NCSX Memorandum

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

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

From: W. Reiersen

Date: 1/18/2001

Re: Minutes of 1/17 Engineering telecon

An engineering telecon was held on January 17. The objective of the meeting was to leave with a clear understanding of what work and deliverables are required to be completed in the next six weeks.

Phil Heitzenroeder started the meeting by reporting on some design features that appear desirable for assembly. He would like to pre-assemble the stellarator core in thirds, if possible, prior to bringing the sub-assemblies into the test cell for final assembly. The best place for pre-assembly would be the empty TFTR test cell. Two concerns with assembling the stellarator core in thirds are size (can we fit it through the door into the NCSX test cell?) and weight (can we lift one third of the stellarator core with an upgraded overhead crane?). Heitzenroeder argued for a bolted joint on the v=0.5 plane for final assembly. With a 150C bakeout (assuming a 350C stand-alone liner), the bolted joint could use double Viton seals with a pumped inter-space. The bolts would be tightened from the inside of the vacuum vessel. This should create a reliable joint and avoid problems associated with welding (weld distortion and very tight space) during final assembly. This would allow many of the in-vessel components to be installed prior to final assembly and greatly expedite the assembly process. Another advantage of the bolted joint would be that the machine would be disassemble-able. This could be a significant advantage in the event that a major failure or reconfiguration was required. The main concerns appeared to be the extra space and complexity required for the bolted joint.

The three (one-third) machine sectors would be brought together by moving them radially inward. Nelson indicated that it might be necessary to bring the three sectors together simultaneously to avoid interferences. Brown will develop a concept for the base assembly that is consistent with this assembly approach.

Cole discussed NB access in the reduced size machine. The reduced size machine presented by Cole was reduced by a factor of 0.80 from the previous (1.7m) design. The reference size is 0.82 times the previous design. Cole indicated that he would update the model accordingly. The model that Cole presented had the beam well aimed at the plasma. The beam was almost entirely within the plasma except at a few isolated locations. However, it is plausible that the heat loads on the first wall might be easily tolerated due to the fact that the beam was emerging from the plasma and that only the fringes of the beam would infringe on the first wall and at a very slight angle of incidence. It is also conceivable that the first wall could be moved a bit further away to avoid this interference altogether. We agreed that this probably did not present a feasibility problem and would pursue it in more detail after the PVR. The outboard legs of the modular coils on the v=0 symmetry plane and of the modular coils adjacent to the coils on the v=0 symmetry plane were a greater concern (as seen in the figure below).

The modular coils, photographically shrunk from the 1017 modular coil design, clearly encroach on the vacuum vessel. Ditto for the TF coils, which might pose an even more severe constraint. We should try to solve the NB access problem by moving the outer legs of the modular and TF coils to avoid interference with the VV and drift ducts. If this is not possible, then we might have to make the case that we need to go to 18 coils after the PVR.

Nelson provided a nice comparison of the build elements for the previous and new reduced size designs (as shown in the figure below).

In the layout above, the thickness of the SOL and VV/FW envelope was held fixed, which is a reasonable assumption. This means a disproportionate reduction in the size of the winding packs for the modular coils needs to be made. The current machine parameters were based on a photographic reduction in the machine size. Folding these fixed build elements into the calculations will increase the current density and may limit the field that can be attained with a 0.2s flattop. ORNL should define the radial build for the reduced size machine and the new winding pack dimensions ASAP. Reiersen should recalculate the performance parameters upon receiving the new coil dimensions.

Nelson also provided an update on the costs based on his spreadsheet calculations for the reduced size device. The cost of the stellarator core (WBS 1) came down $8.3M from the 1.7m device. The data Nelson provided suggested that further cost reductions are required to meet our $55M bogey. Nelson and Heitzenroeder discussed their plans to get input on costs from vendors. ORNL is preparing a technical data package for the reduced size machine. They expect to be finished this week. ORNL will contact the group at Y12 for input on machining costs. ORNL will contact Southern Centrifugal and Rondelet(?) for input on casting costs for coil structures. PPPL will contact US Bronze for input on casting costs for coil structures and for casting costs and feasibility for the vacuum vessel. PPPL will contact Everson for input on winding costs. PPPL will contact Kharkov for input on vacuum vessel costs and fabrication processes. Simmons noted that the contract with Kharkov has not been signed so it is not clear whether we will be successful in getting input from them for the PVR. Input is expected back the week of February 7. A list of upcoming cost and schedule reviews has been posted on the Web. WBS 1 costs based on vendor inputs are scheduled for review February 7.

Brown prepared a presentation showing an alternate design concept. ORNL show review the concept and determine next steps.

Brooks provided a very informative review of the progress that has been made in trim coil design. He showed that the critical locations are near the inboard and outboard midplanes at the v=0 (banana-shaped) cross section. This is where the coils are physically closest to the resonant surfaces. It also suggests that the proximity of the coils to the plasma will be a strong factor in determining the amp-turn requirements for the coils. We need to show for the PVR that there exists a plausible design solution for trim coils. After much discussion, it was decided that Brooks would pursue the trim coil design on a surface offset 5cm behind the nominal first wall surface. The nominal first wall surface is located 2cm off the reference plasma boundary on the inboard side and 10cm off on the outboard side. It appeared that we could get by with the fewest number of coils and electrical circuits by designing a set of picture frame coils for the m=5 resonance and a separate set for the m=6 resonance. This would hopefully result in the lowest cost solution. Brooks will define the geometry for these coils and pass them to ORNL. ORNL will resolve interferences with the neutral beams and other immutable features and pass back a revised geometry to Brooks to recalculate currents and effectiveness. Once the coil geometry and currents have been set, a design concept for the trim coils will be developed. Hopefully, they can be conduction cooled to an actively cooled support structure (like the vacuum vessel on the inboard side). Coil current and voltage requirements will be generated for the multi-turn coils and passed on to the electrical power folks for power supply design and costing.

Reiersen closed the meeting with a review of upcoming milestones and deliverables. We are on an exceedingly tight schedule preparing for the PVR. Please pay strict attention to the upcoming milestones and deliverables so we can stay on track for our PVR preparations.

The next Engineering telecon will be held next Wednesday, January 24, at 1:30pm. Please provide the following information in advance of the meeting:

Assess feasibility of bringing in one-third of the stellarator core into the NCSX test cell and lifting it with an overhead crane (Chrzanowski/ORNL)

Provide comparative assessment of bolted v. welded joint for final assembly, recommendation for PVR (ORNL)

Define radial build for reduced size machine and new winding pack dimensions (ORNL). Recalculate performance parameters (Reiersen).

Update assessment of NB access at reduced (0.82) size (Cole). Is beam scraping required? Is there a 21 coil solution or do we need to go to 18 coils?

Provide assessment of Brown’s alternate design concept (Nelson).

The telecons have been running TOO LONG. If you could provide requested info via e-mail in advance of the meeting, we could cut down on the material that we really need to go over. In addition, I will post an agenda prior to the telecon with scheduled time slots. Those folks who are interested in only a subset of the items on the agenda could plan on attending only part of the meeting. Thank you for your continued patience and hard work!