This custom-made AC plasma welding torch was produced to solve a specific problem faced by an international Civil Aircraft Manufacturer and a well know Welding Research Institution. This investigation was looking at the potential of using the hard-to-weld copper bearing aluminium 7000 series alloys for future aerospace structures. Our plasma welding torch made possible the keyhole welding of thick sections in a hard access situation while requiring welding currents of up to 400amps AC. The plasma welding process was proved to be the only way of providing a solution to the problem of micro porosity and critically high weld integrity with this difficult material.