21 November 2001

Presentations

Minutes

Our weekly telecon was held on November 21.  The main topic of discussion was the aftermath of the PAC meeting the preceding week.  At the PAC meeting, it was strongly suggested that a single design - one that satisfies both engineering and physics constraints - be presented and that all analyses be based on that single design.  This approach represents a significant departure from the direction in which we were heading.

Our initial plan was indeed to have a unified design by the end of August.  By the end of October, we still did not have a unified design so the Project made a decision to adopt a design that did satisfy engineering constraints (for instance, two coils not occupying the same space) and use that as the basis for engineering design, analysis, and costing for the CDR - even if it was a bit light on physics performance.  In parallel, the coil and plasma design folks would go off and generate a plasma configuration and coil design that satisfied both engineering and physics constraints.  It would be presented at the CDR and adopted as the engineering baseline thereafter.  John Willis (OFES), the PAC, and the Director's Office took exception to this approach, so the Project is responding accordingly.

We do not know how long it will take to develop this unified design.  There are some really promising prospects that we are beginning to look at in more detail.  However,  there is a class of engineering analyses - thermal and structural analyses of the modular coils and vacuum vessel - that take a long time to complete.  In fact, we have never performed a complete structural analysis of either the modular coils or the vacuum vessel.  One reason is that we never had coils that did not bump into each other.  It would be prudent to initiate these activities ASAP on the present engineering (1102) design.  It can be reasonably argued that the results would be germane to the unified coil design as well, provided that it is not radically different.

In order to proceed with these analyses, we need to develop waveforms (and related data) for the reference scenarios.  Neil Pomphrey will provide equilibria for the S1 (vacuum), S2 (full current, low beta), and S3 (full current, high beta) states.  Williamson and Brooks have provided the technical data that Pomphrey needs to perform the analysis.  Once Pomphrey has generated the equilibria, Reiersen will generate the waveforms and associated data.  Nelson will generate an analysis plan and supporting R&D to establish the feasibility of the design at the CDR.

There was discussion about the resistance of the cable conductor.  In past thermal analyses, we modeled the conductor as an OFHC (100% IACS) copper bar with a 75% copper fraction.  In actuality, the copper strands have a helical pitch to them.  If there was no cross-talk between the strands, the effective length would be greater and the effective area would be less, than a copper bar with the same copper fraction.  Chrzanowski has done some very preliminary tests of the cable conductor which suggest that there is a difference between a copper bar and cable conductor with the same copper fraction.  In addition, it was noted that if the strands are cold-worked, this could have a deletrious impact on resistivity, particularly at cryogenic temperature.  Nelson to propose interim guidance and R&D plans to determine conductor resistance.

In the 1102 design, the constraint on minimum radius of curvature was relaxed to ~10cm.  This will result in substantial keystoning of the conductor, which will have to be taken into account designing the winding form.  There was a concern that with these tight bends, the current center might actually shift.  Calculations by Schmidt suggest that the movement of the current center should be much less than a millimeter, which is a relief.

Tom Brown presented an alternative structural concept for the modular coils.  In this concept, grooves for 3 modular coils would be cast and machined into the outside of a shell segment that covered one half of a field period.  Brown expressed a concern that it might not be possible to machine the grooves in the trough region.  Nelson indicated a desire to further review the concept before passing it along to industry for comment as part of the manufacturing studies.  He cautioned us that we don't want them to spend time considering something we might see as fundamentally flawed.

Mike Cole presented an update on the development of the engineering design (1102).  Excellent progress has been made in developing Pro/E models of the modular coils and vacuum vessel.  Modular coil segments have been modeled.  Likewise, the vacuum vessel has been modeled and populated with ports.

David Williamson provided a comparison of the 1102 coil design with the 0918 coil design.  The 0918 coil design has much more ripple, perhaps due its use of a Fourier coil description instead of a spline description.  The 1102 produces smoother coils that do not encroach on the vacuum vessel or overlap.  Williamson showed that there are substantial areas where the radius of curvature is less than 14cm.  These could not be corrected without substantially worsening the fitting error.

Phil Heitzenroeder provided an update on the manufacturing studies.  Draft procurement specifications were posted on the Web by COB on Wednesday, November 21.  Pro/E models are now available on the PPPL FTP server.

Please forward any comments or corrections to reiersen@pppl.gov

(last edited on 11/27/2001 04:46 PM )