion and does not involve grid staggering for the electric and magnetic fields. These features are especially valuable in modeling the wakefield acceleration of particles in plasmas. The proposed algorithm is implemented in the code PLARES-PIC, and the test simulations of laser plasma interactions are compared to the ones done with the quasi-cylindrical FDTD PIC code CALDER-CIRC.
Particle-in-cell study of the ion-to-electron sheath transition
NASA Astrophysics Data System (ADS)
Scheiner, Brett; Baalrud, Scott D.; Hopkins, Matthew M.; Yee, Benjamin T.; Barnat, Edward V.
2016-08-01
The form of a sheath near a small electrode, with bias changing from below to above the plasma potential, is studied using 2D particle-in-cell simulations. When the electrode is biased within Te/2 e below the plasma potential, the electron velocity distribution functions (EVDFs) exhibit a loss-cone type truncation due to fast electrons overcoming the small potential difference between the electrode and plasma. No sheath is present in this regime, and the plasma remains quasineutral up to the electrode. The EVDF truncation leads to a presheath-like density and flow velocity gradients. Once the bias exceeds the plasma potential, an electron sheath is present. In this case, the truncation driven behavior persists, but is accompanied by a shift in the maximum value of the EVDF that is not present in the negative bias cases. The flow moment has significant contributions from both the flow shift of the EVDF maximum, and the loss-cone truncation.
Finite grid instability and spectral fidelity of the electrostatic Particle-In-Cell algorithm
Huang, C. -K.; Zeng, Y.; Wang, Y.; Meyers, M. D.; Yi, S.; Albright, B. J.
2016-06-07
The origin of the Finite Grid Instability (FGI) is studied by resolving the dynamics in the 1D electrostatic Particle-In-Cell (PIC) model in the spectral domain at the single particle level and at the collective motion level. The spectral fidelity of the PIC model is contrasted with the underlying physical system or the gridless model. The systematic spectral phase and amplitude errors from the charge deposition and field interpolation are quantified for common particle shapes used in the PIC models. Lastly, it is shown through such analysis and in simulations that the lack of spectral fidelity relative to the physical systemmore » due to the existence of aliased spatial modes is the major cause of the FGI in the PIC model.« less
CPIC: A Parallel Particle-In-Cell Code for Studying Spacecraft Charging
NASA Astrophysics Data System (ADS)
Meierbachtol, Collin; Delzanno, Gian Luca; Moulton, David; Vernon, Louis
2015-11-01
CPIC is a three-dimensional electrostatic particle-in-cell code designed for use with curvilinear meshes. One of its primary objectives is to aid in studying spacecraft charging in the magnetosphere. CPIC maintains near-optimal computational performance and scaling thanks to a mapped logical mesh field solver, and a hybrid physical-logical space particle mover (avoiding the need to track particles). CPIC is written for parallel execution, utilizing a combination of both OpenMP threading and MPI distributed memory. New capabilities are being actively developed and added to CPIC, including the ability to handle multi-block curvilinear mesh structures. Verification results comparing CPIC to analytic test problems will be provided. Particular emphasis will be placed on the charging and shielding of a sphere-in-plasma system. Simulated charging results of representative spacecraft geometries will also be presented. Finally, its performance capabilities will be demonstrated through parallel scaling data.
BOA, Beam Optics Analyzer A Particle-In-Cell Code
Thuc Bui
2007-12-06
The program was tasked with implementing time dependent analysis of charges particles into an existing finite element code with adaptive meshing, called Beam Optics Analyzer (BOA). BOA was initially funded by a DOE Phase II program to use the finite element method with adaptive meshing to track particles in unstructured meshes. It uses modern programming techniques, state-of-the-art data structures, so that new methods, features and capabilities are easily added and maintained. This Phase II program was funded to implement plasma simulations in BOA and extend its capabilities to model thermal electrons, secondary emissions, self magnetic field and implement a more comprehensive post-processing and feature-rich GUI. The program was successful in implementing thermal electrons, secondary emissions, and self magnetic field calculations. The BOA GUI was also upgraded significantly, and CCR is receiving interest from the microwave tube and semiconductor equipment industry for the code. Implementation of PIC analysis was partially successful. Computational resource requirements for modeling more than 2000 particles begin to exceed the capability of most readily available computers. Modern plasma analysis typically requires modeling of approximately 2 million particles or more. The problem is that tracking many particles in an unstructured mesh that is adapting becomes inefficient. In particular memory requirements become excessive. This probably makes particle tracking in unstructured meshes currently unfeasible with commonly available computer resources. Consequently, Calabazas Creek Research, Inc. is exploring hybrid codes where the electromagnetic fields are solved on the unstructured, adaptive mesh while particles are tracked on a fixed mesh. Efficient interpolation routines should be able to transfer information between nodes of the two meshes. If successfully developed, this could provide high accuracy and reasonable computational efficiency.
Zaslavsky, V. Yu.; Ginzburg, N. S.; Glyavin, M. Yu.; Zheleznov, I. V.; Zotova, I. V.
2013-04-15
We perform 3D particle-in-cell simulations of terahertz gyrotrons with two different configurations of the interaction space. For a gyrotron with conventional cylindrical configuration of the interaction cavity, we demonstrate reasonable agreement between simulations and experimental results, including output frequency, structure of the higher-order operating mode (TE{sub 17,4}), output power, and ohmic losses. For a novel planar gyrotron scheme with transverse energy extraction, a possibility of further increasing the oversized factor with the single-mode operation regime retained is shown. Frequency detuning by mechanical variation of the gap between waveguide plates is also demonstrated.
NASA Astrophysics Data System (ADS)
Gassmöller, Rene; Bangerth, Wolfgang
2016-04-01
Particle-in-cell methods have a long history and many applications in geodynamic modelling of mantle convection, lithospheric deformation and crustal dynamics. They are primarily used to track material information, the strain a material has undergone, the pressure-temperature history a certain material region has experienced, or the amount of volatiles or partial melt present in a region. However, their efficient parallel implementation - in particular combined with adaptive finite-element meshes - is complicated due to the complex communication patterns and frequent reassignment of particles to cells. Consequently, many current scientific software packages accomplish this efficient implementation by specifically designing particle methods for a single purpose, like the advection of scalar material properties that do not evolve over time (e.g., for chemical heterogeneities). Design choices for particle integration, data storage, and parallel communication are then optimized for this single purpose, making the code relatively rigid to changing requirements. Here, we present the implementation of a flexible, scalable and efficient particle-in-cell method for massively parallel finite-element codes with adaptively changing meshes. Using a modular plugin structure, we allow maximum flexibility of the generation of particles, the carried tracer properties, the advection and output algorithms, and the projection of properties to the finite-element mesh. We present scaling tests ranging up to tens of thousands of cores and tens of billions of particles. Additionally, we discuss efficient load-balancing strategies for particles in adaptive meshes with their strengths and weaknesses, local particle-transfer between parallel subdomains utilizing existing communication patterns from the finite element mesh, and the use of established parallel output algorithms like the HDF5 library. Finally, we show some relevant particle application cases, compare our implementation to a
NASA Astrophysics Data System (ADS)
Vu, H. X.; Bezzerides, B.; Dubois, D. F.
1998-11-01
A fully kinetic, reduced-description particle-in-cell (RPIC) model is presented in which deviations from quasineutrality, electron and ion kinetic effects, and nonlinear interactions between low-frequency and high-frequency parametric instabilities are modeled correctly. The model is based on a reduced description where the electromagnetic field is represented by three separate temporal WKB envelopes in order to model low-frequency and high-frequency parametric instabilities. Because temporal WKB approximations are invoked, the simulation can be performed on the electron time scale instead of the time scale of the light waves. The electrons and ions are represented by discrete finite-size particles, permitting electron and ion kinetic effects to be modeled properly. The Poisson equation is utilized to ensure that space-charge effects are included. Although RPIC is fully three dimensional, it has been implemented in only two dimensions on a CRAY-T3D with 512 processors and on the Accelerated Strategic Computing Initiative (ASCI) parallel computer at Los Alamos National Laboratory, and the resulting simulation code has been named ASPEN. Given the current computers available to the authors, one and two dimensional simulations are feasible to, and have been, performed. Three dimensional simulations are much more expensive, and are not feasible at this time. However, with rapidly advancing computer technologies, three dimensional simulations may be feasible in the near future. We believe this code is the first PIC code capable of simulating the interaction between low-frequency and high-frequency parametric instabilites in multiple dimensions. Test simulations of stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), and Langmuir decay instability (LDI), are presented.
Nuter, R.; Gremillet, L.; Lefebvre, E.; Levy, A.; Ceccotti, T.; Martin, P.
2011-03-15
A novel numerical modeling of field ionization in PIC (Particle In Cell) codes is presented. Based on the quasistatic approximation of the ADK (Ammosov Delone Krainov) theory and implemented through a Monte Carlo scheme, this model allows for multiple ionization processes. Two-dimensional PIC simulations are performed to analyze the cut-off energies of the laser-accelerated carbon ions measured on the UHI 10 Saclay facility. The influence of the target and the hydrocarbon pollutant composition on laser-accelerated carbon ion energies is demonstrated.
Finite element simulation of articular contact mechanics with quadratic tetrahedral elements.
Maas, Steve A; Ellis, Benjamin J; Rawlins, David S; Weiss, Jeffrey A
2016-03-21
Although it is easier to generate finite element discretizations with tetrahedral elements, trilinear hexahedral (HEX8) elements are more often used in simulations of articular contact mechanics. This is due to numerical shortcomings of linear tetrahedral (TET4) elements, limited availability of quadratic tetrahedron elements in combination with effective contact algorithms, and the perceived increased computational expense of quadratic finite elements. In this study we implemented both ten-node (TET10) and fifteen-node (TET15) quadratic tetrahedral elements in FEBio (www.febio.org) and compared their accuracy, robustness in terms of convergence behavior and computational cost for simulations relevant to articular contact mechanics. Suitable volume integration and surface integration rules were determined by comparing the results of several benchmark contact problems. The results demonstrated that the surface integration rule used to evaluate the contact integrals for quadratic elements affected both convergence behavior and accuracy of predicted stresses. The computational expense and robustness of both quadratic tetrahedral formulations compared favorably to the HEX8 models. Of note, the TET15 element demonstrated superior convergence behavior and lower computational cost than both the TET10 and HEX8 elements for meshes with similar numbers of degrees of freedom in the contact problems that we examined. Finally, the excellent accuracy and relative efficiency of these quadratic tetrahedral elements was illustrated by comparing their predictions with those for a HEX8 mesh for simulation of articular contact in a fully validated model of the hip. These results demonstrate that TET10 and TET15 elements provide viable alternatives to HEX8 elements for simulation of articular contact mechanics. PMID:26900037
On the Numerical Dispersion of Electromagnetic Particle-In-Cell Code : Finite Grid Instability
Meyers, Michael David; Huang, Chengkun; Zeng, Yong; Yi, Sunghwan; Albright, Brian James
2014-07-15
The Particle-In-Cell (PIC) method is widely used in relativistic particle beam and laser plasma modeling. However, the PIC method exhibits numerical instabilities that can render unphysical simulation results or even destroy the simulation. For electromagnetic relativistic beam and plasma modeling, the most relevant numerical instabilities are the finite grid instability and the numerical Cherenkov instability. We review the numerical dispersion relation of the electromagnetic PIC algorithm to analyze the origin of these instabilities. We rigorously derive the faithful 3D numerical dispersion of the PIC algorithm, and then specialize to the Yee FDTD scheme. In particular, we account for the manner in which the PIC algorithm updates and samples the fields and distribution function. Temporal and spatial phase factors from solving Maxwell's equations on the Yee grid with the leapfrog scheme are also explicitly accounted for. Numerical solutions to the electrostatic-like modes in the 1D dispersion relation for a cold drifting plasma are obtained for parameters of interest. In the succeeding analysis, we investigate how the finite grid instability arises from the interaction of the numerical 1D modes admitted in the system and their aliases. The most significant interaction is due critically to the correct representation of the operators in the dispersion relation. We obtain a simple analytic expression for the peak growth rate due to this interaction.
Fundamentals of plasma simulation
Forslund, D.W.
1985-01-01
With the increasing size and speed of modern computers, the incredibly complex nonlinear properties of plasmas in the laboratory and in space are being successfully explored in increasing depth. Of particular importance have been numerical simulation techniques involving finite size particles on a discrete mesh. After discussing the importance of this means of understanding a variety of nonlinear plasma phenomena, we describe the basic elements of particle-in-cell simulation and their limitations and advantages. The differencing techniques, stability and accuracy issues, data management and optimization issues are discussed by means of a simple example of a particle-in-cell code. Recent advances in simulation methods allowing large space and time scales to be treated with minimal sacrifice in physics are reviewed. Various examples of nonlinear processes successfully studied by plasma simulation will be given.
Whistler turbulence heating of electrons and ions: Three-dimensional particle-in-cell simuations
Gary, S. Peter; Hughes, R. Scott; Wang, Joseph
2016-01-14
In this study, the decay of whistler turbulence in a collisionless, homogeneous, magnetized plasma is studied using three-dimensional particle-in-cell simulations. The simulations are initialized with a narrowband, relatively isotropic distribution of long wavelength whistler modes. A first ensemble of simulations at electron betamore » $${\\beta }_{{\\rm{e}}}$$ = 0.25 and ion-to-electron mass ratio $${m}_{{\\rm{i}}}$$/$${m}_{{\\rm{e}}}$$ = 400 is carried out on a domain cube of dimension $$L{\\omega }_{\\mathrm{pi}}$$/c = 5.12 where $${\\omega }_{\\mathrm{pi}}$$ is the ion plasma frequency. The simulations begin with a range of dimensionless fluctuating field energy densities, $${\\epsilon }_{{\\rm{o}}}$$, and follow the fluctuations as they cascade to broadband, anisotropic turbulence which dissipates at shorter wavelengths, heating both electrons and ions. The electron heating is stronger and preferentially parallel/antiparallel to the background magnetic field $${{\\boldsymbol{B}}}_{{\\rm{o}}};$$ the ion energy gain is weaker and is preferentially in directions perpendicular to $${{\\boldsymbol{B}}}_{{\\rm{o}}}$$. The important new results here are that, over 0.01 < $${\\epsilon }_{{\\rm{o}}}$$ < 0.25, the maximum rate of electron heating scales approximately as $${\\epsilon }_{{\\rm{o}}}$$, and the maximum rate of ion heating scales approximately as $${\\epsilon }_{{\\rm{o}}}^{1.5}$$. A second ensemble of simulations at $${\\epsilon }_{{\\rm{o}}}$$ = 0.10 and $${\\beta }_{{\\rm{e}}}$$ = 0.25 shows that, over 25 < $${m}_{{\\rm{i}}}$$/$${m}_{{\\rm{e}}}\\;$$< 1836, the ratio of the maximum ion heating rate to the maximum electron heating rate scales approximately as $${m}_{{\\rm{e}}}$$/$${m}_{{\\rm{i}}}$$.« less
Particle-in-cell modeling for MJ scale dense plasma focus with varied anode shape
Link, A. Halvorson, C. Schmidt, A.; Hagen, E. C.; Rose, D. V.; Welch, D. R.
2014-12-15
Megajoule scale dense plasma focus (DPF) Z-pinches with deuterium gas fill are compact devices capable of producing 10{sup 12} neutrons per shot but past predictive models of large-scale DPF have not included kinetic effects such as ion beam formation or anomalous resistivity. We report on progress of developing a predictive DPF model by extending our 2D axisymmetric collisional kinetic particle-in-cell (PIC) simulations from the 4 kJ, 200 kA LLNL DPF to 1 MJ, 2 MA Gemini DPF using the PIC code LSP. These new simulations incorporate electrodes, an external pulsed-power driver circuit, and model the plasma from insulator lift-off through the pinch phase. To accommodate the vast range of relevant spatial and temporal scales involved in the Gemini DPF within the available computational resources, the simulations were performed using a new hybrid fluid-to-kinetic model. This new approach allows single simulations to begin in an electron/ion fluid mode from insulator lift-off through the 5-6 μs run-down of the 50+ cm anode, then transition to a fully kinetic PIC description during the run-in phase, when the current sheath is 2-3 mm from the central axis of the anode. Simulations are advanced through the final pinch phase using an adaptive variable time-step to capture the fs and sub-mm scales of the kinetic instabilities involved in the ion beam formation and neutron production. Validation assessments are being performed using a variety of different anode shapes, comparing against experimental measurements of neutron yield, neutron anisotropy and ion beam production.
Final Report for "Gyrotron Design and Evaluation using New Particle-in-Cell Capability"
David N Smithe
2008-05-28
ITER will depend on high power CW gyrotrons to deliver power to the plasma at ECR frequencies. However, gyrotrons can suffer from undesirable low frequency oscillations (LFO’s) which are known to interfere with the gun-region diagnostics and data collection, and are also expected to produce undesirable energy and velocity spread in the beam. The origins and processes leading to these oscillations are poorly understood, and existing gyrotron R&D tools, such as static gun solvers and interaction region models, are not designed to look at time-dependant oscillatory behavior. We have applied a time-domain particle-in-cell method to investigate the LFO phenomenon. Our company is at the forefront of smooth-curved-boundary treatment of the electromagnetic fields and particle emission surfaces, and such methods are necessary to simulate the adiabatically trapped and reflected electrons thought to be driving the oscillations. This approach provides the means for understanding, in microscopic detail, the underlying physical processes driving the low-frequency oscillations. In the Phase I project, an electron gun region from an existing gyrotron, known to observe LFO’s, was selected as a proof-of-principle geometry, and was modeled with the curved-geometry time-domain simulation tool, in order to establish the feasibility of simulating LFO physics with this tool on office-scale, and larger, parallel cluster computers. Generally, it was found to be feasible to model the simulation geometry, emission, and magnetic features of the electron gun. Ultimately, the tool will be used to investigate the origins and life cycle within the trapped particle population. This tool also provides the foundations and validation for potential application of the software to numerous other time-dependant beam and rf source problems in the commercial arena.
Particle-In-Cell Modeling For MJ Dense Plasma Focus with Varied Anode Shape
NASA Astrophysics Data System (ADS)
Link, A.; Halvorson, C.; Schmidt, A.; Hagen, E. C.; Rose, D.; Welch, D.
2014-10-01
Megajoule scale dense plasma focus (DPF) Z-pinches with deuterium gas fill are compact devices capable of producing 1012 neutrons per shot but past predictive models of large-scale DPF have not included kinetic effects such as ion beam formation or anomalous resistivity. We report on progress of developing a predictive DPF model by extending our 2D axisymmetric collisional kinetic particle-in-cell (PIC) simulations to the 1 MJ, 2 MA Gemini DPF using the PIC code LSP. These new simulations incorporate electrodes, an external pulsed-power driver circuit, and model the plasma from insulator lift-off through the pinch phase. The simulations were performed using a new hybrid fluid-to-kinetic model transitioning from a fluid description to a fully kinetic PIC description during the run-in phase. Simulations are advanced through the final pinch phase using an adaptive variable time-step to capture the fs and sub-mm scales of the kinetic instabilities involved in the ion beam formation and neutron production. Results will be present on the predicted effects of different anode configurations. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory (LLNL) under Contract DE-AC52-07NA27344 and supported by the Laboratory Directed Research and Development Program (11-ERD-063) and the Computing Grand Challenge program at LLNL. This work supported by Office of Defense Nuclear Nonproliferation Research and Development within U.S. Department of Energy's National Nuclear Security Administration.
Recent advances in the modeling of plasmas with the Particle-In-Cell methods
NASA Astrophysics Data System (ADS)
Vay, Jean-Luc; Lehe, Remi; Vincenti, Henri; Godfrey, Brendan; Lee, Patrick; Haber, Irv
2015-11-01
The Particle-In-Cell (PIC) approach is the method of choice for self-consistent simulations of plasmas from first principles. The fundamentals of the PIC method were established decades ago but improvements or variations are continuously being proposed. We report on several recent advances in PIC related algorithms, including: (a) detailed analysis of the numerical Cherenkov instability and its remediation, (b) analytic pseudo-spectral electromagnetic solvers in Cartesian and cylindrical (with azimuthal modes decomposition) geometries, (c) arbitrary-order finite-difference and generalized pseudo-spectral Maxwell solvers, (d) novel analysis of Maxwell's solvers' stencil variation and truncation, in application to domain decomposition strategies and implementation of Perfectly Matched Layers in high-order and pseudo-spectral solvers. Work supported by US-DOE Contracts DE-AC02-05CH11231 and the US-DOE SciDAC program ComPASS. Used resources of NERSC, supported by US-DOE Contract DE-AC02-05CH11231.
An incompressible two-dimensional multiphase particle-in-cell model for dense particle flows
Snider, D.M.; O`Rourke, P.J.; Andrews, M.J.
1997-06-01
A two-dimensional, incompressible, multiphase particle-in-cell (MP-PIC) method is presented for dense particle flows. The numerical technique solves the governing equations of the fluid phase using a continuum model and those of the particle phase using a Lagrangian model. Difficulties associated with calculating interparticle interactions for dense particle flows with volume fractions above 5% have been eliminated by mapping particle properties to a Eulerian grid and then mapping back computed stress tensors to particle positions. This approach utilizes the best of Eulerian/Eulerian continuum models and Eulerian/Lagrangian discrete models. The solution scheme allows for distributions of types, sizes, and density of particles, with no numerical diffusion from the Lagrangian particle calculations. The computational method is implicit with respect to pressure, velocity, and volume fraction in the continuum solution thus avoiding courant limits on computational time advancement. MP-PIC simulations are compared with one-dimensional problems that have analytical solutions and with two-dimensional problems for which there are experimental data.
QUICKPIC: A highly efficient particle-in-cell code for modeling wakefield acceleration in plasmas
Huang, C. . E-mail: huangck@ee.ucla.edu; Decyk, V.K.; Ren, C.; Zhou, M.; Lu, W.; Mori, W.B.; Cooley, J.H.; Antonsen, T.M.; Katsouleas, T.
2006-09-20
A highly efficient, fully parallelized, fully relativistic, three-dimensional particle-in-cell model for simulating plasma and laser wakefield acceleration is described. The model is based on the quasi-static or frozen field approximation, which reduces a fully three-dimensional electromagnetic field solve and particle push to a two-dimensional field solve and particle push. This is done by calculating the plasma wake assuming that the drive beam and/or laser does not evolve during the time it takes for it to pass a plasma particle. The complete electromagnetic fields of the plasma wake and its associated index of refraction are then used to evolve the drive beam and/or laser using very large time steps. This algorithm reduces the computational time by 2-3 orders of magnitude. Comparison between the new algorithm and conventional fully explicit models (OSIRIS) is presented. The agreement is excellent for problems of interest. Direction for future work is also presented.
An energy- and charge-conserving, nonlinearly implicit, electromagnetic particle-in-cell algorithm
NASA Astrophysics Data System (ADS)
Chen, Guangye; Chacon, Luis; Knoll, Dana; Daughton, William; CoCoMans (LANL) Team
2013-10-01
A recent proof-of-principle study proposes a nonlinear electrostatic implicit particle-in-cell (PIC) algorithm in one dimension. The algorithm employs a kinetically enslaved Jacobian-free Newton-Krylov (JFNK) method, and conserves energy and charge to numerical round-off. In this study, we generalize the method to electromagnetic simulations in 1D using the Darwin approximation of Maxwell's equations. An implicit, orbit-averaged central finite difference scheme is applied to both the Darwin field equations and the particle orbit equations to produce a discrete system that remains exactly charge-and energy-conserving. Furthermore, the canonical momentum in any ignorable direction is exactly conserved per particle by appropriate interpolations of the magnetic field. A fluid preconditioner targeting the stiffest electron waves has been developed to accelerate the linear GMRES solver of JFNK. We present 1D numerical experiments (e.g. the Weibel instability, kinetic Alfven wave ion-ion streaming instability, etc.) to demonstrate the accuracy and efficiency of the implicit Darwin PIC algorithm, and the performance of the fluid preconditioner.
External circuit integration with electromagnetic particle in cell modeling of plasma focus devices
Seng, Y. S.; Lee, P.; Rawat, R. S.
2015-03-15
The pinch performance of a plasma focus (PF) device is sensitive to the physical conditions of the breakdown phase. It is therefore essential to model and study the initial phase in order to optimize device performance. An external circuit is self consistently coupled to the electromagnetic particle in cell code to model the breakdown and initial lift phase of the United Nations University/International Centre for Theoretical Physics (UNU-ICTP) plasma focus device. Gas breakdown during the breakdown phase is simulated successfully, following a drop in the applied voltage across the device and a concurrent substantial rise in the circuit current. As a result, the plasma becomes magnetized, with the growing value of the magnetic field over time leading to the gradual lift off of the well formed current sheath into the axial acceleration phase. This lifting off, with simultaneous outward sheath motion along the anode and vertical cathode, and the strong magnetic fields in the current sheath region, was demonstrated in this work, and hence validates our method of coupling the external circuit to PF devices. Our method produces voltage waveforms that are qualitatively similar to the observed experimental voltage profiles of the UNU-ICTP device. Values of the mean electron energy before and after voltage breakdown turned out to be different, with the values after breakdown being much lower. In both cases, the electron energy density function turned out to be non-Maxwellian.
Particle-in-Cell Modeling of Magnetized Argon Plasma Flow Through Small Mechanical Apertures
Adam B. Sefkow and Samuel A. Cohen
2009-04-09
Motivated by observations of supersonic argon-ion flow generated by linear helicon-heated plasma devices, a three-dimensional particle-in-cell (PIC) code is used to study whether stationary electrostatic layers form near mechanical apertures intersecting the flow of magnetized plasma. By self-consistently evaluating the temporal evolution of the plasma in the vicinity of the aperture, the PIC simulations characterize the roles of the imposed aperture and applied magnetic field on ion acceleration. The PIC model includes ionization of a background neutral-argon population by thermal and superthermal electrons, the latter found upstream of the aperture. Near the aperture, a transition from a collisional to a collisionless regime occurs. Perturbations of density and potential, with mm wavelengths and consistent with ion acoustic waves, propagate axially. An ion acceleration region of length ~ 200-300 λD,e forms at the location of the aperture and is found to be an electrostatic double layer, with axially-separated regions of net positive and negative charge. Reducing the aperture diameter or increasing its length increases the double layer strength.
Novel methods in the Particle-In-Cell accelerator Code-Framework Warp
Vay, J-L; Grote, D. P.; Cohen, R. H.; Friedman, A.
2012-12-26
The Particle-In-Cell (PIC) Code-Framework Warp is being developed by the Heavy Ion Fusion Science Virtual National Laboratory (HIFS-VNL) to guide the development of accelerators that can deliver beams suitable for high-energy density experiments and implosion of inertial fusion capsules. It is also applied in various areas outside the Heavy Ion Fusion program to the study and design of existing and next-generation high-energy accelerators, including the study of electron cloud effects and laser wakefield acceleration for example. This study presents an overview of Warp's capabilities, summarizing recent original numerical methods that were developed by the HIFS-VNL (including PIC with adaptive mesh refinement, a large-timestep 'drift-Lorentz' mover for arbitrarily magnetized species, a relativistic Lorentz invariant leapfrog particle pusher, simulations in Lorentz-boosted frames, an electromagnetic solver with tunable numerical dispersion and efficient stride-based digital filtering), with special emphasis on the description of the mesh refinement capability. In addition, selected examples of the applications of the methods to the abovementioned fields are given.
Performance of particle in cell methods on highly concurrent computational architectures
M.F.Adams; S. Ethier; N. Wichmann
2009-09-23
Particle in cell (PIC) methods are effective in computing Vlasov-Poisson system of equations used in simulations of magnetic fusion plasmas. PIC methods use grid based computations, for solving Poisson’s equation or more generally Maxwell’s equations, as well as Monte-Carlo type methods to sample the Vlasov equation. The presence of two types of discretizations, deterministic field solves and Monte-Carlo methods for the Vlasov equation, pose challenges in understanding and optimizing performance on today large scale computers which require high levels of concurrency. These challenges arises from the need to optimize two very different types of processes and the interactions between them. Modern cache based high-end computers have very deep memory hierarchies and high degrees of concurrency which must be utilized effectively to achieve good performance. The effective use of these machines requires maximizing concurrency by eliminating serial or redundant work and minimizing global communication. A related issue is minimizing the memory traffic between levels of the memory hierarchy because performance is often limited by the bandwidths and latencies of the memory system. This paper discusses some of the performance issues, particularly in regard to parallelism, of PIC methods. The gyrokinetic toroidal code (GTC) is used for these studies and a new radial grid decomposition is presented and evaluated. Scaling of the code is demonstrated on ITER sized plasmas with up to 16K Cray XT3/4 cores.
Spacecraft charging analysis with the implicit particle-in-cell code iPic3D
Deca, J.; Lapenta, G.; Marchand, R.; Markidis, S.
2013-10-15
We present the first results on the analysis of spacecraft charging with the implicit particle-in-cell code iPic3D, designed for running on massively parallel supercomputers. The numerical algorithm is presented, highlighting the implementation of the electrostatic solver and the immersed boundary algorithm; the latter which creates the possibility to handle complex spacecraft geometries. As a first step in the verification process, a comparison is made between the floating potential obtained with iPic3D and with Orbital Motion Limited theory for a spherical particle in a uniform stationary plasma. Second, the numerical model is verified for a CubeSat benchmark by comparing simulation results with those of PTetra for space environment conditions with increasing levels of complexity. In particular, we consider spacecraft charging from plasma particle collection, photoelectron and secondary electron emission. The influence of a background magnetic field on the floating potential profile near the spacecraft is also considered. Although the numerical approaches in iPic3D and PTetra are rather different, good agreement is found between the two models, raising the level of confidence in both codes to predict and evaluate the complex plasma environment around spacecraft.
Contemporary particle-in-cell approach to laser-plasma modelling
NASA Astrophysics Data System (ADS)
Arber, T. D.; Bennett, K.; Brady, C. S.; Lawrence-Douglas, A.; Ramsay, M. G.; Sircombe, N. J.; Gillies, P.; Evans, R. G.; Schmitz, H.; Bell, A. R.; Ridgers, C. P.
2015-11-01
Particle-in-cell (PIC) methods have a long history in the study of laser-plasma interactions. Early electromagnetic codes used the Yee staggered grid for field variables combined with a leapfrog EM-field update and the Boris algorithm for particle pushing. The general properties of such schemes are well documented. Modern PIC codes tend to add to these high-order shape functions for particles, Poisson preserving field updates, collisions, ionisation, a hybrid scheme for solid density and high-field QED effects. In addition to these physics packages, the increase in computing power now allows simulations with real mass ratios, full 3D dynamics and multi-speckle interaction. This paper presents a review of the core algorithms used in current laser-plasma specific PIC codes. Also reported are estimates of self-heating rates, convergence of collisional routines and test of ionisation models which are not readily available elsewhere. Having reviewed the status of PIC algorithms we present a summary of recent applications of such codes in laser-plasma physics, concentrating on SRS, short-pulse laser-solid interactions, fast-electron transport, and QED effects.
Finite element simulation of impact response of wire mesh screens
NASA Astrophysics Data System (ADS)
Wang, Caizheng; Shankar, Krishna; Fien, Alan
2015-09-01
In this paper, the response of wire mesh screens to low velocity impact with blunt objects is investigated using finite element (FE) simulation. The woven wire mesh is modelled with homogeneous shell elements with equivalent smeared mechanical properties. The mechanical behaviour of the woven wire mesh was determined experimentally with tensile tests on steel wire mesh coupons to generate the data for the smeared shell material used in the FE. The effects of impacts with a low mass (4 kg) and a large mass (40 kg) providing the same impact energy are studied. The joint between the wire mesh screen and the aluminium frame surrounding it is modelled using contact elements with friction between the corresponding elements. Damage to the screen of different types compromising its structural integrity, such as mesh separation and pulling out from the surrounding frame is modelled. The FE simulation is validated with results of impact tests conducted on woven steel wire screen meshes.
An Enriched Shell Element for Delamination Simulation in Composite Laminates
NASA Technical Reports Server (NTRS)
McElroy, Mark
2015-01-01
A formulation is presented for an enriched shell finite element capable of delamination simulation in composite laminates. The element uses an adaptive splitting approach for damage characterization that allows for straightforward low-fidelity model creation and a numerically efficient solution. The Floating Node Method is used in conjunction with the Virtual Crack Closure Technique to predict delamination growth and represent it discretely at an arbitrary ply interface. The enriched element is verified for Mode I delamination simulation using numerical benchmark data. After determining important mesh configuration guidelines for the vicinity of the delamination front in the model, a good correlation was found between the enriched shell element model results and the benchmark data set.
Nuclear Thermal Rocket Element Environmental Simulator (NTREES) Upgrade Activities
NASA Technical Reports Server (NTRS)
Emrich, William J. Jr.; Moran, Robert P.; Pearson, J. Boise
2012-01-01
To support the on-going nuclear thermal propulsion effort, a state-of-the-art non nuclear experimental test setup has been constructed to evaluate the performance characteristics of candidate fuel element materials and geometries in representative environments. The facility to perform this testing is referred to as the Nuclear Thermal Rocket Element Environment Simulator (NTREES). This device can simulate the environmental conditions (minus the radiation) to which nuclear rocket fuel components will be subjected during reactor operation. Test articles mounted in the simulator are inductively heated in such a manner so as to accurately reproduce the temperatures and heat fluxes which would normally occur as a result of nuclear fission and would be exposed to flowing hydrogen. Initial testing of a somewhat prototypical fuel element has been successfully performed in NTREES and the facility has now been shutdown to allow for an extensive reconfiguration of the facility which will result in a significant upgrade in its capabilities
3D finite element simulations of high velocity projectile impact
NASA Astrophysics Data System (ADS)
Ožbolt, Joško; İrhan, Barış; Ruta, Daniela
2015-09-01
An explicit three-dimensional (3D) finite element (FE) code is developed for the simulation of high velocity impact and fragmentation events. The rate sensitive microplane material model, which accounts for large deformations and rate effects, is used as a constitutive law. In the code large deformation frictional contact is treated by forward incremental Lagrange multiplier method. To handle highly distorted and damaged elements the approach based on the element deletion is employed. The code is then used in 3D FE simulations of high velocity projectile impact. The results of the numerical simulations are evaluated and compared with experimental results. It is shown that it realistically predicts failure mode and exit velocities for different geometries of plain concrete slab. Moreover, the importance of some relevant parameters, such as contact friction, rate sensitivity, bulk viscosity and deletion criteria are addressed.
Simulation of two-dimensional waterflooding using mixed finite elements
Chavent, G.; Jaffre, J.; Cohen, G.; Dupuy, M.; Dieste, I.
1982-01-01
A new method for the simulation of incompressible diphasic flows in two dimensions is presented, the distinctive features of which are: (1) reformation of the basic equation and specific choices of the finite element approximation of the same; (11) use of a mixed finite elements method, approximating both scalar and vector functions. Several test examples are shown, including gravity and capillary effects. The use of discontinuous basis functions proved successful for an accurate representation of sharp fronts. 16 refs.
On the numerical dispersion of electromagnetic particle-in-cell code: Finite grid instability
NASA Astrophysics Data System (ADS)
Meyers, M. D.; Huang, C.-K.; Zeng, Y.; Yi, S. A.; Albright, B. J.
2015-09-01
The Particle-In-Cell (PIC) method is widely used in relativistic particle beam and laser plasma modeling. However, the PIC method exhibits numerical instabilities that can render unphysical simulation results or even destroy the simulation. For electromagnetic relativistic beam and plasma modeling, the most relevant numerical instabilities are the finite grid instability and the numerical Cherenkov instability. We review the numerical dispersion relation of the Electromagnetic PIC model. We rigorously derive the faithful 3-D numerical dispersion relation of the PIC model, for a simple, direct current deposition scheme, which does not conserve electric charge exactly. We then specialize to the Yee FDTD scheme. In particular, we clarify the presence of alias modes in an eigenmode analysis of the PIC model, which combines both discrete and continuous variables. The manner in which the PIC model updates and samples the fields and distribution function, together with the temporal and spatial phase factors from solving Maxwell's equations on the Yee grid with the leapfrog scheme, is explicitly accounted for. Numerical solutions to the electrostatic-like modes in the 1-D dispersion relation for a cold drifting plasma are obtained for parameters of interest. In the succeeding analysis, we investigate how the finite grid instability arises from the interaction of the numerical modes admitted in the system and their aliases. The most significant interaction is due critically to the correct representation of the operators in the dispersion relation. We obtain a simple analytic expression for the peak growth rate due to this interaction, which is then verified by simulation. We demonstrate that our analysis is readily extendable to charge conserving models.
On the numerical dispersion of electromagnetic particle-in-cell code: Finite grid instability
Meyers, M.D.; Huang, C.-K.; Zeng, Y.; Yi, S.A.; Albright, B.J.
2015-09-15
The Particle-In-Cell (PIC) method is widely used in relativistic particle beam and laser plasma modeling. However, the PIC method exhibits numerical instabilities that can render unphysical simulation results or even destroy the simulation. For electromagnetic relativistic beam and plasma modeling, the most relevant numerical instabilities are the finite grid instability and the numerical Cherenkov instability. We review the numerical dispersion relation of the Electromagnetic PIC model. We rigorously derive the faithful 3-D numerical dispersion relation of the PIC model, for a simple, direct current deposition scheme, which does not conserve electric charge exactly. We then specialize to the Yee FDTD scheme. In particular, we clarify the presence of alias modes in an eigenmode analysis of the PIC model, which combines both discrete and continuous variables. The manner in which the PIC model updates and samples the fields and distribution function, together with the temporal and spatial phase factors from solving Maxwell's equations on the Yee grid with the leapfrog scheme, is explicitly accounted for. Numerical solutions to the electrostatic-like modes in the 1-D dispersion relation for a cold drifting plasma are obtained for parameters of interest. In the succeeding analysis, we investigate how the finite grid instability arises from the interaction of the numerical modes admitted in the system and their aliases. The most significant interaction is due critically to the correct representation of the operators in the dispersion relation. We obtain a simple analytic expression for the peak growth rate due to this interaction, which is then verified by simulation. We demonstrate that our analysis is readily extendable to charge conserving models.
Progress in 3D Particle-In-Cell Modeling of Space-Charge-Dominated Ion Beams for Heavy-Ion Fusion
NASA Astrophysics Data System (ADS)
Friedman, A.; Callahan, D. A.; Grote, D. P.; Langdon, A. B.; Lund, S. M.; Haber, I.
1996-11-01
The ion beam in an induction accelerator for HIF is a non-neutral plasma, and is effectively simulated using familiar particle-in-cell (PIC) techniques, with the addition of a description of the accelerating and confining elements. The WARP code incorporates electrostatic 3D and r,z PIC models; a number of techniques are used in the 3D package, WARP3d, to increase accuracy and efficiency. These include solution of Poisson's equation with subgrid-scale resolution of internal boundary placement, a bent-system model using ``warped'' coordinates, and parallel processing. In this paper we describe recent applications to HIF experiments, including a high-current electrostatic-quadrupole injector at LBNL, and bending and recirculation experiments at LLNL. We also describe new computational techniques being studied, including higher-order integrators and subcycling methods aimed at allowing larger timesteps, and a ``fat-slice'' model which affords efficient examination of collective modes that transfer thermal energy between degrees of freedom.
Process control of large-scale finite element simulation software
Spence, P.A.; Weingarten, L.I.; Schroder, K.; Tung, D.M.; Sheaffer, D.A.
1996-02-01
We have developed a methodology for coupling large-scale numerical codes with process control algorithms. Closed-loop simulations were demonstrated using the Sandia-developed finite element thermal code TACO and the commercially available finite element thermal-mechanical code ABAQUS. This new capability enables us to use computational simulations for designing and prototyping advanced process-control systems. By testing control algorithms on simulators before building and testing hardware, enormous time and cost savings can be realized. The need for a closed-loop simulation capability was demonstrated in a detailed design study of a rapid-thermal-processing reactor under development by CVC Products Inc. Using a thermal model of the RTP system as a surrogate for the actual hardware, we were able to generate response data needed for controller design. We then evaluated the performance of both the controller design and the hardware design by using the controller to drive the finite element model. The controlled simulations provided data on wafer temperature uniformity as a function of ramp rate, temperature sensor locations, and controller gain. This information, which is critical to reactor design, cannot be obtained from typical open-loop simulations.
SUPG Finite Element Simulations of Compressible Flows for Aerothermodynamic Applications
NASA Technical Reports Server (NTRS)
Kirk, Benjamin S.
2007-01-01
This viewgraph presentation reviews the Streamline-Upwind Petrov-Galerkin (SUPG) Finite Element Simulation. It covers the background, governing equations, weak formulation, shock capturing, inviscid flux discretization, time discretization, linearization, and implicit solution strategies. It also reviews some applications such as Type IV Shock Interaction, Forward-Facing Cavity and AEDC Sharp Double Cone.
Discrete Element Method Simulation of Nonlinear Viscoelastic Stress Wave Problems
NASA Astrophysics Data System (ADS)
Tang, Zhiping; Horie, Y.; Wang, Wenqiang
2002-07-01
A DEM(Discrete Element Method) simulation of nonlinear viscoelastic stress wave problems is carried out. The interaction forces among elements are described using a model in which neighbor elements are linked by a nonlinear spring and a certain number of Maxwell components in parallel. By making use of exponential relaxation moduli, it is shown that numerical computation of the convolution integral does not require storing and repeatedly calculating strain history, so that the computational cost is dramatically reduced. To validate the viscoelastic DM2 code1, stress wave propagation in a Maxwell rod with one end subjected to a constant stress loading is simulated. Results excellently fit those from the characteristics calculation. The code is then used to investigate the problem of meso-scale damage in a plastic-bonded explosive under shock loading. Results not only show "compression damage", but also reveal a complex damage evolution. They demonstrate a unique capability of DEM in modeling heterogeneous materials.
Discrete Element Method Simulation of Nonlinear Viscoelastic Stress Wave Problems
NASA Astrophysics Data System (ADS)
Wang, Wenqiang; Tang, Zhiping; Horie, Y.
2002-07-01
A DEM(Discrete Element Method) simulation of nonlinear viscoelastic stress wave problems is carried out. The interaction forces among elements are described using a model in which neighbor elements are linked by a nonlinear spring and a certain number of Maxwell components in parallel. By making use of exponential relaxation moduli, it is shown that numerical computation of the convolution integral does not require storing and repeatedly calculating strain history, so that the computational cost is dramatically reduced. To validate the viscoelastic DM2 code[1], stress wave propagation in a Maxwell rod with one end subjected to a constant stress loading is simulated. Results excellently fit those from the characteristics calculation. The code is then used to investigate the problem of meso-scale damage in a plastic-bonded explosive under shock loading. Results not only show "compression damage", but also reveal a complex damage evolution. They demonstrate a unique capability of DEM in modeling heterogeneous materials.
Particle-In-Cell Modeling for MegaJoule Dense Plasma Focus
NASA Astrophysics Data System (ADS)
Link, Anthony
2015-11-01
Megajoule scale dense plasma focus (DPF) Z-pinches with deuterium gas fill are compact devices capable of producing 1012 neutrons per shot but past predictive models of large-scale DPF have not included kinetic effects such as ion beam formation or anomalous resistivity. We report on progress of developing a predictive DPF model by extending our 2D axisymmetric collisional kinetic particle-in-cell (PIC) simulations from the 4 kJ, 200 kA LLNL DPF to 1 MJ, 2 MA Gemini DPF using the PIC code LSP. These new simulations are by far the most detailed and computationally intensive DPF simulations run to date. They incorporate electrodes, an external pulsed-power driver circuit, and model the plasma from insulator lift-off through the pinch phase. To accommodate the vast range of relevant spatial and temporal scales involved in the Gemini DPF within the available computational resources, the simulations were performed using a new hybrid fluid-to-kinetic model. This new approach allows single simulations to begin in an electron/ion fluid mode from insulator lift-off through the 5-6 μs run-down of the 50 + cm anode, then transition to a fully kinetic PIC description during the run-in phase, when the current sheath is 2-3 mm from the central axis of the anode. Simulations are advanced through the final pinch phase using an adaptive variable time-step to capture the fs and sub-mm scales of the kinetic instabilities involved in the ion beam formation and neutron production. An anode shape scan as well as a scan in stored energy/charging voltage has been performed. A comparison of MJ performance for different drivers will be presented. Validation assessments are being performed, comparing against experimental measurements of neutron yield, neutron anisotropy and plasma density. Prepared by LLNL under Contract DE-AC52-07NA27344. This work supported by the U.S. Department of Energy's National Nuclear Security Administration. Computing support for this work came from the LLNL
NASA Astrophysics Data System (ADS)
Ramsay, M. G.; Arber, T. D.; Sircombe, N. J.
2016-03-01
In order for detailed, solid density particle-in-cell (PIC) simulations to run within a reasonable time frame, novel approaches to modelling high density material must be employed. For the purposes of modelling high intensity, short pulse laser-plasma interactions, however, these approaches must be consistent with retaining a full PIC model in the low-density laser interaction region. By replacing the standard Maxwell field solver with an electric field update based on a simplified Ohm's law in regions of high electron density, it is possible to access densities at and above solid without being subject to the standard grid and time step constraints. Such a model has recently been implemented in the PIC code EPOCH. We present the initial results of a detailed two-dimensional simulation performed to compare the adapted version of the code with recent experimental results from the Orion laser facility.
Xiao, Jianyuan; Liu, Jian; Qin, Hong; Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 ; Yu, Zhi
2013-10-15
Smoothing functions are commonly used to reduce numerical noise arising from coarse sampling of particles in particle-in-cell (PIC) plasma simulations. When applying smoothing functions to symplectic algorithms, the conservation of symplectic structure should be guaranteed to preserve good conservation properties. In this paper, we show how to construct a variational multi-symplectic PIC algorithm with smoothing functions for the Vlasov-Maxwell system. The conservation of the multi-symplectic structure and the reduction of numerical noise make this algorithm specifically suitable for simulating long-term dynamics of plasmas, such as those in the steady-state operation or long-pulse discharge of a super-conducting tokamak. The algorithm has been implemented in a 6D large scale PIC code. Numerical examples are given to demonstrate the good conservation properties of the multi-symplectic algorithm and the reduction of the noise due to the application of smoothing function.
Crystal level simulations using Eulerian finite element methods
Becker, R; Barton, N R; Benson, D J
2004-02-06
Over the last several years, significant progress has been made in the use of crystal level material models in simulations of forming operations. However, in Lagrangian finite element approaches simulation capabilities are limited in many cases by mesh distortion associated with deformation heterogeneity. Contexts in which such large distortions arise include: bulk deformation to strains approaching or exceeding unity, especially in highly anisotropic or multiphase materials; shear band formation and intersection of shear bands; and indentation with sharp indenters. Investigators have in the past used Eulerian finite element methods with material response determined from crystal aggregates to study steady state forming processes. However, Eulerian and Arbitrary Lagrangian-Eulerian (ALE) finite element methods have not been widely utilized for simulation of transient deformation processes at the crystal level. The advection schemes used in Eulerian and ALE codes control mesh distortion and allow for simulation of much larger total deformations. We will discuss material state representation issues related to advection and will present results from ALE simulations.
System and Method for Finite Element Simulation of Helicopter Turbulence
NASA Technical Reports Server (NTRS)
McFarland, R. E. (Inventor); Dulsenberg, Ken (Inventor)
1999-01-01
The present invention provides a turbulence model that has been developed for blade-element helicopter simulation. This model uses an innovative temporal and geometrical distribution algorithm that preserves the statistical characteristics of the turbulence spectra over the rotor disc, while providing velocity components in real time to each of five blade-element stations along each of four blades. for a total of twenty blade-element stations. The simulator system includes a software implementation of flight dynamics that adheres to the guidelines for turbulence set forth in military specifications. One of the features of the present simulator system is that it applies simulated turbulence to the rotor blades of the helicopter, rather than to its center of gravity. The simulator system accurately models the rotor penetration into a gust field. It includes time correlation between the front and rear of the main rotor, as well as between the side forces felt at the center of gravity and at the tail rotor. It also includes features for added realism, such as patchy turbulence and vertical gusts in to which the rotor disc penetrates. These features are realized by a unique real time implementation of the turbulence filters. The new simulator system uses two arrays one on either side of the main rotor to record the turbulence field and to produce time-correlation from the front to the rear of the rotor disc. The use of Gaussian Interpolation between the two arrays maintains the statistical properties of the turbulence across the rotor disc. The present simulator system and method may be used in future and existing real-time helicopter simulations with minimal increase in computational workload.
Applications of finite element simulation in orthopedic and trauma surgery.
Herrera, Antonio; Ibarz, Elena; Cegoñino, José; Lobo-Escolar, Antonio; Puértolas, Sergio; López, Enrique; Mateo, Jesús; Gracia, Luis
2012-04-18
Research in different areas of orthopedic and trauma surgery requires a methodology that allows both a more economic approach and the ability to reproduce different situations in an easy way. Simulation models have been introduced recently in bioengineering and could become an essential tool in the study of any physiological unity, regardless of its complexity. The main problem in modeling with finite elements simulation is to achieve an accurate reproduction of the anatomy and a perfect correlation of the different structures, in any region of the human body. Authors have developed a mixed technique, joining the use of a three-dimensional laser scanner Roland Picza captured together with computed tomography (CT) and 3D CT images, to achieve a perfect reproduction of the anatomy. Finite element (FE) simulation lets us know the biomechanical changes that take place after hip prostheses or osteosynthesis implantation and biological responses of bone to biomechanical changes. The simulation models are able to predict changes in bone stress distribution around the implant, so allowing preventing future pathologies. The development of a FE model of lumbar spine is another interesting application of the simulation. The model allows research on the lumbar spine, not only in physiological conditions but also simulating different load conditions, to assess the impact on biomechanics. Different degrees of disc degeneration can also be simulated to determine the impact on adjacent anatomical elements. Finally, FE models may be useful to test different fixation systems, i.e., pedicular screws, interbody devices or rigid fixations compared with the dynamic ones. We have also developed models of lumbar spine and hip joint to predict the occurrence of osteoporotic fractures, based on densitometric determinations and specific biomechanical models, including approaches from damage and fracture mechanics. FE simulations also allow us to predict the behavior of orthopedic splints
Numerical modeling of laser tunneling ionization in explicit particle-in-cell codes
Chen, M.; Cormier-Michel, E.; Geddes, C.G.R.; Bruhwiler, D.L.; Yu, L.L.; Esarey, E.; Schroeder, C.B.; Leemans, W.P.
2013-03-01
Methods for the calculation of laser tunneling ionization in explicit particle-in-cell codes used for modeling laser–plasma interactions are compared and validated against theoretical predictions. Improved accuracy is obtained by using the direct current form for the ionization rate. Multi level ionization in a single time step and energy conservation have been considered during the ionization process. The effects of grid resolution and number of macro-particles per cell are examined. Implementation of the ionization algorithm in two different particle-in-cell codes is compared for the case of ionization-based electron injection in a laser–plasma accelerator.
Parallel finite element simulation of large ram-air parachutes
NASA Astrophysics Data System (ADS)
Kalro, V.; Aliabadi, S.; Garrard, W.; Tezduyar, T.; Mittal, S.; Stein, K.
1997-06-01
In the near future, large ram-air parachutes are expected to provide the capability of delivering 21 ton payloads from altitudes as high as 25,000 ft. In development and test and evaluation of these parachutes the size of the parachute needed and the deployment stages involved make high-performance computing (HPC) simulations a desirable alternative to costly airdrop tests. Although computational simulations based on realistic, 3D, time-dependent models will continue to be a major computational challenge, advanced finite element simulation techniques recently developed for this purpose and the execution of these techniques on HPC platforms are significant steps in the direction to meet this challenge. In this paper, two approaches for analysis of the inflation and gliding of ram-air parachutes are presented. In one of the approaches the point mass flight mechanics equations are solved with the time-varying drag and lift areas obtained from empirical data. This approach is limited to parachutes with similar configurations to those for which data are available. The other approach is 3D finite element computations based on the Navier-Stokes equations governing the airflow around the parachute canopy and Newtons law of motion governing the 3D dynamics of the canopy, with the forces acting on the canopy calculated from the simulated flow field. At the earlier stages of canopy inflation the parachute is modelled as an expanding box, whereas at the later stages, as it expands, the box transforms to a parafoil and glides. These finite element computations are carried out on the massively parallel supercomputers CRAY T3D and Thinking Machines CM-5, typically with millions of coupled, non-linear finite element equations solved simultaneously at every time step or pseudo-time step of the simulation.
Diffusive mesh relaxation in ALE finite element numerical simulations
Dube, E.I.
1996-06-01
The theory for a diffusive mesh relaxation algorithm is developed for use in three-dimensional Arbitary Lagrange/Eulerian (ALE) finite element simulation techniques. This mesh relaxer is derived by a variational principle for an unstructured 3D grid using finite elements, and incorporates hourglass controls in the numerical implementation. The diffusive coefficients are based on the geometric properties of the existing mesh, and are chosen so as to allow for a smooth grid that retains the general shape of the original mesh. The diffusive mesh relaxation algorithm is then applied to an ALE code system, and results from several test cases are discussed.
Stressed mirror polishing: finite element simulation of mirror blank deformation
NASA Astrophysics Data System (ADS)
Han, Yu; Lu, Lihong
2014-08-01
The theoretical principle of Stressed Mirror Polishing (SMP) is introduced, including the representation method of elastic deformation, the formulations of discrete bending moment and shearing force. A Finite Element Analysis (FEA) simulation model of has been set up by ANSYS software. The warping facility in this model is consisted of 36 aluminum alloy arms equally distribute on the ambit of mirror blank. Two forces are applied on each arm to provide bending moment and shearing force. Taking type 82 segment of Thirty Meters Telescope (TMT) primary mirror for example, a FEA simulation of mirror blank deformation has been performed. Simulation result shows that, the deformation error is 33μm PV. The theoretical deformation PV value is 205μm and the simulation deformation PV value is 172μm, converging rate reaches to 0.84 in a single warping cycle. After three or four warping cycles, the residue error may converge into 1μm.
Galerkin finite-element simulation of a geothermal reservoir
Mercer, J.W., Jr.; Pinder, G.F.
1973-01-01
The equations describing fluid flow and energy transport in a porous medium can be used to formulate a mathematical model capable of simulating the transient response of a hot-water geothermal reservoir. The resulting equations can be solved accurately and efficiently using a numerical scheme which combines the finite element approach with the Galerkin method of approximation. Application of this numerical model to the Wairakei geothermal field demonstrates that hot-water geothermal fields can be simulated using numerical techniques currently available and under development. ?? 1973.
Finite-element simulation of thermoemission electron guns
NASA Astrophysics Data System (ADS)
Greenfield, D.
2006-05-01
The peculiarity of the numeric simulation of the thermoemission electron guns consists in the principal necessity of taking into account the contribution of the electrons' charge into the potential distribution in the beam formation region. Ths fact makes the mathematical model essentially nonlinear especially in the high-perveance operation mode. Moreover, the charge density is extremely high in the vicinity of emitting surfaces, rising infinitely in the limit of zero initial velocities. A special semi-analytical approach has been applied to deal with the charge singularity. Being combined with traditional finite-element numerical techniques, this approach provides an efficient way to simulate thermoemission electron guns.
Modeling and Simulation of a Nuclear Fuel Element Test Section
NASA Technical Reports Server (NTRS)
Moran, Robert P.; Emrich, William
2011-01-01
"The Nuclear Thermal Rocket Element Environmental Simulator" test section closely simulates the internal operating conditions of a thermal nuclear rocket. The purpose of testing is to determine the ideal fuel rod characteristics for optimum thermal heat transfer to their hydrogen cooling/working fluid while still maintaining fuel rod structural integrity. Working fluid exhaust temperatures of up to 5,000 degrees Fahrenheit can be encountered. The exhaust gas is rendered inert and massively reduced in temperature for analysis using a combination of water cooling channels and cool N2 gas injectors in the H2-N2 mixer portion of the test section. An extensive thermal fluid analysis was performed in support of the engineering design of the H2-N2 mixer in order to determine the maximum "mass flow rate"-"operating temperature" curve of the fuel elements hydrogen exhaust gas based on the test facilities available cooling N2 mass flow rate as the limiting factor.
Finite element simulation of temperature dependent free surface flows
NASA Technical Reports Server (NTRS)
Engelman, M. S.; Sani, R. L.
1985-01-01
The method of Engelman and Sani (1984) for a finite-element simulation of incompressible surface flows with a free and/or moving fluid interface, such as encountered in crystal growth and coating and polymer technology, is extended to temperature-dependent flows, including the effect of temperature-dependent surface tension. The basic algorithm of Saito and Scriven (1981) and Ruschak (1980) has been generalized and implemented in a robust and versatile finite-element code that can be employed with relative ease for the simulation of free-surface problems in complex geometries. As a result, the costly dependence on the Newton-Raphson algorithm has been eliminated by replacing it with a quasi-Newton iterative method, which nearly retains the superior convergence properties of the Newton-Raphson method.
Discrete Element Method Simulations of Ice Floe Dynamics
NASA Astrophysics Data System (ADS)
Calantoni, J.; Bateman, S. P.; Shi, F.; Orzech, M.; Veeramony, J.
2014-12-01
Ice floes were modeled using LIGGGHTS, an open source discrete element method (DEM) software, where individual elements were bonded together to make floes. The bonds were allowed to break with a critical stress calibrated to existing laboratory measurements for the compressive, tensile, and flexural strength of ice floes. The DEM allows for heterogeneous shape and size distributions of the ice floes to evolve over time. We simulated the interaction between sea ice and ocean waves in the marginal ice zone using a coupled wave-ice system. The waves were modeled with NHWAVE, a non-hydrostatic wave model that predicts instantaneous surface elevation and the three-dimensional flow field. The ice floes and waves were coupled through buoyancy and drag forces. Preliminary comparisons with field and laboratory measurements for coupled simulations will be presented.
Simulating Space Capsule Water Landing with Explicit Finite Element Method
NASA Technical Reports Server (NTRS)
Wang, John T.; Lyle, Karen H.
2007-01-01
A study of using an explicit nonlinear dynamic finite element code for simulating the water landing of a space capsule was performed. The finite element model contains Lagrangian shell elements for the space capsule and Eulerian solid elements for the water and air. An Arbitrary Lagrangian Eulerian (ALE) solver and a penalty coupling method were used for predicting the fluid and structure interaction forces. The space capsule was first assumed to be rigid, so the numerical results could be correlated with closed form solutions. The water and air meshes were continuously refined until the solution was converged. The converged maximum deceleration predicted is bounded by the classical von Karman and Wagner solutions and is considered to be an adequate solution. The refined water and air meshes were then used in the models for simulating the water landing of a capsule model that has a flexible bottom. For small pitch angle cases, the maximum deceleration from the flexible capsule model was found to be significantly greater than the maximum deceleration obtained from the corresponding rigid model. For large pitch angle cases, the difference between the maximum deceleration of the flexible model and that of its corresponding rigid model is smaller. Test data of Apollo space capsules with a flexible heat shield qualitatively support the findings presented in this paper.
High-order finite element methods for cardiac monodomain simulations.
Vincent, Kevin P; Gonzales, Matthew J; Gillette, Andrew K; Villongco, Christopher T; Pezzuto, Simone; Omens, Jeffrey H; Holst, Michael J; McCulloch, Andrew D
2015-01-01
Computational modeling of tissue-scale cardiac electrophysiology requires numerically converged solutions to avoid spurious artifacts. The steep gradients inherent to cardiac action potential propagation necessitate fine spatial scales and therefore a substantial computational burden. The use of high-order interpolation methods has previously been proposed for these simulations due to their theoretical convergence advantage. In this study, we compare the convergence behavior of linear Lagrange, cubic Hermite, and the newly proposed cubic Hermite-style serendipity interpolation methods for finite element simulations of the cardiac monodomain equation. The high-order methods reach converged solutions with fewer degrees of freedom and longer element edge lengths than traditional linear elements. Additionally, we propose a dimensionless number, the cell Thiele modulus, as a more useful metric for determining solution convergence than element size alone. Finally, we use the cell Thiele modulus to examine convergence criteria for obtaining clinically useful activation patterns for applications such as patient-specific modeling where the total activation time is known a priori. PMID:26300783
High-order finite element methods for cardiac monodomain simulations
Vincent, Kevin P.; Gonzales, Matthew J.; Gillette, Andrew K.; Villongco, Christopher T.; Pezzuto, Simone; Omens, Jeffrey H.; Holst, Michael J.; McCulloch, Andrew D.
2015-01-01
Computational modeling of tissue-scale cardiac electrophysiology requires numerically converged solutions to avoid spurious artifacts. The steep gradients inherent to cardiac action potential propagation necessitate fine spatial scales and therefore a substantial computational burden. The use of high-order interpolation methods has previously been proposed for these simulations due to their theoretical convergence advantage. In this study, we compare the convergence behavior of linear Lagrange, cubic Hermite, and the newly proposed cubic Hermite-style serendipity interpolation methods for finite element simulations of the cardiac monodomain equation. The high-order methods reach converged solutions with fewer degrees of freedom and longer element edge lengths than traditional linear elements. Additionally, we propose a dimensionless number, the cell Thiele modulus, as a more useful metric for determining solution convergence than element size alone. Finally, we use the cell Thiele modulus to examine convergence criteria for obtaining clinically useful activation patterns for applications such as patient-specific modeling where the total activation time is known a priori. PMID:26300783
NASA Astrophysics Data System (ADS)
Majzoobi, A.; Joshi, R. P.; Neuber, A. A.; Dickens, J. C.
2015-10-01
Particle-in-cell simulations are performed to analyze the efficiency, output power and leakage currents in a 12-Cavity, 12-Cathode rising-sun magnetron with diffraction output (MDO). The central goal is to conduct a parameter study of a rising-sun magnetron that comprehensively incorporates performance enhancing features such as transparent cathodes, axial extraction, the use of endcaps, and cathode extensions. Our optimum results demonstrate peak output power of about 2.1 GW, with efficiencies of ˜70% and low leakage currents at a magnetic field of 0.45 Tesla, a 400 kV bias with a single endcap, for a range of cathode extensions between 3 and 6 centimeters.
Majzoobi, A.; Joshi, R. P. Neuber, A. A.; Dickens, J. C.
2015-10-15
Particle-in-cell simulations are performed to analyze the efficiency, output power and leakage currents in a 12-Cavity, 12-Cathode rising-sun magnetron with diffraction output (MDO). The central goal is to conduct a parameter study of a rising-sun magnetron that comprehensively incorporates performance enhancing features such as transparent cathodes, axial extraction, the use of endcaps, and cathode extensions. Our optimum results demonstrate peak output power of about 2.1 GW, with efficiencies of ∼70% and low leakage currents at a magnetic field of 0.45 Tesla, a 400 kV bias with a single endcap, for a range of cathode extensions between 3 and 6 centimeters.
Initial Operation of the Nuclear Thermal Rocket Element Environmental Simulator
NASA Technical Reports Server (NTRS)
Emrich, William J., Jr.; Pearson, J. Boise; Schoenfeld, Michael P.
2015-01-01
The Nuclear Thermal Rocket Element Environmental Simulator (NTREES) facility is designed to perform realistic non-nuclear testing of nuclear thermal rocket (NTR) fuel elements and fuel materials. Although the NTREES facility cannot mimic the neutron and gamma environment of an operating NTR, it can simulate the thermal hydraulic environment within an NTR fuel element to provide critical information on material performance and compatibility. The NTREES facility has recently been upgraded such that the power capabilities of the facility have been increased significantly. At its present 1.2 MW power level, more prototypical fuel element temperatures nay now be reached. The new 1.2 MW induction heater consists of three physical units consisting of a transformer, rectifier, and inverter. This multiunit arrangement facilitated increasing the flexibility of the induction heater by more easily allowing variable frequency operation. Frequency ranges between 20 and 60 kHz can accommodated in the new induction heater allowing more representative power distributions to be generated within the test elements. The water cooling system was also upgraded to so as to be capable of removing 100% of the heat generated during testing In this new higher power configuration, NTREES will be capable of testing fuel elements and fuel materials at near-prototypic power densities. As checkout testing progressed and as higher power levels were achieved, several design deficiencies were discovered and fixed. Most of these design deficiencies were related to stray RF energy causing various components to encounter unexpected heating. Copper shielding around these components largely eliminated these problems. Other problems encountered involved unexpected movement in the coil due to electromagnetic forces and electrical arcing between the coil and a dummy test article. The coil movement and arcing which were encountered during the checkout testing effectively destroyed the induction coil in use at
A nonlinear dynamic finite element approach for simulating muscular hydrostats.
Vavourakis, V; Kazakidi, A; Tsakiris, D P; Ekaterinaris, J A
2014-01-01
An implicit nonlinear finite element model for simulating biological muscle mechanics is developed. The numerical method is suitable for dynamic simulations of three-dimensional, nonlinear, nearly incompressible, hyperelastic materials that undergo large deformations. These features characterise biological muscles, which consist of fibres and connective tissues. It can be assumed that the stress distribution inside the muscles is the superposition of stresses along the fibres and the connective tissues. The mechanical behaviour of the surrounding tissues is determined by adopting a Mooney-Rivlin constitutive model, while the mechanical description of fibres is considered to be the sum of active and passive stresses. Due to the nonlinear nature of the problem, evaluation of the Jacobian matrix is carried out in order to subsequently utilise the standard Newton-Raphson iterative procedure and to carry out time integration with an implicit scheme. The proposed methodology is implemented into our in-house, open source, finite element software, which is validated by comparing numerical results with experimental measurements and other numerical results. Finally, the numerical procedure is utilised to simulate primitive octopus arm manoeuvres, such as bending and reaching. PMID:23025686
Finite element simulation of food transport through the esophageal body
Yang, Wei; Fung, Tat Ching; Chian, Kerm Sim; Chong, Chuh Khiun
2007-01-01
The peristaltic transport of swallowed material in the esophagus is a neuro-muscular function involving the nerve control, bolus-structure interaction, and structure-mechanics relationship of the tissue. In this study, a finite element model (FEM) was developed to simulate food transport through the esophagus. The FEM consists of three components, i.e., tissue, food bolus and peristaltic wave, as well as the interactions between them. The transport process was simulated as three stages, i.e., the filling of fluid, contraction of circular muscle and traveling of peristaltic wave. It was found that the maximal passive intraluminal pressure due to bolus expansion was in the range of 0.8-10 kPa and it increased with bolus volume and fluid viscosity. It was found that the highest normal and shear stresses were at the inner surface of muscle layer. In addition, the peak pressure required for the fluid flow was predicted to be 1-15 kPa at the bolus tail. The diseases of systemic sclerosis or osteogenesis imperfecta, with the remodeled microstructures and mechanical properties, might induce the malfunction of esophageal transport. In conclusion, the current simulation was demonstrated to be able to capture the main characteristics in the intraluminal pressure and bolus geometry as measured experimentally. Therefore, the finite element model established in this study could be used to further explore the mechanism of esophageal transport in various clinical applications. PMID:17457965
Neutrino-driven wind simulations and nucleosynthesis of heavy elements
NASA Astrophysics Data System (ADS)
Arcones, A.; Thielemann, F.-K.
2013-01-01
Neutrino-driven winds, which follow core-collapse supernova explosions, present a fascinating nuclear-astrophysics problem that requires an understanding of advanced astrophysics simulations, the properties of matter and neutrino interactions under extreme conditions, the structure and reactions of exotic nuclei, and comparisons with forefront astronomical observations. The neutrino-driven wind has attracted vast attention over the last 20 years as it was suggested as a candidate for the astrophysics site where half of the heavy elements are produced via the r-process. In this review, we summarize our present understanding of neutrino-driven winds from the dynamical and nucleosynthesis perspectives. Rapid progress has been made during recent years in understanding the wind with improved simulations and better micro physics. The current status of the fields is that hydrodynamical simulations do not reach the extreme conditions necessary for the r-process, and the proton or neutron richness of the wind remains to be investigated in more detail. However, nucleosynthesis studies and observations already point to neutrino-driven winds to explain the origin of lighter heavy elements, such as Sr, Y, Zr.
Finite Element Simulation of Metal-Semiconductor-Metal Photodetector
Guarino, G.; Donaldson, W.R.; Mikulics, M.; Marso, M.; Kordos, P.; Sobolewski, R.
2009-08-19
The successful application of finite element analysis to ultrafast optoelectronic devices is demonstrated. Finite element models have been developed for both an alloyed- and surface-contact metal–semiconductor–metal photodetectors. The simulation results agree with previously reported experimental data. The alloyed device, despite having a somewhat larger capacitance, has a non-illuminated region of lower resistance with a more-uniform and deeper-penetrating electric field and carrier transport current. The latter explains, in terms of the equivalent lumped parameters, the experimentally observed faster response of the alloyed device. The model is further used to predict improved responsivity, based on electrode spacing and antireflective coating. We project that increasing the depth of the alloyed contact beyond approximately half of the optical penetration depth will not yield significantly improved responsivity.
Identification of micro parameters for discrete element simulation of agglomerates
NASA Astrophysics Data System (ADS)
Palis, Stefan; Antonyuk, Sergiy; Dosta, Maksym; Heinrich, Stefan
2013-06-01
The mechanical behaviour of solid particles like agglomerates, granules or crystals strongly depends on their micro structure, e.g. structural defects and porosity. In order to model the mechanical behaviour of these inhomogeneous media the discrete element method has been proven to be an appropriate tool. The model parameters used are typically micro parameters like bond stiffness, particle-particle contact stiffness, strength of the bonds. Due to the lack of general methods for a direct micro parameter determination, normally laborious parameter adaptation has to be done in order to fit experiment and simulation. In this contribution a systematic and automatic way for parameter adaptation using real experiments is proposed. Due to the fact, that discrete element models are typically systems of differential equations of very high order, gradient based methods are not suitable. Hence, the focus will be on derivative free methods.
Nuclear Thermal Rocket Element Environmental Simulator (NTREES) Upgrade Activities
NASA Technical Reports Server (NTRS)
Emrich, William
2013-01-01
A key technology element in Nuclear Thermal Propulsion is the development of fuel materials and components which can withstand extremely high temperatures while being exposed to flowing hydrogen. NTREES provides a cost effective method for rapidly screening of candidate fuel components with regard to their viability for use in NTR systems. The NTREES is designed to mimic the conditions (minus the radiation) to which nuclear rocket fuel elements and other components would be subjected to during reactor operation. The NTREES consists of a water cooled ASME code stamped pressure vessel and its associated control hardware and instrumentation coupled with inductive heaters to simulate the heat provided by the fission process. The NTREES has been designed to safely allow hydrogen gas to be injected into internal flow passages of an inductively heated test article mounted in the chamber.
Assessing performance and validating finite element simulations using probabilistic knowledge
Dolin, Ronald M.; Rodriguez, E. A.
2002-01-01
Two probabilistic approaches for assessing performance are presented. The first approach assesses probability of failure by simultaneously modeling all likely events. The probability each event causes failure along with the event's likelihood of occurrence contribute to the overall probability of failure. The second assessment method is based on stochastic sampling using an influence diagram. Latin-hypercube sampling is used to stochastically assess events. The overall probability of failure is taken as the maximum probability of failure of all the events. The Likelihood of Occurrence simulation suggests failure does not occur while the Stochastic Sampling approach predicts failure. The Likelihood of Occurrence results are used to validate finite element predictions.
Finite Element Simulation of Diametral Strength Test of Hydroxyapatite
Ozturk, Fahrettin; Toros, Serkan; Evis, Zafer
2011-01-17
In this study, the diametral strength test of sintered hydroxyapatite was simulated by the finite element software, ABAQUS/Standard. Stress distributions on diametral test sample were determined. The effect of sintering temperature on stress distribution of hydroxyapatite was studied. It was concluded that high sintering temperatures did not reduce the stress on hydroxyapatite. It had a negative effect on stress distribution of hydroxyapatite after 1300 deg. C. In addition to the porosity, other factors (sintering temperature, presence of phases and the degree of crystallinity) affect the diametral strength of the hydroxyapatite.
Large-eddy simulation using the finite element method
McCallen, R.C.; Gresho, P.M.; Leone, J.M. Jr.; Kollmann, W.
1993-10-01
In a large-eddy simulation (LES) of turbulent flows, the large-scale motion is calculated explicitly (i.e., approximated with semi-empirical relations). Typically, finite difference or spectral numerical schemes are used to generate an LES; the use of finite element methods (FEM) has been far less prominent. In this study, we demonstrate that FEM in combination with LES provides a viable tool for the study of turbulent, separating channel flows, specifically the flow over a two-dimensional backward-facing step. The combination of these methodologies brings together the advantages of each: LES provides a high degree of accuracy with a minimum of empiricism for turbulence modeling and FEM provides a robust way to simulate flow in very complex domains of practical interest. Such a combination should prove very valuable to the engineering community.
Leap frog integrator modifications in highly collisional particle-in-cell codes
NASA Astrophysics Data System (ADS)
Hanzlikova, N.; Turner, M. M.
2014-07-01
Leap frog integration method is a standard, simple, fast, and accurate way to implement velocity and position integration in particle-in-cell codes. Due to the direct solution of kinetics of particles in phase space central to the particle-in-cell procedure, important information can be obtained on particle velocity distributions, and consequently on transport and heating processes. This approach is commonly associated with physical situations where collisional effects are weak, but can also be profitably applied in some highly collisional cases, such as occur in semiconductor devices and gaseous discharges at atmospheric pressure. In this paper, we show that the implementation of the leap frog integration method in these circumstances can violate some of the assumptions central to the accuracy of this scheme. Indeed, without adaptation, the method gives incorrect results. We show here how the method must be modified to deal correctly with highly collisional cases.
NASA Astrophysics Data System (ADS)
Ho, C. Y.; Leung, R. C. K.; Zhou, K.; Lam, G. C. Y.; Jiang, Z.
2011-09-01
One-step direct aeroacoustic simulation (DAS) has received attention from aerospace and mechanical high-pressure fluid-moving system manufacturers for quite some time. They aim to simulate the unsteady flow and acoustic field in the duct simultaneously in order to investigate the aeroacoustic generation mechanisms. Because of the large length and energy scale disparities between the acoustic far field and the aerodynamic near field, highly accurate and high-resolution simulation scheme is required. This involves the use of high order compact finite difference and time advancement schemes in simulation. However, in this situation, large buffer zones are always needed to suppress the spurious numerical waves emanating from computational boundaries. This further increases the computational resources to yield accurate results. On the other hand, for such problem as supersonic jet noise, the numerical scheme should be able to resolve both strong shock waves and weak acoustic waves simultaneously. Usually numerical aeroa-coustic scheme that is good for low Mach number flow is not able to give satisfactory simulation results for shock wave. Therefore, the aeroacoustic research community has been looking for a more efficient one-step DAS scheme that has the comparable accuracy to the finite-difference approach with smaller buffer regions, yet is able to give accurate solutions from subsonic to supersonic flows. The conservation element and solution element (CE/SE) scheme is one of the possible schemes satisfying the above requirements. This paper aims to report the development of a CE/SE scheme for one-step DAS and illustrate its robustness and effectiveness with two selected benchmark problems.
Steady and Unsteady Nozzle Simulations Using the Conservation Element and Solution Element Method
NASA Technical Reports Server (NTRS)
Friedlander, David Joshua; Wang, Xiao-Yen J.
2014-01-01
This paper presents results from computational fluid dynamic (CFD) simulations of a three-stream plug nozzle. Time-accurate, Euler, quasi-1D and 2D-axisymmetric simulations were performed as part of an effort to provide a CFD-based approach to modeling nozzle dynamics. The CFD code used for the simulations is based on the space-time Conservation Element and Solution Element (CESE) method. Steady-state results were validated using the Wind-US code and a code utilizing the MacCormack method while the unsteady results were partially validated via an aeroacoustic benchmark problem. The CESE steady-state flow field solutions showed excellent agreement with solutions derived from the other methods and codes while preliminary unsteady results for the three-stream plug nozzle are also shown. Additionally, a study was performed to explore the sensitivity of gross thrust computations to the control surface definition. The results showed that most of the sensitivity while computing the gross thrust is attributed to the control surface stencil resolution and choice of stencil end points and not to the control surface definition itself.Finally, comparisons between the quasi-1D and 2D-axisymetric solutions were performed in order to gain insight on whether a quasi-1D solution can capture the steady and unsteady nozzle phenomena without the cost of a 2D-axisymmetric simulation. Initial results show that while the quasi-1D solutions are similar to the 2D-axisymmetric solutions, the inability of the quasi-1D simulations to predict two dimensional phenomena limits its accuracy.
Geometric integration of the Vlasov-Maxwell system with a variational particle-in-cell scheme
NASA Astrophysics Data System (ADS)
Squire, J.; Qin, H.; Tang, W. M.
2012-08-01
A fully variational, unstructured, electromagnetic particle-in-cell integrator is developed for integration of the Vlasov-Maxwell equations. Using the formalism of discrete exterior calculus [Desbrun et al., e-print arXiv:math/0508341 (2005)], the field solver, interpolation scheme, and particle advance algorithm are derived through minimization of a single discrete field theory action. As a consequence of ensuring that the action is invariant under discrete electromagnetic gauge transformations, the integrator exactly conserves Gauss's law.
Geometric integration of the Vlasov-Maxwell system with a variational particle-in-cell scheme
Squire, J.; Tang, W. M.; Qin, H.
2012-08-15
A fully variational, unstructured, electromagnetic particle-in-cell integrator is developed for integration of the Vlasov-Maxwell equations. Using the formalism of discrete exterior calculus [Desbrun et al., e-print arXiv:math/0508341 (2005)], the field solver, interpolation scheme, and particle advance algorithm are derived through minimization of a single discrete field theory action. As a consequence of ensuring that the action is invariant under discrete electromagnetic gauge transformations, the integrator exactly conserves Gauss's law.
Geometric Integration Of The Vlasov-Maxwell System With A Variational Particle-in-cell Scheme
J. Squire, H. Qin and W.M. Tang
2012-03-27
A fully variational, unstructured, electromagnetic particle-in-cell integrator is developed for integration of the Vlasov-Maxwell equations. Using the formalism of Discrete Exterior Calculus [1], the field solver, interpolation scheme and particle advance algorithm are derived through minimization of a single discrete field theory action. As a consequence of ensuring that the action is invariant under discrete electromagnetic gauge transformations, the integrator exactly conserves Gauss's law.
First experience with particle-in-cell plasma physics code on ARM-based HPC systems
NASA Astrophysics Data System (ADS)
Sáez, Xavier; Soba, Alejandro; Sánchez, Edilberto; Mantsinen, Mervi; Mateo, Sergi; Cela, José M.; Castejón, Francisco
2015-09-01
In this work, we will explore the feasibility of porting a Particle-in-cell code (EUTERPE) to an ARM multi-core platform from the Mont-Blanc project. The used prototype is based on a system-on-chip Samsung Exynos 5 with an integrated GPU. It is the first prototype that could be used for High-Performance Computing (HPC), since it supports double precision and parallel programming languages.
Finite element analysis simulations for ultrasonic array NDE inspections
NASA Astrophysics Data System (ADS)
Dobson, Jeff; Tweedie, Andrew; Harvey, Gerald; O'Leary, Richard; Mulholland, Anthony; Tant, Katherine; Gachagan, Anthony
2016-02-01
Advances in manufacturing techniques and materials have led to an increase in the demand for reliable and robust inspection techniques to maintain safety critical features. The application of modelling methods to develop and evaluate inspections is becoming an essential tool for the NDE community. Current analytical methods are inadequate for simulation of arbitrary components and heterogeneous materials, such as anisotropic welds or composite structures. Finite element analysis software (FEA), such as PZFlex, can provide the ability to simulate the inspection of these arrangements, providing the ability to economically prototype and evaluate improved NDE methods. FEA is often seen as computationally expensive for ultrasound problems however, advances in computing power have made it a more viable tool. This paper aims to illustrate the capability of appropriate FEA to produce accurate simulations of ultrasonic array inspections - minimizing the requirement for expensive test-piece fabrication. Validation is afforded via corroboration of the FE derived and experimentally generated data sets for a test-block comprising 1D and 2D defects. The modelling approach is extended to consider the more troublesome aspects of heterogeneous materials where defect dimensions can be of the same length scale as the grain structure. The model is used to facilitate the implementation of new ultrasonic array inspection methods for such materials. This is exemplified by considering the simulation of ultrasonic NDE in a weld structure in order to assess new approaches to imaging such structures.
Spectral Element Simulations of Rupture Dynamics along kinked faults
NASA Astrophysics Data System (ADS)
Vilotte, J.; Festa, G.; Madariaga, R.
2005-12-01
Numerical simulation of earthquake source dynamics provides key elements for ground-motion prediction and insights into the physics of dynamic rupture propagation. Faulting is controlled by non-linear frictional interactions and damage within the fault zone. Important features of the earthquakes dynamics, such as rupture velocity, arrest phase and high-frequency radiation are believed to be strongly influenced by the geometry of the faults (kinks, jogs and forks). Data analysis as well as kinematic inversions have pointed out potential links between super-shear and geometry, as in the case of the Denali and Izmit earthquakes. Finally, recent laboratory experiments of sub- and super-shear rupture propagation along kink interfaces have shed new lights on these phenomena. We present here spectral element simulations of the dynamic rupture propagation along kinked and curved fault interfaces, a problem that has been experimentally investigated by Rousseau and Rosakis (2003). Depending on the state of the initial stress, we numerically analyze the mechanics of the dynamical fault branching for sub- and super-shear rupture propagation. Special interest is devoted to source directivity effects and high frequency generation related to the branching process. Implications for strong motion analysis will be discussed. This work was supported by the SPICE - Research and Training project
Numerical Simulations of Instabilities in Single-Hole Office Elements
NASA Technical Reports Server (NTRS)
Ahuja, Vineet; Hosangadi, Ashvin; Hitt, Matthew A.; Lineberry, David M.
2013-01-01
An orifice element is commonly used in liquid rocket engine test facilities either as a flow metering device, a damper for acoustic resonance or to provide a large reduction in pressure over a very small distance in the piping system. While the orifice as a device is largely effective in stepping down pressure, it is also susceptible to a wake-vortex type instability that generates pressure fluctuations that propagate downstream and interact with other elements of the test facility resulting in structural vibrations. Furthermore in piping systems an unstable feedback loop can exist between the vortex shedding and acoustic perturbations from upstream components resulting in an amplification of the modes convecting downstream. Such was the case in several tests conducted at NASA as well as in the Ariane 5 strap-on P230 engine in a static firing test where pressure oscillations of 0.5% resulted in 5% thrust oscillations. Exacerbating the situation in cryogenic test facilities, is the possibility of the formation of vapor clouds when the pressure in the wake falls below the vapor pressure leading to a cavitation instability that has a lower frequency than the primary wake-vortex instability. The cavitation instability has the potential for high amplitude fluctuations that can cause catastrophic damage in the facility. In this paper high-fidelity multi-phase numerical simulations of an orifice element are used to characterize the different instabilities, understand the dominant instability mechanisms and identify the tonal content of the instabilities.
Finite Element Modeling, Simulation, Tools, and Capabilities at Superform
NASA Astrophysics Data System (ADS)
Raman, Hari; Barnes, A. J.
2010-06-01
Over the past thirty years Superform has been a pioneer in the SPF arena, having developed a keen understanding of the process and a range of unique forming techniques to meet varying market needs. Superform’s high-profile list of customers includes Boeing, Airbus, Aston Martin, Ford, and Rolls Royce. One of the more recent additions to Superform’s technical know-how is finite element modeling and simulation. Finite element modeling is a powerful numerical technique which when applied to SPF provides a host of benefits including accurate prediction of strain levels in a part, presence of wrinkles and predicting pressure cycles optimized for time and part thickness. This paper outlines a brief history of finite element modeling applied to SPF and then reviews some of the modeling tools and techniques that Superform have applied and continue to do so to successfully superplastically form complex-shaped parts. The advantages of employing modeling at the design stage are discussed and illustrated with real-world examples.
Nuclear Thermal Rocket Element Environmental Simulator (NTREES) Upgrade Activities
NASA Technical Reports Server (NTRS)
Emrich, William J., Jr.
2014-01-01
Over the past year the Nuclear Thermal Rocket Element Environmental Simulator (NTREES) has been undergoing a significant upgrade beyond its initial configuration. The NTREES facility is designed to perform realistic non-nuclear testing of nuclear thermal rocket (NTR) fuel elements and fuel materials. Although the NTREES facility cannot mimic the neutron and gamma environment of an operating NTR, it can simulate the thermal hydraulic environment within an NTR fuel element to provide critical information on material performance and compatibility. The first phase of the upgrade activities which was completed in 2012 in part consisted of an extensive modification to the hydrogen system to permit computer controlled operations outside the building through the use of pneumatically operated variable position valves. This setup also allows the hydrogen flow rate to be increased to over 200 g/sec and reduced the operation complexity of the system. The second stage of modifications to NTREES which has just been completed expands the capabilities of the facility significantly. In particular, the previous 50 kW induction power supply has been replaced with a 1.2 MW unit which should allow more prototypical fuel element temperatures to be reached. The water cooling system was also upgraded to so as to be capable of removing 100% of the heat generated during. This new setup required that the NTREES vessel be raised onto a platform along with most of its associated gas and vent lines. In this arrangement, the induction heater and water systems are now located underneath the platform. In this new configuration, the 1.2 MW NTREES induction heater will be capable of testing fuel elements and fuel materials in flowing hydrogen at pressures up to 1000 psi at temperatures up to and beyond 3000 K and at near-prototypic reactor channel power densities. NTREES is also capable of testing potential fuel elements with a variety of propellants, including hydrogen with additives to inhibit
Unstructured finite element simulations of compressible phase change phenomena
NASA Astrophysics Data System (ADS)
Shams, Ehsan; Yang, Fan; Zhang, Yu; Sahni, Onkar; Shephard, Mark; Oberai, Assad; Scientific Computation Research Center (Scorec) Team
2015-11-01
Modeling interactions between compressible gas flow and multiple combusting solid objects, which may undergo large deformations, is a problem with several challenging aspects that include, compressible turbulent flows, shocks, strong interfacial fluxes, discontinuous fields and large topological changes. We have developed and implemented a mathematically consistent, computational framework for simulating such problems. Within our framework the fluid is modeled by solving the compressible Navier Stokes equations with a stabilized finite element method. Turbulence is modeled using large eddy simulation, while shocks are captured using discontinuity capturing methods. The solid is modeled as a hyperelastic material, and its deformation is determined by writing the constitutive relation in a rate form. Appropriate jump conditions are derived from conservations laws applied to an evolving interface, and are implemented using discontinuous functions at the interface. The mesh is updated using the Arbitrary Lagrangian Eulerian (ALE) approach, and is refined and adapted during the simulation. In this talk we will present this framework and will demonstrate its capabilities by solving canonical phase change problems. We acknowledge the support from Army Research Office (ARO) under ARO Grant # W911NF-14-1-0301.
A finite element simulation of biological conversion processes in landfills
Robeck, M.; Ricken, T.
2011-04-15
Landfills are the most common way of waste disposal worldwide. Biological processes convert the organic material into an environmentally harmful landfill gas, which has an impact on the greenhouse effect. After the depositing of waste has been stopped, current conversion processes continue and emissions last for several decades and even up to 100 years and longer. A good prediction of these processes is of high importance for landfill operators as well as for authorities, but suitable models for a realistic description of landfill processes are rather poor. In order to take the strong coupled conversion processes into account, a constitutive three-dimensional model based on the multiphase Theory of Porous Media (TPM) has been developed at the University of Duisburg-Essen. The theoretical formulations are implemented in the finite element code FEAP. With the presented calculation concept we are able to simulate the coupled processes that occur in an actual landfill. The model's theoretical background and the results of the simulations as well as the meantime successfully performed simulation of a real landfill body will be shown in the following.
High speed finite element simulations on the graphics card
Huthwaite, P.; Lowe, M. J. S.
2014-02-18
A software package is developed to perform explicit time domain finite element simulations of ultrasonic propagation on the graphical processing unit, using Nvidia’s CUDA. Of critical importance for this problem is the arrangement of nodes in memory, allowing data to be loaded efficiently and minimising communication between the independently executed blocks of threads. The initial stage of memory arrangement is partitioning the mesh; both a well established ‘greedy’ partitioner and a new, more efficient ‘aligned’ partitioner are investigated. A method is then developed to efficiently arrange the memory within each partition. The technique is compared to a commercial CPU equivalent, demonstrating an overall speedup of at least 100 for a non-destructive testing weld model.
Modeling bistable behaviors in morphing structures through finite element simulations.
Guo, Qiaohang; Zheng, Huang; Chen, Wenzhe; Chen, Zi
2014-01-01
Bistable structures, exemplified by the Venus flytrap and slap bracelets, can transit between different configurations upon certain external stimulation. Here we study, through three-dimensional finite element simulations, the bistable behaviors in elastic plates in the absence of terminate loads, but with pre-strains in one (or both) of the two composite layers. Both the scenarios with and without a given geometric mis-orientation angle are investigated, the results of which are consistent with recent theoretical and experimental studies. This work can open ample venues for programmable designs of plant/shell structures with large deformations, with applications in designing bio-inspired robotics for biomedical research and morphing/deployable structures in aerospace engineering. PMID:24211939
High speed finite element simulations on the graphics card
NASA Astrophysics Data System (ADS)
Huthwaite, P.; Lowe, M. J. S.
2014-02-01
A software package is developed to perform explicit time domain finite element simulations of ultrasonic propagation on the graphical processing unit, using Nvidia's CUDA. Of critical importance for this problem is the arrangement of nodes in memory, allowing data to be loaded efficiently and minimising communication between the independently executed blocks of threads. The initial stage of memory arrangement is partitioning the mesh; both a well established `greedy' partitioner and a new, more efficient `aligned' partitioner are investigated. A method is then developed to efficiently arrange the memory within each partition. The technique is compared to a commercial CPU equivalent, demonstrating an overall speedup of at least 100 for a non-destructive testing weld model.
Adaptive model reduction for nonsmooth discrete element simulation
NASA Astrophysics Data System (ADS)
Servin, Martin; Wang, Da
2016-03-01
A method for adaptive model order reduction for nonsmooth discrete element simulation is developed and analysed in numerical experiments. Regions of the granular media that collectively move as rigid bodies are substituted with rigid bodies of the corresponding shape and mass distribution. The method also support particles merging with articulated multibody systems. A model approximation error is defined and used to derive conditions for when and where to apply reduction and refinement back into particles and smaller rigid bodies. Three methods for refinement are proposed and tested: prediction from contact events, trial solutions computed in the background and using split sensors. The computational performance can be increased by 5-50 times for model reduction level between 70-95 %.
Accelerated finite element elastodynamic simulations using the GPU
Huthwaite, Peter
2014-01-15
An approach is developed to perform explicit time domain finite element simulations of elastodynamic problems on the graphical processing unit, using Nvidia's CUDA. Of critical importance for this problem is the arrangement of nodes in memory, allowing data to be loaded efficiently and minimising communication between the independently executed blocks of threads. The initial stage of memory arrangement is partitioning the mesh; both a well established ‘greedy’ partitioner and a new, more efficient ‘aligned’ partitioner are investigated. A method is then developed to efficiently arrange the memory within each partition. The software is applied to three models from the fields of non-destructive testing, vibrations and geophysics, demonstrating a memory bandwidth of very close to the card's maximum, reflecting the bandwidth-limited nature of the algorithm. Comparison with Abaqus, a widely used commercial CPU equivalent, validated the accuracy of the results and demonstrated a speed improvement of around two orders of magnitude. A software package, Pogo, incorporating these developments, is released open source, downloadable from (http://www.pogo-fea.com/) to benefit the community. -- Highlights: •A novel memory arrangement approach is discussed for finite elements on the GPU. •The mesh is partitioned then nodes are arranged efficiently within each partition. •Models from ultrasonics, vibrations and geophysics are run. •The code is significantly faster than an equivalent commercial CPU package. •Pogo, the new software package, is released open source.
NASA Astrophysics Data System (ADS)
Rossi, Francesco; Londrillo, Pasquale; Sgattoni, Andrea; Sinigardi, Stefano; Turchetti, Giorgio
2012-12-01
We present `jasmine', an implementation of a fully relativistic, 3D, electromagnetic Particle-In-Cell (PIC) code, capable of running simulations in various laser plasma acceleration regimes on Graphics-Processing-Units (GPUs) HPC clusters. Standard energy/charge preserving FDTD-based algorithms have been implemented using double precision and quadratic (or arbitrary sized) shape functions for the particle weighting. When porting a PIC scheme to the GPU architecture (or, in general, a shared memory environment), the particle-to-grid operations (e.g. the evaluation of the current density) require special care to avoid memory inconsistencies and conflicts. Here we present a robust implementation of this operation that is efficient for any number of particles per cell and particle shape function order. Our algorithm exploits the exposed GPU memory hierarchy and avoids the use of atomic operations, which can hurt performance especially when many particles lay on the same cell. We show the code multi-GPU scalability results and present a dynamic load-balancing algorithm. The code is written using a python-based C++ meta-programming technique which translates in a high level of modularity and allows for easy performance tuning and simple extension of the core algorithms to various simulation schemes.
NASA Technical Reports Server (NTRS)
Poppe, A. R.; Halekas, J. S.; Delory, G. T.; Farrell, W. M.; Angelopoulos, V.; McFadden, J. P.; Bonnell, J. W.; Ergun, R. E.
2012-01-01
As an airless body in space with no global magnetic field, the Moon is exposed to both solar ultraviolet radiation and ambient plasmas. Photoemission from solar UV radiation and collection of ambient plasma are typically opposing charging currents and simple charging current balance predicts that the lunar dayside surface should charge positively; however, the two ARTEMIS probes have observed energydependent loss cones and high-energy, surface-originating electron beams above the dayside lunar surface for extended periods in the magnetosphere, which are indicative of negative surface potentials. In this paper, we compare observations by the ARTEMIS P1 spacecraft with a one dimensional particle-in-cell simulation and show that the energy-dependent loss cones and electron beams are due to the presence of stable, non-monotonic, negative potentials above the lunar surface. The simulations also show that while the magnitude of the non-monotonic potential is mainly driven by the incoming electron temperature, the incoming ion temperature can alter this magnitude, especially for periods in the plasma sheet when the ion temperature is more than twenty times the electron temperature. Finally, we note several other plasma phenomena associated with these non-monotonic potentials, such as broadband electrostatic noise and electron cyclotron harmonic emissions, and offer possible generation mechanisms for these phenomena.
NASA Astrophysics Data System (ADS)
Chen, G.; Chacón, L.
2015-12-01
For decades, the Vlasov-Darwin model has been recognized to be attractive for particle-in-cell (PIC) kinetic plasma simulations in non-radiative electromagnetic regimes, to avoid radiative noise issues and gain computational efficiency. However, the Darwin model results in an elliptic set of field equations that renders conventional explicit time integration unconditionally unstable. Here, we explore a fully implicit PIC algorithm for the Vlasov-Darwin model in multiple dimensions, which overcomes many difficulties of traditional semi-implicit Darwin PIC algorithms. The finite-difference scheme for Darwin field equations and particle equations of motion is space-time-centered, employing particle sub-cycling and orbit-averaging. The algorithm conserves total energy, local charge, canonical-momentum in the ignorable direction, and preserves the Coulomb gauge exactly. An asymptotically well-posed fluid preconditioner allows efficient use of large cell sizes, which are determined by accuracy considerations, not stability, and can be orders of magnitude larger than required in a standard explicit electromagnetic PIC simulation. We demonstrate the accuracy and efficiency properties of the algorithm with various numerical experiments in 2D-3V.
NASA Astrophysics Data System (ADS)
Zhang, Ya; Li, Lian; Jiang, Wei; Yi, Lin
2016-07-01
A one dimensional quantum-hydrodynamic/particle-in-cell (QHD/PIC) model is used to study the interaction process of an intense proton beam (injection density of 1017 cm‑3) with a dense plasma (initial density of ~ 1021 cm‑3), with the PIC method for simulating the beam particle dynamics and the QHD model for considering the quantum effects including the quantum statistical and quantum diffraction effects. By means of the QHD theory, the wake electron density and wakefields are calculated, while the proton beam density is calculated by the PIC method and compared to hydrodynamic results to justify that the PIC method is a more suitable way to simulate the beam particle dynamics. The calculation results show that the incident continuous proton beam when propagating in the plasma generates electron perturbations as well as wakefields oscillations with negative valleys and positive peaks where the proton beams are repelled by the positive wakefields and accelerated by the negative wakefields. Moreover, the quantum correction obviously hinders the electron perturbations as well as the wakefields. Therefore, it is necessary to consider the quantum effects in the interaction of a proton beam with cold dense plasmas, such as in the metal films. supported by National Natural Science Foundation of China (Nos. 11405067, 11105057, 11275007)
Impact and Penetration of Granular Materials by Discrete Element Simulations
NASA Astrophysics Data System (ADS)
Garvin, Justin W.; Lechman, Jeremy B.; Lane, J. Matthew D.
2008-03-01
Granular material response to impact is important in a range of fields, from munitions delivery, to meteorite collision and crater formation. Recently a model for the force experienced on a penetrator has been proposed [L.S. Tsimring and D. Volfson, Powders and Grains 2005, 1215-1223] and shown to fit experimental data well [H. Katsuragi and D.J. Durian, Nature Physics, Vol. 3, June 2007]. This model describes two components of the force: i) a velocity dependent, depth independent term related to the inertial force required to mobilize a volume of grains in front of the penetrator; and ii) a velocity independent, depth dependent, Coulomb friction-like term. In the current study, massively parallel, discrete element simulations have been performed to study the penetration of a large spherical impactor into a multi-million particle bed of granular material. Results agree with previous work for slow impact speeds (< 400cm/s). In addition, the current work extends the comparison with the proposed model to higher speeds (˜1000cm/s). The physics of the phenomenon is discussed along with the challenges for modeling and simulation in the even higher velocity regime.
Physical Fidelity in Particle-In-Cell Modeling of Small Debye-Length Plasmas
Shadwick, B. A.; Schroeder, C. B.
2009-01-22
The connection between macro-particle shape functions and non-physical phase-space 'heating' in the particle-in-cell (PIC) algorithm is examined. The development of fine-scale phase-space structures starting from a cold initial condition is shown to be related to spatial correlations in the interpolated fields used in the Lorentz force. It is shown that the plasma evolution via the PIC algorithm from a cold initial condition leads to a state that is not consistent with that of a thermal plasma.
Particle-in-cell modeling of gas-confined barrier discharge
NASA Astrophysics Data System (ADS)
Levko, Dmitry; Raja, Laxminarayan L.
2016-04-01
Gas-confined barrier discharge is studied using the one-dimensional Particle-in-Cell Monte Carlo Collisions model for the conditions reported by Guerra-Garcia and Martinez-Sanchez [Appl. Phys. Lett. 106, 041601 (2015)]. Depending on the applied voltage, two modes of discharge are observed. In the first mode, the discharge develops in the entire interelectrode gap. In the second mode, the discharge is ignited and develops only in the gas layer having smaller breakdown voltage. The one-dimensional model shows that for the conditions considered, there is no streamer stage of breakdown as is typical for a traditional dielectric barrier discharge.
Geometric integration of the Vlasov-Maxwell system with a variational particle-in-cell scheme
NASA Astrophysics Data System (ADS)
Squire, Jonathan; Qin, Hong; Tang, William
2012-10-01
A fully variational, unstructured, electromagnetic particle-in-cell integrator is developed for integration of the Vlasov-Maxwell equations. Using the formalism of Discrete Exterior Calculus [1], the field solver, interpolation scheme and particle advance algorithm are derived through minimization of a single discrete field theory action. As a consequence of ensuring that the action is invariant under discrete electromagnetic gauge transformations, the integrator exactly conserves Gauss's law. This work was supported by USDOE Contract DE-AC02-09CH11466.[4pt] [1] M. Desbrun, A. N. Hirani, M. Leok, and J. E. Marsden, (2005), arXiv:math/0508341
Physical Fidelity in Particle-In-Cell Modeling of Small Debye-Length Plasmas
Shadwick, B.A.; Schroeder, C.B.
2008-08-01
The connection between macro-particle shape functions and non-physical phase-space"heating" in the particle-in-cell (PIC) algorithm is examined. The development of fine-scale phasespace structures starting from a cold initial condition is shown to be related to spatial correlations in the interpolated fields used in the Lorentz force. It is shown that the plasma evolution via the PIC algorithm from a cold initial condition leads to a state that is not consistent with that of a thermal plasma.
A spectral, quasi-cylindrical and dispersion-free Particle-In-Cell algorithm
NASA Astrophysics Data System (ADS)
Lehe, Rémi; Kirchen, Manuel; Andriyash, Igor A.; Godfrey, Brendan B.; Vay, Jean-Luc
2016-06-01
We propose a spectral Particle-In-Cell (PIC) algorithm that is based on the combination of a Hankel transform and a Fourier transform. For physical problems that have close-to-cylindrical symmetry, this algorithm can be much faster than full 3D PIC algorithms. In addition, unlike standard finite-difference PIC codes, the proposed algorithm is free of spurious numerical dispersion, in vacuum. This algorithm is benchmarked in several situations that are of interest for laser-plasma interactions. These benchmarks show that it avoids a number of numerical artifacts, that would otherwise affect the physics in a standard PIC algorithm - including the zero-order numerical Cherenkov effect.
Elements of Regolith Simulant's Cost Structure--Why Rock Is NOT Cheap
NASA Technical Reports Server (NTRS)
Rickman, Douglas L.
2009-01-01
The cost of lunar regolith simulants is much higher than many users anticipate. After all, it is nothing more than broken rock. This class will discuss the elements which make up the cost structure for simulants. It will also consider which elements can be avoided under certain circumstances and which elements might be altered by the application of additional research and development.
Particle-in-cell Simulations with Charge-Conserving Current Deposition on Graphic Processing Units
NASA Astrophysics Data System (ADS)
Kong, Xianglong; Huang, Michael; Ren, Chuang; Decyk, Viktor
2010-11-01
We present an implementation of a fully relativistic, electromagnetic PIC code, with charge-conserving current deposition, on graphics processing units (GPUs) with NVIDIA's massively multithreaded computing architecture CUDA. A particle-based computation thread assignment was used in the current deposition scheme and write conflicts among the threads were resolved by a thread racing technique. A parallel particle sorting scheme was also developed and used. The implementation took advantage of fast on-chip shared memory. The 2D implementation achieved a one particle-step process time of 2.28 ns for cold plasma runs and 8.53 ns for extremely relativistic plasma runs on a GTX 280 graphic card, which were respectively 90 and 29 times faster than a single threaded state-of-art CPU code. A comparable speedup was also achieved for the 3D implementation.
Ion-acoustic shocks with reflected ions: modelling and particle-in-cell simulations
NASA Astrophysics Data System (ADS)
Liseykina, T. V.; Dudnikova, G. I.; Vshivkov, V. A.; Malkov, M. A.
2015-10-01
> Non-relativistic collisionless shock waves are widespread in space and astrophysical plasmas and are known as efficient particle accelerators. However, our understanding of collisionless shocks, including their structure and the mechanisms whereby they accelerate particles, remains incomplete. We present here the results of numerical modelling of an ion-acoustic collisionless shock based on the one-dimensional kinetic approximation for both electrons and ions with a real mass ratio. Special emphasis is paid to the shock-reflected ions as the main driver of shock dissipation. The reflection efficiency, the velocity distribution of reflected particles and the shock electrostatic structure are studied in terms of the shock parameters. Applications to particle acceleration in geophysical and astrophysical shocks are discussed.
Nitsche Extended Finite Element Methods for Earthquake Simulation
NASA Astrophysics Data System (ADS)
Coon, Ethan T.
Modeling earthquakes and geologically short-time-scale events on fault networks is a difficult problem with important implications for human safety and design. These problems demonstrate a. rich physical behavior, in which distributed loading localizes both spatially and temporally into earthquakes on fault systems. This localization is governed by two aspects: friction and fault geometry. Computationally, these problems provide a stern challenge for modelers --- static and dynamic equations must be solved on domains with discontinuities on complex fault systems, and frictional boundary conditions must be applied on these discontinuities. The most difficult aspect of modeling physics on complicated domains is the mesh. Most numerical methods involve meshing the geometry; nodes are placed on the discontinuities, and edges are chosen to coincide with faults. The resulting mesh is highly unstructured, making the derivation of finite difference discretizations difficult. Therefore, most models use the finite element method. Standard finite element methods place requirements on the mesh for the sake of stability, accuracy, and efficiency. The formation of a mesh which both conforms to fault geometry and satisfies these requirements is an open problem, especially for three dimensional, physically realistic fault. geometries. In addition, if the fault system evolves over the course of a dynamic simulation (i.e. in the case of growing cracks or breaking new faults), the geometry must he re-meshed at each time step. This can be expensive computationally. The fault-conforming approach is undesirable when complicated meshes are required, and impossible to implement when the geometry is evolving. Therefore, meshless and hybrid finite element methods that handle discontinuities without placing them on element boundaries are a desirable and natural way to discretize these problems. Several such methods are being actively developed for use in engineering mechanics involving crack
Lower extremity finite element model for crash simulation
Schauer, D.A.; Perfect, S.A.
1996-03-01
A lower extremity model has been developed to study occupant injury mechanisms of the major bones and ligamentous soft tissues resulting from vehicle collisions. The model is based on anatomically correct digitized bone surfaces of the pelvis, femur, patella and the tibia. Many muscles, tendons and ligaments were incrementally added to the basic bone model. We have simulated two types of occupant loading that occur in a crash environment using a non-linear large deformation finite element code. The modeling approach assumed that the leg was passive during its response to the excitation, that is, no active muscular contraction and therefore no active change in limb stiffness. The approach recognized that the most important contributions of the muscles to the lower extremity response are their ability to define and modify the impedance of the limb. When nonlinear material behavior in a component of the leg model was deemed important to response, a nonlinear constitutive model was incorporated. The accuracy of these assumptions can be verified only through a review of analysis results and careful comparison with test data. As currently defined, the model meets the objective for which it was created. Much work remains to be done, both from modeling and analysis perspectives, before the model can be considered complete. The model implements a modeling philosophy that can accurately capture both kinematic and kinetic response of the lower limb. We have demonstrated that the lower extremity model is a valuable tool for understanding the injury processes and mechanisms. We are now in a position to extend the computer simulation to investigate the clinical fracture patterns observed in actual crashes. Additional experience with this model will enable us to make a statement on what measures are needed to significantly reduce lower extremity injuries in vehicle crashes. 6 refs.
Explicit high-order non-canonical symplectic particle-in-cell algorithms for Vlasov-Maxwell systems
Xiao, Jianyuan; Qin, Hong; Liu, Jian; He, Yang; Zhang, Ruili; Sun, Yajuan
2015-11-01
Explicit high-order non-canonical symplectic particle-in-cell algorithms for classical particle-field systems governed by the Vlasov-Maxwell equations are developed. The algorithms conserve a discrete non-canonical symplectic structure derived from the Lagrangian of the particle-field system, which is naturally discrete in particles. The electromagnetic field is spatially discretized using the method of discrete exterior calculus with high-order interpolating differential forms for a cubic grid. The resulting time-domain Lagrangian assumes a non-canonical symplectic structure. It is also gauge invariant and conserves charge. The system is then solved using a structure-preserving splitting method discovered by He et al. [preprint arXiv: 1505.06076 (2015)], which produces five exactly soluble sub-systems, and high-order structure-preserving algorithms follow by combinations. The explicit, high-order, and conservative nature of the algorithms is especially suitable for long-term simulations of particle-field systems with extremely large number of degrees of freedom on massively parallel supercomputers. The algorithms have been tested and verified by the two physics problems, i.e., the nonlinear Landau damping and the electron Bernstein wave. (C) 2015 AIP Publishing LLC.
Explicit high-order non-canonical symplectic particle-in-cell algorithms for Vlasov-Maxwell systems
Xiao, Jianyuan; Liu, Jian; He, Yang; Zhang, Ruili; Qin, Hong; Sun, Yajuan
2015-11-15
Explicit high-order non-canonical symplectic particle-in-cell algorithms for classical particle-field systems governed by the Vlasov-Maxwell equations are developed. The algorithms conserve a discrete non-canonical symplectic structure derived from the Lagrangian of the particle-field system, which is naturally discrete in particles. The electromagnetic field is spatially discretized using the method of discrete exterior calculus with high-order interpolating differential forms for a cubic grid. The resulting time-domain Lagrangian assumes a non-canonical symplectic structure. It is also gauge invariant and conserves charge. The system is then solved using a structure-preserving splitting method discovered by He et al. [preprint http://arxiv.org/abs/arXiv:1505.06076 (2015)], which produces five exactly soluble sub-systems, and high-order structure-preserving algorithms follow by combinations. The explicit, high-order, and conservative nature of the algorithms is especially suitable for long-term simulations of particle-field systems with extremely large number of degrees of freedom on massively parallel supercomputers. The algorithms have been tested and verified by the two physics problems, i.e., the nonlinear Landau damping and the electron Bernstein wave.
Accelerated finite element elastodynamic simulations using the GPU
NASA Astrophysics Data System (ADS)
Huthwaite, Peter
2014-01-01
An approach is developed to perform explicit time domain finite element simulations of elastodynamic problems on the graphical processing unit, using Nvidia's CUDA. Of critical importance for this problem is the arrangement of nodes in memory, allowing data to be loaded efficiently and minimising communication between the independently executed blocks of threads. The initial stage of memory arrangement is partitioning the mesh; both a well established ‘greedy' partitioner and a new, more efficient ‘aligned' partitioner are investigated. A method is then developed to efficiently arrange the memory within each partition. The software is applied to three models from the fields of non-destructive testing, vibrations and geophysics, demonstrating a memory bandwidth of very close to the card's maximum, reflecting the bandwidth-limited nature of the algorithm. Comparison with Abaqus, a widely used commercial CPU equivalent, validated the accuracy of the results and demonstrated a speed improvement of around two orders of magnitude. A software package, Pogo, incorporating these developments, is released open source, downloadable from http://www.pogo-fea.com/ to benefit the community.
3D finite element simulation of TIG weld pool
NASA Astrophysics Data System (ADS)
Kong, X.; Asserin, O.; Gounand, S.; Gilles, P.; Bergheau, J. M.; Medale, M.
2012-07-01
The aim of this paper is to propose a three-dimensional weld pool model for the moving gas tungsten arc welding (GTAW) process, in order to understand the main factors that limit the weld quality and improve the productivity, especially with respect to the welding speed. Simulation is a very powerful tool to help in understanding the physical phenomena in the weld process. A 3D finite element model of heat and fluid flow in weld pool considering free surface of the pool and traveling speed has been developed for the GTAW process. Cast3M software is used to compute all the governing equations. The free surface of the weld pool is calculated by minimizing the total surface energy. The combined effects of surface tension gradient, buoyancy force, arc pressure, arc drag force to drive the fluid flow is included in our model. The deformation of the weld pool surface and the welding speed affect fluid flow, heat flow and thus temperature gradients and molten pool dimensions. Welding trials study is presented to compare our numerical results with macrograph of the molten pool.
Efficient finite element simulation of slot spirals, slot radomes and microwave structures
NASA Technical Reports Server (NTRS)
Gong, J.; Volakis, J. L.
1995-01-01
This progress report contains the following two documents: (1) 'Efficient Finite Element Simulation of Slot Antennas using Prismatic Elements' - A hybrid finite element-boundary integral (FE-BI) simulation technique is discussed to treat narrow slot antennas etched on a planar platform. Specifically, the prismatic elements are used to reduce the redundant sampling rates and ease the mesh generation process. Numerical results for an antenna slot and frequency selective surfaces are presented to demonstrate the validity and capability of the technique; and (2) 'Application and Design Guidelines of the PML Absorber for Finite Element Simulations of Microwave Packages' - The recently introduced perfectly matched layer (PML) uniaxial absorber for frequency domain finite element simulations has several advantages. In this paper we present the application of PML for microwave circuit simulations along with design guidelines to obtain a desired level of absorption. Different feeding techniques are also investigated for improved accuracy.
Hewett, D.W.; Francis, G.E.; Max, C.E.
1990-06-29
Evidence from magnetospheric and solar flare research supports the belief that collisionless magnetic reconnection can proceed on the Alfven-wave crossing timescale. Reconnection behavior that occurs this rapidly in collisionless plasmas is not well understood because underlying mechanisms depend on the details of the ion and electron distributions in the vicinity of the emerging X-points. We use the direct implicit Particle-In-Cell (PIC) code AVANTI to study the details of these distributions as they evolve in the self-consistent E and B fields of magnetic reconnection. We first consider a simple neutral sheet model. We observe rapid movement of the current-carrying electrons away from the emerging X-point. Later in time an oscillation of the trapped magnetic flux is found, superimposed upon continued linear growth due to plasma inflow at the ion sound speed. The addition of a current-aligned and a normal B field widen the scope of our studies.
Three-dimensional plasma particle-in-cell calculations of ion thruster backflow contamination
Roy, R.I.S.; Hastings, D.E.; Taylor, S.
1996-10-01
A fully three-dimensional hybrid plasma particle-in-cell model for multi-computer environments was developed to assess the spacecraft backflow contamination of an ion thruster. Results of plume backflow are presented for a 13-cm xenon ion thruster operating with a current level of 0.4 A on a model spacecraft. The computational domain was over 40 m{sup 3} in volume, and used over 35 million particles representing charge-exchange (CEX) xenon ions produced in the plume. Results obtained on a massively parallel 256-node Cray T3D clearly show the plasma density enhancement around the spacecraft due to the CEX ions. Three-dimensional results are compared with the results of a two-dimensional axisymmetric model to explore the three-dimensionality of the backstreaming flowfield. 15 refs., 14 figs., 1 tab.
Particle-in-Cell Calculationsof the Electron Cloud in the ILCPositron Damping Ring Wigglers
Celata, C.M.; Furman, M.A.; Vay, J.-L.; Grote, D.P.
2007-07-01
The self-consistent code suite WARP-POSINST is being used to study electron cloud effects in the ILC positron damping ring wiggler. WARP is a parallelized, 3D particle-in-cell code which is fully self-consistent for all species. The POSINST models for the production of photoelectrons and secondary electrons are used to calculate electron creation. Mesh refinement and a moving reference frame for the calculation will be used to reduce the computer time needed by several orders of magnitude. We present preliminary results for cloud buildup showing 3D electron effects at the nulls of the vertical wiggler field. First results from a benchmark of WARP-POSINST vs. POSINST are also discussed.
A 2-D Implicit, Energy and Charge Conserving Particle In Cell Method
McPherson, Allen L.; Knoll, Dana A.; Cieren, Emmanuel B.; Feltman, Nicolas; Leibs, Christopher A.; McCarthy, Colleen; Murthy, Karthik S.; Wang, Yijie
2012-09-10
Recently, a fully implicit electrostatic 1D charge- and energy-conserving particle-in-cell algorithm was proposed and implemented by Chen et al ([2],[3]). Central to the algorithm is an advanced particle pusher. Particles are moved using an energy conserving scheme and are forced to stop at cell faces to conserve charge. Moreover, a time estimator is used to control errors in momentum. Here we implement and extend this advanced particle pusher to include 2D and electromagnetic fields. Derivations of all modifications made are presented in full. Special consideration is taken to ensure easy coupling into the implicit moment based method proposed by Taitano et al [19]. Focus is then given to optimizing the presented particle pusher on emerging architectures. Two multicore implementations, and one GPU (Graphics Processing Unit) implementation are discussed and analyzed.
Strozzi, D. J.; Tabak, M.; Larson, D. J.; Divol, L.; Kemp, A. J.; Bellei, C.; Marinak, M. M.; Key, M. H.
2012-07-15
Transport modeling of idealized, cone-guided fast ignition targets indicates the severe challenge posed by fast-electron source divergence. The hybrid particle-in-cell (PIC) code Zuma is run in tandem with the radiation-hydrodynamics code Hydra to model fast-electron propagation, fuel heating, and thermonuclear burn. The fast electron source is based on a 3D explicit-PIC laser-plasma simulation with the PSC code. This shows a quasi two-temperature energy spectrum and a divergent angle spectrum (average velocity-space polar angle of 52 Degree-Sign ). Transport simulations with the PIC-based divergence do not ignite for >1 MJ of fast-electron energy, for a modest (70 {mu}m) standoff distance from fast-electron injection to the dense fuel. However, artificially collimating the source gives an ignition energy of 132 kJ. To mitigate the divergence, we consider imposed axial magnetic fields. Uniform fields {approx}50 MG are sufficient to recover the artificially collimated ignition energy. Experiments at the Omega laser facility have generated fields of this magnitude by imploding a capsule in seed fields of 50-100 kG. Such imploded fields will likely be more compressed in the transport region than in the laser absorption region. When fast electrons encounter increasing field strength, magnetic mirroring can reflect a substantial fraction of them and reduce coupling to the fuel. A hollow magnetic pipe, which peaks at a finite radius, is presented as one field configuration which circumvents mirroring.
Wieggers, R. C.; Goedheer, W. J.; Akdim, M. R.; Bijkerk, F.; Zegeling, P. A.
2008-01-01
We present a kinetic simulation of the plasma formed by photoionization in the intense flux of an extreme ultraviolet lithography (EUVL) light source. The model is based on the particle-in-cell plus Monte Carlo approach. The photoelectric effect and ionization by electron collisions are included. The time evolution of the low density argon plasma is simulated during and after the EUV pulse and the ion-induced sputtering of the coating material of a normal incidence collector mirror is computed. The relation between the time and position at which the ions are created and their final energy is studied, revealing how the evolution and the properties of the sheath influence the amount of sputtered material. The influence of the gas pressure and the source intensity is studied, evaluating the behavior of Ar{sup +} and Ar{sup 2+} ions. A way to reduce the damage to the collector mirror is presented.
Schwarze, M.; Reese, S.
2007-05-17
Finite element simulations of sheet metal forming processes are highly non-linear problems. The non-linearity arises not only from the kinematical relations and the material formulation, furthermore the contact between workpiece and the forming tools leads to an increased number of iterations within the Newton-Raphson scheme. This fact puts high demands on the robustness of finite element formulations. For this reason we study the enhanced assumed strain (EAS) concept as proposed in [1]. The goal is to improve the robustness of the solid-shell formulation in deep drawing simulations.
NASA Astrophysics Data System (ADS)
Daldorff, Lars K. S.; Tóth, Gábor; Gombosi, Tamas I.; Lapenta, Giovanni; Amaya, Jorge; Markidis, Stefano; Brackbill, Jeremiah U.
2014-07-01
Computational models based on a fluid description of the plasma, such as magnetohydrodynamic (MHD) and extended magnetohydrodynamic (XMHD) codes are highly efficient, but they miss the kinetic effects due to the assumptions of small gyro radius, charge neutrality, and Maxwellian thermal velocity distribution. Kinetic codes can properly take into account the kinetic effects, but they are orders of magnitude more expensive than the fluid codes due to the increased degrees of freedom. If the fluid description is acceptable in a large fraction of the computational domain, it makes sense to confine the kinetic model to the regions where kinetic effects are important. This coupled approach can be much more efficient than a pure kinetic model. The speed up is approximately the volume ratio of the full domain relative to the kinetic regions assuming that the kinetic code uses a uniform grid. This idea has been advocated by [1] but their coupling was limited to one dimension and they employed drastically different grid resolutions in the fluid and kinetic models. We describe a fully two-dimensional two-way coupling of a Hall MHD model BATS-R-US with an implicit Particle-in-Cell (PIC) model iPIC3D. The coupling can be performed with identical grid resolutions and time steps. We call this coupled computational plasma model MHD-EPIC (MHD with Embedded PIC regions). Our verification tests show that MHD-EPIC works accurately and robustly. We show a two-dimensional magnetosphere simulation as an illustration of the potential future applications of MHD-EPIC.
Simulating Cardiac Electrophysiology Using Unstructured All-Hexahedra Spectral Elements
Cuccuru, Gianmauro; Fotia, Giorgio; Maggio, Fabio; Southern, James
2015-01-01
We discuss the application of the spectral element method to the monodomain and bidomain equations describing propagation of cardiac action potential. Models of cardiac electrophysiology consist of a system of partial differential equations coupled with a system of ordinary differential equations representing cell membrane dynamics. The solution of these equations requires solving multiple length scales due to the ratio of advection to diffusion that varies among the different equations. High order approximation of spectral elements provides greater flexibility in resolving multiple length scales. Furthermore, spectral elements are extremely efficient to model propagation phenomena on complex shapes using fewer degrees of freedom than its finite element equivalent (for the same level of accuracy). We illustrate a fully unstructured all-hexahedra approach implementation of the method and we apply it to the solution of full 3D monodomain and bidomain test cases. We discuss some key elements of the proposed approach on some selected benchmarks and on an anatomically based whole heart human computational model. PMID:26583112
A finite element simulation system in reservoir engineering
Gu, Xiaozhong
1996-03-01
Reservoir engineering is performed to predict the future performance of a reservoir based on its current state and past performance and to explore other methods for increasing the recovery of hydrocarbons from a reservoir. Reservoir simulations are routinely used for these purposes. A reservoir simulator is a sophisticated computer program which solves a system of partial differential equations describing multiphase fluid flow (oil, water, and gas) in a porous reservoir rock. This document describes the use of a reservoir simulator version of BOAST which was developed by the National Institute for Petroleum and Energy Research in July, 1991.
An 8-node tetrahedral finite element suitable for explicit transient dynamic simulations
Key, S.W.; Heinstein, M.W.; Stone, C.M.
1997-12-31
Considerable effort has been expended in perfecting the algorithmic properties of 8-node hexahedral finite elements. Today the element is well understood and performs exceptionally well when used in modeling three-dimensional explicit transient dynamic events. However, the automatic generation of all-hexahedral meshes remains an elusive achievement. The alternative of automatic generation for all-tetrahedral finite element is a notoriously poor performer, and the 10-node quadratic tetrahedral finite element while a better performer numerically is computationally expensive. To use the all-tetrahedral mesh generation extant today, the authors have explored the creation of a quality 8-node tetrahedral finite element (a four-node tetrahedral finite element enriched with four midface nodal points). The derivation of the element`s gradient operator, studies in obtaining a suitable mass lumping and the element`s performance in applications are presented. In particular, they examine the 80node tetrahedral finite element`s behavior in longitudinal plane wave propagation, in transverse cylindrical wave propagation, and in simulating Taylor bar impacts. The element only samples constant strain states and, therefore, has 12 hourglass modes. In this regard, it bears similarities to the 8-node, mean-quadrature hexahedral finite element. Given automatic all-tetrahedral meshing, the 8-node, constant-strain tetrahedral finite element is a suitable replacement for the 8-node hexahedral finite element and handbuilt meshes.
Towards parallel I/O in finite element simulations
NASA Technical Reports Server (NTRS)
Farhat, Charbel; Pramono, Eddy; Felippa, Carlos
1989-01-01
I/O issues in finite element analysis on parallel processors are addressed. Viable solutions for both local and shared memory multiprocessors are presented. The approach is simple but limited by currently available hardware and software systems. Implementation is carried out on a CRAY-2 system. Performance results are reported.
Pegasus: A new hybrid-kinetic particle-in-cell code for astrophysical plasma dynamics
NASA Astrophysics Data System (ADS)
Kunz, Matthew W.; Stone, James M.; Bai, Xue-Ning
2014-02-01
We describe Pegasus, a new hybrid-kinetic particle-in-cell code tailored for the study of astrophysical plasma dynamics. The code incorporates an energy-conserving particle integrator into a stable, second-order-accurate, three-stage predictor-predictor-corrector integration algorithm. The constrained transport method is used to enforce the divergence-free constraint on the magnetic field. A δf scheme is included to facilitate a reduced-noise study of systems in which only small departures from an initial distribution function are anticipated. The effects of rotation and shear are implemented through the shearing-sheet formalism with orbital advection. These algorithms are embedded within an architecture similar to that used in the popular astrophysical magnetohydrodynamics code Athena, one that is modular, well-documented, easy to use, and efficiently parallelized for use on thousands of processors. We present a series of tests in one, two, and three spatial dimensions that demonstrate the fidelity and versatility of the code.
Advanced 3D electromagnetic and particle-in-cell modeling on structured/unstructured hybrid grids
Seidel, D.B.; Pasik, M.F.; Kiefer, M.L.; Riley, D.J.; Turner, C.D.
1998-01-01
New techniques have been recently developed that allow unstructured, free meshes to be embedded into standard 3-dimensional, rectilinear, finite-difference time-domain grids. The resulting hybrid-grid modeling capability allows the higher resolution and fidelity of modeling afforded by free meshes to be combined with the simplicity and efficiency of rectilinear techniques. Integration of these new methods into the full-featured, general-purpose QUICKSILVER electromagnetic, Particle-In-Cell (PIC) code provides new modeling capability for a wide variety of electromagnetic and plasma physics problems. To completely exploit the integration of this technology into QUICKSILVER for applications requiring the self-consistent treatment of charged particles, this project has extended existing PIC methods for operation on these hybrid unstructured/rectilinear meshes. Several technical issues had to be addressed in order to accomplish this goal, including the location of particles on the unstructured mesh, adequate conservation of charge, and the proper handling of particles in the transition region between structured and unstructured portions of the hybrid grid.
Plume expansion of a laser-induced plasma studied with the particle-in-cell method
NASA Astrophysics Data System (ADS)
Ellegaard, O.; Nedelea, T.; Schou, J.; Urbassek, H. M.
2002-09-01
The initial stage of laser-induced plasma plume expansion from a solid in vacuum and the effect of the Coulomb field have been studied. We have performed a one-dimensional numerical calculation by mapping the charge on a computational grid according to the particle-in-cell (PIC) method of Birdsall et al. It is assumed that the particle ablation from a surface with a fixed temperature takes place as a pulse, i.e. within a finite period of time. A number of characteristic quantities for the plasma plume are compared with similar data for expansion of neutrals as well as fluid models: Density profiles n( x, t), velocity distributions of ions u( x, t), distribution functions for velocities F( vx) of ions or electrons as well as the time dependence of kinetic energy Ekin( t) for both type of particles. We found a significant increase in the velocities of the ions at the expense of field potential energy as well as electron energy. We have estimated the time constant for energy transfer between the electrons and the ions. The scaling of these processes is given by a single parameter determined by the Debye length obtained from the electron density in the plasma outside the surface.
A two-dimensional (azimuthal-axial) particle-in-cell model of a Hall thruster
Coche, P.; Garrigues, L.
2014-02-15
We have developed a two-dimensional Particle-In-Cell model in the azimuthal and axial directions of the Hall thruster. A scaling method that consists to work at a lower plasma density to overcome constraints on time-step and grid-spacing is used. Calculations are able to reproduce the breathing mode due to a periodic depletion of neutral atoms without the introduction of a supplementary anomalous mechanism, as in fluid and hybrid models. Results show that during the increase of the discharge current, an electron-cyclotron drift instability (frequency in the range of MHz and wave number on the order of 3000 rad s{sup −1}) is formed in the region of the negative gradient of magnetic field. During the current decrease, an axial electric wave propagates from the channel toward the exhaust (whose frequency is on the order of 400 kHz) leading to a broadening of the ion energy distribution function. A discussion about the influence of the scaling method on the calculation results is also proposed.
Deploying electromagnetic particle-in-cell (EM-PIC) codes on Xeon Phi accelerators boards
NASA Astrophysics Data System (ADS)
Fonseca, Ricardo
2014-10-01
The complexity of the phenomena involved in several relevant plasma physics scenarios, where highly nonlinear and kinetic processes dominate, makes purely theoretical descriptions impossible. Further understanding of these scenarios requires detailed numerical modeling, but fully relativistic particle-in-cell codes such as OSIRIS are computationally intensive. The quest towards Exaflop computer systems has lead to the development of HPC systems based on add-on accelerator cards, such as GPGPUs and more recently the Xeon Phi accelerators that power the current number 1 system in the world. These cards, also referred to as Intel Many Integrated Core Architecture (MIC) offer peak theoretical performances of >1 TFlop/s for general purpose calculations in a single board, and are receiving significant attention as an attractive alternative to CPUs for plasma modeling. In this work we report on our efforts towards the deployment of an EM-PIC code on a Xeon Phi architecture system. We will focus on the parallelization and vectorization strategies followed, and present a detailed performance evaluation of code performance in comparison with the CPU code.
Fulfillment of the kinetic Bohm criterion in a quasineutral particle-in-cell model
NASA Astrophysics Data System (ADS)
Ahedo, Eduardo; Santos, Robert; Parra, Félix I.
2010-07-01
Quasineutral particle-in-cell models of ions must fulfill the kinetic Bohm criterion, in its inequality form, at the domain boundary in order to match correctly with solutions of the Debye sheaths tied to the walls. The simple, fluid form of the Bohm criterion is shown to be a bad approximation of the exact, kinetic form when the ion velocity distribution function has a significant dispersion and involves different charge numbers. The fulfillment of the Bohm criterion is measured by a weighting algorithm at the boundary, but linear weighting algorithms have difficulties to reproduce the nonlinear behavior around the sheath edge. A surface weighting algorithm with an extended temporal weighting is proposed and shown to behave better than the standard volumetric weighting. Still, this must be supplemented by a forcing algorithm of the kinetic Bohm criterion. This postulates a small potential fall in a supplementary, thin, transition layer. The electron-wall interaction is shown to be of little relevance in the fulfillment of the Bohm criterion.
Fulfillment of the kinetic Bohm criterion in a quasineutral particle-in-cell model
Ahedo, Eduardo; Santos, Robert; Parra, Felix I.
2010-07-15
Quasineutral particle-in-cell models of ions must fulfill the kinetic Bohm criterion, in its inequality form, at the domain boundary in order to match correctly with solutions of the Debye sheaths tied to the walls. The simple, fluid form of the Bohm criterion is shown to be a bad approximation of the exact, kinetic form when the ion velocity distribution function has a significant dispersion and involves different charge numbers. The fulfillment of the Bohm criterion is measured by a weighting algorithm at the boundary, but linear weighting algorithms have difficulties to reproduce the nonlinear behavior around the sheath edge. A surface weighting algorithm with an extended temporal weighting is proposed and shown to behave better than the standard volumetric weighting. Still, this must be supplemented by a forcing algorithm of the kinetic Bohm criterion. This postulates a small potential fall in a supplementary, thin, transition layer. The electron-wall interaction is shown to be of little relevance in the fulfillment of the Bohm criterion.
Effect of collisions on dust particle charging via particle-in-cell Monte-Carlo collision
Rovagnati, B.; Davoudabadi, M.; Lapenta, G.; Mashayek, F.
2007-10-01
In this paper, the effect of collisions on the charging and shielding of a single dust particle immersed in an infinite plasma is studied. A Monte-Carlo collision (MCC) algorithm is implemented in the particle-in-cell DEMOCRITUS code to account for the collisional phenomena which are typical of dusty plasmas in plasma processing, namely, electron-neutral elastic scattering, ion-neutral elastic scattering, and ion-neutral charge exchange. Both small and large dust particle radii, as compared to the characteristic Debye lengths, are considered. The trends of the steady-state dust particle potential at increasing collisionality are presented and discussed. The ions and electron energy distributions at various locations and at increasing collisionality in the case of large particle radius are shown and compared to their local Maxwellians. The ion-neutral charge-exchange collision is found to be by far the most important collisional phenomenon. For small particle radius, collisional effects are found to be important also at low level of collisionality, as more ions are collected by the dust particle due to the destruction of trapped ion orbits. For large particle radius, the major collisional effect is observed to take place in proximity of the presheath. Finally, the species energy distribution functions are found to approach their local Maxwellians at increasing collisionality.
NASA Astrophysics Data System (ADS)
Patacchini, L.; Hutchinson, I. H.
2009-04-01
A new explicit time-reversible orbit integrator for the equations of motion in a static homogeneous magnetic field - called Cyclotronic integrator - is presented. Like Spreiter and Walter's Taylor expansion algorithm, for sufficiently weak electric field gradients this second order method does not require a fine resolution of the Larmor motion; it has however the essential advantage of being symplectic, hence time-reversible. The Cyclotronic integrator is only subject to a linear stability constraint ( ΩΔ t < π, Ω being the Larmor angular frequency), and is therefore particularly suitable to electrostatic Particle In Cell codes with uniform magnetic field where Ω is larger than any other characteristic frequency, yet a resolution of the particles' gyromotion is required. Application examples and a detailed comparison with the well-known (time-reversible) Boris algorithm are presented; it is in particular shown that implementation of the Cyclotronic integrator in the kinetic codes SCEPTIC and Democritus can reduce the cost of orbit integration by up to a factor of ten.
Unphysical kinetic effects in particle-in-cell modeling of laser wakefield accelerators.
Cormier-Michel, Estelle; Shadwick, B A; Geddes, C G R; Esarey, E; Schroeder, C B; Leemans, W P
2008-07-01
Unphysical heating and macroparticle trapping that arise in the numerical modeling of laser wakefield accelerators using particle-in-cell codes are investigated. A dark current free laser wakefield accelerator stage, in which no trapping of background plasma electrons into the plasma wave should occur, and a highly nonlinear cavitated wake with self-trapping, are modeled. Numerical errors can lead to errors in the macroparticle orbits in both phase and momentum. These errors grow as a function of distance behind the drive laser and can be large enough to result in unphysical trapping in the plasma wake. The resulting numerical heating in intense short-pulse laser-plasma interactions grows much faster and to a higher level than the known numerical grid heating of an initially warm plasma in an undriven system. The amount of heating, at least in the region immediately behind the laser pulse, can, in general, be decreased by decreasing the grid size, increasing the number of particles per cell, or using smoother interpolation methods. The effect of numerical heating on macroparticle trapping is less severe in a highly nonlinear cavitated wake, since trapping occurs in the first plasma wave period immediately behind the laser pulse. PMID:18764064
Particle-in-cell modeling of Dual Segmented Langmuir Probe on PROBA2
NASA Astrophysics Data System (ADS)
Imtiaz, Nadia; Marchand, Richard
2015-11-01
We model the current characteristics of the Dual Segmented Langmuir Probe (DSLP), which is a part of the scientific payload of the ESA satellite PROBA2. It is used for the directional measurement of plasma parameters in the ionosphere at an altitude of approximately 725 km. The DSLP consists of two independent segmented Langmuir probes. Each probe is partitioned into eight collectors: seven electrically insulated spherical segments and a Guard electrode (the rest of the sphere and a small post). The current characteristics of the DSLP are computed by using the 3D particle-in-cell code PTetra. The model is electrostatic and it accounts for a uniform background magnetic field. The computed characteristics of different probe segments exhibit significant variation which depends on their orientation with respect to the ram direction. The floating potential and ion current branch of the I-V curves of each segment illustrate the directional sensitivity of the DSLP. It is found that the magnetic field also affects the electron current branch of the I-V curves of certain segments on the DSLP. The I-V curves computed with and without the ambient magnetic field are then used to estimate the electron temperature. This study will be helpful to understand the floating potential and electron temperature anisotropies measured by the DSLP.
Large-eddy simulation in complex domains using the finite element method
McCallen, R.C.; Kornblum, B.T.; Kollman, W.
1996-11-12
Finite element methods (FEM) are demonstrated in combination with large-eddy simulations (LES) as a valuable tool for the study of turbulent, separating channel flows, specifically the flow over a backward facing step.
Fotos, P G; Spyrakos, C C; Bernard, D O
1990-01-01
The finite element method has been used to determine the stress distribution generated by the initial placement of a simulated preset bracket-type orthodontic appliance utilizing titanium-nickel alloy archwire. PMID:2256565
Effective Simulation of Delamination in Aeronautical Structures Using Shells and Cohesive Elements
NASA Technical Reports Server (NTRS)
Davila, Carlos G.; Camanho, Pedro P.; Turon, Albert
2007-01-01
A cohesive element for shell analysis is presented. The element can be used to simulate the initiation and growth of delaminations between stacked, non-coincident layers of shell elements. The procedure to construct the element accounts for the thickness offset by applying the kinematic relations of shell deformation to transform the stiffness and internal force of a zero-thickness cohesive element such that interfacial continuity between the layers is enforced. The procedure is demonstrated by simulating the response and failure of the Mixed Mode Bending test and a skin-stiffener debond specimen. In addition, it is shown that stacks of shell elements can be used to create effective models to predict the inplane and delamination failure modes of thick components. The results indicate that simple shell models can retain many of the necessary predictive attributes of much more complex 3D models while providing the computational efficiency that is necessary for design.
A Finite Element Model for Simulation of Carbon Dioxide Sequestration
Bao, Jie; Xu, Zhijie; Fang, Yilin
2015-07-23
We present a hydro-mechanical model, followed by stress, deformation, and shear-slip failure analysis for geological sequestration of carbon dioxide (CO2). The model considers the poroelastic effects by taking into account of the two-way coupling between the geomechanical response and the fluid flow process. Analytical solutions for pressure and deformation fields were derived for a typical geological sequestration scenario in our previous work. A finite element approach is introduced here for numerically solving the hydro-mechanical model with arbitrary boundary conditions. The numerical approach was built on an open-source finite element code Elmer, and results were compared to the analytical solutions. The shear-slip failure analysis was presented based on the numerical results, where the potential failure zone is identified. Information is relevant to the prediction of the maximum sustainable injection rate or pressure. The effects of caprock permeability on the fluid pressure, deformation, stress, and the shear-slip failure zone were also quantitatively studied. It was shown that a larger permeability in caprock and base rock leads to a larger uplift but a smaller shear-slip failure zone.
Spectral Element Method for the Simulation of Unsteady Compressible Flows
NASA Technical Reports Server (NTRS)
Diosady, Laslo Tibor; Murman, Scott M.
2013-01-01
This work uses a discontinuous-Galerkin spectral-element method (DGSEM) to solve the compressible Navier-Stokes equations [1{3]. The inviscid ux is computed using the approximate Riemann solver of Roe [4]. The viscous fluxes are computed using the second form of Bassi and Rebay (BR2) [5] in a manner consistent with the spectral-element approximation. The method of lines with the classical 4th-order explicit Runge-Kutta scheme is used for time integration. Results for polynomial orders up to p = 15 (16th order) are presented. The code is parallelized using the Message Passing Interface (MPI). The computations presented in this work are performed using the Sandy Bridge nodes of the NASA Pleiades supercomputer at NASA Ames Research Center. Each Sandy Bridge node consists of 2 eight-core Intel Xeon E5-2670 processors with a clock speed of 2.6Ghz and 2GB per core memory. On a Sandy Bridge node the Tau Benchmark [6] runs in a time of 7.6s.
Taylor, Z A; Cheng, M; Ourselin, S
2008-05-01
The use of biomechanical modelling, especially in conjunction with finite element analysis, has become common in many areas of medical image analysis and surgical simulation. Clinical employment of such techniques is hindered by conflicting requirements for high fidelity in the modelling approach, and fast solution speeds. We report the development of techniques for high-speed nonlinear finite element analysis for surgical simulation. We use a fully nonlinear total Lagrangian explicit finite element formulation which offers significant computational advantages for soft tissue simulation. However, the key contribution of the work is the presentation of a fast graphics processing unit (GPU) solution scheme for the finite element equations. To the best of our knowledge, this represents the first GPU implementation of a nonlinear finite element solver. We show that the present explicit finite element scheme is well suited to solution via highly parallel graphics hardware, and that even a midrange GPU allows significant solution speed gains (up to 16.8 x) compared with equivalent CPU implementations. For the models tested the scheme allows real-time solution of models with up to 16,000 tetrahedral elements. The use of GPUs for such purposes offers a cost-effective high-performance alternative to expensive multi-CPU machines, and may have important applications in medical image analysis and surgical simulation. PMID:18450538
NASA Technical Reports Server (NTRS)
Emrich, William J., Jr.
2014-01-01
To support the on-going nuclear thermal propulsion effort, a state-of-the-art non nuclear experimental test setup has been constructed to evaluate the performance characteristics of candidate fuel element materials and geometries in representative environments. The facility to perform this testing is referred to as the Nuclear Thermal Rocket Element Environment Simulator (NTREES). This device can simulate the environmental conditions (minus the radiation) to which nuclear rocket fuel components will be subjected during reactor operation. Prototypical fuel elements mounted in the simulator are inductively heated in such a manner so as to accurately reproduce the temperatures and heat fluxes which would normally occur as a result of nuclear fission in addition to being exposed to flowing hydrogen. Recent upgrades to NTREES now allow power levels 24 times greater than those achievable in the previous facility configuration. This higher power operation will allow near prototypical power densities and flows to finally be achieved in most prototypical fuel elements.
Finite Element Simulations to Explore Assumptions in Kolsky Bar Experiments.
Crum, Justin
2015-08-05
The chief purpose of this project has been to develop a set of finite element models that attempt to explore some of the assumptions in the experimental set-up and data reduction of the Kolsky bar experiment. In brief, the Kolsky bar, sometimes referred to as the split Hopkinson pressure bar, is an experimental apparatus used to study the mechanical properties of materials at high strain rates. Kolsky bars can be constructed to conduct experiments in tension or compression, both of which are studied in this paper. The basic operation of the tension Kolsky bar is as follows: compressed air is inserted into the barrel that contains the striker; the striker accelerates towards the left and strikes the left end of the barrel producing a tensile stress wave that propogates first through the barrel and then down the incident bar, into the specimen, and finally the transmission bar. In the compression case, the striker instead travels to the right and impacts the incident bar directly. As the stress wave travels through an interface (e.g., the incident bar to specimen connection), a portion of the pulse is transmitted and the rest reflected. The incident pulse, as well as the transmitted and reflected pulses are picked up by two strain gauges installed on the incident and transmitted bars as shown. By interpreting the data acquired by these strain gauges, the stress/strain behavior of the specimen can be determined.
Rocha, Bernardo M.; Kickinger, Ferdinand; Prassl, Anton J.; Haase, Gundolf; Vigmond, Edward J.; dos Santos, Rodrigo Weber; Zaglmayr, Sabine; Plank, Gernot
2011-01-01
Electrical activity in cardiac tissue can be described by the bidomain equations whose solution for large scale simulations still remains a computational challenge. Therefore, improvements in the discrete formulation of the problem which decrease computational and/or memory demands are highly desirable. In this study, we propose a novel technique for computing shape functions of finite elements. The technique generates macro finite elements (MFEs) based on the local decomposition of elements into tetrahedral sub-elements with linear shape functions. Such an approach necessitates the direct use of hybrid meshes composed of different types of elements. MFEs are compared to classic standard finite elements with respect to accuracy and RAM memory usage under different scenarios of cardiac modeling including bidomain and monodomain simulations in 2D and 3D for simple and complex tissue geometries. In problems with analytical solutions, MFEs displayed the same numerical accuracy of standard linear triangular and tetrahedral elements. In propagation simulations, conduction velocity and activation times agreed very well with those computed with standard finite elements. However, MFEs offer a significant decrease in memory requirements. We conclude that hybrid meshes composed of MFEs are well suited for solving problems in cardiac computational electrophysiology. PMID:20699206
Simulation of 3D tumor cell growth using nonlinear finite element method.
Dong, Shoubing; Yan, Yannan; Tang, Liqun; Meng, Junping; Jiang, Yi
2016-06-01
We propose a novel parallel computing framework for a nonlinear finite element method (FEM)-based cell model and apply it to simulate avascular tumor growth. We derive computation formulas to simplify the simulation and design the basic algorithms. With the increment of the proliferation generations of tumor cells, the FEM elements may become larger and more distorted. Then, we describe a remesh and refinement processing of the distorted or over large finite elements and the parallel implementation based on Message Passing Interface to improve the accuracy and efficiency of the simulation. We demonstrate the feasibility and effectiveness of the FEM model and the parallelization methods in simulations of early tumor growth. PMID:26213205
NASA Technical Reports Server (NTRS)
Stewart, Mark E.; Schnitzler, Bruce G.
2015-01-01
This paper compares the expected performance of two Nuclear Thermal Propulsion fuel types. High fidelity, fluid/thermal/structural + neutronic simulations help predict the performance of graphite-composite and cermet fuel types from point of departure engine designs from the Nuclear Thermal Propulsion project. Materials and nuclear reactivity issues are reviewed for each fuel type. Thermal/structural simulations predict thermal stresses in the fuel and thermal expansion mis-match stresses in the coatings. Fluid/thermal/structural/neutronic simulations provide predictions for full fuel elements. Although NTP engines will utilize many existing chemical engine components and technologies, nuclear fuel elements are a less developed engine component and introduce design uncertainty. Consequently, these fuel element simulations provide important insights into NTP engine performance.
Bluff Body Flow Simulation Using a Vortex Element Method
Anthony Leonard; Phillippe Chatelain; Michael Rebel
2004-09-30
Heavy ground vehicles, especially those involved in long-haul freight transportation, consume a significant part of our nation's energy supply. it is therefore of utmost importance to improve their efficiency, both to reduce emissions and to decrease reliance on imported oil. At highway speeds, more than half of the power consumed by a typical semi truck goes into overcoming aerodynamic drag, a fraction which increases with speed and crosswind. Thanks to better tools and increased awareness, recent years have seen substantial aerodynamic improvements by the truck industry, such as tractor/trailer height matching, radiator area reduction, and swept fairings. However, there remains substantial room for improvement as understanding of turbulent fluid dynamics grows. The group's research effort focused on vortex particle methods, a novel approach for computational fluid dynamics (CFD). Where common CFD methods solve or model the Navier-Stokes equations on a grid which stretches from the truck surface outward, vortex particle methods solve the vorticity equation on a Lagrangian basis of smooth particles and do not require a grid. They worked to advance the state of the art in vortex particle methods, improving their ability to handle the complicated, high Reynolds number flow around heavy vehicles. Specific challenges that they have addressed include finding strategies to accurate capture vorticity generation and resultant forces at the truck wall, handling the aerodynamics of spinning bodies such as tires, application of the method to the GTS model, computation time reduction through improved integration methods, a closest point transform for particle method in complex geometrics, and work on large eddy simulation (LES) turbulence modeling.
Partition of the contact force network obtained in discrete element simulations of element tests
NASA Astrophysics Data System (ADS)
Huang, Xin; O'Sullivan, Catherine; Hanley, Kevin J.; Kwok, Chung-Yee
2016-01-01
The transmission of stress within a granular material composed of rigid spheres is explored using the discrete element method. The contribution of contacts to both deviatoric stress and structural anisotropy is investigated. The influences of five factors are considered: inter-particle friction coefficient, loading regime, packing density, contact model, and boundary conditions. The data generated indicate that using the above-average normal contact force criterion to decompose the contact force network into two subsets with distinct contributions to stress transmission and structural anisotropy is not robust. The characteristic normal contact forces marking the transition from negative to positive contribution to the overall deviatoric stress and structural anisotropy are not unique values but vary during shearing. Once the critical state is attained (i.e., once shearing continues at a constant deviator stress and solid fraction), the characteristic normal contact force remains approximately constant and this critical state characteristic normal force is observed to decrease with increasing inter-particle friction. The characteristic normal contact force considering the contribution to deviatoric stress has a power-law relationship with the mean effective stress at the critical state.
Neurosurgery simulation using non-linear finite element modeling and haptic interaction
NASA Astrophysics Data System (ADS)
Lee, Huai-Ping; Audette, Michel; Joldes, Grand R.; Enquobahrie, Andinet
2012-02-01
Real-time surgical simulation is becoming an important component of surgical training. To meet the realtime requirement, however, the accuracy of the biomechancial modeling of soft tissue is often compromised due to computing resource constraints. Furthermore, haptic integration presents an additional challenge with its requirement for a high update rate. As a result, most real-time surgical simulation systems employ a linear elasticity model, simplified numerical methods such as the boundary element method or spring-particle systems, and coarse volumetric meshes. However, these systems are not clinically realistic. We present here an ongoing work aimed at developing an efficient and physically realistic neurosurgery simulator using a non-linear finite element method (FEM) with haptic interaction. Real-time finite element analysis is achieved by utilizing the total Lagrangian explicit dynamic (TLED) formulation and GPU acceleration of per-node and per-element operations. We employ a virtual coupling method for separating deformable body simulation and collision detection from haptic rendering, which needs to be updated at a much higher rate than the visual simulation. The system provides accurate biomechancial modeling of soft tissue while retaining a real-time performance with haptic interaction. However, our experiments showed that the stability of the simulator depends heavily on the material property of the tissue and the speed of colliding objects. Hence, additional efforts including dynamic relaxation are required to improve the stability of the system.
Braunmueller, F. Tran, T. M.; Alberti, S.; Genoud, J.; Hogge, J.-Ph.; Tran, M. Q.; Vuillemin, Q.
2015-06-15
A new gyrotron simulation code for simulating the beam-wave interaction using a monomode time-dependent self-consistent model is presented. The new code TWANG-PIC is derived from the trajectory-based code TWANG by describing the electron motion in a gyro-averaged one-dimensional Particle-In-Cell (PIC) approach. In comparison to common PIC-codes, it is distinguished by its computation speed, which makes its use in parameter scans and in experiment interpretation possible. A benchmark of the new code is presented as well as a comparative study between the two codes. This study shows that the inclusion of a time-dependence in the electron equations, as it is the case in the PIC-approach, is mandatory for simulating any kind of non-stationary oscillations in gyrotrons. Finally, the new code is compared with experimental results and some implications of the violated model assumptions in the TWANG code are disclosed for a gyrotron experiment in which non-stationary regimes have been observed and for a critical case that is of interest in high power gyrotron development.
NASA Technical Reports Server (NTRS)
Adams, M. L.; Padovan, J.; Fertis, D. G.
1980-01-01
A general purpose squeeze-film damper interactive force element was developed, coded into a software package (module) and debugged. This software package was applied to nonliner dynamic analyses of some simple rotor systems. Results for pressure distributions show that the long bearing (end sealed) is a stronger bearing as compared to the short bearing as expected. Results of the nonlinear dynamic analysis, using a four degree of freedom simulation model, showed that the orbit of the rotating shaft increases nonlinearity to fill the bearing clearance as the unbalanced weight increases.
Felice, Maria V.; Velichko, Alexander; Wilcox, Paul D.; Barden, Tim J.; Dunhill, Tony K.
2014-02-18
A hybrid model to simulate the ultrasonic array response from stress corrosion cracks is presented. These cracks are branched and difficult to detect so the model is required to enable optimization of an array design. An efficient frequency-domain finite element method is described and selected to simulate the ultrasonic scattering. Experimental validation results are presented, followed by an example of the simulated ultrasonic array response from a real stress corrosion crack whose geometry is obtained from an X-ray Computed Tomography image. A simulation-assisted array design methodology, which includes the model and use of real crack geometries, is proposed.
NASA Technical Reports Server (NTRS)
Sawyer, P. L.
1980-01-01
The paper describes the simulation approach for the finite element machine (FEM), a special-purpose computer for structural analysis calculations under development at the NASA-Langley Research Center. The FEM consists of an array (1000 or more) of general-purpose microcomputers performing structural analysis in an asychronous parallel manner. A simulator of sufficient flexibility to model the behavior of the FEM on many levels has been designed and coded, and verification has begun using the experimental FEM hardware. The structure of the simulator is described, and preliminary simulation results are presented.
Design of a high-speed digital processing element for parallel simulation
NASA Technical Reports Server (NTRS)
Milner, E. J.; Cwynar, D. S.
1983-01-01
A prototype of a custom designed computer to be used as a processing element in a multiprocessor based jet engine simulator is described. The purpose of the custom design was to give the computer the speed and versatility required to simulate a jet engine in real time. Real time simulations are needed for closed loop testing of digital electronic engine controls. The prototype computer has a microcycle time of 133 nanoseconds. This speed was achieved by: prefetching the next instruction while the current one is executing, transporting data using high speed data busses, and using state of the art components such as a very large scale integration (VLSI) multiplier. Included are discussions of processing element requirements, design philosophy, the architecture of the custom designed processing element, the comprehensive instruction set, the diagnostic support software, and the development status of the custom design.
Finite Element Simulation of Sheet Metal Forming Process Using Local Interpolation for Tool Surfaces
Hama, Takayuki; Takuda, Hirohiko; Takamura, Masato; Makinouchi, Akitake; Teodosiu, Cristian
2005-08-05
Treatment of contact between a sheet and tools is one of the most difficult problems to deal with in finite-element simulations of sheet forming processes. In order to obtain more accurate tool models without increasing the number of elements, this paper describes a new formulation for contact problems using interpolation proposed by Nagata for tool surfaces. A contact search algorithm between sheet nodes and the interpolated tool surfaces was developed and was introduced into the static-explicit elastoplastic finite-element method code STAMP3D. Simulations of a square cup deep drawing process with a very coarsely discretized punch model were carried out. The simulated results showed that the proposed algorithm gave the proper drawn shape, demonstrating the validity of the proposed algorithm.
Dean Stull
2016-05-24
Experimental results from several studies exploring the impact of pH and acid volume on the stripping of rare earth elements (REEs) loaded onto ligand-based media via an active column. The REEs in this experiment were loaded onto the media through exposure to a simulated geothermal brine with known mineral concentrations. The data include the experiment results, rare earth element concentrations, and the experimental parameters varied.
Review of correlation methods for evaluating finite element simulations of impact injury risk.
Wang, Qian; Gabler, Hampton C
2008-01-01
Finite element models have been used to understand human injury responses in various crash configurations. Most of the model validations were limited to qualitative descriptions. Quantitative analysis was needed for the validation of finite element models against experimental results. The purpose of this study is to compare the existing correlation techniques and to determine the best method to use for evaluating finite element simulations of impact injury risk in vehicle crashes. Five correlation methods in the literature were reviewed for systematic comparisons between simulations and tests. A full frontal impact test of a 1997 Geo Metro was simulated. The finite element model of a 1997 Geo Metro was obtained from NCAC finite element model archive. The acceleration and velocity responses of the vehicle seat were extracted from the simulation and compared to the test data. Evaluations of the validation methods were based on the analysis results compared to the suggested criteria. Performance of the different methods showed that the Comprehensive Error Factor method was the best overall correlation method, and therefore was recommended for assessing occupant injury potentials in vehicle accidents. PMID:19141927
A parallel finite element simulator for ion transport through three-dimensional ion channel systems.
Tu, Bin; Chen, Minxin; Xie, Yan; Zhang, Linbo; Eisenberg, Bob; Lu, Benzhuo
2013-09-15
A parallel finite element simulator, ichannel, is developed for ion transport through three-dimensional ion channel systems that consist of protein and membrane. The coordinates of heavy atoms of the protein are taken from the Protein Data Bank and the membrane is represented as a slab. The simulator contains two components: a parallel adaptive finite element solver for a set of Poisson-Nernst-Planck (PNP) equations that describe the electrodiffusion process of ion transport, and a mesh generation tool chain for ion channel systems, which is an essential component for the finite element computations. The finite element method has advantages in modeling irregular geometries and complex boundary conditions. We have built a tool chain to get the surface and volume mesh for ion channel systems, which consists of a set of mesh generation tools. The adaptive finite element solver in our simulator is implemented using the parallel adaptive finite element package Parallel Hierarchical Grid (PHG) developed by one of the authors, which provides the capability of doing large scale parallel computations with high parallel efficiency and the flexibility of choosing high order elements to achieve high order accuracy. The simulator is applied to a real transmembrane protein, the gramicidin A (gA) channel protein, to calculate the electrostatic potential, ion concentrations and I - V curve, with which both primitive and transformed PNP equations are studied and their numerical performances are compared. To further validate the method, we also apply the simulator to two other ion channel systems, the voltage dependent anion channel (VDAC) and α-Hemolysin (α-HL). The simulation results agree well with Brownian dynamics (BD) simulation results and experimental results. Moreover, because ionic finite size effects can be included in PNP model now, we also perform simulations using a size-modified PNP (SMPNP) model on VDAC and α-HL. It is shown that the size effects in SMPNP can
Tang Haibin; Cheng Jiao; Liu Chang; York, Thomas M.
2012-07-15
A two-dimensional axisymmetric electromagnetic particle-in-cell code with Monte Carlo collision conditions has been developed for an applied-field magnetoplasmadynamic thruster simulation. This theoretical approach establishes a particle acceleration model to investigate the microscopic and macroscopic characteristics of particles. This new simulation code was used to study the physical processes associated with applied magnetic fields. In this paper (I), detail of the computation procedure and results of predictions of local plasma and field properties are presented. The numerical model was applied to the configuration of a NASA Lewis Research Center 100-kW magnetoplasmadynamic thruster which has well documented experimental results. The applied magnetic field strength was varied from 0 to 0.12 T, and the effects on thrust were calculated as a basis for verification of the theoretical approach. With this confirmation, the changes in the distributions of ion density, velocity, and temperature throughout the acceleration region related to the applied magnetic fields were investigated. Using these results, the effects of applied field on physical processes in the thruster discharge region could be represented in detail, and those results are reported.
NASA Astrophysics Data System (ADS)
Tang, Hai-Bin; Cheng, Jiao; Liu, Chang; York, Thomas M.
2012-07-01
A two-dimensional axisymmetric electromagnetic particle-in-cell code with Monte Carlo collision conditions has been developed for an applied-field magnetoplasmadynamic thruster simulation. This theoretical approach establishes a particle acceleration model to investigate the microscopic and macroscopic characteristics of particles. This new simulation code was used to study the physical processes associated with applied magnetic fields. In this paper (I), detail of the computation procedure and results of predictions of local plasma and field properties are presented. The numerical model was applied to the configuration of a NASA Lewis Research Center 100-kW magnetoplasmadynamic thruster which has well documented experimental results. The applied magnetic field strength was varied from 0 to 0.12 T, and the effects on thrust were calculated as a basis for verification of the theoretical approach. With this confirmation, the changes in the distributions of ion density, velocity, and temperature throughout the acceleration region related to the applied magnetic fields were investigated. Using these results, the effects of applied field on physical processes in the thruster discharge region could be represented in detail, and those results are reported.
NASA Astrophysics Data System (ADS)
Pekárek, Z.; Lahuta, M.; Hrach, R.
2007-04-01
In this contribution we estimate the performance of various Poisson equation solvers applied to the Particle-In-Cell plasma models. The solvers determine the practical usability of complex PIC models, especially in three dimensions. The performance is measured on 2D models with grids of various sizes, the methods studied are SOR, conjugate gradients, LU decomposition, FACR and multigrid methods. The results confirm the efficiency of the direct methods tested, namely the LU decomposition method and FACR. The advantages of using LU decomposition as a part of the multigrid method on larger grids are discussed as well.
Dean Stull
2016-05-24
This document describes the method and results of an in-situ experiment used to confirm that ligand bleed from a sorptive media can be contained. The experiment focused on maintaining the media's sorption of rare earth elements (REE) obtained from a simulated geothermal brine doped with known mineral concentrations.
Simulation of Aircraft Landing Gears with a Nonlinear Dynamic Finite Element Code
NASA Technical Reports Server (NTRS)
Lyle, Karen H.; Jackson, Karen E.; Fasanella, Edwin L.
2000-01-01
Recent advances in computational speed have made aircraft and spacecraft crash simulations using an explicit, nonlinear, transient-dynamic, finite element analysis code more feasible. This paper describes the development of a simple landing gear model, which accurately simulates the energy absorbed by the gear without adding substantial complexity to the model. For a crash model, the landing gear response is approximated with a spring where the force applied to the fuselage is computed in a user-written subroutine. Helicopter crash simulations using this approach are compared with previously acquired experimental data from a full-scale crash test of a composite helicopter.
NASA Technical Reports Server (NTRS)
Taylor, B. K.; Casasent, D. P.
1989-01-01
The use of simplified error models to accurately simulate and evaluate the performance of an optical linear-algebra processor is described. The optical architecture used to perform banded matrix-vector products is reviewed, along with a linear dynamic finite-element case study. The laboratory hardware and ac-modulation technique used are presented. The individual processor error-source models and their simulator implementation are detailed. Several significant simplifications are introduced to ease the computational requirements and complexity of the simulations. The error models are verified with a laboratory implementation of the processor, and are used to evaluate its potential performance.
NASA Astrophysics Data System (ADS)
Jacob, Anaïs; Mehmanparast, Ali
2016-07-01
The effects of microstructure, grain and grain boundary (GB) properties on predicted damage paths and indicative crack propagation direction have been examined for a polycrystalline material using mesoscale finite element simulations. Numerical analyses were carried out on a compact tension specimen geometry containing granular mesh structures with random grain shapes and sizes of average diameter 100μm. Nanoindentation tests were performed to investigate the dependency of mesoscale hardness measurements on the indentation location with respect to grain and GB regions. Finite element results have shown that under tensile loading conditions, the predicted damage paths are very sensitive to the granular mesh structure, GB properties and individual grain properties. Furthermore, finite element results have revealed that the cracking mode (i.e., transgranular/intergranular) and maximum crack deviation angle are strongly dependent on the material microstructures employed in simulations.
Fully Integrated EAS-Based Solid-Shell Finite Elements in Implicit Sheet Metal Forming Simulations
Valente, R.A. Fontes; Cardoso, R.P.R.; Alves de Sousa, R.J.; Parente, M.P.L.; Jorge, R.M. Natal
2005-08-05
In this communication sheet metal forming problems are analyzed with the Finite Element Method and a fully-integrated solid-shell element, based on the Enhanced Assumed Strain (EAS) method. Among the solid-shell element's distinguish features, it should be mentioned the solely use of the EAS approach in dealing with either transverse and volumetric-based locking pathologies, thus avoiding the inclusion of other mixed methods into the formulation. The adopted methodology is then able to successfully deal with small thickness shell problems within the incompressible range, aspects commonly appearing in sheet metal forming modeling with solid elements.Simulations of this type of forming processes are mainly solved resorting to membrane and shell-type finite elements, included in explicit commercial programs. Nevertheless, the presented solid-shell formulation, within a fully implicit approach, provides reliable solutions when compared to experimental results. It is also worth mentioning that the present solid-shell formulation encompasses a minimum set of enhancing strain variables, if compared to other fully integrated hexahedral finite elements in the literature.In order to assess the performance of the presented formulation, the S-Rail Forming problem of an aluminum alloy is described and analyzed, with the results being compared to experimental and numerical simulation data.
Radhakrishnan, B.; Sarma, G.; Zacharia, T.
1998-11-01
A novel simulation technique for predicting the microstructure and texture evolution during thermomechanical processing is presented. The technique involves coupling a finite element microstructural deformation model based on crystal plasticity with a Monte Carlo simulation of recovery and recrystallization. The finite element model captures the stored energy and the crystallographic orientation distributions in the deformed microstructure. The Monte Carlo simulation captures the microstructural evolution associated with recovery and recrystallization. A unique feature of the Monte Carlo simulation is that it treats recrystallization as a heterogeneous subgrain growth process, thus providing the natural link between nucleation and growth phenomena, and quantifying the role of recovery in these phenomena. Different nucleation mechanisms based on heterogeneous subgrain growth as well as strain induced boundary migration are automatically included in the recrystallization simulation. The simulations are shown to account for the extent of prior deformation on the microstructure and kinetics of recrystallization during subsequent annealing. The simulations also capture the influence of the presence of cube orientations in the initial microstructure, and the operation of non-octahedral slip during deformation of fcc polycrystals, on the recrystallization texture.
Herbold, E. B.; Walton, O.; Homel, M. A.
2015-10-26
This document serves as a final report to a small effort where several improvements were added to a LLNL code GEODYN-L to develop Discrete Element Method (DEM) algorithms coupled to Lagrangian Finite Element (FE) solvers to investigate powder-bed formation problems for additive manufacturing. The results from these simulations will be assessed for inclusion as the initial conditions for Direct Metal Laser Sintering (DMLS) simulations performed with ALE3D. The algorithms were written and performed on parallel computing platforms at LLNL. The total funding level was 3-4 weeks of an FTE split amongst two staff scientists and one post-doc. The DEM simulations emulated, as much as was feasible, the physical process of depositing a new layer of powder over a bed of existing powder. The DEM simulations utilized truncated size distributions spanning realistic size ranges with a size distribution profile consistent with realistic sample set. A minimum simulation sample size on the order of 40-particles square by 10-particles deep was utilized in these scoping studies in order to evaluate the potential effects of size segregation variation with distance displaced in front of a screed blade. A reasonable method for evaluating the problem was developed and validated. Several simulations were performed to show the viability of the approach. Future investigations will focus on running various simulations investigating powder particle sizing and screen geometries.
Multiple-contact discrete-element model for simulating dense granular media.
Brodu, Nicolas; Dijksman, Joshua A; Behringer, Robert P
2015-03-01
This article presents a new force model for performing quantitative simulations of dense granular materials. Interactions between multiple contacts (MC) on the same grain are explicitly taken into account. Our readily applicable MC-DEM method retains all the advantages of discrete-element method simulations and does not require the use of costly finite-element methods. The new model closely reproduces our recent experimental measurements, including contact force distributions in full 3D, at all compression levels of the packing up to the experimental maximum limit of 13%. Comparisons with classic simulations using the nondeformable spheres approach, as well as with alternative models for interactions between multiple contacts, are provided. The success of our model, compared to these alternatives, demonstrates that interactions between multiple contacts on each grain must be included for dense granular packings. PMID:25871097
A real-time blade element helicopter simulation for handling qualities analysis
NASA Technical Reports Server (NTRS)
Du Val, Ronald W.
1989-01-01
A simulation model which utilizes parallel processing platforms is described in terms of its contributions to improved real-time helicopter simulation. The FLIGHTLAB parallel processing environment is explained, and the relative advantages of the blade element and rotor map models for rigid and elastic articulated blades are discussed. A UH-60 simulation is conducted by means of a rigid model with 14 degrees of freedom, as well as an elastic model with 26 degrees of freedom, to compare trim conditions, longitudinal static margins, and longitudinal and lateral frequency responses. The FLIGHTLAB system is shown to facilitate restructuring for parallel processing as well as the systematic comparison of a variety of models. The system can facilitate the comparison of rigid and elastic blade element rotor models at NASA-Ames and other research facilities.
The simulation of electrostatic coupling intra-body communication based on finite-element models
NASA Astrophysics Data System (ADS)
Song, Yong; Yang, Guang; Hao, Qun; Wang, Ming
2008-12-01
Intra-body Body Communication (IBC) is a communication technology in which human body is used as a signal transmission medium. Due to its unique characters, IBC technology is proposed as a novel and promising technology for personal area network (PAN), computer network access, implant biomedical monitoring, human energy transmission, etc. In this paper, investigation has been done in the computer simulation of the electrostatic coupling IBC by using the developed finite-element models, in which (1) the incidence and reflection of electronic signal in the upper arm model were analyzed by using the theory of electromagnetic wave, (2) the finite-element models of electrostatic coupling IBC were developed by using the electromagnetic analysis package of ANSYS software, (3) the signal attenuation of electrostatic coupling IBC were simulated under the conditions of different signal frequency, electrodes direction, electrodes size and transmission distance. Finally, some important conclusions are deduced on the basis of simulation results.
Investigation of Radar Propagation in Buildings: A 10 Billion Element Cartesian-Mesh FETD Simulation
Stowell, M L; Fasenfest, B J; White, D A
2008-01-14
In this paper large scale full-wave simulations are performed to investigate radar wave propagation inside buildings. In principle, a radar system combined with sophisticated numerical methods for inverse problems can be used to determine the internal structure of a building. The composition of the walls (cinder block, re-bar) may effect the propagation of the radar waves in a complicated manner. In order to provide a benchmark solution of radar propagation in buildings, including the effects of typical cinder block and re-bar, we performed large scale full wave simulations using a Finite Element Time Domain (FETD) method. This particular FETD implementation is tuned for the special case of an orthogonal Cartesian mesh and hence resembles FDTD in accuracy and efficiency. The method was implemented on a general-purpose massively parallel computer. In this paper we briefly describe the radar propagation problem, the FETD implementation, and we present results of simulations that used over 10 billion elements.
Gen Purpose 1-D Finite Element Network Fluid Flow Heat Transfer System Simulator
Energy Science and Technology Software Center (ESTSC)
1993-08-02
SAFSIM (System Analysis Flow Simulator) is a FORTRAN computer program to simulate the integrated performance of systems involving fluid mechanics, heat transfer, and reactor dynamics. SAFSIM provides sufficient versatility to allow the engineering simulation of almost any system, from a backyard sprinkler system to a clustered nuclear reactor propulsion system. In addition to versatility, speed and robustness are primary SAFSIM development goals. SAFSIM contains three basic physics modules: (1) a one-dimensional finite element fluid mechanicsmore » module with multiple flow network capability; (2) a one-dimensional finite element structure heat transfer module with multiple convection and radiation exchange capability; and (3) a point reactor dynamics module with reactivity feedback and decay heat capability. SAFSIM can be used for compressible and incompressible, single-phase, multicomponent flow systems.« less
Tang, Y.; Kline, J.A. Sr.
1996-12-01
Nonlinear boundary element analysis provides a more accurate and detailing tool for the design of switched reluctance machines, than the conventional equivalent-circuit methods. Design optimization through more detailed analysis and simulation can reduce development and prototyping costs and time to market. Firstly, magnetic field modeling of an industrial switched reluctance machine by boundary element method is reported in this paper. Secondly, performance prediction and dynamic simulation of motor and control design are presented. Thirdly, magnetic forces that cause noise and vibration are studied, to include the effects of motor and control design variations on noise in the design process. Testing of the motor in NEMA 215-Frame size is carried out to verify the accuracy of modeling and simulation.
A novel enriched CB shell element method for simulating arbitrary crack growth in pipes
NASA Astrophysics Data System (ADS)
Zhuang, Zhuo; Cheng, Binbin
2011-08-01
In this work, a novel numerical method is developed for simulating arbitrary crack growth in pipes with the idea of enriched shape functions which can represent the discontinuity independent of the mesh. The concept of the enriched shape functions is introduced into the continuum-based (CB) shell element. Due to the advantage of CB shell element, the shell thickness variation and surface connection can be concerned during the deformation. The stress intensity factors of the crack in the CB shell element are calculated by using the `equivalent domain integral' method for 3D arbitrary non-planar crack. The maximum energy release rate is used as a propagation criterion. This method is proved able to capture arbitrary crack growth path in pipes which is independent of the element mesh. Numerical examples of different fracture patterns in pipes are presented here.
Generalized finite element dynamic modelling and simulation for flexible robot manipulators
NASA Astrophysics Data System (ADS)
Zhou, Feng
1993-01-01
The finite element approach is used to model multi-link flexible robotic manipulators. The kinematic character of flexible manipulators is analyzed using body-fixed and link element attached coordinates. Dynamic equations for flexible robot manipulators are then derived. The position of each point on the link is expressed using a transformation matrix, and the kinetic and potential energy for each element is computed and summed over all the elements. The Lagrangian formulation is applied to set up the dynamic equations of the system. Computational simulations are performed on single- and two-link manipulators with and without torque to check the validity and correctness of the derived dynamic equations. The Runge-Kutta method is used to solve the dynamic equations for flexible manipulators on which all the joints are revolute.
Accelerating spectral-element simulations of seismic wave propagation using local time stepping
NASA Astrophysics Data System (ADS)
Peter, D. B.; Rietmann, M.; Galvez, P.; Nissen-Meyer, T.; Grote, M.; Schenk, O.
2013-12-01
Seismic tomography using full-waveform inversion requires accurate simulations of seismic wave propagation in complex 3D media. However, finite element meshing in complex media often leads to areas of local refinement, generating small elements that accurately capture e.g. strong topography and/or low-velocity sediment basins. For explicit time schemes, this dramatically reduces the global time-step for wave-propagation problems due to numerical stability conditions, ultimately making seismic inversions prohibitively expensive. To alleviate this problem, local time stepping (LTS) algorithms allow an explicit time-stepping scheme to adapt the time-step to the element size, allowing near-optimal time-steps everywhere in the mesh. Numerical simulations are thus liberated of global time-step constraints potentially speeding up simulation runtimes significantly. We present here a new, efficient multi-level LTS-Newmark scheme for general use with spectral-element methods (SEM) with applications in seismic wave propagation. We fit the implementation of our scheme onto the package SPECFEM3D_Cartesian, which is a widely used community code, simulating seismic and acoustic wave propagation in earth-science applications. Our new LTS scheme extends the 2nd-order accurate Newmark time-stepping scheme, and leads to an efficient implementation, producing real-world speedup of multi-resolution seismic applications. Furthermore, we generalize the method to utilize many refinement levels with a design specifically for continuous finite elements. We demonstrate performance speedup using a state-of-the-art dynamic earthquake rupture model for the Tohoku-Oki event, which is currently limited by small elements along the rupture fault. Utilizing our new algorithmic LTS implementation together with advances in exploiting graphic processing units (GPUs), numerical seismic wave propagation simulations in complex media will dramatically reduce computation times, empowering high
Efficient simulation of incompressible viscous flow over multi-element airfoils
NASA Technical Reports Server (NTRS)
Rogers, Stuart E.; Wiltberger, N. Lyn; Kwak, Dochan
1993-01-01
The incompressible, viscous, turbulent flow over single and multi-element airfoils is numerically simulated in an efficient manner by solving the incompressible Navier-Stokes equations. The solution algorithm employs the method of pseudo compressibility and utilizes an upwind differencing scheme for the convective fluxes, and an implicit line-relaxation scheme. The motivation for this work includes interest in studying high-lift take-off and landing configurations of various aircraft. In particular, accurate computation of lift and drag at various angles of attack up to stall is desired. Two different turbulence models are tested in computing the flow over an NACA 4412 airfoil; an accurate prediction of stall is obtained. The approach used for multi-element airfoils involves the use of multiple zones of structured grids fitted to each element. Two different approaches are compared; a patched system of grids, and an overlaid Chimera system of grids. Computational results are presented for two-element, three-element, and four-element airfoil configurations. Excellent agreement with experimental surface pressure coefficients is seen. The code converges in less than 200 iterations, requiring on the order of one minute of CPU time on a CRAY YMP per element in the airfoil configuration.
Efficient simulation of incompressible viscous flow over single and multi-element airfoils
NASA Technical Reports Server (NTRS)
Rogers, Stuart E.; Wiltberger, N. L.; Kwak, Dochan
1992-01-01
Incompressible viscous turbulent flows over single- and multiple-element airfoils are numerically simulated in an efficient manner by solving the incompressible Navier-Stokes equations. The solution algorithm uses the method of pseudocompressibility with an upwind-differencing scheme for the convective fluxes and an implicit line-relaxation scheme to study high-lift take-off and landing configurations and to compute lift and drag at various angles of attack up to stall. Two different turbulence models are tested in computing the flow over an NACA 4412 airfoil. The approach used for multiple-element airfoils involves the use of multiple zones of structured grids fitted to each element. Two different approaches are compared: a patched system of grids and an overlaid Chimera system of grids. Computational results are presented for two-element, three-element, and four-element airfoil configurations. Excellent agreement with experimental surface-pressure coefficients is seen. The code converges in less than 200 iterations, requiring on the order of one minute of CPU time on a CRAY YMP per element in the airfoil configuration.
Efficient simulation of incompressible viscous flow over multi-element airfoils
NASA Technical Reports Server (NTRS)
Rogers, Stuart E.; Wiltberger, N. Lyn; Kwak, Dochan
1992-01-01
The incompressible, viscous, turbulent flow over single and multi-element airfoils is numerically simulated in an efficient manner by solving the incompressible Navier-Stokes equations. The computer code uses the method of pseudo-compressibility with an upwind-differencing scheme for the convective fluxes and an implicit line-relaxation solution algorithm. The motivation for this work includes interest in studying the high-lift take-off and landing configurations of various aircraft. In particular, accurate computation of lift and drag at various angles of attack, up to stall, is desired. Two different turbulence models are tested in computing the flow over an NACA 4412 airfoil; an accurate prediction of stall is obtained. The approach used for multi-element airfoils involves the use of multiple zones of structured grids fitted to each element. Two different approaches are compared: a patched system of grids, and an overlaid Chimera system of grids. Computational results are presented for two-element, three-element, and four-element airfoil configurations. Excellent agreement with experimental surface pressure coefficients is seen. The code converges in less than 200 iterations, requiring on the order of one minute of CPU time (on a CRAY YMP) per element in the airfoil configuration.
Simulation of dynamic fracture using peridynamics, finite element modeling, and contact.
Littlewood, David John
2010-11-01
Peridynamics is a nonlocal extension of classical solid mechanics that allows for the modeling of bodies in which discontinuities occur spontaneously. Because the peridynamic expression for the balance of linear momentum does not contain spatial derivatives and is instead based on an integral equation, it is well suited for modeling phenomena involving spatial discontinuities such as crack formation and fracture. In this study, both peridynamics and classical finite element analysis are applied to simulate material response under dynamic blast loading conditions. A combined approach is utilized in which the portion of the simulation modeled with peridynamics interacts with the finite element portion of the model via a contact algorithm. The peridynamic portion of the analysis utilizes an elastic-plastic constitutive model with linear hardening. The peridynamic interface to the constitutive model is based on the calculation of an approximate deformation gradient, requiring the suppression of possible zero-energy modes. The classical finite element portion of the model utilizes a Johnson-Cook constitutive model. Simulation results are validated by direct comparison to expanding tube experiments. The coupled modeling approach successfully captures material response at the surface of the tube and the emerging fracture pattern. The coupling of peridynamics and finite element analysis via a contact algorithm has been shown to be a viable means for simulating material fracture in a high-velocity impact experiment. A combined peridynamics/finite element approach was applied to model an expanding tube experiment performed by Vogler, et al., in which loading on the tube is a result of Lexan slugs impacting inside the tube. The Lexan portion of the simulation was modeled with finite elements and a Johnson-Cook elastic-plastic material model in conjunction with an equation-of-state law. The steel tube portion of the simulation was modeled with peridynamics, an elastic
Finite element simulation of extrusion of optical fiber preforms: Effects of wall slip
NASA Astrophysics Data System (ADS)
Zhang, Zhi Feng; Zhang, Yilei
2016-03-01
Extrusion has been successfully used to fabricate optical fiber preforms, especially microstructured ones. Although simplified mathematical model has been used to calculate the extrusion pressure or speed, more frequently die design and extrusion process optimization depend on trial and error, which is especially true for complex die and preform design. This paper employs the finite element method (FEM) to simulate the billet extrusion process to investigate the relationship between the extruding pressure, the billet viscosity, the wall slip condition and the extruding speed for extrusion of rod preforms. The slipping wall boundary condition is taken into account of the finite element model, and the simulated extruding pressure agrees with the one experimental value reported preciously. Then the dependence of the extruding speed on the extruding pressure, billet viscosity and the slip speed is systematically simulated. Simulated data is fitted to a second order polynomial model to describe their relationship, and the terms of the model are reduced from nine to five by using a statistical method while maintaining the fitting accuracy. The FEM simulation and the fitted model provide a convenient and dependable way to calculate the extrusion pressure, speed or other process parameters, which could be used to guide experimental design for future preform extrusion. Furthermore, the same simulation could be used to optimize die design and extrusion process to improve quality of extruded preforms.
NASA Astrophysics Data System (ADS)
Kusoglu Sarikaya, C.; Rafatov, I.; Kudryavtsev, A. A.
2016-06-01
The work deals with the Particle in Cell/Monte Carlo Collision (PIC/MCC) analysis of the problem of detection and identification of impurities in the nonlocal plasma of gas discharge using the Plasma Electron Spectroscopy (PLES) method. For this purpose, 1d3v PIC/MCC code for numerical simulation of glow discharge with nonlocal electron energy distribution function is developed. The elastic, excitation, and ionization collisions between electron-neutral pairs and isotropic scattering and charge exchange collisions between ion-neutral pairs and Penning ionizations are taken into account. Applicability of the numerical code is verified under the Radio-Frequency capacitively coupled discharge conditions. The efficiency of the code is increased by its parallelization using Open Message Passing Interface. As a demonstration of the PLES method, parallel PIC/MCC code is applied to the direct current glow discharge in helium doped with a small amount of argon. Numerical results are consistent with the theoretical analysis of formation of nonlocal EEDF and existing experimental data.
Nuclear Thermal Rocket Element Environmental Simulator (NTREES) Phase II Upgrade Activities
NASA Technical Reports Server (NTRS)
Emrich, William J.; Moran, Robert P.; Pearson, J. Bose
2013-01-01
To support the on-going nuclear thermal propulsion effort, a state-of-the-art non nuclear experimental test setup has been constructed to evaluate the performance characteristics of candidate fuel element materials and geometries in representative environments. The facility to perform this testing is referred to as the Nuclear Thermal Rocket Element Environment Simulator (NTREES). This device can simulate the environmental conditions (minus the radiation) to which nuclear rocket fuel components will be subjected during reactor operation. Test articles mounted in the simulator are inductively heated in such a manner so as to accurately reproduce the temperatures and heat fluxes which would normally occur as a result of nuclear fission and would be exposed to flowing hydrogen. Initial testing of a somewhat prototypical fuel element has been successfully performed in NTREES and the facility has now been shutdown to allow for an extensive reconfiguration of the facility which will result in a significant upgrade in its capabilities. Keywords: Nuclear Thermal Propulsion, Simulator
A 3D finite element simulation model for TBM tunnelling in soft ground
NASA Astrophysics Data System (ADS)
Kasper, Thomas; Meschke, Günther
2004-12-01
A three-dimensional finite element simulation model for shield-driven tunnel excavation is presented. The model takes into account all relevant components of the construction process (the soil and the ground water, the tunnel boring machine with frictional contact to the soil, the hydraulic jacks, the tunnel lining and the tail void grouting). The paper gives a detailed description of the model components and the stepwise procedure to simulate the construction process. The soil and the grout material are modelled as saturated porous media using a two-field finite element formulation. This allows to take into account the groundwater, the grouting pressure and the fluid interaction between the soil and slurry at the cutting face and between the soil and grout around the tail void. A Cam-Clay plasticity model is used to describe the material behaviour of cohesive soils. The cementitious grouting material in the tail void is modelled as an ageing elastic material with time-dependent stiffness and permeability. To allow for an automated computation of arbitrarily long and also curvilinear driving paths with suitable finite element meshes, the simulation procedure has been fully automated. The simulation of a tunnel advance in soft cohesive soil below the ground water table is presented and the results are compared with measurements taken from the literature. Copyright
Design Considerations for the Nuclear Thermal Rocket Element Environmental Simulator (NTREES)
NASA Technical Reports Server (NTRS)
Emrich, Bill; Kirk, Daniel
2006-01-01
Nuclear Thermal Rockets or NTR's have been suggested as a propulsion system option for vehicles traveling to the moon or Mars. These engines are capable of providing high thrust at specific impulses at least twice that of today s best chemical engines. The performance constraints on these engines are mainly the result of temperature limitations on the fuel coupled with a limited ability to withstand chemical attack by the hot hydrogen propellant. To operate at maximum efficiency, fuel forms are desired which can withstand the extremely hot, hostile environment characteristic of NTR operation for at least several hours. The simulation of such an environment would require an experimental device which could simultaneously approximate the power, flow, and temperature conditions which a nuclear fuel element (or partial element) would encounter during NTR operation. Such a simulation would allow detailed studies of the fuel behavior and hydrogen flow characteristics under reactor like conditions to be performed. The goal of these simulations would be directed toward expanding the performance envelope of NTR engines over that which was demonstrated during the Rover and NERVA nuclear rocket programs of the 1970's. Currently, such a simulator is nearing completion at the Marshall Space Flight Center, and will shortly be used in the future to evaluate a wide variety of he1 element designs and the materials of which they are constructed. This present work addresses the initial experimental objectives of the Nuclear Thermal Rocket Element Environmental Simulator or NTREES and some of the design considerations which were considered prior to and during its construction.
Simulation of the optical performance of refractive elements to mimic the human eye focusing
NASA Astrophysics Data System (ADS)
Diaz-Gonzalez, G.; Santiago-Alvarado, Agustín.; Cruz-Félix, Ángel S.
2015-09-01
Refractive optics has evolved and incorporated new elements in optical systems every day, such as conventional lenses, tunable lenses, GRIN lenses, diffractive lenses, intraocular lenses, etc. Some of these elements are reported in the literature together with different proposed models of the human eye. In this work, optical properties of some of these lenses will be studied, and simulations of their behavior will be done in order to analyze which one is better for imaging process. Such lenses will be incorporated in an optical system that mimics the human eye behavior. Analysis and obtained results are reported, as well as the proposed optical system. Finally, we present the conclusions of the work.
Finite element simulations involving simultaneous multiple interface fronts in phase change problems
NASA Technical Reports Server (NTRS)
Ouyang, Tianhong; Tamma, Kumar K.
1992-01-01
The present paper describes the simulation of phase change problems involving simultaneous multiple interface fronts employing the finite element method. Much of the past investigations employing finite elements have been restricted to primarily a single phase change situation. The existence of more than one phase, that is, the presence of multiple phase fronts poses certain challenges and further complications. However, the results provide a very interesting thermal behavior for this class of problems. In this paper, attention is focused on fixed grid methods and the trapezoidal family of one-step methods using the enthalpy formulations. Illustrative examples which handle simultaneous multiple fronts in phase change problems are presented.
An Ellipsoidal Particle-Finite Element Method for Hypervelocity Impact Simulation. Chapter 1
NASA Technical Reports Server (NTRS)
Shivarama, Ravishankar; Fahrenthold, Eric P.
2004-01-01
A number of coupled particle-element and hybrid particle-element methods have been developed for the simulation of hypervelocity impact problems, to avoid certain disadvantages associated with the use of pure continuum based or pure particle based methods. To date these methods have employed spherical particles. In recent work a hybrid formulation has been extended to the ellipsoidal particle case. A model formulation approach based on Lagrange's equations, with particles entropies serving as generalized coordinates, avoids the angular momentum conservation problems which have been reported with ellipsoidal smooth particle hydrodynamics models.
Mixed Electromagnetic and Circuit Simulations using Higher-Order Elements and Bases
Champagne, N J; Rockway, J D; Jandhyala, V
2003-06-18
In this paper, an approach to couple higher-order electromagnetic surface integral equations to circuit simulations is presented. Terminals are defined that connect circuit elements to contacts modeled on the distributed electromagnetic domain. A modified charge-current continuity equation is proposed for a generalized KCL connection at the contacts. The distributive electromagnetic integral equations are developed using higher-order bases and elements that allow both better convergence and accuracy for modeling. The resulting scheme enables simultaneous solution of electromagnetic integral equations for arbitrarily-shaped objects and SPICE-like modeling for lumped circuits, and permits design iterations and visualization of the interaction between the two domains.