Roadrunner Open Science: important strides taken
Open Science (unclassified work) on Roadrunner, the world's first petaflop/s computer, resulted in significant breakthroughs in materials, astronomy, and laser plasma science. Presented here are images, movies, and brief explanations of the exciting new work done on Roadrunner by seven Principal Investigators (P.I.s):
Laser Plasma Interaction using the VPIC (particle-in-cell) code, Lin Yin, P.I.
Fusion experiments in the National
Ignition Facility (NIF) at Lawrence
Livermore National Laboratory are
scheduled to begin in 2010. In these,
over a million joules of laser energy are
focused within a gas-filled hohlraum (a
container for radiation experiments).
We are studying the physics of onset
and saturation of stimulated Raman
scattering (SRS) in the fundamental
building block of a NIF laser beam, a
single laser speckle. Unlike the linear
growth of SRS, the nonlinear physics
was not well understood. This simulation
shows isosurfaces of the electrostatic
fields associated with RS bursts; the
wave fronts exhibit bending or “bowing,” arising from nonlinear electron
trapping, as well as self-focusing, which
breaks up the phase fronts. This study is
only possible on Roadrunner, where at-scale
kinetic simulations of laser-plasma
interaction in 3D at realistic laser speckle
and multispeckle scales can be done at unprecedented size, speed, and fidelity.
Additional resources: Advances in Kinetic Plasma Simulation
with VPIC and Roadrunner SciDAC Conference, 2009
Parallel Replica Nanowires using the ParRep-AMD code, Arthur Voter, P.I.
We can now begin to understand how materials behave down to the nanometer scale, where the motion of even a single atom can sometimes change mechanical or electrical properties. We are simulating the stretching process of metallic nanowires. Using Roadrunner, we can slow down the simulation to see exactly what is happening during the stretching, many times more than previously possible, to observe the formation of networks of stacking faults (highlighted in red) between atoms.
Magnetic Reconnection using the VPIC (particle-in-cell) code, Bill Daughton, P.I.
Magnetic reconnection is a basic plasma
process involving the rapid conversion of
magnetic field energy into various forms
of plasma kinetic energy. These types
of dynamical changes are conveniently
viewed in terms of the breaking and
reconnection of magnetic field lines,
thus explaining the origin of the term
magnetic reconnection. The process is
thought to play an important role in
solar ares (a source of solar energetic
particles), geomagnetic substorms,
magnetic fusion devices, and a wide
variety of astrophysical problems. This
simulation features highly elongated
electron current layers that are unstable
to flux rope formation over a wide range
of angles. These plasma instabilities
cause the sheets to break into filaments as
illustrated by an isosurface of the current
density colored by the plasma density.
HIV phylogenetics using the ML code, Tanmoy Bhattcharya P.I.
This colored tree is a large set of HIV
sequences collected to find properties
of HIV right after transmission. The underlying computational problem is
to take all of this sequence data (here
10442 strings of ~3873 nucleotides) and
find a model of how the virus evolved
over time. When a node on the tree is
near another node, that means that one
virus is similar to another virus. When
nodes are separated by a number of
intermediate nodes (white), that means
that the model would estimate there
were parent, grandparent, etc. viruses
that lived (and possibly died) along the
way to those two forms. Roadrunner
found an evolutionary model where the
sequences of one patient rarely overlap
with sequences of another patient. One
important goal is to identify possible
vaccine target areas.
Roadrunner Universe using the MC3 code, Salman Habib, P.I.
Dark matter and dark energy are
the dominant components of the
Universe. From modern sky surveys
we have a comprehensive picture of
the evolution history of the Universe
and its fundamental make-up: 23%
dark matter (a large fraction of which
is in localized clumps called halos),
and 73% in a smooth “dark energy”
component. The Roadrunner Universe
project is creating the largest-ever
high-resolution simulations of the
distribution of matter in the Universe.
A comprehensive database of all the
Roadrunner Universe simulations
will become an essential component
of Dark Universe science for years to
come. Shown is the velocity field of
the dark matter halos from one of the
Roadrunner cosmology simulations.
The simulation tracked almost
70 billion particles. Due to
gravity, the particles form
bound structures, the halos.
Each halo in this graph consists
of at least 10 particles and is
shown as an arrow, colored
by its velocity. This is a time
snapshot of 1/64 of the full
simulation volume, which was
see also Abstract of Hybrid petacomputing meets cosmology: The Roadrunner Universe project, Salman Habib et al., 2009 J. Phys.: Conf. Ser. 180 012019 (10pp)
Ejecta and Spall using the SPaSM code, Tim Germann, P.I.
We studied how copper reacts when
shocked, using SPaSM (scalable parallel
short-range molecular dynamics), a
computer code that simulates processes
such as shock waves in solids at
nanosecond time scales. We use SPaSM
to understand how materials deform
and fail at the molecular level, allowing
better materials design and prediction
of their lifetime at full strength. Many
fundamental materials phenomena
take place at length and time scales just
beyond those presently accessible by
molecular dynamics (MD) simulations.
Roadrunner, along with improvements
in methodology, makes simulations of
more realistic spatial and temporal scales
possible. SPaSM was successfully used
to perform the fastest MD simulation to
date, reaching ~369 TFlop/s on the full
Direct Numerical Simulation of Reacting Turbulence, Daniel Livescu, P.I.
In the field of fluid dynamics,
understanding turbulence, the behavior
of fluids under stress, remains one of the
unsolved problems in physics. This
study focuses on the interactions of flame
and turbulence, under complex
conditions, as those encountered in the
early stages of a type 1a supernova.
There is a complicated phenomenology
associated with these interactions, from
the suppression of the smallest vortex
tubes due to the flame “fire polishing,”
enhancement of intermediate turbulent
scales, to the rapid acceleration of the flame itself to large velocities, which is
one of the important open questions
related to the supernova modeling.
The Roadrunner architecture was
instrumental in showing excellent
performance using large structured fluid
dynamics codes and the possibility of
tackling complex turbulence problems.