IN A last-ditch bid to realise the 50-year-old dream of making limitless
electricity from the same reactions that power the Sun, physicists last week
presented their final cut-down design for a nuclear fusion reactor. They warn
that unless governments now find the 3.5 billion euros (拢2 billion) needed
to build the reactor, the dream will die.
The international fusion project has been in limbo for two years, ever since
funding governments balked at the original price tag of 7 billion euros.
Researchers have since drastically scaled down their ambitions. Speaking at a
fusion conference organised by the International Atomic Energy Agency in
Sorrento last week, Evgenii Velikhov, Russia鈥檚 leading fusion scientist, says
that if a decision to begin construction is not made soon, 鈥渙ur future is very
bleak鈥�. Umberto Finzi, the European Commission鈥檚 coordinator for energy and the
environment, warns that if governments fail to back the new design, practical
fusion energy research will fade away.
The US, Europe, Japan and the Soviet Union began working together on fusion
in 1986, but by the time the design for the International Thermonuclear
Experimental Reactor (ITER) was finalised in 1998 the political climate was very
different. US support for fusion had dwindled and Russia had little money to put
on the table.
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The US pulled out of the project last year, and fusion researchers in Europe,
Japan and Russia have since been reworking the design, cutting the original
capital cost in half. Finzi points out that the cost of building the reactor, if
spread over 10 years, is only 25 per cent of the 1.4 billion euros already spent
on fusion research worldwide every year. Behind the scenes at Sorrento, Finzi
was busy preparing the ground for negotiations next year on a funding package
between Europe and Japan.
The principle of the revamped ITER is the same as before: inside a large
doughnut-shaped vessel known as a 鈥渢okamak鈥�, powerful magnetic fields contain a
plasma of the hydrogen isotopes deuterium and tritium. When heated to over 100
million degrees, the deuterium and tritium nuclei fuse to form alpha particles
and neutrons. The alpha particles reheat the plasma while the energy of the
neutrons can be extracted.
Many of the key parameters of the new design have shrunk. The amount of power
to be generated has been reduced from 1500 to 500 megawatts, while the volume of
plasma has dropped from 2000 to 837 cubic metres. Crucially, the reactor is no
longer aiming to 鈥渋gnite鈥� the plasma. Ignition occurs when the alpha particles
provide enough energy to sustain the reaction, and no further input of heat is
needed. The aim now is to provide 67 per cent of the plasma鈥檚 energy from alpha
particles, a figure that cannot be achieved by any of the existing small
research tokamaks.
Despite the need to input energy, the reduced ITER should produce ten times
as much energy as it consumes. No other tokamak has yet produced surplus power,
though the JET fusion reactor at Culham in Oxfordshire has come close.
Experiments at JET over the past few months have for 5 seconds reached the
levels of plasma pressure, density and confinement required for ITER. 鈥淲e have
made steady progress on all fronts,鈥� says JET鈥檚 leader, Jerome Pamela. 鈥淚鈥檓 sure
ITER will work.鈥�
Apart from the design, the other burning question for ITER researchers is
where it will be built. Possible sites include Cadarache in southern France and
three locations in Japan. But Canada, an associate ITER member, has proposed
building the reactor next to an existing nuclear complex at Clarington, west of
Toronto. This has the advantage that tritium is already produced there, and it
would also be an acceptable compromise between Europe and Japan. In addition,
ITER scientists hope this location may entice the US to rejoin the project.
