DE1673257A1 - Two-wire ion source, especially for mass spectrometers - Google Patents

Description

Patent attorney DT. CUWJS REINLÄNDER PATENT ADVOCATE

DIPL-ING. H. KLAUS BERNHARDT V1 P117 D

8000 MÖNCHEN 23 MAINZERSTR. 5

■ · [O / ν b O /

ASSOCIATES
Palo Alto / California, USA

Two-wire ion source, especially for mass spectrometers

Priority: March 23, 1966 - United States
Ser. Ifo, 556,921

The invention relates generally to ion sources for mass spectrometers, and more particularly to an improved ion source with / several alternative sources for generating the ionizing electron beam of the ion source so that if one of the electron emitters fails, the other emitter can be activated to reduce the dead time of the
To reduce the spectrometer required to replace the wire.

So far only one is used in ion sources for cycloid mass spectrometers

single electroben emitter used to ionize the beam To generate electrons. Usually this emitter works in a relatively hostile environment, since the glow emitter is exposed to the ionized gas, and accordingly gas kamyias the emitter

109823/160 8

attack very easily, so that this becomes brittle, which again becomes a early failure leads. In general, the emitter consists of a material for example rhenium, which resists becoming brittle, your erosion of the metal is subject to ion bombardment. Bie The lifetimes of such rhenium emitters vary in practice a few hours and months. As soon as the emitter fails, the mass spectrometer must opened, i.e. exposed to the atmosphere in order to be able to change the wire, and then reassembled, baked out and to its operating pressure in the range of, for example, to Torr to be evacuated. At best, this wire replacement is time-consuming, usually taking half a day or more.

According to the invention, a double wire with associated switching networks is provided in order to be able to switch to a reserve wire, so that operation can be resumed quickly without the burnt-out wire having to be replaced before the reserve wire also fails. If the two-wire ion source according to the invention is used, the mean dead time _{becomes t through.} Wire failure at least halved.

The invention is intended to provide an improved. Ion source for mass spectrometers be made available «; which is particularly useful for cycloids Mass spectrometry.

According to the invention, a reserve emitter is used in an ion source, so that if the primary emitter fails, operation on the reserve emitter switched over and operation of the ion source resumed. can be.

10982S / 1608

According to a preferred embodiment of the. According to the invention, the primary emitter and the reserve emitter are arranged at opposite ends of the electron beam path, so that one emitter serves as a beam collector for the other emitter, so that the emitters are placed
is facilitated in the ion source.

According to a special embodiment of the invention, the emitters have an additional electron collector in order to serve as collector electrodes to be able to fulfill better. ·

According to a further special embodiment of the invention, the
Emitter an associated switching network to short-circuit the wire ends of the KoI-lektor-emitter arrangement, so that they can work properly as a collector, even if the wire is interrupted by breaking or burning.

Further features and advantages of the invention emerge from the following description in conjunction with the drawing; show it"
Fig. 1 is a partially schematic partial side view of a cycloid
Mass spectrometer incorporating features of the invention;

FIG. 2 shows a partial circuit diagram for the potential source which is connected to the analysis 3ier electrode arrangement according to FIG. 1; FIG.
3 shows a partial section through the ion source along the line 5-5
in Fig. 1}

'Fig. 4 shows a partial section along the line 4-4 in Fig. 3; and
5 shows a circuit diagram for the control of the ionizing electron beam and the switching network for the two wires of the ion source
according to Figures 3 and 4 /

109825/1808 - / 4

In Fig. 1, a cycloidal mass spectrometer is shown. More specifically, a series of generally rectangular ring electrode 1 is isolated accommodated in a thin rectangular vacuum vessel 2, which is shown only partially, and there by an unillustrated heavy rectangular Flansch.gehalten, closing one end of the _# · vacuum vessel.

The separate rings 1 of the electrode assembly are on slightly untex'schiedlichen electrical potentials, which are derived from a voltage source 5 via lines 4, which are connected to node 5 a voltage divider 6 are connected. The different Potentials on the various rings ensure an area of uniform electrical field Ξ in the hollow interior of the ring electrode arrangement. The electric field E is directed parallel to the development line of the ring electrode arrangement.

The electrode arrangement is immersed in a uniform region of a magnetic field H which is directed at right angles to the direction of the electric field E. The field II is expediently generated with an electromagnet 7, wherein the vacuum vessel · 2 is arranged in the narrow gap formed between two pole shoes 8 of the magnet " ¹ J if = t.

In operation, the vessel Z is evacuated with a pump 10 to a suitable low pressure of, for example, 10 ~ Torr. In the analysis section with the electrode assembly 1 to be analyzed gas is from a

109825/16 0-8

BATH

Source 9 is introduced into the analysis section through the vacuum vessel 2 via an inlet pipe 11, for example made of stainless steel. The inlet pipe 11 supplies gas at a desired rate at a ine ion source 12. Ln the ion source ionizes the gas and projected through a slot in the magnetic field with the electric PeLd.E II crossed the analysis section.

Under the influence of the crossed fields, the ions pass through cycloids Lanes. However, only ions of a certain mass number are used in a -specific strength of E and H focused on a detector slit 13, that at a certain focal distance from the source and on that the same electrical potential is arranged. An ion detector 14 is arranged behind the slot 1] 5 and provides an output voltage corresponding to the number of ions analyzed with a certain predetermined level focused mass number, if such ions are present.

The output voltage is fed to an amplifier T5 in which the The detected signal is amplified and the Y-axis unites! X-Y-Sohreibers 16 .lagufiihrt is where it depends on a wobble-the magnetic field; strength H is recorded, which frewär from a wobble generator 17; t will. The Schreiber-Io thereby delivers a range of measurements analyzing sample.

In b ¹ igiiren 3 and 4 i ^iJ t 12, the ion source with more öiinz.elhaiten Darge-3 shares. It consists of elnar im v / esentliohen geHchloaenen, cylindricwri, metallic 1 υ nitriding chamber 21, beiapLaliJwöiJij au a rhodium-pla fc

./O

OÜB25 / 10O8

BATH

made of stainless steel. The Karrmer 21 is divided transversely into three separate electrodes 22, 23 and 24, with the insulation panels '25, ^wherein: game- '', from 0, IJ mm (0.005 ") thick mica, so that the electrodes 22 - 24_ in operation An Eridwand 26 of the Kammex ^v 21 has a central opening at 27, 'to form a gas inlet channel which is in gas communication with an, insulating window segment 11' of the gas inlet tube 11, to au analyzing gas into the To admit ionization chamber 21. The other end wall 20 of the ionization chamber 21 is provided with an axial bore 2 $ with a large diameter, which is closed with two knife edge plates 31. The knife edges of the plates 31 are slightly apart so that an ion outlet gap 32 of for example 0.0-1 mm (0.004 ") width is formed5 (Ιίέ length is equal to the diameter of the bore 29 · The longitudinal extent of the outlet gap 32 is in the direction parallel • to the direction of the magnetic field of the H that prevails in the ion chamber 21.

The center electrode 25 of the ion chamber 21 is provided on opposite sides with a cylindrical bore 35 or 33 ', the axes of the bores being coaxial with the direction of the magnetic field H. An Electrcmenemitter-Anoi'dnuiig 34 i- ³ ^ arranged outside the bore 33 and projects a stream of electrons across the Kaimer 21 to the opposite bore 33 '· The beam is focused by the magnetic field H. The electron beam serves to ionLa laren gas on its v / ege. The ions generated are removed from the ionization area through the ion beam exit slit 32 with potentials at the electrodes 22 - 24, so that an ion beam 35 is used in the cycloid mass

1 0 0 ö 2 B / 1 8 0 Ö

BATH ORIGINAL

-. ■ - ■■ - 7 -

spectrometer is formed. The ion source 12 with three electrodes forms the subject of the application filed at the same time (attorney's file V1 Pi16 D) of the applicant.

A second, identical electron emitter arrangement 36 is arranged at the end of the beam path 37, where it serves as a beam collector for the first emitter arrangement 34 when the first emitter 54 is in operation. The emitter assemblies each have a precisely machined block 38 of insulating material such as Mycalex manufactured by Mycalex Corporation of America. The insulating block 58 has a threaded transverse bore 59j in which a long screw 4I is seated, which extends through a slot / \ 2 in the edge of the electrode 22. The screw has a washer 43 suf and when the screw is screwed into block J8 and tightened it serves to clamp block 38 with the emitter to electrode 22.

The emitter arrangement contains a wire-shaped emitter 44, for example from 0.18 mm (7 mil) rhenium wire, the transverse eur axis of the ionization caimer 21 is directed and sits on two conductive supports 45, the . expediently consist of two llaschinensclirauben, which are in threaded holes are screwed into the insulating block 38. An auxiliary IC collector electrode 46 »for example from 0.13 && (θ, 005") thick Holydan of 5.05 mm (0.120 ") long and 0.20 mm (0.0S0") wide is electrically conductive connected at one end to one of the emitter supports 45. Of the The auxiliary air collector 46 is located behind the E, -. Iittt; r 44 and is used for dapu, EIhIc-

■ ■. = ... / ti

1O982 & / 10O8

BAD ORfGlMAL

to receive trons from the beam which were not detected by the associated emitter wire 44 when this emitter arrangement is used as a collector for the corresponding emitter arrangement 36. Operating voltages are fed to the emitter arrangements 34 and 36 via the supports 45, as described in greater detail in connection with FIG. 5 will be explained.

The operating voltages for the three ionization chamber electrodes 22, 23 and 24 are derived from a variable voltage power supply 47. When the ion source 12 is operated for a positive ion beam, the reflector electrode 22 is at positive potential operated, for example 160-200 volts, derived from a power supply; the potential relates to the beam exit electrode 24, which preferably works on earth potential. The center electrode 23 is at a potential in the middle between the reflector and the output electrode 22 and 24, respectively. The potential for the center electrode is from a voltage divider 48 with a center tap derived, which exercises the power supply 47 is. To the CJuelle To operate as a negative ion source, the connections become the power supply 47 turned over, and the fields E and H in the cycloid Analysis section also reversed.

In Fig. 5 is the electrical circuit for the ionizing electron beam shown, including the current control and the alternative circuit. One of the wires 44 serves as an emitter, and the opposite one Wire with the auxiliary collector electrode serves as the collector.

10982S / 1608

The functions of the both emitter arrangements reversed, if desired. AC heating current at a suitably low voltage of e.g. '6 YoIt derived from a winding 51 of a magnetic amplifier 50, which is derived from a suitable source 52 through a second winding 53 will. The heating power is fed to a first two-pole changeover switch 54, which in the right switching position according to FIG. 5 is the left wire arrangement 36 feeds.

The anode voltage for the emitter arrangement 36 is derived from a variable power supply 55, which can be set between 5 and 100 volts and is located between the wire 44 and the center electrode 23, which serves as the anode. Under the influence of the anode voltage and the focusing of the magnetic field H, the electrons form a ribbon shaped beam of about 1.02 mm (0,04Q ^ir) width and 0.18 mn (0.007 ") thickness, across the ionization chamber 21 for opposite collector-emitter arrangement 34. The opposite emitter arrangement 34 'at the end of the beam is connected to the terminal of a second two-pole changeover switch 56 which is coupled to the first switch 54 by a mechanical connection 57. The terminals of the switch 56 are short-circuited, so that both ends of the wire 44 are short-circuited in the right closed position of the switch and are at the same potential as the associated auxiliary collector electrode 46.

The collector-emitter arrangement 34 ^w i ^r <l preferably operated at a potential which is positive with respect to the anode electrode 23, by one

... / 10

T0982S / 1808

full capture of the beam on wire 44 and auxiliary collector 46 to ensure. There is a corresponding voltage source 58 of, for example, +20 volts between the short circuit switch 56 and the Anode 23

It is desirable to measure and control the electron beam current because this determines the intensity of the ion beam. In the circuit between the emitter short-circuit switch 56 and the anode 23 is therefore an ammeter 59, ^m ^ cL * ^{em it} is measured beam current and a current amplifier 61 with adjustable gain; the output of this amplifier is fed to a control winding 62 of the magnetic amplifier 50. The beam current measured by the measuring instrument 59 is adjusted to the desired level by adjusting the gain of the amplifier 61. Increasing the current gain of the amplifier 61 causes a higher current in the control winding 62, thereby increasing the saturation of the core of the magnetic amplifier is caused, whereby the heating power is reduced and thus the electron beam current is reduced.

If the primary emitter arrangement 36 fails, the coupled switches 54 and 56 are simply switched over, so that the functions of the emitter arrangements 36 and 34 are reversed. Even if the wire 44 '' l ^he works as a collector, interrupted by a burn or break, the arrangement is still operating normally as Stiiahlkollektor. This is because the auxiliary collector 46 is provided and because both ends of the wire 44 are short-circuited together with the collector electrode 46 via switch 56.

10982S / 1608

Claims (3)

Claims 1. Ion source with a 'room in which gaseous substances are ionized by bombarding them with an electron beam, an acceleration device for ions generated in the ionization area, with which they are accelerated through an opening defining a beam to generate an ion beam, and an electron beam generation device, with which der.Elektronenstrahl is formed and projected through the ionizing area, characterized in that a second electron beam generating device is provided as an alternative to the first device, with which an electron beam can also be shaped and projected through the ionizing area, so that if the first beam generating device, the second beam generating device can be excited in order to maintain the operation of the ion source. 2. Ion source according to claim 1, characterized in that the second Beam generation device as a beam collector for the first emitter ore Eugungs-device is used when the first beam generating device works in normal operation. 109825/1608 3. Ion source according to claim 1 or 2, characterized in that at least the first beam generating device a wire-shaped glow emitter and an associated collector electrode electrically connected to the wire emitter for capturing the electron beam from the second beam generating device, so that a better Collector effect of the beam generating device is made possible. 4 «Ion source according to claim 1, 2 or 3 with at least one wire-shaped Emitter, characterized in that an electrical switching network is connected to each wire-like emitter, with which the wire ends for operation as a collector electrode for the other beam generation. Device can be short-circuited electrically. 5 · Ion source according to one of claims 1-4 »characterized in that that the two beam generating devices are arranged on opposite sides of the ionization area. β ο ion source according to one of claims 1-5 »in which the ionization area is housed in a chamber having two end walls and an intermediate side wall which includes the ionizing area therethrough characterized in that the beam generating means are arranged are that they direct their electron beam across the partition from one side to the opposite side. 109825/1608