Speaker
Description
MegaGauss facilities provide a unique environment to study materials under extreme conditions. This not only concerns samples exposed to the magnetic field in the center of a coil, but also the coil itself. The present study focuses on the deformation of copper single-turn coils (STC), specifically analyzing the impact on the material microstructure. While generating the field, STC undergo magnetic pressure giving rise to their radial expansion and axial compression. These deformations occur on a timescale of a few microseconds, leading to exceptionally high deformation speeds. The primary objective of this research is to quantify the changes in copper microstructure resulting from these rapid and intense deformations.
Three types of STC were selected, each representing a different level of magnetic field exposure. “Raw coils” did not generate any magnetic fields and thus served as reference material. “Intermediate field coils” successfully generated a magnetic field without being destroyed. These were used to study the effects of non-destructive deformations induced by the magnetic field. “Maximum field coils” were destroyed during the process of generating a high magnetic field and thus represented extreme deformation conditions in our study.
To quantify the impact of deformation on copper microstructure, Vickers microhardness measurements were locally performed across relevant conductor cross sections, revealing both softening and work-hardening (135HV0.1) effects depending on position. Experimental results where then compared with finite element simulations taking into account local current distributions, heating, magnetic pressure and deformation experienced by the conductor while generating the magnetic field
Our preliminary study demonstrates that substantial local changes in microhardness can be measured as a result of the deformation of STC during magnetic field generation in the MegaGauss facility. Observations are in good agreement with numeric calculations of the pressure and temperature distribution in STC indicating a competition between annealing, driven by high local temperature (~2500 K) on the one hand, and work hardening caused by the magnetic pressures (~10 GPa) and deformations with microsecond duration on the other hand.
