JP5532720B2 - Coaxial magnetized plasma generator - Google Patents

Description

  The present invention relates to a coaxial magnetized plasma generator, and more particularly to a coaxial magnetized plasma generator capable of generating spheromak plasma with high efficiency and high brightness.

  As an apparatus for generating spheromak plasma, a coaxial magnetized plasma generating apparatus is known. The coaxial magnetized plasma generating apparatus generates plasma by applying a voltage between an external electrode and an internal electrode arranged coaxially and causing a discharge between both electrodes. At this time, when a bias magnetic field is applied to the plasma, it is emitted in a state including the bias magnetic field together with the magnetic field due to the discharge current, and becomes spheromak plasma. Here, the spheromak plasma is one in which both confined magnetic fields of poloidal and toroidal are generated by the current flowing in itself, and the coordination is self-organized so as to preserve the magnetic helicity of the magnetic field structure.

  For example, Patent Document 1 discloses a coaxial magnetized plasma generator that generates spheromak plasma by applying a DC discharge of a capacitor between an external electrode and an internal electrode. Patent Document 2 discloses a coaxial magnetized plasma generating apparatus that generates a spheromak plasma by applying a single pulse current from a capacitor between an external electrode and an internal electrode.

JP 2006-310101 A JP-A-9-115686

  However, in the power supply circuit used for the coaxial magnetized plasma generator, the load current must rise to a predetermined value in a short time, and a capacitor for charging / discharging in the power supply circuit in order to make the rise characteristic steep The capacity of must be reduced. However, if the capacitance of the capacitor is small, the load current is attenuated in a short time, so that it is difficult to emit plasma for a long time.

  In addition, in the coaxial magnetized plasma generating apparatus of Patent Document 1 or Patent Document 2, in order to obtain highly efficient light emission, a high voltage charge / discharge circuit or the like corresponding to that is required, and insulation, noise, EUV light source, X-ray, etc. It has been a problem in applying to light sources.

  Further, the coaxial magnetized plasma generating apparatus described in Patent Document 1 is a direct current discharge because the applied current is a direct current from a capacitor, and the coaxial magnetized plasma generating apparatus described in Patent Document 2 Is a long pulse discharge. In such a discharge, it is known that the electrode is damaged by a thermal load on the electrode. This damage to the electrode shortens the life of the electrode itself, and the scraped electrode material becomes debris, causing fogging and damage to the window of the coaxial magnetized plasma generator.

  In view of such circumstances, the present invention provides a coaxial magnetized plasma generating apparatus capable of generating high-efficiency and high-intensity plasma and further extending the life of electrodes and reducing fogging and damage of windows due to debris. It is something to try.

  In order to achieve the above-described object of the present invention, a coaxial magnetized plasma generating apparatus according to the present invention generates a plasma between an outer conductor, an inner conductor arranged coaxially with the outer conductor, and the outer conductor and the inner conductor. A plasma generation gas supply unit for supplying gas; an electromagnetic coil for generating a bias magnetic field between the outer conductor and the inner conductor; and a power supply circuit for applying a continuous pulse signal between the outer conductor and the inner conductor. To do.

  Here, the power supply circuit may apply a continuous pulse signal whose duty ratio is changed.

  The power supply circuit may apply a continuous pulse signal with a duty ratio of 1: 5.

  The power supply circuit may include an insulated gate bipolar transistor.

  Furthermore, the power supply circuit may include a snubber circuit including a parallel circuit of a capacitor and a resistor and a diode connected in series thereto, and the snubber circuit may be connected in parallel to the insulated gate bipolar transistor. .

  The capacitor of the snubber circuit may be composed of a plurality of capacitor groups connected in parallel and in series.

  The coaxial magnetized plasma generating apparatus of the present invention has an advantage that plasma generation with high efficiency and high brightness is possible. Further, there are advantages that the life of the electrode can be extended and the fogging and damage of the window due to debris can be reduced.

FIG. 1 is a schematic cross-sectional view in the longitudinal direction for explaining the configuration of the coaxial magnetized plasma generator of the present invention. FIG. 2 is a circuit diagram for explaining a power supply circuit of the coaxial magnetized plasma generator of the present invention. FIG. 3 is a circuit diagram for explaining an example in which the power supply circuit includes a snubber circuit. FIG. 4 is a circuit diagram for explaining a more specific example of the snubber circuit of the power supply circuit of the coaxial magnetized plasma generator of the present invention. FIG. 5 is a graph for explaining a change in luminance of the plasma output with respect to the applied current. FIG. 6 is a graph for explaining the temporal change of the radiation light output in the vacuum ultraviolet region of the coaxial magnetized plasma generator of the present invention. FIG. 7 is a schematic cross-sectional view in the longitudinal direction for explaining the configuration of the opposingly arranged coaxially magnetized plasma generator of the present invention. FIG. 8 is a graph for explaining the temporal change of the radiated light output in the vacuum ultraviolet region of the opposingly arranged coaxial magnetized plasma generator of the present invention.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view in the longitudinal direction for explaining the configuration of the coaxial magnetized plasma generator of the present invention. As shown in the figure, the coaxial magnetized plasma generating apparatus of the present invention mainly includes an outer conductor 1, an inner conductor 2, a plasma generation gas supply unit 3, an electromagnetic coil 4, and a power supply circuit 5.

  The outer conductor 1 is made of a cylindrical conductor. The inner conductor 2 is disposed coaxially with the outer conductor 1. The plasma generation gas supply unit 3 is configured to supply a plasma generation gas between the outer conductor 1 and the inner conductor 2. The electromagnetic coil 4 generates a bias magnetic field between the outer conductor 1 and the inner conductor 2. Furthermore, the power supply circuit 5 which is the most characteristic configuration of the present invention applies a continuous pulse signal between the outer conductor 1 and the inner conductor 2. Hereinafter, each part will be described in more detail. The continuous pulse signal means a continuous pulse voltage applied between the outer conductor and the inner conductor or a continuous pulse current flowing at that time.

  In the coaxial magnetized plasma generating apparatus of the illustrated example, the outer conductor 1 and the inner conductor 2 are fixed at their placement positions while being insulated by an insulating member 6 at one end, and plasma is emitted from here at the other end. Open end. Further, the inner conductor 2 and the plasma generation gas supply unit 3 are integrated, and a plasma generation gas, for example, helium gas, is provided in the space between the plasma generation gas supply unit 3 and the outer conductor 1 and the inner conductor 2. Or argon gas or the like is supplied.

  In the illustrated example, the electromagnetic coil 4 is disposed on the outer periphery of the outer conductor 1. The electromagnetic coil 4 applies a bias magnetic field to the plasma generated between the outer conductor 1 and the inner conductor 2. Thereby, since the plasma is emitted in a state including a magnetic field due to the discharge current and a bias magnetic field, spheromak plasma is generated.

  The coaxial magnetized plasma generator of the present invention is not particularly limited to the configuration of these illustrated examples, and any structure can be used as long as it is a coaxial magnetized plasma generator that can generate spheromak plasma. It doesn't matter.

  Next, the most characteristic power supply circuit of the present invention will be described. The power supply circuit 5 applies a continuous pulse signal between the outer conductor 1 and the inner conductor 2 as described above. In order to apply the continuous pulse signal, the power supply circuit 5 performs inverter control on the power supply (capacitor) using, for example, a transistor, and generates a continuous pulse signal of, for example, a rectangular wave. The coaxial magnetized plasma generator uses a high voltage power source. For this reason, it is preferable to use an insulated gate bipolar transistor (IGBT) capable of switching large power at high speed as the transistor. Hereinafter, the circuit configuration of the power supply circuit will be described in more detail with reference to FIG.

  FIG. 2 is a circuit diagram for explaining a power supply circuit of the coaxial magnetized plasma generator of the present invention. As illustrated, the power supply circuit 5 includes a capacitor 51, a transistor 52, and a resistor R. The capacitor 51 is a charge / discharge capacitor, and the voltage of the capacitor 51 is applied between the outer conductor 1 and the inner conductor 2 via the resistor R. The transistor 52 is an insulated gate bipolar transistor as described above, and is ON / OFF controlled by a control signal to the gate, and the DC output of the capacitor 51 is applied in a continuous pulse form between the outer conductor 1 and the inner conductor 2. To do. Note that the transistor is not limited to an insulated gate bipolar transistor as long as it can switch high power at high speed, and may be another transistor, a switching circuit, or the like.

  Note that a snubber circuit may be provided in the power supply circuit in order to prevent destruction of the transistor due to overvoltage or overcurrent (surge) in the power supply circuit. FIG. 3 is a circuit diagram for explaining an example in which the power supply circuit includes a snubber circuit. As illustrated, the snubber circuit 60 is connected to the transistor 52 in parallel. The snubber circuit 60 includes a parallel circuit of a capacitor 61 and a resistor 62 and a diode 63 connected in series thereto.

  Here, in order to protect the transistor from a broadband surge, the capacitor 61 in FIG. 3 may be multi-staged. FIG. 4 is a circuit diagram for explaining a more specific example of the snubber circuit of the power supply circuit of the coaxial magnetized plasma generator of the present invention. Note that the values of resistors and capacitors in the figure are merely examples, and are not limited to these. As illustrated, the capacitor 61 of the snubber circuit 60 is composed of a plurality of capacitors connected in parallel and in series. More specifically, a series circuit of three capacitors, a parallel circuit of two capacitors, and a circuit in which three parallel circuits of two capacitors are connected in series are connected in parallel. Two diodes 63 are connected in series. If the snubber circuit 60 is configured in this manner, the transistor can be prevented from being destroyed by a wider range of surges.

  In the coaxial magnetized plasma generating apparatus of the present invention configured as described above, plasma is generated as follows. First, a plasma generation gas is supplied from the plasma generation gas supply unit 3. When a continuous pulse signal is applied by the power supply circuit 5 to the space between the outer conductor 1 and the inner conductor 2, a discharge is generated between the outer conductor 1 and the inner conductor 2, and a discharge current flows to generate plasma. . The generated plasma generates a magnetic field in a poloidal direction and a toroidal direction by a bias magnetic field generated by the electromagnetic coil 4 together with a magnetic field generated by the discharge current, and is emitted from the open ends of the outer conductor 1 and the inner conductor 2 as spheromak plasma. The released spheromak plasma does not diffuse immediately but is released at a high speed in the form of a plasma mass.

  Unlike the conventional direct current discharge or single pulse discharge, the coaxial magnetized plasma generator of the present invention that discharges by a continuous pulse signal of the power supply circuit makes the applied signal a pulse waveform, thereby discharging the capacitor from the capacitor for a long time. Can be maintained. That is, by discharging the discharge from the capacitor in a continuous pulse manner, it is possible to suppress the attenuation of the capacitor output rather than the direct current discharge. Therefore, since the power supply circuit output can be maintained for a long time with a high output, high energy plasma can be generated for a long time.

  In the coaxial magnetized plasma generator of the present invention, the thermal load on the electrode is reduced by discharging the continuous pulse signal. For this reason, the life of the electrode is extended, and since the electrode is less damaged, fogging and damage of the window due to debris can be reduced.

  Furthermore, in the power supply circuit of the coaxial magnetized plasma generating apparatus of the present invention, the continuous pulse signal is not limited to a rectangular wave (duty ratio 1: 2), and is configured to output a continuous pulse signal with a changed duty ratio. May be. That is, the control signal for the transistor of the power supply circuit is input so that the duty ratio is changed. Thereby, a power supply circuit is comprised so that the continuous pulse signal with which duty ratio was changed may be applied between an outer conductor and an inner conductor.

  Hereinafter, the effect when the duty ratio is changed will be described. In the following description, the configuration shown in FIG. 1 was used for the configuration of the coaxial magnetized plasma generator, and the configuration shown in FIG. 4 was used for the configuration of the power supply circuit.

  FIG. 5 is a graph for explaining the change in luminance of the plasma output. The upper part represents the change over time of the applied current, and the lower part represents the change over time in the luminance of the plasma output. This graph is a result of luminance change with respect to time of a spectrum of about 470 nm, which is a spectrum line of helium, using helium gas as a plasma generation gas. FIG. 5A shows changes over time in applied current and luminance in the case of conventional DC discharge as a comparative example. FIG. 5B shows changes over time in applied current and luminance when continuous pulse control is performed so as to obtain a rectangular wave (duty ratio 1: 2). FIG. 5C shows changes in applied current and luminance with time when continuous pulse control is performed so that the duty ratio is 1: 5. The duty ratio is expressed as pulse width versus pulse period. In the illustrated example, the pulse period is 10 kHz.

  As shown in the figure, the luminance of the plasma output when using the power supply circuit that applies the continuous pulse signal of the present invention is higher than the luminance of the plasma output when using the conventional power supply circuit of FIG. It can be seen that the brightness is increased and plasma is emitted for a long time. Further, as shown in FIG. 5C, when the plasma generation gas is helium gas, when a continuous pulse signal with a changed duty ratio is applied, the brightness can be further increased and the time can be increased. I understand. In the case of a continuous pulse signal with a duty ratio of 1: 5, it can be seen that the brightness is increased by 200% or more compared to the case of a duty ratio of 1: 2. This is considered to be due to the effect of abnormal reheating caused by the magnetic reconnection in the spheromak plasma generation process due to the application of the continuous pulse signal. Note that the duty ratio is not limited to 1: 5 as long as it has a pulse width and a pulse period sufficient to generate plasma, and other duty ratios may be used. Further, the duty ratio may be determined according to the plasma generation gas to be used and the wavelength using the plasma.

  Next, the radiation output applicable to a short wavelength light source such as EUV will be described. In the above-mentioned example, the time change of the luminance of the wavelength of about 470 nm, which is the spectral line of helium gas, has been described. However, the coaxial magnetized plasma generation apparatus of the present invention can also use the short-wavelength radiation output. For example, when the inner conductor is made of a metal containing iron, when the synchrotron radiation output of about 158 nm, which is a spectral line in the vacuum ultraviolet region of iron, which is one of the constituent elements of the inner conductor, is measured, the above-mentioned wavelength of 470 nm is obtained. Luminescence could be observed in the same manner as the change in luminance over time. Furthermore, although the ion species was not specified, sufficient light emission could be observed even in a shorter wavelength band up to about 40 nm near the measurement limit of the spectrometer. Therefore, the coaxial magnetized plasma generator of the present invention can be applied to an EUV light source or the like.

  In FIG. 6, the graph of the time change of the synchrotron radiation output in the vacuum ultraviolet region of the coaxial magnetized plasma generator of this invention is shown. The graph shows the radiation output of about 158 nm, which is a spectral line in the vacuum ultraviolet region of iron when helium gas is used as the plasma generation gas and continuous pulse control with a duty ratio of 1: 5 and 1: 2 is performed, respectively. Is measured. In addition, since the measurement system in vacuum ultraviolet was constructed so that the output would be positive, the output is opposite to the graph shown in FIG. As can be seen from this graph, at a wavelength of about 158 nm, which is an iron spectral line, the luminance is higher in the case of a continuous pulse with a duty ratio of 1: 2 with a long discharge time than with a duty ratio of 1: 5. I understand that. This is because the inner conductor is sputtered by extending the discharge time once, and the metal used for the inner conductor is mixed in by the plasma generation gas, so that the brightness of the spectral line corresponding to the iron used for the inner conductor is increased. It is thought that it was because Therefore, the luminance of the spectral line corresponding to the material of the inner conductor can be increased by appropriately changing the duty ratio of the continuous pulse signal so as to increase the discharge time, such as 1: 2. In addition, the material of the inner conductor is not limited to iron but can be appropriately changed to lead or the like, whereby the luminance of the spectral line having a desired wavelength can be increased.

  As described above, according to the coaxially magnetized plasma generating apparatus of the present invention, when the wavelength to be used suffices with the wavelength of the spectral line of the plasma generating gas, the internal conductor is eroded by setting the duty ratio of the continuous pulse signal to 1: 5, for example. It is possible to extend the life of the electrode by controlling so as not to occur. Furthermore, when using light having a wavelength that is not the spectral line wavelength of the plasma generation gas, a metal material having a spectral line having a desired wavelength is used for the inner conductor, and the duty ratio of the continuous pulse signal is increased. It is also possible to increase the brightness of the wavelength of the spectral line of the metal material of the inner conductor by adjusting so that the metal material of the inner conductor is sputtered and mixed into the plasma generation gas.

  Next, a description will be given of a counter-arrangement type coaxial magnetized plasma generating apparatus that uses a plasma heating mechanism in which the coaxial magnetized plasma generating apparatuses of the present invention are arranged facing each other and collided with spheromak plasmas generated respectively. FIG. 7 is a schematic cross-sectional view in the longitudinal direction for explaining the configuration of the opposingly arranged coaxially magnetized plasma generator of the present invention. In the figure, the same reference numerals as those in FIG. 1 denote the same parts. 7 basically uses two coaxially magnetized plasma generators shown in FIG. 1, and the emission surfaces are arranged opposite to each other so that the central axes coincide with each other, and a magnetic flux holding container is provided between them. 10 is connected. More specifically, as shown in FIG. 7, the magnetic flux holding container 10 joins the open end of the cylindrical outer conductor 1, and opens a window in a plane perpendicular to the central axis of the outer conductor 1. The unit 11 is included.

  In the opposed arrangement type coaxial magnetized plasma generating apparatus having such a configuration, a continuous pulse signal from the power supply circuit 5 is applied between the outer conductor 1 and the inner conductor 2 at the same timing. Thereby, spheromak plasma is emitted from the open end of the outer conductor 1, the plasma mass collides in the magnetic flux holding container 10, and light with high emission intensity is obtained from the window portion 11.

  When using short-wavelength spectral lines, it is preferable that the temperature of the plasma be as high as possible. In the case of the opposed arrangement type coaxial magnetized plasma generating apparatus, it is heated at the time of collision of the plasma, and this thermal energy can be used, so that the brightness of the short wavelength spectrum is further increased. For this reason, in the opposed arrangement type coaxial magnetized plasma generating apparatus using two than the case of one coaxial magnetized plasma generating apparatus, the luminance can be improved more than the total light quantity of two by the thermal energy at the time of collision. In FIG. 8, the graph of the time change of the radiated light output in the vacuum ultraviolet region of the opposing arrangement type | mold coaxial magnetized plasma generator of this invention is shown. The graph shows the radiation output of about 158 nm, which is a spectral line in the vacuum ultraviolet region of iron when helium gas is used as the plasma generation gas and continuous pulse control with a duty ratio of 1: 5 and 1: 2 is performed, respectively. Is measured. Compared with the result of one coaxial magnetized plasma generator of FIG. 6, it can be seen that the amount of emitted light is increased by about 20 times in the oppositely arranged coaxial magnetized plasma generator. Therefore, it can be seen that the opposed arrangement type coaxial magnetized plasma generating apparatus is advantageous in increasing the amount of plasma emission.

  As described above, according to the coaxial magnetized plasma generating apparatus of the present invention, plasma with very high energy can be emitted for a long time as compared with the continuous pulse voltage and the continuous pulse current generated by the power supply circuit. Highly efficient and bright plasma generation is possible. Furthermore, by controlling the duty ratio, the thermal load of the electrode can be reduced, the life of the electrode can be extended, and since the electrode is less damaged, fogging and damage of the window due to debris can be reduced. Since plasma having a confined magnetic field configuration can be generated, a decrease in plasma temperature due to contact with the container wall can also be reduced.

  Further, by changing the duty ratio, it is also possible to increase the brightness of the spectral lines of the metal of the inner conductor by mixing the metal into the plasma generation gas so as to cut the inner conductor. Moreover, if it is an opposing arrangement type | mold coaxial magnetized plasma production | generation apparatus, a plasma can be produced | generated more strongly by raising plasma temperature.

  Therefore, the coaxial magnetized plasma generation apparatus of the present invention can be applied in various applications such as an EUV light source for next-generation lithography and an X-ray light source for medical / inspection.

  The coaxial magnetized plasma generating apparatus of the present invention is not limited to the illustrated example described above, and various modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Outer conductor 2 Inner conductor 3 Plasma generation gas supply part 4 Electromagnetic coil 5 Power supply circuit 6 Insulation member 51 Capacitor 52 Transistor 60 Snubber circuit 61 Capacitor 62 Resistance 63 Diode

Claims (6)

A coaxial magnetized plasma generator for generating spheromak plasma, the coaxial magnetized plasma generator,
An outer conductor,
An inner conductor disposed coaxially with the outer conductor;
A plasma generation gas supply unit for supplying a plasma generation gas between the outer conductor and the inner conductor;
An electromagnetic coil that generates a bias magnetic field between the outer conductor and the inner conductor;
A power supply circuit for applying a continuous pulse signal between the outer conductor and the inner conductor;
A coaxial magnetized plasma generating apparatus comprising:   The coaxial magnetized plasma generating apparatus according to claim 1, wherein the power supply circuit applies a continuous pulse signal whose duty ratio is changed.   3. The coaxial magnetized plasma generating apparatus according to claim 2, wherein the power supply circuit applies a continuous pulse signal having a duty ratio of 1: 5.   4. The coaxial magnetized plasma generating apparatus according to claim 1, wherein the power supply circuit includes an insulated gate bipolar transistor. 5.   5. The coaxial magnetized plasma generating apparatus according to claim 4, wherein the power supply circuit includes a snubber circuit including a parallel circuit of a capacitor and a resistor and a diode connected in series to the capacitor and the resistor, and the snubber circuit includes the insulated gate bipolar. A coaxial magnetized plasma generating apparatus connected in parallel to a transistor.   6. The coaxial magnetized plasma generating apparatus according to claim 5, wherein the capacitor of the snubber circuit includes a plurality of capacitors connected in parallel and in series.