ECR ION SOURCE AND METHOD FOR OPERATING AN ECR ION SOURCE

Abstract

An ECR (Electron Cyclotron Resonance) ion source includes a plasma chamber having a circular cylindrical cross-section, magnets for generating a magnetic field for confinement of the plasma in the plasma chamber, and a microwave generator disposed outside the plasma chamber and generating at least two microwave signals. Several antennas protrude radially into the plasma chamber with a predetermined angular offset . The antennas receive phase-shifted microwave signals from the microwave generator and radiate linearly polarized microwaves, which in turn produce a circularly polarized microwave inside the plasma chamber. A method for operating an ECR ion source is also described.

Claims

1. An ECR (Electron Cyclotron Resonance) ion source comprising: a plasma chamber having a circular cylindrical cross-section, magnets for generating a magnetic field for confinement of the plasma in the plasma chamber, and a microwave generator disposed outside the plasma chamber and generating at least two microwave signals, a plurality of antennas protruding radially into the plasma chamber with a predetermined angular offset , the antennas receiving phase-shifted microwave signals from the microwave generator and radiating linearly polarized microwaves which in turn produce a circularly polarized microwave inside the plasma chamber.

2. The ECR ion source of claim 1, comprising two antennas arranged on a circle of the circular-cylindrical cross section of the plasma chamber.

3. The ECR ion source of claim 1, comprising several pairs of antennas arranged in different cross-sectional planes of the circular-cylindrical cross section of the plasma chamber.

4. The ECR ion source of claim 1, wherein the predetermined angular offset is 90 and the linearly polarized microwaves are phase-shifted by 90.

5. The ECR ion source of claim 1, comprising three antennas arranged on a circle of the circular-cylindrical cross section of the plasma chamber with an angular offset of 120, and the linearly polarized microwaves are phase-shifted relative to one another by 120.

6. The ECR ion source of claim 1, comprising n antennas arranged on a circle of the circular-cylindrical cross section of the plasma chamber with an angular offset of (360/n), and the linearly polarized microwaves are phase-shifted relative to one another by (360/n).

7. The ECR ion source of claim 1, further comprising coaxial cables that transport the microwave signals from the microwave generator to the plurality of antennas.

8. The ECR ion source of claim 1, wherein the antennas feeding the microwaves into the plasma chamber are designed as rod antennas.

9. A method for operating an ECR (Electron Cyclotron Resonance) ion source, comprising: generating a magnetic field for confinement of the plasma in the plasma chamber; feeding a plurality of microwave signals via coaxial cables to a plurality of antennas arranged on a circular cylindrical cross-section of the plasma chamber and having an angular offset , and radiating with the plurality of antennas a plurality of phase-shifted linearly polarized microwaves into the plasma chamber, and superimpose the plurality of phase-shifted linearly polarized microwaves inside the plasma chamber to form a circularly polarized microwave.

10. The method according to claim 9, wherein the plurality of phase-shifted linearly polarized microwaves have a mutual phase shift of (360/n), wherein n is a number of the antennas and the angular offset of the antennas is =(360/n).

11. The method according to claim 9, wherein the plurality of antennas are arranged in pairs, and the microwave signals applied to the pair-wise arranged antennas have a mutual phase shift =90.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Further details, features and advantages of embodiments of the invention result from the following description of exemplary embodiments with reference to the appended drawings, which show in:

[0031] FIG. 1: a longitudinal section through an ECR ion source, and

[0032] FIG. 2: a cross section of the plasma chamber of an ECR ion source.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0033] FIG. 1 shows schematically a longitudinal section of an ECR ion source 1. The ECR ion source 1 essentially consists of an evacuated plasma chamber 2, in which the plasma is generated. Furthermore, magnets 3 in the shape of ring magnets are arranged around the plasma chamber 2 on both sides of the circular-cylindrical plasma chamber with a spacing there between, in which the magnetic field lines 7 are then distributed, as indicated, and the plasma is generated in the enclosed area.

[0034] The circular cylinder of the plasma chamber 2 is closed on one side, while the aperture 6, through which the directed particle beam can exit the plasma chamber 2, is disposed on the other side. Linearly polarized microwaves are fed into the plasma chamber 2 via antennas 4, wherein the microwaves are generated outside of the ECR ion source 1 in a microwave generator 8 and supplied to the antennas 4 via a coaxial cable. 5 The antennas 4 protrude radially into the circular cylinder of the plasma chamber 2.

[0035] the illustrated exemplary embodiment, two antennas 4 are provided. The arrangement of the antennas 4 is central for the applied phase shift of the microwave signals, with their superposition producing particularly efficient circularly polarized microwaves, which are used to heat the electrons that move in the space between the magnets 3 around the magnetic field lines 7 in a spiral pattern.

[0036] FIG. 2 shows a schematic side view of a plasma chamber 2 in the plane of the antennas 4, with the circular cylindrical cross section clearly visible. According to the illustrated advantageous embodiment of the invention, two antennas 4 constructed as rod antennas protrude radially into the interior of the plasma chamber 3 with an angular offset alpha of 90 degrees on the circle. The antennas 4 are connected via coaxial cables 5 to the unillustrated microwave generator.

[0037] While the invention has been illustrated and described as embodied in an ECR ion source and operating an ECR ion source, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.