ARIES Engineering Conference Call

20 July 1998

Documented by L. Waganer


Participants:
(DOE) *
(UCSD)Mau, Ron Miller, Tillack, Wang
(PPPL) *
(GA) Bob Miller
(UW) El-Guebaly, Khater, Mogahed, Sviatoslavsky
(FPA) *
(RPI) Steiner
(ANL) Sze
(Boeing) Waganer
(INEEL) Dave Petti

Administrative

The date of the next ARIES meeting was discussed. Mark Tillack and Farrokh Najmabadi had a conflict on the planned ANL meeting date of August 6-7. The group agreed that August 20-21 would be best, pending approval of Bill Dove who was not on the conference call. [PS, Bill Dove had schedule conflicts until mid-September. The date is now established as September 17-18 at PPPL.]

Systems Studies

Ron Miller discussed a higher beta case provided by Chuck Kessel. The beta was nominally 60%, but a derated value of 55% was used to minimize disruptions. It was presented as a June 17 pre-strawman case. The higher beta case did not result in an expected lower COE. The 3.2 m major radius and recirculating power for a 1 GWe case remained nearly the same as previous cases. Ron Miller will discuss the results with Ron Stambaugh to help understand this result.

Plasma Physics

Ron Stambaugh noted that, per the recent Physics conference call, GA has been assessing a new quasi-strawman case with higher-beta capability. Coils resulting from the EFIT code are more elongated than the normal ARIES-ST designs. The plasma triangularity should be 0.6 but the results indicated only a value of 0.5 had been achieved. More coils may be necessary inside the TF coils to obtain the higher triangularity. Most other parameters are similar to those of Kessel's case. The inner shielding standoff remains 85 cm. Beta is 54% and BetaN is 7.4. Jim Lueur said that the vertical (plasma) shift associated with this case is very stable, with reasonable growth rates. For the N=0 stability mode, the ideal conducting wall should be placed at 1.75 times the plasma minor radius. From the zero-D code results, Pete Politizer suggested the plasma could be started up with high bootstrap conditions by heating the plasma strongly from the beginning of startup. Starting with a small plasma, the plasma density would be adjusted to remain at the Greenwald limit. A deuterium neutral beam would be used to heat the plasma, ramping up to final plasma current conditions in a few seconds. The next step is to develop detailed plasma equibria with vertical stability by using a 1-D transport simulation.

TK Mau obtained the GA plasma data on an EQDISK file format for his analysis. He assumed less than 100% bootstrap current, with approximately 5% of the current in the outer plasma region. He used 40 MW of neutral beam heating (injected energy of 120 KeV) for the edge heating. He expects to complete his analysis in two weeks.

Bob Miller discussed the inboard plasma edge physics without an inboard divertor slot. The choice of surface materials is crucial to the physics as well as the engineering solution. Tungsten would have a negative impact on the breeding ratio as well as introduce high-Z impurities into the plasma. Carbon would be better for the plasma, but carbon might not be a good engineering solution.

Engineering

Mark Tillack started the engineering discussion by highlighting the outstanding design issues. The inboard shield will be sized for once-through helium cooling, yet keep the radial build as small as possible (approximately 20% helium by volume). The helium coolant temperature range would be 300°C up to 500°C, which results in a maximum structural temperature of 550°C (the structural temperature might be able to be increased to 600°C which would increase the maximum coolant temperature by a like amount). The surface heat flux will be 0.8 to 1.0 MW/m2 over the inboard shield and a lesser value on the outboard region. The total surface heat intercepted in the FW system will be 70 MW. Igor noted that the current first wall for once-through helium cooling is 3 cm thick. Laila El-Guebaly noted that the current inboard shield radial build is defined to be 20 cm shield and 3 cm first wall.

Laila completed the neutronics analysis of cooling the inboard first wall and shield with several coolants including helium and heavy water (D2O). It was hoped the heavy water option would have space advantages of water cooling and not capture neutrons as strongly as regular water. However, helium continues to show advantages over the D2O cooling, with a tritium breeding ratio equal or greater than 1.1. The heavy water cooling would require dumping the inboard surface and volumetric heating (~400 MW) and would also require a complex tritium removal system.

Mark also noted that they are working on improving the heat transfer coefficients assumed in the first wall. Presently 10% of the electric power being generated is recirculated to remove the thermal power in the power core. He noted the tradeoff of enhancing the heat transfer coefficient by internal tube surface roughening which increases pumping power and lowers the net power.

Dai-Kai discussed the comparison of helium and water cooling in the inboard region. He will incorporate all the suggestions to improve the cooling and minimize the radial build. He agreed to evaluate an increase in the helium pressure to help improve the heat transfer coefficient.

Hesham Khater is investigating the impact of using tungsten as the plasma facing material on parts of the inboard shield and divertor surfaces. He is awaiting the recommendation on the location and thickness. He is assuming one major plasma disruption during a power core lifetime, but needs data on the coil stored energy. He is assuming a 1-ms disruption.

Mark Tillack mentioned that UCSD is analyzing the stresses in the first wall and blanket, benchmarking their work with the EU DEMO blanket results.

The recommended technique of providing a long-lasting tungsten divertor surface remains to be determined. One option is the ThermoCore porous surface, which acts as a porous metal heat exchanger. Another option is an application of many small diameter tungsten rods, which are free to expand and contract without surface cracking. However, the installation technique and reliability of this approach has not been determined.

Dai-Kai mentioned several issues associated with the ancillary heat transport systems. There will be a high partial pressure of tritium in the primary helium heat transfer system. This will require an extensive tritium removal system. He prefers silicon carbide as the heat transfer and structural material of the primary heat exchanger, but SiC joint technology will have to be developed. A pinch-point problem remains. Dai-Kai would like to combine the heat inputs from the helium coolant with those of the lithium lead blanket heat inputs for an integrated system with better performance capabilities.

Les Waganer mentioned that Wayne Reiersen had provided TF centerpost and outer coil configurations for the coil cost estimate. He and Jerry Wille have been conferring on possible fabrication techniques that would significantly reduce the installed cost of these components.