Ion source for generating negatively charged ions

 

The invention is a source for generating H-minus ions which requires no servicing. By dispensing the conventional caesium and through the external high-frequency heating of a ceramic chamber for the plasma, freedom from maintenance can be achieved.

Fields of Application

The typical field of application for this powerful H-minus source is the synchrotron and the tandem generator. Utilising it as an H-minus source in sciences (e.g. in the semiconductor technology) makes sense as well. Coupled with a tandem generator, it is possible to utilise the source as a screening device. It can also be used for the convenient production of positive ions. The source has no filament which could wear out and enables an especially clean ion generation due to the used ceramic chamber. As a result, it can be used in coating surfaces and in manufacturing semiconductors.

Problem

In previous ion sources for negative particles, caesium has always been used in order to generate electrons. Since caesium is hygroscopic, several problems with the supply occurred during the ventilation of the vacuum chambers. In addition to this, only trained personnel are allowed to operate with caesium, which has to be burnt in the air. As a consequence, a reliable permanent operation with a high-frequency source with an internal antenna in the plasma was not feasible.

Innovation

Compared to the previously used high-frequency H-minus sources, the walls of the plasma chamber of the presented new source are made of ceramics. Heating the plasma can therefore be conducted externally through an RF antenna. The plasma is held by a permanent magnetic field multicusp. The ignition of the source is performed with a tandem source, which utilises the increased pressure in the gas supply. This enables the production of a sufficient number of electrons for the ignition. A specially designed converter at the output of the plasma chamber enhances the generation of H-minus particles. This also used for the formation of the extracted beam.

Advantages

The amount of the H-minus ion particle output rate is substantially higher and more reliable compared to the yield of the previous sources of this type.
Moreover, the highest H-minus currents, which were produced without the use of caesium, have been measured with this source.
This is unique worldwide.
In addition to that, the reliability of the arrangement has been tested for several years. There is no need for the usual maintenance and dismantling of the source any longer.

Development status

The source has been operated for years for HERA with currents of 40 mA. The high-frequency output can be produced inexpensively by a semiconductor generator, which is developed at DESY.