ARIES Project Conference Call
9 February 1998
Documented by L. Waganer
|(UCSD)|| Mau, Miller, Najmabadi, Tillack, Wang
|(PPPL)|| Jardin, Reiersen
|(UW)|| El-Guebaly, Khater, Mogahed
The possible dates for the next ARIES project meeting were discussed. It
was decided to hold the next meeting in San Diego on Wednesday, 29 April,
starting at 1:00 pm and continuing through 11:00 am on Friday, 1 May 1998.
The date for the next project conference call will be 2 March (Monday).
The phone number will be 314-232-3502.
Ron Stambaugh and Steve Jardin are considering attending the Culham meeting
in March. Other participants will be F. Najmabadi, M. Tillack, R. Miller,
D-K Sze, L. Waganer, and TK Mau.
Mark Tillack reported that the FED papers associated with ARIES have been
printed, and a limited number of copies have been distributed. Mark is
trying to bundle the papers together for an ARIES mailing; but he needs any
extra copies the principal authors might receive.
Plasma Stability - Steve Jardin reported that the baseline
configurations, A=1.6, now seem to be vertically stable. The previously
reported unstable conditions were due to an error in the code being used by
PPPL. The passive walls were assumed to be 5-cm-thick tungsten and located
at 0.5 times the plasma minor radius (a) from the plasma boundary. This
suggests that the conducting walls are roughly 1.0 m from the first wall.
Laila El-Guebaly encouraged Steve to evaluate a similar set of walls placed
behind the blanket/manifolds approximately at 1.4 m from the first wall.
The conducting wall system consists of two walls, approximately 1.6 times
the minor radius poloidally high, separated by some vertical distance, and
centered on the midplane. Steve will distribute a sketch documenting the
geometry. Cases exhibit ideal stability on a reasonable time scale, but
investigation of control requirements are just starting. Ron Stambaugh said
that the results from the GA calculations supported a high sensitivity to
triangularity for kink stability. Thus, a high triangularity of 0.6 is
favored, while a triangularity as low as 0.5 would be marginal. Farrokh
Najmabadi thought that 0.45 would represent too much of a technical risk
and 0.5 would be a better choice.
Ron Stambaugh reported some spreadsheet analysis results that pointed to
plasma geometry and operating regimes that might offer potential benefit to
increase the overall plant Q.
- There is a strong experimental basis for tHe* / tE as low as 4 from JT-60U and ASDEX
Upgrade. This lower value gives a 5% helium concentration in ARIES-ST
instead of the present 15% in the strawman. This lower helium
concentration would raise the fusion power output by about 30-50%. These
results are obtained in ELMing H-mode or in L-mode. The assumptions made
in constructing ARIES-ST equilibria essentially correspond to an L-mode
edge, and so these low values of tHe*
/ tE are consistent. Farrokh was
concerned that the tritium inventory and the burnup fraction might be
unacceptable with these conditions. It would also be difficult to control
the position of the plasma flux lines on the inboard region without an
inboard control coil.
- Ron Stambaugh suggested that the fusion power could be significantly
increased if the elements of the inboard radial build that were not TF coil
copper or plasma-related were lessened. For each 10 cm eliminated, the
fusion power would triple. At the last meeting, the total thickness was
about 49.5 cm. A 30-cm-thick shield was changed to 20 cm which would help.
Perhaps the 5-cm-thick gap between the shield and centerpost could be
eliminated, but Wayne Reiersen and Mark Tillack responded that a nominal
gap is required to insure the ability to assemble the shield and allow for
thermal expansion. The 5 cm is considered to be at operating temperature.
Ron also thought the 10-cm-thick scrapeoff layer could be eliminated (see
above). Inner wall limiter plasmas have been operated in both H-mode and
in L-mode with internal transport barriers (for 5 seconds, DIII-D last
week) with H factors as high as needed in the ARIES-ST strawman. .
- The final suggestion by Ron was to increase beta to help improve the
power level. At A=1.4 to 1.6 and k=3, there is
some incremental improvement in beta. But at k=3.4, there is significant improvement in beta. Ron
volunteered to send some of his better cases to PPPL to compare the results
with the two codes.
Heating and Current Drive - TK Mau reported that he and Mark
Tillack had conferred on the geometry and sizes of the lower frequency,
fast wave (LFFW) systems being considered. The antenna array is located in
a recessed box located toroidially around the plasma chamber. The box is
recessed approximately 25 cm from the first wall surface. There is some
question if a Faraday shield is required given that the antenna is recessed
and may be constructed of the same material as other plasma facing
Neutral beams (NB) with an energy level of approximately 3 MeV have a
nominal power density of 200-300 MW/m2, which would suggest only
a few small penetrations would be required for the 40 MW power level
required. The problem is that once the geometry of beams is established,
the beams will only drive currents in one direction.
TK noted that although the LFFW may be good for on-axis CD, it may not
be appropriate for initial heating and current drive during startup. High
Harmonic Fast Wave (HHFW) may be required for startup, heating and off-axis
current drive. One advantage of HHFW is its small antenna size.
Blanket - Mark Tillack reported that D-K Sze had completed some
additional thermal-hydraulic analyses. These analyses indicated improved
power handling capabilities for the first wall, perhaps up to 0.9
MW/m2 peak. But not up to 1.0 MW/m2, since this
would require a first wall that is too thin to serve as a high-pressure
containing wall - id est, insufficient bending stiffness. The
Engineering Group needs to seriously examine the power handling capability
of the inboard first wall and shield.
Neutronic Analyses - Laila El-Guebaly noted that she had
completed a 3-D neutron wall loading (NWL) analysis for the ARIES-ST with a
straight centerpost case. The analysis indicated that the average NWL in
the inboard divertor region (above the upper X-point or below the lower
X-point) is a factor of 10 lower than the average NWL between the upper and
lower X-points on the inboard first wall and shield. This means that the
current inboard shield thickness of 20 cm could be thinned to approximately
10 cm in the divertor region if necessary. Wayne Reiersen suggested that
the added area might be required for helium flow improvement. This area
probably could not be used for flaring the centerpost because of
maintenance and assembly complications.
Laila said she would distribute the radial build data on 13 February.
Maintenance and Configuration - Xueren Wang said that he has been
working on the building configuration and the subsystem layout. Eight
large power supplies are located immediately outside the biological shield
near the power core midplane. The cryopumps are also located near the
shield but on a different floor. These components were sized from the GA
pilot plant drawings.
Xueren has also been evaluating the capability to support the gravity
loads of the power core during operation. He has been assessing the
ability of removable structure to support the entire weight of the core
LOCA Analyses - Mark Tillack reported that E. Mogahed and Dai-Kai
Sze have agreed on the time-dependent transport of LOCA heat along the long
centerpost. E. Mogahed explained that the peak temperature remains similar
to a short time analysis, but the time to reach the coil leads temperature
is more than five days.
Magnet Design and Analysis - Wayne Reiersen affirmed the need for
the clearance between the centerpost and the inboard shield. The area
would also contain the components necessary for thermal conduction during
Ron Miller said that he is working on the list of changes requested by W.
Reiersen. By the end of this week, Ron thought he would be able to input
the radial build (from Laila?). He also has been working with Ron
Stambaugh on benchmarking the code against the GA physics. He hoped to
have a strawman data set soon.
Alternate Applications Studies
Les Waganer reported that he is in the process of reviewing prior fusion
hydrogen and synfuel production concepts and reports to help establish a
database of information in case the project decides to assess hydrogen
production by fusion.