ARIES Project Meeting Minutes
26 January 2011
UCSD, San Diego, CA
Documented by L. Waganer
Ref: Agenda and Presentation Links: Meeting Agenda
Welcome/Agenda - Mark Tillack welcomed the ARIES team to the UCSD campus at a new location/room in EBU I. Les Waganer reviewed the day's agenda that had been shortened to only one day. A few GA guests attended the meeting to become acquainted with the ARIES program. Later Alan Turnbull gave the proposed GA plans for FY11 effort on the ARIES Study.
Next meeting and call - Tentatively, the next conference call may be in early March and a meeting in April. Les Waganer will poll the team for the best dates.
Plans and General Scope
Status and Update of the ARIES Project - Farrokh Najmabadi stressed the importance of making progress on the physics and engineering modeling for the systems code to enable the selection and examination of the four corners for the conservative to aggressive options. It is important to identify key actions to be accomplished in order to complete the program on time.
ARIES Task Results
Comments on the ARIES-ACT 1/2011 Strawman - Laila El-Guebaly highlighted the key features in the 1/2011 strawman, namely updated costing algorithms, 2009$, and elimination of LSA credits. The results featured the use of aggressive engineering technology with the SiC/LiPb blankets, helium-cooled divertor and low temperature superconductors with either conservative or aggressive physics modeling. Laila showed the prior ARIES-AT geometry along with the geometry for the two new cases, which are slightly larger in size than ARIES-AT, but with lower NWL. Laila compared the volumes and costs of the major components for the prior pre-strawman and the new strawman and pointed out the differences. The volume and cost of the LiPb has been corrected to include the factor for the BOP LiPb mass. Les Waganer is suggesting a lower unit cost for 90% enriched LiPb, but this issue is not yet resolved. Both Laila and Les are searching for a cost basis for large production quantities of enriched lithium.
The new strawman show a few changes in the recirculating power values and more updating is needed. Laila then reviewed each major cost account and highlighted any significant differences. Laila also noted the influence of the new indirect cost algorithms that were adopted from Gen IV guidelines. Laila reflected that the engineering and cost modeling is becoming more consistent with the ability to parametrically examine engineering options. Remaining areas that need more definition include:
Future work involves checking the new costing accounts provided by L. Waganer and evaluated by the new ARIES System Code.
Needful Systems Code Modifications - Lane Carlson discussed the recent code improvements including new algorithms, code structure, enhanced modeling and much needed documentation. Many team members have contributed to this improvement effort that was necessary for the systems modeling as requested by Farrokh Najmabadi. Lane illustrated a detailed record of code modifications and improvements that he and others have been accomplishing. Lane then presented the incorporation of many of the improvements that have been requested with illustrative examples. Lane concluded with a summary of the corrections and modifications incorporated and a list of additional items needed before the next strawman is issued. See the list at the end of the agenda for specific actions.
Updates and Status of the ARIES Systems Code [1) Aspect ratio scan systems solutions, 2) FW and divertor heat flux calculation, 3) ELM heat load specification] - Chuck Kessel continues to examine a broader spectrum of advanced tokamak physics parameters with more refined modeling. He then applies both physics and engineering filters to examine the intrinsic characteristics of the power plants to find the most attractive and robust operating, multi-dimensional parameter space. The real challenge is to examine the multi-dimensional parameter space with the limitations of 2-D and 3-D graphics. Multiple parameter scans are shown to illustrate meaningful trends out of the millions of data sets. Scans of the major and minor radii, combined with key parameter filters provide insight to trends and limitations.
Chuck outlined the equations and geometry for determining the FW and divertor heat loads. This then leads to the specification for the normal and off-normal transient heat loads (disruptions and ELMs) on these PFC surfaces.
Engineering Models in the ARIES System Code, Part II - Mark Tillack noted that in the prior ARIES meetings, the need for improved power modeling, power flows, thermal conversion and pump efficiencies and power density limits was stressed. Mark clearly identified the needed actions to be accomplished so that a unified plan could be implemented. Mark parameterized the pumping power requirements for the three types of helium-cooled divertors being considered as a function of surface heat flux. Another part of the pumping power definition is the MHD-induced pressure drops in the LiPb-cooled blanket, which is most serious for the inboard region with higher field strength, smaller passages and higher velocity flows. The efficiencies of pumps and mechanical turbine compressors were reviewed and new recommended values established.
From prior meetings, there were some questions about the validity of the thermal conversion efficiencies relating to NWL. Mark concluded the effect is caused by internal heat transfer, which is very design dependent. For the DCLL blanket, the surface heat flux has minimal effect below 0.5 MW/m2. Hence, the original algorithms for efficiency will be used in systems analysis for the time being. The LLNL plasma edge modeling expertise will be valuable to refine the surface heat flux modeling of the first wall and divertor regions.
The next steps are to refine the blanket divertor thermal modeling with new hardware options being considered for incorporation.
Update on GA Contributions and Plans for ARIES - Alan Turnbull summarized a two-part study approach to update an analysis of ELM scenarios with the intent of investigating an ELM-free plasma operation and then to perform a self-consistent analysis of the design points.
Alan described several ELM-free scenarios observed in existing experiments along with small ELM scenarios (shaping of ELMs, type II ELMs and type III ELMs). Alan also proposed to examine the essential physics of ELM-free and small ELMs observed in experimental tokamaks. Then the relevant physics can be modeled and scaled to the ARIES plasma size. It is widely understood that the steep edge gradients are both the cause and consequence of improved confinement in the H-mode and believed that they are also the precursor to an ELM event. Lithium-conditioning may hold promise for ELM-free operations per those in NSTX.
A benchmark study between GATO and ELITE is intended to resolve discrepancies between stability codes. This effort will continue with the goal to resolve the code discrepancies.
Alan is also interested in how the ELM-free profiles from present plasma discharges scale to the ARIES regime (especially coupling of edge pedestal stability, role of nearby wall, and the physics of the ELM suppression).
The essence of the GA proposal is to perform a self-consistent analysis of the ARIES design points to arrive at either an ELM-free plasma or with one with small ELMs.
Poloidal Distribution of ARIES-ACT Neutron Wall Loading - As an introduction, Laila El-Guebaly defined the ARIES-ACT plasma and PFC geometries. These geometries were used to create the geometric models for their neutronic 3-D codes. There are three neutron source sampling options. The exact neutron source distribution is not available yet, so the uniform source was selected to check the geometry and roughly determine the inboard blanket, outboard blanket and divertor NWLs. Laila suggested some modifications to the CAD drawing (e.g., SOL thickness, curved inboard wall and change to X-point location). Future work will involve the actual neutron and radiation source distributions that will be provided by C. Kessel.
Further Modifications to the ARIES T-tube Divertor Concept - Jeremy Burke summarized the past work on the T-tube divertor. The original design had constant cross-sections on the input and output headers, but the new design uses tapered headers to deliver more uniform flows. Jeremy showed the stress, pressure drop and maximum temperature for the new design concept. Armor thicknesses of 1 and 5 mm were analyzed (5-mm thick armor caused a maximum heat flux drop of 3-5%). Neutron irradiation will reduce the thermal conductivity by 5-10%.
Future work will involve additional internal design improvements, perhaps a flow diverter in the cartridge and a modified outer wall to make the joint design easier to fabricate. Different inlet and outlet temperatures will be analyzed along with joint fabrication analysis.
Studying Thermal Creep on a Sample Using ANSYS - Dara Navaei defined creep as a rate-dependent material with non-linear deformation under a constant load. It is also time-dependent with a rapid initial deformation, a plateau region of rather uniform rate and then a final more rapid increasing rate. ANSYS can model the first two creep stages. The divertor operates at a high temperature around 600-700°C. Creep will relax the secondary stress and decrease the total stress at operating conditions.
An ANSYS model specimen with EUROFER 97 RAFM steel properties at 650°C was analyzed and showed the typical creep strain curve within a small experimental error.
Updates on Design and Analyses of the Plate-Type Divertor - Xueren Wang summarized the current design parameters for the helium-cooled combined plate and finger (HCPF) divertor, the helium-cooled T-tube (HCTT) divertor and the helium-cooled flat plate (HCFP) divertor. The HCPF has a slightly higher heat load capacity (15 MW/m2 as compared to 13 MW/m2 for the HCTT design and 10 MW/m2 for the HCFP design) for generally the same operating temperatures and pressures. Xueren is trying to simplify the HCFP design to achieve higher heat fluxes. He analyzed his design improvements and then compared the three designs. The T-tube design can handle the highest heat load at the prescribed pumping power. The finger design can handle even higher heat loads. Xueren showed several thermal performance graphs for the new design. The simplified HCFP divertor can now handle up to 11 MW/m2 of heat flux. Further modifications are needed to increase the minimum tungsten temperatures up to 800°C.
Fracture Mechanics of Tungsten and Tungsten Alloys (No Slides) - Jake Blanchard just joined the ARIES team to investigate the fracture mechanics of tungsten and tungsten alloys to look at cracks and help increase the performance boundaries of the current divertor and first wall designs. He is planning on using both 2-D and 3-D analyses for these applications. He has done similar and relevant analyses in his HAPL work.
Update on Metrics for MFE/IFE Progress toward ARIES - Dale Meade noted that IFE has been getting a lot of attention for their recent experimental progress on NIF, while MFE has not been able to convey to the decision makers their technical progress level. There is a new National Academy of Science Committee to review IFE that will help formulate the future of IFE. Dale provided several key slides from the review. He then compared the relative progress of MFE and IFE to highlight the similarities and differences.
Update on the Fusion Nuclear Science Program Study Activity - Chuck Kessel is the key person in the Fusion Nuclear Science Program Study Activity and has been instrumental in the gathering and analyzing the necessary data needs. Chuck showed the ARIES team a document he and Mark Tillack have been assembling that contains the current data and data assumptions and requirements for a Demo plant (or power plant). This detailed data set contains data related to the plasma and the key power core subsystems. This data set is needed to establish a credible design basis for the Demo. If the data are needed, but not yet available, this data need will provide the basis for future research and development efforts. Chuck encouraged the team to review the document for areas that need additional definition and to provide that needed information.
Action Items Assigned - Les Waganer compiled a list of action items from the meeting and it is shown at the end of the Meeting Agenda as a link to the list.