# Viktor K. Decyk's research while affiliated with University of California, Los Angeles and other places

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## Publications (238)

We derive the kinetic theory of fluctuations in physically and numerically stable particle-in-cell (PIC) simulations of electrostatic plasmas. The starting point is the single-time correlations at the simulation start between the statistical fluctuations of weighted densities of macroparticle centers in the plasma particle phase-space. The single-t...

Non‐Gaussian distributions are commonly observed in collisionless space plasmas. Generating samples from non‐Gaussian distributions is critical for the initialization of particle‐in‐cell simulations that investigate their driven and undriven dynamics. To this end, we report a computationally efficient, robust tool, Chebsampling, to sample general d...

This paper discusses how to improve the Boris pusher used to advance relativistic charged particles in fixed electromagnetic fields. We first derive a simpler solution to a flaw previously discovered by others. We then derive a new analytic Boris pusher that is a minor modification to the original split-time scheme, except for the calculation of {\...

High-fidelity modeling of plasma-based acceleration (PBA) requires the use of 3D fully nonlinear and kinetic descriptions based on the particle-in-cell (PIC) method. Three-dimensional PIC algorithms based on the quasi-static approximation (QSA) have been successfully applied to efficiently model the beam-plasma interaction. In a QSA-PIC algorithm,...

Non-Gaussian distributions are commonly observed in collisionless space plasmas. Generating samples from non-Gaussian distributions is critical for the initialization of particle-in-cell simulations that investigate their driven and undriven dynamics. To this end, we report a computationally efficient, robust tool, Chebsampling, to sample general d...

Next-generation high-power laser systems that can be focused to ultra-high intensities exceeding 10²³ W/cm² are enabling new physics regimes and applications. The physics of how these lasers interact with matter is highly nonlinear, relativistic, and can involve lowest-order quantum effects. The current tool of choice for modeling these interaction...

The three-dimensional (3D) quasi-static particle-in-cell (PIC) algorithm is a very efficient method for modeling short-pulse laser or relativistic charged particle beam–plasma interactions. In this algorithm, the plasma response, i.e., plasma wave wake, to a non-evolving laser or particle beam is calculated using a set of Maxwell’s equations based...

Furthering our understanding of many of today’s interesting problems in plasma physics – including plasma based acceleration and magnetic reconnection with pair production due to quantum electrodynamic effects – requires large-scale kinetic simulations using particle-in-cell (PIC) codes. However, these simulations are extremely demanding, requiring...

A customized finite-difference field solver for the particle-in-cell (PIC) algorithm that provides higher fidelity for wave-particle interactions in intense electromagnetic waves is presented. In many problems of interest, particles with relativistic energies interact with intense electromagnetic fields that have phase velocities near the speed of...

Next-generation high-power laser systems that can be focused to intensity $>10^{23}$ W/cm$^2$ enable new physics and applications. Matter interacting with these lasers is highly nonlinear, relativistic, and involves non-classical processes such as radiation reaction (RR) and quantum effects. The current tool of choice for modeling these interaction...

A customized finite-difference field solver for the particle-in-cell (PIC) algorithm that provides higher fidelity for wave-particle interactions in intense electromagnetic waves is presented. In many problems of interest, particles with relativistic energies interact with intense electromagnetic fields that have phase velocities near the speed of...

The particle-in-cell (PIC) method is widely used to model the self-consistent interaction between discrete particles and electromagnetic fields. It has been successfully applied to problems across plasma physics including plasma based acceleration, inertial confinement fusion, magnetically confined fusion, space physics, astrophysics, high energy d...

Furthering our understanding of many of today's interesting problems in plasma physics---including plasma based acceleration and magnetic reconnection with pair production due to quantum electrodynamic effects---requires large-scale kinetic simulations using particle-in-cell (PIC) codes. However, these simulations are extremely demanding, requiring...

The 3D quasi-static particle-in-cell (PIC) algorithm is a very efficient method for modeling short-pulse laser or relativistic charged particle beam-plasma interactions. In this algorithm, the plasma response to a non-evolving laser or particle beam is calculated using Maxwell's equations based on the quasi-static approximate equations that exclude...

The particle-in-cell (PIC) method is widely used to model the self-consistent interaction between discrete particles and electromagnetic fields. It has been successfully applied to problems across plasma physics including plasma based acceleration, inertial confinement fusion, magnetically confined fusion, space physics, astrophysics, high energy d...

A range of nonlinear wave structures, including Langmuir waves, unipolar electric fields, and bipolar electric fields, are often observed in association with whistler-mode chorus waves in near-Earth space. We demonstrate that the three seemingly different nonlinear wave structures originate from the same nonlinear electron trapping process by whist...

A range of nonlinear wave structures, including Langmuir waves, unipolar electric fields and bipolar electric fields, are often observed in association with whistler-mode chorus waves in the near-Earth space. We demonstrate that the three seemingly different nonlinear wave structures originate from the same nonlinear electron trapping process by wh...

UPIC-EMMA 2.0 is an open source (available on GitHub) fully parallelized spectral Particle-In-Cell (PIC) code. Inherited from the time-tested UPIC framework, it utilizes the message-passing interface (MPI) for parallel processing and a multi-tasking library was implemented to enable mixed multi-tasking and MPI. The full set of Maxwell equations is...

The UCLA Particle-in-Cell and Kinetic Simulation Software Center (PICKSC) aims to support an international community of PIC and plasma kinetic software developers, users, and educators; to increase the use of this software for accelerating the rate of scientific discovery; and to be a repository of knowledge and history for PIC. We discuss progress...

The electron beam-plasma system is ubiquitous in the space plasma environment. Here, using a Darwin particle-in-cell method, the excitation of electrostatic and whistler instabilities by a gyrating electron beam is studied in support of recent laboratory experiments. It is assumed that the total plasma frequency (ωpe) is larger than the electron cy...

The evolution of the whistler anisotropy instability relevant to whistler-mode chorus waves in the Earth's inner magnetosphere is studied using kinetic simulations and is compared with satellite observations. The electron distribution is constrained by the whistler anisotropy instability to a marginal stability state and presents an upper bound of...

One aim of the Particle-In-Cell and Kinetic Simulation Center (PICKSC) at UCLA is to coordinate a community development of educational software for undergraduate and graduate courses in plasma physics and computer science. The rich array of physical behaviors exhibited by plasmas can be difficult to grasp by students. If they are given the ability...

Recently it was proposed in [A. F. Lifschitz, et. al., J. Comp. Phys. 228, 1803 (2009)] that laser wakefield acceleration could be modeled efficiently using a particle-in-cell code in cylindrical coordinates if the fields and currents were expanded into Fourier modes in the azimuthal angle, ɸ. We have implemented this algorithm into OSIRIS, includi...

In this paper we present a customized finite-difference-time-domain (FDTD) Maxwell solver for the particle-in-cell (PIC) algorithm. The solver is customized to effectively eliminate the numerical Cerenkov instability (NCI) which arises when a plasma (neutral or non-neutral) relativistically drifts on a grid when using the PIC algorithm. We control...

When modeling laser wakefield acceleration (LWFA) using the particle-in-cell (PIC) algorithm in a Lorentz boosted frame, the plasma is drifting relativistically at βbc 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 curre...

This paper investigates how the physics of the whistler anisotropyinstability (WAI) is affected by variations in the electron thermal velocity vte, referred to here in terms of the ratio v̂te=vte/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 d...

The massively parallel, nonlinear, three-dimensional (3D), toroidal, electrostatic, gyrokinetic, particle-in-cell (PIC), Cartesian geometry UCAN code, with particle ions and adiabatic electrons, has been successfully exercised to identify non-diffusive transport characteristics in present day tokamak discharges. The limitation in applying UCAN to l...

When modeling laser wakefield acceleration (LWFA) using the particle-in-cell
(PIC) algorithm in a Lorentz boosted frame, the plasma is drifting
relativistically at $\beta_b c$ towards the laser, which can lead to a
computational speedup of $\sim \gamma_b^2=(1-\beta_b^2)^{-1}$. Meanwhile, when
LWFA is modeled in the quasi-3D geometry in which the el...

We present results from a preliminary study on model-ing Laser wakefield acceleration (LWFA) with OSIRIS in a Lorentz boosted frame using a quasi-3D algorithm. In the quasi-3D algorithm, the fields and currents are expanded into azimuthal harmonics and only a limited number of harmonics are kept. Field equations in (r, z) space are solved for a des...

The next generation of supercomputers will likely consist of a hierarchy of parallel computers. If we define each supercomputer node as a parameterized abstract machine, then it's possible to design algorithms independently of the hardware. Such an abstract machine can be defined to consist of a collection of vector (SIMD) processors, each with a s...

A hybrid Maxwell solver for fully relativistic and electromagnetic (EM)
particle-in-cell (PIC) codes is described. In this solver, the EM fields are
solved in $k$ space by performing an FFT in one direction, while using finite
difference operators in the other direction(s). This solver eliminates the
numerical Cerenkov radiation for particles movin...

We demonstrate that a live-programming environment can be used to harness and add runtime interactivity to scientific simulation codes. Through a set of examples using a Particle-In-Cell (PIC) simulation framework we show how the real-time, human-in-the-loop interactivity of liveprogramming can be incorporated into traditional "offline" and develop...

When using an electromagnetic particle-in-cell (EM-PIC) code to simulate a
relativistically drifting plasma, a violent numerical instability known as the
numerical Cerenkov instability (NCI) occurs. The NCI is due to the unphysical
coupling of electromagnetic waves on a grid to wave-particle resonances,
including aliased resonances, i.e., $\omega +...

We have designed Particle-in-Cell algorithms for emerging architectures. These algorithms share a common approach, using fine-grained tiles, but different implementations depending on the architecture. On the GPU, there were two different implementations, one with atomic operations and one with no data collisions, using CUDA C and Fortran. Speedups...

Simulating laser wakefield acceleration (LWFA) in a Lorentz boosted frame in
which the plasma drifts towards the laser with $v_b$ can speedup the simulation
by factors of $\gamma^2_b=(1-v^2_b/c^2)^{-1}$. In these simulations the
relativistic drifting plasma inevitably induces a high frequency numerical
instability that contaminates the interested p...

This is the working summary of the Accelerator Science working group of the
Computing Frontier of the Snowmass meeting 2013. It summarizes the computing
requirements to support accelerator technology in both Energy and Intensity
Frontiers.

We present improvements to the three-dimensional (3D) quasi-static
particle-in-cell (PIC) algorithm, which is used to efficiently model
short-pulse laser and particle beam-plasma interactions. In this
algorithm the fields including the index of refraction created by a
static particle/laser beam are calculated. These fields are then used to
advance...

We examine numerical issues related to modeling laser wakefield acceleration (LWFA) in a Lorentz boosted frame. We present some theoretical results on a numerical instability that results from a relativistic plasma drift on a grid. We compare these predictions with results obtained from a finite difference time domain
(FDTD) code OSIRIS and a spec...

The numerical instability observed in the Electromagnetic-Particle-in-cell
(EM-PIC) simulations with a plasma drifting with relativistic velocities is
studied using both theory and computer simulations. We derive the numerical
dispersion relation for a cold plasma drifting with a relativistic velocity and
find an instability attributed to the coupl...

A detailed understanding of electron stopping and scattering in plasmas
with variable values for the number of particles within a Debye sphere
is still not at hand. Presently, there is some disagreement in the
literature concerning the proper description of these processes.
Detailed theoretical models exist for the stopping power of a single
relati...

Particle-in-Cell (PIC) codes are widely used throughout plasma physics.
Nevertheless, there is considerable confusion about what precisely is
the mathematical model behind PIC codes and whether PIC codes converge
to such a model. This numerical study is intended to shed light on these
issues. Our basic hypothesis is that a Klimontovich equation wit...

There are several relevant plasma physics scenarios where highly
nonlinear and kinetic processes dominate. Further understanding of these
scenarios is generally explored through relativistic particle-in-cell
codes such as OSIRIS [1], but this algorithm is computationally
intensive, and efficient use high end parallel HPC systems, exploring
all leve...

QuickPIC is a 3D parallel quasi-static Particle-In-Cell (PIC) code,
which is developed with a PIC framework UPIC. Recently, a new 2D field
solver for calculating the plasma response to the drive beam in QuickPIC
has been developed. It is based on a new set of Maxwell equations (under
the quasi-static approximation) which is using transverse Coulomb...

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 [1] are
computatio...

The massively parallel, nonlinear, 3D, toroidal, electrostatic,
gyrokinetic, PIC, Cartesian geometry UCAN code, with particle ions and
adiabatic electrons, has been successfully exercised to identify
non-diffusive transport characteristics in DIII-D-like discharges. The
limitation in applying UCAN to larger scale discharges is the 1D domain
decompo...

A detailed understanding of electron stopping and scattering in plasmas with variable values for the number of particles within a Debye sphere is still not at hand. Presently, there is some disagreement in the literature concerning the proper description of these processes. Theoretical models assume electrostatic (Coulomb force) interactions betwee...

The traditional view regarding the reduction of turbulence-induced transport across a stable sheared flow invokes a reduction of the characteristic length scale in the direction perpendicular to the flow as a result of the shearing and stretching of eddies caused by the differential pull exerted in the direction of the flow. A reduced effective tra...

We use electrostatic partice-in-cell (PIC) simulations and theory to study the damping of 1D plasma waves. We consider the linear regime where the asymptotic damping rate is much bigger than the bounce frequency. In this regime the waves are typically very small and often below the thermal noise in simulations and experiments. These waves can be st...

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...

We present an implementation of a 2D fully relativistic, electromagnetic particle-in-cell code, with charge-conserving current deposition, on parallel graphics processors (GPU) with CUDA. The GPU implementation achieved a one particle-step process time of 2.52ns for cold plasma runs and 9.15ns for extremely relativistic plasma runs, which are respe...

Satellite observations in the inner magnetosphere have shown the presence of a highly anisotropic temperature distribution with perpendicular temperature about 10 times the parallel temperature. A linear theory and two-dimensional particle in cell simulation study has been carried out for this event to understand the physics of the wave generation,...

Fast Ignition studies require a detailed understanding of electron scattering, stopping, and energy deposition in plasmas with variable values for the number of particles within a Debye sphere. Presently there is disagreement in the literature concerning the proper description of these processes. Developing and validating proper descriptions requir...

The complexity of the phenomena involved in several relevante plasma physics scenarios, where highly nonlinear and kinetic processes dominate, makes purely theoretical descriptions impossible. Further understanding of these scenarios requires detailed numerical modelling, but fully relativistic particle-in-cell codes such as OSIRIS [1] are computat...

We investigate through theory and PIC simulations the Landau-damping of plasma waves with finite plasma parameter. We concentrate on the linear regime, gammaphiB, where the waves are typically small and below the thermal noise. We simulate these condition using 1,2,3D electrostatic PIC codes (BEPS), noting that modern computers now allow us to simu...

On July 24, 2003, when the Cluster 4 satellite crossed the magnetic equator at about 4.5 RE radial distance on the dusk side (˜15 MLT), whistler wave emissions were observed below the local electron gyrofrequency (fce) in two bands, one band above one-half the gyrofrequency (0.5fce) and the other band below 0.5fce. A careful analysis of the wave em...

For the past 80 years, the instrument of choice in experimental high-energy physics has been particle accelerators, with the newest being the Large Hadron Collider (LHC) at CERN. The construction cost alone for the LHC machine is nearly 10 billion dollars. It is clear that if the same technology is used then the world's next atom smasher" at the en...

Transport scaling of energetic particles by ion temperature gradient microturbulence in magnetized plasmas is studied in massively paralleled gyrokinetic particle-in-cell simulations. It is found that the diffusivity decreases drastically at high particles energy E to plasma temperature T ratio because of the averaging effects of the large gyroradi...

On July 24, 2003, when the Cluster satellites crossed the magnetic equator at about 4.5 RE radial distance on the dusk side (~ 15 MLT) emissions were observed below the local electron gyrofrequency in two bands, one band above one-half the gyrofrequency and the other band below one-half the gyrofrequency, which is typical of chorus emissions propag...

Computer simulations of stimulated Raman scattering (SRS) indicate that the instability is bursty in time and space, leading to finite-size plasma waves in both the longitudinal and transverse directions. Using particle-in-cell (PIC) simulations with an external, ponderomotive impulse driver, we present the results of detailed study of the nonlinea...

Recent particle-in-cell (PIC) simulations (L. Yin et al., PRL 99, 265004 (2007) and B. Winjum's poster) of stimulated Raman scattering (SRS) in multiple dimensions indicate that plasma wavefront bowing and localization are important potential nonlinear saturation mechanisms. We present here the results of detailed PIC simulations in which an extern...

It has been recently found that radial transport ceases to behave diffusively in the presence of a radially-sheared poloidal zonal flow, becoming instead strongly subdiffusive [1]. The same behavior is observed in other simulations, suggesting that the mechanism responsible is rather general. In numerical simulations of 2D-turbulence, the change in...

We are characterizing transport using particles in gyrokinetic simulations of ion channel turbulence in tokamaks with the 3D global toroidal nonlinear parallel particle-in-cell UCAN code. Tracking of simulation particles through space and time and especially multiple processors, including restarts with different numbers of tagged particles, is now...

The concept and designs of plasma-based advanced accelerators for high energy physics and photon science are modelled 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 re...

A pipelining algorithm to overcome the limitation on scaling quasi-static particle-in-cell models of relativistic beams in plasmas to a very large number of processors is described. The pipelining algorithm uses multiple groups of processors and optimizes the job allocation on the processors in parallel computing. The algorithm is implemented on th...

It is argued that the usual understanding of the suppression of radial turbulent transport across a sheared zonal flow based on a reduction in effective transport coefficients is, by itself, incomplete. By means of toroidal gyrokinetic simulations of electrostatic, ion-temperature-gradient turbulence, it is found instead that the character of the r...

New emerging multi-core technologies can achieve high performance, but algorithms often need to be redesigned to make effective use of these processors. We will describe a new approach to Particle-in-Cell (PIC) codes and discuss its application to Graphical Processing Units.

It is shown that the usual picture for the suppression of turbulent transport across a stable sheared flow based on a reduction of diffusive transport coefficients is, by itself, incomplete. By means of toroidal gyrokinetic simulations of electrostatic, collisionless ion-temperature-gradient turbulence, it is found that the nature of the transport...

Chorus emissions that propagate in the whistler wave band are observed in the inner magnetosphere and may play a role in the acceleration of electrons. To understand how these waves are generated and what their effects are on electrons, a study has been carried out using Cluster satellite observations and particle in cell simulations. The WBD, STAF...

Simulating the electron cloud effect on a beam that circulates thousands of turns in circular machines is highly computationally demanding. A novel algorithm, the pipelining algorithm is applied to the fully parallelized quasi-static particle-in-cell code QuickPIC to overcome the limit of the maximum number of processors can be used for each time s...

We are continuing to characterize transport in gyrokinetic calculations of ion channel turbulence in tokamaks with the three-dimensional global toroidal nonlinear parallel particle-in-cell UCAN code. In particular, we are taking full advantage of the extended particle manager in UCLA's own PLIB library of massively parallel particle and field manag...

A novel approach to detect the existence of scale‐free transport in turbulent flows, based on the characterization of its Lagrangian characteristics, is presented and applied to two situations relevant for tokamak plasmas. The first one, radial transport in the presence of near‐critical turbulence, has been known for quite some time to yield scale‐...