Terascale Supernova Initiative Research Articles

Simulations of coherent nonlinear neutrino flavor transformation in the core collapse supernova environment

We describe a set of codes developed under the auspices of the Terascale Supernova Initiative to simulate the coherent, nonlinear evolution of the neutrino and antineutrino fields in the core collapse supernova environment. Ours are the first simulations to include quantum entanglement of neutrino flavor evolution on different neutrino trajectories. We find that neutrinos and antineutrinos can undergo coherent, collective transformations of their flavors which could affect supernova dynamics and nucleosynthesis.

CHEETAH: circuit-switched high-speed end-to-end transport architecture testbed

We propose a circuit-switched high-speed end-to-end transport architecture (CHEETAH) as a networking solution to provide high-speed end-to-end circuit connectivity to end hosts on a dynamic call-by-call basis. Not only is it envisioned as a complementary service to the basic connectionless service provided by today's Internet; it also relies on and leverages the presence of this service. Noting the dominance of Ethernet in LANs and SONET/SDH in WANs, CHEETAH circuits consists of Ethernet segments at the ends and Ethernet-over-SONET segments in the wide area. In this article we explain the CHEETAH concept and describe a wide-area experimental network testbed we have deployed based on this concept. The network testbed currently extends between Raleigh, North Carolina, Atlanta, Georgia, and Oak Ridge, Tennessee, and uses off-the-shelf switches. We have created CHEETAH software to run on end hosts to enable automated use of this network by applications. Our first users of this network testbed and software is the terascale supernova initiative (TSI) project researchers, who plan to use this network for large file transfers and remote visualizations.

Supernova neutrino challenges

A principal `supernova neutrino challenge' is the computational difficulty of six-dimensional neutrino radiation hydrodynamics. The variety of resulting approximations has provoked a long history of uncertainty in the core-collapse supernova explosion mechanism, but recent work highlighting low-mode convection and a newly-recognized instability in spherical accretion shocks may signal (yet another) resolution. As part of its goal of elucidating the explosion mechanism, the Terascale Supernova Initiative is committed to meeting the full complexity of the computational challenge. The understanding of supernova neutrino emission gained in detailed simulations provides a potential basis for learning about two major remaining unknowns in neutrino flavor mixing: the value of the mixing angle $\theta_{13}$, and distinguishing between ``normal'' and ``inverted'' mass hierarchies.

Logistical networking: a global storage network**This work is supported by the Department of Energy SciDAC Program (esp. Terascale Supernova Initiative) under grant #DE-FC02-01ER25465 and by the Center for Gyokinetic Particle Simulation of Turbulent Transport in Burning Plasmas, under award #DE-FG02-04ER25651. Additional support was provided by the Center for Information Technology Research (CITR) of the University of Tennessee. The infrastructure used

The absence of an adequate distributed storage infrastructure for data buffering has become a significant impediment to the flow of work in the wide area, data intensive collaborations that are increasingly characteristic of leading edge research in several fields. One solution to this problem, pioneered under DOE's SciDAC program, is Logistical Networking, which provides a framework for a globally scalable, maximally interoperable storage network based on the Internet Backplane Protocol (IBP). This paper provides a brief overview of the Logistical Networking (LN) architecture, the middleware developed to exploit its value, and a few of the applications that some of research communities have made of it.

Multigroup models of the convective epoch in core collapse supernovae

Understanding the explosion mechanism of core collapse supernovae is a problem that has plagued nuclear astrophysicists since the first computational models of this phenomenon were carried out in the 1960s. Our current theories of this violent phenomenon center around multi-dimensional effects involving radiation-hydrodynamic flows of hot, dense matter and neutrinos. Modeling these multi-dimensional radiative flows presents a computational challenge that will continue to stress high-performance computing beyond the teraflops to the petaflop level. In this paper we describe a few of the scientific discoveries that we have made via terascale computational simulations of supernovae under the auspices of the SciDAC-funded Terascale Supernova Initiative.

Toward five-dimensional core-collapse supernova simulations

The computational difficulty of six-dimensional neutrino radiation hydrodynamics has spawned a variety of approximations, provoking a long history of uncertainty in the corecollapse supernova explosion mechanism. Under the auspices of the Terascale Supernova Initiative, we are honoring the physical complexity of supernovae by meeting the computational challenge head-on, undertaking the development of a new adaptive mesh refinement code for self-gravitating, six-dimensional neutrino radiation magnetohydrodynamics. This code—called GenASiS, for General Astrophysical Simulation System—is designed for modularity and extensibility of the physics. Presently in use or under development are capabilities for Newtonian self-gravity, Newtonian and special relativistic magnetohydrodynamics (with ‘realistic’ equation of state), and special relativistic energy- and angle-dependent neutrino transport—including full treatment of the energy and angle dependence of scattering and pair interactions.

Modeling supernovae: Braving a bold new frontier

The death of a massive star, called a core collapse supernova, is among the most energetic events in the universe, exploding with so much force it can be compared to 10/sup 28/ individual megaton bombs exploding at once. Researchers need powerful supercomputers capable of generating and storing terabytes and petabytes of data to simulate complex models. The US Department of Energy created the TeraScale Supernova Initiative (TSI) to do just that. The $9 million program - made up of the ORNL and eight US universities - aims to discover exactly how a supernova occurs. The scientists' charge is to perform 3D simulations of the radiation of the enormous amounts of neutrino energy and the resulting turbulent fluid flow that propels elements into space. So far, the team has generated 2D simulations, made possible because of terascale computers. They have created some 3D models, but not to the realistic detail the team needs. The team is using some of the most powerful types of computers available, capable of handling many terabytes of data. With these computers, 4,000 to 5,000 processor hours take just days - as opposed to months with a one-processor supercomputer. The team's computers include Seaborg, located at the National Energy Research Scientific Computing Center, Cheetah, located at the Center for Computational Science at ORNL, and Eagle, also located at ORNL. Use of these three computers and others like it have led to new discoveries by enabling multidimensional simulations.