The plasma fueling group of the Oak Ridge National Laboratory (ORNL) Fusion Energy Division plasma technology section is devoted to the development and application of fueling systems for use in fusion plasma confinement devices. The development of pellet injectors capable of injecting 1 to 10 mm diameter pellets of frozen hydrogenic isotopes at speeds up to 3 km/s has been pioneered by this group.
The work done by the ORNL plasma fueling group is a part of the U.S. Fusion Energy Science program and is primarily supported by the Office of Fusion Energy Science in the U.S. Department of Energy.
Pellet injection systems developed at ORNL have been installed on experimental fusion devices around the world including the Joint European Torus (JET) in the United Kingdom, Tore Supra in France, DIII-D at General Atomics in San Diego, CA, and the Tokamak Fusion Test Reactor (TFTR) at the Princeton Plasma Physics Laboratory in Princeton, NJ.
Specific Topics
Recent Papers and Talks:
Pellet
Fueling Technology Development Leading to Efficient Fueling of ITER Burning
Plasmas, APS04 Paper, Baylor, L.R., et al., APS 2004 to be
published in Phys Plasmas.
Pellet
Delivery and Survivability through Curved Guide Tubes for Fusion Fueling and its
Implication for ITER, SOFE04 Paper, Combs, S.K., et al., SOFE 2004 to be
published in Fusion Eng. Des.
Production and Innovative Applications of Cryogenic Solid Pellets, Gouge, M.J., et al., Advances in Cryo. Eng. 45 (2000) 1763.
VTL Review Talk - Technology , Combs, S.K., et al., May 2000.
VTL Review Talk - Reactor Fueling , Gouge, M.J., et al., May 2000.
VTL Review Talk - Tritium , Fisher,P.W., et al., May 2000.
VTL Review Talk - Applications , Baylor, L.R., et al., May 2000.
VTL Review Talk - Disruption Mitigation , Fisher,P.W, et al., May 2000.
Improved
Core Fueling on DIII-D APS99 Paper, Baylor, L.R., et al., APS
1999 Phys Plasmas 7 (2000) 1878.
Improved
Core Fueling on DIII-D APS99 Talk, Baylor, L.R., et al., APS
1999 Seattle.
New
pellet injection schemes on DIII-D, Combs, S.K., et al., 1999 SOFE
conference in Albuquerque.
DIII-D Pellet Fueling Location EPS99 Paper,
Baylor, L.R., et al., EPS 1999 Maastricht.
DIII-D Pellet Fueling Location EPS99 Poster,
Baylor, L.R., et al., EPS 1999 Maastricht.
Pellet fueling efficiency on DIII-D,
Baylor, L.R., et al., 1998 PSI conference in San Diego.
Deposition of fuel pellets in tokamaks,
Baylor, L.R., et al., 1998 ANS conference in Nashville.
High-field-side pellet injection technology,
Combs, S.K., et al., 1998 ANS conference in Nashville.
Fueling of ITER-scale plasmas, Gouge, M.J.,
et al., 1998 ANS conference in Nashville.
TPOP-II Tritium fueling at a reactor scale,
Fisher, P.W., et al., 1998 ANS conference in Nashville
Plasma Fueling, Pumping, and Tritium Handling Considerations for FIRE, Fisher, P.W., et al., 1997 ANS conference in Albuquerque, NM
A summary paper on pellet injector technology developments was presented at the 1996 SOFT conference in Lisbon and a paper on fueling systems for fusion energy was presented at the 1996 IAEA conference at Montreal.
These papers are available in PDF format. To view and print these files, you may download a free Adobe Acrobat Reader.
High Field Side Pellet Injection
Injection of D2 pellets into the DIII-D tokamak from an inner wall
injection port located 30cm above the horizontal midplane has been recently
performed. The resulting measured mass deposition profile shows a strong
retention and inward drift of ablatant toward the magnetic axis. The
figure below contrasts the resulting density profile change from an inner wall
injected pellet with one injected from the low field side (outside midplane).
Density limit experiments
Recent experiments on DIII-D have been performed with the ORNL DIII-D pellet
injector to investigate the density limit of ELMing and ELM free H-mode tokamak
plasmas. In these experiments, 2.7 and 4 mm pellets are injected during the
current flattop of NBI heated plasmas. Central densities in excess of 1.5x1020
m-3 have been produced leading to line average densities in excess of
the empirical Greenwald density limit by 50% while maintaining H-mode
confinement that is 1.5*tITER-89P. An example is shown below where
the line average density is maintained 30% above the Greenwald limit for more
that 1 second.
Tritium pellet formation
The formation of tritium pellets is currently under investigation by our group
as part of the ITER fueling system development effort. A repeating pneumatic
injector has been constructed at ORNL and shipped to TSTA (Tritium Systems Test
Assembly) at Los Alamos National Laboratory for experiments in forming and
accelerating tritium and combination tritium-deuterium pellets. Initial
experiments were successful in making the largest hydrogenic pellets to date and
accelerating them to speeds of 1000 m/s. The following picture shows an 8mm
cylindrical tritium pellet as it is fired out of the pellet injector through a
guide tube.
Solid tritium extrusion and an
8mm tritium pellet leaving a guide tube at 1000 m/s.
The ITER fueling system being designed as part of the ITER FEAT consists of a
gas puffing system capable of providing up to 500 Pa-m3/s of DT fuel
and a pellet injection system capable of providing DT pellets at fueling rates
up to 100 Pa-m3/s. The pellet injection is performed by two
centrifuge injectors mounted inside a remote handling cask coupled to a midplane
port. A pneumatic gun is retained in the design as an alternative if R&D
shows difficulties with accelerating large pellets with a centrifuge. Each of
the two centrifuge injectors has 3 extruders that operate in tandem to provide a
steady stream of ice (H, D, T, or DT). Each injector is capable of supplying 100
Pa-m3/s throughput. The gas injection system consists of 2 ring
manifolds with 5 injection points each. The response time of the system has been
minimized in the design to be on the order of 100 ms. For more information on
the ITER fueling system design, contact Larry
Baylor at ORNL.
International Pellet Ablation Database
An international pellet ablation database (IPADBASE) has been formed to
enable studies of pellet ablation theories that are used to describe the physics
of ablating fuel pellets in a tokamak plasma. In the initial configuration, data
from JET, Tore Supra, DIII-D, FTU, TFTR, ASDEX-U, and T-10 have been included.
The database contains measurements of pellet mass, speed, plasma electron
density and temperature profiles, and pellet ablation light emission. A paper
describing the initial database and a statistical analysis of the pellet
penetration depth has been published in Nuclear Fusion (Nuc. Fusion 37 (1997)
445.). A preprint of this IPADBASE paper is
available to view from your Web browser. For access to the data in the IPADBASE,
contact the principle investigators Larry Baylor at ORNL and Alain
Geraud at CEA Cadarache. The EXCEL
4.0 data files that make up the database are available..
A recently devised scheme to minimize the tritium inventory in a fusion
reactor plasma is that of isotopic tailoring. By using tritium rich pellet
fueling in conjunction with deuterium gas puffing, the inventory of tritium in
the first wall components of the reactor can be kept at a minimum while
maintaining the tritium level in the plasma necessary to maintain the fusion
process. A reprint of a recently published Isotopic
Tailoring paper (Fusion Tech, 28, 1995, p1644) is
available to view from your Web browser.
At present, a long pulse high-throughput pellet feed system for a centrifuge
pellet injector is under development. This pellet feed system has recently
produced greater than 1000 pellets in one batch. These 2.6mm pellets have been
produced at 10 Hz and with high reliability. Acceleration is accomplished with a
cantenary arbor rotating at 50 Hz that produces pellets with a nominal velocity
of 500 m/s. For more information on the ongoing centrifuge pellet injector
development at ORNL, contact Steve Combs at ORNL.
Continuous
Extruder Development
A continuous deuterium extruder is under development at ORNL to provide a
steady-state stream of deuterium ice for feeding a centrifuge or light gas gun
type pellet injector. The system is designed to use 3 or more extruders running
in tandem with only one active at a time while the others refill and produce
more ice. For more information on the continuous extruder development, contact
Steve Combs at ORNL.
Non-fusion related
work
A paper published on the use of a cryogenic xenon droplet generator for
use in a compact laser plasma x-ray source by M J Gouge and PW Fisher, Rev.
Sci. Instr., 68, No. 5, 1997, 2158-2162.
Field emission arrays are under development at ORNL for semiconductor lithography applications. For details see recent papers such as V.I. Merkulov, D.H. Lowndes, L.R. Baylor, ``Field emission studies of smooth and nanostructured carbon films'', Appl. Phys. Lett., 75, (1999) 1228 and L.R. Baylor, et al., "Digital Electrostatic e-beam Array Lithography (DEAL)", J. Vac. Sci. Tech. B 20 (2002) 2646.
For more information on fusion and plasma technology see Plasma
on the Internet.
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times since 1-Jun-1997.
This page was created by L.R.Baylor.
Last revised: 27-Feb-2006 (lrb). (Disclaimer)