The experimental part of an integrated approach to design and optimization of plasma arc cutting devices will be presented; in particular results obtained through diagnostics based on high speed imaging and Schlieren photography and some evidences obtained through experimental procedures. High speed imaging enabled to investigate start-up transition phenomena in both pilot arc and transferred arc mode, anode attachment behaviour during piercing and cutting phases, cathode attachment behaviour during start-up transient in PAC torches with both retract and high frequency pulse pilot arc ignition. Schlieren photography has been used to better understand the interaction between the plasma discharge and the front. The behaviour of hafnium cathodes at high current levels at the beginning of their service life was experimentally investigated, with the final aim of characterizing phenomena that take place during those initial piercing and cutting phases and optimizing the initial shape of the surface of the emissive insert.