Laboratoire National des Champs Magnétiques Pulsés CNRS – INSA

Personnel involved:
High Field Installation
Permanent: Julien Billette (coils), Paul Frings (coils&generator), Franck Giguel (50% :coils), Bertrand Griffe
(generator)
Non permanent: Jérome Béard (coils), Julien Mauchain (X-coils)
Collaboration: mainly within DENUF: H.Jones, Oxford University; J.Perenboom, Universiteit Nijmegen; T.
Hermannsdorfer, Hochfeldlabor Dresden;
High Field Coils
Coils to generate high magnetic fields are subjected to enormous Lorentz forces that have a tendency to explode
the coil. To contain these forces one can use stronger conductors or add internal (non-conducting, or a least not
current carrying) reinforcement. These measures cause however higher losses and thus a more rapid rise of the
temperature limiting the pulse duration. Optimized coil design for pulsed coils is therefore always a compromise
between conductivity and mechanical strength.
copper stainless steel coils
The most evident, and in theory also the most efficient, way to contain the forces in a coil is to have wire of
sufficient strength. The development of copper wire with a heavily cold-worked stainless steel jacket (UTS of
the total wire ~1000MPa) permits in principle to wind straight forward coils with such a wire that can achieve
fields in excess of 60 T. However these coils showed short lifetimes, with a tendency of the lifetime to decrease
with coil volume. We believe that this is due to insulation problems caused by high pressures inside the coil.
This problem is probably the combination of a chemically inert stainless steel surface (difficult to adhere to) and
the hardness of the surface. This combination is believed to promote “puncture” of the isolation at high contact
forces. So for the time being the production of this type of coils is stopped.
distributed reinforcement coils
A flexible way to handle the balance between strength and conductivity is to reinforce every layer of the coil by
the minimum required thickness of reinforcement. This reinforcement can easily cope with the hoop-stress but
the axial load is difficult to transfer into the external reinforcement, and this is one of the factors (the other is the
problem of plastic backflow) that limits the highest field that can be generated in such a way in a reliable manner.
copper zylon
This techniques was first tested with the combination of a ductile (and highly conductive) copper wire. After
solving some minor technical problems (for instance the transition of one layer to the next), these coils turned
out to be a reliable source for user fiels up to 60 T. The inclusion of thermally not well conducting fibers caused
unfortunately long cool-down times.
glidcop zylon
In order to pass the 60 T frontier for reliable user fields a stronger, but still ductile, conductor has to be used. By
choosing glidcop we recently managed to generate 70 T user fields. The first coil has been tested elsewhere and
is waiting to be installed in one of the specially adapted cells.
stainless zylon
To show the potential of this technique, we also produced a coil consisting of copper-stainless steel wire. With
this combination of strong, but not so ductile wire, and zylon reinforcement a field of more than 79 T was
realized, in agreement with the calculations. Due to the limitations of our generator these tests had to be
performed at the NHMFL in Los Alamos (US). This approach can at this moment not be fully exploited in
Toulouse due to the limitations of our generators. A project for an adapted generator is now underway.
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