Measuring device and measuring method

Abstract

To provide a measuring device and a measuring method that can measure a longitudinal phase spatial distribution of a pulsed charged particle beam.SOLUTION: A measuring device (1) comprises: a conversion mechanism (11) which uses a deflection magnet (11a) to convert a linear path (P1) of a charged particle beam into a planar path (P2) including a plurality of paths (P21-P23) that charged particles differing in energy pass through; and a measuring mechanism (12) which measures a longitudinal phase spatial distribution of the charged particle beams as a secondary intensity distribution of probe laser light having changed in a polarization direction through an electrooptical crystal (12b) with the charged particle beams.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a measurement device and a measurement method for measuring the longitudinal phase space distribution of a pulsed electron beam. [Background technology]

[0002] A measurement method using the electro-optic effect is known as a method for measuring the time distribution of a pulsed electron beam (see Non-Patent Document 1). Here, the time distribution of an electron beam refers to the density distribution on the time axis of the electron group that constitutes the electron beam.

[0003] In this measurement method, a probe laser beam with a specific polarization direction is incident on an electro-optic crystal as an electron beam passes near the crystal. The polarization direction of the probe laser beam passing through the electro-optic crystal is changed by the Coulomb field of the electrons that make up the electron beam. Therefore, by selectively detecting the probe laser beam whose polarization direction has been changed by the Coulomb field of the electrons, the time distribution of the electron beam can be measured.

[0004] For example, in the spatial decoding method, a probe laser beam is obliquely incident on an electro-optic crystal, and the probe laser beam that passes through the electro-optic crystal is incident on an image sensor via a polarizer, allowing the time distribution of the electron beam to be measured as a one-dimensional spatial intensity distribution of the probe laser beam incident on the image sensor.

[0005] The measurement method using the electro-optic effect has the advantage that the time distribution of the electrons constituting the electron beam can be measured in a single shot and non-destructively. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] K. Huang,et al., "Electro-optic spatial decoding on the spherical-wavefront Coulomb fields of plasma electron sources", ,Scientific Reports 8, 2938 (2018) Summary of the Invention [Problem to be solved by the invention]

[0007] Now, knowledge of the longitudinal phase space distribution of a pulsed charged particle beam (e.g., an electron beam) is extremely important for achieving effective acceleration or control of the charged particle beam. Here, the longitudinal phase space refers to a two-dimensional space with time on one axis and energy or momentum on the other axis, and the longitudinal phase space distribution of a charged particle beam refers to the density distribution in the longitudinal phase space of the charged particles that make up the charged particle beam. By referring to the longitudinal phase space distribution of a charged particle beam, for example, it is possible to know the magnitude relationship between the energy of electrons at an early time (located at the front end of the beam) and the energy of electrons at a late time (located at the rear end of the beam).

[0008] However, no method for easily measuring the longitudinal phase space distribution of a charged particle beam has been known.

[0009] As mentioned above, the time distribution of an electron beam can be measured non-destructively by using an electro-optic crystal. Therefore, by measuring the energy distribution of the electron beam (the density distribution on the energy axis of the electron group that constitutes the electron beam) after measuring the time distribution, it is possible to measure both the time distribution and the energy distribution of the electron beam. However, what is obtained in this case is merely the projection of the longitudinal phase space distribution onto the spatial and time axes. Therefore, even if both the time distribution and the energy distribution of the electron beam are referenced, it is not possible to know, for example, the magnitude relationship between the energy of early electrons and that of late electrons.

[0010] One aspect of the present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a measurement device and a measurement method that can easily measure the longitudinal phase space distribution of a pulsed charged particle beam. [Means for solving the problem]

[0011] A measurement device according to a first aspect of the present invention is a measurement device for measuring the longitudinal phase space distribution of a pulsed charged particle beam, and includes a conversion mechanism that uses a deflection magnet to convert the linear path of the charged particle beam into a planar path including multiple paths through which charged particles of different energies pass, and a measurement mechanism that measures the longitudinal phase space distribution of the charged particle beam as a two-dimensional intensity distribution of probe laser light whose polarization direction has been changed in an electro-optic crystal by the charged particle beam.

[0012] The above configuration has the effect of making it possible to measure the longitudinal phase space distribution of a charged particle beam with a single shot.

[0013] In the measurement device according to aspect 2 of the present invention, in addition to the configuration of aspect 1, the electro-optic crystal is arranged so that its end face faces the planar path, and the measurement mechanism measures the longitudinal phase space distribution of the charged particle beam as a two-dimensional intensity distribution of probe laser light whose polarization direction is changed by the Coulomb field of the charged particles that constitute the charged particle beam.

[0014] By employing the above configuration, the longitudinal phase space distribution of a charged particle beam can be measured in a single shot and non-destructively.

[0015] A measurement device according to a third aspect of the present invention, in addition to the configuration of the first aspect, further includes a radiator arranged on the planar path, and a focusing lens that focuses, on the electro-optic crystal, electromagnetic waves that are generated by transition radiation or Cherenkov radiation from the surface or the interior of the radiator when each charged particle constituting the charged particle beam is incident on the radiator, and the measurement mechanism is configured to measure the longitudinal phase space distribution of the charged particle beam as a two-dimensional intensity distribution of probe laser light whose polarization direction is changed by the electromagnetic waves focused on the optical crystal.

[0016] By employing the above configuration, the longitudinal phase space distribution of a charged particle beam can be measured in a single shot.

[0017] In a measuring device according to aspect 4 of the present invention, in addition to the configuration of any one of aspects 1 to 3, the measuring mechanism includes the electro-optical crystal, a first polarizer arranged in front of the electro-optical crystal, a second polarizer arranged in back of the electro-optical crystal, an imaging lens arranged in back of the second polarizer, and an image sensor arranged in back of the imaging lens.

[0018] By employing the above configuration, it is possible to improve the resolution of the longitudinal phase space distribution of the charged particle beam obtained by measurement.

[0019] In addition to the configuration of any one of the first to fourth aspects, the measuring device according to the fifth aspect of the present invention employs a configuration in which the measuring device is divided into multiple cells by a dividing line along the energy axis and / or a dividing line along the time axis.

[0020] By employing the above configuration, it is possible to improve either or both of the time resolution and the spatial resolution of the longitudinal phase space distribution of the charged particle beam obtained by measurement.

[0021] A measuring device according to a sixth aspect of the present invention employs the configuration of any one of the first to fifth aspects, in which the charged particles are electrons.

[0022] By employing the above configuration, the longitudinal phase space distribution of the electron beam can be measured in a single shot.

[0023] A measurement method according to a seventh aspect of the present invention is a measurement method for measuring the longitudinal phase space distribution of a pulsed charged particle beam, and includes a conversion step of converting, using a deflection magnet, a linear path of the charged particle beam into a planar path including a plurality of paths through which charged particles of different energies pass, and a measurement step of measuring the longitudinal phase space distribution of the charged particle beam as a two-dimensional intensity distribution of probe laser light whose polarization direction has been changed in an electro-optic crystal by the charged particle beam.

[0024] The above configuration has the effect of making it possible to measure the longitudinal phase space distribution of a charged particle beam with a single shot. [Effects of the Invention]

[0025] Advantageous Effects of Invention According to one aspect of the present invention, an effect is achieved in that the longitudinal phase space distribution of a charged particle beam can be easily measured. [Brief explanation of the drawings]

[0026] [Figure 1] 1A and 1B are diagrams showing the configuration of a measurement device according to an embodiment of the present invention, in which (a) is a top view of the measurement device, and (b) is a side view of the measurement device and a front view of an electro-optic crystal provided in the measurement device. [Figure 2] 2 is a graph schematically showing an example of a longitudinal phase space distribution of an electron beam measured by the measurement device shown in FIG. 1. [Figure 3] 2A and 2B are diagrams showing a modified example of the measurement device shown in Fig. 1, in which (a) is a top view of the measurement device, and (b) is a side view of the measurement device and a front view of an electro-optic crystal provided in the measurement device. [Figure 4] 3(a) is a front view showing a modified example of the electro-optic crystal provided in the measurement device shown in FIG. 1, and FIG. 3(b) is a front view showing a modified example of the electro-optic crystal provided in the measurement device shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0027] (Configuration of measuring device) The configuration of a measurement device 1 according to one embodiment of the present invention will be described with reference to Fig. 1. Fig. 1(a) is a top view of the measurement device 1, and Fig. 1(b) is a side view of the measurement device 1 and a front view of an electro-optic crystal 12b. In the following description, the spatial coordinate system (X, Y, Z) and the beam coordinate system (X', Y', Z') shown in Fig. 1 will be used as appropriate.

[0028] The measurement device 1 is a device for measuring the longitudinal phase space distribution of a pulsed charged particle beam. In this embodiment, electrons are assumed as the charged particles. However, the charged particles are not limited to electrons and may be protons or ions.

[0029] As shown in FIG. 1, the measurement device 1 includes a conversion mechanism 11 and a measurement mechanism 12.

[0030] The conversion mechanism 11 is a mechanism for converting the linear path P1 of the electron beam into a planar path P2 including a plurality of paths through which electrons of different energies pass, using a bending magnet 11a. Note that Fig. 1 illustrates, as typical paths, path P21 through which electrons having high energy E1 pass, path P22 through which electrons having intermediate energy E2 pass, and path P23 through which electrons having low energy E3 pass.

[0031] In this embodiment, the conversion mechanism 11 is composed of a deflection magnet 11a arranged on the linear path P1 of the electron beam.

[0032] The deflection magnet 11a bends the path of each electron constituting the electron beam with a curvature according to the energy of the electron, thereby converting the linear path P1 into a planar path P2.

[0033] The measurement mechanism 12 is a mechanism for measuring the longitudinal phase spatial distribution of the electron beam as a two-dimensional intensity distribution of the probe laser light whose polarization direction has been changed in the electro-optic crystal 12b by the electron beam. The electro-optic crystal 12b is plate-shaped and is arranged so that its end face faces the planar path P2. In other words, the electro-optic crystal 12b is arranged near the planar path P2 so that its entrance and exit faces are perpendicular to a plane including the planar path P2. The distance between the planar path P2 and the electro-optic crystal 12b is, for example, 0.1 mm or more and 1 mm or less. The electro-optic crystal 12b can be, for example, a GaP crystal or a ZnTe crystal. The thickness of the electro-optic crystal 12b can be set arbitrarily depending on the required time resolution, for example, 10 μm or more and 100 μm or less. The probe laser light is obliquely incident on the electro-optic crystal 12b in synchronization with the timing at which the electron beam passes near the electro-optic crystal 12b. The angle of incidence of the probe laser beam on the electro-optic crystal 12b is, for example, 20° to 45°. For example, an ultrashort pulse laser can be used as the probe laser beam. The pulse duration of the probe laser beam can be set arbitrarily depending on the required time resolution, for example, 30 fs.

[0034] In this embodiment, the measurement mechanism 12 is composed of a first polarizer 12a, an electro-optic crystal 12b, a second polarizer 12c, an imaging lens 12d, and an image sensor 12e, which are arranged on the optical path Q of the probe laser light.

[0035] The first polarizer 12a is disposed before the electro-optic crystal 12b so that the entrance surface and exit surface are perpendicular to the optical path Q of the probe laser light. The first polarizer 12a selectively transmits the probe laser light having a specific polarization direction (which may be linearly polarized or circularly polarized).

[0036] The second polarizer 12c is disposed after the electro-optic crystal 12b so that its entrance and exit surfaces are perpendicular to the optical path Q of the probe laser light. The second polarizer 12c selectively transmits the probe laser light whose polarization direction has been changed by the electron beam in the electro-optic crystal 12b. For example, a Wollaston prism can be used as the second polarizer 12c.

[0037] The imaging lens 12d is disposed after the second polarizer 12c so that its principal plane is perpendicular to the optical path Q of the probe laser light. The imaging lens 12d focuses the probe laser light that has passed through the second polarizer 12c onto each point on the image sensor 12e.

[0038] The image sensor 12e is disposed after the imaging lens 12d so that its incident surface is perpendicular to the optical path Q of the probe laser light. The image sensor 12e detects the two-dimensional intensity distribution of the probe laser light that has passed through the second polarizer 12c, i.e., the probe laser light whose polarization direction has been changed by the electron beam in the electro-optic crystal 12b.

[0039] In the measurement device 1, when an electron beam passes near the electro-optic crystal 12b, the polarization direction of the probe laser light passing through the electro-optic crystal 12b is changed by the Coulomb field of the electrons that make up the electron beam.

[0040] In this case, the change in the polarization direction of the probe laser light passing through the region on the positive Y-axis side of electro-optic crystal 12b is caused by high-energy electrons, and the change in the polarization direction of the probe laser light passing through the region on the negative Y-axis side is caused by low-energy electrons. This is because the action of deflection magnet 11a aligns the paths of electrons with different energies along the Y-axis, and because the Coulomb field of the electrons has an intensity distribution that is biased toward the positive Z-axis and the negative Z-axis due to the relativistic effect.

[0041] Furthermore, the change in the polarization direction of the probe laser light passing through the region on the positive side of the Z axis of the electro-optic crystal 12b is caused by electrons that arrive early (at the front end of the electron beam), and the change in the polarization direction of the probe laser light passing through the region on the negative side of the Z axis is caused by electrons that arrive early (at the rear end of the electron beam). This is because the probe laser light is obliquely incident on the electro-optic crystal 12b.

[0042] Therefore, by using the second polarizer 12c, the imaging lens 12d, and the image sensor 12e to selectively detect the two-dimensional intensity distribution of the probe laser light whose polarization direction has changed in the electro-optic crystal 12b, the longitudinal phase spatial distribution of the electron beam can be obtained.

[0043] 2 is a graph schematically showing an example of the two-dimensional intensity distribution of the probe laser light detected by the image sensor 12e, i.e., the vertical phase space distribution of the electron beam measured by the measurement device 1. The Y'-axis of the beam coordinate system corresponds to the energy axis, and the Z'-axis of the beam coordinate system corresponds to the time axis. The graph shown in FIG. 2 shows that the energy of early electrons is relatively low, and the energy of late electrons is relatively high.

[0044] In the longitudinal phase space distribution of the electron beam measured by the measurement device 1, the time resolution is, for example, about 30 fsec, and the relative energy resolution is, for example, about 0.1%.

[0045] (Modification of the measuring device) A modified example of the measurement apparatus 1 (hereinafter referred to as measurement apparatus 1A) will be described with reference to Fig. 3. Fig. 3(a) is a top view of the measurement apparatus 1A, and Fig. 3(b) is a side view of the measurement apparatus 1A. In the following description, the spatial coordinate system (X, Y, Z) and the beam coordinate system (X', Y', Z') shown in Fig. 3 will be used as appropriate. The measurement apparatus 1A differs from the measurement apparatus 1 in the following points.

[0046] The first difference is that the conversion mechanism 11 of the measurement device 1A is composed of two deflection magnets 11a and 11b. The deflection magnet 11a converts the linear path P1 of the electron beam into a planar path P2 in which the paths of electrons with different energies are spaced apart gradually. The deflection magnet 11b converts the planar path P2 of the electron beam into a planar path P3 in which the paths of electrons with different energies are spaced apart at a constant interval.

[0047] The second difference is that the measurement apparatus 1A includes a radiator 13 arranged on the planar path P3 of the electron beam. When each electron constituting the electron beam enters the radiator 13, an electromagnetic wave is emitted by transition radiation or Cherenkov radiation from the surface or interior of the radiator 13. The radiator 13 may be, for example, a glass block or a thin metal film.

[0048] The third difference is that measurement apparatus 1A includes a condenser lens 14 on the optical path of the electromagnetic waves generated by transition radiation or Cherenkov radiation from the surface or interior of radiator 13. Collector lens 14 is composed of a pair of concave mirrors 14a and 14b. Collector lens 14 focuses the electromagnetic waves generated by transition radiation or Cherenkov radiation emitted from the interior or surface of radiator 13 onto electro-optic crystal 12b.

[0049] In the measurement device 1A, when the electrons constituting the electron beam are incident on the radiator 13, an electromagnetic wave is emitted as transition radiation or Cherenkov radiation from the surface or the interior of the radiator 13, and this electromagnetic wave changes the polarization direction of the probe laser light passing through the electro-optic crystal 12b.

[0050] In this case, the change in the polarization direction of the probe laser light passing through the region on the positive Y-axis side of electro-optic crystal 12b is caused by high-energy electrons, and the change in the polarization direction of the probe laser light passing through the region on the negative Y-axis side is caused by low-energy electrons. This is because radiator 13 and condenser lens 14 are arranged so that the electromagnetic waves originating from high-energy electrons are focused on the positive Y-axis side of electro-optic crystal 12b, and the electromagnetic waves originating from low-energy electrons are focused on the negative Y-axis side of electro-optic crystal 12b.

[0051] Furthermore, the change in the polarization direction of the probe laser light passing through the region on the positive side of the Z axis of the electro-optic crystal 12b is caused by electrons that arrive early (at the front end of the electron beam), and the change in the polarization direction of the probe laser light passing through the region on the negative side of the Z axis is caused by electrons that arrive early (at the rear end of the electron beam). This is because the probe laser light is obliquely incident on the electro-optic crystal 12b.

[0052] Therefore, by selectively detecting the two-dimensional intensity distribution of the probe laser light whose polarization direction has been changed in the electro-optic crystal 12b using the second polarizer 12c, the imaging lens 12d, and the image sensor 12e, the longitudinal phase spatial distribution of the electron beam can be obtained. The resolution of the obtained longitudinal phase spatial distribution is about 30 fs on the time axis and about 0.1% on the energy axis.

[0053] (Modification of electro-optic crystal) A modified example of the electro-optic crystal 12b provided in the measurement devices 1 and 1A will be described with reference to Fig. 4. Fig. 4(a) is a front view of the electro-optic crystal 12b provided in the measurement device 1, and Fig. 4(b) is a front view of the electro-optic crystal 12b provided in the measurement device 1A.

[0054] As shown in Figures 4(a) and 4(b), electro-optic crystal 12b according to this modification is divided into a plurality of cells 12b' by dividing lines perpendicular to the energy axis (the Y' axis of the beam coordinate system). In this case, each cell 12b' has a rectangular plate-like shape with a main surface having a short side parallel to the Y axis and a long side parallel to the Z axis. Adjacent cells 12b' may be separated by, for example, a metal coating formed on the end face.

[0055] When the electro-optic crystal 12b according to this modification is used in the measurement device 1, the region on the electro-optic crystal 12b where the Coulomb field of electrons having each energy causes a change in the polarization direction of the probe laser light can be limited to the cell 12b' corresponding to that energy, thereby improving the energy resolution of the longitudinal phase space distribution of the electron beam obtained by the measurement device 1.

[0056] Furthermore, when the electro-optic crystal 12b according to this modification is used in the measurement apparatus 1A, the region on the electro-optic crystal 12b where the change in the polarization direction of the probe laser light is caused by the electromagnetic wave originating from the electrons having each energy can be limited to the cell 12b' corresponding to that energy, thereby improving the energy resolution of the longitudinal phase space distribution of the electron beam obtained by the measurement apparatus 1A.

[0057] The electro-optic crystal 12b may be divided into a plurality of cells 12b' by dividing lines perpendicular to the time axis (Z' axis of the beam coordinate system) instead of or in addition to dividing lines perpendicular to the energy axis. In the former case, each cell 12b' has a rectangular plate-like shape with a main surface having a short side parallel to the Z axis and a long side parallel to the Y axis. In this case, the time resolution of the longitudinal phase spatial distribution of the electron beam can be improved. In the latter case, each cell 12b' has a square (or rectangular close to a square) plate-like shape with a main surface. In this case, the energy axis direction and time resolution of the longitudinal phase spatial distribution of the electron beam can be improved.

[0058] (Additional notes) The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in the above-described embodiments are also included in the technical scope of the present invention. Furthermore, the application of the present invention is not limited to semiconductor devices, and can be applied to general products manufactured through multiple processes. [Explanation of symbols]

[0059] 1. Measuring equipment 11 Conversion mechanism 11a,11b Bending magnet 12 Measuring mechanism 12a First polarizer 12b Electro-optic crystal 12c 2nd polarizer 12d imaging lens 12e image sensor 13 Radiator 14 Condenser lens 14a,14b concave mirror

Claims

1. A measurement apparatus for measuring a longitudinal phase space distribution of a pulsed charged particle beam, comprising: a conversion mechanism that converts the linear path of the charged particle beam into a planar path including a plurality of paths through which charged particles of different energies pass, using a deflection magnet; a measurement mechanism for measuring the longitudinal phase space distribution of the charged particle beam as a two-dimensional intensity distribution of probe laser light whose polarization direction has been changed in an electro-optic crystal by the charged particle beam; A measuring device characterized by:

2. the electro-optic crystal is disposed so that an end face faces the planar path; the measurement mechanism measures the longitudinal phase space distribution of the charged particle beam as a two-dimensional intensity distribution of probe laser light whose polarization direction is changed by a Coulomb field of the charged particles constituting the charged particle beam; 2. The measuring device according to claim 1.

3. a radiator disposed on the planar path; a focusing lens that focuses, on the electro-optic crystal, electromagnetic waves that are generated by transition radiation or Cherenkov radiation from a surface or an interior of the radiator when charged particles that constitute the charged particle beam are incident on the radiator, the measurement mechanism measures the longitudinal phase space distribution of the charged particle beam as a two-dimensional intensity distribution of probe laser light whose polarization direction is changed by the electromagnetic wave focused on the electro-optic crystal; 2. The measuring device according to claim 1.

4. the measurement mechanism includes the electro-optical crystal, a first polarizer arranged in front of the electro-optical crystal, a second polarizer arranged in rear of the electro-optical crystal, an imaging lens arranged in rear of the second polarizer, and an image sensor arranged in rear of the imaging lens.

4. The measuring device according to claim 1, wherein the measuring device is a measuring device for measuring a temperature of the object.

5. The electro-optic crystal is divided into a plurality of cells by one or both of a dividing line along an energy axis and a dividing line along a time axis.

5. The measuring device according to claim 1, wherein the measuring device is a measuring device for measuring a temperature of the object.

6. the charged particles are electrons; The measuring device according to any one of claims 1 to 5.

7. A measurement method for measuring a longitudinal phase space distribution of a pulsed charged particle beam, comprising: a conversion step of converting the linear path of the charged particle beam into a planar path including a plurality of paths through which charged particles of different energies pass, using a bending magnet; and a measuring step of measuring the longitudinal phase space distribution of the charged particle beam as a two-dimensional intensity distribution of probe laser light whose polarization direction has been changed in an electro-optic crystal by the charged particle beam. A measuring method characterized by:

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