News Archives - Page 3 of 3

NSF highlights plasma-accelerator PIC simulations

April 23, 2015 by Benjamin Winjum

NSF has highlighted research done by QuickPIC for the FACET simulations. See link here.

QuickPIC makes the Nature cover

April 23, 2015 by Benjamin Winjum

Breakthrough in plasma-based accelerator research is facilitated using QuickPIC, a code based on the UPIC Framework. Recently, a team of researchers from SLAC and UCLA demonstrated a milestone in plasma based accelerator research. Using two properly space electron bunches, they were able to demonstrate efficient transfer of energy from a drive electron beam to a second trailing electron beam. The planning and interpretation of the experiment relied on QuickPIC as well as OSIRIS.

Nature article: M. Litos et al., Nature 515, 92 (2014) | General science write-up in Nature News and Views: Accelerator physics: Surf’s up at SLAC | More links...

OSIRIS is now GPU and Intel Phi enabled

April 1, 2015 by Benjamin Winjum

PICKSC members, notably Adam Tableman, Viktor Decyk, and Ricardo Fonseca, have developed strategies for porting PIC codes to many-core architectures including GPUs and Intel Phi processors. Some of these ideas have been implemented into OSIRIS so that it is GPU and Intel Phi enabled.

The GPU version of OSIRIS is fully operational in one, two and three dimensions, with support for most of the features of OSIRIS. Dynamic GPU load balancing/tuning is included and the code is fully MPI ready and capable of running on thousands of GPU nodes, with tailored support for Fermi and Kepler generations.

PICKSC members get INCITE award

January 1, 2015 by Benjamin Winjum

90 million processor hours on the IBM Blue Gene/Q Machine at Argonne National Laboratory have been awarded to Frank Tsung (PI), Warren Mori (Co-PI), Ben Winjum, and Viktor Decyk as a 2015 Incite Award for ““Petascale Simulations of Laser Plasma Interactions Relevant to IFE”. Read more

The Research Summary for the Award:

Inertial (laser-initiated) fusion energy (IFE) holds incredible promise as a source of clean and sustainable energy for powering devices. However, significant obstacles to obtaining and harnessing IFE in a controllable manner remain, including the fact that self-sustained ignition has not yet been achieved in IFE experiments. This inability is attributed in large part to excessive laser-plasma instabilities (LPIs) encountered by the laser beams.

LPIs such as two-plasmon decay and stimulated Raman scattering can absorb, deflect, or reflect laser light, disrupting the fusion drive, and can also generate energetic electrons that threaten to preheat the target. Nevertheless, IFE schemes like shock ignition (where a high-intensity laser is introduced toward the end of the compression pulse) could potentially take advantage of LPIs to generate energetic particles to create a useful shock that drives fusion. Therefore, developing an understanding of LPIs will be crucial to the success of any IFE scheme.

The physics involved in LPI processes is complex and highly nonlinear, involving both wave- wave and wave-particle interactions and necessitating the use of fully nonlinear kinetic computer models, such as fully explicit particle-in-cell (PIC) simulations that are computationally intensive and thus limit how many spatial and temporal scales can be modeled.

By using highly optimized PIC codes, however, researchers will focus on using fully kinetic simulations to study the key basic high energy density science directly relevant to IFE. The ultimate goal is to develop a hierarchy of kinetic, fluid, and other reduced-description approaches that can model the full space and time scales, and close the gap between particle- based simulations and current experiments.

Verification and Convergence Properties of Particle-in-Cell Codes

December 15, 2014 by joesrocha

Despite the wide use of PIC codes throughout plasma physics for over 50 years, there still does not appear to be a consensus on the mathematical model that PIC codes represent. PICKSC researchers have recently found that a conventional spectral PIC code can be shown to converge to a spectral gridless code with finite-size particles, indicating that the appropriate underlying model of PIC codes is the Klimontovich equation with finite-size particles as opposed to the Vlasov equation or a statistical model such as the Vlasov-Boltzmann equation. Read more

Using gridless codes developed by Viktor Decyk for both electrostatic and electromagnetic cases, the energy evolution of a 1D, periodic, thermal plasma was shown to converge exactly (within machine precision) as the number of Fourier modes, the particle size, and the time step were varied. Following this, the researchers compared a conventional spectral PIC code to the gridless code, showing the convergence of electrostatic and electromagnetic PIC codes to the gridless code as the cell size was varied and the particle size was kept constant. They further verified conditions for which electron plasma waves had the proper dispersion relation. Interestingly, these convergence tests suggested that when using PIC codes with Gaussian-shaped particles, convergence occurred when using grid sizes less than half the electron Debye length and a particle size of approximately one Debye length, contrasting slightly with conventional PIC usage of equal grid sizes and particles sizes.

[B. J. Winjum, J. J. Tu, S. S. Su, V. K. Decyk, and W. B. Mori, “Verification and Convergence Properties of a Particle-In-Cell Code”, to be published.]

PICKSC members get BlueWaters access

October 24, 2014 by Benjamin Winjum

The UCLA Simulation of Plasmas Group and the OSIRIS Consortium have been given access to Blue Waters, one of the most powerful supercomputing machines in the world. Blue Waters is supported by the National Science Foundation and the University of Illinois at Urbana-Champaign, and it is managed by the National Center for Supercomputing Applications. The UCLA group hopes to use their access to investigate scientific questions about inertial fusion energy, plasma-based acceleration, energetic particle generation in the cosmos, and magnetotail substorms.

Dr. Tsung’s presentation for the group at the 2014 Blue Waters Symposium may be viewed here.

PICKSC hosts first annual workshop

September 25, 2014 by Benjamin Winjum

The UCLA Particle-in-Cell (PIC) and Kinetic Simulation Software Center (PICKSC) hosted a workshop on enabling software interoperability within the PIC community. We invited the primary developers of about a dozen major PIC codes used in the study of Laser Plasma Interactions (LPI), as well as a few developers from other areas. The LPI community shares intellectual ideas about simulations effectively, but has rarely shared the software itself. There is no large community code. Almost all the developers we invited accepted, indicating a strong interest in this topic.

The workshop was held at UCLA from Sept 22-24, 2014. The four sessions were primarily organized as discussions, with short presentations to add additional material. The first major topic was whether interoperability was desired and what it actually means. There was agreement on a wide number of issues:

The desire for a code of ethics, acknowledgment when code is reused. This could be an acknowledgement in a publication, references to papers, or authorship in a publication. The latter might be appropriate if a shared code enabled new research capability.
Desire for standard problems to verify or validate new codes or modified codes, including a database of physics benchmarks with standard inputs. One would like to easily reproduce the results of a paper, in hours, not months, with an independently developed code.
Desire for common display formats.
Interoperability of software may be enabled via middleware, with simple interfaces.
Desire for workflow interoperability between different codes, using output of one code as input to another.

The second major topic was how to enable software interoperability. The attendees discussed and compared units, data structures and objects used in the various codes. Two languages were in common use in the community, Fortran and C/C++. Scripting languages (often Python) was sometimes used to glue components together. Fortran2003 has standard interoperability with C which simplifies language interoperability. There were two common types of units in use, dimensionless units and SI. Dimensionless units are used by those who adhere to the philosophy that a simulation represents many actual physical systems. Translating units is generally straightforward, but can be tricky since not everything is well documented. Some codes had public units for input/output but different units internally. Among object-oriented codes, there was a wide variety of classes with different dependences. It was felt that only simple objects could actually interoperate at this time. Different parallel domain decompositions used in the code could also pose a problem, but this was not extensively discussed.

The third major topic was how to enable interoperability of algorithms. There was a consensus that providing a simple unit test for each new algorithm, which compares the algorithm with some analytic solution and could be run and executed independently of the actual PIC code. The use of skeleton codes (or mini-apps) to illustrate how a collection of algorithms interoperate was also discussed. There was a consensus that PICKSC can serve as a focal point of PIC codes containing pointers between various codes in the community.

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