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Advanced Technology and Materials
Inside a tokamak fusion reactor, within the space of just a few meters,
the temperature goes from 10 times that of the sun to near absolute zero.
In addition to the huge blast of heat that must be converted to energy,
the plasma created within the reactor chamber emits a torrent of neutrons
that can quickly make the chamber walls radioactive and brittle. One of
the largest research efforts at UCLA, outside of biomedical research, is
concentrated in developing new materials and techniques that will provide
solutions to these problems. Such noteworthy UCLA scientists and engineers
as Mohamed Abdou, Nasr Ghoniem and Alfred Wong are involved in this research
and in taking advantage of the potential of plasmas to aid in processing
materials and disposing of hazardous wastes.
 Abdou, a professor in the UCLA Mechanical, Aerospace and Nuclear Engineering
Department and codirector of UCLA’s Institute of Plasma and Fusion Research
(IPFR), is working to develop “first wall” and “heat flux” components to
line tokamak fusion chambers and absorb the flow of heat and plasma particles
that results from the fusion burn. This first wall is built on the surface
of what is, in effect, a very hot star. Since any solid would soon be destroyed
by the enormous heat, Abdou and his colleagues coat the walls with a flowing
layer of replenishable liquid metal, such as lithium. The liquid metal
absorbs the particles without suffering the radiation damage that solid
materials experience. At the same time, the flowing metal is an excellent
way to transfer the fusion heat that will ultimately be converted to energy.
But metals -- liquid or otherwise -- are also excellent conductors of
electricity, which leads to a unique set of problems. When the flowing
metal moves inside the powerful magnetic fields used to contain the fusion
plasma, it is pushed and pulled, like the plasma, by magnetic forces. The
study of how a flowing metal interacts with a magnetic field is known as
magnetohydrodynamics (MHD). “For the past 10 years,” Abdou says, “we have
been studying -- both computationally and experimentally -- the behavior
of flowing liquid metals in the geometric and magnetic environment of the
tokamak fusion reactor.”
To test their computations, Abdou and his group have built an experimental
facility called MeGA Loop (for “metal goes around”) to investigate how
liquid metal film flows on a plate in strong magnetic fields. “The initial
film flow experiments have verified some of the predictions of the numerical
model,” Abdou says. An upgrade of this facility to accommodate even stronger
fields, more closely duplicating conditions in magnetic fusion reactors,
has been requested by the U.S. Department of Energy.
Abdou’s group is also looking to liquid walls as a way of protecting
inertial confinement fusion chambers from the destructive effects of tiny
nuclear explosions. In a commercial ICF power plant, five fuel pellets
are detonated every second, tearing holes in the flowing liquid lining
of the fusion chamber. Somehow, the tattered metal wall has to be repaired
in the short interval between blasts. In addition, the chamber’s vacuum
must be maintained so that the powerful laser or ion beams are not absorbed
before they strike the pellet. The windup is that vaporized material and
splashed liquid must be removed from the chamber every fifth of a second.
Abdou’s group is energetically pursuing solutions to these and other problems.
Deuterium and tritium, the two isotopes of hydrogen, are the easiest
elements to burn in a fusion reactor. But when deuterium and tritium fuse,
in addition to heat, they release neutrons. The neutrons themselves are
harmless. However, they can make some materials radioactive. (Exactly how
radioactive depends on the nature of the materials. Most conventional materials
will stay radioactive for thousands of years.) Disposing of these materials
presents many of the same problems as disposing of the waste generated
by fission power plants.
 Nasr Ghoniem, a professor in UCLA’s Mechanical, Aerospace and Nuclear
Engineering Department, has invented the world’s first low activation alloys
for fusion applications. These alloys, called ferritic steels, indeed become
radioactive when they absorb the neutrons of a fusion reaction, but this
radioactivity decays with a half life of only about 100 years. Ghoniem
is now working on ceramic materials with even lower activations than steel.
 Some plasmas are so hot that they can burn virtually any material. Alfred
Wong, a professor of physics and astronomy and codirector of the IPFR,
has invented a plasma torch that can burn hazardous wastes. So hot is Wong’s
torch that it breaks down waste compounds into component elements. “It’s
really the ultimate form of recycling,” says Wong.
Power Plays...
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