EP1657737A2 - Procedure for the production of a multipolar electrode arrangement as well as a multipolar electrode arrangement - Google Patents

Abstract

The method involves fixing multiple rod-shaped electrode blanks to one or more carrier members (4). The end portions (6) of the carrier members are processed simultaneously with the electrode banks to form respective electrodes (2) whose cross-section has a circular portion and a non-circular, hyperbolic portion, and carrier elements with two differently shaped, matched end portions. An independent claim is included for a multipolar electrode arrangement.

Description

The invention relates to a method for producing a multi-pole electrode arrangement for focusing or mass filtering a charged particle beam, the arrangement comprising a plurality of elongate electrodes arranged parallel to an axis.

The invention further relates to such a multi-pole electrode arrangement, wherein a plurality of electrodes are attached to one or more support elements separately formed by the electrodes and wherein each electrode has a cross-section with a circular portion and a non-circular, in particular substantially hyperbolic, portion.

Multi-pole electrode arrangements for the separation or for the separate detection of ions of different specific charge have long been known, for example, from German Patent 944 900, which explains the basic principles of mass spectrometers.

From EP 0 572 687 A1 a special construction of a mass filter is also known, which has hyperbolically shaped, ground from preformed castings electrodes, which are bolted together with the interposition of insulating pieces.

Furthermore, from German Patent Application DT 26 25 660 A1 discloses to provide hyperbolic shaped electrode surfaces in pairs on a ceramic body are arranged, wherein two such ceramic bodies are held together by rings.

Furthermore, it is known from Japanese Patent Application JP 58204464A to use electrodes with a special cross section in a holder. For this purpose, first recesses are formed within the holder. Subsequently, the electrodes are attached to the recesses. The holder is annular and encloses all four electrodes of the electrode assembly.

Furthermore, German Patent Application DE 195 11 248 A1 discloses a process for producing a glass quadrupole.

From US 2003/0178564 A1, an electrode arrangement is also known, in which two electrodes and a ring-like holder are integrally formed.

The above-mentioned electrode arrangements, however, have the disadvantage that the electrodes must be precisely aligned in a very complex alignment process, with even the slightest deviations with respect to the parallelism of the electrodes leading to undesired inaccuracies and analytical measurement errors.

To solve this problem, DE 692 07 183 T2 proposes to work out a number of, namely four hyperbolic, electrodes from a cylindrical blank by electroerosion. It is intended to eliminate the time-consuming alignment process associated with other preformed electrodes.

However, the manufacturing method described in the latter document has the disadvantage that it is based on electro-erosion, either on wire electrode electrical erosion or electrical erosion by means of a molding. A disadvantage of this manufacturing method is the roughness of the surface resulting from the electrical discharge. The wire electrode electrical erosion also has the disadvantage of increased inaccuracy in the areas where the wire bulges during machining. The electric erosion with a correspondingly shaped fitting has the disadvantage that a lot of material removed by electroerosion and also the fitting must be renewed again and again, which is particularly problematic because the fitting itself can only be made consuming. In addition, the fitting itself can only be made relatively inaccurate. The process is thus extremely complex and costly.

The invention is therefore based on the technical problem of improving the production of electrodes in electrode arrangements, in particular to propose a process by means of which a precisely aligned electrode arrangement can be provided with little effort.

The invention solves this problem by means of a method for producing a multipolar electrode arrangement according to claim 1 and by means of an electrode arrangement according to claim 10.

According to the invention, the starting point is a rod-shaped electrode blank, which is then processed together with one or more further electrode blanks in order to give it a hyperbolic shape in a section. Under a rod-shaped electrode blank is to be understood in addition to a solid solid rod blank and a hollow rod-shaped or hollow rod-like electrode blank, i. an electrode blank which is tube-shaped. The blank has a circular cross-section. A hollow rod-like or tubular-like blank has the advantage of lower material requirements. However, the wall thickness of a hollow rod-like or tube-like electrode blank is to be dimensioned such that a sufficient thickness remains even after the machining. Before processing, the electrode blank is fastened to one or more carrier elements, so that a later alignment within the electrode arrangement is dispensed with.

Advantageously, two electrodes are formed on a single support element extending fore and aft, or substantially, or wholly, along the electrodes or part of the electrodes fixed and then processed together, and preferably by grinding the electrode blanks by means of a grindstone, which already has the negative shape of the later hyperbolic shape of the electrodes and of the end portions of the or the support elements.

Preferably, two half shells produced in this way are formed consisting of two electrodes and two carrier elements and then connected to one another, in particular screwed.

In a preferred embodiment it is provided that each support member has two end portions, one of which is concave and the other convex. The convex and concave shapes are adapted to one another in such a way that the convex shape of the one carrier element can be joined with the concave shape of the other carrier element in order to ensure a precisely defined position of the two carrier elements relative to each other. During the processing of the electrode blanks, it is particularly preferred to simultaneously process the end sections of the carrier elements so that these shapes are formed.

In a particularly preferred embodiment, the electrode blanks are fastened with the interposition of at least one insulating member on the carrier or elements for the electrical insulation of the electrode blank and the carrier element. Advantageously, this insulating member consists of a non-conductor, such as quartz or quartz glass or ceramic.

Particularly preferably, each electrode blank and / or each carrier element made of graphite or a metal or an alloy with a low heat or linear expansion coefficient, for example, less than 8 · 10 ^-6 K ^-1 . This coefficient of expansion is substantially equal to the coefficient of thermal expansion or expansion coefficient of the insulating member. In particular, the amount of the difference of the expansion coefficient of the graphite, metal or alloy and the coefficient of expansion of the insulating member is smaller than 2 × 10 ^-6 K ^-1 . In this way, a permanent connection between the metal and the Isolierorgan be prepared, for example. By soldering or gluing. If the insulating member is made of quartz or quartz glass, preferably, the material is an iron-nickel alloy, for example an alloy with about 36 weight percent nickel and the remaining portion of iron, for example, as a material 1.3912 (German Stahlschlüssel) or under the Denomination Invar 36 is sold. If, in one embodiment, the insulating member is made of ceramic, the material is preferably an alloy with the main components nickel, iron and cobalt, for example with a share of 29 weight percent nickel, 53 weight percent iron and 17 weight percent cobalt, for example, as the material 1.3981 ( German steel key) or under the name Vacon / Nilo Alloy K is sold.

und für den eingeschlossenen Winkel β der Tangenten im jeweiligen dieser Schnittpunkte gilt: $$\mathrm{\beta }\le 45°.$$

An electrode for such a multi-pole electrode arrangement preferably has a cross-section with a circular section and a non-circular, in particular substantially hyperbolic section, wherein for the angle centered on the circular center of the circular section α between the intersections of the circular section and the non-circular section circular section applies: $$\mathrm{\alpha }\ge 45°$$

and for the included angle β of the tangents in each of these intersections: $$\mathrm{\beta }\le 45°,$$

This particular angle specification enables a favorable transition of the hyperbolic electrode section into the circular electrode section. In principle, this transition region is particularly sensitive because field distortions can occur in this area, which can lead to inaccurate analytical measurement results. The transition region is advantageously formed without sharp edges.

Fig. 1

eine perspektivische Ansicht einer mehrpoligen Elektrodenanordnung gemäß einem Ausführungsbeispiel der vorliegenden Erfindung;

Fig. 2

eine stirnseitige Ansicht der in Fig. 1 gezeigten Elektrodenanordnung;

Fig. 3

eine stirnseitige Ansicht einer von zwei in Fig. 2 gezeigten Halbschalen;

Fig. 3A

die stirnseitige Ansicht gemäß Fig. 3 zusammen mit einem Schleifstein zur Bearbeitung der Elektrodenanordnung;

Fig. 3B

eine perspektivische Ansicht einer mehrpoligen Elektrodenanordnung gemäß einem weiteren Ausführungsbeispiel der Erfindung;

Fig. 4

eine schematische Querschnittsansicht eines Elektrodenrohlings mit Veranschaulichung der nach der Bearbeitung entstehenden hyperbolischen Fläche an der Elektrode und

Fig. 5 bis 7

schematische Querschnittsansichten weiterer Elektrodenrohlinge.

Further advantageous embodiments will become apparent from the dependent claims and from the closer explained with reference to the accompanying drawings embodiments. In the drawings show:

Fig. 1

a perspective view of a multi-pole electrode assembly according to an embodiment of the present invention;

Fig. 2

an end view of the electrode assembly shown in Figure 1;

Fig. 3

an end view of one of two shells shown in Figure 2;

Fig. 3A

the front view of Figure 3 together with a grindstone for processing the electrode assembly.

Fig. 3B

a perspective view of a multi-pole electrode assembly according to another embodiment of the invention;

Fig. 4

a schematic cross-sectional view of an electrode blank illustrating the resulting after processing hyperbolic surface at the electrode and

Fig. 5 to 7

schematic cross-sectional views of other electrode blanks.

Fig. 1 shows a multipolar electrode assembly 1 for focusing or mass filtering a charged particle beam. The electrode arrangement has four elongate electrodes 2 arranged parallel to an axis, which are fastened to carrier elements 4 with the interposition of insulating pieces 3. In this case, each electrode is fastened to two carrier elements 4, namely a front and a rear carrier element with the interposition of an insulating piece 3 in each case. This attachment is done, for example. By gluing or soldering.

FIG. 2 shows the electrode arrangement from FIG. 1 in an end view. Each support member 4 is formed substantially semicircular arc.

In this way, in each case two electrodes 2, which are each connected via insulating 3 with a support member 4, a half-shell of the electrode assembly 1. Several such support elements 4 - in the example shown, there are two such support elements 4 - are then joined together so that they have a form a closed multipart supporting body 5, which encloses the electrodes 2.

The end portions 6 of each support element 4 are different, but designed to correspond. That an end portion 6 of a first support member 4 is formed such that an end portion of a second support member is so assembled with the end portion of the first support member that a self-centering of the two support elements occurs. For this purpose, a first end portion 6 of a support member 4 is convex, while the other end portion of the same support member has a corresponding concave shape. For example, the convex shaped end portion is roof-shaped, i. formed with two substantially mutually angled, substantially flat surfaces, while the concave-shaped end portion with a corresponding negative mold, i. is formed as a channel with two angularly arranged mutually, substantially flat surfaces.

As indicated in FIG. 1, one end section of a carrier element 4 has a bore 7, in particular a threadless bore, while the other end section of the carrier element or the opposite end section of the opposing, engaged carrier element has a threaded bore (not shown), in which a screw 8 can be screwed. All four support elements 4 are identical. It can thus be worked with a single form of support elements.

The electrodes 2 are advantageously made of graphite or a metal or an alloy with a low coefficient of expansion, such as iron-nickel alloys or iron-nickel-cobalt alloys, such as Invar, Vacon or a similar material. The insulating pieces 3 are formed of a non-conductor, such as quartz or quartz glass, ceramic or plastic.

Also, the semicircular support members 4 are made of graphite or a metal or alloy, advantageously with a low coefficient of expansion, such as iron-nickel alloys or iron-nickel-cobalt alloys, e.g. Invar or a similar material made. In particular, they are made of the same material as the electrodes 2.

After the electrodes 2 of a half-shell 5 have first been glued or soldered onto the front and rear support element 4 with the interposition of the insulating pieces 3, the electrodes and preferably also the end sections 6 of the support elements 4 are machined. Machining takes place by shaping grinding, erosion and / or other shaping methods in such a way that in a single operation on the first round electrode blanks a substantially hyperbolic or similar curved surface and at the end portions 6 of the support elements 4 each have a convex and a concave contour arises.

In the manner described, two half-shells are formed and then screwed by means of the screws 8 and the bore 7 and the threaded holes, not shown, to form a quadrupole mass filter. Fig. 3 shows one of the two half-shells in an enlarged view. Fig. 3A shows this half-shell and a grindstone S for processing the electrodes 2 and the end portions 6 of the support elements 4. This grindstone S is placed on the electrodes 2 and the end portions 6 and for grinding the grindstone S relative to the electrodes 2 and End sections 6 in the longitudinal direction of the electrodes and pushed back until the electrodes 2 and the end portions 6 of the support elements have received the desired shape.

3B shows a further embodiment of an electrode arrangement 1 'according to the invention which, like the embodiment shown in the figures described above, comprises four elongate electrodes 2 arranged in parallel, which are fastened to support elements 4' by means of insulating pieces 3 '. In contrast to the embodiment shown in Fig. 1 are However, in this embodiment, it is sufficient for each half-shell only a support member 4 'to be provided on which then, for example, two electrodes 2 are attached. By means of these elongated carrier elements 4 ', the electrodes 2 can be readily attached to a plurality of further locations, in particular with the interposition of further insulating pieces 3' on the respective carrier element 4 '. This achieves a further fixing of the position of the electrodes 2 and in particular can prevent or substantially reduce distortion of the electrodes 2. In the embodiment shown in FIG. 3B, the upper support element 4 'has an opening A, which, however, serves only to illustrate the interior of this electrode arrangement 1'. Thanks to this outbreak A, it can be seen that the electrodes 2 are fastened to the respective carrier element 4 'by means of further insulating pieces 3', for example in the middle of the electrode arrangement 1 '. The outbreak A, however, has purely actorial reasons. That is, the support elements 4 'are preferably without such breakthroughs (apart from holes or tapped holes for attachment of the support elements 4' together or breakthroughs to improve Abpumpeigenschaften and thus a vacuum within the electrode assembly) is formed.

However, apart from the length, the support elements 4 'shown in FIG. 3B do not differ substantially from the support elements 4 shown in FIGS. 1 to 3A, so that reference is made to the statements with respect to the other figures.

Although the formation of a quadrupole with two half-shells was described above. However, other multi-pole electrode arrangements can also be formed by means of the described method with a corresponding structure. For example. Alternatively, a hexapol can also be produced by means of the described method, which consists either of two half shells with three electrodes each or three third shells with two electrodes each.

Alternatively, an octopole can also be produced by means of the described method be that then either consists of four quarter-shells with two electrodes or two half-shells with four electrodes.

All such electrode arrangements have in common that the electrodes 2 are arranged at equal angles with respect to the central axis of the electrode arrangement. In this way one achieves a high symmetry of the field forming between the electrodes.

The described method results in an electrode arrangement with extremely straight electrode rods, which have a very high parallelism to each other, wherein the overall arrangement can be mounted substantially completely symmetrically due to the formation of the end portions. The accuracies of the electrode surfaces which can be achieved with one another thanks to this production method are in the range of less than 1 μm. Despite these high accuracies, the production of the individual partial shells (half shells, third shells, quarter shells, etc.) can be carried out with little effort.

It has also been found that a hyperbolic shape of the electrodes only gives very good results if the electrode bodies are relatively wide, so that the field distortions which can be caused by sharp cutting off of the field do not interfere. In contrast, round electrodes in the center of the arrangement have a large field error, which, however, decreases to the edge of the respective electrodes, where the field error becomes smaller, because there the field does not abruptly stop, but runs smoothly through the rounding.

In view of this finding, an electrode shape was found which is shown in Fig. 4 in more detail. 4, a round rod electrode blank 9 is shown, which has a circular contour. This blank 9 is - in the orientation shown in FIG. 4 - ground prior to machining on its right side, so that it receives a hyperbolic shape 10. The corresponding hyperbolic section HA is defined by the angle α, which refers to the circle center of the electrode blank 9 and between the intersections P, P 'of the through refers to the grinding forming circular portion KA and the hyperbolic portion HA. This angle α is advantageously greater than or equal to 45 °. Preferably, the angle α is between 45 ° and 90 °.

At each of these points of intersection P or P ', a tangent can be placed both on the circle K circumscribing the blank and a further tangent on the hyperbola of the hyperbolic section HA. Both tangents include an angle β, which is preferably less than or equal to 45 °, in particular less than or equal to 30 °. In the examples shown in FIGS. 3 and 4, the angle α is about 90 ° and the angle β is about 14 °.

In Fig. 4, the hyperbola symptoms are also shown in dashed lines. Their intersection is denoted by M. Preferably, this point of intersection coincides with the center M of the electrode arrangement. The smallest distance of the finished ground electrode, ie the distance between the hyperbolic section HA of the electrode to the center M of the electrode arrangement is shown in FIG. 4 as r ₀ . Fig. 4 schematically illustrates only one quadrant of a quadrupole with the center M.

FIGS. 5 to 7 show further examples of processed or ground round rods. In the example according to FIG. 5, the round bar blank 9 is ground in such a way that the hyperbolic section HA has an angle α = 54.4 °. At such an angle, the angle β is 3.3 °.

In the example according to FIG. 6, the round bar blank 9 is ground in such a way that the hyperbolic section HA has an angle α = 87.4 °. At such an angle, the angle β is 14 °.

Electrodes ground as shown in Figs. 5 and 6 have the advantage of smooth transition of the hyperbolic section HA to the circular section KA of the electrode. Furthermore, only a small part of the electrode blank has to be removed. In addition, cost-effective Round rods are used as starting material. In this way, inexpensive electrodes for multi-pole electrode assemblies can be produced with high dimensional accuracy.

However, the invention is not limited to the above-described ratios of the hyperbolic portion HA to the circular portion KA. The invention also allows a shift of the illustrated ratios in favor of the hyperbolic section HA. An example of this is shown in FIG. 7. In this example, the angle of the hyperbolic section HA α = 171.1 °. This results in an angle β = 57.1 °.

All numerical values mentioned above do not limit the invention to such numerical values. In particular, deviations of +/- 10 to 30% of these numerical values are also to be regarded as disclosed.

Claims (11)

A method of manufacturing a multi-pole electrode assembly (1) for focusing or mass filtering a charged particle beam, the assembly comprising a plurality of elongate electrodes (2) arranged parallel to an axis, the method comprising the steps of: a) fixing a plurality of round-rod-shaped electrode blanks (9) - but only a part of the total number of electrodes (2) provided for the electrode arrangement (1) - to one or more support elements (4), b) simultaneous processing of end portions (6) of the support element or elements (4) together with the electrode blanks (9) attached to this or these support elements (4) in a single pass, such that each electrode blank (9) becomes one by machining Electrode (2), which has a cross section with a circular portion (KA) and a non-circular, in particular substantially hyperbolic, portion (HA), and at the end of this simultaneous processing, the or each of the support elements (4) two different having shaped end portions (6) adapted to each other in shape, c) the steps a) and b) are carried out repeatedly until the total number of electrodes (2) provided for the electrode arrangement (1) is provided, one or more individual carrier elements (4) being respectively provided in step a) to be used for fastening and d) the support elements (4) together with attached electrodes (2) are joined together such that a plurality of support elements (4) form one or more closed and the electrodes (2) enclosing multi-part support body (5). A method according to claim 1, characterized in that in step a) the electrode blanks (9) with the interposition of at least one insulating member (3) on the or the support elements (4) for electrical insulation of the electrode blank (9) and support element (4) are attached. A method according to claim 2, characterized in that the insulating member (3) consists of a non-conductor, in particular quartz or quartz glass, ceramic and / or plastic. Method according to one of the preceding claims, characterized in that each electrode blank (9) and / or each support element (4) made of graphite or a metal or an alloy, wherein the coefficient of thermal expansion of the graphite or metal or alloy is substantially equal to Thermal expansion coefficient of the insulating member (3). Method according to one of the preceding claims, characterized in that each carrier element (4) has two end sections (6), one of which is concave and the other convex. Method according to one of the preceding claims, characterized in that each support element (4) at each end portion (6) has a bore (7) or threaded bore. A method according to claim 6, characterized in that each carrier element (4) at one of its two end portions (6) has a threadless bore (7) and at its other end portion has a threaded bore. Method according to one of the preceding claims, characterized in that the machining is carried out by grinding, erosion and / or other shaping processes. Method according to one of the preceding claims, characterized that in each case a Isolierorgans (are attached to two support elements (4) 3) in step a) two electrode blanks (9) by means of which steps a) and b) are carried out two times, so that four electrodes (2) for the electrode arrangement (1 ) are provided and in step d) in each case two carrier elements (4) to a multi-part support body (5) are joined together. A multipolar electrode arrangement for focusing or mass filtering a charged particle beam, the arrangement comprising a plurality of elongated electrodes (2) arranged parallel to an axis, wherein: a) two or more electrodes (2) but only a part of the total number of electrodes (2) provided for the electrode arrangement (1) are attached to one or more support elements (4) formed separately from the electrodes (2), b) each electrode (2) has a cross-section with a circular section (KA) and a non-circular, in particular substantially hyperbolic, section (HA), c) each carrier element (4) has two differently shaped, but adapted in shape to each other end portions (6) and d) the support elements (4) together with attached electrodes (2) are joined together such that a plurality of support elements (4) form one or more closed and the electrodes (2) enclosing multi-part support body (5). Multipole electrode arrangement according to Claim 10, characterized in that each electrode (2) is fastened in each case with the interposition of at least one insulating member (3) on the carrier element or elements (4) for the electrical insulation of electrode (2) and carrier element (4).

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