Measurement of Superconducting Busbars Models for the LHC Main Dipole

The LHC main dipoles will be connected in series by superconducting busbars, consisting of a superconducting cable brazed onto a stabilizing copper profile. In case of a quench detection, protection heaters will be activated to drive the magnet to theresistive state. In addition, the magnet will be protected by a bypass diode. In order to limit quench propagation, the excitation current is ramped down at an initial rate of 113 A/s and with a time constant equal to 104 s. When a busbar quenches, its temperature must stay below safe values. Comparative measurements of a hollow and a solid busbar were performed in 1.9 K superfluid helium, 4.2 K liquid helium and 4.2 K gaseous helium during the current ramp down. We describe the experimental set-up and report the results. The development of temperatures, the quench propagation velocities as well as the residual resistance ratio (RRR) were measured. The busbar stabilized by a solid copper profile was found to be the most appropriate choice.