Verification and validation for magnetic fusion

Dramatic progress in the scope and power of plasma simulations over the past decade has extended our understanding of these complex phenomena. However, as codes embody imperfect models for physical reality, a necessary step toward developing a predictive capability is demonstrating agreement, without bias, between simulations and experimental results. While comparisons between computer calculations and experimental data are common, there is a compelling need to make these comparisons more systematic and more quantitative. Tests of models are divided into two phases, usually called verification and validation. Verification is an essentially mathematical demonstration that a chosen physical model, rendered as a set of equations, has been accurately solved by a computer code. Validation is a physical process which attempts to ascertain the extent to which the model used by a code correctly represents reality within some domain of applicability, to some specified level of accuracy. This paper will cover principles and practices for verification and validation including lessons learned from related fields.