The latest version of ALEGRA, a computer code used by departments Labs-wide to model Z-machine implosions and hostile nuclear weapons environments, was released earlier this month.
"This release is significant because the new version turns ALEGRA into a true code framework," says Dan Carroll (9231), ALEGRA team leader. "It now can be much more easily used for a wider array of applications."
Besides departments at Sandia, some Department of Defense customers also employ ALEGRA to model non-nuclear weapons effects.
ALEGRA (the name stands for Arbitrary Lagrangian Eulerian General Research Application) is one of two code frameworks being developed by DOE’s Accelerated Strategic Computing Initiative (ASCI) program. The idea behind these frameworks is to develop certain common capabilities needed by many application codes only once and let the other codes use these capabilities.
Dan says that ALEGRA has been "morphing" into a framework over the last year.
"Since ALEGRA was already a successful finite element code supporting many key application areas, the decision was made to move ALEGRA in the direction of becoming a framework to better support the codes in these application areas."
The culmination of this effort is the recent release of Version 4.0.
Sandia researchers initially developed ALEGRA in 1991 as a shock wave physics code used to model high-speed impact and penetration
phenomena involving a variety of materials. As computer hardware evolved, the code was rewritten to accommodate the newly developing massively parallel computational engines, like Sandia’s Teraflop computer, ASCI Red.
In 1995 ALEGRA was expanded to model electromechanical properties — piezoelectric materials — giving researchers a new tool to simulate the shock-activated power supply in the neutron generator, for example.
Three years later ALEGRA integrated another advanced physics model with the capability to model magnetohydrodynamic (MHD) phenomena — the interaction between magnetic fields and electrically conducting materials.
For researchers working with the Z accelerator, this aspect opens new horizons. ALEGRA provides the ability to understand the complexity of the formation and compression of hot plasmas to generate the extreme X-ray environment needed to simulate a nuclear explosion.
"ALEGRA is critical to the future success of the high-energy-density physics research performed in the Pulsed Power Center," says Tom Mehlhorn, Manager of Target and Z-Pinch Theory Dept. 1674. "It is already being used to understand and design experiments on the Z accelerator. As the capability matures, it will provide simulations that will lay the foundation for an upgrade to Z machine and to design and build future z-pinch machines."
He says the ALEGRA framework includes physics modules that allow his engineers and researchers to simulate most of the major activities in the high-energy-density physics program — z-pinches, shock physics, radiation-hydro-dynamics, and electron-photon transport.
Dan says the Z machine work is only half the story of how ALEGRA is used. The other half falls in the area of modeling hostile environments — the effects of exploding nuclear weapons on another nuclear weapon. One user is Mark Kiefer, Manager of Electromagnetics and Plasma Physics Analysis Dept. 1642.
"Basically, our efforts to use the ALEGRA framework are going very well," Mark says. "We are making progress much faster than we expected would be possible. Our efforts to migrate our simulation methods to the ALEGRA framework were dictated by our realization that we are at the limit of the complexity for our current simulation codes. We really cannot take these older codes any farther without a prohibitive amount of work.
"All of our observations can be summed up with the conclusion that we cannot succeed in our nuclear weapon or pulsed power applications without taking advantage of the ALEGRA framework. One of the big advantages of the framework that we are looking forward to exploiting is the ability to test new models and algorithms on a short time scale. This will allow my staff of engineers and scientists more time to do science and engineering."
His area uses ALEGRA to implement full-wave electromagnetic techniques for certifying the W76-1 to normal environments, for design and performance of the W76-1 radar fuze, to couple those techniques with charged particle-in-cell techniques for certifying to hostile environments, and for modeling power flow in pulsed power accelerators.