Ionizing Device

Abstract

Ion source for use in an ion pump or other apparatus, comprising a secondary-emissive cylinder accommodating a grid. A high-frequency voltage is applied between these two electrodes so that the transit time of the diametrically moving electrons is one whole period or a multiple thereof.

Description

The invention relates to an ionizing device in which the electrons producing the ionization of the available gases perform oscillatory movements under the action of an electric high-frequency field inside a circle-cylindrical electrode inside which a circle-cylindrical grid electrode is arranged, while the transit times of the electrons are such that the electrons strike the secondary-emissive surface of the outer electrode in the same phase as that in which they leave said surface.

In application Ser. No. 718,047, filed Apr. 2, 1968 an arrangement is disclosed in which inside the grid an ion collecting electrode is arranged for the case in which the ionizing device forms part of a getter ion pump. In the case of an ion source a suction electrode is provided.

The invention has for its object to provide a simpler arrangement.

According to the invention in an ionizing device in which the electrons producing the ionization of the available gases perform oscillatory movements under the action of a high-frequency electric field inside a circular-cylindrical electrode, inside of which a grid electrode is arranged, while the transit times of the electrons are such that the electrons strike the secondary-emissive surface of the outer electrode in the same phase as that in which they leave said surface, the space inside the grid-shaped electrode is completely free, while the transit time of the electrons from the surface of the secondary-emissive electrode to the opposite side thereof is one complete period of the electric high-frequency field or an integral multiple thereof.

In contrast to the arrangement disclosed in the prior Patent Application, in which the oscillatory movements of the electrons are performed across the rods of the grid and back on the same side, the electrons in the device according to the invention travel through the circular-cylindrical grid electrode. As a result the distance covered may be more advantageous so that the possibility of ionization is increased. Because all electrons pass approximately through the axis of the electrode system, they are capable of producing an important space charge which is further amplified by the electrons released from the gas atoms. In this negative space charge the ions can stay in high concentration without diffusing outwardly so that a plasma is formed from which the ions can be sucked away by electrodes (not shown) at the axial ends of the coaxial electrode system.

It should be noted that an arrangement is known in which inside a secondary-emissive cylinder a wire-shaped electrode is axially arranged, between which two electrodes an electric high-frequency field is applied, while the resonance requirement is satisfied. However, the space charge in the axis of the system is lower and hence also the ion concentration.

The invention will be described with reference to the drawing, which shows a sectional view at right angles to the axis of the electrode system of an ionizing device.

The cylinder electrode is formed by a stainless-steel sheath 3 having a layer of superficially oxidized silver 2 on the inner side. The diameter of the sheath 3 is 240 mms. The grid 4 consists of copper and has a diameter of 180 mms. Between the electrodes 3 and 4 an alternating voltage is applied which has a frequency of 40 Mc./sec. and an amplitude of 150 v.

Claims

I claim:

1. An ion source comprising a first circular-cylindrical electrode having a secondary-emissive inner surface, a second circular-cylindrical gridlike electron-permeable electrode enclosing an unobstructed space within and concentric with said first electrode and spaced therefrom, a gas-forming ions during an electrical discharge within the space formed by the first electrode, and means to produce a high-frequency electric field between said electrodes having an amplitude and frequency whereby electrons enter said space within said second electrode and produce a space charge there within, the transit time of the electrons being such that the electrons strike the secondary-emissive surface of the first electrode in the same phase as that in which they leave said surface, and the transit time of the electrons from the secondary-emissive surface towards the opposite side thereof is at least one complete period of the electric high-frequency field.