JPS5836457B2 - micro high ongen - Google Patents

Description

[Detailed description of the invention] The present invention relates to improvements in microwave discharge ion sources.

In conventional microwave discharge ion sources, a microwave oscillator is electrically connected to a discharge box.

In ion sources, the discharge box is generally held at a high potential, either positive or negative, so in conventional ion sources, the microwave oscillator and microwave transmission line had to be held at the same high potential as the discharge box. .

For this reason, the power supply for the microwave oscillator must also be maintained at the same potential, making it difficult to take measures for insulation.

The present invention eliminates the above-mentioned drawbacks of the prior art by installing a choke structure for microwaves in the middle of the microwave transmission circuit, that is, between the microwave oscillation circuit and the discharge box.

FIG. 1 shows an example of a conventional microwave ion source, in which the discharge box is coaxial.

As can be seen from the figure, the microwave oscillator 1 and the microwave oscillator power source 8 are directly electrically connected to the discharge box 4 via the waveguide 2 and the coaxial line 3.

5 is an electromagnetic coil that generates a magnetic field in the discharge box 4; 6 is an ion extraction lens; 7 is an ion beam; and 29 is an insulator that allows microwaves to pass through and maintains a vacuum.

In this figure, a microwave transmission line in which a waveguide 2 and a coaxial line 3 are connected is used, but it is clear that the same thing can be done using only the waveguide 2 or a coaxial line.

It is also clear that if the ion extraction lens 6 is not installed, it can be used as a plasma source.

FIG. 2 is a diagram illustrating a waveguide choke structure used in the present invention.

9 is a choke flange, 10 is a flange, and 11 is an insulator.

In this figure, the distances between A and B and between B and C are each one wavelength.

Therefore, the microwave that enters this gap from point A passes through point B, is reflected at point C, and returns.

At this time, this reflected wave and the input wave interfere with each other to form a standing wave, but since the length between B and C is one wavelength, B
At the point, the wall current becomes zero.

Therefore, microwaves will not leak out from the gap at point B.

Also, since the distance between A and C is half the wavelength, the impedance seen through this gap at point A is zero, so from a microwave perspective, it is the same as if this gap does not exist.

By using such a choke structure in the middle of the waveguide 2 shown in FIG. 1, it becomes possible to use the microwave oscillator 1 and its power supply 8 at ground potential.

FIG. 3 shows another embodiment of the present invention, in which a choke structure is applied to the coaxial line.

The outer conductor has a choke structure similar to that of a waveguide.

The distance between D and E of the inner conductor is one wavelength.

In this case, the inner conductor 4 is short-circuited in terms of microwaves and insulated in terms of DC electricity, so the same effect as in the above case can be obtained.

In the figure, the left side is the discharge chamber 4, and the right side is the microwave oscillator side.

In this embodiment, the insulator 11 also serves as a vacuum seal (insulator 29 in FIG. 1).

However, separate from the insulator 11, another insulator may be installed on the left side of the insulator 11.

When the ion source is used at a high voltage of several tens of kilovolts or more, one stage of insulation as shown in FIGS. 2 and 3 may not be sufficient to withstand the voltage.

Figure 4 shows that in order to maintain dielectric strength even in such a case,
This shows an example of a two-stage structure.

12 and 13 are resistors, which are used to apply a fixed ratio of potential to each part.

Although FIG. 4 shows a case where the choke structure has two stages, it is possible to withstand pressures of 100 KV or more by increasing the number of stages.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an outline of a conventional microwave ion source, and FIGS. 2, 3, and 4 are diagrams showing embodiments of the present invention. In the figure, 1... microwave oscillator, 2...
・Waveguide, 3... Coaxial line, 4... Discharge box, 5... Electromagnetic coil, 6... Ion extraction lens system, 7... ...Ion beam, 8.
...Microwave oscillation power supply, 9...Choke flange, 10...Flange, 11...
...Insulator disk, 12.13...Resistor.

Claims (1)

[Claims] 1. In a microwave discharge type ion source consisting of a microwave oscillator, a microwave transmission circuit, and a discharge box, a choke structure is provided in the middle of the microwave transmission circuit, so that direct current flows between the microwave oscillator and the discharge box. A microwave ion source characterized by being electrically insulated and short-circuited from a microwave perspective.