Ion trap and mass spectrometer with annular ion storage cell

Abstract

The present invention comprises a first annular end cap electrode (4a) and a second annular end cap electrode (4b) with an annular ion storage cell (5) formed therebetween, and a plurality (N) of radially inner disk-shaped ring electrodes (E 1,i ) and multiple (N) radially outer disk-shaped ring electrodes (E 2,i The present invention relates to an ion trap (2) comprising such an ion trap (2) and a disk-shaped ring electrode (E) for storage, selection, excitation and / or detection of ions (6) in an annular ion storage cell (5). 1,i , E 2,i The present invention also relates to a mass spectrometer (1) having a mass analyzer (4) and a control device (3) designed to operate the end cap electrodes (4a, 4b).

Description

[Technical field]

[0001] The present invention relates to a (Fourier transform) ion trap comprising a first annular end cap electrode and a second annular end cap electrode forming an annular ion storage cell therebetween. The ion trap is therefore a circular or toroidal ion trap. The present invention also relates to a mass spectrometer comprising such an ion trap. [Background technology]

[0002] US Patent No. 9,035,245 B2 describes a mass spectrometer with an electric FT ion trap. The FT ion trap has a ring electrode and two end cap electrodes, each of which has a hyperbolic shape, forming a non-annular ion storage cell between them, separated by the hyperbolic electrode. In general, the two end cap electrodes are connected to a virtual ground potential, and an HF storage signal in the form of a high frequency alternating current is applied to the ring electrode. An electric field (quadrupole field) is formed in the ion trap through the HF storage signal, which allows ions or charged particles to be stably stored in the ion trap.

[0003] As an alternative to ion traps with a hyperbolic quadrupole or Paul trap geometry, M. Aliman and A. Glasmachers, "A novel electric ion resonance cell design with high signal-to-noise ratio and low distortion for Fourier transform mass spectrometry", Journal of the American Society for Mass Spectrometry, Vol. 10, No. 10, October 1999, propose a different geometry in which the ring electrode is replaced by a cylinder of disk-shaped ring electrodes extending axially from the first end cap electrode to the second end cap electrode. The ring electrodes are axially spaced equidistant. The resulting ion storage cell forms a cylinder with a hyperbolic base and a hyperbolic cap. This ion trap allows for a reduction in the crosstalk currents that occur between the end cap electrodes and the ring electrodes in the case of conventional Paul traps.

[0004] In a three-dimensional FT ion trap, many functions can be performed in situ, such as, for example, ion selection or ion filtering, ion storage, ion excitation and ion detection. From US Pat. No. 10,141,174 B2, the practice is known to perform in such an FT ion trap at least one selective IFT ("inverse Fourier transform") excitation, in particular a SWIFT ("accumulated waveform inverse Fourier transform") excitation, depending on the mass-to-charge ratio of the ions, during ion generation and storage and / or during ion excitation before ion detection. The selective SWIFT excitation can be used in particular for ion selection or ion filtering. For the separation of the ion population stored in the FT ion trap, wavelet and / or FFT methods can be used. For the detection of the ions, noise detection methods can be used.

[0005] The measurement signal generated by the mirror charges at the end cap electrodes can be used to detect the ions. In a mass spectrometer, a mass spectrum can be quickly calculated from the measurement signal using the fast Fourier transform (FFT) or using methods such as harmonic inversion, see for example F. Grossmann et al., "Harmonic inversion of semiclassical short time signals", Chem. Phys. 279 (1997) 355-360. The sensitivity of ion trap mass spectrometers is also high. These performance features are necessary in many applications, for example for fast and accurate detection of the end point from the gas composition of semiconductor processes (so-called end point detection applications).

[0006] However, even in FT ion traps there are several challenges to overcome during the measurement procedure, e.g. these relate to the maximum ion charge and / or the ratio of majority to minority charge carriers that can be stored in the ion trap, the selectivity during ion filtration or ion generation, the filter properties of the ion trap itself, and the separation and detection of ion species of interest.

[0007] The properties of such a small mass spectrometer or of such an ion trap can be severely impaired and limited by excessively large ion charges. For example, low ion concentrations such as 100 ppb cannot be demonstrated unless ion filtration of background gases such as nitrogen is performed. Measurement disturbances in this ion trap can arise due to the so-called space charge problem, which assumes that the detection of ions in an (electrical) FT ion trap is solely acted on by a high-frequency alternating field E. In fact, this applies as long as there are only a limited number of charge carriers of the same sign in the FT ion trap.

[0008] The total number of charge carriers is called the "space charge" or "ion cloud". This space charge affects the potential φ derived from the radio frequency alternating field E, which can be expressed via the Laplace equation (E=-grad(φ)). The effect of the accumulated potential φ due to the space charge in a given volume in the FT ion trap is expressed as (As / m 3 The higher the space charge density ρ (in units of 1000 Hz) and the weaker the corresponding average restoring force in the partial volume due to the high frequency alternating field. This effect is expressed by the Laplace equation for the high frequency alternating field as follows: div(grad(φ))=Δφ=-ρ / ε o ≠0 (1) where εo denotes the dielectric constant in a vacuum and φ denotes the high-frequency alternating potential (see above) belonging to the alternating field E. A large space charge can lead to a large loss of ions and / or a suppression of the measurement signal of small ion populations. To solve the space charge problem, DE 10 2015208188 A1 proposes to spatially separate the ion packets using a suitable SWIFT excitation.

[0009] Another possibility to solve the space charge problem is to enlarge the ion storage cells available for storing ions. For this purpose, so-called toroidal ion traps are used, see for example the article "Design, optimization and initial performance of a toroidal rf ion trap mass spectrometer" by SA Lammert et al., International Journal of Mass Spectroscopy, 212 (2002) 25-40. However, such ion traps have the problem that nonlinear field parts hinder the mass resolution or sensitivity in performing mass analysis. In the cited article, it is proposed to use an asymmetric design of the toroidal ion trap to increase the mass resolution, see also the poster "Toroidal Multipole Expansion for the Design of Circular Ion Traps" by Lammert et al., 62nd ASMS Conference, Baltimore, MD, 15-19, June 2014.

[0010] The paper by Appala Naidu Kotana et al., "Computation of Mathieu stability plot for an arbitrary toroidal ion trap mass spectrometer", International Journal of Mass Spectrometry 414, (2017), 13-22, considers the stability of ion trajectories in a toroidal ion trap. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] U.S. Patent No. 9,035,245 [Patent Document 2] U.S. Pat. No. 10,141,174 [Patent Document 3] DE 102015208188 A1 [Non-patent literature]

[0012] [Non-Patent Document 1] M. Aliman and A. Glasmachers, "A novel electric ion resonance cell design with high signal-to-noise ratio and low distortion for Fourier transform mass spectrometry," Journal of the American Society for Mass Spectrometry, Vol. 10, No. 10, October 1999. [Non-Patent Document 2] SA Lammert et al., "Design, optimization and initial performance of a toroidal rf ion trap mass spectrometer," International Journal of Mass Spectroscopy, 212 (2002) 25-40. [Non-Patent Document 3] Lammert et al., "Toroidal Multipole Expansion for the Design of Circular Ion Traps," 62nd ASMS Conference, Baltimore, MD, 15-19 June 2014. [Non-Patent Document 4] Appala Naidu Kotana et al., "Computation of Mathieu stability plot for an arbitrary toroidal ion trap mass spectrometer," International Journal of Mass Spectrometry 414, (2017), 13-22 Summary of the Invention [Problem to be solved by the invention]

[0013] It is an object of the present invention to provide an ion trap which allows high ion charge and high sensitivity in ion detection, and a mass spectrometer equipped with such an ion trap. [Means for solving the problem]

[0014] This object is achieved by an ion trap of the type mentioned at the beginning, which has a number of radially inner disk-shaped ring electrodes and a number of radially outer disk-shaped ring electrodes that delimit an annular ion storage cell. The annular ion storage cell is bounded radially inside by an inner disk-shaped ring electrode and a circular ring electrode, and radially outside by an outer disk-shaped ring electrode and a circular ring electrode. In general, the number of inner ring electrodes corresponds to the number of outer ring electrodes. The ion trap, or rather the two end cap electrodes and the ring electrode, essentially extend rotationally symmetrically with respect to an axis of symmetry located in the center of the ion trap. The two end cap electrodes axially delimit the (circular) annular ion storage cell. In this respect, disk-shaped means a substantially flat shape, i.e. the inner disk-shaped electrode and the similar outer disk-shaped ring electrode have a radial extension that exceeds their axial extension by more than two times, preferably more than five times, more preferably more than ten times.

[0015] In particular, each of the inner ring electrodes and each of the outer ring electrodes are isolated from each other so that different potentials can be applied to each ring electrode.

[0016] The circular geometry of the ion trap allows for a much larger ion storage cell than conventional Paul trap style 3D ion traps.

[0017] In this way, the maximum ion charge of the ion trap can be increased by more than 5 times or even 10 times compared to the conventional Paul trap. Moreover, the ion trap including the disk-shaped ring electrode can be manufactured in a simple manner. By storing ions in a spatially circular manner in the annular ion storage cell, the space charge problem can be solved by a suitable circular expansion of the ion storage cell, and thus the space charge density ρ can be effectively greatly reduced. If the ion trap designed as above is properly driven, the nonlinear field in the ion storage cell can be suppressed at the same time, and thus a high mass resolution or high sensitivity of the ion trap can be achieved.

[0018] In one embodiment, the inner and outer ring electrodes are positioned at a fixed radial distance from each other. The ion storage cell thus spans a radial distance between a minimum radius determined by the radially outer end face of the inner ring electrode and a maximum radius determined by the radially inner end face of the outer ring electrode. In this manner, ions circulate in a "cold, cooled" state on orbits within the ion trap having a radius halfway between the maximum and minimum radii of the ion storage cell. In this regard, the inner and outer ring electrodes are separated by the ion storage cell.

[0019] In a further embodiment, the radial distance between the inner and outer ring electrodes is smaller than the radius of the annular end cap electrode. Typically, the annular end cap electrode has a hyperbolic shape. The radius of the end cap electrode is understood to be the average value between the maximum and minimum radial extension of the end cap electrode.

[0020] This radius should correspond to at least the generally constant radial distance between the inner and outer ring electrodes.

[0021] In a further embodiment, in each case, the inner ring electrode and the outer ring electrode are arranged on a common plane perpendicular to the axial direction. The planes on which the pairs of respective ring electrodes are arranged are aligned parallel to each other and are arranged to overlap each other with an axial spacing therebetween.

[0022] In one embodiment, in each case, the inner ring electrode and the outer ring electrode, i.e., a pair of ring electrodes, are conductively connected to each other. The ring electrodes conductively connected to each other have the same potential. Each pair of ring electrodes is preferably arranged within the above-described common plane.

[0023] In a further embodiment, for the radial width b of each of the first or second ring electrodes and the axial distance d between two adjacent first or second ring electrodes, d / b < 1 / 4 holds. The distance d between adjacent ring electrodes can be, for example, from about 100 μm to about 1 mm. The width b in the radial direction is from about 400 μm to 4 mm. A high vacuum conductivity of the ion trap can be ensured as compared to a conventional ion trap including solid ring electrodes in order to generate a potential well for ions through an open mechanical structure of the ion trap (where there is no "sealed" space as much as possible) due to the spaced-apart ("discrete") disk-shaped ring electrodes.

[0024] In a further embodiment, the ion trap has N radially inner ring electrodes and N radially outer ring electrodes, and 10 < N < 200 holds for N. It has been shown that a relatively small number of N ring electrodes are sufficient for ions to circulate in a "cryogenic cooling" state on a stable orbit within the ion storage cell.

[0025] In a further embodiment, the first end cap electrode and / or the second end cap electrode are divided in the circumferential direction into at least two annular segments. Typically, two or more segments extend in the circumferential direction over the same angular interval, and if each end cap electrode is divided in the circumferential direction into two segments, both segments extend in the circumferential direction over an angle of about 180° and are electrically insulated from each other by a gap. Thus, three segments extend in the circumferential direction in each case over about 120°, four segments extend in the circumferential direction in each case over about 90°, and so on. If both end cap electrodes are segmented, they usually extend in the circumferential direction over the same angular range. Due to the segmentation, in time division multiplexing operation, the end cap electrodes can be optionally used as excitation electrodes, detection electrodes or measurement electrodes. In this way, all conventional Fourier transform measurement tools can be used in the case of ion traps (e.g. ion filtration, separation of ions, non-destructive detection during ionization or storage) as used in conventional FT ion traps.

[0026] In a further embodiment, the ion trap further comprises an implanter for injecting an ion and / or electron beam, preferably tangentially, in particular pulsed, into the annular ion storage cell. The ions can be generated in an (external) ion source and introduced into the annular ion storage cell via the implanter. Typically, the injection of ions is performed in a pulsed manner, i.e. via a pulsed supply, which may comprise a controllable valve or the like.

[0027] The implanter may have an ion lens or the like to inject or launch ions in a linear trajectory into the annular ion storage cell, the lens being preferably oriented tangentially to the average radius of the annular ion storage cell. The ions are preferably injected into the space between two axially spaced outer ring electrodes of the annular ion storage cell. Injection is preferably performed in a plane perpendicular to the axial direction, i.e. parallel to the ring electrodes.

[0028] The injector may also serve to inject an electron beam into the annular ion storage cell for generating ions directly in the ion trap through impact ionization, in which case the injector may be used to direct the gas to be analyzed into the ion storage cell before the ions are generated using the electron beam.

[0029] Another aspect of the invention relates to a mass spectrometer comprising an ion trap designed as described above and an (electronic) control device designed to operate the disk-shaped ring electrode and the end cap electrodes of the ion trap for storage, selection, excitation and / or detection of ions in the annular ion storage cell. The generation of the HF storage field (see below) and the signals required for excitation, selection / isolation and detection of ions is realized by means of the electronic control device. For this purpose, the control device may include suitable hardware, such as electronic circuits, and / or software. Typically, the signals for excitation, selection and detection are applied to or tapped at the end cap electrodes. However, it is also possible for the control device to provide an excitation signal at the ring electrode for ion excitation.

[0030] As mentioned above, the excitation may involve at least one selective SWIFT ("Stored Waveform Inverse Fourier Transform") excitation according to the mass-to-charge ratio of the ions, or possibly a broadband excitation.

[0031] In one embodiment, the controller is located at least partially within the volume area enclosed by the annular ion storage cell. The controller is preferably located at the center of the ion trap or the annular ion storage cell. The controller may be located in a separate vacuum area separated from the annular ion storage cell, for example by a seal, differential pump or housing. However, the controller does not necessarily have to be located at the center of the ion trap, rather the controller, or components of the ion trap required to operate the ion trap, may be located elsewhere in the vicinity of the ion trap.

[0032] In a further embodiment, the control device is designed to operate the disk-shaped ring electrodes to generate respective HF storage voltages to store ions in the ion storage cell. For this purpose, the HF potential generated by the HF generator can be appropriately divided over the individual ring electrodes. Each of the inner ring electrodes is preferably at a different potential. Similarly, each of the outer ring electrodes is at a different potential. Preferably, each of the inner and outer ring electrodes is at the same potential, e.g. a potential V that extends quadratically to i. RF,i (t) can be applied to the i-th ring electrode, and the HF potential V RF Starting from (t), for example, the harmonic potential V RF (t)=V max sin(ωt), which is defined as follows: V RF,i (t)=V RF (t)(1-i 2 / N 2 ) (2) Here, -N≦i≦N applies for i, i.e., a total number of 2N+1 inner ring electrodes and 2N+1 outer ring electrodes arranged equidistant from each other in the axial direction (Z direction) are available; see also the paper by M. Aliman and A. Glasmachers exemplified at the beginning.

[0033] The ring electrodes do not necessarily have to be equidistant, and the HF voltage V applied to each pair of inner and outer ring electrodes is RF,iIt is understood that (t) does not necessarily have to be divided according to equation (2). The application of voltages to each ring electrode can be done using a matching network and a voltage divider network, for example with parallel switched resistors and capacitors, as described in the paper by M. Aliman and A. Glasmachers, which is incorporated by reference in its entirety into the contents of this application. The HF storage field of the ring electrodes can be used to realize a spatially circular ion storage, in which ions move in a "cryo-cooled" state along a circular orbit. Such an HF storage field has a relatively small nonlinear field portion, thus enabling ion detection with high mass resolution.

[0034] In one embodiment, the control device is designed to determine the time-related dispersion of ions pulsed into the ion storage cell based on the ion signals recorded on the different segments of the end cap electrode. Once ions are pulsed into the annular ion storage cell, i.e. in the form of ion packets, and thus initially excited, it is possible to determine, based on the recorded ion signals, how the ion dispersion progresses with increasing storage time (higher mobility ions proceed faster). Here, it proves advantageous to be able to record a separate ion signal on each segment of the end cap electrode(s).

[0035] In this way, conclusions can be drawn, for example, regarding the spatial distribution of the ion population and pressure-dependent processes within the ion trap. Time-limited cooling with a suitable damping gas (e.g. helium) can be introduced to obtain conclusions regarding ion mobility.

[0036] In one embodiment, the control device is designed to deflect the electron beam tangentially incident on the annular ion storage cell along a circular trajectory. As further described above, at least one (pulsed) electron beam can be injected into the ion storage cell for flexible ion generation and storage. Furthermore, since electrons (with elementary charge e and velocity ve) are at least 3-4 orders of magnitude lighter than the ions to be detected, the electron beam can be substantially independently deflected such that it travels along a circular trajectory through the generation of a sufficiently small time-limited induction B, during which it passes through all segments of the annular ion storage cell when a Lorentz force F acts on the electron beam according to the following equation: TIFF0007660103000001.tif6150(3)

[0037] By forcing the electron beam onto a circular orbit, particularly efficient electron ionization can be achieved, allowing for great flexibility in ion generation, storage and injection.

[0038] Further features and advantages of the invention emerge from the following description of exemplary embodiments of the invention based on the figures of the drawing, which show the essential details of the invention, and from the claims. The individual features can in each case be realized individually or in combination, in any desired combination in the variants of the invention.

[0039] Example embodiments are illustrated in the schematic drawings and explained in the following description. [Brief description of the drawings]

[0040] [Figure 1] FIG. 1 shows a schematic representation of a cross section of a mass spectrometer with an ion trap that includes an annular ion storage cell. [Diagram 2] FIG. 2 is a top view on the annular ion storage cell of FIG. 1 including segmented end cap electrodes. [Diagram 3] FIG. 13 shows a detailed representation of multiple outer and inner disk-shaped ring electrodes radially delimiting a storage cell. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] In the following description of the drawings, the same reference numbers are used for identical components or components having the same functionality.

[0042] 1 is a schematic cross-sectional view of a mass spectrometer 1 having an ion trap 2 and an electronic controller 3. The ion trap 2 comprises a first annular end cap electrode 4a at an upper axial direction Z of an XYZ coordinate system, and a second annular end cap electrode 4b at a lower axial direction Z, between which an annular ion storage cell 5 is formed. The two end cap electrodes 4a, 4b each have a hyperbolically curved surface facing the ion storage cell 5, as is customary for ion traps in the Paul trap configuration.

[0043] The annular ion storage cell 5 extends radially symmetrically with respect to an axial direction Z of the XYZ coordinate system. In the cross-sectional view of FIG. 1, the radial direction corresponds to the X direction of the XYZ coordinate system. In the radial direction X, the ion storage cell 5 is bounded by a number or N of radially inner disk-shaped ring electrodes E 1,i (i=1,...,N) on the inside, and a number or N of radially outer disk-shaped ring electrodes E 2,i (i=1,...,N) on the outside. A number of N radially inner ring electrodes E 1,i are arranged overlapping each other in the axial direction Z. Thus, a plurality of N radially outer ring electrodes E 2,i are also arranged overlapping each other in the axial direction Z.

[0044] The annular ion storage cell 5 is arranged in the radial direction X with an inner ring electrode E 1,i and outer ring electrode E 2,i The inner and outer ring electrodes E 1,i , E 2,iThe radial distance 2r0 between them is smaller than the radius R of the two end cap electrodes 4a, 4b. The radius R of the end cap electrodes 4a, 4b corresponding to the average radius R of the ion storage cell 5 extends in the radial direction X through the centers of the two end cap electrodes 4a, 4b.

[0045] The ion storage cell 5 has a minimum radius R-r0 determined by the radially outer end face of the inner ring electrode E 1,i and a maximum radius R+r0 determined by the radially inner end face of the outer ring electrode E 2,i and extends in the radial direction X between them. Through a constant distance 2r0 between the ring electrodes E 1,i and E 2,i ions 6 in the "cryogenic cooling" state can circulate inside the ion trap 2 in an orbit corresponding to the average radius R of the annular ion storage cell 5.

[0046] In the illustrated example, the number N of the inner ring electrodes E 1,i corresponds to the number N of the outer ring electrodes E 2,i

[0047] In the illustrated example, 10 < N < 200 applies to this quantity N. To enable ions 6 in the "cryogenic cooling" state to circulate in a stable orbit inside the annular ion storage cell 5, it has been shown that a relatively small number N of ring electrodes E 1,i and E 2,i is sufficient.

[0048] As can be seen from FIGS. 1 and 3, the ring electrodes E 1,i and E 2,i are arranged in pairs in a common plane X,Y perpendicular to the axial direction Z. In any case, the two ring electrodes E 1,i and E 2,i arranged in the common plane X, Y are connected to each other via electrical leads or electrical contacts not shown in the drawing, that is, they are at the same potential. The electrical contacts can also be provided via the control device 3. The width b of each disk-shaped first ring electrode E 1,i in the radial direction X, and the two adjacent first ring electrodes E 1,i and E​1,i+1 For the distance d in the axial direction Z between the second ring electrode E 2,i and the two adjacent second ring electrodes E 2,i , E 2,i+1 The same holds true for the distance d in the axial direction Z between the two points, d / b<1 / 4.

[0049] Adjacent ring electrode E 1,i , E 1,i+1 Or E 2,i , E 2,i+1 The distance d between them can be, for example, about 100 μm to about 1 mm. The width b in the radial direction X is therefore about 400 μm to 4 mm. To create a potential well for the ions 6 through the open mechanical structure of the ion trap 2 due to the spaced apart ("discrete") disk-shaped ring electrodes E1,i, E2,i, solid ring electrodes are used to ensure a higher vacuum conductivity of the ion trap 2 compared to conventional ion traps.

[0050] As can be seen in Fig. 2, the first end cap electrode 4a is divided in the circumferential direction into four annular segments Q1, Q2, Q3, Q4, each of which extends circumferentially over an angle of 90°. The second end cap electrode 4b is accordingly divided into four annular segments Q1, Q2, Q3, Q4 as well (not shown in the drawing). Due to this segmentation, in a time-multiplexed operation of the control device 3, the end cap electrodes 4a, 4b can be used optionally as excitation electrodes, filtering electrodes or measuring electrodes.

[0051] The control device 3 is in signal connection with each of the four segments Q1, Q2, Q3, Q4 of the first end cap electrode 4a and with each of the four segments Q1, Q2, Q3, Q4 of the second end cap electrode 4b for transmitting excitation signals and receiving ion or measurement signals. By way of example, FIG. 1 shows two such measurement signals S1, S2 emanating from the first segment Q1 of the first or second end cap electrode 4a, 4b, respectively, generated by mirror charges of excited ions 6 stored in the ion storage cell 5. Based on these ion signals S1, S2, which are usually evaluated separately, and on further ion signals recorded in the second to fourth segments Q2, Q3, Q4, it is possible to establish the time-related dispersion of the ions 6 (with more mobile ions travelling faster) injected in a pulse into the annular ion storage cell 5.

[0052] In this way, but in some cases with non-segmented end cap electrodes 4a, 4b, the ion trap 2 can apply all conventional Fourier transform measurement tools as used in conventional FT ion traps, such as ion filtration, separation and non-destructive detection of ions during ionization or storage, etc. In particular, the ion trap 2 can also perform SWIFT excitation, for example, as described in U.S. Patent No. 10,141,174 B4, which is incorporated herein by reference in its entirety.

[0053] As further mentioned above, typically the controller 3 operates the end cap electrodes 4a, 4b or respective segments Q1, Q2, Q3, Q4 of the end cap electrodes 4a, 4b for selection, excitation and detection of ions 6 in the ion storage cell 5.

[0054] The control device 3 is also designed to store the ions 6 in the ion storage cell 5. To this end, the control device 3 controls the disk-shaped ring electrode E to generate a respective HF storage voltage VRF,i. 1,i , E 2,i or the corresponding HF storage voltage V RF,iIt has an HF generator 8 and a resistance network to apply 1,i E 2,i A given harmonic HF storage voltage V RF (t)=V max sin(ωt) etc. can be divided in the form described in the paper by Aliman and A. Glasmachers for example (in this case, or when using equation (2), -N / 2 < i < N / 2 applies to i). Note that for each HF storage voltage V 1,i E 2,i of each individual ring electrode E RF、i The division of the HF storage voltage V RF (t) across can also be done in ways other than those described here.

[0055] In the examples shown in FIGS. 1 and 2, the control device 3 is disposed entirely within the volume area 7 surrounded by the annular ion storage cell 5. The control device 3 is disposed at the center of the ion trap 2 or the annular ion storage cell 5 and does not project axially Z beyond the annular ion storage cell 5. The control device 3 can be disposed in another vacuum area separated from the annular ion storage cell 5 by, for example, a seal, differential pumping, or a housing. Through such an arrangement of the control device 3, a particularly compact mass spectrometer 1 can be achieved.

[0056] The control device 3 is also designed to operate the injection device 9 shown in FIG. 2, which in the illustrated example serves to inject the ions 6 into the annular ion storage cell 5 in a tangential direction, typically in pulses. The injection device 9 can have a controllable, particularly pulsed inlet or inlet system, such as a controllable valve, for injecting the ions 6 of the gas to be analyzed, generated by an (external) ion source not shown in the drawing, into the mass spectrometer 1 or the annular ion storage cell 5. For this purpose, the injection device 9 can have an ion lens, not particularly shown in the drawing, which injects the ions 6 into the annular ion storage cell 5 on a straight track aligned tangentially with respect to the average radius R of the annular ion storage cell 5 as can be seen in FIG. 2.

[0057] In the illustrated example, ions 6 are injected in the axial direction Z centrally between the end cap electrodes 4 a, 4 b in a plane X, Y perpendicular to the axial direction Z, so that the ions 6 travel in a circular orbit 11 in a non-excited state in the center of the ion storage cell 5.

[0058] In the example shown here, the adjacent outer ring electrode E 2,i , E 2,i+1 The distance d between two adjacent ring electrodes E 2,i , E 2,i+1 ions 6 between them into the annular ion storage cell 5, i.e. there is no need to provide an additional inlet for injecting ions 6 into the annular ion storage cell 5.

[0059] The mass spectrometer 1, and in particular the annular ion storage cell 5, is arranged in a housing, not shown in the drawings, which separates the mass spectrometer 1 from its surroundings, such as a process chamber containing the gas to be analysed.

[0060] In the ion trap 2, and in particular in the ion storage cell 5, a vacuum is created by means of a vacuum pump, not shown in the drawing. Thus, in the ion storage cell 5, apart from the ions 6 of the gas to be analysed, there is only background gas, which typically has a very low pressure.

[0061] In the example shown, the implanter 9 is designed to generate and inject an electron beam 10 into the annular ion storage cell 5 in addition to injecting the ions 6. As can be seen in FIG. 2, this electron beam 10 is also fed tangentially to the ion storage cell 5. The control device 3 activates the end cap electrodes 4a, 4b in order to generate a Lorentz force on the electron beam 10 according to equation (3) above and to deflect it onto a circular orbit 11 in the ion storage cell 5. The electron beam 10 serves to generate ions 6 directly in the ion storage cell 5 through impact ionization. The generation of ions 6 in the ion storage cell 5 can be carried out on a neutral gas to be analyzed, which is fed into the ion storage cell 5 via the implanter 9 or possibly via a separate inlet, before the ions 6 of the gas to be analyzed are generated in situ in the ion storage cell 5 using the electron beam 10.

[0062] In summary, the above-described annular or circular ion trap 2 can be used to significantly expand the available ion storage cell 5 without significantly expanding the structural space of the ion trap 2. Through the electronic controller 3, it is also possible to enforce a spatial circular ion storage in which the ions 6 move in a circular orbital pattern. In this way, a circular expansion of the ion storage cell 5 is achieved, minimizing space charge problems and thus improving the measurement resolution compared to conventional FT ion traps. [Explanation of symbols]

[0063] 1 Mass spectrometer 2. Ion trap 3. Electronic control device 4a First annular end cap electrode 4b Second annular end cap electrode 5. Annular ion storage cell 6. Ion 7 Volume Area 8 HF generator E 1,1 ~E 1,N Radial inner disk-shaped ring electrode E 2,1 ~E 2,N Radial outer disk-shaped ring electrode R Radius of the end cap electrode S1 Measurement signal S2 measurement signal V RF,i HF accumulation voltage

Claims

1. A mass spectrometer comprising: An ion trap (2) comprising a first annular end cap electrode (4a) and a second annular end cap electrode (4b), with an annular ion storage cell (5) formed between the first annular end cap electrode (4a) and the second annular end cap electrode (4b); The ion trap comprises a number (N) of radially inner disk-shaped ring electrodes (E 1,i ) and a plurality (N) of radially outer disk-shaped ring electrodes (E 2,i ) a control device (3) designed to operate the disk-shaped ring electrodes (E 1,i , E 2,i ) and the end cap electrodes (4 a, 4 b) for storage, selection, excitation and / or detection of ions (6) in said annular ion storage cell (5), The control device (3) is designed to determine the time-related dispersion of the ions (6) injected in pulses into the ion storage cell (5) based on ion signals (S1, S2) recorded at different circumferentially divided segments (Q1, Q2, Q3, Q4) of the end cap electrodes (4a, 4b).

2. The inner ring electrode (E 1,i ) and the outer ring electrode (E 2,i ) are at a constant radial distance from each other (2r 0 ) will be placed in 10. The mass spectrometer of claim 1.

3. The inner ring electrode (E 1,i ) and the outer ring electrode (E 2,i ) the radial distance (2r 0 ) is smaller than the radius (R) of the annular end cap electrodes (4a, 4b); 3. A mass spectrometer according to claim 1 or 2.

4. In either case, the inner ring electrode (E 1,i ) and the outer ring electrode (E 2,i ) are arranged on a common plane (X, Y) perpendicular to the axial direction (Z); A mass spectrometer according to any one of claims 1 to 3.

5. In either case, the inner ring electrode (E 1,i ) and the outer ring electrode (E 2,i ) are conductively connected to each other; A mass spectrometer according to any one of claims 1 to 4.

6. Each disk-shaped inner or outer ring electrode (E 1,i , E 2,i ) and the width b of the two adjacent inner or outer ring electrodes (E 1,i , E 1,i+1 ;E 2,i , E 2,i+1 ) for each distance d in the axial direction (Z) between the 5. The mass spectrometer of claim 4.

7. N radially inner ring electrodes (E 1,i ), and N radially outer ring electrodes (E 2,i ) with N being 10<N<200; A mass spectrometer according to any one of claims 1 to 6.

8. the first end cap electrode (4a) and / or the second end cap electrode (4b) are circumferentially divided into at least two annular segments; A mass spectrometer according to any one of claims 1 to 7.

9. and at least one injector (9) for injecting ions (6) and / or an electron beam (10) into said annular ion storage cell (5). A mass spectrometer according to any one of claims 1 to 8.

10. the control device (3) is at least partially disposed within a volume area (7) surrounded by the annular ion storage cell (5); A mass spectrometer according to any one of claims 1 to 9.

11. The control device (3) controls the disk-shaped ring electrode (E 1,i , E 2,i ) to activate the respective HF storage voltages (V RF、i ) and storing ions (6) in said ion storage cell (5), A mass spectrometer according to any one of claims 1 to 10.

12. said control device (3) being designed to direct an electron beam (10) tangentially incident on said annular ion storage cell (5) along a circular trajectory (11); A mass spectrometer according to any one of claims 1 to 11.

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