Attachments

Lead and transition design (Paul Fogarty- A, B)
Lead locations (David Williamson)
Keystoning (Wayne Reiersen – A, B)
Key considerations (Nelson)

Discussion. The purpose of the meeting was to select a winding scheme, either the reference one-in-hand or a multiple-in-hand option. One of the critical issues was field errors associated with the multiple-in-hand options, which have higher current and an uncompensated lead section. Art Brooks previously did a calculation that indicated that the field errors would be OK (<1% islands) with the three-in-hand option. However, this was based on an idealization of the geometry in the lead/transition region and might not be achievable. Paul Fogarty (Fogarty - A) provided some nice design concepts for the lead/transition region in a three-in-hand option that convinced us that Brooks’ calculation did accurately depict the geometry, although the loop size would have to increase by about 50% with an attendant increase in the field error at the plasma. (Following the telecon, an updated concept for the lead/transition region was provided in Attachment Fogarty-B). The increase in island size was judged to be manageable (<1.5% islands).

In order for the island to be this small, the lead locations are important. Brooks identified the area around 90% of the poloidal length as a good location from the perspective of field errors. Dave Williamson found regions close to this location where the leads could be located, putting to rest another concern with the multiple-in-hand option.

One motivation for considering the multiple-in-hand option is to reduce keystoning. Keystoning introduces risk in the design and fabrication (holding tolerances) and impacts the current density and achievable field. Reiersen discussed recent keystoning tests and their implications on achievable field. The results indicated that a higher field could be achieved with the three-in-hand option than with the reference one-in-hand option based on current density considerations. However, even with the three-in-hand option, the achievable field might be less than the goal of 1.7T.

Nelson pointed out that the change in height due to keystoning was actually being scaled by the width²/radius of curvature and thought that intuitively, this should scale as the width x height/radius. Following the meeting, Reiersen went back to reconstruct why this particular scaling was being used and reported that the constant of proportionality actually scaled with the aspect ratio (Reiersen – B).

Nelson reviewed the factors that needed to be considered in the selection and recommended the three-in-hand option. This selection was endorsed by the project (Reiersen). Following the meeting, Zarnstorff proposed an alternate insulation scheme that would improve the current density in the three-in-hand option. The project is considering this alternative.