14
LARGE
CORPORATIONS
Bilfinger Noell GmbH, Würzburg, Germany
ASG Superconductors SpA, Genoa, Italy
“Nature determined the form for us.“
The superconducting magnetic coils
for Wendelstein 7-X
The plasma being studied at Wendelstein 7-X is 100 million degrees hot. Ring-shaped,
twisted magnetic fields confine the plasma and thermally isolate it from the cold vessel
walls. In stellarator-type fusion devices the magnetic field is determined exclusively by
the geometry of the outer magnetic coils. For more than ten years, scientists had searched for
the ideal magnetic field cage using a supercomputer. Their calculations became reality in the
bizarre coil windings. The technical realization of the coil geometry was extremely challenging
for Bilfinger Noell GmbH. It set up a consortium and a European network involving many subcontractors
and solved numerous engineering problems:
The consortium partners Bilfinger Noell GmbH and ASG Superconductors SpA developed
methods to bring the superconductor into the spatially complex shape. Suitable winding moulds
were built and successfully introduced. Bilfinger Noell acquired valuable experience in the
design of the steel casings and their manufacture using an optimized casting process, the
embedding of the winding packages in the steel casings and their high-precision mechanical
machining.
In the event of an emergency shutdown, the coils have to withstand very high voltages and
must be extremely robust. Each individual coil was therefore subjected to various tests with
voltages of up to 13,000 volts. One particularly sensitive high-voltage test, which IPP developed
with Bilfinger Noell specifically for the factory test, was conducted in a dilute gas atmosphere.
Deficiencies in the electrical insulation of the coils caused visible discharges, which could then
be rapidly located and repaired. This – extraordinarily strict – “Paschen test” set new standards
for the quality assurance of superconducting magnets.
The team of Bilfinger Noell GmbH has developed remarkable expertise in the
completion of this contract. This competence has since been used successfully for
other projects, for example at ITER US for the Paschen test facility. The GSI Helmholtz
Center for Heavy Ion Research awarded the company a contract for the production of
superconducting magnets for the international particle accelerator FAIR in Darmstadt.
ASG Superconductors used the experience gained with the Wendelstein 7-X coils in a
consortium that applied for the manufacturing of the ITER toroidal field coils and is now
fabricating the EU winding packages for the international test reactor.