The
superconducting cables designed for the ITER fusion reactor (cost: 16
billion euros) are unable to withstand the planned forty to sixty
thousand charge cycles. Barring a solution, the troubled mega-experiment
will suffer still more delays and cost overruns. About one third of
total expenditures for the reactor are devoted to the superconducting
magnet system. UT researcher Arend Nijhuis thinks he has the solution.
He has calculated that a different configuration will make the cables
more robust. In the first week of March, ITER will run an experiment
costing half a million euros to see whether this theoretical solution
will actually work in practice.
The
success of the ITER nuclear fusion reactor is dependent on the quality
of the superconducting cables making up the superconducting magnets.
These magnets keep the plasma in the reactor in check. The problem with
the current cables is that they degrade too quickly. Tests were
conducted in which the cables were subjected to tremendous
electromagnetic forces at extremely low temperatures. The results show
that the current cables are not capable of withstanding the scheduled
40,000 to 60,000 charge cycles, as recently reported in Nature
and other sources. (The organization behind ITER itself is very
cautious when it comes to publicizing any issues related to the
reactor).
UT
researcher Arend Nijhuis of the Energy, Materials & Systems
research group of Professor Marcel ter Brake has designed a new cable
configuration together with his project group. They have been working on
their calculations for three years. The new configuration entails a
completely different braid of the 864 individual wires of 0.8-mm thickness which make up the superconducting cables. The thin brittle
wires run more in parallel in Nijhuis’s configuration and are therefore
better supported. The biggest problem was to devise a cable
configuration that would not only provide good support for the wires,
but that would also lead to reduced warming of the superconductors due
to eddy currents causing AC loss. This solution means the cables can
withstand greater mechanical loads and that they will heat up far less
than the cables currently scheduled for installation in the reactor.
Ultimate test
A
test costing nearly a half million euros will be run in Switzerland in
the first week of March to see if Nijhuis’s solution is feasible. A
3.5-m long cable will be subjected to an intense electromagnetic charge
at extremely low temperatures several thousand times. If the tests show
that the cable’s performance does not deteriorate, then this
configuration will be suitable for the ITER reactor. In addition to
Nijhuis’s design, three other cable configurations will also be tested.
Nijhuis is fully convinced that his design will withstand the test with
flying colours. “My model does not indicate even the slightest
deterioration,” states Nijhuis resolutely. The test results are expected
in April.
ITER (background)
ITER
is an international project in which stakeholders are researching the
scientific and technical feasibility of fusion as an energy source. The
ITER reactor, which is being built in Cadarache, France, should be able
to produce 500 MW of electricity.
Nuclear
fusion requires extremely high temperatures of up to 150 million
degrees C in order to form plasma (ionized gas). Since no material can
withstand these temperatures, the fuel (a mixture of two isotopes of
hydrogen: deuterium and tritium) must be kept trapped in extremely
energetic magnetic fields. The magnets that produce these fields are
composed of giant coils of superconducting cables.
