Starlite Project Meeting Minutes
9-10 December, 1996
Princeton Plasma Physics Laboratory
Attendees: L. Bromberg, S. Dean, B. Dove, L. El-Guebaly, P.
Heitzenroeder,
S. Jardin, C. Kessel, T.K. Mau, R. Miller, F. Najmabadi, W. Reiersen, D.
Steiner,
R. Stambaugh, , D-K. Sze, M. Tillack, L. Waganer
Guests: Numerous guests from PPPL
Attachments: Meeting agenda
Summary
The kickoff meeting for the Advanced Concept Studies Program was
held at PPPL on 9-10 December 1996, mainly to define and initiate
the next year's study effort. The draft of the Starlite ARIES-RS
final report is currently being reviewed within the team. The
results of the recent low aspect ratio (LAR) assessment, both
physics and engineering, were reviewed along with more recent LAR
physics results by PPPL and GA. Technical experts from PPPL
briefed the group on the goals, requirements, and preliminary
design information of the NSTX experiment to be constructed at
PPPL.
General
Steve Jardin welcomed the Starlite ARIES group to PPPL and
reviewed the two-day agenda. Farrokh Najmabadi summarized the
main areas to be investigated by the team over the next year or
two. The principal focus of the study will be to evaluate key
elements of the LAR (AKA the spherical tokamak (ST)) approach in
more detail. This independent evaluation will provide information
to help guide decision makers on the direction and benefits of
future LAR machines. This LAR investigation will be the majority
effort this year, with lessor efforts in two other areas. The
second area will be the investigation of selected technical issues
common to a general class of advanced fusion concepts, such as the
ability to handle higher surface and volume heat loads (higher
power density). The third effort will be to investigate alternate
non-electric applications for fusion. L. Waganer will lead this
effort.
As a sidebar, F. Najmabadi noted that the Starlite Utility
Advisory Committee recently reviewed the ARIES-RS results. While
satisfied with the design and projected technical performance,
they noted the overall design did not meet their expected COE goal
to be 20% cheaper than the likely competition.
Bill Dove stated that he was pleased with the ARIES-RS results and
is looking forward to seeing the published final report. He noted
the main result of achieving a high performance design with good
safety features and an attractive environmental approach. He
expects DOE to conduct a formal review of the final study results.
He also mentioned the need for the conceptual electrical power
plants to achieve attractive COE projections in, or below, the
range of the competition. He would like to extend the outreach of
the ARIES-RS results and not solely rely on the current approach
of presenting papers at technical conferences. He is expecting
the group to investigate some alternate approaches and
applications for fusion.
Bill Dove related that the system studies budget has been cut
almost in half, down to $1.5M. This budget will likely remain at
this level for the near future. This lower funding level has
reduced the breadth and scope of the team. The main players are
UCSD, University of Wisconsin, and PPPL plus several other
important participants from other institutions. Don Steiner asked
if DOE has abandoned the idea of a demo or commercial power plant.
No, rather DOE and Congress view the current embodiments as too
large and expensive. They are asking the community to find new,
innovative ways to provide a power source with smaller
developmental steps. For the moment, the community should
concentrate on the physics and technology aspects. Farrokh
commented that our group should concentrate on the power plant
design, identify the critical R&D needs, look at the end products,
and highlight constraints that may be relaxed (or eliminated). We
do not need to define the R&D pathways or estimate their costs (at
this point).
Status of LAR Tokamaks
Martin Peng, program manager for the PPPL NSTX, reviewed the
worldwide activities on the low aspect ratio or spherical
tokamaks. There is a great deal of new experimental results being
released and reviewed. The results indicate high stable average
total beta (25-45%) with dynamic pressure-gradient driven current
fractions in the range of 50-90%. These plasmas need conductive
shells to get high beta values (without shells the total beta will
be around 25%). The results also indicate high confinement
values. They have strong magnetic wells and pressure gradients.
Martin noted that theoretical data would suggest the ST plasmas
will have thick scrape-off layers and diverter channels inferring
easier power handling capabilities for these machines.
Several new ST machines are being planned and developed to build
upon new experimental results. Non-inductive formed plasmas are
being demonstrated with coaxial helicity injection (CHI) in HIT,
SPEX, and TXT. Pressure-gradient driven currents are being
created in CDX-U, and DIII-D. Efficient heating and current
sustainment will permit steady-state operations in CDX-U, HIT-II,
SPHEX, and START. Some of the ST machines operating are START
(Culham, 91), HIT (U. of Wash), CDX-U (PPPL, 94), TS-3 (U. of
Tokyo, 93), Medusa (U. of WI, 94), and TST (U. of ??, 95). Under
construction are ETE (INPE, Brazil), Globus-M (IOFFE), MAST
(Culham, 98?), and Pegasus (U. of WI).
Overview of NSTX Experiment
Masa Ono presented an overview of the planned NSTX experiment to
be developed by PPPL, ORNL, and Columbia University. The device
will be a spherical tokamak at an aspect ratio of 1.25. It will
investigate non-inductive start-up, current stabilization, profile
control, plasma confinement and transfer, pressure-limited and
self-driven currents, scrape-off layer and divertor physics,
stability margins, and resilience to disruption. Its mission is
related to the Volume Neutron Source (VNS). It is designed to
have a high total beta (25-45%); high pressure-gradient driven
current fraction (50-90%); fully relaxed, non-inductively
sustained current profiles; and operate in a collisionless regime.
The plasma current will be 1 MA for a pulse duration of 5 seconds.
Heating will be 5 MW of NBI, 3 MW of fast wave RF, and 400 kW of
25 GHz ECRH. The center column will be fully replaceable. The
construction phase began in FY1996 and operation of the experiment
is expected to begin in 1999. The experiment will be located in
the TFTR D-site hot cell.
Outlook for New Energy Technologies in the 21st Century
Prof. Robert Socolow, Director of the Princeton University Center
for Energy and Environmental Studies, reviewed his thoughts on the
US' and world's energy future and possible sources to satisfy our
expected energy needs. The general perception is that energy is
not an urgent problem to be solved. Rather, the question of
adequate energy resources, and companion question of environmental
impact, may be postponed to some future time when the level of
urgency increases. However, he feels these important issues must
be dealt with in the near future. He noted that most researchers
feel that by 2050, the world's energy demand will double or
triple. There is not sufficient energy capability and resources
to meet this demand without significant environmental
impact. PCAST used the groundrule that, in the near-term, the
greenhouse effect will be acknowledged but the principal energy
source will continue to be fossil fuels. Fusion could help as an
energy source in the future, but Rob feels fusion is handicapped
by three current perceptions: (a) the unit size must be very
large, (b) it is mainly an electric generating device, and (c) it
is a nuclear process. He believes fusion can co-exist with
fission as an energy supplier. He thinks our ultimate competition
will be "green" fossil fuel energy sources that release no carbon
products to the atmosphere, resulting in a hydrogen economy. He
views this to be very beneficial to the commercialization of an
efficient fuel cell.
ARIES Engineering Assessment of the LAR Tokamak
Mark Tillack reviewed the results of the recently completed ARIES
assessment of several critical LAR engineering elements. To help
assess these elements in the context of an actual machine, a
commercial LAR device was defined to deliver the requisite 1000
MWe to the grid. The derived machine characteristics determined
the machine size and performance. Notable characteristics were
the recirculating power requirements that influenced the machine
size. A shield was employed with the copper center post to help
lessen the electrical resistance increase, minimize the
embrittling effects, and enable Class C waste privileges. When
asked the reason for choosing the aspect ratio of 1.25, Farrokh
said that both aspect ratios of 1.4 and 1.25 were evaluated and
were judged to be roughly similar, except for a higher total beta
for the 1.25 case which was the determining factor for selection.
C. Kessel mentioned that this next year's activity will be to
continue to explore and optimize the LAR aspect ratio parameter
for a commercial device.
Examination of NSTX Engineering Issues
John Spitzer, PPPL, presented the main parameters of the NSTX
machine: major radius of 85.4Êcm, minor radius of 68.0 cm, aspect
ratio of 1.26, and plasma current of 1.0 MA. He felt that the
center stack (post) was the most critical NSTX system. Within
that system, the high-strength porcelain insulator, which
electrically isolates the center stack from the vacuum vessel and
coils and allows differential movement between the TF and OH
coils, is the most difficult system to design. Electrical
isolation is required because of the coaxial helicity injection
(CHI) current drive. The bellows and insulator have undergone
several design changes to accommodate necessary configuration
changes. The vacuum chamber from the S-1 Spheromak experiment is
being modified for this experiment. Several TFTR neutral beam
coils are being used for the NSTX poloidal field coils. Active
and passive vertical stability plates are shown inside the vacuum
chamber. Both single and double null operation are being planned.
Divertors are not shown at present but are being developed.
Proposal for New Innovative High Heat Flux Blanket
Dai-Kai Sze presented a new blanket concept that may accommodate
the high heat flux environment of a LAR, have a high coolant exit
temperature, and still use low-activation materials. He proposed
using high pressure helium as the coolant. The coolant first
enters the first wall region that is an enclosing shell of
ferritic steel (FS) around the entire blanket module. The coolant
flows radially inward toward the plasma; and then at the center of
the module, it returns through the central breeder, reflector, and
shield regions. The structural material for the inner regions is
SiC which contains the breeder material and insulates the FS from
the higher blanket material. The blanket, reflector, and shield
will bring the coolant temperature to superheater temperatures of
approximately 1000 C. This will enable the use of the higher
efficiency Brayton cycle thermal conversion system. The main
helium coolant stream will also be used as the tritium purge
stream. This is a new concept, so it will have to be thoroughly
evaluated.
Applying the Integrated-Blanket-Coil to the ST Central
Column
Don Steiner explained how the Integrated-Blanket-Coil (IBC)
concept of uses a liquid metal to both cool a component and
conduct a current through it. This liquid metal concept would
avoid the waste disposal problems and eliminate the radiation
damage problems inherent with a copper center post. Maintenance
would also be significantly simplified if the life of the center
post is extended. If the temperature of the liquid metal can be
elevated, some of the captured heat can be more efficiently
recovered. The downside arguments are that lithium and sodium are
more resistive, which translates into more power loss and MHD
effects that may induce significant pumping power requirements.
Don will lead the assessment of the IBC concept for the center
column application.
Summary of Engineering Tasks and Planning
M. Tillack reviewed the Engineering Group's tasks and organization
for FY97. The primary focus will be on a LAR design study with
some contributions toward more general MFE design innovation and
assessment of critical issues. ANL will work on blanket concept
development and power density studies. PPPL will concentrate on
magnet systems and design/analysis of the center post. The
University of Wisconsin will provide design, neutronic analysis,
mechanical analysis, materials assessment, and safety support for
the centerpost, blanket, and the overall system. UCSD will
provide the plant configuration and maintenance development,
design integration, CAD design development, thermal analysis, and
divertor design development.
Mark also defined general (ARIES-LAR) milestones to be completed
in certain time periods:
- Dec 96 - Mar 97:
- Concept Development
- Mar 97 - Jun 97:
- Concept Selection (Bill Dove suggested a mid-point design
report here.)
- Jun 97 - Sep 97:
- Design Evaluation
- Sep 97 - Dec 97:
- Final System Analysis (F. Najmabadi suggested a zeroth-order
integrated design point then.)
The group recognized that there are at least four independent LAR
or ST design concepts representative of power production systems
that need to be objectively compared. This comparison will
highlight the inherent assumptions and the underlying precepts
that lead to differing configurations and performance projections.
The four concepts identified are: GA (Stambaugh), Culham, Peng,
and ARIES-LAR (Mar97 version). These concept comparisons will be
led by Ron Miller (systems) and supported by M. Tillack
(engineering), S. Jardin (physics), and D. Steiner (general).
Results are to be reported at the March meeting.
Review of LAR Physics Assessment
Steve Jardin reviewed the equilibrium and vertical stability
analysis results that encompassed a range of LAR plasma
configurations involving aspect ratios, elongations,
triangularity, with and without conducting shells, and with and
without active vertical stability feedback coils. As the aspect
ratio decreases, the self-consistent elongation and triangularity
increase at rates which depend on the current profile and
pressure. As the elongation and triangularity become more
pronounced, conducting walls and/or feedback coils must be added
to maintain stability. At higher elongation conditions, the
conducting wall must be located closer to the plasma surface. It
is estimated that, with conducting walls and active feedback, LARs
may be operated at elongations of 1.5 to 2 times the natural
elongation for that condition. MHD and bootstrap current analyses
found stable conditions with high bootstrap fractions, but current
drive was required for both on-axis and off-axis locations. Since
the off-axis current drive (CD) is very inefficient, cases with
high bootstrap current but requiring only on-axis CD were sought
and a few cases were found. The downside was that, whereas the
less efficient cases were stable to all kink modes, the more
efficient bootstrap cases required difficult stability analyses
for higher order kink modes. Steve suggested a more complete
vertical stability study at higher elongation conditions,
extension of the MHD stability study to higher elongations and
more shapes, and development of an understanding of the bridging
between high-bootstrap, high beta LAR plasmas and the reverse
shear plasmas at higher aspect ratios. Chuck Kessel will lead the
latter study.
Overview of LAR Current Drive Scoping Study Results
T.K. Mau reviewed the CD requirements, RF techniques investigated,
analysis codes used, and physical system optimization parameters.
His conclusions were: CD power requirements depend on bootstrap
current fraction and alignment with overall current requirement
and off-axis CD very inefficient; hence, both off-axis and edge
bootstrap alignment are very crucial. He concluded that it is
possible to sustain equilibrium with efficient on-axis CD, but
off-axis CD is still required for startup and detailed profile
control. The trapped particle degradation to CD efficiency for
off-axis drive needs to be modeled more accurately. Chiu at GA
suggested that the previous Starlite off-axis CD efficiency
estimates may be pessimistic. He would also like to look at NBI
and electron Bernstein wave CD techniques.
Examination of Physics Issues at Low Aspect Ratio
Stan Kaye stated the mission of NSTX is to investigate plasma
confinement and particle transport in a larger LAR device, plasma
stability and resilience to disruption, non-inductive plasma
initiation and current sustainment, and scrape off layer and
divertor physics. The NSTX is expected to exhibit a high average
total beta (25-45%), have a high pressure gradient driven current
factor (50-90%), and have a fully-relaxed plasma with a non-
inductively driven current. This will be one of the only LAR or
ST experiments that will have high power auxiliary heating of the
plasma. The START experiment is the other one. Global
confinement results from NSTX are hoped to bridge the gap to
conventional tokamaks. High beta operation is a consequence of
low aspect ratio, but ballooning modes are a limiting factor. The
conducting shell is essential for a vertically-stabilized plasma.
Plasma rotation is important for effective wall stabilization.
For to use high harmonic fast wave, bootstrap current, CHI and
NBI. They are expecting the divertor heat flux to be in the range
of 8 to 16 MW/m2. If the steady-state heat flux exceeds
12 MW/m2, they will sweep the flux lines on the divertor to spread
the maximum heat flux.
GA Physics Perspective on Potential of a LAR Device
Ron Stambaugh presented a series of LAR machines encompassing a
physics performance machine, a pilot plant, a power plant, and a
DHe3 machine. He stated that GA stability study results indicate
that a LAR can be constructed and operated with high beta(n), high
beta(t), 100% bootstrap current fraction, and stable to low n
kinks and n=0 with a conducting shell. He would propose curve
fitting his data with an expression relating beta(n) to the
inverse of the square of the aspect ratio, (bn Ä 1/A2). He also
thinks the pressure gradient at the edge can be greater than zero
and a radiative mantle can be used on the edge to minimize the
heat load on the divertor. He also feels the center post should
be bare, without a shield. This is because he feels the
embrittlement and the radiation-induced resistance increase in the
centerpost copper is not a problem and that the requirement for
Class C disposal could be waived. He also believes that copper is
mandatory for use in all divertors including commercial machines.
The comparison of the LAR concepts will help resolve some of these
differences.
Summary of Physics Tasks and Planning
T.K. Mau led off with a proposal to more thoroughly investigate CD
system options, namely:
- On axis:
- Electron Bernstein Wave
- RF Helicity Injection
- NBI
- DC or Coaxial Helicity Injection
- Off axis:
- Mode Conversion
- ECH
He also proposed implementing a CURRAY model to estimate the
efficiency of the HFFW system:
- Investigate sensitivity of power to current profiles
- Determine CD system efficiency with respect to aspect ratio
and electron temperature
- Investigate sensitivity to startup scenarios and parameters
Chuck Kessel proposed in the area of plasma vertical stability
and control to:
- Determine the natural plasma shape (elongation and
triangularity) in a uniform vertical field as a function of
plasma inductance, beta (poloidal), aspect ratio, and plasma
current.
- Address requirements for vertical position control to
produce elongation and triangularity values larger than natural
values.
In the area of ideal MHD stability analysis, he proposed to:
- Examine the ideal MHD stability of plasmas in the range
between 1.25 and 2.5
- Examine how RS plasmas connect to LAR plasmas
- Examine the bootstrap(BS) current fraction versus betan
dependence as a function of aspect ratio to determine if there
is a more optimal value
- Examine more extreme plasma shaping (e.g. elongation ~ 4)
for stability and BS benefits
Ron Stambaugh proposed to:
- Provide (physics) consultation to the project
- Redo beta limit optimization study with finite edge pressure
gradient
- Determine beta limit from A-1.2 to 1.8 with reduced
parameter variation
- Investigate self-consistent 1-D transport simulations of
unusual profile current drive requirements and confinement
times
- Briefly look at divertor issues from particle control and
pumping
- Assess upper limit on elongation reactive power versus
elongation/natural elongation
- Assess the need for divertor coils
- Assess non-transformer startup capabilities using the PF
coils only.
Steve Jardin summarized all the future physics effort as:
- UCSD (TK Mau) will investigate the divertor power balance on
a 0-D basis and determine the RF startup scenario.
- GA will assess the ideal stability limit for an aspect ratio
and elongation search and p'>0 at edge. GA will also do
transport calculations using self consistent profiles with
neoclassical ci and a radiative mantle. On the divertor, GA
will determine the X-point geometry as well as the natural
divertor geometry.
- PPPL will complete the natural stability study with maximum
and minimum elongation values (aspect ratio and elongation
search) and the physics connection to the RS regime. They
will also determine the startup scenario, including non-RF
solutions.
Innovative Approaches Applied to ARIES Systems Analysis
With the reduced LANL funding level, Ron Miller will be
responsible for all the systems analysis and code modeling
efforts. He noted the continuing trend within fission plants to
increase the capacity factor so that a majority of US plants have
a 3-year average above 70%, with many plants above 85%. Ron
elucidated some new concepts and techniques in the field of
Systems Analysis that may bring new analysis tools to the fusion
systems studies. Ron discussed the Response Surface Methodology
and how that approach of a search over a multi-dimensional
parameter space might lead to better results. This is opposed to
our historical approach of a local parameter search about a
discrete design point (strawman). The difficulty lies in the need
to fully define and parameterize the engineering and physics
database for all systems so that they work and interact properly
and seamlessly over the entire multi-dimensional parameter space
being surveyed. It was judged we do not have sufficient
resources, manpower, and time to accomplish the fully parametric
approach.
Wrap-up
Mark Tillack summarized the ARIES-RS Final Report Chapter status,
which is mainly in the draft stage and being reviewed by chapter
co-authors and senior editors. Delinquent chapters are the
blanket, divertor, and the magnet systems. Completion of final
drafts are expected in January, 1997. It was decided to have four
meetings per year, with the next one to coincide with the
US/Japanese Reactor Studies Workshop @ UCSD near the end of March
1997. The second may be in June, perhaps at UWisc. Also a
meeting may be coordinated with the 17th IEEE/NPSS meeting to be
held in San Diego 6-10 October 1996.
Agenda
ARIES Low-A Kickoff Meeting
Princeton Plasma Physics Laboratory
Monday Dec. 9, B318 PPPL
AM ------------------
8:30 coffee and donuts
9:00 - S. Jardin - Discussion of Agenda, Logistics, Status of Reports
9:15 - F. Najmabadi Opening remarks, project directions, meeting objectives
9:30 - Bill Dove OFES perspectives
9:45 - Martin Peng Status of worldwide activities on LAR tokamaks
10:30 - break
10:45 - Masa Ono Overview of the NSTX experiment
11:30 - Rob Socolow The outlook for new energy technologies in the 21st century
(Princeton University, Center for Energy & Environmental Studies)
[Note: This talk has a Required Reading prerequisite
Chapter 1 of the PCAST report, by Socolow and Holdren]
PM ------------------
2:00 - Mark Tillack
Review of ARIES engineering assessment of the LAR tokamak
2:30 - J. Spitzer
NSTX engineering issues
3:00 - Dai Kai Sze
Innovative blanket concept He/(FS+SiC)/Li2O/Be
3:15 - D. Steiner
Applications of IBC to spherical tokamaks
3:30-5:30
Discussion of engineering issues and tasks
7:00 Dinner at Good Time CharleyÕs (Route 27 in Kingston)
Tuesday Dec. 10 B318 PPPL
AM ------------------
8:30
9:00 - S.Jardin, T.K. Mau
Review of ARIES physics assessment of the LAR tokamak
9:30 - Stan Kaye
Princeton plasma physics activities supporting the LAR tokamak
10:00 - Ron Stambaugh
Edge physics and other issues for the LAR tokamak
10:30 - Discussion of physics issues and tasks
T.K. Mau ... comments on current drive options
C. Kessel ... comments on stability studies
12:00 - Other Topics:
R. Miller.. "Innovations in Systems Analysis"
PM ------------------
2:00 - 3:00
Discussion of scope and direction of ARIES project
LAR tokamak design and analysis
Non-electric applications
Critical issues and design innovations
3:00 - 4:00
Discussion of FY97 work plan
4:00 Adjourn