Environmental Engineering Reference
In-Depth Information
Attempts of controlled fusion processes have been conducted since the 1950s. So far only
limited success has been achieved; here, success means that an equal or greater amount of energy
is released as was consumed in the fusion experiment, the so-called “break-even” point. Optimistic
estimates predict that commercial power plants based on fusion will be operative in the next 40-50
years. Pessimistic estimates claim that fusion-type power plants will never be practical, or they
will be too expensive compared to power plants based on fission reactors or renewable energy, let
alone fossil energy.
6.6.1
Magnetic Confinement
Most approaches to plasma confinement and inducement to fusion rely on magnetic field confine-
ment. The magnetic field is created inside cylindrical coils in which a current flows. The cylindrical
coils form a circle, so that the magnetic field has the shape of a toroid (doughnut). The plasma
particles travel in helical revolutions along the magnetic field lines.
The first toroidal magnetic field reactor was constructed in the former USSR, hence the acronym
Tokamak,
short in Russian for toroidal magnetic chamber. Further confinement of the plasma is
provided by an additional current flowing in the plasma itself. The plasma current is induced by
transformer action from external coils. The plasma is heated by a combination of the resistive dis-
sipation from the current flowing in the plasma and from external sources, such as radio-frequency
waves. Also, energetic particles may be injected into the plasma, such as high-velocity ions from
an accelerator.
Tokamak-type fusion machines are operating in Russia, Europe, Japan, and United States.
In 1993, the Tokamak reactor at the Princeton Plasma Physics Laboratory using the deuterium-
tritium fusion achieved a nominal temperature of 100 million degrees and a power of 5 million
watts for about 4 seconds. Plans are underway to build a $1.2 billion International Thermonuclear
Experimental Reactor, jointly funded by the United States, Japan, Russia, and several European
countries. This facility will use deuterium-tritium as a fuel and superconducting magnets for
confinement.
6.6.2
Laser Fusion
Laser-induced fusion apparatuses are operating at the Lawrence Livermore Laboratory, California;
Los Alamos Laboratories, New Mexico; and Rochester University, New York.
A fuel (e.g., a mixture of deuterium and tritium) is contained in a small (1-mm) sphere made
of glass or steel. The mixture is irradiated with several high-intensity laser beams. The sphere is
compressed and heated by implosion. The glass or steel outer layer evaporates. The temperature
of the content gases increases to tens of millions degrees, and the pressure rises to thousands of
atmospheres. Laser beams of megajoules of energy are employed in very short pulses, a billionth
of a second long. The power at the center of the sphere reaches 1E(15) W. The initial beam is from
a neodymium-glass laser radiating at 1
m. A crystal is used to generate higher harmonics in the
ultraviolet range. Unfortunately, the laser system operates at about 1% efficiency, so that 99% of
the input energy does not result in light emission. Higher-efficiency lasers pulsing at a higher rate
will be necessary for break-even power production, let alone for a commercial power plant.
Plans are underway to build the National Ignition Facility at the Lawrence Livermore Labo-
ratory, California, employing a deuterium-tritium fuel and 192 laser beams.
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