FY2010 - Oak Ridge National Laboratory

Director’s R&D Fund—
Ultrascale Computing and Data Science
and the international fusion reactor, ITER (which if successful could help ensure the energy supply of
humanity for centuries to come). By enabling a predictive capability, this project may have direct impact
on the success of ITER and the U.S. magnetic fusion program and may contribute to ensure a good
scientific/technological return on U.S. investment in such an experiment. Relevance to scientific
discovery and innovation stems from the strong connection with two offices of the DOE Office of
Science: the Office of Fusion Energy Science and the Office of Applied Scientific Computing Research.
Success in this project will contribute to the core goals of both offices and will contribute to U.S.
scientific prominence in the world.
Results and Accomplishments
Several key milestones have been met in this project to date. These include (1) mathematical proof of
elimination of finite-grid instability and exact energy conservation with implicit PIC; (2) generalization of
the delta-f energy-conserving approach to full-f; and (3) the assessment of particle subcycling and orbit
averaging in implicit PIC. The first accomplishment is a key development, as it demonstrates our premise
that fully implicit, energy-conserving PIC can be free of deleterious numerical instabilities, both spatial
and temporal. This paves the road to truly efficient kinetic modeling of plasmas, which is the main goal of
this project. The second accomplishment enables the treatment of completely general temperature
profiles, which was a major limitation of earlier work. This is another important aspect of this project,
necessary for the development of a first-principles predictive capability. The third and final
accomplishment proves our premise that the accurate integration of orbits in phase space is of the essence
for a reliable long-term simulation using implicit time-stepping techniques. In particular, we have proved
that a careful numerical treatment of particle orbits is directly related to good momentum conservation
properties, and that lack of care in this regard results in late-time solution degradation. Put together, these
accomplishments place this effort on a very solid scientific foundation and set the stage for strong future
impact.
05387
Soft-Error Resilience for Future-Generation High-Performance
Computing Systems
Christian Engelmann and Sudharshan S. Vazhkudai
Project Description
The premise of this project is that soft errors, that is, uncorrected bit flips in computer chip logic caused
by thermal and voltage variations as well as natural radiation, will be the main cause of interruptions in
future high-performance computing (HPC) systems due to smaller circuit sizes, lower voltages, and
increased component count. Based on the exa-scale roadmap, vendors have to find the right balance
between resilience and power consumption. While they will offer extensive soft error detection support to
avoid silent data corruption (SDC), soft error correction will be limited to save power. This has two
consequences. First, fewer soft errors will be masked by the hardware. Second, the risk of SDC remains
as its prevention is still an active area of research. This project targets two different solutions to alleviate
the issue of soft errors: (1) checkpoint storage virtualization to improve checkpoint/restart times and
(2) software redundancy to eliminate rollback/recovery.
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