Difference in Stability Between Edge and Center in a Rutherford Cable

Abstract

Abstract-Keystoned superconducting Rutherford cables are widely used in accelerator magnets like in the LHC at CERN. An essential requirement in the cable design is its stability against local heat releases in the magnet windings originating from for example, strand movement or beam loss. Beam loss is the highest at the coil inner radius of the magnet, where also the magnetic field peaks. Also the local compaction of the cable is maximum here and hence the helium content minimum. When performing stability measurements on several superconducting Nb-Ti cables used in LHC dipole and quadrupole magnets, we observed that the stability against point-like heat disturbances is much worse very close to the cable edges as compared to the central part of the cable. The main reason is related to the geometry of the cable causing variation of many parameters across the cable width, like inter-strand electrical resistance, inter-strand heat conductivity, cooled strand surfaces and RRR. In this paper we show results of new stability experiments and thoroughly compare the data with results obtained with the numerical network model CUDI, which is updated for stability simulations.

Critical Current and Stability of High-${\rm J}_{\rm c}$${\rm Nb}_{3}{\rm Sn}$ Rutherford Cables for Accelerator Magnets

“…Interestingly, the kink is at the same position as for the center heater and for currents lower than the kink the QE is similar to the center heater. This is unlike previous work done on Nb-Ti [11], where it was shown that the single strand behavior was the same, but the kink in the QE curve shifts.…”

Nb3Sn Wire Shape and Cross-Sectional Area Inhomogeneity in Rutherford Cables

“…This cross sectional area variations explain at least partly the cabling induced critical current and nvalue degradation that is observed even in Nb-Ti cables that are not strain sensitive. The relatively small wire cross section at the thin cable edge may also contribute to the reduced thermal stability at the thin edge of Rutherford cables [9].…”

Stability of superconducting Rutherford cables for accelerator magnets

“…Measurements [57] show that the cable edge is more likely to quench than the cable center position. The exact geometry of a cable determines thermal and electrical exchange between strands.…”

“…Neutron tomography experiments and optical measurements have been performed on lhc 01 cables to reveal all geometry parameters of the cross-section of the cable [57]. Neutron tomography provides cross-section images obtained by analyzing transparency variations between the different materials.…”