Inductively coupled plasma device

Abstract

To increase the possibility of igniting and sustaining inductively coupled plasma at atmospheric pressure.SOLUTION: An inductively coupled plasma device includes a plasma torch 7, a coil 6 connected to a transistor-type high-frequency power supply and wound around the plasma torch, and a retention promotion unit 74 that promotes retention of gas within the plasma torch under atmospheric pressure.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an inductively coupled plasma device. [Background technology]

[0002] Patent Document 1 describes a method for igniting a plasma torch, in which high-frequency energy generated by a high-frequency induction coil wound around the outer periphery of a predetermined region of a tube having one end as a closed end surface and the other end as an open end surface opening into a chamber is applied to a core gas injected into the tube to obtain a high-temperature plasma fire. A vacuum exhaust device for connecting a pipe is provided inside the tube, and a lid member capable of abutting against the open end surface of the tube to close it is provided in a chamber that constantly maintains normal pressure, and the lid member is configured to be attracted to or detached from the open end surface depending on the pressure difference between the chamber and the tube. At the time of ignition, the lid member is abutted against the open end surface of the tube where the injection of core gas has been stopped, and the vacuum exhaust device is driven to generate a glow discharge by high-frequency energy in the tube that has been brought into a predetermined reduced pressure state, and then the core gas is gradually injected into the tube to convert the glow discharge into a high-temperature plasma fire, and at the same time, the lid member is configured to be detached by its own weight from the open end surface of the tube that has approached normal pressure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 61-68900 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 describes that when generating plasma, a vacuum exhaust device is driven to create a predetermined reduced pressure state.

[0005] The present invention aims to increase the possibility of igniting and sustaining an inductively coupled plasma at atmospheric pressure. [Means for solving the problem]

[0006] In order to achieve the above object, the inductively coupled plasma device of the present invention comprises a plasma torch, a coil connected to a transistor-type high-frequency power supply and wound around the plasma torch, and a retention promotion unit that promotes retention of gas inside the plasma torch under atmospheric pressure. Effect of the Invention

[0007] According to the present invention, it is possible to increase the possibility of igniting and maintaining an inductively coupled plasma under atmospheric pressure. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is an explanatory diagram of an inductively coupled plasma device. [Diagram 2] FIG. 2 is a cross-sectional view of a plasma torch. [Diagram 3] FIG. 11 is an explanatory diagram showing another example of a circuit. [Figure 4] FIG. 11 is a cross-sectional view of a plasma torch according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the present invention will be described based on the illustrated embodiment, however, the present invention is not limited to the embodiment described below.

[0010] <Studies conducted by the inventor> First, the inventors conducted the following studies.

[0011] In a conventional inductively coupled plasma device, it is possible to ignite a thermal plasma at atmospheric pressure by using a high frequency current of about several MHz from a vacuum tube power supply. Alternatively, when using a transistorized power supply (performance-wise, around 400 kHz), it is known to ignite thermal plasma by drawing a vacuum inside the torch (at a vacuum of around 100 Pa). In other words, the disadvantage of a drop in output frequency caused by replacing a vacuum tube power supply with a transistorized power supply is compensated for by creating a vacuum inside the torch, making it possible to ignite thermal plasma.

[0012] Regarding the vacuum tube power supplies used for thermal plasma ignition under atmospheric pressure, many vacuum tube parts are no longer in production and the power efficiency is relatively poor. Therefore, thermal plasma ignition using transistor power supplies is desirable. On the other hand, since the vacuum equipment required to create a vacuum inside the torch is somewhat costly, it would be ideal if the vacuum equipment was not required.

[0013] Based on the above findings, the inventor of the present invention has come up with an invention for igniting thermal plasma at atmospheric pressure (i.e., without using a vacuum facility) using a transistor-type power supply of about 400 kHz. The embodiment of the invention will be described below.

[0014] First Embodiment 1 and 2, the inductively coupled plasma device 1 includes a high-frequency power supply 2 equipped with a transistor of about 400 kHz, a matching transformer 3, a first capacitor group 4 and a second capacitor group 5, and a plasma torch 7 around which a coil 6 is wound. Note that the plasma torch 7 is not shown in FIG.

[0015] 1, a high-frequency power supply 2 and a coil 6 are connected via a matching transformer 3. The winding ratio of the primary side to the secondary side of the matching transformer 3 is, for example, 4:1. The matching transformer 3 and an upper end 61 of the coil 6 are connected via a first capacitor group 4, and the matching transformer 3 and a lower end 62 of the coil 6 are connected via a second capacitor group 5.

[0016] The first capacitor group 4 includes 13 capacitor subgroups connected in series, and each subgroup includes three capacitors connected in parallel. The 13 subgroups are called the first subgroup, the second subgroup, ..., and the thirteenth subgroup from the power supply side to the load side. The power supply side end of the tenth subgroup 410 is short-circuited with the load side end of the eleventh subgroup 411. The power supply side end of the twelfth subgroup 412 is short-circuited with the load side end of the thirteenth subgroup 413. The capacitance of each capacitor is, for example, 0.2 μF.

[0017] The second capacitor group 5 includes 13 capacitor subgroups connected in series, each of which includes three capacitors connected in parallel, each of which has a capacitance of, for example, 0.2 μF.

[0018] As shown in Fig. 2, the plasma torch 7 has a tubular main body 71 made of quartz glass. The axial direction of the main body 71 is the up-down direction. A coil 6 made of a metal pipe is wound around the main body 71. Cooling water for cooling the coil flows through the hollow part of the metal pipe.

[0019] An inner tube 71a made of quartz glass and having an axial dimension smaller than that of the main body 71 is provided coaxially with the main body 71. The lower end of the main body (i.e., outer tube) 71 and the lower end of the inner tube 71a are generally aligned in the up-down direction. In this way, the plasma torch 7 has a partial double tube structure.

[0020] A gas supply unit 72 is provided to close the lower end openings of the main body 71 and the inner tube 71a. This gas supply unit 72 is connected to a gas tank (not shown) and supplies argon gas into the main body 71. A hole 72a extending in the vertical direction is formed in the center of the gas supply unit 72. A thin and long electrode 73 that serves as a trigger for plasma ignition is inserted into this hole 72a. Specific examples of the electrode 73 include a tungsten rod and a carbon rod, but the electrode 73 is not limited to these. The electrode 73 is configured to be able to advance and retreat relative to the main body 71.

[0021] Gas flow paths 72b and 72c are provided around the hole 72a in the gas supply part 72 to supply argon gas into the main body part 71. The gas flow path 72b is connected to the inside of the inner pipe 71a, and the gas flow path 72c is inside the main body part (i.e., the outer pipe) 71 and is connected to the outside of the inner pipe 71a.

[0022] A lid 74 made of phenol resin is disposed on the upper end of the main body 71 so as to close the upper end opening. The lid 74 is provided with a vertical hole 74a communicating with the inside of the main body 71. The purpose of the lid 74 is to retain the argon gas heated by the non-equilibrium plasma inside the torch. Also, by providing the lid 74, the pressure inside the torch increases slightly when argon gas is supplied, preventing outside air from entering the torch. If the torch were closed with a lid without hole 74a, argon gas would escape from a gap between the torch and the lid, which would be roughly the error between the two. If the lid were simply placed on the top end of the torch, the lid would be unstable and may float when argon gas is supplied. In addition, argon gas leaking out from the gap between the torch and the lid may come into contact with the coil directly, causing an arc discharge outside the torch and resulting in ignition failure. To prevent this, hole 74a is provided to allow excess argon gas to escape above the torch.

[0023] In the inductively coupled plasma device 1 as described above, the procedure for plasma ignition is as follows. First, in the first step, argon gas is supplied to the main body 71 to fill the inside of the torch with argon gas. The arrows shown in Fig. 2 indicate the flow of argon gas. Next, in the second step, a high-frequency current is passed through the coil 6, causing the coil lower end 62 to become high voltage. Then, the electrode 73 is inserted inside the main body 71. Since argon gas is easily ionized, an arc discharge occurs between the lowest coil turn (one turn of the coil) of the coil, which is at high voltage, and the electrode 73, which is at earth potential. At this time, the lid 74 prevents the argon gas heated by the non-equilibrium plasma from diffusing outside the main body 71 . In the third step, the argon gas is heated and a thermal plasma is ignited. If the lid 74 is simply placed on the top end of the torch, the impact of ignition will blow the lid off. After ignition, the electrode 73 is stored outside the main body 71.

[0024] The second and third steps will now be described in more detail. When an arc discharge is occurring, the magnetic field inside the torch fluctuates due to the high-frequency current flowing through coil 6, switching the magnetic poles (north pole, south pole) at both ends of coil 6 (Ampere's law). An electric field is created inside the torch in the opposite direction to the coil current to cancel out the generated magnetic field (Faraday's Law). The electrons generated by the arc discharge move (are heated) under the influence of the electric field. When a moving electron collides with an argon atom, it ionizes it, and the argon atom splits into an argon ion and an electron. The split electron is accelerated by the effect of an electric field and collides with another argon atom, ionizing it again. In this way, ionization occurs one after another. When the arc discharge spreads throughout the torch and the argon ions also begin to undergo thermal motion, a thermal plasma is ignited.

[0025] A plasma in which the energy of electrons is higher than that of argon ions and has not yet reached thermal equilibrium is called a non-equilibrium plasma. A plasma in which the energy of electrons is approximately equal to the energy of argon ions is called a thermal plasma (or thermal equilibrium plasma).

[0026] The inductively coupled plasma device 1 uses a transistor-type power supply 2 of about 400 kHz and is capable of increasing the possibility of igniting and maintaining induction thermal plasma of argon gas under atmospheric pressure. Because it is under atmospheric pressure, vacuum equipment is not required. In addition, because a transistor-type power supply is used, it is possible to avoid the use of vacuum tube-type power supplies, the parts of which are often no longer in production. Furthermore, the provision of the lid 74 allows the argon gas, which has been heated by the non-equilibrium plasma and thus becomes even lighter, to remain in the torch, making it easier to generate the subsequent thermal plasma.

[0027] 1, in the inductively coupled plasma device 1, a plurality of resonant capacitors are distributed and arranged in the first capacitor group 4 and the second capacitor group 5. The effect of this will be described below in comparison with FIG.

[0028] 3 shows a coil 9 as a comparative example. An upper end 91 of the coil 9 is connected to a matching transformer (output of 100 volts, for example), and no capacitor is connected between the upper end 91 and the matching transformer. A lower end 92 of the coil 9 is connected to the matching transformer via a capacitor group 93. As an example, if the potential on the upper end 91 side is taken as a reference potential (0 volts), when the voltage at both ends of the coil 9 is 12,000 volts, the potential of the lower end 92 of the coil 9 is 12,000 volts.

[0029] In the inductively coupled plasma device 1, if the potential at the connection point between the first capacitor group 4 to which the upper end 61 of the coil 6 is connected and the matching transformer 3 (with an output of 100 volts, for example) is taken as the reference potential, then, for example, the potential at the upper end 61 of the coil 6 is −5000 volts and the potential at the lower end of the coil 6 is 7000 volts. The voltage at both ends of the coil 6 is 12000 volts, which is the same as that of the coil 9.

[0030] In this way, although the voltage of coil 6 and coil 9 is the same at 12,000 volts, the potential of the lower end of coil 6 can be made lower than that of coil 9. In this way, according to the inductively coupled plasma device 1, since a plurality of resonant capacitors are distributed and arranged in the first capacitor group 4 and the second capacitor group 5, the potential of the upper end and the lower end of the coil can be made lower without changing the coil voltage. This prevents discharge with the earth potential, and also suppresses leakage from the cooling water. Furthermore, by changing the capacitor balance between the upper end side and the lower end side of the coil, the potential of the upper end and the lower end of the coil can be changed. In addition, because the coil current is an alternating current, the voltage changes sign over time, and the voltage has real and imaginary parts. However, for ease of understanding, these points have been omitted from the above explanation of potential and voltage.

[0031] <Second embodiment> In the first embodiment described above, the lid 74 is used as a retention promoting member for promoting gas retention in the main body 71, but this is not limited thereto. FIG. 4 shows a plasma torch 7a. The same reference numerals are used for parts common to the plasma torch 7 shown in FIG. 2. The upper end of the main body 71 around which the coil 6 is wound is provided with an extension tube 75, which is cylindrical and has the same radial dimension as the main body 71, instead of the lid 74. The coil 6 is not wound around the extension tube 75. The extension tube 75 can also promote gas retention in the main body 71, like the lid 74.

[0032] If the coil current is increased, there is a possibility that thermal plasma will ignite regardless of the presence or absence of the lid 74 and the extension cylinder portion 75. However, an increase in the coil current causes problems such as heat generation in the coil itself and an increase in the coil voltage, making stable ignition difficult. In contrast, according to the first and second embodiments described above, gas retention in the main body 71 is promoted, so that it is possible to increase the possibility of stable ignition and maintenance of thermal plasma while suppressing an increase in the coil current.

[0033] Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications and changes can be made based on the technical concept of the present invention. [Explanation of symbols]

[0034] 1. Inductively coupled plasma device 2. Transistor-type high-frequency power supply 3 Matching transformer 4,5 Capacitor group 410~413 Capacitor subgroup 6 Coils 61 Upper end 62 Lower end 7, 7a Plasma torch 71 Main body 71a Inner tube 72 Gas Supply Section 73 Electrode 74 Lid 75 Extension cylinder part

Claims

1. Plasma torch and, A transistorized high-frequency power supply is connected to the coil wound around the plasma torch, A retention-promoting unit that promotes the retention of gas within the plasma torch under atmospheric pressure, An inductively coupled plasma device equipped with [specific features / equipment].

2. The inductively coupled plasma apparatus according to claim 1, wherein the retention promoting unit is a lid provided to close the opening of the plasma torch.

3. The inductively coupled plasma apparatus according to claim 1, wherein the retention promoting unit is a plasma torch extension unit connected to the axial end of the plasma torch.

4. A capacitor connected between one end of the coil and the transistorized high-frequency power supply, A capacitor connected between the other end of the coil and the transistorized high-frequency power supply. An inductively coupled plasma apparatus according to any one of claims 1 to 3, further comprising:

Images