Note: Electroplating process for connectorizing superconducting NbTi cables

Experiments done at cryogenic temperatures below the 4.2 K temperature of liquid helium frequently require superconducting coaxial cables to efficiently transmit high-frequency signals while minimizing heat transfer to the experiment's cold stage. These cables are often made of niobium-titanium (NbTi) alloy which is difficult to solder directly. This note describes a new electroplating procedure for plating NbTi coax directly with copper, which enables connector attachment matching the structural and electrical properties of standard coaxial cables. Here, a cable is first electrochemically coated with a thin oxide layer and then electroplated with copper in an acidic copper sulfate solution. The procedure has modest safety requirements and may be carried out in a standard vented laboratory fume hood.