Hardware Reference
In-Depth Information
A full-resolution magnetosphere simulation is an exascale computing prob-
lem. As an inherently multi-scale problem, reconnection is initiated as a small-
scale problem around individual electrons that eventually leads to a large-
scale reconfiguration of a magnetic field. Recent simulations have revealed
that electron kinetic physics is not only important in triggering reconnec-
tion [6, 5, 7, 10, 14, 11, 15], but also in its subsequent evolution. This finding
suggests a need for modeling details of electron motion, which poses severe
computational challenges for 3D simulations of reconnection.
The advent of petascale computers together with advances in particle simu-
lations are now enabling scientists to conduct simulations that are a thousand
times larger than the previous state of the art. Recent simulations of colli-
sionless magnetic reconnection used a highly optimized particle code called
VPIC [1]. The increased computational capability is providing scientists with
the first glimpse of details of collisionless reconnection in 3D. This chapter
focuses on large data management and analysis challenges, and demonstrates
the effectiveness of using a larger two-trillion-particle run conducted at the
National Energy Research Scientific Computing center (NERSC) located at
the Lawrence Berkeley National Laboratory.
19.2 Science Use Case
Computational plasma physicists are generally interested in understanding
the structure of high-dimensional phase space distributions. For example, in
order to understand the physical mechanisms responsible for producing mag-
netic reconnection in a collisionless plasma, it is important to characterize
the symmetry properties of the particle distribution, such as agyrotropy [13].
Agyrotropy is a quantitative measure of the deviation of the distribution from
cylindrical symmetry about the magnetic field. Another question of significant
practical importance in studies of magnetic reconnection is the characteriza-
tion of energetic particles. Particle properties of interest include spatial loca-
tion (x;y;z), energy, and projection of velocity components on the directions
parallel and perpendicular to the magnetic field (U
k
,U
?;1
,U
?;2
).
The main scientific questions addressed in this experiment are as follows:
Analysis of highly energetic particles:
{ Are the highly energetic particles preferentially accelerated along
the magnetic field?
{ What is the spatial distribution of highly energetic particles?
What are the properties of particles near the reconnection hot spot (the
so-called X-line)?
