Magnetics Business & Technology - November/December 2021 - 18

RESEARCH & DEVELOPMENT
Superconducting Dipole Magnets Completed at FAIR, GE Wins Power Conversion Contract
Pausing to celebrate the completion of all 110 dipole magnets at FAIR
The production of all 110 superconducting dipole magnets has
been completed at FAIR in Darmstadt, Germany, marking an
important step at one of the world's biggest scientific research
projects. In another development related to the new facility's
massive SIS100 ring accelerator, GE Power Conversion has been
selected to provide power converters for the main dipole and
quadupole magnets for it.
The production of all 110 superconducting dipole magnets for the
new heavy ion accelerator with a circumference of 1.1 kilometers
was completed in early August, along with corresponding cold
tests at the final operating temperature of -269 degrees. Various
sophisticated magnets and entire magnet systems will ensure that
the ion beam is precisely guided and focused. The dipoles, mainly
needed for deflecting the particle beam, make up more than a
quarter of all 415 fast ramped superconducting magnets utilized in
the SIS100.
The successful production of the modules and their testing represents
the largest series of accelerator components ever manufactured
by order of GSI. The completion is an important milestone
on the way to installation in the tunnel, which is scheduled to
begin in the second half of next year. Bilfinger Noell in Wurzburg,
one of the few European manufacturers of superconducting magnets,
was contracted for series production.
The dipoles are superferric magnets, consisting of a superconducting
coil and an iron yoke to guide the magnetic field. The particular
feature of the magnets is the superconducting coil, in which
a special superconducting cable is used. This nuclotron cable,
originally developed for the ring accelerator Nuklotron at the Joint
Institute for Nuclear Research in Dubna, Russia, is particularly
suitable for generating rapidly ramped magnetic fields.
The cable consists of a copper-nickel tube. Around this tube
strands of niobium-titanium, a common superconductor, are
coiled. The original design was optimized with regard to the requirements
of FAIR. It is cooled with liquid helium and operated at
a temperature of 4.5 Kelvin. The design of the magnets allows to
integrate vacuum chambers for the ion beam, whose wall temperature
is also just above absolute zero. Thus, the chamber walls
act like a super pump onto which the remaining particles of the
beam vacuum keep attached. The extremely low remaining gas
pressure made possible by is a mandatory precondition for the
acceleration of heavy ion beams with highest intensities. Highest
particle intensities are part of the specifications of the FAIR facility,
which offers a wide variety of new experimental possibilities.
Each of the magnets, which weigh about three tons and are three
meters long, is subjected to a comprehensive test program. The
quality control of the production as well as several tests under
room temperature conditions are performed in Wurzburg before
shipment to Darmstadt. Among other things, the geometric precision
of the inner aperture and the electrical properties of the coil
were measured as part of the so-called FAT (Factory Acceptance
Test). Bilfinger Noell succeeded in making the production so
precise over the entire series that the deviations of the geometry
of the field-determining pole shoes were always less than 50
micrometers from the nominal geometry.
After delivery to GSI, all 110 dipole modules were subjected to
testing at the final operating temperature of 4.5 K. To cool the
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