The United States High Luminosity Large Hadron Collider Accelerator Upgrade Project (US-HL-LHC AUP) is designing and fabricating 11 Q1/Q3 cold masses for the interaction regions of the LHC. Each cold mass contains two 4.2 m quadrupole magnets. The Nb3Sn quadrupole magnets operate in superfluid He at 1.9 K with a nominal field gradient of 132.6 T/m. The design and fabrication of the through and local buses for the cold masses is carried out at Applied Physics and Superconducting Technology Division at Fermilab (FNAL). The bus-bars consist of two superconductive NbTi cables soldered together and wrapped in Kapton.
This paper reports the characterization of the bus-bar thermo-electric properties to validate the bus design and assure quench protection. Calculations have been performed to estimate the quench integral, the quench propagation velocity and the maximum voltage developed in the bus. The bus design was validated testing the cable together with a short Nb3Sn magnet in the vertical test facility of Applied Physics and Superconducting Technology Division at FNAL.
The test demonstrated that the bus design is sound; no spontaneous quench took place up to 17870 A current value. Temperature margins were measured to be higher than the required 5 K for the High-Luminosity Q1/Q3 triplet bus at nominal operating current. Protection studies revealed that the bus can be adequately protected using 100 mV voltage threshold value for the entire current range the magnet will operate in the LHC tunnel. Results of quench propagation velocity and quench integral measurements as a function of temperature and current are also presented in this paper.