ARIES Engineering Conference Call

Administrative

Laila El-Guebaly reported that the US-Japan Workshop on Spherical Tokamaks held last week in Madison, WI. was well attended despite the snow storm. Steve Jardin gave a presentation on the physics and engineering analyses and results for the ARIES ST study.

General Summary

Mark Tillack led the discussion with the following points being discussed.

• Configuration Control - Mark Tillack mentioned that he wanted to document the current engineering configuration. The use of a Design Data Book similar to the ARIES-RS book is planned. Also included will be the engineering drawings of the power core (see below). At present, a preliminary elevation view is available for evaluation and assessment. Mark stressed that after the next project meeting, the 3-D modeling will begin.

• Elevation View - Mark noted that the current elevation view is largely notional at present and does not accurately reflect the latest, and certainly not the final, strawman configuration. But it is felt that it is within 10% of the final geometry. It does contain the concept of the spherical shell for return TF legs. Wayne Reiersen noted that the thickness of the return TF legs should be proportional to a 1/R relationship to maintain constant cross-sectional area. Moreover the area in the TF legs should be on the order of 10 times the area in the centerpost. Xueren should finish up the inner power core drawing for transmission to Wayne Reiersen. Wayne will complete the TF coil layer within a week and send it back to Xueren for drawing completion.

• Power Core Configuration - Maintenance is still planned to be accomplished from the bottom, with insertion and extraction of the power core via large hydraulic pistons. A vendor has been found that can supply a piston with a lift capability of 1000 tonnes; hence, approximately six pistons will be required to support the empty power core. There will be passive structural beams to support the power core during the operational periods in place of the hydraulic lift system. These are shown in an ARIES-ST elevation view of the power core.

  

  The inboard shield has once-through cooling, and therefore the coolant should be routed from top to bottom through the blanket/shield. Since the coolant will be hot and the shield cold, it was decided best to route it behind the blanket as part of the hot structures.

  The coolant path from the top of the centerpost is a special case, and probably will not be routed back to the bottom, since it's outside the vacuum boundary. Since it was agreed to try use the TF shell as the VV, all joints and breaks in the TF system must be covered by bellows of some kind, TBD.

  Dai-Kai Sze mentioned that the lithium-lead flow is a once-through approach (Mark noted after the call that the PbLi coolant comes in the bottom, turns at the top and then comes out the bottom, which would correspond to twice through. D-K Sze has started on a inboard shield flow arrangement for the helium coolant systems, which will be provided to M. Tillack. Dai-Kai thought it would not be a problem to locally reroute the helium and LiPb coolants around the heating and current drive components in the outboard region. Dai-Kai also agreed to consider modifying the blanket geometry away from modular construction and toward single-piece construction.

  Mark referenced the drawing which placed the vacuum vessel outside the PF coils, but Wayne Reisersen noted that at the January meeting, the group had decided to place the vacuum vessel inside spherical TF coil legs. The group discussed whether or not the TF shell could serve as a vacuum vessel since it must have breaks. Wayne said that, based on his discussions with Charlie Neumeyer, they felt the TF shell would not need slits, and that bellows could be used at breaks to provide leak-tight vacuum. So it was affirmed that the vacuum boundary would be just inside the TF outer coil legs.

  The position of the upper and lower two PF coils is not finalized yet. Locating them either inside or outside the TF coils is being considered. The innermost one would be difficult to locate outside because of the thickness of the TF coils near the centerpost. Therefore, the TF coil configuration should be established and then the location of the PF coils will be evaluated. The thickness of the upper TF shell may approach a meter.

  The position of the TF coil leads was discussed. The position shown in the current elevation view is just above the midplane. E. Mogahed suggested moving them closer to the centerpost. However, a connection near the centerpost is in the thickest TF coil cross-section which would make it difficult to make the connection. Moving the lead connections to the bottom would place them in the maintenance area, which would be undesirable. Therefore it was decided to keep them close to where they are currently shown.

  The vacuum pumping ducts are located at the top of the machine, provided there is adequate vacuum conductance from the vacuum port at the bottom of the machine. The vacuum pumps would be located close to the device at the upper level.

• Uniformity of TF Coil Currents - Wayne Reiersen reported that he had met with Charlie Neumeyer who felt the power supplies could be regulated sufficiently to have nearly identical currents. Thus the currents in the legs should be close to identical and there should be no current sharing. The method of construction of the TF shell is yet to be determined, but HIPPing is possible.

• Centerpost Configuration - Mark Tillack said that UCSD had decided to retain the inboard divertor slot as a conservative design approach. The level of particle and heat flux is low on the inboard; hence, a design solution should be achievable. The plasma physics of a limited or diverted plasma is similar in this geometry. With the retention of the inboard divertor slot, the centerpost will be straight and the joule losses will be higher than with a flared centerpost (CP). The decision to use cold or warm water cooling has not been resolved yet. Wayne Reiersen agreed to conduct a trade study to make a design decision on the centerpost cooling.

• Centerpost Resistivity - Hesham Khater reported that he had rerun the radiation damage calculation for the straight centerpost and would forward the data to R. Miller and W. Reiersen for their use. Laila mentioned that, if the centerpost is radially larger, she can use a thinner shield for similar waste disposal ratings. She will provide a parametric relationship of CP copper radius to shield thickness for input into the systems code to help quantify the centerpost trade studies.

• Retention of Tritium in SiC Insulator - Dai-Kai Sze said he had talked to Rion Causey who had some additional data on the retention of tritium in SiC. Dai-Kai will distribute the data to interested team members.

• RF Heating and Current Drive Options - Mark Tillack reported that T.K. Mau is evaluating LFFW (low-frequency fast-wave) system for central current drive. Another system is needed for current profile control. T.K. has defined the general characteristics of a HHFW (high-harmonic fast-wave) system for profile control. In both cases, the FW coverage is large, but the amount of material and depth into the blanket are small, such that the impacts are felt to be acceptable. Neutral beams are still the backup option.

• Passive LOCA Cooling Option - Les Waganer remarked that he had distributed a design option that would not impose an operational heat leak, but would be an effective passive conductive heat transfer approach between the hot shield and the cool centerpost. The group agreed that this approach would solve the LOCA conductance problem. (Following the call, Dai-Kai expressed concern that in a vacuum, the surface contact of small spheres would provide insufficient conductance. However, addition of a gas would probably provide adequate conductance.)

• Pre-Strawmen Computer Results - Ron Miller briefly reviewed his seven pre-strawmen results (A through G) to quantify incremental physics and engineering changes. Part of the analysis is to understand the differences between the more aggressive GA design (high beta, no CP shield, flared CP, and a higher copper filling fraction in the CP) and the more conservative ARIES design. One of the parameters investigated is to increase the neon concentration in order to raise the plasma radiation factor to the range of 50%; however, 40% seems to be the current limit.

  Ron also included a table on the web site which listed results regarding the straight versus flared centerpost with different filling fractions.