ARIES Project Conference Call

22 January 1998

Documented by L. Waganer



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

Administrative

The minutes of the 7-9 January ARIES project meeting have been distributed for review. Comments should be sent to Waganer by Friday, 23 January, to be incorporated.

The date for the next project meeting was discussed. Several of the project members plan on attending the IAEA meeting in Culham, but not nearly a quorum to hold a meeting in Culham. There is not sufficient time to have a meeting ahead of the Culham meeting. Several conflicting meeting were in the latter half of March and early April. L. Waganer agreed to query the team about the possible meeting dates of 15-17 April.

The likely participants at the Culham meeting are F. Najmabadi, M. Tillack, R. Miller, S. Jardin, D-K Sze, L. Waganer, and possibly, W. Reiersen.

The next phone call is scheduled for 9 February at 11:30 CST. L. Waganer will obtain a number (the new one is 314-232-3502).

Plasma Physics

Les Waganer reported from Steve Jardin that PPPL is working on the physics cases but no noteworthy results are available.

TK Mau investigated the ability of high energy neutral beams to provide on-axis current drive in the spherical tokamak. He checked with John Mandrekas who had benchmarked his NFREYA code for some ITER-CDA current drive cases with 1.3 MeV neutral beams (Z=1 + impurities) with the ACCOME code. Multistep ionization is important for the beam penetration in high beam enegy and high density cases. TK felt there was sufficient understanding of the physics for the high energy deposition. During the last meeting, there was a question whether the peaking of the beam deposition in the central region was real or just an artifact of the numerics. TK believes that the peaking is a real phenomenon, as the diameter of the single beam is around 0.5 m and is aimed at the magnetic axis. Bob Miller suggested that Ron Stambaugh is knowledgeable of this technology and should be sought for advice. TK will follow up on this issue.

TK also investigated more background on LFFW. He talked to Dick Majeski of PPPL on his LFFW experience on the Phaedrus-T experiment. A CD efficiency of 0.4% was inferred at a temperature 100 eV. The LFFW current drive used a high toroidal mode number with two closely-packed antenna loops that were small in toroidal width because of the small plasma size and the low Te. An LFFW antenna would be physically longer in the toroidal direction in an ARIES-ST plasma.

Bob Miller reported on the GA plasma analysis efforts since the meeting. GA reviewed the vertical stability cases previously analyzed and considered stable. But, similar cases, more recently analyzed by PPPL, are thought to be very unstable in the vertical direction. L. Waganer inquired if the continuity of the stabilizing shell was the difference and Bob agreed that he thought that was about the only remaining possible difference. The PPPL and GA codes are very similar and the input data are nearly identical. We noted that PPPL has an action item to investigate a continuous shell case.

The physics group is planning to investigate plasmas with both 100% and 90% bootstrap currents. The group also suggested a physics conference call to validate inputs and approaches in order to achieve a vertically stable plasma with a passive shell.

Systems Studies

Ron Miller reported that the new ARIES spherical tokamak physics, although not incorporated yet, are expected to degrade the power core performance and, hence, the resultant economics. Ron is investigating a new, simpler code subroutine to optimize the power core design parameters to make the code run faster and more efficiently. The modified power core geometry has not been accomplished yet. Ron mentioned concern about the PF coil stresses noted by Leslie Bromberg. He feels the positioning of the PF coils may not be correct, but he anticipates that the new coil positioning by Kessel will help reduce the coil currents, energies, and costs.

Engineering

Blankets, Divertors, and Power Core Configuration - - Mark Tillack noted that there has been no progress on the thermal-hydraulic and thermo-mechanical analyses. He reviewed the changes anticipated on the power core that were derived from the recent meeting. Xuenen mentioned that the coil data from PPPL has been received but it did not match those of UCSD. However both sets will be superseded by the new strawman data. Once the strawman data has been developed, Wayne Reiersen will construct an appropriate TF coil set and forward that set to Xueren. He can then take the PF coil locations from Chuck Kessel and Ron Miller and add the necessary support structures. The shield thicknesses will be modified to be 20 cm inboard, 87 cm behind the divertors, and 40 cm outboard. Xueren emphasized that he needed representative sizes of the power supplies, cryopumps, and busbars. GA should have some data on power supplies. L. Waganer also suggested contacting Russ Doerner of UCSD as he has data regarding similar power supplies associated with the PISCES-Upgrade experiment. We should not limit ourselves to using a single floor around the power core, rather assume a multifloor arrangement to support and closely locate the heavy, bulky equipment to the power core.

Blanket - D-K Sze has been looking at the velocity of LiPb in the interspace between the ferritic steel blanket structure and the (SiC) thermal insulator. He concluded the flow is insufficient (< a mm/s) to maintain a sufficiently low tritium inventory in this interspace. Dai-Kai also contacted Rion Causey who validated that the tritium solubility in SiC was correct as presented at the January meeting. Dai-Kai also affirmed that the time constant is significant, which decreases the ability of the copper centerpost to conduct the heat of a LOCA up or down the centerpost in a timely fashion. He and E. Mogahed agreed to coordinate on thermal conduction assumptions to arrive at a consistent engineering conduction model of the centerpost.

On the thermal-hydraulic analyses within the first wall and blanket, Dai-Kai and Mark Tillack agreed to coordinate their analyses and data. Dai-Kai agreed to initiate the analysis and send the data and results to Mark for review. Dai-Kai noted that, at the APEX meeting, Steve Zinkle reported a broader range of material operational temperature limits as compared to those offered by Mike Billone. Steve recommended a vanadium operational temperature limit of 400-700íC and ferritic steel of 250-300íC up to 550íC.

LOCA Analyses - E. Mogahed is anxious to redo his analysis, but he requires updated information regarding the thicknesses, masses, thermal connections, and initial thermal conditions of the power core. The group felt that some of the data would not change. Dai-Kai offered to work with E. Mogahed to establish those early assumptions that can be finalized, but other details must await the design analysis following the next strawman.

Magnet Design and Analysis - Wayne Reiersen said that he had forwarded the PPPL ProE drawings of the TF coil system to Xueren. Xueren noted that the file did not conform to the most recent strawman; hence, it could not be used as a specific design. But the file did validate the transfer process, and some of the general design features could be used. Wayne reviewed the upcoming process to obtain plasma and coil data from the systems code, develop the TF design, and transmit that data to the remainder of the team for the development of the remainder of the subsystems.

Neutronic Analyses - Laila El-Guebaly looked at the effect of tungsten in the ferritic steel structure on the tritium breeding ratio (TBR). She received a database from Fischer (FzK-Germany) on the development of the EU demo blanket. In their solid breeder (SB) blanket with lots of beryllium, the use of 1.5 wt.% tungsten lowered the TBR by ~5%, whereas in the EU LiPb blanket, the tungsten had no effect. In the SB blanket, changing the tungsten content from 1.5% to 1.1%, increased the TBR by 2%. In our ARIES-ST blanket containing LiPb, the tungsten should have no effect on the TBR. Also the tungsten should not affect the waste disposal rating. Hence, there is no need to do a trade study, as requested in the recent meeting, to reduce the 2% tungsten content in the ORNL 9Cr-2WVTa ferritic steel used in our LiPb blanket

Laila also reviewed the first wall, blanket, and shielding geometry changes to be implemented in her 3-D neutronic model. Dai-Kai suggested that she should conduct a 1-D parametric analysis to assess the impact of the FW thickness on TBR. Laila noted that a similar parametric analysis was already done and reported in the June 1997 meeting. The group suggested waiting to conduct the 3-D analysis until the design has been developed from the next strawman. Wayne Reiersen suggested that a new criteria is needed to keep the neutron damage to less than 0.1 dpa on the outer TF coils, including the upper and lower legs. Laila said she would add this design requirement for the outboard and divertor shielding.

Safety Analyses - Hesham Khater noted that indeed the centerpost resistivity calculation will need to be redone in light of the thinner inboard shield.

Disruption Analyses - A. Hassanein will be (was?) asked to calculate the effects of a plasma disruption, including the thermal energy dump on the plasma surfaces and the electrical energy dump on the TF and PF coil sets.