Experimental investigation of ion parameters in a cathodic arc plasma operated with nitrogen gas

The ion kinetic energy and ion density was determined for the plasma generated in the outer region of the arc channel in a pulsed low-pressure cathodic arc. The device was operated with N₂ gas and with a Ti cathode within the pressure range 10^-2-150 Pa, with a peak current of 520 A. A retarding field analyzer, a spherical Langmuir probe, and a calorimetric system were employed. The resulting kinetic energy for both Ti⁺ and Ti⁺⁺ ions was 40±3 eV at the cathode spots. The obtained values for the ion density are in agreement with those predicted by hydrodynamic models with spherical symmetry if the ion current penetrating into the outer region is taken as 10% of the total discharge current. It was also found that the ion density increases (and the ion kinetic energy decreases) with the filling pressure, a fact that can be attributed to an ion slowing by elastic collisions with neutrals. This behavior cannot be explained with the presence of a shock wave separating a plasma region from an unperturbed neutral gas region