Test results of TQS03: A LARP shell-based Nb₃Sn quadrupole using 108/127 conductor

Abstract

Abstract. Future insertion quadrupoles with large apertures and high gradients will be required for the Phase II luminosity upgrade (10 35 cm -2 s -1 ) of the Large Hadron Collider (LHC). Although improved designs, based on NbTi, are being considered as an intermediate step for the Phase I upgrade, the Nb 3 Sn conductor is presently the best option that meets the ultimate performance goals for both operating field and temperature margin. As part of the development of Nb 3 Sn magnet technology, the LHC Accelerator Research Program (LARP) developed and tested several 1-meter long, 90-mm aperture Nb 3 Sn quadrupoles. The first two series of magnet used OST MJR 54/61 (TQ01 series) and OST RRP 54/61 (TQ02 series) strands. The third series (TQ03) used OST RRP 108/127 conductor. The larger number of sub-elements and the consequent reduction of the effective filament size, together with an increased fraction of copper and a lower Jc were expected to improve the conductor stability. The new coils were tested in the TQS03 series using a shell structure assembled with keys and bladders. The objective of the first test (TQS03a) was to evaluate the performances of the 108/127 conductor and, in particular, its behaviour at 1.9 K, while the second test (TQS03b) investigated the impact on high azimuthal pre-stress on the magnet performance. This paper reports on TQS03 fabrication, the strain gauge measurements performed during assembly, cool-down, excitation and the quench behaviour of the two magnets.

Performance of a ${\rm Nb}_{3}{\rm Sn}$ Quadrupole Under High Stress

“…The keystone angle is 1.05 0.1 degree and the insulation thickness is 125 microns. This conductor has been demonstrated to be stable at 1.9 K [7].…”

“…As described in [7] and shown in Figs. 8 and 9, TQS03a was first trained at 4.3 K. The first quench reached 79% of the estimated short sample .…”

“…The data exhibit a linear azimuthal unloading of the pole piece. Due to the intentional low initial pre-stress applied in TQS03a [7], the preload was insufficient to keep the pole turn in contact with the pole piece. The appearance of a knee in the plot stress versus square of the current indicates a tendency of the pole turn to separate from the pole piece, tearing apart the epoxy bonding the pole turn to the pole.…”

“…The TQS03 magnet used the shell-based structure. The primary purpose of this series was to validate the performance of the OST RRP 108/127 strand [6] as detailed in [7]. In addition, the TQS03 goal was to perform tests under variable preload conditions.…”

Limits to High Field Magnets for Particle Accelerators

“…These measurements are particularly tricky since the real condition of stress of the cable in the magnet is hard to achieve in a sample. A few experiments on magnets, loaded with increasing stress, have shown negligible performance degradation up to 200 MPa [16]. Indeed, the larger stress is on the lower field regions and one should always be extremely careful in generalizing these results.…”