Observation of Electromagnetic Transients in a Nb3Sn 4-layer Dipole Mirror Magnet

TL;DR

This study reports the detection of electromagnetic transients and coil motion in a Nb3Sn dipole magnet during testing, revealing stick-slip behavior linked to quench events and providing insights into magnet stability.

Contribution

It introduces a new differential current measurement approach and a simple coil shift model to understand quench-related transients in Nb3Sn dipole magnets.

Findings

Detected fast current changes preceding quenches

Identified coil motion as a key factor in quench initiation

Proposed a reversible stick-slip coil shift model

Abstract

During testing of the Stress Managed Cosine-Theta dipole mirror magnet SMCTM1, magnet quenches were observed following large voltage spikes in the half-coil voltage taps which preceded normal quench initiation. Following some recent work at CERN measuring power current converter transients in relation to flux jumps, an additional differential current probe was added to the magnet instrumentation. Measurements of this probe, as well as the half coil voltage taps show a fast and substantial current change preceding the quench, hinting at coil motion. A simple model based on relative shift of the inner and outer layer coils was developed which suggests the magnitude of coil shift events is on the estimated relative coil shift from the magnet constraint conditions. The behavior is shown to be reversible and characteristic of stick-slip.