Laboratoire National des Champs Magnétiques Pulsés CNRS – INSA

Field generation
Technical perspectives
Introduction
The continuous quest for higher and higher magnetic fields is part of a more general trend of studying
matter under more and more extreme conditions, like very high pressures or very low temperatures. At
the same time, the ongoing improvements of superconducting magnet technology (state of the art 23,5
Tesla) force the high field facilities to increase the field strength they can propose to their users to
higher values, in order to be able to offer sufficient added value and to provide a convincing reason for
their existence. An ad-hoc criterion that has been respected over the last decades is that when going
from superconducting magnets to resistive magnets to pulsed magnets, the maximum field strength
doubles each time.
Recent developments in superconducting technology suggest that superconducting magnets will cross
the 25 T mark within the next 5 years. High Tc superconductors offer in principle a potential to go
much higher, but major materials processing issues have to be solved before such a potential can be
realized. The current maximum value for a DC resistive magnetic field is 45 T (a hybrid magnet at the
NHMFL in Tallahassee, with similar hybrid magnet projects underway in Grenoble (see below),
Nijmegen and Heifei), whereas a 60 T hybrid project is being considered by the NHMFL. For purely
resistive magnets, the field record is at 35 T (Grenoble and Tallahassee), but the LNCMI-G has an
ongoing program to push this value towards 40 T by 2012 and a similar project exists at the NHMFL.
For non-destructive pulsed magnets, the maximum field value is 89 T (obtained at the NHMFL in Los
Alamos with a multi-coil system, with similar projects underway in Dresden and Toulouse). The Los
Alamos and Dresden projects are aiming at 100 Tesla, and are steadily progressing towards that aim.
The Toulouse facility can not currently develop a credible 100 T project, because of the limitations of
its current high voltage capacitor bank and because of security issues with the magnet cells. In the
context of the Contrat Plan Etat Region Midi Pyrénées 2007-2013, an extension of the building with
explosion-safe cells and fast high voltage modules are foreseen, that will remedy these problems,
which will open the route towards 100 T, and that will allow the LNCMI-T to maintain its long term
international competitiveness.
To go beyond the field limits imposed by the mechanical properties of current engineering materials,
one has to accept that the magnet is destroyed during a magnetic field pulse. The use of a very fast
(sub microsecond rise time) high voltage (60 kV) and high current (2 MA) generator allows the use of
single turn coils that are destroyed during a field pulse without harming the experimental setup inside
the coil. Such an installation has been constructed at the LNCMI-T and will be progressively put into
use to study matter under extremely high magnetic fields (up to 300 T).
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