DE1448178A1 - Mass spectrometer tube - Google Patents

Description

LEYBOLD-HERAEUS GMBH & CO KG., Cologne-Bayental ^ 769

P 1Μ8 I78.8 April 2, 1968

Mass spectrometer tube

The invention relates to a mass spectrometer tube for the detection of ions of different masses, in particular for partial pressure measuring devices in the high vacuum area, which is formed by the electron radiation of a cathode in an ion source Ions are passed as an ion beam through a separating section, at whose separating electrodes a high-frequency alternating field of variable frequency is applied, so that only ions with a mass corresponding to the frequency present in each case .Access a collecting electrode, the current of which is used as a measured variable for the proportion of this specific ion mass in the present mixture serves.

When operating mass spectrometers of the type described is A residual current is superimposed on the current portion (ion current) of the collecting electrode given by the portion of the ion mass, which has a zero magnitude, i.e. also in the case of the resonance condition the frequency of the ion masses far away, does not disappear, Otherwise it is pressure-dependent and frequency-dependent and can have both positive and negative signs. This residual current reduces the detection sensitivity of components of low intensity and, especially at higher pressures, can assume such large values that a perfect Analysis of the individual components is no longer possible. Every reduction in the residual current therefore means an increase the detection sensitivity and an expansion of the application range of such measuring devices in the areas of higher pressures.

In order to reduce the residual flow, arrangements are already made for the bottom floor which the separation system, i.e. those with high frequency

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frequency-fed separators, between further grid electrodes Include with negative potential. It is also a mechanical shielding of the ion source from the Separation system in the form of a diaphragm became known, the opening of which allows the ion beam to pass through, the effect of the However, both shielding grids that are at negative potential are not sufficient. The mechanical shield between the ion source and the separation system brings the additional disadvantage that both subspaces of the ion source and the separation system must be evacuated individually. Such an arrangement is particularly useful when using the mass spectrometer as a partial pressure meter disadvantageous in high vacuum technology. This principle also includes training as a built-in measuring system impossible »in which all electrodes are attached to a common surface, so that the measuring system is immediate can be used in the vacuum recipient.

The investigations carried out have shown the following with regard to the cause of the disruptive residual current:

1. It can non-resonant charged particles the separation system leave and find a speed component deviating from the direction of the ion beam, Although they bypass the separation system at least partially in the free interior of the tube, electric field forces exist, which they accelerate towards the collecting electrode,

2. Resonant or non-resonant particles generate on impact Secondary particles on the surfaces of the separation system, preferably secondary electrons, v / which are also velocity components deviating from the ion beam direction, and also outside the The separating system to the collecting electrode.

3. The ion source does not have an ideal bundling of the ion beam with parallel directional winding components of all ions. As a result of the finite opening angle, ions can also appear at the edge zone of the separation system and from there outside this separation system for collecting

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electrode get.

The invention is based on the object, a mass spectrometer tube to create, in which is achieved by the special arrangement and design of shielding elements that only ions that the separation system is intended to use have passed through, get to the collecting electrode, while stray particles are largely held back by the shielding elements and therefore cannot make a contribution to the current component of the collecting electrode. According to the invention This is achieved by, that the ion source through the cylinder That the ion collector electrode is shielded by the shield against from the central axis of an ion beam over the cross section delimited by the circular recess deviating particles is shielded, and that the ion source and the ion collector electrode are on the same central axis lie. In particular, various embodiments of such a complete shield are possible. With an advantageous Embodiment is a shielding element as the anode Ion source made up of two coaxial cylinder pieces lying one behind the other formed of different diameters, the cylinder piece of smaller diameter on the side of the separating distance and is terminated at both of its end faces by electrically conductive grid electrodes. These grid electrodes can be metallically connected to the cylinder piece.

Another advantageous embodiment provides a hairpin shape shaped cathode of the ion source, this hairpin cathode with its tip an opening of a diaphragm electrode pierces, which in turn is arranged within the cylinder piece of larger diameter of the anode. In the Diaphragm electrode attached in the immediate vicinity of the cathode is at a potential value which is preferably negative is set in relation to the cathode potential.

In connection with the anode of the ion source made of two cylinder pieces the built-up shielding element can also surround the cathodes with another tubular shielding electrode, which also on the side facing away from the isolating distance

BATH ORIGINAL 809805/1 102

is completed with a grid electrode. The cathode that Grid electrode and the further tubular shielding electrode are located preferably on cathode potential.

It can also be advantageous to have a Provide tubular shielding part which extends into the region of the separating distance and at least the latter Separating grids overlaid. In a modified version, the entire isolating distance or a substantial part of it is covered by this shielding. It can be useful in this case an arrangement which, in a manner known per se, between the last has a braking grid and an electrically pretensioned shielding grid between this electrically pretensioned shielding grid and the collecting electrode is a perforated disc electrode, preferably with the potential of the tubular shielding element to be arranged.

The measures described result in a very considerable reduction of the residual current achieved with a corresponding increase in detection sensitivity. Apart from the individual useful It appears to be fundamental to embodiments of the shielding elements It is important to use full shielding, i.e. for both the ion source and the collecting electrode. The results The investigations have shown that neither the shielding of the ion source nor that of the collecting electrode alone enables a satisfactory residual current suppression even with a complicated geometrical and electrical design.

In the drawing are two embodiments of a mass spectrometer tube shown schematically according to the invention: it shows:

FIG. 1 a mass spectrometer tube with a cathode cylinder, FIG. 2 a mass spectrometer tube with a hairpin cathode.

The cross-section of a cylindrical shape can be seen in both figures Mass spectrometer tube 1, which can be connected to a vacuum apparatus, not shown, with a connector.

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In the tube 1 of FIG. 1 there is a coiled hot cathode and an anode 4lo of an ion source, visor grids 5 and 6 Braking grid 7, a collecting electrode 8lo and a separating strip consisting of separating electrodes 9 to 19 are arranged. The hot cathode 3I0 is from a cathode cylinder lying at the cathode potential 311, the base area of which is designed as a grid 312 is that the cathode on the side of the S ^ .atsens 2 shields.

The anode 40 of the ion source consists of two concentric tubular cylinders of different diameters 411 and 412 connected to one another by a circular ring disk 413, the cylinder of larger diameter 411 being the cathode cylinder; 315 partially overlaps and contains a further Si tz electrode 4l4 in its interior. On the string of the anode 4lo facing the separating distance, eir is located on the tubular sylinoe 412. Exit grille 415.

The ion trap electrode 810 is completely surrounded by a shield 812 which is also at Kaonc-dan potential, apart from a circular recess 811. The shielding i: ann in Perm a cylinder 813 over the entire isolating distance g i; his CGSN or at least the separator electrode 19 via catch "as ais Figure 2 shows?.

In FIG. 2, a hairpin cathode 32o can be seen in the tube 1, the tip of which pierces an opening in a diaphragm electrode 321. An anode 42o corresponding to the anode 4io in FIG. 1 is composed, similarly, of chrome-plated cylinder parts 421 and 422 with the interposition of a circlip disk 423, the cylinder 421 surrounding the sliding electrode 321. On the cylinder part 422, grid electrodes 424 and 425 are provided in the area of the end faces, the shielding 813 of the collecting electrode. In the example shown in FIG.

The hot cathode 3I0 or 32o is powered by a hot battery 2o heated. The high-frequency voltage for the grids 9-19 of the isolating distance is supplied by a tunable high-frequency generator 21. A Measuring device 22 grounded on one side shows that of the collecting electrode

ORIGINAL BATHROOM 809805/1102

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BATH ORIGINAL

Claims (6)

1. Mass spectrometer for persistence of ions of different Masses, especially for partial pressure gauges in high vacuum areas, wherein the ions formed by the electron radiation of a cathode in an ion source as an ion beam a separating distance are passed, at whose separating electrodes a high-frequency alternating field of variable frequency is applied, so that only ions with a mass corresponding to the respective existing frequency to a collecting electrode arrive whose current as a measured variable for the proportion of this particular Ion mass in the present mixture is used, characterized by the fact that the ion source (31o), (32o) is shielded by the cylinder (412, ^ 22J that the ions on Catcher electrode (8lo) through the shield (812, 813) against from the central axis of an ion beam over the through the circular Recess (811) limited cross-section different particles is shielded, and that the ion source and the ion collector electrode lie on the same central axis. 2. mass spectrometer tube according to claim 1, dadu rc h characterized in that a shielding element as the anode of the ion source consists of two coaxial cylinder pieces lying one behind the other different diameter is formed, the cylinder piece of smaller diameter on the side of the separating distance and is terminated at both of its end faces by an electrically conductive grid electrode. 3. mass spectrometer tube according to claim 1, characterized characterized in that the cathode of the ion source is designed in the shape of a hairpin and has an opening with its tip a diaphragm electrode durohstösst, which in turn inside the cylinder piece of larger diameter of the anode is arranged. 809805/1 102 4. mass spectrometer tube according to claim 1, characterized marked that the cathode of the ion source lies within a cathode cylinder, which is connected to it by the. Separating distance facing away from the side is completed with an electrically conductive grid electrode, and that the anode consists of two coaxially one behind the other tubular sections, which also through in the area of the free end faces electrically conductive grids are complete. 5. mass spectrometer tube according to any one of claims 1-4, d a through characterized in that the collecting electrode has a tubular shielding part which extends extends into the area of the separating distance and covers at least the last separating grille. 6. mass spectrometer tube according to claim 5, dadu rch gekennze ichnet that in an arrangement that is in a known manner between the last separating grille the separating distance and the collecting electrode has a braking grid and an electrically pretensioned shielding grid between these electrically pre-stressed shielding grid and the collecting electrode a perforated disk electrode is provided at the potential of the tubular shielding element. COPY 809805/1 102