Dynamic Strain and Temperature Instrument for NCSX Coil Development

The National Compact Stellarator Experiment (NCSX), a fusion research device, is being designed for improved plasma confinement and stability by applying a novel three-dimensional magnetic field configuration. The external magnetic field shaping is implemented by using 18 stellarator coils that are in a quasi-axisymmetric configuration and installed as toroidal modules. Emphasizing both plasma properties and geometrical constraints has been used for optimizing coil-winding shapes. Such modular coils are wound by using flexible, copper cable conductors that are compacted into rectangular shapes. Once wound, the conductor is vacuum impregnated with epoxy. The epoxy-filled conductor becomes a monolithic copper epoxy composite. Prototype coils have been designed, fabricated, and tested for the NCSX modular coil development. Physical properties, such as strains and temperatures on the prototype coils measured under simulation tests, are very important for designing reliable and long lifetime NCSX modular coils. During the simulation tests, the sensors have to be attached at different locations on the coils and would be immersed inside the liquid nitrogen pool. The signals measured from conventional electrical sensors could be degraded by the strong electromagnetic noises generated by the exciting current flowing in the test coil. To improve accuracy of strain and temperature test data, the fiber-optic strain measurement system that was developed for the spallation neutron source (SNS) mercury target development, is applied to the NCSX coil development. The miniature fiber-optic sensors are attached on the test coils at locations where the data of dynamic strains and temperatures are very important and of interest to engineers. Engineers could use the measured data to benchmark and improve sophisticated computer modeling codes for modular coils design. In this paper, the instrument for measuring strains and temperatures and test data collected from room temperatures to -190degC will be presented and discussed