Unification of fully implicit fluid edge-plasma transport codes

The authors are developing a modular 2-D edge-plasma transport code that incorporates pieces from three existing fully implicit codes: LEDGE, NEWEDGE, and NEWT-1D. The modularity allows the users to choose from different physics models and numerical algorithms, and allows new models to be introduced in a straightforward manner. The new code is named UEDGE. The physical model of the plasma is given by the Graginskii equations with the addition of anomalous transport across the magnetic field lines. Plasma currents and cross-field E x B and diamagnetic drifts have been added. The code is written for multi-species to include various charge states of impurities, but initially will contain an average-ion description for the impurities. The neutral gas model contains two species, a charge-exchange group and a Franck-Condon group. The atomic physics data for ionization, charge-exchange, and radiation come from ADPAK. The use of a fully-implicit method requires calculating the Jacobian matrix, which can then be solved by direct or iterative methods. As the solution of the matrix typically takes the majority of the computer time, the authors present a timing comparison between a direct Newton method, an iterative Newton method, a preconditioned Krylov Newton method, and time-dependent schemes. The overall structure of the code is described together with a set of sample problems