National Compact Stellarator Experiment Vacuum Vessel External Flux Loops Design and Installation

The national compact stellarator experiment (NCSX) will have an extensive set of external magnetic diagnostics. These include flux loops on the exterior surface of the vacuum vessel. Data from these sensors will be integrated with other magnetic sensors and used for plasma control and to constrain magnetic equilibrium reconstructions. NCSX is currently under construction at the Princeton Plasma Physics Laboratory (PPPL). The ex-vessel flux loops must be installed during machine construction since they will ultimately be trapped in the space between the vacuum vessel and the modular coil support shell. Detailed designs have been completed, locator templates have been fabricated and approximately one third of the 225 total loops have been installed as of mid February 2007. Modeling was performed by PPPL to determine the optimum size, placement and number of turns. Engineering of the flux loops was challenging as they must be accurately positioned, optimized geometry maintained and they must be robust and reliable in a bake and cryogenic environment for the lifetime of NCSX. Designs for the ex-vessel flux loops that meet these requirements are presented.