阅读说明：本技术 一种环形微波等离子体谐振腔 (Annular microwave plasma resonant cavity ) 是由 蔡冰峰 刘志坚 黄文俊 曾建军 岳静 于 2020-05-08 设计创作，主要内容包括：本发明公开了一种环形微波等离子体谐振腔,涉及微波等离子体谐振腔领域,包括：谐振腔壳体,其内设有一腔体；第一截止波导,其固定在谐振腔壳体的一端,第一截止波导包括一收容于腔体内的筒体,筒体与谐振腔壳体形成一环形空腔,且筒体上设有多条狭缝；第二截止波导,其固定在谐振腔壳体的另一端,第二截止波导至少部分伸入腔体内以与筒体相连,并与筒体连通形成一用于收容石英反应管的安装孔。本发明中的环形微波等离子体谐振腔能使负载反射系数S<Sub>11</Sub>维持在较低的水平,并能够提高微波能量的耦合率,以获得高密度的等离子体。(The invention discloses an annular microwave plasma resonant cavity, which relates to the field of microwave plasma resonant cavities and comprises the following components: the resonant cavity shell is internally provided with a cavity; the first cut-off waveguide is fixed at one end of the resonant cavity shell and comprises a cylinder body accommodated in the cavity, the cylinder body and the resonant cavity shell form an annular cavity, and a plurality of slits are arranged on the cylinder body; and the second cut-off waveguide is fixed at the other end of the resonant cavity shell, at least part of the second cut-off waveguide extends into the cavity to be connected with the cylinder and is communicated with the cylinder to form a mounting hole for accommodating the quartz reaction tube. The annular microwave plasma resonant cavity can lead the load reflection coefficient S to be higher than the load reflection coefficient 11 The plasma is maintained at a low level, and the coupling ratio of microwave energy can be improved to obtain high-density plasma.)

1. A toroidal microwave plasma resonator, comprising:

the resonant cavity shell (1) is internally provided with a cavity (11);

the first cut-off waveguide (2) is fixed at one end of the resonant cavity shell (1), the first cut-off waveguide (2) comprises a cylinder (21) accommodated in the cavity (11), the cylinder (21) and the resonant cavity shell (1) form an annular cavity, and a plurality of slits (22) are arranged on the cylinder (21);

and the second cut-off waveguide (3) is fixed at the other end of the resonant cavity shell (1), at least part of the second cut-off waveguide (3) extends into the cavity (11) to be connected with the cylinder (21), and is communicated with the cylinder (21) to form a mounting hole (4) for accommodating a quartz reaction tube (8).

2. A toroidal microwave plasma resonator according to claim 1, wherein: and a third cut-off waveguide (5) is fixed at each of two ends of the resonant cavity shell (1), the two third cut-off waveguides (5) are respectively sleeved on the first cut-off waveguide (2) and the second cut-off waveguide (3), each third cut-off waveguide (5) is provided with a through hole communicated with the mounting hole (4), and each third cut-off waveguide (5) is provided with a choke groove (51).

3. A toroidal microwave plasma resonator according to claim 2, wherein: and two sides of the bottom end of the resonant cavity shell (1) are respectively provided with a cooling water pipe (6), and two third cut-off waveguides (5) are internally provided with first cooling water channels (52) communicated with the corresponding cooling water pipes (6).

4. A toroidal microwave plasma resonator according to claim 3, wherein: the rectangular waveguide cooling water system is characterized in that a rectangular waveguide inlet (12) is formed in the outer side of the bottom end of the resonant cavity shell (1), a rectangular waveguide (7) is arranged on the rectangular waveguide inlet (12), and the rectangular waveguide (7) is located between the two cooling water pipes (6).

5. A toroidal microwave plasma resonator according to claim 4, wherein: and second cooling water channels are arranged on two sides of the rectangular waveguide (7), and third cooling water channels (13) communicated with the corresponding second cooling water channels are arranged on two sides of the resonant cavity shell (1).

6. A toroidal microwave plasma resonator according to claim 1, wherein: each slit (22) is parallel to the axis of the annular cavity.

7. A toroidal microwave plasma resonator according to claim 6, wherein: the number of the slits (22) is three or four.

8. A toroidal microwave plasma resonator according to claim 1, wherein: the length of the slit (22) is 1/4 lambda-lambda, the width of the slit (22) is 1/20 lambda-1/10 lambda, wherein lambda is the wavelength of the microwave.

9. A toroidal microwave plasma resonator according to claim 2, wherein: the width of the choke groove (51) is 1/4 lambda-lambda, the depth of the choke groove (51) is 1/8 lambda-1/2 lambda, and lambda is the wavelength of the microwave.

10. A toroidal microwave plasma resonator according to claim 2, wherein: the two third cut-off waveguides (5) are fixed on the resonant cavity shell (1) through screws.

Technical Field

The invention relates to a plasma resonant cavity, in particular to an annular microwave plasma resonant cavity.

Background

The PCVD (Microwave Activated Plasma Chemical Vapor Deposition) process is one of the main processes for preparing optical fiber preform core rods. The microwave plasma has the advantages of large energy, strong activity, high density of excited plasma, stable work, no electrode pollution and the like, and is very suitable for the deposition of the optical fiber preform. Under the low pressure, the raw material gas (mainly SiCl4, GeCl4, POCl3, O2, C2F6 and the like) entering the quartz reaction tube is partially ionized into an activated plasma state due to the action of high-frequency microwaves, and the active ions can rapidly react to form reaction products which are deposited on the inner surface of the tube wall in a glass state. Since the microwave plasma cavity is rapidly moved and a single layer is deposited with a thin thickness, it is easy to manufacture a fine and complicated refractive index profile.

A microwave plasma resonant cavity for exciting plasma chemical vapor deposition is a core device of a PCVD deposition machine tool. At present, the existing microwave plasma resonant cavities for manufacturing the optical fiber perform mainly have a coaxial type and a cylindrical type, wherein the coaxial type microwave plasma resonant cavity is suitable for processing a quartz reaction tube with a relatively smaller outer diameter, and the cylindrical type microwave plasma resonant cavity is suitable for processing a quartz reaction tube with a relatively larger outer diameter, and both the two types of microwave plasma resonant cavities have respective defects.

The coaxial microwave plasma resonant cavity is not suitable for manufacturing a large-diameter optical fiber preform due to structural limitation. When high-power microwaves are input, the cavity and the coaxial line waveguide are easy to heat, and the resonant cavity or the coaxial line waveguide can be burnt in severe cases.

The cylindrical microwave plasma resonant cavity has the problem that the load is difficult to match, namely the reflection coefficient S of the load can not be ensured₁₁Is small enough. Because the doped SiO2 after vitrification is deposited in a molten glass state in the PCVD deposition processThe thickness of the tube wall of the quartz tube reaction tube is gradually increased, the inner diameter of the reaction tube is continuously reduced, the plasma density and the shape are changed, so that the load of the resonant cavity is changed, and the load reflection coefficient S is changed₁₁This will increase and there is a possibility that the loads will not match. In addition, the load reflection coefficient S₁₁The increase means that the reflected power is increased, the microwave energy absorbed by the load is reduced, and the energy utilization efficiency of the whole microwave system is also reduced, so that the working load of the microwave matching element is increased or the microwave matching element is damaged in severe cases.

Disclosure of Invention

In view of the defects in the prior art, the invention aims to provide a method for enabling the load reflection coefficient S₁₁The ring-shaped microwave plasma resonant cavity can maintain a low level and can improve the coupling rate of microwave energy so as to obtain high-density plasma.

In order to achieve the above purposes, the technical scheme adopted by the invention is as follows:

a toroidal microwave plasma resonator comprising:

the resonant cavity shell is internally provided with a cavity;

the first cut-off waveguide is fixed at one end of the resonant cavity shell and comprises a cylinder body accommodated in the cavity, the cylinder body and the resonant cavity shell form an annular cavity, and a plurality of slits are arranged on the cylinder body;

and the second cut-off waveguide is fixed at the other end of the resonant cavity shell, at least part of the second cut-off waveguide extends into the cavity to be connected with the cylinder and is communicated with the cylinder to form a mounting hole for accommodating a quartz reaction tube.

In some embodiments, a third cut-off waveguide is fixed at each of two ends of the resonator housing, the two third cut-off waveguides are respectively sleeved on the first cut-off waveguide and the second cut-off waveguide, each of the two third cut-off waveguides is provided with a through hole communicated with the mounting hole, and each of the third cut-off waveguides is provided with a choke groove.

In some embodiments, a cooling water pipe is respectively disposed on two sides of the bottom end of the resonant cavity housing, and a first cooling water channel communicated with the corresponding cooling water pipe is disposed in each of the two third cut-off waveguides.

In some embodiments, a rectangular waveguide inlet is formed in the outer side of the bottom end of the resonant cavity shell, a rectangular waveguide is arranged on the rectangular waveguide inlet, and the rectangular waveguide is located between the two cooling water pipes.

In some embodiments, a second cooling water channel is disposed on each of two sides of the rectangular waveguide, and a third cooling water channel communicated with the corresponding second cooling water channel is disposed on each of two sides of the resonator housing.

In some embodiments, each of the slits is parallel to the axis of the annular cavity.

In some embodiments, the number of slits is three or four.

In some embodiments, the slits have a length of 1/4 λ - λ and a width of 1/20 λ -1/10 λ, wherein λ is the wavelength of the microwaves.

In some embodiments, the width of the choke groove is 1/4 λ - λ and the depth of the choke groove is 1/8 λ -1/2 λ, where λ is the wavelength of the microwaves.

In some embodiments, two of the third stop waveguides are fixed to the resonator housing by screws.

Compared with the prior art, the invention has the advantages that:

the annular microwave plasma resonant cavity is provided with an annular cavity structure with a slit coupling structure, because the slit is parallel to the axis of the annular cavity, the current of the inner wall of the cavity is cut off, a radiation slot antenna is formed, simultaneously, microwave energy is coupled to a quartz reaction tube and plasma through the radiation slot antenna, and in the PCVD deposition process, along with the increase of the tube wall thickness of the quartz reaction tube, the load reflection coefficient S of the annular microwave plasma resonant cavity is increased₁₁Still maintained at a low level. Meanwhile, the coupling rate of microwave energy can be improved by isolating the plasma from the microwave plasma resonant cavity and adopting a mode of coupling the microwave energy by the slit waveguideHigh density plasma can be obtained. In addition, the third cut-off waveguide with the choke groove is additionally arranged at the two ends of the resonant cavity shell, so that microwave leakage is reduced. In addition, a water cooling structure is added on the main body structure of the annular microwave plasma resonant cavity, so that the size deformation of the cavity at high temperature is reduced.

Drawings

FIG. 1 is a side view of a toroidal microwave plasma cavity in an embodiment of the present invention;

FIG. 2 is a front view of a toroidal microwave plasma cavity in an embodiment of the present invention;

FIG. 3 is a cross-sectional view taken along A-A of FIG. 1;

FIG. 4 is a sectional view taken along the direction B-B in FIG. 2 when the number of slits is 3;

FIG. 5 is a sectional view taken along the direction B-B in FIG. 2 when the number of slits is 4;

FIG. 6 is a graph showing the load reflection coefficient S of a toroidal microwave plasma resonator and other types of microwave plasma resonators in accordance with an embodiment of the present invention₁₁A comparison graph of the curves of the wall thickness of the quartz reaction tube.

In the figure: 1-resonant cavity shell, 11-cavity, 12-rectangular waveguide inlet, 13-third cooling water channel, 2-first cut-off waveguide, 21-cylinder, 22-slit, 3-second cut-off waveguide, 4-mounting hole, 5-third cut-off waveguide, 51-choke groove, 52-first cooling water channel, 6-cooling water pipe, 7-rectangular waveguide, 8-quartz reaction pipe and 9-plasma.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Referring to fig. 1 to 4, an embodiment of the present invention provides a ring-shaped microwave plasma resonator including a resonator housing 1, a first cut-off waveguide 2, and a second cut-off waveguide 3.

Wherein, the resonant cavity shell 1 is provided with a cavity 11 therein. In the present embodiment, the material of the resonator housing 1 may be copper, brass, aluminum alloy, or stainless steel.

The first cut-off waveguide 2 is fixed at one end of the resonant cavity shell 1, the first cut-off waveguide 2 includes a cylinder 21 accommodated in the cavity 11, the cylinder 21 and the resonant cavity shell 1 form an annular cavity, and the cylinder 21 is provided with a plurality of slits 22. The slit 22 can cut off the current on the inner wall of the cavity to form a radiation slit antenna, and the microwave energy can be coupled to the quartz reaction tube 8 and the plasma 9 through the slit 22.

And the second cut-off waveguide 3 is fixed at the other end of the resonant cavity shell 1, at least part of the second cut-off waveguide 3 extends into the cavity 11 to be connected with the cylinder 21, and is communicated with the cylinder 21 to form a mounting hole 4 for accommodating a quartz reaction tube 8.

In this embodiment, since the first cut-off waveguide 2 includes a cylinder 21, on one hand, the cylinder 21 forms a ring-shaped cavity with the resonator housing 1, and on the other hand, the cylinder 21 is also used to mount the quartz reaction tube 8, so that the plasma mounted in the quartz reaction tube 8 is isolated from the ring-shaped cavity by the cylinder 21. Meanwhile, as the plurality of slits 22 are further arranged on the cylinder 21, the microwave energy is prevented from being directly loaded to the plasma 9 and coupled to the quartz reaction tube and the plasma 9 through the slits, so that the plasma 9 has small influence on the resonant cavity which is a ring-shaped cavity, the coupling efficiency of the microwave energy can be improved, and the high-density plasma can be obtained.

As a better implementation, each slit 22 in the present embodiment is parallel to the axis of the annular cavity, and since the slits 22 are parallel to the axis of the annular cavity, the microwave energy can be better coupled to the quartz reaction tube 8 and the plasma 9 through the slits 22.

As a better implementation manner, in this embodiment, a third cut-off waveguide 5 is fixed at both ends of the resonator housing 1, two third cut-off waveguides 5 are respectively sleeved on the first cut-off waveguide 2 and the second cut-off waveguide 3, each of the two third cut-off waveguides 5 is provided with a through hole communicated with the mounting hole 4, and each of the third cut-off waveguides 5 is provided with a choke groove 51. Preferably, two of the third cut-off waveguides 5 in this embodiment are fixed on the resonator housing 1 by screws, and the material of the third cut-off waveguides 5 may be copper, brass, stainless steel or silicon carbide.

When the microwave plasma resonant cavity works, due to the existence of the plasma 9, the structure of the third cut-off waveguide 5 with the choke groove 51 and the plasma 9 can be approximately seen as a section of coaxial waveguide, and due to the addition of the choke groove 51, the attenuation of the microwave transmitted by the equivalent coaxial waveguide is greatly increased, so that the microwave energy leaked from the microwave plasma resonant cavity can be reduced.

Preferably, in order to better reduce the microwave energy leaked from the microwave plasma resonant cavity, the width of the choke groove 51 in the embodiment is 1/4 λ - λ, and the depth of the choke groove 51 is 1/8 λ -1/2 λ, where λ is the wavelength of the microwave.

As a better implementation manner, two sides of the bottom end of the resonator housing 1 in this embodiment are respectively provided with a cooling water pipe 6, and a first cooling water channel 52 communicated with the corresponding cooling water pipe 6 is provided in each of the two third stop waveguides 5.

In addition, a rectangular waveguide inlet 12 is formed in the outer side of the bottom end of the resonant cavity housing 1 in the embodiment, a rectangular waveguide 7 is arranged on the rectangular waveguide inlet 12, and the rectangular waveguide 7 is located between the two cooling water pipes 6.

Furthermore, both sides of the rectangular waveguide 7 are provided with a second cooling water channel, and both sides of the resonator housing 1 are provided with a third cooling water channel 13 communicated with the corresponding second cooling water channel.

Preferably, in this embodiment, the second cooling water channel and the third cooling water channel 13 on one side are also communicated with the corresponding cooling water pipe 6, and the lower part of the cooling water pipe 6 has 4 pipeline outlets in total, and can be connected with an external circulating water supply pipeline in a series or parallel manner. Because the circulating water pipeline is arranged to cool the microwave plasma resonant cavity, the size deformation of the microwave plasma resonant cavity can be reduced, and the requirement of working in the high-temperature environment of the microwave plasma resonant cavity is met. Preferably, the cooling water inlet pressure in the embodiment is 2-6 Bar, the total inlet flow is 5-30L/min, and the inlet temperature is 15-35 ℃.

As a better implementation, the number of the slits 22 in this embodiment is three or four, and it is understood that the number of the slits 22 can be set reasonably according to actual needs.

Referring to fig. 4, when the number of the slits 22 is three, in order to increase the coupling of the slits 22 to the energy in the quartz reaction tube 8, the angle θ between the two slits 22 at the connection with the rectangular waveguide 7 in the present embodiment is 60 to 120 °, the length of the slit 22 is 1/4 λ to λ, and the width of the slit 22 is 1/20 λ to 1/10 λ, where λ is the wavelength of the microwave.

Referring to fig. 5, when the number of the slits 22 is four, in order to increase the energy coupling of the slits 22 into the quartz reaction tube 8, the included angle θ between the two slits 22 at the connection with the rectangular waveguide 7 in the present embodiment is 40 to 120 °, and the included angle β between the two slits 22 at the side is 40 to 100 °. The length of the slit 22 is 1/4 lambda-lambda, and the width of the slit 22 is 1/20 lambda-1/10 lambda, where lambda is the microwave wavelength.

After the annular microwave plasma resonant cavity in the embodiment is adopted, as shown in fig. 6, compared with other types of microwave plasma resonant cavities, in the PCVD deposition process, as the thickness of the tube wall of the quartz reaction tube increases, the load reflection coefficient S is increased₁₁Still maintained at a low level. The microwave energy is now almost entirely absorbed by the load (mainly the plasma) to maximize the energy efficiency of the entire microwave system.

In summary, in the annular microwave plasma resonant cavity of the present invention, by providing the annular cavity structure having the slit coupling structure, since the slit is parallel to the axis of the annular cavity, the current on the inner wall of the cavity is cut off, and a radiation slot antenna is formed, and simultaneously, the microwave energy passes through the radiationThe slot antenna is coupled to the quartz reaction tube and the plasma, and the load reflection coefficient S of the slot antenna is increased along with the increase of the tube wall thickness of the quartz reaction tube in the PCVD deposition process₁₁Still maintained at a low level. Meanwhile, the coupling rate of microwave energy can be improved by isolating the plasma from the microwave plasma resonant cavity and adopting a mode of coupling the microwave energy by the slit waveguide, and high-density plasma can be obtained. In addition, the third cut-off waveguide 5 with choke grooves is added at two ends of the resonant cavity shell 1, so that microwave leakage is reduced. In addition, a water cooling structure is added on the main body structure of the annular microwave plasma resonant cavity, so that the size deformation of the cavity at high temperature is reduced.

In the description of the present application, it should be noted that the terms "upper", "lower", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, which are only for convenience in describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and operate, and thus, should not be construed as limiting the present application. Unless expressly stated or limited otherwise, the terms "mounted," "connected," and "connected" are intended to be inclusive and mean, for example, that they may be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.

It is noted that, in the present application, relational terms such as "first" and "second", and the like, are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The above description is merely exemplary of the present application and is presented to enable those skilled in the art to understand and practice the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.