JP4718982B2 - Ion analyzer - Google Patents

Description

  The present invention relates to a Thomson parabolic ion analyzer that analyzes the specific charge and kinetic energy of ions generated from an ion generation source.

  The Thomson parabola type ion analyzer deflects ions by passing ions flying from a source in a specific direction through an electromagnetic field and detects the arrival position of the ions after the deflection. Thus, the specific charge and kinetic energy of the ions can be analyzed.

  The ion analyzer described in Non-Patent Document 1 uses a solid track detection element to detect the distribution of the arrival positions of ions after being deflected by an electromagnetic field. The solid track detection element used here is a plastic flat plate-like member, and a polymer chain is broken by the incidence of high-speed ions, thereby recording the ion incidence position. When this solid track detection element is etched in a sodium hydroxide solution for several hours, the hole opened with the incidence of ions expands. Then, by observing the distribution of holes in the solid track detection element after etching under a microscope, it is possible to detect the distribution of the positions where the ions after being deflected by the electromagnetic field have reached the solid track detection element, The specific charge and kinetic energy of the ions can be analyzed.

The ion analyzer described in Non-Patent Document 2 uses a microchannel plate (hereinafter referred to as “MCP”) to detect the distribution of arrival positions of ions after being deflected by an electromagnetic field. The MCP can detect the arrival position of the ions after being deflected by the electromagnetic field in real time, and thus can analyze the specific charge and kinetic energy of the ions in real time.
R. Weber, et al., "Thomson parabola time-of-flight ionspectrometer", Rev. Sci. Instrum., Vol.57, No.7, pp.1251-1253 (1986). W. Mroz, et al., "Observation of different Ta and Pt ion groups produced by laser radiation with the intensities of Iλ2 ~ 1015 Wcm-2μm2", Rev. Sci. Instrum., Vol.69, No.3, pp.1349 -1352 (1998).

  Since the ion analyzer described in Non-Patent Document 1 requires etching of the solid track detection element and observation under a microscope, real-time ion analysis is impossible and is inefficient. In contrast, the ion analyzer described in Non-Patent Document 2 can perform real-time ion analysis using MCP, and is highly efficient in this respect.

MCP needs to be used in a high vacuum environment with an atmospheric pressure of 10 ⁻⁵ Pa or less. However, in the case of a laser plasma experiment in which a laser shot is used for the generation of ions in the ion generation source, a large amount of gas is released from the ion generation source along with the laser shot, so it is difficult to use MCP. is there. Furthermore, MCP has a problem that it is expensive.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a highly efficient and inexpensive ion analyzer capable of real-time ion analysis.

An ion analyzer according to the present invention is a Thomson parabolic ion analyzer that analyzes the specific charge and kinetic energy of ions generated from an ion generation source, and (1) a specific direction among ions generated from the ion generation source A collimator that selectively outputs ions that fly to (2), and (2) forms an electric field and a magnetic field that are each perpendicular to the specific direction and parallel to each other. An electromagnetic field generator that deflects ions by the electromagnetic field, and (3) a main surface perpendicular to the specific direction, and the ions that have reached through the electromagnetic field formed by the electromagnetic field generator are incident on the main surface, A plastic scintillator that generates light from the ion incident position; (4) a light detection unit that detects light generated from the plastic scintillator; and (5) a light detection unit. Based on the detection result selection, an analysis unit for analyzing a specific charge and kinetic energy of the ions generated from the ion source, the light is, generated in the plastic scintillator provided between the (6) plastic scintillator and the light detecting portion And an optical filter that transmits the light to the light detection unit .

In this ion analyzer, the ions generated from the ion source and passed through the collimator are deflected by the electric field and the magnetic field while flying through the space where the electromagnetic field is formed by the electromagnetic field generator, and enter the main surface of the plastic scintillator. To do. As ions are incident on the plastic scintillator, light is generated from the ion incident position, and the light passes through the optical filter and is detected by the light detection unit. Incidence of noise light (for example, a scattered component of laser light applied to the ion generation source) to the photodetector is blocked by the optical filter. Then, the specific charge and kinetic energy of the ions generated from the ion generation source are analyzed by the analysis unit based on the detection result by the light detection unit.

  As described above, the ion analyzer according to the present invention does not require a high vacuum, not an expensive MCP, and a high vacuum in order to detect ions generated from the ion generation source and reaching the electromagnetic field generation unit. An inexpensive plastic scintillator is used. In addition, this ion analyzer can detect light generated by the plastic scintillator with the incidence of ions by the light detection unit, and analyze the specific charge and kinetic energy of the ions by the analysis unit based on the detection result. Therefore, this ion analyzer is capable of real-time ion analysis and is highly efficient and inexpensive.

  The ion analyzer according to the present invention preferably further includes a metal foil that is provided between the electromagnetic field generator and the plastic scintillator, prevents noise light from entering the plastic scintillator, and allows ions to pass through. In this case, the incidence of noise light (for example, a scattered component of laser light irradiated on the ion generation source) to the plastic scintillator can be blocked by the metal foil (for example, aluminum foil). This metal foil may be a single sheet. However, since there is a possibility that a minute hole exists in an extremely thin metal foil and there is a risk of noise light passing through the hole, two sheets (or three sheets) are available. Or more).

  It is preferable that the ion analyzer according to the present invention further includes a control unit that controls ion generation in the ion generation source based on an analysis result by the analysis unit. In this case, since the ion generation in the ion generation source is controlled by the control unit based on the analysis result by the analysis unit, the ion generation in the ion generation source can always be maintained in the optimum state.

  The light detection unit includes a CCD camera that images the light generation distribution in the plastic scintillator, and the analysis unit calculates the specific charge and kinetic energy of the ions generated from the ion generation source based on the light generation distribution imaged by the CCD camera. It is preferable to analyze. Alternatively, the light detection unit includes a position detection type element that detects a barycentric position of the light generation distribution in the plastic scintillator, and the analysis unit is generated from the ion generation source based on the barycentric position detected by the position detection type element. It is also suitable to analyze the specific charge and kinetic energy of the ions. Alternatively, the light detection unit includes one or a plurality of light receiving elements that detect light generated at individual positions in the plastic scintillator, and the analysis unit is generated from the ion generation source based on the detection result by the light receiving elements. It is also suitable to analyze the specific charge and kinetic energy of the ions. In addition, the light detection unit preferably has a gate function for detecting light only for a predetermined period after a lapse of a certain time from the time of ion generation in the ion generation source. Can be removed.

  According to the present invention, it is possible to provide an ion analyzer that can perform real-time ion analysis and is highly efficient and inexpensive.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a configuration diagram of an experimental system including an ion analyzer 1 according to the present embodiment. The ion analyzer 1 is of a Thomson parabola type that analyzes the specific charge and kinetic energy of ions generated from the ion generation source 9, and includes a collimator 11, an electromagnetic field generator 12, metal foils 13a and 13b, a plastic scintillator 14, An optical filter 15, a light detection unit 16, an analysis unit 17, and a display unit 19 are provided. In addition to the ion analyzer 1, the experimental system shown in FIG. 1 further includes a laser device 6, a pulse waveform adjustment unit 7, a condensing optical system 8, an ion generation source 9, a vacuum container 10, and a control unit 18. Is also included.

  Inside the vacuum vessel 10, a collimator 11, an electromagnetic field generator 12, metal foils 13a and 13b, a plastic scintillator 14, an optical filter 15 and a light detector 16 are arranged. In addition to these, the condensing optical system 8 and ion generation A source 9 is arranged. Further, an analysis unit 17, a control unit 18, and a display unit 19 are arranged outside the vacuum vessel 10, and in addition to these, a laser light source 6 and a pulse waveform adjustment unit 7 are arranged. The vacuum vessel 10 is connected to exhaust means for exhausting the inside of the vacuum vessel 10.

  The laser light source 6 outputs pulsed laser light with high energy (for example, several TW) to be irradiated on the ion generation source 9. The pulse waveform adjustment unit 7 controls and outputs the pulse waveform of the laser beam output from the laser light source 6. As a technique for controlling the pulse waveform of laser light, a technique disclosed in Japanese Patent No. 3713350 is known. The condensing optical system 8 in the vacuum vessel 10 condenses the laser beam output from the pulse waveform adjustment unit 7 and irradiates the ion generation source 9 with it. The ion generation source 9 generates ions according to the laser shot.

  The collimator 11 has an opening, and selectively outputs ions generated from the ion generation source 9 that pass through the opening (that is, ions flying in a specific direction) to the electromagnetic field generation unit 12. The electromagnetic field generator 12 forms an electric field and a magnetic field that are perpendicular to the specific direction (that is, the flight direction of the input ions) and parallel to each other, and the ions output from the collimator 11 are It passes through an electromagnetic field, and ions are deflected by the electromagnetic field. This ion deflection will be further described later with reference to FIG.

  The metal foils 13a and 13b are provided between the electromagnetic field generator 12 and the plastic scintillator 14 and prevent the incidence of noise light (for example, the scattered component of the laser light irradiated on the ion source 9) to the plastic scintillator 14. And allows ions to pass through. A single metal foil may be provided between the electromagnetic field generator 12 and the plastic scintillator 14, but there may be a minute hole in the extremely thin metal foil, and noise light passes through the hole. Since there is a danger, it is preferable to provide two (or three or more) metal foils. As these metal foils 13a and 13b, for example, an aluminum foil having a thickness of 0.8 μm is used. The stopping power of the aluminum foil depends on the film thickness. When the thickness is 0.8 μm, it is about 100 keV for protons and about 200 keV for deuterons.

  The plastic scintillator 14 has a main surface perpendicular to the specific direction (that is, the flight direction of ions input to the electromagnetic field generator 12). The plastic scintillator 14 is incident on the main surface by ions that have been deflected by the electromagnetic field formed by the electromagnetic field generator 12 and arrived through the metal foils 13a and 13b, and generate light from the ion incident position.

  Generally, the fluorescence decay time of a scintillator made of inorganic crystals (NaI, LiI, CsI, etc.) is 0.2 μs or more. In contrast, the fluorescence decay time of a plastic scintillator made of an organic fluorescent material (naphthalene, anthracene, p-terphenyl, PBD, etc.) is about 1 ns to several tens ns and is short. The ion analyzer 1 according to the present embodiment can eliminate the influence of X-ray incidence as described later by using the plastic scintillator 14 having a short fluorescence decay time.

  The plastic scintillator 14 is, for example, NE102A manufactured by NE TECHNOLOGY, and has a thickness of 0.1 mm. By reducing the thickness in this way, sensitivity to X-rays can be suppressed. In addition, for incident charged particles, one photon is emitted for every 100 eV energy loss inside the plastic scintillator 14. In the Thomson parabolic ion analyzer 1, the energy of ions entering the plastic scintillator 14 is assumed to be about 100 keV to 10 MeV, and therefore, it is expected to emit about 1,000 to million photons.

  The optical filter 15 is provided between the plastic scintillator 14 and the light detection unit 16, selectively transmits the light generated by the plastic scintillator 14 to the light detection unit 16, and generates noise light (for example, for the light detector 16). The incidence of the scattering component of the laser light irradiated on the ion generation source 9 is blocked. For example, the wavelength of the laser light output from the laser light source 6 and focused and irradiated on the ion generation source 9 is 800 nm, and the wavelength of the light generated by the plastic scintillator 14 upon ion incidence is 410 nm.

  The light detection unit 16 detects light generated by the plastic scintillator 14 and transmitted through the optical filter 15. The light detection unit 16 preferably has a gate function capable of detecting light only for a predetermined period after a lapse of a certain time from the time of ion generation in the ion generation source 9. The analysis unit 17 analyzes the specific charge and kinetic energy of ions generated from the ion generation source 9 based on the detection result by the light detection unit 16.

  Preferably, the light detection unit 16 includes a CCD camera that images the light generation distribution in the plastic scintillator 14, and the analysis unit 17 generates from the ion generation source 9 based on the light generation distribution imaged by the CCD camera. The specific charge and kinetic energy of the ions are analyzed. Alternatively, the light detection unit 16 includes a position detection type element (PSD) that detects the barycentric position of the light generation distribution in the plastic scintillator 14, and the analysis unit 17 is based on the barycentric position detected by the position detection type element. The specific charge and kinetic energy of the ions generated from the ion generation source 9 are analyzed. Alternatively, the light detection unit 16 includes one or a plurality of light receiving elements (for example, PIN photodiodes) that detect light generated at individual positions in the plastic scintillator 14, and the analysis unit 17 includes the light receiving elements. Based on the detection result, the specific charge and kinetic energy of the ions generated from the ion generation source 9 are analyzed.

  The control unit 18 controls the ion generation in the ion generation source 9 based on the analysis result by the analysis unit 17. Specifically, the control unit 18 adjusts the pulse waveform of the laser beam by the pulse waveform adjustment unit 7, condensing irradiation of the laser beam to the ion generation source 9 by the condensing optical system 8, and in the ion generation source 9 Any one of the laser beam irradiation positions is controlled to maintain the ion generation in the ion generation source 9 in the optimum state. The display unit 19 displays the analysis result obtained by the analysis unit 17.

  FIG. 2 is a perspective view of the collimator 11, the electromagnetic field generator 12, and the plastic scintillator 14 included in the ion analyzer 1 according to the present embodiment. This figure is for explaining ion deflection in the electromagnetic field formed by the electromagnetic field generator 12, and illustration of the metal foils 13a and 13b provided between the electromagnetic field generator 12 and the plastic scintillator 14 is omitted. Has been. In this figure, an xyz rectangular coordinate system is shown for convenience of explanation. The z-axis is parallel to the flight direction (indicated by the alternate long and short dash line in the figure) of the ions generated from the ion generation source 9 that have passed through the minute aperture 11a of the collimator 11. The y axis is parallel to the direction of the electric field E and the magnetic field M formed by the electromagnetic field generator 12.

  The electromagnetic field generator 12 includes a pair of electrodes 121 and 122 as means for generating the electric field E, and includes a pair of magnets 123 and 124 as means for generating the magnetic field M. Each of the pair of electrodes 121 and 122 is on a flat plate having a main surface parallel to the xz plane, and is provided so as to sandwich the flight path of ions that have passed through the opening 11a of the collimator 11. When a DC voltage is applied to, a DC electric field E in the y direction is formed. Each of the pair of magnets 123 and 124 is on a flat plate having a main surface parallel to the xz plane, and is provided so as to sandwich the flight path of ions that have passed through the opening 11a of the collimator 11, and is in the y direction. The direct current magnetic field M is formed. Each of the magnets 123 and 124 may be a permanent magnet or an electromagnet. Each of the electric field E and the magnetic field M only needs to be applied when ions fly, and may be a pulse.

  The ions that pass through the opening 11a of the collimator 11 and fly in the z direction are deflected by the electric field E and the magnetic field B while flying in the space where the electromagnetic field is formed by the electromagnetic field generator 12, and are parallel to the xy plane. It enters the main surface of the plastic scintillator 14 (indicated by a broken line in the figure). In this deflection, the ions are deflected in the y direction by the amount corresponding to the specific charge (= ion valence / ion mass) by the electric field E, and are also deflected in the x direction by the amount corresponding to the kinetic energy by the magnetic field M. receive. The ions subjected to such a deflection reach any position on the parabola that differs depending on the specific charge on the main surface of the plastic scintillator 14. Moreover, the ion incident position on the parabola corresponding to a certain specific charge differs depending on the kinetic energy of the ions. Therefore, the specific charge and kinetic energy of ions generated from the ion generation source 9 can be analyzed by detecting the ion incident position on the main surface of the plastic scintillator 14 (the position where light is generated in response to the ion incidence). .

  The ion analyzer 1 according to the present embodiment does not require a high vacuum, not an expensive MCP, which requires a high vacuum in order to detect ions generated from the ion generation source 9 and reaching the electromagnetic field generator 12. An inexpensive plastic scintillator 14 is used. Further, the ion analyzer 1 detects light generated by the plastic scintillator 14 with the incidence of ions by the light detector 16 and immediately analyzes the specific charge and kinetic energy of the ions by the analyzer 17 based on the detection result. can do. Therefore, the ion analyzer 1 can perform real-time ion analysis, and is highly efficient and inexpensive.

3 shows an electromagnetic field generation unit 12, a plastic scintillator 14, and a light detection unit 16 (light reception elements 16 _{1 to} 16 _N ) when a plurality of light reception elements are used as the light detection unit 16 in the ion analyzer 1 according to the present embodiment. FIG. In this figure, the analysis unit 17, the control unit 18, and the display unit 19 are shown as a block diagram, while the metal foils 13a and 13b provided between the electromagnetic field generation unit 12 and the plastic scintillator 14 are not shown. Also, the optical filter 15 provided between the plastic scintillator 14 and the photodetector 16 is not shown. Also in this figure, an xyz rectangular coordinate system is shown for convenience of explanation.

A parabola drawn by ions deflected by the electromagnetic field generator 12 reaching the main surface of the plastic scintillator 14 can be accurately obtained by calculation according to the ion species. Therefore, the light receiving elements 16 _{1 to} 16 _N can be arranged at positions where light can be generated in the plastic scintillator 14 as ions are incident. Here, N is an integer of 2 or more. Alternatively, one end face of the optical fiber may be disposed at a position where light can be generated in the plastic scintillator 14 with ion incidence, and a light receiving element may be provided on the other end face side of the optical fiber. It is possible to achieve a high position resolution.

The analysis unit 17 analyzes the specific charge and kinetic energy of ions generated from the ion generation source 9 based on the detection results by these light receiving elements 16 _{1 to} 16 _N. At this time, the analysis unit 17 may analyze the specific charge and kinetic energy of ions by analysis using software, but may also analyze the specific charge and kinetic energy of ions by processing using hardware.

FIG. 4 is a diagram illustrating a hardware configuration example of the analysis unit 17 of the ion analyzer 1 according to the present embodiment. The analysis unit 17 shown in this figure can be used when the light detection unit 16 includes _N light receiving elements 16 _{1 to} 16 _N as shown in FIG. N resistors each having a resistance value R are connected in series between the output terminal of each light receiving element 16 _n and the ground potential. n is an integer of 1 or more and N or less. The current output from the output terminal of the light receiving elements 16 _n represents a j (n). The output potential of the output terminal of each light receiving element 16 _n is represented as V _A (n). In addition, the output potential at the position of the resistance division ratio “(N−n): n” in the resistor array between the output terminal of each light receiving element 16 _n and the ground potential is represented as V _B (n).

For each light receiving element 16 _n , the output potential V _A (n) is expressed by the following equation (1), and the output potential V _B (n) is expressed by the following equation (2). The ratio of the sum of output potentials V _A (n) and the sum of output potentials V _B (n) is expressed by the following equation (3). This expression (3) represents the position of the center of gravity of the current generation distribution on the parabola in the plastic scintillator 14 (that is, the center of gravity of the kinetic energy distribution of ions).

  By adopting the hardware configuration as shown in FIGS. 3 and 4 as described above, the specific charge and kinetic energy of ions can be analyzed at high speed in real time, and further, ion generation by the control unit 18 can be performed. This control can also be performed at high speed. Note that the control of the ion generation by the control unit 18 can be performed based on any one or combination of information such as the number of ions, the average kinetic energy, and the distribution of ion species. Can be acquired. The same applies to the case where the light detection unit 16 includes a position detection type element (PSD).

  FIG. 5 is a diagram illustrating one timing example of the operation of the ion analyzer 1 according to the present embodiment. FIG. 4A shows the timing at which the laser beam output from the laser light source 6 is focused and irradiated on the ion generation source 9. FIG. 4B shows the timing at which ions and noise light generated from the ion generation source 9 with laser light irradiation reach the plastic scintillator 14. FIG. 3C shows the timing at which the light detection unit 16 detects the light generated from the plastic scintillator 14 with the incidence of ions.

  The plastic scintillator 14 not only emits light when ions are incident, but also emits noise light from the laser light source 6 or X-rays generated when, for example, high-speed electrons collide with some member. The light generated in the plastic scintillator 14 with the incidence of noise light or X-rays becomes background noise with respect to the light generated in the plastic scintillator 14 with the incidence of ions, and is therefore preferably removed as follows. .

  The flight speed of a proton with a kinetic energy of 10 MeV is about one-tenth of the speed of light, and generally the flight speed of ions to be analyzed is even slower. On the other hand, the speed of X-rays is the speed of light. If the distance between the ion source 9 and the plastic scintillator 14 is about 9 cm, the time at which the ions generated from the ion source 9 reach the plastic scintillator 14 and the X-rays generated simultaneously with the generation of the ions enter the plastic scintillator 14. There is a time difference of about 3 ns from the arrival time (FIG. 5B). Since the fluorescence decay time of the plastic scintillator 14 is about 2 ns, the light emission from the plastic scintillator 14 due to X-ray incidence and the light emission from the plastic scintillator 14 due to ion incidence are temporally separated.

  Therefore, the light detection unit 16 has a temporal gate function, and as shown in FIG. 5, a predetermined period after a certain time has elapsed from the time of ion generation in the ion generation source 9 (plastic associated with ion incidence). By detecting light only during the period of light emission by the scintillator 14, the influence of X-ray incidence can be eliminated.

It is a block diagram of the experiment system containing the ion analyzer 1 which concerns on this embodiment. 1 is a perspective view of a collimator 11, an electromagnetic field generator 12, and a plastic scintillator 14 included in an ion analyzer 1 according to the present embodiment. FIG. 3 is a perspective view of the generator 12, the plastic scintillator 14, and the light detector 16 when a plurality of light receiving elements are used as the light detector 16 in the ion analyzer 1 according to the present embodiment. It is a figure which shows the hardware structural example of the analysis part 17 of the ion analyzer 1 which concerns on this embodiment. It is a figure which shows the 1 timing example of operation | movement of the ion analyzer 1 which concerns on this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Ion analyzer, 6 ... Laser light source, 7 ... Pulse waveform adjustment part, 8 ... Condensing optical system, 9 ... Ion generation source, 10 ... Vacuum container, 11 ... Collimator, 12 ... Electromagnetic field generation part, 13a, 13b ... Metal foil, 14 ... plastic scintillator, 15 ... optical filter, 16 ... photodetection unit, 17 ... analysis unit, 18 ... control unit, 19 ... display unit.

Claims (7)

A Thomson parabolic ion analyzer that analyzes the specific charge and kinetic energy of ions generated from an ion source,
A collimator that selectively outputs ions flying in a specific direction among the ions generated from the ion generation source;
An electromagnetic field generator that forms an electric field and a magnetic field that are each perpendicular to the specific direction and parallel to each other, pass ions output from the collimator through the electromagnetic field, and deflect the ions by the electromagnetic field;
A plastic scintillator that has a main surface perpendicular to the specific direction, and that enters the main surface with ions that have arrived through an electromagnetic field formed by the electromagnetic field generation unit, and generates light from the ion incident position;
A light detection unit for detecting light generated from the plastic scintillator;
An analysis unit that analyzes specific charges and kinetic energy of ions generated from the ion generation source based on a detection result by the light detection unit;
An optical filter that is provided between the plastic scintillator and the light detection unit and selectively transmits light generated by the plastic scintillator to the light detection unit;
An ion analyzer characterized by comprising:   The ion analyzer according to claim 1, further comprising a metal foil provided between the electromagnetic field generation unit and the plastic scintillator, which prevents noise light from entering the plastic scintillator and allows ions to pass therethrough. .   The ion analyzer according to claim 1, further comprising a control unit that controls ion generation in the ion generation source based on an analysis result by the analysis unit. The light detection unit includes a CCD camera that images a light generation distribution in the plastic scintillator,
The analysis unit analyzes specific charges and kinetic energy of ions generated from the ion generation source based on the light generation distribution imaged by the CCD camera.
The ion analyzer according to claim 1. The light detection unit includes a position detection type element that detects a gravity center position of a light generation distribution in the plastic scintillator,
The analysis unit analyzes the specific charge and kinetic energy of ions generated from the ion generation source based on the position of the center of gravity detected by the position detection type element;
The ion analyzer according to claim 1. The light detection unit includes one or more light receiving elements for detecting light generated at individual positions in the plastic scintillator,
The analysis unit analyzes specific charges and kinetic energy of ions generated from the ion generation source based on a detection result by the light receiving element;
The ion analyzer according to claim 1. The ion analyzer according to claim 1, wherein the light detection unit has a gate function for detecting light only for a predetermined period after a lapse of a predetermined time from the time of ion generation in the ion generation source.

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