Impact of COMPASS-U vacuum vessel and the first wall structures on signals of in-vessel magnetic diagnostic coils
Abstract
The paper evaluates the impact of metallic structures of the COMPASS-U tokamak design on signals measured by in-vessel magnetic diagnostic coils. The eddy current shielding caused by the tokamak conductive structures of the vacuum vessel and plasma facing components is evaluated using finite element analysis performed by ANSYS Maxwell software.
The simulation of the sudden shifts in the radial or vertical position of the plasma column returns 33-45% amplification of the tangential field component that from the most part would be analogous to a simple lumped circuit model approximation, despite the complex 3D shape of the nearby plasma facing components. The simulation of a rotating helical filament close to plasma edge (approximating a rotating magnetic island magnetohydrodynamic (MHD) structure) reveals an unexpected spatial modulation of the magnitude attenuation coefficient of up to 45% for the tangential field component across different positions relative to the PFC holders.
Both results have led to the described conclusions for the sensor positioning design, specifically to the decision to install plasma position feedback sensors in between the robust holders of the PFC tiles, and the plasma MHD activity sensors strictly symmetrically with respect to these PFC structures.