Energy Efficiency of Resistive High Field Magnets: Aspects of Magnet Technology, Power Supply Operation and Field Quality

The design and operation of resistive high field magnets require research and development in materials science, power supply engineering and instrumentation. Recently, their energy efficiency has become a very important concern. In our contribution we report on recent advances on an energy efficient use of the 24 MW resistive magnets at the French National High Magnetic Field Laboratory at Grenoble (LNCMI) that can reduce their energy consumption by up to 20%, for a given user experiment. This saving is possible due to a special architecture of the LNCMI high field magnets. Namely, the total magnetic field is provided by two independent concentric sub magnets exhibiting different field characteristics, i.e., absolute field values for a given current and spatial field distributions. As both sub-magnets can be powered in an independent way, their currents can be tuned to minimize the total electrical power for a target magnetic field requested by the user. This enables energy efficient operation. However, the consequences of strain enhancement on magnet safety and life time due to higher current densities in the inner sub magnet have to be considered. LNCMI magnet design, power supply and instrumentation teams have recently implemented this innovative operation mode in a collaborative project. We will present its technical realization including electrical power modelling, magnet load estimations as well as first benchmark experiments including NMR. Finally, we will discuss the perspectives of this operation mode for innovative user experiments.