JP5241578B2 - Induction thermal plasma generation method and apparatus - Google Patents

Description

  The present invention relates to an induction thermal plasma generation method, and more particularly to a method for generating thermal plasma by supplying high-frequency power to an induction coil via an impedance matching circuit, and an apparatus for generating thermal plasma by this method.

  In general, thermal plasma has a high temperature and a large heat capacity, and can quickly heat an object to be heated. Further, by applying an electromagnetic field from the outside, the thermal plasma flow is controlled to achieve a desired temperature, speed, A thermal plasma having a shape can be generated. For this reason, it is widely applied to oxide reduction, plasma spray coating generation, plasma CVD (chemical vapor deposition) method, MHD (electromagnetic fluid) power generation, powder generation of refractory metal, and the like.

  In particular, high-frequency induction thermal plasma can realize a high-temperature hot plasma space rich in reactivity without an electrode. Therefore, compared to direct-current plasma that uses arc discharge between electrodes, it is based on sputtering and melting of electrode metal. It has a feature that it is possible to form a clean, high-temperature, high-speed plasma medium that is free from contamination problems. This feature is very advantageous in the raw material production field in that the contamination with impurities is extremely small and the reaction can be promoted in any medium (inert atmosphere, oxidizing atmosphere, reducing atmosphere, etc.).

As an apparatus for generating such high-frequency induction thermal plasma, for example, Patent Document 1 discloses an inductively coupled plasma apparatus as shown in FIG.
A MOSFET inverter circuit 16 is connected to the three-phase AC power supply 10 via a three-phase full-wave rectifier circuit 12 and a smoothing capacitor 14. An induction coil 22 is wound around the discharge tube 20 of the plasma torch 18, and an output terminal of the MOSFET inverter circuit 16 is connected to both ends of the induction coil 22 via an impedance matching circuit 24.

  The impedance matching circuit 24 sets the resonance frequency of the load impedance including the plasma load within the drive frequency region of the inverter circuit 16 in order to efficiently supply the power from the inverter circuit 16 to the plasma inside the discharge tube 20. It performs impedance matching and comprises a matching transformer 26 and resonant capacitors 28 and 30. The primary coil of the matching transformer 26 is connected to the output terminal of the inverter circuit 16, and the resonant capacitors 28 and 30 are connected between the secondary coil of the matching transformer 26 and the induction coil 22. A series resonance circuit 32 is formed by the secondary coil of the matching transformer 26, the resonance capacitors 28 and 30 and the induction coil 22, and the plasma load is included by changing the capacitance of the resonance capacitors 28 and 30. The resonance frequency of the load impedance can be adjusted.

  Normally, as the resonant capacitors 28 and 30 connected to both ends of the induction coil 22, those having substantially the same electrostatic capacitance are selected, and when a high frequency current is passed through the induction coil 22, The neutral potential is formed at substantially the center.

  The three-phase alternating current supplied from the three-phase alternating current power supply 10 is rectified by the three-phase full-wave rectifier circuit 12 and smoothed by the smoothing capacitor 14, and then converted into high-frequency power by the inverter circuit 16, and the impedance matching circuit 24 To the induction coil 22. By flowing a high-frequency large current through the induction coil 22 in this way, a high voltage is applied to the gas introduced into the discharge tube 20 that has been previously decompressed, and the thermal plasma is ignited.

JP-A-11-251088

However, in the conventional inductively coupled plasma apparatus as described above, in order to realize the generation of plasma, the inside of the discharge tube 20 is decompressed to a very high vacuum state, and then a large coil voltage is applied to the induction coil 22. It is necessary to generate plasma by applying. Japanese Patent Application Laid-Open No. 61-161138 discloses a method of generating plasma by induction heating with a metal piece arranged at the center of a high-frequency induction coil and triggering thermoelectrons emitted from the metal piece, and A method for generating plasma using a glow discharge generated by reducing the plasma space as a fire type is disclosed. Furthermore, as described in Japanese Patent Application Laid-Open No. 62-86700, there is also a method of generating plasma by using a high voltage generated by applying a voltage using a Tesla coil in a decompressed plasma space as a trigger.
The present invention has been made to solve such problems, and an induction thermal plasma generation method and apparatus capable of generating thermal plasma under a higher pressure than before or by applying a coil voltage smaller than that of the prior art. The purpose is to provide.

An induction thermal plasma generation method according to the present invention is an induction thermal plasma generation method for generating thermal plasma by supplying high frequency power to an induction coil via an impedance matching circuit including capacitance means. It has a pair of adjustable capacitances connected to one end side and the other end side, respectively, and at least when the thermal plasma is ignited, the capacitance of the pair of capacitances is different from each other. and wherein approximately equal to Rukoto each other.

The induction thermal plasma generating apparatus according to the present invention, the induction thermal plasma generator for generating thermal plasma by supplying high frequency power to the induction coil through an impedance matching circuit including the capacitance means, the capacitance means, the induction coil has one end and the other end a pair of capacitance adjustable capacitance connected respectively to the pair of capacitance is set to different capacity upon ignition of at least the thermal plasma, approximately equal to each other after the ignition of the thermal plasma characterized Rukoto set to capacity.

Et al is a ignition determination means for determining whether the thermal plasma is ignited, when the thermal plasma is determined not yet ignited by ignition determination means set to different capacity pair of capacitance, the ignition determination means after the thermal plasma is determined to be ignited is preferably provided with a control means for setting substantially have equal capacity to each other a pair of capacitance.

  According to the present invention, at least when the thermal plasma is ignited, the capacitance of the impedance matching circuit is biased so that the capacitance of the capacitance means is equal to or greater than a predetermined value on one end side and the other end side of the induction coil. Compared to the case where there is no voltage, a larger voltage is generated between one end or the other end of the induction coil and the end of the plasma torch, and thermal plasma is applied under a higher pressure than before or by applying a smaller coil voltage than before. It is possible to generate the effect.

It is a circuit diagram which shows the structure of the induction thermal plasma generator which concerns on Embodiment 1 of this invention. 3 is a circuit diagram showing a series resonance circuit used in the induction thermal plasma generator according to Embodiment 1. FIG. It is a circuit diagram which shows the series resonance circuit used for the conventional induction thermal plasma generator. FIG. 5 is a circuit diagram showing a configuration of an induction thermal plasma generator according to a second embodiment. FIG. 5 is a circuit diagram showing a configuration of an induction thermal plasma generator according to a third embodiment. FIG. 6 is a circuit diagram showing a configuration of an induction thermal plasma generator according to a fourth embodiment. It is a figure which shows the result of an Example. It is a circuit diagram which shows the structure of the conventional induction thermal plasma generator.

Hereinafter, the present invention will be described in detail based on preferred embodiments shown in the drawings.
Embodiment 1
FIG. 1 shows the configuration of an induction thermal plasma generator according to Embodiment 1 of the present invention. A MOSFET inverter circuit 16 is connected to the three-phase AC power supply 10 via a three-phase full-wave rectifier circuit 12 and a smoothing capacitor 14. An induction coil 22 is wound around the discharge tube 20 of the plasma torch 18, and an output terminal of the MOSFET inverter circuit 16 is connected to both ends of the induction coil 22 via an impedance matching circuit 34.
That is, the induction thermal plasma generation apparatus according to the first embodiment has an impedance matching circuit 34 connected between the inverter circuit 16 and the induction coil 22 instead of the impedance matching circuit 24 in the conventional apparatus shown in FIG. Is.

The impedance matching circuit 34 includes a matching transformer 26 and a resonance capacitor 36. The primary coil of the matching transformer 26 is connected to the output terminal of the inverter circuit 16, and the secondary coil of the matching transformer 26 is connected. A resonant capacitor 36 is connected between one end 26 a and one end 22 a of the induction coil 22. The other end 26b of the secondary coil of the matching transformer 26 and the other end 22b of the induction coil 22 are directly connected to each other.
A series resonance circuit 38 is formed by the secondary coil of the matching transformer 26, the resonance capacitor 36, and the induction coil 22. The capacitance (hereinafter referred to as capacitance) C of the resonance capacitor 36 is set so that the resonance frequency of the series resonance circuit 38 including the plasma load is within the drive frequency region of the inverter circuit 16. The resonant capacitor 36 constitutes the capacitance means of the present invention.

  The discharge tube 20 of the plasma torch 18 has, for example, a double tube structure composed of an inner cylinder and an outer cylinder made of quartz, respectively, and is cooled by circulating cooling water between the inner cylinder and the outer cylinder. Thus, the inner cylinder that receives heat from the thermal plasma flame generated in the plasma torch 18 is prevented from becoming too hot. The upper end and the lower end of the discharge tube 20 constitute a plasma torch 18, respectively.

Next, the operation of the induction thermal plasma generator according to the first embodiment will be described.
The three-phase alternating current supplied from the three-phase alternating current power supply 10 is rectified by the three-phase full-wave rectifier circuit 12 and smoothed by the smoothing capacitor 14, and then converted into high-frequency power by the inverter circuit 16, and the impedance matching circuit 32. To the induction coil 22.

  At this time, as shown in FIG. 2, a high-frequency voltage V0 transformed according to the turn ratio of the matching transformer 26 is generated in the secondary coil of the matching transformer 26, and thereby the resonance capacitor 36 A high-frequency current flows, and a voltage V <b> 1 is generated between both ends of the resonance capacitor 36. Here, when the resonance frequency of the series resonance circuit 38 is close to the drive frequency of the inverter circuit 16, the impedance of the series resonance circuit 38 becomes small and a large current flows through the series resonance circuit 38. Voltage V1 has a relationship of V0 << V1 with respect to the high-frequency voltage V0 of the secondary coil of the matching transformer 26, and a high voltage substantially equal to V1 is applied across the induction coil 22. Further, a neutral potential is formed at substantially the central portion A of the secondary coil, and the upper end and the lower end of the discharge tube 20 are also supported by electrically grounded metal parts to become a neutral potential. Therefore, the voltage between the other end 22b of the induction coil 22 directly connected to the other end 26b of the secondary coil of the matching transformer 26 and the lower end of the discharge tube 20 is V0. A high voltage substantially equal to V1 is formed between 22a and the upper end of the discharge tube 20. Then, this high voltage is applied to the gas introduced into the discharge tube 20 that has been decompressed in advance, and thermal plasma is ignited.

  For comparison, FIG. 3 shows a circuit diagram of a series resonance circuit 32 in the conventional induction thermal plasma generator shown in FIG. In this series resonant circuit 32, there are a pair of resonant capacitors 28 and 30 connected in series with each other. Therefore, in order to make the impedance of the series resonant circuit 38 in the first embodiment shown in FIG. The capacitances of the resonance capacitors 28 and 30 are 2C with respect to the capacitance C of the resonance capacitor 36 of the first embodiment.

  When the high-frequency voltage V0 is generated in the secondary coil of the matching transformer 26, a high-frequency current flows through the pair of resonant capacitors 28 and 30, and a voltage V1 / 2 is generated between both ends of the resonant capacitors 28 and 30, respectively. . For this reason, a neutral potential is formed at approximately the center A of the secondary coil of the matching transformer 26 and a neutral potential is formed at approximately the center B of the induction coil 22. Here, when the resonance frequency of the series resonance circuit 32 is close to the drive frequency of the inverter circuit 16, the relationship V0 << V1 / 2 is established between the voltage V1 / 2 and the voltage V0. A voltage substantially equal to V1 / 2 is formed between the end 22b and the central portion B and between the one end 22a of the induction coil 22 and the central portion B. Further, since the upper end and the lower end of the discharge tube 20 are also at a neutral potential, between the other end 22b of the induction coil 22 and the lower end of the discharge tube 20 and between the one end 22a of the induction coil 22 and the discharge tube 20 A voltage substantially equal to V1 / 2 is also formed between the upper end portions. As described above, when the series resonant circuit 32 in which the resonant capacitors 28 and 30 having the capacitance 2C are connected to both ends of the induction coil 22 is used, the voltage applied to the gas in the discharge tube 20 is approximately V1 /. 2.

  That is, in the first embodiment, the resonance capacitor 36 is connected only to one end 22a side of both ends of the induction coil 22, so that the resonance capacitors 28 and 30 having the same capacity are respectively connected to both ends of the induction coil 22. Compared to this circuit, it is possible to apply almost twice the voltage to the gas in the discharge tube 20. For this reason, thermal plasma is likely to be generated, and thermal plasma can be generated under a pressure higher than that of the prior art or by supplying a high frequency power smaller than that of the prior art.

Embodiment 2
FIG. 4 shows the configuration of the induction thermal plasma generator according to the second embodiment. In this induction thermal plasma generator, an impedance matching circuit 40 is connected between the inverter circuit 16 and the induction coil 22 instead of the impedance matching circuit 34 in the apparatus of the first embodiment shown in FIG. Other circuits and elements are the same as those used in the apparatus of the first embodiment.

  The impedance matching circuit 40 includes a matching transformer 26 and resonant capacitors 42 and 44, and the resonant capacitor 42 is disposed between one end 26 a of the secondary coil of the matching transformer 26 and one end 22 a of the induction coil 22. A resonance capacitor 44 is connected between the other end 26 b of the secondary coil of the matching transformer 26 and the other end 22 b of the induction coil 22. A series resonance circuit 46 is formed by the secondary coil of the matching transformer 26, the resonance capacitors 42 and 44, and the induction coil 22. The resonant capacitors 42 and 44 have capacitors C1 and C2 that are biased so as to have a ratio r of a predetermined value or more. For example, C2 = r · C1 is set. However, r> 1. These resonant capacitors 42 and 44 constitute the capacitance means of the present invention.

In this manner, the resonant capacitor 42 having the capacitance C1 and the resonant capacitor 44 having the capacitance C2 (= r · C1) are connected to each other in series in the series resonant circuit 46, so that the secondary coil of the matching transformer 26 is connected to the secondary coil. When the high-frequency voltage V0 is generated, a voltage r times the voltage generated between both ends of the resonance capacitor 44 is generated between both ends of the resonance capacitor. For this reason, when the resonance frequency of the series resonance circuit 46 is close to the drive frequency of the inverter circuit 16, a neutral potential is formed at a position that is biased toward the other end 22 b side from the central portion B of the induction coil 22. A high voltage substantially equal to the voltage across the resonance capacitor 42 is formed between the one end 22a of the discharge tube 22 and the upper end of the discharge tube 20.
As a result, as in the first embodiment, it is possible to generate thermal plasma under a higher pressure than before or by applying a small coil voltage.

Embodiment 3
FIG. 5 shows the configuration of the induction thermal plasma generator according to the third embodiment. In this induction thermal plasma generator, the impedance matching circuit 48 is connected between the inverter circuit 16 and the induction coil 22 instead of the impedance matching circuit 40 in the apparatus of the second embodiment shown in FIG. A current sensor 50 and a voltage sensor 52 for detecting 16 input currents and input voltages, respectively, are arranged, and a determination circuit 54 and a control circuit 56 are sequentially connected to the current sensor 50 and the voltage sensor 52. Other circuits and elements are the same as those used in the apparatus of the second embodiment.

  The impedance matching circuit 48 includes a matching transformer 26 and variable capacitors 58 and 60, and the variable capacitor 58 is provided between one end 26 a of the secondary coil of the matching transformer 26 and one end 22 a of the induction coil 22. The variable capacitor 60 is connected between the other end 26 b of the secondary coil of the matching transformer 26 and the other end 22 b of the induction coil 22. A series resonance circuit 62 is formed by the secondary coil of the matching transformer 26, the variable capacitors 58 and 60, and the induction coil 22. These variable capacitors 58 and 60 constitute the capacitance means of the present invention.

The determination circuit 54 determines whether or not thermal plasma has been ignited in the discharge tube 20 of the plasma torch 18 based on the input current and input voltage of the inverter circuit 16 detected by the current sensor 50 and the voltage sensor 52. is there.
The control circuit 56 controls the capacities of the variable capacitors 58 and 60 of the impedance matching circuit 48 based on the determination result by the determination circuit 54. Specifically, when the determination circuit 54 determines that the thermal plasma has not yet ignited, the control circuit 56 biases the capacities of the variable capacitors 58 and 60 so that the ratio is equal to or greater than a predetermined value. After it is determined by 54 that the thermal plasma has been ignited, the capacitances of the variable capacitors 58 and 60 are set to be substantially equal to each other.
The current sensor 50, the voltage sensor 52, and the determination circuit 54 constitute the ignition determination means of the present invention, and the control circuit 56 constitutes the control means of the present invention.

Since plasma is an ionized gas, the load impedance value varies greatly before and after the generation of thermal plasma. For this reason, the presence or absence of ignition of thermal plasma can be determined by monitoring the input current and input voltage of the inverter circuit 16 that supplies high-frequency power to the induction coil 22 via the impedance matching circuit 48.
Therefore, in the third embodiment, the current sensor 50 and the voltage sensor 52 detect the input current and the input voltage of the inverter circuit 16, respectively, and thermal plasma is generated in the discharge tube 20 of the plasma torch 18 based on the detected values. The determination circuit 54 determines whether or not ignition has occurred.

When the determination circuit 54 determines that the thermal plasma has not yet ignited, the control circuit 56 controls the variable capacitors 58 and 60 so that the capacitances of the variable capacitors 58 and 60 become a ratio equal to or greater than a predetermined value. To bias. As a result, it is possible to generate thermal plasma under a higher pressure than before or by supplying a high frequency power smaller than that of the conventional one.
On the other hand, after the determination circuit 54 determines that the thermal plasma has ignited, the control circuit 56 controls the variable capacitors 58 and 60 so that the capacitances of the variable capacitors 58 and 60 are substantially equal to each other. Thereby, a uniform electromagnetic field long in the axial direction is formed in the discharge tube 20 of the plasma torch 18, and the thermal plasma long in the axial direction can be stably maintained.

Embodiment 4
FIG. 6 shows the configuration of the induction thermal plasma generator according to the fourth embodiment. This induction thermal plasma generator optically monitors the discharge tube 20 of the plasma torch 18 from the outside in place of the current sensor 50, voltage sensor 52, and determination circuit 54 in the apparatus of the third embodiment shown in FIG. The optical element 64 is disposed in the vicinity of the plasma torch 18 and a determination circuit 66 is connected to the optical element 64. Other circuits and elements are the same as those used in the apparatus of the third embodiment.

Since the thermal plasma emits extremely strong light, when the discharge tube 20 of the plasma torch 18 is made of a light-transmitting material such as quartz, the light emitted from the discharge tube 20 to the outside should be monitored. Thus, it can be detected whether or not the thermal plasma is ignited in the discharge tube 20.
Therefore, in the fourth embodiment, the light emitted from the discharge tube 20 is captured by the optical element 64 disposed in the vicinity of the plasma torch 18, and the plasma torch 18 is based on the light reception signal obtained by the optical element 64. The determination circuit 66 determines whether or not the thermal plasma has ignited in the discharge tube 20. For example, the determination circuit 66 can determine that the thermal plasma has ignited when the received light intensity captured by the optical element 64 exceeds a predetermined threshold value.
As the optical element 64, an imaging device such as a video camera can be used in addition to an optical sensor that detects the intensity of visible light.

When the determination circuit 66 determines that the thermal plasma has not yet ignited, the control circuit 56 controls the variable capacitors 58 and 60 so that the capacitances of the variable capacitors 58 and 60 are equal to or greater than a predetermined value. To bias. As a result, it is possible to generate thermal plasma under a higher pressure than before or by supplying a high frequency power smaller than that of the conventional one.
On the other hand, after the determination circuit 66 determines that the thermal plasma has ignited, the control circuit 56 controls the variable capacitors 58 and 60 so that the capacitances of the variable capacitors 58 and 60 are substantially equal to each other. Thereby, a uniform electromagnetic field long in the axial direction is formed in the discharge tube 20 of the plasma torch 18, and the thermal plasma long in the axial direction can be stably maintained.

Example 1
The induction thermal plasma generator of Embodiment 2 shown in FIG. 4 was configured using a high-frequency MOSFET inverter power supply having a rated frequency of 300 kHz to 400 kHz, a maximum power of 50 kW, a rated DC voltage of 250 V, and a rated DC current of 250 A. The discharge tube 20 of the plasma torch 18 has a double tube structure having an inner cylinder with an inner diameter of 70 mm and a length of 316 mm, and the induction coil 22 has an 8-turn outer diameter of 132 mm, a coil conductor diameter of 14 mmφ, and a coil length of 158 mm. I used something.

  As the resonant capacitors 42 and 44 in the impedance matching circuit 40, each unit capacitor is short-circuited by a short-circuit bus bar with respect to a circuit in which eight unit capacitors each having a capacitance of 0.33 μF are connected in series. Adjustable in 5 ways: 0, 2 in series (0.165 μF), 4 in series (0.0825 μF), 6 in series (0.055 μF), 8 in series (0.0412 μF) It was used.

  Then, while changing the capacitance C1 of the resonant capacitor 42 and the capacitance C2 of the resonant capacitor 44, and fixing the internal pressure of the discharge tube 20 of the plasma torch 18 to 80 Pa, the direct current is gradually increased to 250 A, and ignition is performed. The experiment was conducted.

  The result of the experiment is shown in FIG. There are a total of nine combinations of the capacitance C1 of the resonance capacitor 42 and the capacitance C2 of the resonance capacitor 44 that are possible under the above operating conditions. In the attached combinations, it was confirmed that the thermal plasma was ignited, but in the combinations marked with x, the ignition of the thermal plasma could not be confirmed. Note that C1 and C2 in FIG. 7 are represented by the number of unit capacitors connected in series, respectively.

That is, the thermal plasma can be ignited only when either one of the resonance capacitors 42 and 44 has zero unit capacitors and the other unit has six or eight unit capacitors connected in series.
By biasing the capacity of the resonant capacitor 42 connected to one end 22a of the induction coil 22 and the resonant capacitor 44 connected to the other end 22b so as to have a ratio of a predetermined value or more, thermal plasma is ignited even under the same operating condition. It was confirmed that it became easy to do.

Example 2
As the discharge tube 20 of the plasma torch 18, the double tube structure having the inner tube with a length of 316 mm used in Example 1 and the double tube structure having an inner tube with a length of 386 mm are used. An experiment was conducted on the pressure at which ignition was possible. As the resonance capacitors 42 and 44, one of these unit capacitors is set to 0 and the other is connected to 8 unit capacitors in series, and the internal pressure of the discharge tube 20 is set to various values. Then, it was confirmed whether or not the thermal plasma was ignited while gradually increasing the direct current supplied to the induction coil 22 to 250A. Other conditions were the same as those in Example 1.

The results of the experiment are as follows.
(1) A series connection (0.0412 μF) of eight unit capacitors is used as the resonance capacitor 42 connected to one end 22 a of the induction coil 22, and the resonance capacitor 44 connected to the other end 22 b of the induction coil 22 is When unit capacitor is 0,
It was confirmed that the apparatus using the inner cylinder having a length of 316 mm ignites at a maximum of 140 Pa, and the apparatus using the inner cylinder having a length of 386 mm ignites at a maximum of 180 Pa.
(2) The resonance capacitor 42 connected to the one end 22a of the induction coil 22 is zero unit capacitor, and the resonance capacitor 44 connected to the other end 22b of the induction coil 22 is a series connection of eight unit capacitors (0. 0412 μF)
It was confirmed that the apparatus using the inner cylinder having a length of 316 mm ignites at a maximum of 95 Pa, and the apparatus using an inner cylinder having a length of 386 mm ignites at a maximum of 130 Pa.

Thus, when the same induction coil 22 was used, the thermal plasma could be ignited at a pressure of about 100 Pa.
In addition, as in the conventional apparatus shown in FIG. 8, in the case where the capacitances of the pair of resonance capacitors connected to both ends of the induction coil 22 are the same, in order to ignite the thermal plasma, Even in a vacuum state of about 10 Pa, the thermal plasma did not ignite spontaneously, and could not be ignited unless a high voltage generated by applying a voltage using a Tesla coil was used as a trigger.

  In the above-described first to fourth embodiments, the modulated induction thermal plasma can be maintained by amplitude-modulating the high-frequency current supplied to the induction coil 22 into an arbitrary waveform. For example, a DC-DC converter circuit may be inserted between the three-phase full-wave rectifier circuit 12 and the MOSFET inverter circuit 16 so that the output of the DC-DC converter circuit follows the modulation signal from the modulation waveform generator. If the modulated induction thermal plasma is maintained in this way, the temperature of the thermal plasma can be controlled in detail according to the target of various treatments using the plasma.

The present invention can be applied to various processes using induction thermal plasma.
In addition, each of the above-described first to fourth embodiments and examples show examples of the present invention, and the present invention is not limited to these, and the scope of the present invention is not deviated. Needless to say, various changes and improvements may be made.

DESCRIPTION OF SYMBOLS 10 Three-phase alternating current power supply 12 Three-phase full-wave rectifier circuit 14 Smoothing capacitor 16 MOSFET inverter circuit 18 Plasma torch 20 Discharge tube 22 Induction coil 26 Matching transformer 34, 40, 48 Impedance matching circuit 28, 30, 36, 42, 44 Resonance Capacitor 38.46.62 Series resonance circuit 50 Current sensor 52 Voltage sensor 54, 66 Determination circuit 56 Control circuit 58.60 Variable capacitor 64 Optical element

Claims (3)

In an induction thermal plasma generation method for generating thermal plasma by supplying high frequency power to an induction coil through an impedance matching circuit including a capacitance means,
The capacitance means has a pair of capacitance adjustable capacitances connected to one end side and the other end side of the induction coil, respectively.
At least during the thermal plasma ignition different capacity of the pair of capacitance from each other racemate,
Induction thermal plasma generating method comprising substantially equal to Rukoto each other the capacity of the pair of capacitance after ignition of the thermal plasma. In an induction thermal plasma generator for generating thermal plasma by supplying high-frequency power to an induction coil via an impedance matching circuit including a capacitance means,
The capacitance means has a pair of capacitance adjustable capacitances connected to one end side and the other end side of the induction coil, respectively.
The pair of capacitance is at least set to different capacity during ignition of the thermal plasma, after ignition of the thermal plasma is set substantially equal capacitance to each other induction thermal plasma generator according to claim Rukoto. Ignition determination means for determining whether or not the thermal plasma has ignited;
When it is determined by the ignition determining means that the thermal plasma has not yet ignited, the pair of capacitances are set to different capacities, and after the ignition determining means determines that the thermal plasma has been ignited, the pair of capacitances are mutually connected. induction thermal plasma generator according to claim 2, and a control means for setting substantially have equal capacitance.

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