Laboratoire National des Champs Magnétiques Pulsés CNRS – INSA

apid cooling coils
The distributed reinforcement coils have very low radial stresses. Therefore annular cooling channels can easily
be integrated. By adding 1 cooling channel the cooldown time is decreased with a factor of 3.5 A simplified
analysis, based on infinitely long coils and infinite heat of evaporation of the liquid nitrogen, gives a gain equal
to (n+1)², n is the number of channels. The development of rapid-cooling coils has greatly enhanced the
efficiency and ease of use for our users.
multi-coils
One way to obtain higher fields with existing materials is to build a set of nested coils that are energised
consecutively. The increase in the number of free parameters for the coil design logically leads to coils with
improved performance and permits moreover to use special wires that are only available in limited quantities or
with limited sections. The drawback of this approach is however a more complicated system that is less easy to
use since the field pulse has two (or more) largely different rise-times. This approach was tested and
implemented with EU funding and permitted to generate fields above 75 T.
single-turn coils
The limit for the field that can be generated with the currently available engineering materials seems to be
around 100 T. To go beyond this limit, one has to accept that the coil is destroyed during the pulse. By using a
very fast (rise time sub microsecond) and high current (> 1 MA) generator, in combination with single turn coils,
one can generate fields up to 300 T, without destroying the experiment inside the coil (which of course is
destroyed). An installation of this type has been installed at the LNCMP and is currently under test.
special geometry coils
Sometimes an experiment needs a magnet where, contrary to the standard solenoids with a cylindrical axial hole,
the field is not parallel to the access. Examples are diffraction on magnetic systems and experiments involving
polarised radiation. The request for such type of coils was greatly enhanced by the construction of a
transportable generator that permits the production of pulsed high magnetic fields at other large installations like
high power lasers, neutron sources and synchrotrons (we performed experiments at the ERSF, LULI and ILL).
wide angle access
The first special coil for X-ray scattering increased the accessible scattering angles to ±30 degrees. The idea of
for this coil was to obtain a conical bore by removing the wires close to the bore but far from the centre that are
not very efficient anyhow. This resulted in a > 30 T coil that has at the moment produced more then 10000
pulses and is still in operation.
split coil
In order to have a full circle of diffraction angles accessible and to have at the same time the magnetic field
perpendicular to the scattering vector a split coil for fields of over 30 T has been constructed and tested.
X-coils
In order to optimise the product B²l (where B is the component of the magnetic field perpendicular to the path l)
for birefringence experiments, a set of two slightly tilted racetrack coils has been developed. The first X-coils
produced B²l values of 25 T²m. Improved versions are under test that will surpass 150 T²m
Generator
To energise pulsed field coils one needs a lot of energy (several MJ) in a short time (~50 ms or less). Such
powers can not easily be obtained from the electrical grid. The well known solution to this is intermediate
stockage in a high-voltage capacitor bank.
14 MJ generator and two 0.17 MJ small generators
The main generator of the laboratory is a 14 MJ, 65 kA, 24 kV generator. This generator exists since ten years. It
was built with an analogue control system. This analogue control proved to cause a lot of problems and
moreover the company that produced the system disappeared. The overcome this problem and make the
generator more reliable it was decided to replace the analogue control by a digital one realised by a series of
distributed PLC’s (programmable controllers). After this major intervention the generator now works very
reliable and has a more flexible interface for the users. Moreover, since all the control is programmed in software
it can easily be adapted to new requirements. Recently we implemented a complete logging and access-control
system. This is required by the EU funding for the visitor programme and allows at the same time to store
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