JPS63184299A - Plasma apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a plasma device that generates plasma using microwave discharge and is used for laser excitation or plasma processing.

[Conventional technology]

Conventionally, there are various types of plasma devices that utilize microwave discharge, such as laser devices, light source devices, plasma processing devices, and ion sources.

Figure 8 shows, for example, Journal of Applied
Physics Vol, 49. Aγ, July
19γg, P, 3γ53 A sectional view showing a conventional gas laser device as a plasma device, and FIG. 9 is a B-B i plane view in FIG. In the figure (
3) is a waveguide that transmits microwaves, I3υ is a waveguide taper provided in a part of this waveguide, The laser discharge tube (to) is a laser gas inlet provided at the end of the laser discharge tube, cMJ is also a laser gas outlet, and (to) is a cooling gas arranged to surround the laser discharge tube (33). Air supply pipe, (to) is a cooling gas inlet provided at the end of this cooling gas air supply pipe, C171 is also a cooling gas outlet, (to) is a Brewster window provided at both ends of the laser discharge tube 3z. , 01 is an anode for the original nine books for DC discharge.

In a conventional gas laser device as described above.

A laser gas such as CO2 laser gas is introduced into the laser emission IIyco from a laser gas inlet (toward), while a TEjQ mode microwave is excited in the waveguide +31. This waveguide (31) has a waveguide taper Gυ inside, and the inner diameter of the waveguide (3) is minimum at the position where the laser discharge tube ω is installed.

At this position, the microwave electric field is at its maximum. This strong microwave electric field destroys the laser gas in the laser discharge tube (2), generates plasma, and excites the laser medium. At this time, for example, low-temperature N2 is
Laser oscillation conditions can be obtained by flowing gas at high speed, cooling the laser discharge tube from the outside, and appropriately selecting discharge conditions such as laser gas pressure. Laser oscillation is performed by providing a mirror for laser oscillation (not shown).

[Study points that invention attempts to solve]

In the conventional gas laser device as described above, since a closed laser discharge tube 32 is used, when conductive plasma is generated, a coaxial mode microwave is generated using the plasma in the laser discharge tube as an inner conductor. mode becomes dominant, and the microwave electric field in the plasma becomes an electric field whose main component is a component parallel to the tube wall of the laser discharge tube G3, and the microwaves penetrating into the plasma are absorbed into the tube of the laser discharge tube C33. The mode is incident perpendicularly to the wall, that is, the plasma boundary.

In this way, in a discharge generated by microwaves incident perpendicularly to the plasma boundary, the microwave electric field decreases from the discharge tube wall toward the inside, but because the discharge plasma has constant voltage characteristics, the microwave electric field decreases. The difference in electric field causes a large change in current density, resulting in the generation of a significantly non-uniform plasma concentrated near the wall of the discharge tube.

This situation is shown in the sectional view of FIG. C31 in the figure
1 is a waveguide 9 taper, C13 is a laser discharge tube, (
69) is the electric field line of the microwave electric field + (70) is the plasma. In conventional gas laser devices that utilize microwave discharge, non-uniform plasma as shown in Figure 10 is generated, making it difficult to create an appropriate state for laser excitation throughout the discharge, and the laser resonator There was a problem that the laser output and efficiency were low because the mode and plasma overlapped. In fact, the device shown in Figure 8 uses a 132Hz Nohalus microwave with a frequency of 2.45G) fz and a pulse width of 1μs with a peak power of 2.
When operated at 6 kW, an average output of only 15 mW was obtained. This is thought to be because due to the non-uniformity of the discharge explained by Superior C, it was possible to operate only with a very low pulse duty of 1 μ5,132 Hz in pulse width, that is, about 1/10,000.

The above explanation has been given using a gas laser device as an example of conventional plasma mounting, but various problems have also occurred in other plasma devices due to non-uniform discharge.

This invention was made to solve the above-mentioned problems, and its object is to obtain a plasma device that generates spatially uniform microwave discharge plasma.

[Means for solving problems]

A gas laser device according to the present invention is formed between a conductor wall forming a part of a micro circuit such as a waveguide and a conductor provided opposite to the conductor wall. The space is filled with laser gas and plasma is generated by microwave discharge using pulsed microwaves.

[Effect]

In the plasma device according to the present invention, since there is a conductor wall with frost guide columns higher than the plasma, which faces the dielectric body which is the microwave incidence window, the terminal end of the incident microwave is not directed to the four electric conductor walls. 'QLk, which penetrates between the uN body and the conductor wall, flows in the plasma,
With pulsed microwaves, a spatially uniform plasma is generated.

Plasma becomes more uniform spatially.

〔Example〕

FIG. 1 is an overview diagram showing a gas laser device according to an embodiment of the present invention, in which (1) is a magnetron which is a microwave launcher, (2) is a waveguide, and (3 is a waveguide (2). Expanding horn m tracheid with a width of ; (4) is a microwave coupling window *
(51 is a mirror for laser oscillation, (6) is a laser head section, and FIG. 2 is a sectional view taken along FIG. 1 A-A showing details of the laser head section (6). As shown in Figure 2, the laser head part (6) has a structure of a ridge waveguide type microwave cavity, which is a layer of the microwave circuit.
In the figure, * (61) is the cavity-74) al wall following the micro temporary bonding window (4), (62) and (66) are the ridges formed at the center of the cross section of this cavity wall, (
64) is a helmet formed on one of these (62).

(65) is a conductor wall forming a part of the microwave circuit, and in this embodiment, the wall surface of the groove (64) is used. (66) is a dielectric material such as alumina provided opposite to this conductive wall (65), and (67) is a dielectric material such as alumina that is provided to face the conductive wall (65), and (67) is a dielectric material such as alumina that is provided to face the conductive wall (65). A discharge space is formed between the body wall (65) and the dielectric (66), and a laser gas such as CO2 laser gas is sealed in this discharge space (67).

Further, (68) is a cooling water channel formed in the ridges (62) and (63).

On the other hand, the power source for driving the magnetron (1) is constructed as shown in FIG. In Fig. 3, a commercial frequency AC power source E is converted into DC by a rectifier and smoothing circuit fil), and this DC is converted to, for example, 20KH by a DC-AC inverter circuit 0z.
It is converted into high frequency alternating current like z.

This high-frequency alternating current is boosted by transformer +13, and capacitor C, diode D1. It is converted into a high-voltage pulsating current by the half-wave voltage doubler rectifier circuit I composed of D2.

Applied to the magnetron (1). a9 is a filament power source for the magnetron (1).

In the gas laser device according to the present invention configured as shown in FIGS. 1 to 3, microwaves generated by a magnetron ill pass through a waveguide (2) and a horn waveguide (
3), and is efficiently coupled to the laser head section (6) by performing impedance matching at the microwave coupling window (4). As shown in the cross-sectional view of FIG. 2, the laser head section (6) has a ridge cavity shape, and the microwaves are concentrated between the ridges (62) and (63).

The strong % magnetic field of this concentrated microwave causes the discharge space (
The laser gas sealed in 67) is discharged to generate plasma, and the laser medium is excited. Here, the laser oscillation conditions are obtained by flowing cooling water into the cooling channel (68) to cool the discharge plasma and appropriately selecting the discharge conditions such as the pressure of the laser gas. Laser oscillation light can be obtained by forming a laser resonator with another mirror (not shown).At this time, in the gas laser device according to the present invention, a conductive wall forming a part of the microwave circuit is used. Microwave discharge is performed in the discharge space (67) formed between the electric conductor wall (65) and the IH body (66), which is provided opposite to this conductor wall (65) and serves as a microwave incidence window. Therefore, the microwave is incident only from one side of the plasma, and the phenomenon in which the microwave mode of the "dowa" mode with the plasma as the inner conductor becomes dominant does not occur, and the microwave is injected from the desired micro-absorption mode. It is possible to cause discharge to occur.

Furthermore, when the microwave circuit forms a micro-limb mode having an electric field component perpendicular to the boundary between the body (66) and the plasma, as in the ridge cavity shown in FIG. Since the body walls (65) are placed facing each other, the conductor walls (65) also have an electric field component perpendicular to them, creating an electric field that circulates the plasma. At this time, even if plasma is generated that waits for 24 hours, it will not enter the microwave because there is a conductive wall (65) that is several orders of magnitude higher in conductivity than the plasma, facing the dielectric (66) that is the microwave incidence window. The current at the end of the microwave flows through this conductor wall (65), and the flow passes through the conductor wall (65).
5) The nearby electric field is forced approximately perpendicular to the surface of the conductor wall (65) to maintain the electric field through the plasma. Therefore, the microwave penetrates into the plasma, a current flows through the plasma, and the continuity of the current results in a spatially uniform discharge plasma. This situation is shown in the enlarged sectional view of FIG. In the figure, (69) is the frost energy i of the microwave electric field,
(70) is discharge plasma. According to the gas laser device according to the present invention, uniform discharge as shown in FIG. 4 can be obtained. However, nodes of the discharge occur in the direction perpendicular to the paper plane of FIG. 4, that is, in the length direction of the discharge, depending on the mode of the microwave.

In the embodiment of the present invention, the power source shown in FIG. 3 is used as a power source for a magnetron, which is a microwave excavator that generates microwaves. The microwave generated by the magnetron driven by this power source has a waveform as shown in FIG. That is, pulsed microwaves interrupted by high-frequency waves are generated. The pulse duty of this pulsed microwave can be set to a very large value, for example 0.1 to 0.4, compared to that of a conventional pulsed microwave. In addition, the pulse wave number can be very high, such as several tens of Ki (z). When the apparatus shown in Figs. It was confirmed that the length of the cut becomes shorter and the length becomes more uniform in the length direction.Also, if the pulse frequency is about 500Hz or higher, temporal modulation of plasma parameters is suppressed and the cut length becomes more uniform in the length direction. A uniform plasma is generated.

By obtaining a uniform discharge as described above, it is easy to bring the entire discharge into the optimal state for laser excitation, and the overlap between the laser resonator mode and the plasma is good, making it possible to achieve a uniform discharge using conventional microwave discharge. It is possible to obtain laser excavation with an order of magnitude higher efficiency and higher output than the gas laser device K.

FIG. 6, which shows an experimental example by the present inventors, is a graph of the experimental results when the device with the configuration shown in FIGS. 1 to 3 and a discharge length of 300 m111 is applied to a CO21/- ther. The axis is the microwave input, and the vertical axis is the co2 laser output and efficiency. Here, 2M as a magnetron
120 (manufactured by Hitachi) to generate microwaves of approximately 2.45 GHz. The pulse frequency is 20 KHz and the pulse duty is 0.4. As shown in Figure 6, a maximum output of 24 W and a maximum efficiency of 10.5% were obtained, and an output that was three orders of magnitude higher than the CO2 laser output of 15 W reported in the conventional example shown in Figure 6. In addition, it was confirmed that in the conventional example, only pulsed rooting could be obtained, whereas in the apparatus according to the present invention, although the microwave is pulsed, the laser can perform Y rooting.

In the above embodiment, an inverter is used as the magnetron's power source, but the pulse micronumber may be generated using a chopper-type power source that is applied to the magnetron from a high-voltage DC power source through a switching element. Furthermore, although a laser device is shown as the plasma device in the above embodiment, the present invention may also be applied to an ion source or a power plasma processing device.

The effect of making the discharge uniform spatially and over 9 hours is similar.

In addition, in the above embodiment, the microwave circuit uses a full ridge wire, a groove is formed in the ridge, and the groove is covered with a dielectric material to form a discharge space. It is also possible to use a kou-xing 1-sho route as shown in Figure 7. In Fig. 7, (67) is the discharge space,
(61) and (65) are an outer conductor and an inner conductor, respectively, constituting a coaxial line.

(66) is a dielectric material such as a quartz glass tube. With such a configuration, even if plasma is generated in the discharge space by pulsed microwaves, it is the same as that shown in FIG. 2.

The discharge becomes uniform. In addition, there is a conductive wall that forms part of the microwave circuit, and this 2j! A discharge space is formed between the electrical wall and the dielectric material provided opposite to the electrical wall.

As long as it excites a microwave mode that has an electric field component perpendicular to the boundary between the dielectric material and the discharge space, that is, the plasma, any configuration can be used in conjunction with pulsed microwaves as shown in Figure 2 and Figure 2. Similar to the case shown in FIG. 7, the effect of making the discharge more uniform can be obtained.

Furthermore, in the above embodiment, the conductor and plasma are in contact with each other, but even if a thin dielectric layer such as a dielectric coating layer is provided on the surface of the conductor, this dielectric layer will have a large effect on the electric field distribution of microwaves. Needless to say, the above effect is not impaired since there is no influence.

〔Effect of the invention〕

As described above, according to the present invention, in a plasma device, the conductor wall that constitutes a part of the microwave circuit and the
A plasma generation medium is sealed in a space formed between a dielectric material provided opposite to an electric wall, and a microwave circuit generates a microphone mode having a component perpendicular to the boundary with the dielectric material. Since pulsed microwaves are excited within the temporary micro circuit, a spatially uniform plasma can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an overview diagram showing a gas laser device as a plasma device according to an embodiment of the present invention, and FIG. 2 is a diagram showing FIG. 1 A-A.
FIG. 3 is a power supply circuit diagram of a microwave oscillator according to an embodiment of the present invention. Figure 4 is an enlarged cross-sectional view of the main part explaining the state of discharge in Figure 2, Figure 5 is a diagram showing the waveform of the microwave generated using the power supply in Figure 3, and Figure 6 is the diagram shown in Figure 1. Graphs showing laser oscillation characteristics in the embodiments shown in FIGS.
The figure is a sectional view showing another embodiment of the present invention, FIG. 8 is a sectional view showing a conventional gas laser device, and FIG. 9 is a sectional view taken along the line B-B in FIG.
FIG. 10 is a cross-sectional view illustrating the state of discharge in a conventional gas laser device. In the figure, (65) is a conductive wall that forms part of the microwave circuit, (66) is a dielectric, (67)
is the discharge space. (70) is discharge plasma. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (4)

[Claims] (1) In a plasma device that generates plasma by microwave discharge in a microwave circuit, a conductive wall forming a part of the microwave circuit and a dielectric provided opposite to the conductive wall are used. A plasma generation medium that generates the plasma is enclosed in the space formed between the two, and the microwave circuit forms a microwave mode having an electric field component perpendicular to the boundary between the dielectric and the plasma. A plasma device characterized by exciting pulsed microwaves within a microwave circuit. (2) The plasma device according to claim 1, wherein the pulse frequency of the pulsed microwave is 500 Hz or more. (3) Pulsed microwaves are driven by a power source that converts direct current into alternating current with a frequency higher than the commercial frequency using an AC-DC inverter, boosts the voltage using a transformer, and then generates a pulsating high voltage using a half-wave voltage doubler circuit. The plasma device according to claim 1, characterized in that the plasma is generated by a microwave oscillator. (4) The plasma apparatus according to claim 1, wherein the pulsed microwave is generated by a microwave oscillator driven by a high-voltage pulsed power supply in which high-voltage direct current is intermittent by a switching element.