Steering mirror

Abstract

This steering mirror can maintain a high resonant frequency even when its size is increased, and shortens the settling time during control. [Solution] A steering mirror that adjusts the direction of travel by reflecting laser light in an arbitrary direction, comprising: a mirror body that reflects the laser light; a support part that supports the mirror body; and a gimbal mechanism interposed between the mirror body and the support part, having a plurality of rotation axes that can tilt the mirror body at an arbitrary angle with respect to the support part, wherein at least one of the plurality of rotation axes is made of an elastically deformable columnar member with both ends fixed, and the mirror body rotates as the columnar member twists.

Description

Technical Field

[0001] The present invention relates to a steering mirror that reflects laser light in an arbitrary direction.

Background Art

[0002] In recent years, research has been actively conducted towards the practical application of a laser fusion reactor that generates energy by irradiating a fuel pellet composed of deuterium and tritium with high-power laser light to cause implosion and produce a fusion reaction.

[0003] As a laser fusion reactor, a spherical fuel pellet is projected at high speed using a fuel projection mechanism inside the reactor body for extracting energy, and high-power pulsed laser light is uniformly irradiated on the fuel pellet that has reached a predetermined position (for example, the central position) inside the reactor body from all directions to cause a fusion reaction. There is a fuel projection type. In such a fuel projection type, energy is continuously generated by repeating the projection of the fuel pellet and the irradiation of the laser light at a rate of several times per second, and it is considered that power generation of several million kilowatts can be performed by guiding this to the outside.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, in the fuel projection method described above, the position of the fuel pellets projected onto the reactor body is not always constant. Due to slight changes in friction between the fuel projection mechanism and the fuel pellets, the position shifts slightly (a few millimeters) each time a pellet is projected. Therefore, it is being considered to place a steering mirror equipped with a gimbal mechanism having multiple rotation axes in the optical path of the laser beam, and to drive an actuator each time a fuel pellet is projected to finely adjust the reflection angle, thereby irradiating the center of the shifted fuel pellet with the laser beam.

[0006] In order to increase the energy output of a laser fusion reactor, it is necessary to shorten the period for projecting fuel pellets and the period for irradiating with pulsed laser light, thereby causing fusion reactions to occur continuously at short intervals. However, the response speed of the steering mirror becomes the rate-limiting factor in this process. In other words, when the actuator is driven to change the tilt angle of the steering mirror's reflective surface in steps, the settling time until the tilt angle stabilizes near the target value becomes the rate-limiting factor. In particular, steering mirrors used in laser fusion reactors to reflect high-power laser light tend to be large in size, which lowers the resonant frequency and makes it easier for the settling time during control to become longer.

[0007] The present invention has been made in view of these problems, and its main objective is to provide a steering mirror that can maintain a high resonant frequency even when its size is increased and that can shorten the settling time during control. [Means for solving the problem]

[0008] In order to solve the above problems, the inventors diligently conducted research and found that in conventional steering mirrors, the hinge part of the gimbal mechanism uses components with a wide range of motion, such as bearings, which results in insufficient rigidity in the drive degrees of freedom (Pitch and Yaw), and thus the resonant frequency becomes low. The inventors then conceived the idea that by deliberately using a fixed rigid hinge in the hinge part where movement is required, the rigidity around the rotation axis of the gimbal mechanism can be increased, and a high resonant frequency can be maintained at the expense of a narrower range of motion, leading to the present invention.

[0009] In other words, the steering mirror according to the present invention is a steering mirror that adjusts the direction of travel by reflecting laser light in an arbitrary direction, comprising: a mirror body that reflects the laser light; a support part that supports the mirror body; and a gimbal mechanism interposed between the mirror body and the support part, having a plurality of rotation axes that can tilt the mirror body at an arbitrary angle with respect to the support part, wherein at least one of the plurality of rotation axes is made of an elastically deformable columnar member with both ends fixed, and the mirror body rotates around the rotation axis by twisting the columnar member.

[0010] In this configuration, at least one of the multiple rotation axes of the gimbal mechanism is made of an elastically deformable columnar member with both ends fixed, and the mirror body rotates around the rotation axis by twisting this columnar member. This allows for increased rigidity compared to systems that use bearings with a high degree of freedom as the rotation mechanism. As a result, a high resonant frequency can be maintained even if the size of the mirror body is large, and the settling time during control can be shortened. Furthermore, the resonant frequency of the entire structure can be adjusted by changing the cross-sectional shape of the columnar member used as the rotation axis.

[0011] Preferably, the steering mirror is configured such that each of the multiple rotation axes is made up of an elastically deformable columnar member with both ends fixed, and the mirror body rotates around each rotation axis as each columnar member twists. In this way, since each of the multiple rotating shafts is composed of columnar members with both ends fixed, the overall rigidity of the structure can be further increased, allowing for the maintenance of a high resonant frequency and further shortening the settling time during control.

[0012] A specific embodiment of the steering mirror includes a gimbal mechanism comprising a first rotating frame connected to the support and rotatable about a first rotation axis, and a second rotating frame that supports the mirror body and is connected to the first rotating frame, and rotatable about a second rotation axis intersecting the first rotation axis, wherein one end of the columnar member constituting the first rotation axis is fixed to the support and the other end is fixed to the first rotating frame, and one end of the columnar member constituting the second rotation axis is fixed to the first rotating frame and the other end is fixed to the second rotating frame.

[0013] Furthermore, it is preferable that the steering mirror has a replaceable columnar member. In this way, the resonant frequency can be easily adjusted according to the application by replacing the columnar members with those of different cross-sectional shapes or sizes.

[0014] Furthermore, in order to further increase rigidity and maintain a higher resonant frequency, it is preferable that the columnar member be made of metal.

[0015] A preferred specific embodiment of the columnar member is one having a shaft portion with a constant cross-sectional shape along the axial direction and connecting portions provided at both ends in the axial direction.

[0016] Furthermore, the effects of the present invention described above become even more pronounced when the steering mirror is used in a laser fusion reactor to adjust the direction of travel by reflecting laser light used to irradiate the fuel. [Effects of the Invention]

[0017] According to the steering mirror configured as described above, even if the size increases, a high resonance frequency can be maintained, and the settling time during control can be shortened.

Brief Description of the Drawings

[0018] [Figure 1] A diagram schematically showing a laser fusion reactor according to an embodiment of the present invention. [Figure 2] A perspective view schematically showing the steering mirror of the embodiment. [Figure 3] A front view schematically showing the steering mirror of the embodiment. [Figure 4] A side view schematically showing the steering mirror of the embodiment. [Figure 5] A top view schematically showing the steering mirror of the embodiment. [Figure 6] A perspective view schematically showing the configuration around the rotation axis of the steering mirror of the embodiment. [Figure 7] A diagram schematically showing the configuration of the control mechanism of the steering mirror of the embodiment.

Modes for Carrying Out the Invention

[0019] Hereinafter, the steering mirror 100 according to an embodiment of the present invention will be described based on the drawings.

[0020] The steering mirror 100 of this embodiment is used in a laser fusion reactor 200 that generates energy by imploding fuel pellets P (for example, small spherical fuel composed of deuterium and tritium; however, the constituent elements and shape are not limited thereto) by irradiating them with high-power laser light to cause a nuclear fusion reaction. Specifically, as shown in Figure 1, the laser fusion reactor 200 comprises a reactor body V, a fuel projection mechanism F that projects fuel pellets P into the reactor body V at high speed (for example, about 100 m / s), and a laser irradiation mechanism L that irradiates the fuel with laser light (implosion laser light) in time with the fuel when it reaches a predetermined irradiation position R set in the reactor body V. In this laser fusion reactor 200, fuel pellets P are projected into the reactor body V by the fuel projection mechanism F at a constant period (for example, about 10 Hz), and laser light is sequentially irradiated from the laser irradiation mechanism L to these successively projected fuel pellets P.

[0021] The laser irradiation mechanism L comprises a laser light source L1 that emits laser light and an optical system L2 that guides the laser light emitted from the laser light source L1 to the fuel pellets P projected into the reactor body V. The laser fusion reactor 200 is equipped with multiple laser irradiation mechanisms L, and can simultaneously irradiate the fuel pellets P projected into the reactor body V with laser light from multiple directions (all around).

[0022] The laser light source L1 is capable of outputting high-energy pulsed laser light at a high repetition frequency (e.g., about 10 Hz) sufficient to implode the fuel pellet P, and is installed outside the reactor body V.

[0023] The optical system L2 is equipped with multiple mirrors that reflect laser light. This optical system L2 is equipped with a steering mirror 100 (also called a movable mirror) that reflects the laser light in any direction to adjust its direction of travel. The laser irradiation mechanism L adjusts the direction of travel of the laser light by moving the steering mirror 100, so that the laser light can irradiate the fuel pellet P, which is slightly (a few millimeters) off the center of the irradiation position R each time it is projected onto the reactor body V, with laser light.

[0024] The following provides a detailed explanation of the steering mirror 100.

[0025] As shown in Figures 2 to 5, the steering mirror 100 comprises a mirror body 1 that reflects high-energy implosion laser light, a support part 2 that supports the mirror body 1, a gimbal mechanism 3 interposed between the mirror body 1 and the support part 2 to tilt the mirror body 1 at an arbitrary angle relative to the support part 2, and a control mechanism 4 that drives the gimbal mechanism 3 to control the tilt angle of the mirror body 1.

[0026] The mirror body 1 has a disc shape with a circular reflective surface 1s. This reflective surface 1s is coated with a dielectric multilayer film using, for example, titanium oxide, barium oxide, or zirconium oxide, to provide high laser damage resistance to high-energy laser light. The surface shape of the mirror's reflective surface 1s may be planar or concave.

[0027] The support portion 2 of this embodiment comprises a plate-shaped base 21 and a pair of support plates 22 that are mounted upright on the surface of the base 21 (also called the base surface 21s). The pair of support plates 22 are positioned so that their face plates face each other. The mirror body 1 is installed so that its outer circumferential surface is sandwiched between the face plates of the pair of support plates 22, and the mirror body 1 is supported by this pair of support plates 22 so that its reflective surface 1s stands approximately perpendicular to the base surface 21s.

[0028] The gimbal mechanism 3 has multiple rotation axes extending in directions that intersect each other. Specifically, this gimbal mechanism 3 includes a first rotation axis 3a, which is a pitch axis that rotates the reflective surface 1s of the mirror body 1 in the vertical direction within a predetermined range, and a second rotation axis 3b, which is a yaw axis that rotates the reflective surface 1s of the mirror body 1 in the horizontal direction within a predetermined range. Here, the first rotation axis 3a is parallel to the base surface 21s, and the second rotation axis 3b is set to be perpendicular to the first rotation axis 3a. In the following, the optical axis direction of the mirror body 1 at the reference position (initial position) where the rotation angle of each rotation axis of the gimbal mechanism 3 is 0° (i.e., the direction perpendicular to the reflective surface 1s and perpendicular to the first rotation axis 3a and the second rotation axis 3b) will be defined as the reference axis direction.

[0029] More specifically, the gimbal mechanism 3 comprises a first rotating frame 31 connected to the support plate 22 of the support section 2 and rotatable about a first rotation axis 3a, and a second rotating frame 32 that supports the mirror body 1 and is connected to the first rotating frame 31 and rotatable about a second rotation axis 3b. The first rotating frame 31 is an annular plate shape, and its outer circumferential surface is connected to the pair of support plates 22 via the first rotation axis 3a. The second rotating frame 32 is also an annular plate shape, and its outer diameter is smaller than the inner diameter of the first rotating frame 31. This second rotating frame 32 is mounted inside the first rotating frame 31. Specifically, the outer circumferential surface of the second rotating frame 32 is connected to the inner circumferential surface of the first rotating frame 31 via the second rotation axis 3b. The mirror body 1 is then fitted inside the second rotating frame 32.

[0030] Furthermore, the steering mirror 100 of this embodiment is characterized in that at least one (specifically both) of the first rotation axis 3a and the second rotation axis 3b is made up of an elastically deformable columnar member 5 whose ends are fixed (rigidly fixed), and the mirror body 1 rotates around the rotation axis as this columnar member 5 twists.

[0031] Each columnar member 5 constituting the rotating shaft is made of metal, such as carbon steel, stainless steel, or aluminum, and is replaceable. As shown in Figure 6, this columnar member 5 integrally comprises a shaft portion 51 extending in the axial direction and connecting portions 52 provided at both ends of the shaft portion 51. The shaft portion 51 is columnar in shape with a constant cross-sectional shape along the axial direction, and in this case, its cross-section is circular. The connecting portion 52 is plate-shaped with a larger cross-sectional area than the shaft portion 51 and is provided with bolt holes, etc. (not shown).

[0032] The columnar member 5 constituting the first rotation axis 3a is positioned parallel to the first rotation axis 3a, with one connecting portion 52 fixed to the support plate 22 and the other connecting portion 52 fixed to the outer circumferential surface of the first rotation frame 31. Both of these connecting portions 52 are fastened and fixed, for example, by bolting. The first rotation axis 3a, as configured in this way, causes the columnar member 5 to twist, enabling the mirror body 1 to rotate around the first rotation axis 3a within a range of approximately ±1 milliradian.

[0033] Furthermore, the columnar member 5 constituting the second rotation axis 3b is configured such that one connecting portion 52 is connected to the inner circumferential surface of the first rotation frame 31, and the other connecting portion 52 is connected to the outer circumferential surface of the second rotation frame 32, so as to be parallel to the second rotation axis 3b. Both of these connecting portions 52 are fastened and fixed, for example, by bolting. The second rotation axis 3b, as configured in this way, causes the columnar member 5 to twist, enabling the mirror body 1 to rotate around the second rotation axis 3b within a range of approximately ±1 milliradian.

[0034] Next, the control mechanism 4, which drives the gimbal mechanism 3 to control the tilt angle of the mirror body 1, will be described. The tilt angle of the mirror body 1 referred to here is the tilt angle of the optical axis of the reflective surface 1s of the mirror body 1 with respect to the reference axis direction.

[0035] As shown in Figure 7, the control mechanism 4 includes an actuator 41 that drives the gimbal mechanism 3, an angle detection sensor 42 that detects the tilt angle of the mirror body 1, a fuel position detection sensor 43 that detects the passage position and passage time of fuel pellets P projected into the reactor body V, and a control unit 44 that controls the actuator 41.

[0036] This actuator 41 is configured to expand and contract in the direction of the reference axis in accordance with the voltage output from the control unit 44, and uses, for example, a voice coil motor. The control mechanism 4 of this embodiment includes, as actuators 41, a pair of first actuators 41a for driving the gimbal mechanism 3 around the first rotation axis 3a, and a pair of second actuators 41b for driving the gimbal mechanism 3 around the second rotation axis 3b.

[0037] The first actuator 41a is provided in contact with the back surface of the first rotating frame 31, such that its extension and retraction direction coincides with the direction of the reference axis. Specifically, as shown in Figure 3, the first actuator 41a is provided in a pair, one above the other, on the back surface of the first rotating frame 31 when viewed from the direction of the reference axis, and more specifically, it is provided so as to be located on the second rotation axis 3b.

[0038] The second actuator 41b is provided in contact with the back surface of the second rotating frame 32 such that its extension and retraction direction coincides with the direction of the reference axis. Specifically, as shown in Figure 3, the second actuator 41b is provided in pairs on the left and right sides of the back surface of the second rotating frame 32 when viewed from the direction of the reference axis, and more specifically, it is provided so as to be located on the first rotation axis 3a.

[0039] The angle detection sensor 42 in this embodiment utilizes, for example, an optical lever, and detects the tilt angle of the mirror body 1 by irradiating the back surface of the mirror body 1 with laser light and sensing the reflected light. Specifically, this angle detection sensor 42 comprises an angle detection laser light source (not shown) that emits laser light toward the back surface of the mirror body 1, and a light-receiving element (not shown), such as a PSD (position detection element) or QPD (quadruple photodiode), which senses the laser light reflected from the back surface of the mirror body 1. The light-receiving element outputs an electrical signal (angle information signal) that changes depending on the intensity and position of the received laser light to the control unit 44.

[0040] The fuel position detection sensor 43 detects the time it takes for fuel pellets P projected into the reactor body V by the fuel projection mechanism F to pass through the irradiation position R, and the amount of displacement (passage position) of the fuel pellets P from the center of the irradiation position R. This fuel position detection sensor 43 may be configured using, for example, a plurality of reflective or transmissive photointerrupters (not shown) arranged in the projection direction of the fuel pellets P. The fuel position detection sensor 43 generates a signal (fuel position information signal) indicating the detected passage position and passage time of the fuel pellets P, and outputs this to the control unit 44.

[0041] The control unit 44 outputs control signals to the first actuator 41a and the second actuator 41b based on the angle information signal output from the angle detection sensor 42 and the fuel position information signal output from the fuel position detection sensor 43. Specifically, the control unit 44 calculates the target tilt angle of the mirror body 1 (target tilt angle) based on a predetermined algorithm, using the position of the fuel pellet P indicated by the fuel position information signal. The control unit 44 then compares the calculated target tilt angle with the current tilt angle of the mirror body 1 (measured tilt angle) indicated by the angle information signal, and based on the difference in angles, generates control signals to control the displacement of the first actuator 41a and the second actuator 41b using a predetermined control algorithm, and outputs them to each actuator 41. Specifically, the control unit 44 generates control signals to make the measured tilt angle match the target tilt angle. The control unit 44 generates control signals each time a fuel pellet P is projected from the fuel projection mechanism F and outputs them to each actuator 41.

[0042] In this configuration of the steering mirror 100, each of the multiple rotation axes of the gimbal mechanism 3 is made of an elastically deformable metal columnar member 5 with both ends rigidly fixed. The rotation of this columnar member 5 causes the mirror body 1 to rotate around the rotation axis. This increases rigidity compared to a rotation mechanism that uses bearings with a high degree of freedom. As a result, a high resonant frequency can be maintained even if the size of the mirror body 1 is increased, the settling time during control can be shortened, and high responsiveness can be achieved.

[0043] Furthermore, since the columnar member 5 used as the rotation axis is replaceable, the resonant frequency can be easily adjusted according to the application by replacing the columnar member 5 with one of a different size or cross-sectional shape.

[0044] However, the present invention is not limited to the embodiments described above. For example, the steering mirror 100 of the above embodiment was used to reflect laser light for implosion in a laser fusion reactor 200, but is not limited to this. The steering mirror 100 of other embodiments may be used for other purposes, for example, in a fast-ignition type laser fusion reactor 200 to reflect laser light for heating fuel pellets P, or in other types of laser fusion reactors. The steering mirror 100 of the present invention only needs to reflect laser light for irradiating fuel pellets P projected into the reactor body V in a laser fusion reactor.

[0045] Furthermore, while the gimbal mechanism 3 of the above embodiment was configured such that both the first rotation axis 3a and the second rotation axis 3b were made of columnar members 5 with both ends fixed, it is not limited to this. In other embodiments of the gimbal mechanism 3, either the first rotation axis 3a or the second rotation axis 3b may be configured as a rotation mechanism with a wide range of motion using bearings or the like. The effects of the present invention can be achieved by configuring any of the multiple rotation axes of the gimbal mechanism 3 with columnar members 5 with both ends fixed.

[0046] Furthermore, while the gimbal mechanism 3 in the above embodiment had two rotation axes, a first rotation axis 3a and a second rotation axis 3b, it is not limited to this. In other embodiments, the gimbal mechanism 3 may have three or more rotation axes that intersect with each other.

[0047] Furthermore, although the columnar member 5 constituting the rotation axis was replaceable in the above embodiment, it is not limited to this. In other embodiments of the gimbal mechanism 3, the columnar member 5 constituting the rotation axis may be non-replaceable, for example, by welding both ends together or by being integrally formed with the rotation frame.

[0048] Furthermore, in the gimbal mechanism 3 of the above embodiment, the first rotation axis 3a and the second rotation axis 3b were set to be orthogonal to each other, but this is not limited to this. In other embodiments, the first rotation axis 3a and the second rotation axis 3b may be set to intersect diagonally when viewed from the reference axis direction.

[0049] Furthermore, while the angle detection sensor 42 in the above embodiment utilized an optical lever, it is not limited to this. In other embodiments, the angle detection sensor 42 may use other detectors, such as a potentiometer.

[0050] Furthermore, it goes without saying that the present invention is not limited to the embodiments described above, and various modifications are possible without departing from its spirit. [Explanation of Symbols]

[0051] 200... Laser fusion reactor P...Meat pellets V...furnace body F...Fuel injection mechanism L... Laser irradiation mechanism L1... Laser light source L2...Optical system 100... Steering mirror 1 ···Mirror body 1s...reflective surface 2...Support part 21 ···Base 21s... Base surface 22...Support plate 3. Gimbal mechanism 3a ···First axis of rotation 3b...Second rotation axis 31 ···First Rotating Frame 32 ···Second Rotating Frame 5 ···Columnar member 51 ···Shaft section 52...Connection part 4. Control mechanism 41... Actuator 41a...First Actuator 41b...Second Actuator 42...Angle detection sensor 421... Laser light source 422... Light-receiving element 43 ···Fuel position detection sensor 44... Control Unit R...Irradiation position

Claims

1. A steering mirror that adjusts the direction of travel by reflecting laser light in any direction, The mirror body that reflects the laser light, A support portion that supports the mirror body, The system includes a gimbal mechanism interposed between the mirror body and the support portion, having multiple rotation axes that allow the mirror body to be tilted at any angle relative to the support portion, A steering mirror in which at least one of the plurality of rotation axes is made of an elastically deformable columnar member with both ends fixed, and the mirror body rotates around the rotation axis as the columnar member twists.

2. The steering mirror according to claim 1, wherein each of the plurality of rotation axes is composed of an elastically deformable columnar member with both ends fixed, and the mirror body rotates around each rotation axis as each columnar member twists.

3. The gimbal mechanism, A first rotating frame, connected to the support portion and rotatable around a first rotation axis, The system includes a second rotating frame that supports the mirror body and is connected to the first rotating frame, and is rotatable about a second rotating axis that intersects the first rotating axis, The columnar member constituting the first rotation axis has one end fixed to the support portion and the other end fixed to the first rotation frame. The steering mirror according to claim 2, wherein one end of the columnar member constituting the second rotation axis is fixed to the first rotation frame and the other end is fixed to the second rotation frame.

4. The steering mirror according to claim 1, wherein the columnar member is replaceable.

5. The steering mirror according to claim 1, wherein the columnar member is made of metal.

6. The steering mirror according to claim 1, wherein the columnar member has a shaft portion having a constant cross-sectional shape along the axial direction and connecting portions provided at both ends in the axial direction.

7. A steering mirror according to any one of claims 1 to 6, which adjusts the direction of travel of laser light used to irradiate the fuel in a laser fusion reactor by reflecting the laser light.

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