In this work, plasma system that operates at vacuum was designed and built using a sheet of cobalt metal for the purpose of diagnosing plasma and measuring its parameters, as it is very important to know the processes that accompany plasma generation and are closely related to them, including the electron density in the plasma and its temperature. The spectroscopic diagnosis was done by optical emission spectroscopy (OES) which relies on the calculation of the optical radiation emitted by the plasma to describe plasma parameters in the chemical, molecular, and ionic radiator's near environment, and applied to cobalt metal at vacuum D.C high voltage power supply. The results showed the rise of spectral lines intensity with increasing the applied voltage. The maximum peak of argon gas (ArI) was at the wavelength (811.5311) nm and the maximum peak of cobalt metal (CoI) was at the wavelength of 242 nm, where argon gas was used at the fifth flow per minute with variable voltages (13-21) kV. The results also achieved that the values of electron temperature rises from (0.2708-0.6649) eV with the increase in the applied voltage, as well as the electron density from (8.108-13.851)x1017cm-3 with the stability of the argon gas flow rate at 5 l/min. The length of the plasma was measured at different gas flow rates (1-5) l/min and different applied voltages (13-21) kV that were used in this diagnosis.
