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In support of the National Compact Stellerator Experiment (NCSX), stellerator assembly activities continued this past year at the Princeton Plasma Physics Laboratory (PPPL) in partnership with the Oak Ridge National Laboratory (ORNL). The construction program saw the completion of the first two Half Field-Period Assemblies (HPA), each consisting of three modular coils. The full machine includes six such sub-assemblies. A single HPA consists of three of the NCSX modular coils wound and assembled at PPPL. These geometrically-complex three-dimensional coils were wound using computer-aided metrology and CAD models to tolerances within +/−- 0.5mm. The assembly of these coils required similar accuracy on a larger scale with the added complexity of more individual parts and fewer degrees of freedom for correction. Several new potential positioning issues developed for which measurement and control techniques were developed. To accomplish this, CAD coordinate-based computer metrology equipment and software similar to the solutions employed for winding the modular coils was used. Given the size of the assemblies, the primary tools were both interferometeraided and Absolute Distance Measurement (ADM)-only based laser trackers. In addition, portable Coordinate Measurement Machine (CMM) arms and some novel indirect measurement techniques were employed. This paper will detail both the use of CAD coordinate-based metrology technology and the techniques developed and employed for dimensional control of NSCX sub-assemblies. The results achieved and possible improvements to techniques will be discussed.

The National Compact Stellerator Experiment (NCSX) is being constructed at the Princeton Plasma Physics Laboratory (PPPL) in partnership with the Oak Ridge National Laboratory (ORNL). The complex geometry and tight fabrication tolerances of the NCSX's non-planar coils and vacuum vessel necessitate the use of computerized, CAD-based metrology systems capable of very accurate and reasonably quick measurements. To date, multi-link, portable coordinate measuring machines (pCMM) are used in the fabrication of the non-planar coils. Characterization of the CNC machined coil winding form and subsequent positioning of the conductor centroid (to within +/-0.5 mm) are accomplished via multiple sets of detailed measurements. A laser tracker is used for all phases of work on the vacuum vessel including positioning magnetic diagnostics and vessel ports prior to welding. Future tasks requiring metrology include positioning of the magnet systems and assembly of the three vacuum vessel sub-assemblies onto the final machine configuration. This paper describes the hardware and software used for metrology, as well as the methodology for achieving the required dimensional control and will present an overview of the measurement results to date.

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.