Comparative study between in-situ measurements and a 3D efficient model for the computation of magnetic fields in High Field Polyhelix magnets

The Laboratoire National des Champs Magnetiques Intenses (LNCMI) is a member of the European Magnetic Field Laboratory (EMFL). This is the French facility enabling researchers to perform experiments in the highest possible magnetic fields. The numerical modeling jointly developed with the Center of Modeling and Simulation of Strasbourg (Cemosis) plays an essential role in the understanding and the optimization of such magnets based on the so-called polyhelix technique (a magnet is a set of Copper alloy tubes cut by Electrical Discharge Machining). In the context of this collaboration, a full 3D multi-physics model dedicated to the study of LNCMI resistive high field magnets has been implemented. Applications of this model have shown a 3D behaviour of the magnetic field, specifically in the vicinity of the beginnings and ends of the helical cuts. The effect is greater than what is commonly expected by experts. To validate our model and this unexpected behaviour, dedicated measurement campaigns were carried out both on a real magnet insert and on a low field test bench. In this paper, we will describe the in-situ and low field testbench setups used to perform a 3D mapping of the magnetic field. We will briefly detail the ingredients of our numerical model, especially the parallel algorithm proposed to apply efficiently the Biot and Savart’s law for computing the magnetic field produced by magnet inserts and seen by the researchers. Finally we will present the comparative study based on calculations and measurements that confirm the 3D distribution of the magnetic field and therefore validate to some extent our modeling choices. The periodic variations observed are related to the helical cut of the Polyhelix magnets. This study is an important step in the understanding of Polyhelix magnets behaviour.