Arc images acquired during the anode plume formation with HSC 1 and radiation profiles of the right side of the plume - the red dashed line shows the position of OES measurements, peak current 4.7 kA, arc duration 9.2 ms, Cu I ground state density, excitation temperature, and partial Cu pressure as functions of the distance from the plume centre for six time instants during plume formation, peak current 4.7 kA, arc duration 9.2 ms.