|(UCSD)||Mau, Miller, Najmabadi, Tillack, Wang|
Mark Tillack has arranged for a splinter meeting in San Diego to commence on the morning of 4 May to address the design assumptions associated with the centerpost (CP). Attendance at the centerpost meeting will include key ARIES engineering members plus Ed Cheng, Igor Sviatoslavsky, and Gary Voss (of Culham). The purpose of the meeting is to try to reach agreement or understanding of the decisions by the ARIES and Culham teams to use a shielded CP, TF coil conducting material (Cu or subcooled Al), straight or flared CP, and the need/provisions for an inboard divertor slot.
To fully utilize the presence of G. Voss et al. from Culham, Farrokh Najmabadi is planning a Spherical Tokamak (ST) Physics town meeting commencing at noon on Wednesday, 6 April and running through noon on Thursday. Attendees are expected to be Farrokh Najmabadi, Steve Jardin, Gary Voss, Ron Stambaugh, Ron Miller, Rob Goldston, Ray Fonck, Bill Dove, and Martin Peng. The topic of discussion is similar to the Monday engineering meeting to reach some agreement and consensus as to the common and generic ST physics assumptions, modeling, and impact on the engineering systems and performance of the ST commercial power core.
Farrokh summarized the key points from the March IAEA committee meeting in Culham. Many of the papers reported results and findings from the Culham and ARIES ST commercial power plants. There were many similarities in their design approaches and overall findings. But the differences were most intriguing: subcooled aluminum TF centerpost with a high efficiency cryoplant, higher packing fraction in the optional Culham copper centerpost, lower plasma elongation with higher beta value, no divertor, high thermal conversion efficiency (~45%) with water cooled blankets, and a COE value in the range of 70 mills/kWh (equivalent). The EU presenters discussed the development needs for SiC structural material for fusion. The Japanese presenters reported benefits of the DREAM machine and discussed tokamak design approaches for us as a neutron source. Both EU and JA are comparing the cost of fusion electrical power production with that of advanced fission plants at levels equivalent to 60-100 mills/kWh (US$). Several papers dealt with inertial confinement experimental and power reactors. Two nearly identical papers discussed the CO2 impact and energy payback ratios associated with all major current and potential electrical power generation sources - fusion and solar looked the best on this basis.
The PPPL analyses were done with a bootstrap fraction (BS) set to less than or equal to 100%. Again it was suggested that beta might be increased if this BS requirement were lessened.
Plasma Stability (GA) - Ron Stambaugh suggested that bn should be held fixed, while bp and bt were varied. He also noted that as the stability analyses were evaluated, solutions for higher mode numbers moved the conducting wall closer to the first wall. GA has provided plasma data to Ron Miller for use in the ASC code. Ron Miller thought he might have sufficient data for the ASC code without the related EQDISK files.
Heating and Current Drive) - TK Mau asked if R. Stambaugh intended to analyze the startup requirements for the ST configuration. Ron intends to do the calculations after the final strawman is adopted.
TK is redesigning the 8.5 MHz, low frequency, fast wave (LFFW) current drive antenna configuration. It now has 16 straps, with no Faraday shield. The plasma facing enclosure is 5 m long (toroidally), 2 m high, and 0.35 m deep, which accounts for 6% of the outboard first wall area. Laila and Mark asked TK to work with Xueren to incorporate the existing 2-D sketches into 3-D drawings of the power core sector. TK is concerned that the coax leads may not be compatible with the vertical maintenance scheme. The higher efficiency, neutral beam current drive system remains as an alternate approach.
TK is also defining the High Harmonic Fast Wave (HHFW) system to provide profile control for the plasma. This smaller system uses a folded wave-guide antenna which is approximately 1.47 m wide by 1.1 m high, and 0.4 m thick.
Mark summarized the results of the Engineering Conference Call, along with new inputs from the team:
|Shield Thickness, cm||CP Copper Radius, cm||Waste Disposal Rating|
Hesham Khater mentioned specifying copper alloys with low Nb concentrations to help achieve the desired WDRs. With this grade of copper, Nickel63 is the limiting radioisotope to achieve Class C waste criteria.