Calibrating mix models for NIF tuning

Mixing may play a role in early 'tuning' implosions at the National Ignition Facility (NIF), intended for optimizing target geometry and laser operating parameters prior to the first ignition shots. Turbulent transport models allow mixing to be represented in integrated capsule-plus-hohlraum simulations, so that its effects can be predicted. Such models typically have many adjustable coefficients, so it is important to calibrate the coefficients systematically, whether by comparison to experiments, theory, or detailed higher fidelity simulations. We have begun by comparing to results from high-resolution 2D multimode simulations of a NIF Rev3 CH(Ge) ignition capsule, using the time-varying angle-averaged radial profiles of ion species composition as the calibration reference. 1D implosion simulations are performed with either of two turbulence models, and the models are calibrated so that the 1D composition profiles roughly match the 2D reference profiles at a sequence of five times near the end of the implosion. Details of the reference profiles, however, such as non-monotonicity resulting from structures in the flow, cannot be represented by these models. Parameter searches, besides identifying optimal sets of model coefficients, also exhibit model sensitivity to parameter variations.