JPH0419667B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electric field generator for a mass spectrometer.

[Prior Art] In a mass spectrometer, a toroidal electric field is used to correct aberrations caused by ion energy. As shown in Fig. 4, the toroidal electric field is generated by concentric electrodes E, whose cross-sectional radii of curvature are R _a and R _b ,
It can be made by E′. In Figure 4,
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 the constant C of the toroidal electric field is It is given by the ratio r _a /Re.
In order to make the distortion of the toroidal electric field sufficiently small, the height h of the electrodes is usually 7
It is sufficiently large, more than twice as large.

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. It was a disadvantage to be able to do so.

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. 5, this device consists of a group of linear electrodes A ₁ to _A o arranged vertically symmetrically in the form of concentric arcs, on a single parallel plane that is equally spaced from the central plane L. , 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 potential was close to that of a cylindrical electric field as shown in Figure 6, for example. distribution, 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. 6, it was not very effective.

The present invention has been made in view of this point,
By further improving the proposed device described above, the present invention aims to provide a device that can generate a toroidal electric field without distortion even in a narrow gap.

[Means for Solving the Problems] In order to achieve this object, the electric field generator for a mass spectrometer of the present invention has a central plane that is located on a pair of parallel planes that are equally spaced from each other with a central plane that includes an ion path. Electrically connecting each electrode between a plurality of pairs of concentric arc-shaped linear electrodes arranged vertically symmetrically across a plane and the plurality of concentric arc-shaped linear electrodes arranged on each plane. In order to It is characterized by comprising a power supply means for applying a predetermined potential to each electrode pair based on the information.

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

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. In the figure, reference numerals 1 and 1' indicate magnetic poles arranged in parallel with a predetermined distance apart by spacers Sa and Sb. Thin substrates 2, 2' made of an insulating material such as ceramic are attached to opposing surfaces of the magnetic poles 1, 1', respectively. As shown in FIG. 2, the substrate is given an arcuate shape along the central path of ions, and a thin resistive film is formed on the opposing surfaces by a process such as coating or vapor deposition.
Then, on top of the resistive film, for example, 0.5mm
n concentric arc-shaped electrodes of width A ₁ to A _o (substrate 2), B ₁
~B _o (substrate 2') are arranged at a pitch of 0.5 mm. This electrode pattern can be created, for example, by coating or vapor deposition of a conductor using a mask, or by pattern exposure and etching techniques similar to those used for printed circuit boards used in ordinary electronic devices. The patterns of the two substrates should be symmetrical across the center plane L, in other words, A ₁ and B ₁ , A _o and
B _o is arranged so that it faces directly across the central plane,
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 of, for example, five arc-shaped electrodes Sa1 to Sa5 and Sb1 to Sb1, which are insulated from each other.
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 a certain electric field is formed in a space surrounded by electrodes, the potential at each electrode position will be considered using FIG. 3.

Now, assuming that the electric field is a toroidal electric field that is axially symmetrical with respect to the central axis of rotation q of the ion, the electric potential (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} ] ...(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} were free spaces.
Therefore, an external electric field has a large effect on the electric field in the area surrounded by the electrodes. In this regard, in the present invention, between electrodes A ₁ to A _o and B ₁
There is no free space between ~B _o , but a resistive film, and since the resistive film is electrically connected to the electrode, the potential at the surface of this resistive film is:
The potentials applied to adjacent electrodes are divided according to their positions.

For example, suppose that potentials V ₁ and V ₂ are applied to electrodes A ₁ and A ₂ , respectively, and that A ₁ and A ₂ are located on the circumference of a radius r ₁ and r ₂ from the rotation center axis q, respectively. ,electrode
The potential V at a point at a distance r from the rotation center axis q on the surface of the resistive coating between A ₁ and A ₂ is expressed by the following formula.

V = (V ₁ - V ₂ ) ln (r/r ₂ ) / ln (r ₁ / r ₂ ) + V ₂ ... (2) Therefore, the area surrounded by the electrodes is completely shielded by the resistive film, It is no longer affected by external electric fields, and it becomes possible to create an undisturbed toroidal electric field in this region.

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.

In the above embodiment, the electrodes Sa1 to Sa5 and Sa1 to Sb5 surrounding the side surfaces of the toroidal electric field are simply 5.
Using two circular arc-shaped electrodes, only the calculated potential was applied, but each electrode Sa1~Sa5, Sa1~
Instead of Sb5, linear electrodes such as electrodes A ₁ to A _o and B ₁ to _{B o} may be used, and a resistive film may be placed between them. However, since this side structure does not have much influence on the distribution of the toroidal electric field, a simple structure like the one in the above embodiment is sufficient.

Furthermore, if 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, desired information is selectively read out from the set and supplied to the power supply 3. Toroidal electric fields having different C 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, a plurality of concentric arc-shaped linear electrode groups are arranged facing each other, and an electric field is generated by the linear electrode group, so that it can be installed even in narrow gaps. In addition, since it is filled with a resistor between the linear electrode groups, it is not affected by an external electric field and can generate a toroidal electric field without distortion.

[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 substrate, resistive coating, and linear electrode, and FIG. 3 is a diagram showing the relationship between the linear electrode and the x-y coordinates. Figure 4 shows the toroidal electric field with concentric electrodes E,
Figure 5 is a diagram to explain the electric field generation device proposed by the present inventor earlier, and Figure 6 is a diagram to explain the potential generated by the proposed device. It is a figure showing distribution. 2, 2': Board, 3: Power supply, 4: Memory, 5:
Readout control circuit, A ₁ to A _o , B ₁ to _{B o} : linear electrodes.

Claims (1)

[Claims] 1. A plurality of pairs of concentric arc-shaped linear 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 containing the ion path, and arranged on each of the planes. a plate-like or film-like electric resistor disposed closely between the plurality of concentric arc-shaped linear electrodes so as to electrically connect each electrode; and the plurality of pairs of linear electrodes. storage means for storing information regarding the potential applied to each pair;
An electric field generator for a mass spectrometer, comprising power supply means for applying a predetermined potential to each electrode pair based on information read from the storage means.