Busbar studies for the LHC interaction region quadrupoles

Fermilab (FNAL) and the Japanese high energy physics lab (KEK) are developing the superconducting quadrupole magnets for the interaction regions (IR) of the Large Hadron Collider (LHC). These magnets have a nominal field gradient of 215 T/m in a 70 mm bore and operate in superfluid helium at 1.9 K. The IR magnets are electrically interconnected with superconducting busbars, which need to be protected in the event of a quench. Experiments to determine the most suitable busbar design for the LHC IR magnets and the analysis of the data are presented. The main purpose of the study was to find a design that allows the inclusion of the superconducting busbars in the magnet quench protection scheme, thus avoiding additional quench protection circuitry. A proposed busbar design that was tested in these experiments consists of a superconducting cable, which is normally used for the inner layer of the Fermilab IR quadrupoles, soldered to similar Rutherford type cables as a stabilizer. A series of prototypes with varying numbers and types of stabilizers (one or two stabilizers, pure copper or Cu/NbTi composite) were tested. These samples were characterized with respect to their quench temperature profile and their quench propagation velocity during normal zone growth. From these tests, a suitable design has been determined.