Several cross-sections of the arc plasma column were observed side-on at different distances from the cathode. The arc was operated in argon at atmospheric
pressure with an arc current of 200 A. As a basic diagnostic method we used the Olsen-Richter diagrams. For determination of temperature the Larenz-Fowler-Milne and Boltzmann plot methods were applied. Electron density was measured from the
Stark width of the ArI and ArII lines. The continuum intensity was also measured. The equilibrium state of the plasma near the cathode tip is found to be dependent of
the axial and radial position. In the hot core, the plasma is in the LTE state. Toward outer zones, the plasma state deviates from LTE. It is caused after all by the ArI
ground state overpopulation.