Equilibrium Reconstruction in Stellarators: V3FIT

Equilibrium reconstruction is a crucial capability in the interpretation of tokamak experiments. As stellarator plasma beta or bootstrap currents increase, the configuration of flux surfaces deviates further from that of the vacuum. As a result, there has been a growing need in the stellarator community for a fast, flexible, and easy-to-modify reconstruction code that can be used to determine the 3-D equilibrium state. We have been developing the V3FIT equilibrium reconstruction code in response to this need. Recently, a significant milestone was achieved with the implementation of the V3FIT interferometry/polarimetry diagnostic module, which uses line-integrated quantities to reconstruct both plasma density and magnetic field profiles. This module is not machine-specific, it can accomodate any number of diagnostic beams in virtually any configuration, and it provides data that is both independent and complementary to the information provided by the previously existing magnetic diagnostics module. The implementation of these two important modules has allowed us to begin to shift our focus to the designing of the tightly-coupled algorithms that are expected to be the key to V3FIT's speed and efficiency.