Improved Real-time Equilibrium Reconstruction with Kinetic Constraints on DIII-D

Since not all quantities of interest in tokamak plasmas can be measured directly, real-time equilibrium reconstruction codes (rtEFIT [1]) are used. However, plasma internal profiles remain largely unconstrained when only data from magnetics are used. For real-time algorithms depending on profile accuracy, it is crucial to include data from measurements internal to the plasma. The inclusion of pressure profile fits as constraints has been shown to significantly improve the shape of the reconstructed pressure profile—enabling more accurate representation of the pressure pedestal. Since these first experiments, the robustness of the algorithm against data sparsity has been improved by adding data buffers for the Charge Exchange Recombination Spectroscopy, and Thomson Scattering data. Even though the reconstructed pressure profiles consistently exhibit the pedestal as expected, the reconstructed current density profile does not consistently show the bootstrap peak when expected. To address this shortcoming, real-time equilibrium reconstruction has been extended to receive current density constraints. The current density constraints are calculated using the Sauter model and used for improved reconstruction of the bootstrap current.

[1]: Ferron, J.R., et al, Nucl. Fus. 38(1998)1055 1