JPH0121585B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an analytical device for measuring charged particles, such as a charged particle spectrograph or a mass spectrometer. In the following introduction, a charged particle spectrograph will be mainly described, but the present invention is not limited thereto.

Generally, this type of charged particle spectrograph is equipped with a charged particle optical system having a magnetic field generating element and a particle position detection system configured with a nuclear emulsion plate or the like. Among these, the charged particle optical system images an incident charged particle in the form of a focal line at a position on the particle position detection system according to its momentum or energy. Therefore, in a charged particle spectrograph, by reading the number and position of charged particles on a particle position detection system, a charged particle spectrum of a finite range of momentum or energy can be measured all at once.

Conventionally, charged particle spectrographs have been proposed that can quickly observe and display charged particle spectra within a predetermined momentum or energy range using a data processing device. This charged particle spectrograph has a large number of position detection counters placed at image formation positions of charged particles as a particle position detection system, and has a configuration in which the counting results of each position detection counter are sequentially input to a data processing device. We are prepared.

Here, the index expressing the performance of a charged particle spectrograph usually includes resolution, which indicates the degree of difference in momentum or energy that can be separated and identified, and dispersion, which indicates the distance between the imaging positions of charged particles with different momentum or energy. The resolution and dispersion are mainly determined by the magnetic field and size of the charged particle optical system. For the sake of simplicity, we will discuss momentum resolution and momentum dispersion below unless otherwise specified.
Needless to say, similar arguments can be made regarding energy resolution and energy dispersion. The resolution referred to here refers to the ion optical first-order resolution, and in the ideal case when the image does not have any spread due to aberrations and is analyzed using a particle detection slit whose width can be assumed to be zero, The entire spectrograph system is defined by the ratio P _p /ΔP of the minimum momentum difference ΔP that can be distinguished and the momentum P _p of the standard particle. This one
The next resolution can be expressed as D(Mx _p ) ^-1 . Here, D is the momentum dispersion defined by D・ΔP/P p, which is the magnitude at which the image of the particle beam with momentum P _p + _ΔP is dispersed in the direction perpendicular to the main orbit (corresponding to the optical axis of the optical system). It is about. Also, M is the image magnification, x _p
is the width of the particle source. The effective resolution refers to the effective momentum resolution of the entire system when particle beams are analyzed using a spectrograph equipped with a particle position detector whose minimum width that can identify the position is x _d , and D(Mx _p
+x _d +x _h ) ^-1 . Here, x _h
is the spread due to image aberration. The above-mentioned charged particle spectrograph, which has a configuration combined with a data processing device, uses a counter tube that has a limit to position identification, so the position identification ability (herein referred to as position detection resolution) unique to these detectors is limited. It must also be taken into consideration that it is inferior to that of nuclear emulsions. This means that it is necessary to increase the dispersion compared to when a nuclear emulsion plate is used for particle position detection.

In a charged particle spectrograph that uses a particle position detection counter as a particle position detection system, the relationship between the above-mentioned dispersion and the range of energy or momentum of the charged particle spectrum that can be observed simultaneously (so-called wide range) is I need to think about it. For example, in general, in order to measure a charged particle spectrum having energy or momentum over a wide range, it is desirable that the dispersion be small. Therefore, a high-resolution charged particle spectrograph using a particle position detection counter has too large a dispersion property and is not suitable for performing spectrum measurements over a wide area. Furthermore, as mentioned above, the effective resolution of this spectrograph as a whole is also controlled by the position detection resolution of the counter, so if high effective resolution is required, it will not be effective unless the spectrograph has large dispersion. unable to demonstrate.

It is an object of the present invention to provide a charged particle spectrograph whose resolution and/or dispersion can be varied as required.

Another object of the present invention is to provide a charged particle spectrograph that, when applied to a system using a counter as a particle detection system, can provide dispersion in accordance with the position detection resolution of the counter.

Another object of the present invention is to provide a charged particle spectrograph that can be applied not only to observations over a wide area but also to observations requiring high resolution.

Yet another object of the invention is to provide a highly mobile charged particle spectrograph that can be coupled to data processing equipment.

According to the present invention, in a hybrid magnet type charged particle spectrograph having a dipole magnet and an auxiliary magnet for improving the resolution dispersion of the dipole magnet, the auxiliary magnet is capable of varying at least one of its installation position and installation angle. A charged particle spectrograph that can obtain the required resolution or dispersion can be obtained by placing a quadrupole magnet along the charged particle trajectory and changing the quadrupole magnet according to the purpose of observation.

This will be explained below with reference to the drawings.

Referring to FIGS. 1 and 2, charged particle spectrographs (hereinafter referred to as comparative spectrographs), which are the premise of the present invention, are shown to facilitate understanding of the present invention. This spectrograph focuses charged particles from a particle beam source S _p onto a multiple particle position detection system C arranged along a focal line on a plane of symmetry (hereinafter referred to as the intermediate plane) of a magnetic field (or electric field). It is for the purpose of In practice,
As shown in FIG. 1, this focal line is a curved line that is close to a straight line, and each charged particle is focused on an imaging point I ₁ -I ₀ -I ₂ on the focal line according to its momentum. This spectrograph has a charged particle optical system consisting of a first dipole magnet _D1 installed on the side of the particle beam source _Sp , and a second dipole magnet installed on the side of the particle position detection system C.
D ₂ . To simplify the explanation, in FIG. 1, the standard orbits of both dipole magnets D ₁ and D ₂ are shown as straight lines, and the orbit radii are both r _p , but in general, they may be different.

Normally, the magnetic field boundaries of the first and second dipole magnets D ₁ and D ₂ are designed to be oblique to the charged particle trajectory in order to create convergence and divergence called the magnetic pole effect. Inlet of bipolar magnet _D1 in Fig. 1,
The _D2 exits have oblique angles of α ₁ and α ₂ , respectively.
When crossing these magnetic field boundaries, the charged particle has focal lengths −f ₁₀ = −r _p /tanα ₁ and −f ₂₀ = −r _p / in the intermediate plane, respectively.
It receives a diverging effect corresponding to a concave lens with tan α ₂ , and a converging effect corresponding to a convex lens with +f ₁₀ =+r _p /tan α ₁ and +f ₂₀ = r _p /tan α ₂ in the vertical plane, respectively.

The operation will be explained with reference to FIGS. 1 and 2.
Among the particles emitted from the particle beam source S _p located at a distance a ₀ in front of the entrance of the first dipole magnet D ₁ , particles with standard particle momentum P _p are transferred to the second dipole magnet D _{2 .}
It focuses at a position I ₀ at a distance b ₀ from the exit. Also, particles with momentum P _p +ΔP and P _p −ΔP are I ₁ and I ₂ respectively
image is formed. Now, regarding a particle with standard particle momentum P _p , this particle is ejected from a distance a ₀ ' in the intermediate plane due to the magnetic pole effect at the entrance of the first dipole magnet D ₁ , as shown in Figure 1. It is refracted at the entrance of the first dipole magnet _D1 in such a manner, that is, in a diverging manner. On the other hand, this particle
As shown in the figure, it is refracted at the entrance of the first dipole magnet D ₁ in the vertical plane as if it had started from a position further away than the actual distance a ₀ , ie in the direction of convergence. The particle trajectory is bent by the dipole magnetic field in the first dipole magnet _D1 , and passes through the free space (i.e., the electromagnetic field-free space) between the first and second dipole magnets _D1 and _D2 . As shown in Figure 2, it travels straight along the main orbit and is incident on the second dipole magnet _D2 . The second dipole magnet D ₂ is
Similar to the first dipole magnet _D1 , it bends the trajectory of the particles. The magnetic pole effect at the exit of the second dipole magnet _D2 is within the intermediate plane and at a distance as shown in Figure 1.
While the particles heading towards the position b ₀ ″ are diverged and focused at the position I _{0 at a distance b 0 ,} as shown in Fig. 2,
It acts as a focusing element in the vertical plane and spatially focuses the particles to the position I ₀ . Generally, the dispersion D and resolution R at the imaging point of a spectrograph are expressed by the following equations.

R=(Mx _p θ _p ) ^-1 ∫ ^T _p xd …(1) D=θ _p ^-1 ∫ ^T _p xd …(2) Here, θ _p is the particle's main orbit in the source on the intermediate plane. is the emission angle, x is the width between its orbit and the main orbit, and _T is the total deflection angle of the spectrograph. As is clear from both equations, the magnification M, x/x _p , etc. that determine the resolution and dispersion are uniquely determined once the spectrograph setting conditions are determined and cannot be changed freely. On the other hand, the position resolution of a practical particle position detection counter used for particle position detection is about 1 mm. Therefore, as mentioned above, the applications of this type of spectrograph are very limited.

Referring to FIGS. 3 and 4, a charged particle spectrograph according to an embodiment of the present invention further includes a first spectrograph in addition to the spectrograph shown in FIGS.
It has a configuration in which second quadrupole magnets Q ₁ and Q ₂ are added. Of these, the first quadrupole magnet Q ₁ is connected to the particle beam source S _p and the first dipole magnet D ₁
The second 4-pole magnet
Q ₂ is installed between the second dipole magnet D ₂ and the particle position detection system C. These first and second
For example, the four-pole magnets Q ₁ and Q ₂ can be adjusted in position on the main track using a sliding device driven by hydraulic pressure or an electric motor, or their installation angle relative to the main track can be adjusted using a similar rotary drive device. It shall be possible. In addition, the first and second quadrupolar magnets
Q ₁ and Q ₂ usually act as diverging elements in the intermediate plane and converging elements in the vertical plane. Here, the first 4
The focal length of the polar magnet Q ₁ is ±f ₁ , and the second 4
Let the focal length of the polar magnet Q ₂ be ±f ₂ . Now, in order to compare the comparative spectrograph explained with reference to FIGS. 1 and 2 and the spectrograph of the present invention, the particle beam source S _p and the particle position are placed at the same position as in FIGS. 1 and 2. Consider a case where detection system C is arranged. Under such a premise, the first bipolar magnet D ₁ outlet and the second bipolar magnet D ₂
Let the focal lengths of the exit pole tip effects be ±f ₁ ′ and ±f ₂ ′, respectively.

Next, charged particle trajectories in the charged particle spectrograph with this configuration will be explained. here,
Let the distance between the particle beam source S _p and the center position of the first quadrupole magnet Q ₁ be a ₁ , and let the distance between the particle beam source S _p and the inlet of the first bipolar magnet D ₁ be a ₀ as described above. do. Also, the imaging position I ₀ and the second quadrupole magnet Q ₂
Let the exit distance be b ₁ and let the imaging position I ₀ and the second bipolar magnet exit distance be b ₀ as before. First, the first dipole magnet D ₁ in the intermediate plane
In order to make the charged particle trajectory on the side the same as the trajectory in Figs. 1 and 2, the intersection of the tangent at the incident end of the first dipole magnet _D1 and the main trajectory is S, and the position of the intersection is It is assumed that the distance is a ₀ ' from the inlet of the first bipolar magnet as in FIG. Furthermore, for convenience of explanation, it is assumed for practical purposes that the trajectory in the intermediate plane is approximately parallel to the main trajectory in the free space between the first and second dipole magnets D ₁ and D ₂ .
On the other hand, particles in the vertical plane have the first
After passing the entrance end of the first dipole magnet D ₁ , it is assumed that the first dipole magnet D ₁ moves toward a point I ₁₀ ′ on the main orbit, which is a distance d ₁ ′ from the entrance of the first dipole magnet D 1 . The focal lengths f ₁ and f ₁ ' of the pole tip effects at the entrances of the first quadrupole magnet Q ₁ and the first dipole magnet D ₁ necessary to realize such a trajectory can be expressed by the following equations.

f ₁ = a ₁ (1 + k ₁ ) ^-1/2 …(3) f ₁ ′ = (a ₀ /a ₁ -1) (a ₁ + f ₁ ) + f ₁ / (a ₀ + f ₁₀ -a ₀
/a ₁ ² ) (a ₁ +f ₁ )-(a ₀ +f ₁₀ )f ₁ …(4) (However, k≡a ₁ /a ₀ −a ₁ [1−a ₀ (d ₁ −a ₀ ′) /2a ₀ ′d ₁ ′−(a ₀ −a ₁
)(d ₁ ′−a ₀ ′)] …(5)) As is clear from FIG. 4, as in the present invention,
When the first quadrupole magnet Q ₁ is placed, its trajectory in the vertical plane intersects the main trajectory and an intermediate image I ₀ ' is generated. The resolution of this spectrograph is determined only by the first quadrupole magnet and the first and second dipole magnets.

The spectrograph according to the embodiment of the present invention is the first
It has a resolution 2f ₁₀ /a ₀ +f ₁₀ [(1-a ₁ /a ₀ )a ₁ /f ₁ +1] times that of the one shown in FIG. In practice, f ₁₀ can be chosen to be much larger than a ₀ , so this value is approximately 2 [(1-a ₁ /a ₀ )a ₁ /f ₁
+1].

As is clear from the above equation, the first and second
Particle source S _p for dipole magnets D ₁ and D ₂ of
and without changing the position of the final imaging point I ₀ , the first
When the position a ₁ of the four-pole magnet Q ₁ is changed,
The value of the focal length f ₁ changes, and the resolution of the charged particle optical system, that is, the resolution of the entire spectrograph system changes. Therefore, by adjusting the position of the first quadrupole magnet _Q1 , it is possible to obtain a resolution suitable for the purpose of observation. Furthermore, the third
With the configurations shown in FIGS. 1 and 4, a larger particle collection solid angle can be obtained than with the configurations shown in FIGS. 1 and 2 (see Japanese Patent Application No. 146591/1983). For practical reasons such as measuring high resolution, the focal length is
There is no problem in reversing the sign of f ₁ ′.

Next, the charged particle trajectory on the particle position detector C side will be explained. The particles exiting the first dipole magnet _D1 are placed in the second dipole magnet in the vertical plane.
A point on the main orbit located at a distance d ₂ ′ from the exit of D ₂
A second dipole magnet as emitted from I ₂₀ '
Assume that the light is incident on _D2 entrance. On the other hand, on the intermediate plane, particles are emitted from the second dipole magnet D ₂ toward a point I on the main orbit at a distance b ₀ ' from the center position of the second quadrupole magnet Q ₂ . do. The second dipole magnet D ₂ shown in FIG.
The discussion will proceed assuming that the orbit within is the same as that in Figure 1. Focal lengths f 2 , f of the magnetic pole effect at the exits of the second quadrupole magnet Q ₂ and the second dipole magnet D ₂ necessary for the trajectory based on the above-mentioned assumptions to three-dimensionally focus on the final imaging point _{I 0 2} ' are respectively f ₂ = b ₁ (1 + k) ^-1/2 ... (6) f ₂ ' = (b ₀ /b ₁ -1) (b ₁ + f ₂ ) + f ₂ / (b ₀ + f ₂₀ - b ₀
/b ₁ ² ) (b ₁ +f ₂ )-(b ₀ +f ₂₀ )f ₂ …(7) However, k≡b ₁ /b ₀ −b ₁ [1−b ₀ (d ₂ −b ₀ ′)/ 2b ₀ ′d ₂ ′−b ₀ −b ₁ )(d
₂ ′−b ₀ ′)]…(8).

Compared to the comparative spectrograph, the spectrograph according to the present invention has 2f ₂₀ /b ₀ +f ₂₀ [(1-b ₁ /b ₀ )b ₁
/f ₂ + 1] times the dispersion.

As is clear from this result, the focal length f ₂ of the second quadrupole magnet Q ₂ changes depending on its position _{b 1} , and the dispersion also changes accordingly. Therefore, by adjusting the position b ₁ of the second quadrupole magnet Q ₂ , the dispersion can be set to a value corresponding to the particle position detection system. This means that the dispersion of this charged particle optical system, that is, the dispersion of the entire spectrograph system, can be varied.
Similar to the discussion regarding variable resolution, it is also possible for practical reasons to design the focal length f ₂ ' of the pole tip effect at the exit of the second dipole magnet D ₂ with a different sign.

In the example described above, the position _{b 0} of the final imaging point I 0
The dispersion is changed by adjusting only the position of the second quadrupole magnet Q ₂ and the focal lengths f ₂ and f ₂ ', while keeping the three-dimensional focusing property unchanged.
However, in many cases, moving the particle position detection system in accordance with the parallel movement of the focal line does not pose a problem in practice. In such a case, it is also possible to make b ₀ variable so as to change the dispersion. In addition, except for special cases, the second 4-pole magnet
When we change the magnetic field of Q ₂ (i.e. focal length f ₂ of Q ₂ ),
Since the focal line I ₁ I ₀ I ₂ rotates slightly around I ₀ ,
If the particle position detection system is simply moved in parallel, images other than I ₀ will not be clear. Therefore, even if the dispersion is variable, as a method to always form a clear image at each point on the particle position detection system, the particle position detection system is adjusted to the rotation of the focal line, and the focus line center I ₀ is used as the center. There is a way to rotate it. This method has the advantage that a relatively small drive system is sufficient.
Another method is to rotate the second quadrupole magnet _Q2 with respect to the main orbit in a direction that suppresses rotation of the focal line. This method has the advantage that the direction of incidence of particles into the particle position detection system can always be kept almost constant, and the position resolution does not vary. The inclination angle of the focal line with respect to the main orbit in this case Ψ ₀
The rotation ΔΨ ₀ is given by the following equation.

CotΨ ₀ =D ₀ /DCotΨ+(D/D ₀ −D ₀ /D)CotΨ ₁ −b ₁ ²
/D ₀ f ₂ …(9) ΔΨ ₀ = sin ² Ψ ₀ [D ₀ /Dsin ^-2 Ψ・ΔΨ+(D/D
₀ −D ₀ /D) sin ^-2 Ψ ₁・ΔΨ ₁ +b ₁ /f ₂ {(1+D ² /D ₀ ² )CotΨ ₁ −CotΨ} (
Δb ₁ /b ₁ −Δf ₂ /f ₂ ) +b ₁ /D ₀ f ₂ (2−Db ₁ /D ₀ f ₂ )Δb ₁ −1/D ₀ (b
₁ / f ₂ ) ² (1-Db ₁ /D ₀ f ₂ )Δf ₂ ]...(10) Here, Ψ and D are respectively Q ₂ and the focal line when no magnet is used (i.e., f ₂ →∞) Ψ ₁ is the inclination of the Q ₂ magnetic surface with respect to the main orbit. Also ΔΨ ₀ , ΔΨ ₁ ,
ΔΨ, Δb ₁ , and Δf ₂ are the amounts of change in Ψ ₀ , Ψ ₁ , Ψ, b ₁ , and f ₂ , respectively.

Further, in the embodiment, the intermediate image I ₀ ' is the first and second
_The present invention is not limited thereto in _any way.

The above discussion was about varying the primary resolution of the entire spectrograph system using the Q ₁ magnet and varying the dispersion, that is, the effective resolution of the entire system, using the Q ₂ magnet. The quadrupole magnet placed between the D ₁ inlet and D ₂ outlet has an intermediate function between the functions of both the Q ₁ and Q ₂ quadrupole magnets, and can gently change the resolution and dispersion of the entire spectrograph system. Can be done.
Therefore, as a middle-ground method of use, instead of both Q ₁ and Q ₂ quadrupole magnets, it is also possible to actively utilize a quadrupole magnetic field placed in the middle of a dispersed system such as D ₁ and D ₂ magnets. . Furthermore, a multipole magnet for high-order focusing is placed in free space or immediately after the second dipole magnet _D2 , and the deflection angle of the trajectory in the intermediate plane, primary focusing, secondary focusing, etc. It can also be controlled. As such a multipolar magnet,
The current sheet magnet described in JP-A-53-42550, which is capable of independently generating dipole components, quadrupole components, etc. of a magnetic field, is suitable.
It goes without saying that the present invention can also be applied to a spectrograph that uses an electric field in addition to a magnetic field.
Moreover, it can also be applied to a case where there is only one bipolar magnet.

[Brief explanation of drawings]

Fig. 1 is a plan view of a charged particle spectrograph to be compared with the present invention as seen from the intermediate plane side, Fig. 2 is a sectional view of the spectrograph of Fig. 1 taken along a vertical plane, and Fig. 3 1 is a plan view similar to FIG. 1 of a charged particle spectrograph according to an embodiment of the present invention, and FIG. 4 is a cross-sectional view of the spectrograph of FIG. 3. Explanation of symbols: D ₁ , D ₂ : first and second dipole magnets, Q ₁ , Q ₂ : first and second quadrupole magnets.

Claims (1)

[Claims] 1 A main magnetic field element fixedly arranged along a charged particle trajectory including a predetermined main trajectory, and a main magnetic field element fixedly arranged along the charged particle trajectory to improve the three-dimensional focusing, resolution, and dispersion of the main magnetic field element. The main magnetic field element and the auxiliary magnetic field element constitute a charged particle optical system, and the charged particle optical system directs the charged particles incident on the charged particle optical system to a focal line at a position according to their momentum or energy. Form an image in the form of
In the charged particle analyzer for analyzing the charged particles, the auxiliary magnetic field element is composed of a quadrupole magnetic field element, and the installation position of the quadrupole magnetic field element with respect to the main magnetic field element and the main orbit of the quadrupole magnetic field element are A charged particle analyzer comprising: means for changing the installation angle of the charged particle optical system; and one or both of the resolution and dispersion of the charged particle optical system can be changed by driving the quadrupole magnetic field element. .