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| Spherical
torus |
Plasma science (the study of ionized
gases) is critical to the development
of fusion energy (involving the fusion
of nuclei), which could be an abundant
and attractive energy source in the
future. The spherical torus concept
creates a unique magnetic field structure
to improve plasma stability and confinement
at high pressure. This plasma configuration,
shaped like a sphere with a narrow
hole through the center, can confine
a higher plasma pressure for a given
magnetic field strength than a conventional
tokamak, in which plasma is shaped
like a donut. Conceived in 1985 by
researchers at Oak Ridge National
Laboratory, the spherical torus concept
is now being tested at Princeton Plasma
Physics Laboratory. Preliminary tests
on a small device in the United Kingdom
reached a high ratio of plasma pressure
to applied magnetic field pressure
(called toroidal beta) about 40 percent,
that is roughly three times greater
than the level reached in a tokamak.
Initial results at Princeton are encouraging.
The toroidal beta has reached approximately
22.5 percent; and the energy containment
efficiency improved by as much as
a factor of two when an additional
heating method was applied. The goal
is to produce and maintain high-performance
spherical torus plasmas for pulse
lengths of several seconds.
Scientific Impact:
Initial results at Princeton suggest
that the spherical torus experiment
will have adequate heating power to
test the theoretically predicted toroidal
beta values in the range of 40 percent.
This configuration also offers new
opportunities to advance the science
of high-temperature magnetized plasmas
of interest to the astronomical plasma
physics community.
Social Impact: Because
the amount of fusion power produced
is roughly proportional to the square
of the plasma pressure, the spherical
torus configuration could lead to
smaller, less costly development steps
to economical fusion power plants.
This advance could help promote the
availability of fusion as an attractive
energy source.
Reference: "Features
of Spherical Torus Plasmas," Y.-K.
M. Peng and D. J. Strickler, Nucl.
Fusion Vol. 26 (1986) 576.
"High-harmonic fast magnetosonic wave
coupling, propagation, and heating
in a spherical torus plasma," J. Menard,
R. Majeski, R. Kaita, M. Ono, T. Munsat,
et al., Phys. Plasmas 6,
2002 (1999).
"RF Experiments on Spherical torus
Plasmas," R. Majeski, J. Menard, D.
Batchelor, T. Bigelow, et al., AIP
Conf. Proc. 485, 296 (1999).
URL:
http://www.pppl.gov/projects/pages/nstx.html
Technical Contact:
Don Priester, Research Division, 301-903-3752
Press Contact: Jeff
Sherwood, DOE Office of Public Affairs,
202-586-5806
SC-Funding Office:
Office of Fusion Energy Sciences |
