Design of a High Toughness Epoxy for Superconducting Magnets and Its Key Properties

Abstract

Nb 3 Sn accelerator magnets are poised to enable the luminosity upgrade of the Large Hadron Collider (LHC) at CERN, improving its potential for exploring physics beyond the standard model of particle physics. The prototype Nb 3 Sn magnets consistently need 10-25 quenches to achieve their best performance. A hypothesis is that the long training of these magnets may at least be partially induced by epoxy cracking and bonding failures. In 2018, we showed that several existing epoxies have a higher toughness and less tendency to crack at low temperatures than CTD-101K, the epoxy resin with which almost all Nb 3 Sn accelerator magnets have been impregnated. Here we explore a new high toughness formulation for reducing quench training of Nb 3 Sn accelerator magnets, through combining two amine curing agents to achieve a good glass transition temperature (T g ), adding a viscosity reducer to achieve low viscosity, and experimenting a coupling agent for improved bonding strengths. We report results of comprehensive materials tests, including thermal shock, tensile, compressive, shear tests, viscosity and T g tests.

Improved training in paraffin-wax impregnated Nb3Sn Rutherford cables demonstrated in BOX samples

“…The resins used are the so-called Mix 61 [22], CTD-101K [15], CTD-701X [15] and MY 750 [23], and the wax impregnated samples used paraffin wax. The epoxy resins selected for the comparison with wax have been used in the fabrication of high-field magnets and have varying elastic, plastic and fracture toughness properties [24][25][26] that may influence the training and overall performance of such magnets. Here we assess training, fatigue behaviour and resilience of paraffin wax over multiple powering cycles and a thermal cycle.…”

Impregnation damage monitoring for the canted-cosine-theta magnets using time-domain reflectometry

“…However, one of the key challenges in Nb 3 Sn CCT magnet research involves optimizing the impregnation between cable conductor and coil mandrel to ensure that strain-sensitive Nb 3 Sn superconductor can withstand environmental stresses, including mechanical stress and thermal stress. In recent developments, various enhancement techniques, such as epoxy improvement [9,10], paraffin wax application [11,12], and the utilization of pre-stress [13], have been suggested to address the impregnation optimization. Furthermore, the use of acoustic emission has been proposed to analyze conductor motion and impregnation characteristics during training, enhancing our understanding of mechanical transients [14,15].…”

Training Curves of Nb3Sn Rutherford Cables With a Wide Range of Impregnation Materials Measured in the BOX Facility

“…Possible failures include cracks within the resin volume and debonding between the resin and metal surfaces. To prevent formation of cracks, resins with high toughness are currently being developed [3][4] [5]. Another supposable solution is to add fillers to the resin, which reduces the thermal expansion mismatch and prevents propagation of cracks.…”