ARIES Team Conference Call

13 April 1998

Documented by L. Waganer



Participants:
(DOE) *
(UCSD)Mau, Miller, Najmabadi, Tillack, Wang
(PPPL)Jardin, Reiersen
(GA) Stambaugh
(UW) El-Guebaly, Khater
(FPA) *
(RPI) Steiner
(ANL) Billone
(Boeing) Waganer

Administrative

The next ARIES project meeting dates were affirmed as 4 May (1:30 pm) through 6 May (noon) in San Diego. The following ARIES project meeting is still scheduled for the full days of 6-7 August at ANL. If needed, it was recommended an Engineering or Physics conference call be scheduled for 27 April (Call Les Waganer for a conference call number, if required.)

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.

Plasma Physics

Plasma Stability (PPPL) - Steve Jardin reported that Bob Miller of GA sent the plasma profile data to PPPL for comparative equilibrium and stability analyses. These profiles are broader than the previous ones PPPL had used. PPPL is finding that the GA profiles indeed have high ballooning mode limits, but if you consider the low-n (up to n=6) stabilitylimits with a conducting wall at b/a = 1.2, then the maximum stable beta comes way down. If you restrict the triangularity (d) to be 0.55, then to get the low-n modes stable, the elongation (k) must decrease below 3. The net effect is that at an aspect ratio of 1.6, the maximum stable beta with the GA profiles is about 40%, about the same as for the profiles that the ARIES project is now using. This will be investigated further, and presented in detail at the upcoming project meeting.

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.

Systems Studies

Ron Miller posted the latest strawman, Case J, on his web site over three weeks ago and has received minimal comments from the team. Case J assumes a straight CP but a high copper filling fraction. To assure the team has a unified and common data point for the next project meeting, it was recommended that Case J be adopted as the calculational basis for the next meeting.

Engineering

Mark Tillack agreed that Case J should be adopted for the next meeting. By the end of the week, new CAD drawings would be provided to PPPL for the design development of the TF and PF coils. This would allow a more detailed analysis by Bromberg on the PF coils.

Mark summarized the results of the Engineering Conference Call, along with new inputs from the team: