JPH0430707B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a superimposed field mass spectrometer equipped with an improved electric field generator.

[Prior Art] A mass spectrometer uses a toroidal electric field to correct aberrations caused by ion energy. A toroidal electric field can be created by concentric electrodes E and E' whose cross-sectional radii of curvature are R _a and R _b , as shown in FIG. In Fig. 5, r _a is the rotation radius (rotation center axis q) of the central orbit O of the ion beam passing on the central plane L, Re is the radius of curvature of the equipotential surface passing through this central orbit O, and is the constant of the toroidal electric field. C is given by their ratio r _a /Re. and,
In order to sufficiently reduce the distortion of the toroidal electric field, the height h of the electrodes is usually set to be seven times or more, which is sufficiently large compared to the spacing G between the electrodes.

Incidentally, in a mass spectrometer, it is desired that the magnetic field strength be high in terms of resolution or measurement range, and therefore the magnetic pole spacing must be as narrow as possible. However, in the above-mentioned configuration, the height h of the electrode is large as mentioned above, so in a device such as a superimposed field mass spectrometer that requires the electrode to be housed between the magnetic poles, the spacing between the magnetic poles must be narrowed. I was at a disadvantage because I couldn't do it.

Therefore, the present inventor proposed an electric field generating device that can be installed even in a narrow gap (Japanese Patent Application No. 16635/1982). As shown in FIG. 6, this device consists of linear electrode groups A ₁ to A o arranged vertically symmetrically and concentrically across a central plane L on a pair of parallel planes that are equally spaced apart from each other _. , B ₁ to _{B o} and applying a predetermined potential to each electrode of the linear electrode group according to its position, a toroidal electric field is created in the region sandwiched by the linear electrode group.

[Problems to be solved by the invention] However, when we investigated in detail the electric field generated between the linear electrode groups in such a proposed device, we found that the equipotential surface is a cylindrical electric field as shown in Fig. 7. The distribution was close to , and it was not possible to accurately generate the desired toroidal electric field. This is due to the influence of an external electric field, and even if a ground potential shield was placed outside the linear electrode group at the position indicated by the dashed-dotted line in FIG. 7, it was not very effective.

The present invention has been made in view of this point,
The object of the present invention is to provide a device that can generate a toroidal electric field without distortion even in a narrow gap.

[Means for solving the problem] In order to achieve this object, the present invention includes a means for generating a uniform magnetic field, and a means for generating a uniform magnetic field by superimposing an electric field in a direction orthogonal to the uniform magnetic field. In a superimposed field mass spectrometer equipped with an electric field generating means, the electric field generating means vertically symmetrically sandwiches the central plane on a pair of parallel planes that are equally distanced from each other and sandwiching the central plane orthogonal to the uniform magnetic field. A plurality of pairs of concentric arc-shaped band-shaped electrode groups are provided, which are arranged in parallel so as to substantially follow the equipotential surface of the toroidal electric field to be generated, and information regarding the potential applied to each band-shaped electrode is provided. It is characterized by comprising a storage means for storing information, and a power supply means for applying a predetermined potential to each strip electrode based on the information read from the storage means.

[Example] An example of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows the structure of an embodiment of the present invention, in which reference numerals 1 and 1' indicate magnetic poles arranged in parallel with a predetermined distance apart by spacers Sa and Sb. Insulating substrates 2, 2' are attached to opposing surfaces of the magnetic poles 1, 1', respectively. The substrate is given an arcuate shape along the central ion path O as shown in FIG. 2, and concentric arcuate strip electrodes A ₁ to A _o (substrate 2) are provided on the opposing surfaces. B ₁
~B _o (substrate 2') are implanted with equal spacing D. These electrodes A ₁ -A _o and B ₁ -B _o are implanted in the substrate at an angle along the equipotential surface (broken line) of the toroidal electric field to be generated in the region sandwiched between the substrates. A lead wire drawn out from each electrode of each substrate is connected to a power source 3.

Further, the spacers Sa and Sb are formed by, for example, five circular arc-shaped electrodes Sa1 to Sa5 and Sb1 to
The lead wires made of Sb5 and drawn out from each electrode are also connected to the power source 3.

4 are electrodes A ₁ to A _o , B ₁ to B _o , Sa1 to Sa5, Sb
The memory 4 stores voltages to be applied for all of Sb1 to Sb5.The information stored in the memory 4 is read out by a readout control circuit 5 and supplied to the power source 3 as voltage information for each electrode.

In the above configuration, the electrodes A ₁ to A _o , B ₁ to _{B o} ,
When voltage is applied to Sa1 to Sa5 and Sb1 to Sb5,
An electric field is generated in the space surrounded by the electrodes. Here, when it is assumed that a certain electric field is formed in a space surrounded by electrodes, the potential at each electrode position will be discussed using FIG. 3.

Now, considering the electric field as a toroidal electric field that is axially symmetrical with respect to the central axis of rotation q of the ion, the potential at any position within the electric field is expressed as φ(x, y), then φ
(x, y) is expressed by the following equation using fourth-order approximation.

φ (x, y) = 2V _a [a _{10 X} +a ₂₀ X ² /2+ a ₀₂ Y ² /2+a ₁₂ XY ² / ₂ + _{a 30} X ³ / ⁶ + ^{a 22 4/24} ] ...(1) Here, V _a is the ion acceleration voltage, X, Y are x,
Normalized by dividing y by r _a , X=
It is expressed as x/ _ra , Y=y/ _ra . Also, the coefficient a ₁₀ ~
a ₀₄ is expressed by the following formula when C ₁ =C, C ₂ =dC/dr, and C ₃ =d ² C/dr ² .

a ₁₀ =1 a ₂₀ =-(1+C ₁ ) a ₀₂ =C ₁ a ₁₂ =C ₂ -C ₁ (1+C ₁ ) a ₃₀ =2+2C ₁ -C ₂ +C ₁ ² a ₂₂ =-2C ₁ +2C ₂ +C ₃ −2C ₁ ² −3C ₁ C ₂ +C ₁ ³ a ₄₀ = −6−6C ₁ +3C ₂ −C ₃ −3C ₁ ² +3C ₁ C ₂ −C ₁ ³ a ₀₄ = −C ₁ +C ₂ −C ₃ −C ₁ ² +3C ₁ C ₂ −C ₁ ³ Therefore, by determining V _a and r _a and setting C to a desired value, the coefficients a ₁₀ to a ₀₄ are determined and equation (1) is finalized. By substituting the position of each electrode in (x, y) coordinates into equation (1), the potential at the position of each electrode can be determined. Conversely, if the determined potential is applied to each electrode, a toroidal electric field having a desired coefficient C will be formed in the space surrounded by the electrodes.

At that time, in the proposed device explained earlier, electrode A ₁
~A _o and B ₁ ~ _{B o} are linear, and the electric field from the outside can enter quite freely into the space between each electrode, which greatly affects the electric field in the area surrounded by the electrodes. was. In this regard, in the present invention, the electrodes A ₁ to A _o and B ₁ to _{B o} have a width (length) l.
They are strip-shaped and arranged along the equipotential surface of the toroidal electric field that is to be created inside.
When a strip electrode with such a width is arranged along an equipotential surface, the electric field formed inside is regulated by the entire surface of the strip electrode, resulting in a more accurate toroidal electric field. Furthermore, since the electric field from the outside is shielded by the band-shaped electrode having this width, an accurate toroidal electric field with no disturbances can be obtained from this surface as well.

The memory 4 in FIG. 1 contains (1) as described above.
Information on the potential to be applied to each electrode in order to generate a toroidal electric field with a specific coefficient C determined based on the formula is stored, and the readout control circuit 5 reads out the information and supplies it to the power source 3. Then,
The power source 3 applies a voltage to each electrode based on the information. Therefore, a toroidal electric field is generated in the space surrounded by the electrodes in accordance with the information stored in the memory.

It should be noted that if the width (length) l of the electrodes is too small compared to the spacing D between the electrodes, the effect of the strip-shaped electrodes cannot be expected. Figure 4 shows the relative error (φ - φ′)/φ, (x, y)=(1.0
2 is a graph showing the results of an investigation with respect to point P (mm, 0 mm) while changing l. As you can see from this graph, the electrode width is narrow l=1.0mm (l/D=0.67)
However, due to external influences, the relative error is
Although the relative error is as high as 0.5%, when l and D are approximately equal, the relative error approaches 0.1%, which is practical. Then, as l becomes larger, the relative error decreases exponentially, and l=5 mm (l/D=
0.33) or more, it becomes constant at about 0.001%, and it can be seen that there is no point in increasing l further.

Further, although it is desirable that each electrode be arranged exactly along the equipotential surface, it is possible to generate a toroidal electric field having a desired coefficient C even if there is some deviation. Conversely, by using electrodes placed along the equipotential surface of a toroidal electric field with a certain coefficient C (for example, C = 1.0), we can generate a toroidal electric field with a different coefficient (for example, C = 1.5 or C = 0.5, etc.). It is possible to generate a toroidal electric field.
In that case, it goes without saying that some error will occur in the toroidal electric field generated due to deviation from the equipotential surface.

By the way, the electrodes surrounding the sides of the toroidal electric field
Strip electrodes can be used as Sa1 to Sa5 and Sb1 to Sb5. However, this side structure does not significantly affect the distribution of the toroidal electric field, so various modifications are possible.

Further, a plurality of sets of potential information for generating a toroidal electric field are obtained with different values of C and stored in the memory 4, and desired information is selectively read out from the set and supplied to the power source 3. Then, toroidal electric fields having different C values can be selectively generated.

Furthermore, it goes without saying that magnetic poles are not necessary if an electric field is generated independently rather than a superimposed field.

[Effects of the Invention] As detailed above, according to the present invention, concentric arc-shaped strip electrodes are formed on two surfaces facing each other with a central plane in between, so as to substantially follow the equipotential surface of the toroidal electric field to be generated. Since an electric field is generated by the band-shaped electrode group, it can be installed even in a narrow gap, and a toroidal electric field without distortion can be generated.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a diagram for explaining the shape of the substrate, FIG. 3 is a diagram showing the relationship between the strip electrode and x-y coordinates, and FIG. is the relative error (φ
-φ')/φ by varying l; FIG. 5 is a diagram for explaining the case where a toroidal electric field is created by concentric electrodes E and E'; FIG. 6 is a graph showing the present invention. FIG. 7 is a diagram for explaining the electric field generating device previously proposed by the inventor, and is a diagram showing the distribution of potential actually generated by the proposed device. 2, 2'...board, 3...power supply, 4...memory,
5... Readout control circuit, A ₁ to A _o , B ₁ to B _o ... Strip electrode.

Claims (1)

[Scope of Claims] 1. A superimposed field mass spectrometer comprising means for generating a uniform magnetic field and electric field generating means for generating an electric field in a direction orthogonal to the uniform magnetic field by superimposing it on the uniform magnetic field, The electric field generating means is a plurality of pairs of concentric arc-shaped band electrodes arranged vertically symmetrically across the central plane on a pair of parallel planes that are equally spaced apart from each other across the central plane perpendicular to the uniform magnetic field. ,
A group of strip electrodes arranged in parallel so as to substantially follow the equipotential surface of the toroidal electric field to be generated, a storage means for storing information regarding the potential applied to each strip electrode, and information read from the storage means. 1. A superimposed field mass spectrometer comprising power supply means for applying a predetermined potential to each strip electrode based on the power source. 2 Width l of each electrode of the concentric arc-shaped strip electrode group
The superimposed field mass spectrometer according to claim 1, wherein D is set to be approximately equal to or greater than the electrode spacing D.