|(UCSD)||Mau, Miller, Najmabadi, Tillack, Wang|
M. Tillack reported that the FED proofs are ready for publication at the printers. Also, UCSD is planning to print additional copies for distribution.
Equilibrium Solutions - The PPPL physics group is attempting to find relatively high beta, stable ST plasmas that do not need conducting walls or shells for kink stability. Many of the key plasma parameters remained fixed for the study, such as:
They found an equilibrium condition with a beta of 18-20% and a bootstrap current fraction of 93%. They also found another case with higher beta (27%), but the bootstrap current fraction was reduced to 50%. It was recommended that the former case be evaluated in the systems code. An EQDisk file will be sent to Ron Miller to help evaluate the case. PPPL will complete the evaluation of this data set to determine if it is vertically stable. The TEQ code is not converging on this data set, so the TSC code is being used instead.
Since many of the prior stable equilibrium cases were for bootstrap current fractions close to 1.00, is it possible to relax the engineering constraints if the bootstrap current fraction to less than or equal to 95%? PPPL is looking into that question but has not completed the investigation.
D. Steiner asked the relationship between stability and conduction walls. Steve Jardin summarized that for vertical stability, on a short time scale, the conducting wall is needed; whereas active coils and feedback are required for longer time scales.
The group was becoming concerned about the lack of interaction and reporting from GA, especially regarding the physics around the divertor region. S. Jardin will contact R. Stambaugh as to the GA effort in the physics area. Steve may also contact M. Peng to help collaborate the partitioning of the transport heat.
Current Drive - TK Mau is investigating the neutral particle beam as an on-axis current driver, as it can penetrate to the plasma core if the beam energy is high enough. The low frequency, fast wave current drive option would require an antenna that is too large to be credible.
TK Mau reported some theoretical work by K.C. Shaing of UT-Austin that indicated there can be a ballooning stable plasma solution with a stable, self-consistent, 100% bootstrap, reversed shear equilibrium. No kink stability analysis has been done on this data set.
Mark Tillack now has an Excel spreadsheet from GA which calculates the distribution of the radiation in the divertor region onto the divertor geometry. Mark's current finding is that there is insufficient room for inboard divertor plates unless the centerpost is straight. The flared centerpost does not allow enough room for the inner divertor components. With the straight centerpost and if there is a 20-80% split of radiated power (inboard to outboard) and a 40-60% split of power between the divertor and the core, then the surface of the divertor can accommodate a heat flux of 2 MW/m2 on average and a first wall heat flux around 0.5 MW/m2.
Blanket - Dai Kai said that at the meeting he would concentrate on the technical issues of the ferritic steel (FS) blanket that uses LiPb, helium coolant, and a SiC thermal insulator. Mike Billone is investigating other insulating ceramic materials. Jake Blanchard is working with Sze on the support techniques to mount the 10 g/cc dense blanket. Sze also noted that it is not feasible to use the helium as the coolant and as the tritium purge gas. The resultant flow rate would be too high and the tritium permeation would be unacceptable. It is a problem to find a suitable material for the thermal conversion heat exchanger. D-K Sze noted that the insulating oxide material will be on the inside of the first walls. The plasma facing wall will either be bare or perhaps use a thin boron layer on the surface.
Mike Billone said there is new ferritic steel experimental evidence that the ARIES project should be aware of, especially radiation effects, surface heat flux, operating temperature, DBTT, and service lifetime. Based on recent fast fission test data, there are encouraging low temperature data, but high temperature data are still lacking. L. Waganer noted that in the LOCA analyses the project is interested in the maximum, non-operational temperature the structural material can be subjected to and still remain in service.
Centerpost - Wayne Reiersen has investigated the thermal implications of the previous 2.9 m plasma strawman with a shaped centerpost. He cannot determine that a shaped centerpost would yield the promised factor of two improvement for the average current density. Instead, he finds the current density remaining high over the whole length of the shaped centerpost. This yields a high exit coolant temperature even with a very cold inlet temperature of 30oC. This would result in a highly embrittled copper centerpost. Ron Miller is planning to use a straight centerpost in the next strawman system study parameter set.
At the next meeting, Wayne is also planning to present a TF coil and centerpost configuration that would allow upward vertical maintenance.
Configuration and Maintenance - Xueren Wang is working on the configuration of the outer TF coil legs to enable the downward vertical maintenance. He has completed the centerpost, divertor, inboard shield, outboard blanket and shield. He is in the process of determining the local surface areas.
Safety Studies (LOCA) - H. Khater noted that the wall loading data from the systems code is being used to help define the decay heat of the strawman. E. Mogahed is working on the LOCA analyses for the inboard region, the outboard region and a combination LOCA involving both regions. He is still waiting for confirmation regarding the mechanical approach to enhance the conduction heat transfer from the inboard shield to the copper centerpost (Action: W. Reiersen). There was a question of what level of neutron wall loading should be used - Dai-Kai said that they should use a peak of 7 MW/m2 and an average of 5 MW/m2.
Divertor - The discussion again touched on the basic power distribution assumptions: 50% of the total radiation power to the divertor, of which 20-25% of the divertor power will be directed to the inboard divertor surfaces (see Physics question.) With the present plasma configuration, this amounts to a surface heat flux on the inboard divertor surfaces similar to the ARIES-RS divertor, which is reasonable. We will likely assume a radiative divertor. The outboard slot is around 1.5 m long, using tungsten as the plasma facing component, perhaps similar to the tungsten brush approach being developed by Boeing for the ITER divertor. This is plenty of surface area outboard, but the inboard region and local shielding for the centerpost are problem areas. Mark is favoring the use of a straight centerpost to get sufficient area for the inboard divertor slot, but the centerpost may be shorter to keep the joule losses lower.
Mark will present his findings and recommendation on the liquid metal surface divertors at the upcoming meeting. He presently favors lithium working material as opposed to gallium.