A dual plasma resonator

Abstract

The present invention discloses a dual plasma resonator, comprising an external water-cooling jacket, a resonant cavity placed in the external water-cooling jacket and having a cylindrical thin-walled structure, a waveguide tube connected to the resonant cavity and supporting the resonant cavity, and a lower water-cooling jacket sleeved outside the waveguide tube and supporting the external water-cooling jacket, wherein the resonant cavity and the external water-cooling jacket are provided with stepped circular openings with reduced outer diameters at both ends, and a certain gap is provided between the end of the resonant cavity and the end of the external water-cooling jacket. The dual plasma resonator of the present invention adopts a cylindrical resonant cavity, and through theoretical calculation and design, two plasma balls are generated in the resonant cavity, and the two plasmas distribute the input microwave energy according to the relative position ratio of the waveguide tube and the resonant cavity, so that the reaction speed of the gas raw material can be increased, the uniformity of the reactants can be optimized, and at the same time, the generation of plasma with excessively concentrated energy when high microwave energy is input is avoided, which causes damage to the resonant cavity and the quartz tube.

Description

Technical Field

[0001] The invention relates to the technical fields of optical fiber preform processing, and in particular to a dual plasma resonator. Background Art

[0002] Plasma chemical vapor deposition (PCVD) is one of the main processes for optical fiber preform processing. This process has the characteristics of precise and meticulous control of the deposition process, and the plasma resonator is the core part of the processing equipment. The plasma resonator system consists of two parts: a plasma resonant cavity and a waveguide. The waveguide couples the microwave transmission generated by the microwave generator to the plasma resonant cavity, and transmits high-frequency microwave energy into the quartz liner through the plasma resonant cavity to complete the deposition process. In this process, the matching of plasma and microwave in the resonant cavity is very important. Otherwise, the mismatch between the two will not only affect the coupling effect and cause energy loss, but also easily damage the system components and affect the uniformity and accuracy of deposition.

[0003] The existing plasma resonant cavities used for the manufacture of optical fiber preforms are divided into two different structural types: coaxial type and cylindrical type. Among them, the cylindrical type is easier to realize PCVD processing of large-diameter preforms. The cylindrical resonant cavity has a simple cavity structure, is easy to process and manufacture, and has excellent deposition performance. However, all types of existing resonators are in the form of single plasma, that is, after microwave excitation resonance, a plasma ball is formed in the reaction liner. This will lead to three problems: 1) The energy is too concentrated, and it is easy to damage the resonant cavity when high energy is applied (microwave energy>10kW); 2) Realizing high-energy coupling in a short area of ​​plasma will cause uneven deposition; 3) Realizing high-energy coupling in a short area of ​​plasma will not achieve a linear proportional increase in deposition rate, that is, in the high-power area, the deposition rate will be lower than the expected linear increase value. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a dual plasma resonator which can improve the quality and efficiency of rod making in view of the deficiencies of the above-mentioned prior art.

[0005] The technical solution adopted by the present invention is: a dual plasma resonator, characterized in that it includes an external water-cooling jacket, a resonant cavity placed in the external water-cooling jacket and having a cylindrical thin-wall structure, a waveguide tube connected to the resonant cavity and supporting the resonant cavity, and a lower water-cooling jacket arranged outside the waveguide tube and supporting the external water-cooling jacket, wherein the two ends of the resonant cavity and the external water-cooling jacket are respectively provided with a stepped circular opening with a reduced outer diameter, and a certain gap is provided between the end of the resonant cavity and the end of the external water-cooling jacket.

[0006] According to the above technical solution, the conditions for forming dual plasma are:

[0007] The diameter of the resonant cavity d r =110±10mm

[0008] Through calculation and simulation, in order to ensure the effect of dual plasma, the distance between the dual plasma centers is l p ≥0.4l r ; then the inner cavity length of the dual plasma resonant cavity is required to be l r ≥100mm, at the same time, in order to ensure the matching of equipment use and deposition space, l r ≤200mm

[0009] Under the above conditions, the plasma 90% energy peak width

[0010] l pw =0.15l r

[0011] According to the above technical solution, the parameters of the resonant cavity are defined as follows:

[0012] l r =100mm~200mm,d r =110±10mm,d s =30mm~60mm,

[0013] l s =45mm~60mm

[0014] Among them r is the length of the resonant cavity, d r is the diameter of the resonant cavity, d s is the diameter of the circular openings at both ends of the resonant cavity, l s is the length of the circular openings at both ends, l pw is the plasma energy peak width.

[0015] According to the above technical solution, the opening diameter of the resonant cavity shall not be greater than 75 mm and the length shall not be less than 45 mm.

[0016] According to the above technical solution, the outer wall of the resonance cavity is in close contact with the inner wall of the external water cooling jacket, and the outer end of the opening is in close contact with the opening of the external water cooling jacket.

[0017] According to the above technical solution, the external water-cooling jacket, the resonator, the waveguide tube and the lower water-cooling jacket are detachable structures.

[0018] According to the above technical solution, the external water-cooling jacket, the resonator, the waveguide tube and the lower water-cooling jacket are detachable structures that can be separated along the center line direction and are arranged in a bilaterally symmetrical manner.

[0019] According to the above technical solution, the outer water cooling jacket and the lower water cooling jacket respectively have independent cooling water inlet and outlet interfaces.

[0020] According to the above technical solution, the waveguide tube and the lower water cooling jacket are rectangular structures, and the waveguide tube can be arranged at the axial middle position of the resonant cavity, or at a position deviated from the axial middle position of the resonant cavity.

[0021] The beneficial effects achieved by the present invention are:

[0022] 1. The dual plasma resonator described in the present invention adopts a cylindrical resonant cavity. Through theoretical calculation and design, two plasma balls are generated in the resonant cavity. The two plasmas distribute the input microwave energy according to the relative position ratio of the waveguide and the resonant cavity. This can increase the reaction speed of the gas raw material and optimize the uniformity of the reactants. At the same time, it avoids the generation of plasma with too concentrated energy when high microwave energy is input, which causes damage to the resonant cavity and quartz tube.

[0023] 2. The present invention uses a cylindrical resonant cavity and a rectangular waveguide tube, which can be split in the middle, so that it can be easily and quickly removed from the deposition machine after the deposition process is completed. In this way, the deposition and melting and shrinking functions can be integrated on the same machine. After the deposition is completed, the liner is still installed on the machine to keep the internal atmosphere stable and clean. The resonator is disassembled, and the melting and shrinking torch is started at the same time to heat the liner and maintain the temperature of the liner. In this way, the two problems analyzed above can be completely avoided, and a high-efficiency and high-quality rod making effect can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural diagram of the present invention.

[0025] Figure 2 Schematic diagram of the resonant cavity dimensions.

[0026] Figure 3 Schematic diagram of the state of plasma formation. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings.

[0028] like Figure 1As shown, this embodiment provides a dual plasma resonator, including an external water-cooling jacket 3, a resonant cavity 1 placed in the external water-cooling jacket 3 and having a cylindrical thin-walled structure, a waveguide 5 connected to the resonant cavity 2 and supporting the resonant cavity, and a lower water-cooling jacket 6 sleeved outside the waveguide and supporting the external water-cooling jacket, the resonant cavity 1 and the external water-cooling jacket 3 are respectively provided with a stepped circular opening 2 with a reduced outer diameter at both ends, the outer wall of the resonant cavity 1 is in close contact with the inner wall of the external water-cooling jacket 3, and the outer end of its opening is in close contact with the opening of the external water-cooling jacket. A certain gap is provided between the end of the resonant cavity 1 and the end of the external water-cooling jacket. Among them, the external water-cooling jacket 3 and the lower water-cooling jacket 6 have independent cooling water inlet and outlet interfaces 4 and 7, respectively, and the interface pipe diameter is 1 / 2 inch.

[0029] The following are the resonant conditions for the formation of dual plasma:

[0030] Cylindrical cavity diameter d r =110±10mm mm (this is a necessary condition for forming dual plasma)

[0031] Through calculation and simulation, to ensure the effect of dual plasma:

[0032] That is, the distance between the two plasma centers is l p =0.4l r ;

[0033] The inner cavity length of the dual plasma resonant cavity is required to be l r ≥100mm, at the same time, in order to ensure the matching of equipment use and deposition space, l r ≤200mm

[0034] Under the above conditions, the plasma 90% energy peak width

[0035] l pw =0.15l r

[0036] That is, the parameters of the resonant cavity are defined as follows:

[0037] l r =100mm~200mm,d r =110±10mm,d s =30mm~60mm,

[0038] l s =45mm~60mm

[0039] Among them, l r is the length of the resonant cavity, d r is the diameter of the resonant cavity, d s is the diameter of the circular openings at both ends of the resonant cavity, l sis the length of the circular openings at both ends, l p The distance between the center points of the two plasmas. In addition, the opening diameter of the resonant cavity 1 shall not be greater than 75 mm and the length shall not be less than 45 mm to prevent microwave leakage.

[0040] The working process of the present invention is as follows: under the excitation of microwaves with a frequency of 2.45 GHz, two connected plasmas 9 are generated in a quartz liner 8 passing through the dual plasma resonant cavity, such as Figure 3 As shown. The two plasmas distribute the input microwave energy according to the relative position ratio of the waveguide and the resonant cavity, which can increase the reaction speed of the gas raw material, optimize the uniformity of the reactants, and avoid the generation of plasma with too concentrated energy when high microwave energy is input, causing damage to the resonant cavity and quartz tube. Among them, corresponding to the maximum microwave power of 30kW, the cooling water supply conditions are: inlet pressure 3Bar~4Bar, total cooling water flow rate of 15~20L / min, and the temperature difference between the cooling water inlet and outlet Δt=10~20℃. Such a production process ensures that the inner cavity of the quartz liner tube 8 remains highly clean and does not contact the outside air during the entire rod making process, avoiding the pollution of the inner cavity by moisture and dust.

[0041] In this embodiment, the waveguide 5 and the lower water cooling jacket 6 are both rectangular structures, and a rectangular opening is provided below the resonant cavity 1, and the waveguide 5 is welded at the rectangular opening. The waveguide 5 can be arranged at the middle position of the axial direction of the resonant cavity, or at a position deviated from the middle position of the axial direction of the resonant cavity, and different positions will generate dual plasmas of different energy levels.

[0042] Since the entire rod making process includes deposition and melting and shrinking, it is generally completed in two devices: a deposition machine and a melting and shrinking machine. The liner completes the deposition process on the deposition machine, is then removed from the deposition machine, and then installed on the melting and shrinking machine. This will cause two problems: 1. In the manufacture of many special products, due to the doping of the deposition material, the internal stress of the liner after deposition is very large. The temperature of the liner just after deposition is very high (about 1000℃). The stress will not cause damage at high temperature, but during the disassembly and reinstallation process, if the time is a little longer, the temperature of the liner drops and the liner will break. 2. After the liner is removed from the deposition machine, the inner surface of the liner will inevitably come into contact with the outside air and will be polluted by the external environment, causing problems such as increased water peak, increased attenuation, and wire drawing strength.

[0043] To solve the above problems, the resonator of the present invention adopts a detachable structure, that is, the external water cooling jacket 3, the resonator 1, the waveguide 5 and the lower water cooling jacket 6 are detachable structures. Specifically, its structure is as follows Figure 1 , 2As shown, the external water cooling jacket 3, the resonator 1, the waveguide 5 and the lower water cooling jacket 6 are a detachable structure that can be separated along the center line direction (axial direction) and arranged in a left-right symmetrical manner. That is, the external water cooling jacket 3 and the resonator 1 can be divided into two independent left and right parts along their axial direction, and the two independent parts are connected and fixed by bolts.

[0044] The dual plasma resonator of the present invention can be split from the middle along the axial direction, which greatly facilitates the installation and disassembly of the equipment. After the deposition process is completed, the resonator can be immediately removed to make room, and then the liner can be melted and shrunk using a flame method, avoiding the interference of the resonator with the melting and shrinking space.

Claims

1. A dual plasma resonator, characterized in that: The invention comprises an external water cooling jacket, a resonant cavity which is placed in the external water cooling jacket and has a cylindrical thin-wall structure, a waveguide which is connected to the resonant cavity and supports the resonant cavity, and a lower water cooling jacket which is sleeved outside the waveguide and supports the external water cooling jacket, wherein the resonant cavity and the external water cooling jacket are respectively provided with stepped circular openings with reduced outer diameters at both ends, and a certain gap is provided between the end of the resonant cavity and the end of the external water cooling jacket, and the conditions for forming dual plasmas are as follows: the diameter of the resonant cavity body dr=110±10mm mm, the inner cavity length of the dual plasma resonant cavity lr≥100mm, and the distance between the center points of the dual plasmas lp≥0.4lr; the parameters of the resonant cavity are defined as follows: lr=100mm-200mm, ds=30mm-60mm, ls=45mm-60mm; wherein lr is the length of the resonant cavity body, ds is the diameter of the circular openings at both ends of the resonant cavity, and ls is the length of the circular openings at both ends; the external water cooling jacket, the resonator, the waveguide and the lower water cooling jacket are detachable structures.

2. The dual plasma resonator according to claim 1, characterized in that: The opening diameter of the resonant cavity shall not be greater than 75mm and the length shall not be less than 45mm.

3. The dual plasma resonator according to claim 1, characterized in that: The outer wall of the resonant cavity is in close contact with the inner wall of the external water cooling jacket, and the outer end of the opening of the resonant cavity is in close contact with the opening of the external water cooling jacket.

4. The dual plasma resonator according to claim 1, characterized in that: The outer water cooling jacket, the resonator, the waveguide tube and the lower water cooling jacket are detachable structures which can be separated along the center line direction and are arranged in a bilaterally symmetrical manner.

5. The dual plasma resonator according to claim 1, characterized in that: The outer water cooling jacket and the lower water cooling jacket respectively have independent cooling water inlet and outlet interfaces.

6. The dual plasma resonator according to claim 1, characterized in that: The waveguide tube and the lower water cooling jacket are rectangular structures, and the waveguide tube is arranged at the axial middle position of the resonance cavity or at a position deviating from the axial middle position of the resonance cavity.

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