Technique justification for erosion profile determining of the accelerating electrode of ions gas-discharge source

Аuthors

Dukhopel'nikov D. V.^*, Vorob'ev E. V.^**

Bauman Moscow State Technical University, MSTU, 5, bldg. 1, 2-nd Baumanskaya str., Moscow, 105005, Russia

*e-mail: duh@bmstu.ru
**e-mail: evgsparrow@gmail.com

Abstract

Determining erosion rate of electric rocket engines elements and other gas-discharge devices is the most important stage of their design and testing. The simplest method to determine the surface erosion rate under the ion bombarding may be employing of optically contrasted multilayer coatings pre-applied to the surface under study. The pattern of alternating optically contrasted bands occurs while sputtering these coatings by the non-uniform ion beams. The boundaries between these bands are the lines of equal erosion depth.

The surface slope angle in the erosion zone while a massive material sputtering by a non-uniform ion beam is determined by the equation

 

where M_a is the atomic mass of the material, ρ is its density, S_eff is effective sputtering rate, j is the ion current density, t is the ion beam exposure time, and q is the ion charge.

While selecting a multilayer coating structure computation of separate layers thickness δ_i is performed on the assumption of the required band width and the surface slope angle in the erosion zone

The layers thickness herewith should be selected so that the bands widths on the image repeatedly exceeded the registration resolution of the equipment employed for the sputtered patterns photo-registration. Thus, to obtain accurate results using the represented technique, the correct surface slopes angles a_; determining is required.

At the same time, while sputtering multilayer coatings, different points of the layer, lying in depth, begin sputtering at different time moments, in contrast the massive material. Thus, the necessity occurred to confirm the correctness of application of the expressions, obtained for the massive material, to the layers thicknesses computing of the multilayer coating.

This article is dedicated to the analytical proof of the expressions usage appropriateness to calculate the erosion slope angle and the layers thickness in the depth of the multilayer coating. It shows that these expressions can be used for any layer of any material located in the depth of the multilayer coating of arbitrary structure.

Keywords:

erosion profile, ion bombardment, multilayer coatings, ion-optical system, ion thrusters, accelerated test

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