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Livrables
Coil inserts for advanced research magnets are produced for a user station. These coils boost the magnetic field from 40 T to 70-80 T, therefore making a range of magnetic fields available for scientific experiments.
Coil design and manufacturing were based both on available technology at the start of the project and technology developed in the course.
Key issues in achieving these results are the detailed modelling of the coil structure, the use of advanced conductors and high strength reinforcing fibre material, and manufacturing techniques associated with insert coils.
The construction of a large bore magnet.
The availability of large energy sources automatically gives the opportunity to built magnets with larger sizes and longer pulse-durations as what was state of the art until now.
Building such a large magnet poses extra problems regarding wire production, coil winding and protection of the surroundings and the magnet, in order to minimise damage in case of a failure. Two 45T coils with an inner bore of 100mm were produced. The first magnet suffered from insulation problems that were solved by new techniques for the second one. A third magnet, a copy of the second, is planned.
Three new techniques were developed and tested during the construction of these magnets:
1. The mechanical and electrical joining of several lengths of conductor in one coil
2. The improved insulation by adding glass fibre wrap to the standard kapton wrap insulation in order to cope with the higher forces encountered during winding of large section wire
3. A mechanical protection of a double-walled G10 cylinder filled with grease in order to protect the large outer coil in case of a failure of the inner coil
These results will be used for construction of similar large coils that are foreseen to be installed in the near future in the new, 50MJ, high-field laboratory in Dresden and the renewed 20MW installation in Nijmegen.
There is now at the Laboratoire National pour Champs Magnetiques Pulses, Toulouse, an 80 T class user magnet in its dedicated station as a result of the ARMS project. So far, experiments up to 76 T have been performed. The magnet comprises a coil-ex and a coil-in. The coil-ex is energised with a 14 Mj capacitor bank; the coil-in has a smaller, faster bank. The two fields add and 80 T is achievable but a spare coil-ex is under construction and when until it is ready, the 76 T (itself a record breaking field for a non-destructive, user magnet) will not be exceeded.
In summary:
The implementation of a pulsed double-coil system as a user station has been achieved by
- The construction and/or adaptation of two pulsed generators to the specific requirements of the inner and outer coils,
- The electronic synchronization of the trigger mechanisms for the inner and outer coils,
- The implementation of a common user-interface,
- The construction of an LN2-cryostat for the coils and an LHe bath-type cryostat for low-temperature measurements,
- The outfit of a measurement cell and the implementation of measurement routines taking into account safety aspects.
To furthermore improve its user-friendliness the setup is currently revised. The smaller capacitor bank is upgraded for future coiling developments and relocated to a place outside the measurement cell. An internal call for proposals advertising measurements up to 80T has been issued. The aim of this call is to adapt various measurement techniques to the particular constraints of the double-coil system prior to advertising on a larger international scale. First proposals from outside the ARMS-consortium have nevertheless been received and accepted.
A high-sensitivity magneto-transport experiment at liquid He-temperatures up to 78 T was performed. Due to the extremely low probe signal of the HgSe:Fe-sample of only 0.24 mV at B=0 a sophisticated measuring technique suppressing any kind of perturbing noise including non-compensated spurious pick-up contributions of the finite contact loops had to be applied. For the evaluation of the data a digital lock-in technique with a modulations frequency of about 50 kHZ was necessary. The resultant data demonstrate that after improvement of the grounding of the generator/coil/measuring system without any ground-loops the experimental arrangement is well able to detect magneto transport data in good quality even in the critical regions of the onset of coil-in, where the pick-up voltage are largest. So the improved coil-in/coil-ex system is ready to start user-application even for difficult measuring problems of extremely low probe signals.
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