Training-free demonstration of a 5.4 T Nb₃Sn Canted–Cosine–Theta accelerator dipole impregnated with paraffin wax

Abstract

Lawrence Berkeley National Laboratory (LBNL) is pursuing stress-managed Nb3Sn Canted-Cosine-Theta (CCT) magnet technology for high field accelerator magnets. Although promising results have been reported, improvements in the training performance are desired. This work describes the fabrication and testing campaigns of two subscale Nb3Sn CCT magnets; a baseline impregnated with National High Magnetic Field Laboratory (NHMFL) Mix-61 and a magnet impregnated with paraffin wax. The paraffin magnet reached the short sample limit of the conductor, to within the measurement uncertainty, with no training quenches inside the magnet. In contrast, the baseline magnet reached 80% of the short sample limit after approximately 20 quenches and exhibits some loss of memory after thermal cycles. Inter-layer flexible quench antennas combined with voltage tap data show that all quenches appear identical and originate from a region corresponding to the location of peak field in the cable. Although this success should be replicated at higher fields, these first test results demonstrate the potential for training free Nb3Sn accelerator magnets operating near the short-sample limit.

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

“…Before the thermal cycle, all quenches occurred above 9500 A without training, except for the preceding two quenches at the lead and the splice. All quenches inside the magnet were observed in the inner layer [41]. After the thermal cycle, all quenches occurred around 9600 A without training as well, and quenches were all observed in the inner layer.…”

“…For Sub6, both layers are fully impregnated with paraffin wax. The detailed results of Subscale magnets impregnated with paraffin wax were reported in [41].…”

“…Figure 6(c) depicts the appearance of heaters installed on the lead-side. The primary objective of installing spot heaters was to achieve quench localization through the utilization of the quench antenna [41,42]. However, in this work, the focus is on impregnation monitoring using VNA-based TDR.…”

“…Previous research has demonstrated that cables impregnated with wax exhibit very low adhesion and friction [43]. This characteristic leads to reduced impregnation damage and conductor movement compared to other resin systems [41,44]. The variations in the p value could potentially be attributed to minor deformations of the wax and movement of the conductor.…”