Pellet shattering process for the ITER disruption mitigation system - Part II: synthetic-diagnostics-based fragment tracking, calibration, and validation of simulation models

The present paper describes a methodological approach to perform a meaningful comparison between high-speed video recordings showing the dispersion of a fragment cloud after an impact event and the corresponding numerical simulations of this event. The data acquisition is based on the (automated) analysis of the image data from the experiment in order to detect fragments, to identify them across multiple frames (tracking), and to obtain quantitative data on the number of fragments and their size distribution. This data set is usually incomplete and subject to errors. In the same way, the simulation data are analyzed; these must be prepared in such a way that they are also available as image data with properties as similar as possible to the video recordings. This allows the same fragment analysis procedure to be applied and a fair comparison to be made. The paper describes the procedure applied to the fragmentation of cryogenic pellets (neon and deuterium) for the ITER disruption mitigation system and shows how this approach can be used to calibrate unknown material parameters and validate simulation models.