Computational Atomic Physics for Fusion Energy
Why it Matters: Atomic processes are central to energy transfer in magnetically confined plasmas. The energy balance in fusion devices such as tokamaks depends critically on how the plasma interacts with the walls of the vessel and so accurate ionization and excitation cross section and rate data are critical. Calculations directly support divertor and wall erosion studies at experimental facilities such as DIII-D, Alcator C-Mod, JET, and ASDEX-Upgrade as they test critical design issues for ITER and beyond and support science at advanced light sources, heavy particle storage ring facilities, and cold atom experiments.
Key Challenges: The essence of the problem is to describe the correlated quantum dynamics of free electrons moving in the long-range Coulomb field of a third or fourth body. Requires solution of the time-dependent Schrödinger equation but because multiple ionizations (for example, one photon in with two electrons out) and electron-impact ionizations are involved, both of which are multi-body problems, an 'exact'' description of the system's final state isn't known. This requires a direct solution of the problem by numerical propagation of the time-dependent Schrödinger equation, an enormously computationally demanding task. Time-dependent close-coupling and the R-matrix with pseudo-states methods continue to push the limit of what is possible with each new generation of computing hardware.
Accomplishments: Recent work in this area has resulted in computational milestones carried out in collaboration with an international group of scientists providing measurements at the Berkeley Lab Advanced Light Source synchroton. Examples include the first-ever calculation of atomic nitrogen K-shell spectrum and cross sections; high-resolution absolute photoionization cross-sections for the Ar+ ion, the Li-like boron ions [B2+], and the Be-like C2+, N3+ and O4+ ions. Recent code improvements for relativistic photoionization effects have opened the door to a host of even larger scale calculations on trans-Fe elements, Se, Kr, Xe, Br, Ge,... and more recently Tungsten ions, in support of ongoing experiments at the ALS and even the current flagship NERSC system (Hopper) is being pushed to its limits with calculations on systems like Ca+ and Fe7+.
Investigators: M. S. Pindzola, C. P. Ballance, J. A. Ludlow and others at Auburn University; J. P. Colgan and C. J. Fontes, Los Alamos National Laboratory; B. M. McLaughlin, Harvard Smithsonian Center for Astrophysics
More Information: See, for example, PRL 107, 033001 (2011), J. Phys. B: At. Mol. Opt. Phys. 43 (2010) 225201, PHYSICAL REVIEW A 84, 013413 (2011), and The Atomic Data and Analysis Structure (ADAS) web site.