ARIES Documents -- Meetings ArchiveARIES Conference Call, 10 June 2003
Documented by L. Waganer
Les Waganer noted that the team is reviewing the May Livermore Town and Project Meeting minutes.
Les Waganer mentioned the next ARIES meeting will be held at Georgia Tech on 3-5 September. Said Abdel-Khalik is making arrangements for the hotel. There was some discussion about changing the order of presentations, however this would help some and hinder some. So the order remains as stated at the recent meeting: Sept 3 for ARIES-CS and Sept 4-5 for ARIES-IFE.
Status of ARIES-CS Technical Areas
Assessment of Plasma and Reactor Configurations - Paul Garabedian mentioned the impact of the MHD stability requirements might not be the limiting constraint in its current form as it is on tokamaks. He has some analysis results he wants to show the group in September regarding a three-field configuration similar to NSX. He is working to get the coils as simple as possible (easy to design and fabricate). The trick is to keep the islands from forming.
Long-Poe Ku updated the group on his work and noted similarity with Paul's work. He is working to improve the coils derived from the M50 coils. He is trying to achieve a distance of 120 cm from the center of the coil to the plasma surface, which is identified as D. He said the option to increase the field strength is to improve the plasma performance. He is able to produce plasma stability and transport parameters by matching errors. But the process is time consuming. So far he has two sets of coils that are variations of the M50 coils - one with TF coils and one without TF coils. With the TF coils, the characteristic distance, D, is around 135, 142, and 146 cm as compared to 120 cm in M50. He found that he could increase D by degrading the coil-to-coil distance, which may not be the preferred approach
Paul Garabedian noted that the flux quality is an issue. We can heal islands as done on NCSX, by modifying the coils to minimize resonance conditions. He said the healed islands are robust. Hutch Neilson said the coil perturbations are small, but larger than the coil manufacturing tolerances.
Long-Poe Ku continued by stating trim coils could be used to improve plasma performance. He said that he has been looking in the general configuration space around NCSX, however there are a lot of remaining configurations to be analyzed.
Long-Poe mentioned the two configurations without TF coils. One has a D separation of 1.42 cm and the other 1.47 cm. He said that as the coil-to-coil separation increases, the coils become more complex.
Jim Lyon said that he sent a memo to the group to respond to a question about a base configuration of 8.3 m with a higher beta that seems to be a good configuration. He also mentioned another configuration with a smaller coil to plasma distance, D.
René reminded the group of the engineering plan he proposed at the last meeting. Siegfried Malang and the UCSD group have been working on the maintenance approach and method to access the blanket components. For the sector maintenance approach, the three-field period appears to work better, while for the modular maintenance approach with a port between each pair of adjacent coils, a two field period approach would probably work better. This will be verified through future studies. René said there are CAD drawings of the CS approach on the ARIES web site. He described how the mechanical components of the reactor core could be constructed.
The coils probably have to be warm to be moved, which requires a lengthy time to keep the thermal stresses within tolerable limits. René reiterated that it is very preferable to not have TF or PF coils surrounding the CS coils.
TK Mau is still investigating the correct code to do the ray tracing for the RF system.
Summary - Hutch Neilson is concerned that the study seems concentrating too much in the general vicinity of the NCSX and not exploring more interesting parameter space that might exist elsewhere. Stellarator physics has advanced quite a lot since the NCSX configuration was adopted. He had hoped for more definition and innovation on the coil engineering.
Farrokh Najmabadi noted that the study has not narrowed in on a configuration and welcomes a wide variety of plasma and coil configurations. He thought a town meeting at PPPL in December to discuss and critically compare the approaches, configurations, and stability issues would be beneficial.