University of Wisconsin-Madison Physical Sciences Lab

Friday, April 25th, 2014

PSL recently received funding to assist in upgrading some plasma diagnostics on the National Spherical Torus Experiment (NSTX) located at Princeton Plasma Physics Laboratory (PPPL). The NSTX is currently undergoing a $94-million upgrade, NSTX-U, that will double its current and heating capacity and the strength of the plasma confinement magnets.

PSL mechanical engineer Ken Kriesel and CAD specialist Glen Gregerson are working with Dave Smith of UW-Madison Engineering Physics and George Labik of PPPL to design a new fiber optic front-end assembly for NSTX-U. This will pack nearly double the density of fiber optic bundles into the same small space. Fifty-four bundles (each containing 9 fibers), plus some accessory equipment including thermocouples and air cooling paths, and all the mounting, total hundreds of separate pieces including spacers and fasteners, yet must fit inside a cylindrical volume less than 2.32″ in diameter, previously occupied by its predecessor containing only 28 bundles.

A complicating factor is that since one of the requirements of the NSTX-U upgrade is to reduce the magnetic permeability of the experiment’s components, the choices of materials for machined parts and fasteners are quite limited.

Assembly of the device must be performed in place on NSTX-U, due to the space restrictions present. New features are incorporated to aid what was already a difficult assembly process with 28 fiber bundles, and will be more challenging with the increase to 54 bundles.

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