Ion flux control in hall accelerators

Аuthors

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

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
***e-mail: ivakhnenko@bmstu.ru

Abstract

Hall thrusters are widely used for satellite orbit correction and marching operations for altitude change. At the same time the accelerators designed according to similar schemes acquired wide spread occurrence in vacuum ion plasma technologies as ion-cleaning and nano-scale surface treatment systems.

In a first approximation, in the design of such devices it is assumed that the magnetic field does not affect the ions movement in the accelerating channel. Actually, the ions deflected slightly in azimuthal direction under magnetic field impact, whereby the beam acquires the shape of one-sheet hyperboloid. With the thrusters, it might lead to the plume spread, derating and angular momentum occurrence. This leads to significant divergence of the ion beam in the technological accelerators operating on relatively lightweight argon. For surface cleaning before coating deposition such

divergence of circular beam is acceptable, since maximum processing area is required. However, for dimensional ion beam processing narrow ion beams with Gauss ion current density distribution are required. At the same time, effect of the ion azimuthal deviation does not allow focusing the ion beam of the Hall accelerator only by coning the walls of the acceleration channel.

In this paper, additional magnetic pole was installed for focusing ion beam into a spot with Gauss ion current density distribution along radius at the outlet of the cone acceleration channel of the ion source. This magnet pole produced the magnetic field which vector is opposed to magnetic field vector in the channel. Ion beam in the additional magnetic pole area turns in azimuthal direction, opposite to its turn in the acceleration chamber. As a result, the beam is coned and focused at a specified distance into a spot with maximum ion current density concentrated in the center.

The paper formulates the criterion of optimum ion beam focusing in accelerator with anode layer. The ion current density distribution along the radius of the focused ion beam was measured with the accelerator experimental sample. It was shown that the installation of additional magnetic pole allows focusing the ion beam completely.

The obtained results can be used in the design of ion sources for punctual ion-beam machining of the details for optical and electronic industry.

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Keywords:

Lorentz force, accelerator with anode layer, Hall-effect thruster, ion beam focusing

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