DE1698216A1 - Mass spectrometer and ion manometer - Google Patents

Description

Applicant; General Electric Company

Schenectady, Wew York, USA

Mass spectrometer and ion manometer

The invention "relates to a method and an apparatus for gas analysis, in particular to determine the pressure and the Proportion of the gas components in a low-pressure gas

It is already known to use a mass spectrometer to measure pressure and to determine the gas components in a gas by ionizing the gas molecules and measuring the specific charge of the ions. Such a known mass spectrometer (cf. US Pat. No. 2,939,952) uses a cylindrical and symmetrical high-frequency quadrupole field in order to separate out ions of a certain mass. stable oscillations around the axis of symmetry of the field and reach a measuring device, while ions with a different mass are deflected by the field in order to drift onto the electrodes, **** $ are thus sorted out. In this way, the measuring device carries out a continuous direct current measurement of the stable ions flowing through the mass spectrometer. By changing the JUapli- . Depending on the frequency or the frequency of the field, ions with a different charge can be sorted out and measured so that the gas components of a gas can be determined. A mass spectrometer is also a rotationally symmetrical quadrupoUfit

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used., in which the stable vibrations carrying out lohen continuously due to the inductive load α es Hachfretgnenz * - circle can be measured »■

ι ι Such a mass spectrometer has Deb However iteöfefeal ^ fc ^ dä | because of its continuous measurement: a juntersi limit fcs $ »· sticks if the signal is weaker than the bulge witd ₄ so that below this? Limit no pressure measurements can be performed Mass spectrometer ions with a certain specific η charge door; to store a longer time * in order to generate a large orbit length in. eixtetg '· small spectrometers, while all ions with a different specific charge are sorted out or rejected, and after a certain time interval the number of stored ions must be - "." ■ ". ^: ■ ^l - - ' '

1 .
It is the task of the: B ^ findusg » _ ^

to specify ,, at d | m; Ions "of a certain speafif la rather charge eiiit can be stored and then measured using a mass spectrometer and ion manometer

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of the invention - facing electrodes, which have a memory limit, in which js overlapping unsteady and DC voltages on the electrodes generate a hyperbolic electric field, so that the ions certain specific ladling; entsprercliejad the amount unit Frequency of the voltages during a controllableu are captured or stored. Periodic dls are fed to the electrodes, sucking up the received XoHift

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through openings in an electrode to an electron multiplier subjects and to measuring circles.

In an embodiment according to the invention, a rotationally symmetrical, three-dimensional, unsteady electric field is generated by superimposing high-frequency and DC voltages on opposite electrodes and changing the amplitude or frequency of the voltages, so that particles with a certain specific charge can be stored or ions are continuously generated and stored, and periodically moved out of the trapping field into a measuring circuit. According to an important feature of the invention, the storage time and therefore the sensitivity can be increased when the total pressure to be measured falls.

The invention also allows the mass spectrometer to be operated as an ion manometer, keeping all ions within a larger area specific charge, while volatile or background indications caused by soft X-rays or ions electrically captured by the electrodes, be avoided.

According to another feature of the invention, the mass spectrometer has opposing electrodes for formation. Ion storage spaces an electrode with openings is used, so dfts stored ions periodically from the storage area by supplying a pulse to the slectrodes generating the electric field. . Can be sucked into a measuring circuit.

The invention is further illustrated by the drawing who "den.Es pointers

1 shows a cross section through an exemplary embodiment the invention!

Pig.2 uses the execution example of Pig.1

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Circuit}

Pig. 3 a graphic representation of "certain business savers of the spectrometer according to the invention}

Pig, 4 shows a cross section through a modified embodiment example according to the invention)

Pig.5 a modified electrode according to the invention} and.

Pig. 6 and 7 optional ion injectors to be used

Pig.1 shows a mass spectrometer with a ring electrode 1, the middle surface 2 of which may have been created, for example, by rotating a hyperbolic branch around a vertical axis can also be a hyperboloid. The electrodes are located in a conventional housing 45 which can be evacuated and can be connected to a container 46 containing a gas through a line 47 so that the pressure or the gas components can be measured Electrodes 1 and 3 and a similar insulating sealing ring 6 between corresponding splashes of the electrodes 1 and 4. ^The ring electrode 3aat an opening T, which allows the introduction of gases to be examined into the storage space delimited by the electrodes 1, 3 and 4 just as the introduction an electron beam for ionization of the G * ·· allowed in the storage space * The electrode 3 has a centrally arranged set of openings or a grid 8 through which ions * flow into the storage space after capture or to an ion * · * saiaael electrode 9 on the outside of the storage space 10, which is delimited by the opposing electrodes, can be sucked off

.; To ionize the gases in the safety room 10, an electric * nenetstrahlgenerator with a heater 11 available, the Heizetroa

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of a suitable Power supply such as a battery 12 is · The heater 11 is ehalten on .einem negative potential by a bias voltage _a, which can be applied by conventional means such as a battery ■ 15th The electron gun also has an acceleration electrode 14, which is held at ground potential by earthing via a resistor 15 and which receives a negative pulse from a still to be specified from a pulse source 16 via a capacitor 1? can be supplied, · An electrical using the l'-mass spectrometer of FIG

Circuit is shown in Fig.2 · The electrical circuit has a power supply 18, a pulse circuit 19 and a measuring circuit 20th

The power supply 18, which the operating voltages to the Electrodes 1,5 and 4 emits, has an adjustable DC voltage— Supply 21 and a high frequency generator 22, its voltage

and frequency can be varied. A positive DC voltage potential is connected to the ring electrode 1 from the DC voltage supply 21 applied via a lead 23 · The electrodes 3 and are on a negative DC potential relative -to Ring electrode 1 held by a lead 24. The electrode

can be kept at a somewhat positive or negative potential with respect to the electrode 5 by a bias battery 25. An unsteady potential is applied to the ring electrode 1 by the high-frequency generator 22 through a supply line 26. Two calibrated potentiometers 27 and 28 are connected to the direct voltage supply 21 and the high-frequency generator 22 , respectively. The resistance ratio of the potentiometers 27 and 28 is preferably selected so that when the individual resistances change, the ratio of the direct voltage to the high-frequency voltage remains constant. The magnitude of the voltage of the direct voltage «*

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Supply 21 and the high-frequency generator 22 depends on the y geometry of the special mass spectrometer · The frequency of the high-frequency generator 22 can be 1Ö ⁴ "- 10 Hz *

By the pulse circuit 19 is periodically a short negative pulse delivered to electrode 3. The pulse circuit 19 has an adjustable pulse generator 3Q »the one with the electrode 3 via a capacitor 31 and with the electrode 4 via a high resistance 32 is connected so that the negative voltage pulses from the pulse generator 30 not sent to the electrode 4 will give.

The detection and measurement circuit 20 has a conventional electron multiplier 34t the via an amplifier 35 on an oscilloscope 36 is connected. The output of amplifier 35 is similarly via a diode 37 and an operational amplifier 38 to a Recording device 39 connected.

When operating the mass spectrometer according to the invention, a direct voltage potential is maintained between the ring electrode 1 and the electrodes 3 and 4 and a high-frequency potential m of the ring electrode 1.If the mass spectrometer is connected to a P gas whose gas components and their proportions are to be examined, in AEEN storage space 10 entering "gas ionized by electrons in the Speicherrauo 10 by - the electron gun can be initiated. The operating potentials are applied to the electrodes 1, 3 and 4, us a: Rotationssvometris before s to generate a three-dimensional, unsteady electrical field in the storage space 10. fiaclien charge to Reaonanzsohwin- '. _; . went excited what the amount and frequency of the an dia

Electrodes applied potentials depends, so that they are captured in the storage space and do not collide with the electrodes »

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At the same time, there are calibration. Ions with a different specific Charge on an unstable path and collide with the field generating one Electrodes on which lead them away * Periodically becomes a negative Pulse with a ^ pulse frequency, which is determined by the pressure in the storage space 10 Depends on the openwork electrode 3 fed to the path of the to distort positive ions and the positive ions to the electrode ', and suction through the openings 8 to the collecting anode 9, which the first dynode of an electron multiplier 34 its channel on this Way a signal is generated at the electron multiplier output, that is proportional to the myriad of those stored in memory space 10 Ion is. Shortly before the suction pulse is supplied to the electrode 3 a negative pulse to the electron gun from the pulse generator 16 to interrupt the introduction of electrons into the storage space · By adjusting the iOtentiometer 27 and to change the voltages applied to electrodes 1, 3 and 4, ions with different specific charges can be used · In this way, the mass spectrometer according to the Invention of both quantitative and qualitative investigations of the gases contained in the storage space 10 '.

The advantages achieved with the invention are intended to be based on Pig's stability diagrams. 3 will be explained in more detail. The movement of a charge carrier in the rotationally symmetrical, three-dimensional quadrupole field that is present in the storage space 10 is given by the Hathieu equation : ■ *

(2 / n) ² d ² Z / dt ² + (a-2 * _ cosil t) f «0.

described. In this equation, Z is the distance of the ion * from the mid-plane between electrodes 3 and 4, while is the frequency of the applied high-frequency voltage. Similar equations can also be used for the movement in of the Ä level. a _g and q _z are constants of the Mathieu equation and

have the vert *, __ \ 1118218

a »2a.

In these equations, Z is the minimum distance from electrodes 3 and 4 to the center of the spectrometer on the Z axis Fig. 3 a and q are the coordinates, where the values of this variable] stable, solid paths of the ions in the hatched stability area mean. When operating the device according to the invention as a mass spectrometer, the quotient a / q is selected so that one Edge of the stability area is cut, as indicated by line 40 in Pig. 3 is indicated. This means that there are only ions with one certain specific charge for a given high frequency span "· - voltage and frequency stable. By changing either the high frequency voltage or the frequency, ions of other haters get on stable orbits, each with a certain hatred, and the gas components can be examined qualitatively and quantitatively *

The device according to the invention can also be used as an ion manometer operate. For such an operation, the Quotient a / q selected so that a wide range of stability »· diagrammβ of Fig.3 is cut. For example, shows a line 41 has a value of a * 0, which corresponds to a lack of DC voltage at electrodes 3 and 4. It can also be a different one Tension can be used and a different cutting line can be obtained. Under these conditions ions are within a wide range * ^ specific charge in stable orbits. When operating the Device according to the invention as an ion manometer could pressures. Ii of 3 "10 Torr. For such a measurement the electrodes 3 and 4 were grounded, which corresponds to the line a * 0 in the a-qj stability diagram of FIG. Under these

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■ - 9 * · ■

Conditions were ion laanerhall) one, great shear charge stored in the device at the same time

"A ve s borrowed gate part of the device according to the invention . "consists for" both modes of operation in that ions during one longer, controllable time interval can be stored · In this way small instrument- achieved, the gas in the storage space can during be ionized for a longer period of time and the ions can if desired be pulsed. The storage according to the invention thus enables the integration of the ionic stream without that in the case of an electronic Integration occurring bulging carried out. the Storage also allows the measurement to be extremely small. Partial pressure, when the device is used as a mass spectrometer, and the Measurement of extremely low total pressures when the device is used as

Ion pressure gauge is used. The device according to the invention has. the particular advantage that the sensitivity with a ¹ Sink dea pressure rises because the ions during longer ·? Line; can be integrated at low pressures. Collisions with neutral gas atoms, which sometimes move an ion onto an unstable path and thereby remove it from the storage space, bind less frequently at lower pressures. By pulsing to suck out trapped ions, ion protection is made possible until a large number of them have been trapped. as well as suction for measuring purposes. Venn thus a very low pressure is measured, dl · storage time is so greatly increased, has been captured until a sufficient number of ions, so that the measurement is carried out can be easily m "For example, the distance between the Absaugimpulse * visohen some JU, β ec and hours. The received pulse output β signal is converted into a direct current signal, which means that a peak display amplifier can be registered ^:>

t $ 88477142i .;

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" ¹⁰ " 1699216

The device of Pig.1 and 2 is al · ParttsadruokamalyMt «· *

has been operated with a resolution of 3QQ »where the Attsdruek resolution usually as K / AH with ^ iM as the flpitseBireite - is defined at half the amplitude. This value of the resolution in no way represents a limit value dttx resolution because the ratio a / q (line 40 of Pig.3) 00 can be selected so that the stability area is cut very close to the edge, whereby the resolution is at the expense of the Sensitivity is improved · For a selected value, the achievable resolution τοη depends on the number of high-frequency oscillations of the ions in question and thus on the storage time. By such a selection of the Quo ti en tea a / q, ions can be stored for so long that ions whose

specific. Charge almost but not exactly equal to the quotient and those who are trapped are clenched onto the belt of the device « At the end of a long storage time, the remaining ions are au · * ··> 'Storage space sur Samael electrode from pulsed. The way we * by storing the ions in the device according to the ■ ** finding «a high resolution achieved« you ··· principle of integra- * tion via lepulee is special when measuring low pressures advantageous·

Another advantage of the device according to the invention is taNrte & t in that when the electron beam is switched off, the ions Storage space created before ions are discharged to the collecting electrode. .become, uninvited ropes who are constantly being formed »to ·!

AufpBi.1 to be removed on the electrodes. Metastable Xofttjf * excited atoms and soft X-rays are in surroundi & ev ^'>: removes% x · way, and also the long storage time allowed naoa 4e *''T switching off the Blektronenstranls a grtUere resolution · Seim';' Operation of the device according to the Irfindung is possible. that the lower size of the Druokaesaung only from it

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low can create a vacuum and erhalteq upright / irerden you · ^w eßteohnik means Impulsabsaugung permits eo is waited a long time, is captured to a large number of ions "according to which the ions are removed and measured. If the pressure is very low, the waiting time is simply increased until a sufficient number of% of ions are trapped so that keeeung can be easily performed is, namely by a tip «booster amplifier · The use of an electron multiplier» causes further amplification in order to achieve this result. In Pig. 4 a modified embodiment of the device according to the invention is shown, in which the electrodes are not hyperbolic but hemispherical. Furthermore, it can be seen that the electrodes, although they are not perforated ”

formed and can also consist of a grid · Although the Electrode 42 is shown with a wire mesh as the central section, the entire electrode can also consist of such a The other electrodes can be similar to one another similar material exist, in fact using a

large number of small holes in the electrodes sucked in, through which the ions are sucked out, as small holes mloht ale Fields inside the device as strong as a single ridge Distort the hole.

In the modified execution example according to Hg. 5 1st the Ring electrode 50 not broken, while the two opposite » lying electrodes. 51 and 52 centrally arranged Offhungaihabem " The opening in the electrode 51 is preferably made of the mentioned Grünten designed as a grid, while the electrode JÜ with a central opening for the introduction of ions in front eleventh

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conventional ion source 53 is provided, which can be, for example, a conventional plasma discharge, an ionization chamber, a surface ionization electrode or the like. The ions for the storage space do not need to be introduced through an electrode, but they can also be introduced through another opening at a desired point.

Another feature of the Pig.5 device is that .that a positive voltage pulse 54 is applied to electrode 52 in order to discharge negative ions to a suitable heating circuit which not shown suctioning. In this way, the electrode 52 serves to suction negative ions, just like the electrode 51 positive ions sucked out and measured

When operating the device from FIG. 5, the potential of the electrode 52 pulsed negatively, so that positive ions from the Ion source 53 can get into the storage space 10 · Di · electrode 52 is then held back to its normal potential, and the hating selection as well as the suction of the ions are in the same .Weise as carried out in the device of Pig * 1. By using the ion source 53, ions can suddenly enter the storage space 10 from a conventional source as an ion cloud initiated, which are repeated after each suction pulse can. *

The Pig.6 device is similar to in the Pig.5 device, ions from a conventional ion source initiated, which in turn leads to a plasma discharge, an ionization * * chamber or a surface ionization electrode. at

6 the ions emerge from the ion source Ia the storage space through a small mouthpiece $ 1 that is electric is insulated from an electrode 62. Preferably jumps the mouthpiece 61 not very far into the storage room 10 so that

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the? elder in this tree will not be distorted · eel * operation - »In such a device the energy of the entering ·» Ions are controlled so that they reach the center of the storage space during a certain interval of the high frequency period and have a very low kinetic energy in the middle · Di · «·· process allows the continuous entry of ions into the Storage space instead of the pulsed injection as provided by Pig's device. 5 is made.

The device of Pig.7 shows an arrangement similar to that of Pig. 6, with a mouthpiece 71 similar to the dog piece of the Pig device. 6 in the storage space diagonally to the center line the electrodes protrude. Otherwise the device is

Pig.7 is similar to that of Pig.6.

The device according to the invention can also be used as a leak detector, e.g. for the detection of a probe gas, where helium is a common probe gas for such purposes. This Sondengae can be located outside of the container 46 in Fig.1 · For this one Purpose stationary potentials, namely direct voltage and high frequency potentials are fed to the corresponding electrodes, and a suction pulse of a predetermined duration is applied to the electrode 3. A suitable warning line display device (not dis-

. # forms) indicates a leak in container 46.

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Claims (1)

- 14 - 12.3.1968 / No act 210? 1698216 claims . . . 1. Gate direction for the separation and measurement of the concentration τοα ions different mass, characterized by several _ύ opposing electrodes (1,3,4), which delimit a storage space (10) ", by a device (11 _t 14,7l53t6O) eur emission · sound to be examined ions to the storage space, through a device (18) for applying electrical Potentials at the electrodes in order to form an electric PeId in the storage space by means of a device (28, 27) for controlling the electrical potential and thus the field strength and direction of the electrical field, so that the ions of a certain specific charge do not occur collide with the electrodes, one (3) of the electrodes having an opening (8), through a device (19) for delivering a voltage pulse to one electrode, so that ions contained in the storage space can be sucked off through the opening , and by a device (20) arranged outside the storage space for receiving and measuring the ions sucked off through the opening. 2. Gate direction according to claim 1, characterized in that one (1) of the electrodes is ring-shaped, that sus & tilioh Electrodes (3, 4) are arranged along the axis of the ring electrode, and that one (3) of the additional electrodes has an opening (8) through which the ions run to the measuring device (20) « 3 * gate direction according to claim 2, daduroh marked »ei ·» - » net that the electrical potentials include both a equilibrium potential and an unsteady potential 4 · Door direction according to claim 3, daduroh gekennseiob- · net that the electrons in the storage space (10) through a Hole (7) in the ring electrode (1) for ionizing the gas in the BATH ORIGINAL Storage space can be introduced 5. Apparatus according to claim 3, characterized gekennzei without t that the opening has a grid (8), the looher of which is small are not enough to avoid the electric field in the storage space (10) to distort. 6 · Device according to claim 3 »characterized without e t that the ion measuring device is an electron multiplier (34) and a device (57 »38) for converting the pulse selection signal into a continuous signal 7 · Device according to claim 3 »characterized by oh * net that the other additional electrode (52§62) has an opening ( has that a negative voltage pulse of the one additional electrode (51) can be fed, that a positive voltage pulse the other additional electrode can be fed, and that by a device outside the Spelcherraums through the positive Negative ions removed from the storage space are measurable 8. The device according to claim 6, characterized in that net that the ions can be introduced into the storage space through one (52 | 62) of the additional electrodes from an ion source (53 | 6O) outside ₍ the storage space. 9 · Methods of separating and measuring ions of different types Charge, characterized in that ions be introduced in a closed area (10) that a rotationally symmetrical β, three-dimensional, unsteady electrical PeId is generated in the space, so that ions with a selected hatred to be trapped in the room, and that dl trapped ions to a location outside the construction for Mtßzweoke can be derived. 1088 * 7/1421 BATH ^T -ie- 169 * 216 10. The method according to claim 9t characterized by citnet, that the frequency and the field strength of the unsteady field » changed to trap ions of other specific charge » and that the ions trapped at a specific field strength are diverted and measured 109 * 47/1421 BATHROOM 0RK3INAL Blank page