NCSX Memorandum

To: T. Brown, A. Brooks, H-M. Fan, B. Nelson, D. Williamson, M. Cole, P. Goranson, R. Hatcher, C. Neumeyer, L. Dudek

CC: J. Schmidt, H. Neilson, P. Heitzenroeder, J. Lyon, S. Hirshman, M. Zarnstorff, A. Reiman. L. Berry, D. Strickler, R. Simmons, H. Kugel

From: W. Reiersen

Date: 11/02/00

Re: Minutes of 11/01 Engineering telecon

An engineering telecon was held on 11/01. Williamson presented recent progress in the design of the modular coil option [1]. The structural shell has been moved closer to the windings to provide more effective support for the coils. The shell will be segmented in 21 segments. Each segment will be joined on equi-spaced radial planes. The 21 supplemental TF coils will be mounted on flat plates that are located between the segments on these radial planes. The toroidal excursion of the modular coils extends well beyond the toroidal extent of the structural shell segments. Features need to be added that would allow the modular coils to be attached to adjacent shell segments where the modular coils are otherwise unsupported. Cut-outs in the shell are required for access. These cut-outs need to avoid the 21 parting planes.

The discussion then shifted to trim coils. Brooks has tested a concept for helical trim coils. The concept appears to work well when the coils are located close to the plasma. The m=5 set below did a nice job of suppressing the 3/5 island chain without exciting any other islands. It did this with modest current requirements (<10kA) for both saddles and modulars when located on the nominal winding surface of the saddle coils. An m=6 set for suppressing the 3/6 island chain is also shown. We will incorporate these two helical trim coils into the saddle and modular options. Williamson will define a winding surface for these trim coils for the modular design. The winding surface will be inside the modular coils and outside the vacuum vessel. The windings will be pre-fabricated on panels that are installed in 60° segments prior to installation of the vacuum vessel. Once the winding surface is defined, Brooks will generate the optimum winding path. Williamson will modify the winding path to accommodate access and assembly requirements. Modifications to the winding path must preserve stellarator symmetry. Brown will do the same for the saddle option. Brooks will be exploring concepts other than helical windings in parallel.