ARIES Program
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ARIES-CS Project and Review Meeting Minutes

4-5 October 2006

Princeton Plasma Physics Laboratory

Documented by L. Waganer

Organization ARIES Compact Stellarator
Boeing Waganer
DOE Bolton, Opdenaker (call in)
FZK Malang
General Atomics Turnbull
Georgia Tech  
INL Merrill
MIT Bromberg
PPPL Ku, Nelson, Zarnstorff
UCSD Mau, Najmabadi, Raffray, Tillack, Wang (X.)
UW-Mad El-Guebaly, Wilson (call in)

Ref: Agenda and Presentation Links: Project and Review Meeting Agenda


Welcome - Mike Zarnstoff welcomed the ARIES team for the project meeting. Thanks to Mike for hosting the meeting and providing the refreshments.

Status of ARIES Program Les Waganer reviewed the agenda that had the review presenters giving dry runs with supporting presentations that supported the review presentations. Farrokh Najmabadi reviewed how the formal meeting would be conducted and the formal charge to the panel.

Compact Stellarator Reactor Physics Basis

Preview of Physics and Coil Presentation - Long Poe Ku discussed the ARIES-CS baseline plasma and coil configuration (ARE) that is related to the NCSX baseline configuration (3 field periods, aspect ratio of 4.5, QAS, and major radius of 7.75). This represents the smallest size plasma and coil configuration that satisfies the engineering solution. The physics parameters are quite favorable for this configuration and generally agree with projections from current experiments. Long Poe showed the latest divertor configuration, field line intersections with the plates, and heat flux peaking factors. This plasma and coil configuration moves stellarators closer to tokamaks in aspect ratio and major radius (and competitiveness). Long Poe also discussed alternate plasma and coil designs that are being evaluated (MHH2 and SNS families).

Beta Performance Limits (Terpsichore Analysis - Alan Turnbull indicated his analysis shows the ARE plasma is very stable at the baseline beta of 4.06%. The stability probably depends on profile and shape parameters. The 3/2 modes are predominately unstable when iota equals 2/3 surface enters the plasma edge.

Compact Stellarator Reactor Integrated Systems Assessment

Determination of ARIES-CS Plasma & Device Parameters and Costing - Jim Lyon examined the major factors that determined the ARIES-CS parameters, namely plasma aspect ratio, wall surface area, minimum plasma to mid coil distance, minimum coil to coil distance, and total coil length. The major radius depends on the available plasma-coil space and the neutronics results. Jim examined the optimization capabilities and the results obtained (costs, geometries, and magnetic field strengths). Jim summarized the baseline parameter results (costs and system performance) and compared these values to prior design results. He also examined sensitivities to key performance parameters.

Compact Stellarator Power Core Engineering Assessment

Preview of Power Core Engineering Presentation - Rene Raffray highlighted the key engineering constraints that impact the design and performance of the power plant (coil to plasma distance, NWL peaking factor, maintenance access, and alpha loss). The intent is to "push" all the constraints to better understand the limitations to develop an attractive power plant. The innovative 3-D analysis by UW was developed to yield NWL and radiation flux distributions over the first wall and divertor surface. The radial build was tailored to minimize the coil to plasma distance, thus reducing the power core size and costs while achieving necessary TBR, component lifetime, and plant availability. Complex coil geometries determine access locations for coolant connections, heating systems, vacuum ducts, and maintenance ports. Blankets are optimized for lifetime, TBR, safety, activation, and thermal performance. The port maintenance approach is adapted for the stellarator coil geometries and the blanket/divertor concepts and yields a reasonable availability of ~85%. The superconducting coils are wound inside a continuous monolithic structure to efficiently accommodate the EM loads. An alternative low-cost fabrication approach for the coil structure was proposed to significantly lower the fabrication cost. The divertor design is an innovative helium-cooled approach to handle peak surface fluxes approaching 10 MW/m2. Several accident scenarios were examined and the present design can meet the proposed safety requirements.

Baseline Divertor/Baffle Solution - TK Mau updated his predictive analysis tool and determined that the curved plate results were not accurate. He provided some improved flat plate analysis that had minimal number of particles following the FLs were hitting the FW while most of the particles were impacting the divertor plates. This will probably provide an adequate design for the conceptual design. The divertor pipe arrangement must be changed as the current one is insufficient for adequate shielding.

Baseline ECH Plasma Heating Solution - TK Mau did not provide any new results for the ECH system. The ECH system must provide 24 MW of power total for the startup phase. The design approach of using two 90 bends outside the coil structure, pictured by Wang and Waganer, is the preferred approach. Waganer proposed having an ECH assembly that is completely removed for refurbishment. The empty port will be used for auxiliary maintenance.

Neutron Wall Loading and Heat Flux Distributions - Paul Wilson joined via telephone to present his 3-D NWL and radiation flux results used in the review presentations. The high and low values are not at the same toroidal position. The peak neutron wall loading (NWL) was on the outboard near the zero degree location close to the midplane.

Status of 3-D Analysis and Neutron Streaming Through Penetrations - Laila El-Guebaly provided analysis results that showed inadequate shielding of the divertor cooling pipes and the vacuum pumping ports. She made some suggestions in this regard. Siegfried Malang offered to devise some maintainable design approaches that alleviate the streaming problem.

Design Definition of Stellarator Coil Systems - Leslie Bromberg addressed the fabricated cost of the superconductor and the cost of the coil support structure. He discussed the potential superconductors that might have very low fabricated (not installed) costs. The baseline material will have to be Nb3Sn because of the high field requirement, however high temperature superconductor (HTS) materials have made great improvements in the past few years.

Layout of Power Core Elements and Buildings - Xueren Wang showed the current configuration and concentrated on the changes he made in the ECH, divertor, maintenance, and top view. He has been working with Les Waganer and Rich Peipert on these areas.

Updates on the ARIES-CS Coil Structural Analysis - Xueren has been working on the structural analysis of the coil structure and the blanket module, specifically stress and displacement.

Summary of Low Cost Fabrication of Integrated Coil Structure - Les Waganer said his key slides and results were incorporated into Raffray's charts and need not be repeated.

Maintenance Approach and Availability Analysis - Les Waganer said his key slides and results were incorporated into Raffray's charts.

Safety Assessment Results - Brad Merrill said his key slides and results were incorporated into Raffray's charts.

Compact Stellarator Project Summary

Preview of ARIES CS Summary Presentation - Farrokh Najmabadi summarized the ARIES-CS project goals of being similar in size and competitiveness to advanced tokamak power plants, assess the impact of a more complex shape and geometry, and develop a compact plant design to help formulate the necessary research, development and overall program guidance. He highlighted the areas where the ARIES team had been investigating and the significant physics and engineering results obtained that addressed the project goals.


Formal Project Review Meeting, 5 October 2006

Review Members

Dr. Dale Meade PPPL, Chair

Dr. Wayne Reiersen, PPPL

Dr. Jeffrey Harris, ORNL

Dr. Daniel Driemeyer, Boeing

Additional participants

Dr. Minami Yoda, GT

Dr. Robert Goldston, PPPL

Ref: Agenda and Presentation Links: Project and Review Meeting Agenda

Welcome - Dr. Goldston welcomed the ARIES Review Committee and the ARIES Project Team for the review meeting. He emphasized the importance of the ARIES Project in general and also the significance of analyzing the Compact Stellarator to determine the key areas for future research and development while describing an embodiment of a future power plant.

Administrative - Farrokh Najmabadi introduced the review team members and outlined the review process and the day's agenda.

Formal Project Presentations - These presentations were similar, but updated, from those given the previous day during the project meeting. However, significant comments and questions/answers are noted below for each presentation.

Compact Stellarator Project Summary (Najmabadi)

Meade: Q. What is the plasma volume as compared to tokamak studies and ITER? A. ~700 m3 as compared to 300-400 m3 for advanced ARIES tokamaks and 836 m3 for ITER.

Meade: Q. How firm is the coil design? A. The NCS variant ARE is the baseline design that will be presented by Long Poe Ku.

Meade: Q. Do you calculate the 3-D NWL? A. Yes, the 3-D NWL and heat load will be presented.

Meade: Q. What are the plasma alpha power and the radiation power? A. The power flow diagram will be described by Jim Lyon and Rene Raffray.

Meade: Q. What is the plasma radiation damage to the superconductor? A. It is 1011 rads as compared to 1010 rads for FIRE. The fluence criteria is limiting the machine design.

Reiersen: Q. For conductor option 1, what does the conductor look like? A. ITER-like.

Goldston: Q. Have you considered HTS superconductor, ala ARIES-AT? A. Yes, but the higher field requirement necessitated the use of the Nb3Sn conductor.

Driemeyer: Q. Does the inorganic insulator have higher radiation limits? A. It has the same limits as the organic insulator - 1011 rads.

Reiersen: Q. Is the LCMS a free boundary? A. Yes.

Harris: Q. Does the complexity and parameters of the coils drive the design? Can you relax the MHD limits to ease the engineering parameters? A. Probably, yes.

Driemeyer: Q. Is the MHH2 a larger or more accessible design? A. Yes, it is larger and probably more accessible, but a fully integrated solution would be needed for an equitable comparison.

Compact Stellarator Reactor Physics Basis (Ku)

Meade: Q. Have you analyzed the fast particles? A. Yes, a slide will address this. Use Guiding Centers.

Unknown: Q. Have you identified the outstanding issues? A. Not yet? (I believe Mike Zarnstorff has compiled such a list after the meeting.)

Compact Stellarator Reactor Integrated Systems Assessment (Lyon)

Meade: Q. What is the impact of employing the shield-only designs? A. This is assessed in the full blanket case as compared to the baseline case.

Meade: Q. Does the code have a fixed Availability value? A. The Availability is assumed to be 85%, which is supported by Les Waganer's analysis results. He has also examined the availability of other maintenance options. The systems code can do a sensitivity analysis with range of Availability values. Availability is affected by wall life (3.9 FPY vs. 3.0 is a recent change.)

Meade: Q. What is the cost of maintenance, i.e., assessing longer lifetime blankets? A. We have not made an in-depth assessment of longer lifetime blankets or changing the major radius to achieve a lower NWL (hence, longer life blankets), but such an assessment is possible (lifetime versus larger capital costs trade).

Unknown: Q. What are the unit cost of components and materials? What about complexity factors for stellarators. What about inflation? A. We use unit cost of materials for different materials and complexity of these materials in different complex components. These are adjusted for current costs and related back to prior design studies for comparison. We use the Gross Domestic Product as the price level deflator (inflation) for yearly comparisons. Complexity is somewhat addressed in the materials costs and the methods of fabrication considered.

Compact Stellarator Power Core Engineering Assessment (Raffray)

Reiersen: Q. Is the plasma radiating as much heat as possible? A. Yes

Harris: Q. Do you analyze the heat transfer through complex structures? A. The blanket module is analyzed in 2-D. An assumption of plane strain (no strain in the third dimension) is used to obtain an upper bound stress estimate.

Harris?: Q. What is the basis of the 200 dpa lifetime limit? A.ORNL has provided guidance for the FS structure being used.

Reiersen: Q. What is the criteria for the design stress limit? A. Primary plus secondary stress < 3 x Sm. In our blanket analysis, the primary stress is pressure stress and the secondary stress is thermal stress.

Meade: Q. How many maintenance ports? A. Three primary ports plus 3 auxiliary (ECH) ports.

Reiersen: Q. Have you considered and made provisions for thermal expansion (hot structure vs. cold structure)? A. All hot components are mounted on a hot structure, which can expand freely on the bottom of the structure. However we have not accounted for vertical expansion yet.

Meade: Q. Is there a force balance at the field period interfaces? A. Yes, there is a force balance in all directions except for a net inward radial force. The stress and displacement is shown to be very small at the coil structure period interfaces.

Driemeyer: Q. Are there any halo currents or disruptions to be considered? A. No.

All: Q. Are there any experiments that have wound the coil cables from inside the coil shell into grooves? A. Not to our knowledge. NCSX winds on the internal surface but not in a groove and not an S/C cable. Other stellarator experiments winds S/C in the internal surfaces, but probably not in a groove.

All: Q. What is the method of supporting the divertor and how is maintenance provided? A. Rene Raffray will address that subject.

Unknown: Q. Have you considered a circular coil pack? A. For strength purposes and movement within the coil pack, it is better to have a square or rectangular cable.

All: Comment. The review team is very impressed with the level and fidelity of the analysis and design of a conceptual design that would lead to a commercial power plant. Individual Comments by Reviewers: All reviewers verbally provided feedback and suggestions. Rather than paraphrase their comments, it would be better to wait and view their written comments and recommendations.