Ion Trap and Mass Spectrometer with a Ring-Shaped Ion Storage Cell

Abstract

The present invention relates to an ion trap (2) comprising: a first annular end cap electrode (4a) and a second annular end cap electrode (4b) between which an annular ion storage unit (5) is formed, and a plurality (N) of radially inner disc-shaped annular electrodes and a plurality (N) of radially outer disc-shaped annular electrodes defining the annular ion storage unit (5). The present invention also relates to a mass spectrometer (1) having such an ion trap (2) and a control device (3) which is designed to actuate the disc-shaped annular electrodes and the end cap electrodes (4a, 4b) for storing, selecting, exciting and / or detecting ions (6) in the annular ion storage unit (5).

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, between which an annular ion storage unit is formed. Thus, the ion trap is a circular or annular ion trap. The present invention also relates to a mass spectrometer having such an ion trap. Background Art

[0002] Patent US 9,035,245B2 describes a mass spectrometer having an electrical FT ion trap. The FT ion trap has an annular electrode and two end cap electrodes each having a hyperbolic geometry, between which a non-annular ion storage unit defined by hyperbolic electrical limits is formed. Generally, 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 annular electrode.

[0003] By means of the HF storage signal, an electric field (quadrupole field) is generated in the ion trap, which enables it to store ions or charged particles in the ion trap in a stable manner.

[0004] As an alternative to an ion trap having a hyperbolic quadrupole or Paul trap geometry, in the article "A novel electric ion resonance cell design with high signal-to-noise ratio and low distortion for Fourier transform mass spectrometry" by M. Aliman and A. Glasmachers in the Journal of the American Society for Mass Spectrometry, Volume 10, Number 10, October 1999, a different geometry was proposed: the annular electrode was replaced by a cylinder of disk-shaped annular electrodes extending from a first end cap electrode to a second end cap electrode in the axial direction. The annular electrodes are arranged equidistantly in the axial direction. The resulting ion storage unit forms a cylinder having a hyperbolic bottom and hyperbolic caps. By means of such an ion trap, the crosstalk current occurring between the end cap electrodes and the annular electrode in the case of a conventional Paul trap can be reduced.

[0005] In a three-dimensional FT ion trap, many functions can be performed in situ, such as ion selection or ion filtering, ion storage, ion excitation, and ion detection. It is known from US 10,141,174B2 that in such an FT ion trap, during the generation and storage of ions and / or during the ion excitation before ion detection, at least one selective IFT ("inverse Fourier transform") excitation, in particular SWIFT ("stored waveform inverse Fourier transform") excitation, is performed according to the mass-to-charge ratio of the ions. Selective SWIFT excitation can be used in particular for ion selection or ion filtering. To separate ion populations stored in an FT ion trap, wavelet and / or FFT techniques can be used. In the detection of ions, noise detection techniques can be used.

[0006] To detect ions, a measurement signal generated at the endcap electrode, which is generated by image charges, can be used. In a mass spectrometer, the mass spectrum can be quickly calculated from the measurement signal by means of a fast Fourier transform (FFT) or by means of a method such as harmonic inversion. For example, reference is made to "Harmonic inversion of semiclassical short time signals" published by F. Grossmann et al. in Chem. Phys. Lett. 279 (1997) 355-360. The sensitivity of an ion trap mass spectrometer is also very high. These performance characteristics are required in many applications, for example, to quickly and accurately detect the endpoint (so-called endpoint detection applications) from gas components in semiconductor processes.

[0007] However, in the case of an FT ion trap, there are also some challenges that need to be overcome during the measurement process. These relate, for example, to the maximum ion charge of the ion trap and / or the ratio of the majority charge carriers to the minority charge carriers that can be stored, as well as the selectivity during ion filtering or ion generation, the filter characteristics of the ion trap itself, and the separation and detection of the ion species of interest.

[0008] The characteristics of such a compact mass spectrometer or such an ion trap can be severely impaired and limited by an excessive ion charge. For example, a low ion concentration of, for example, 100 ppb cannot be achieved unless ion filtering is performed on a background gas such as nitrogen. This measurement impairment in the ion trap can be attributed to the so-called space charge problem: in the ion detection in an (electrical) FT ion trap, it is pre-assumed that the high-frequency alternating field E acts alone on the ions. In practice, this applies as long as only a limited number of charge carriers of the same sign are present in the FT ion trap.

[0009] The total number of charge carriers is referred to as the "space charge" or "ion cloud". The space charge effect can be described by Laplace's equation and the electric potential derived from the high-frequency alternating field E . The greater the influence of the space charge in a given volume within the FT ion trap on the storage potential , the greater the space charge density (in units of ) in this volume, and the weaker the average restoring force in the corresponding partial volume originating from the high-frequency alternating field. According to the Laplace equation for the high-frequency alternating field, it follows that:

[0010]

[0011] where represents the permittivity of free space, and represents the high-frequency alternating potential belonging to the alternating field E (see above). Large space charges lead to significant ion losses and / or suppression of the measurement signal for small ion populations. To address the problem of space charge, it is proposed in DE10 2015 208 188A1 to spatially separate ion packets by means of suitable SWIFT excitation.

[0012] Another possibility for solving the space charge problem lies in expanding the ion storage unit available for storing ions. For this purpose, so-called toroidal ion traps are used. For example, see the article by S.A. Lammert et al. in International Journal of Mass Spectroscopy, 212 (2002) 25 - 40, Design, optimization and initial performance of a toroidal rf ion trap mass spectrometer (“Design, optimization and initial performance of a toroidal rf ion trap mass spectrometer”). However, in such an ion trap, there are problems with non-linear field segments that impede mass resolution or sensitivity in mass spectrometry. In the cited article, an asymmetric design of the toroidal ion trap is proposed to increase mass resolution, also refer to the poster by Lammert et al. at the 62nd ASMS Conference held in Baltimore, Maryland from June 15 - 19, 2014, Toroidal Multipole Expansion for the Design of Circular Ion Traps (“Toroidal Multipole Expansion for the Design of Circular Ion Traps”).

[0013] The stability of ion trajectories in a toroidal ion trap is examined in the article "Computation of Mathieu stability plot for an arbitrary toroidal ion trap mass spectrometer" by Appala Naidu Kotana et al. in International Journal of Mass Spectrometry 414 (2017) 13-22. Summary of the Invention

[0014] Task of the invention

[0015] The object of the present invention is to provide an ion trap and a mass spectrometer having such an ion trap, which can achieve high ion charge and high sensitivity in ion detection.

[0016] Object of the invention

[0017] This object is achieved by an ion trap of the type described at the beginning, which has a plurality of radially inner disk-shaped toroidal electrodes and a plurality of radially outer disk-shaped toroidal electrodes, and these toroidal electrodes define a toroidal ion storage unit. The toroidal ion storage unit is defined on the inner side in the radial direction by an inner disk-shaped and circular toroidal electrode, and on the outer side in the radial direction by an outer disk-shaped and circular toroidal electrode. Usually, the number of inner toroidal electrodes corresponds to the number of outer toroidal electrodes. The ion trap, or rather, the two end cap electrodes and the toroidal electrodes, extend substantially rotationally symmetrically about the axis of symmetry centrally arranged in the ion trap. The two end cap electrodes define the (circular) toroidal ion storage unit in the axial direction. Herein, "disk-shaped" means a substantially flat shape, that is, the inner disk-shaped electrode and the similar outer disk-shaped toroidal electrode have a radial extension that exceeds the axial extension by more than twice, preferably more than five times, and more preferably more than 10 times.

[0018] In particular, each inner toroidal electrode and also each outer toroidal electrode are separated from each other to enable different electric potentials to be applied to each toroidal electrode.

[0019] Due to the circular geometry of the ion trap, the ion storage unit can be significantly enlarged compared to a conventional 3D ion trap in the form of a Paul trap.

[0020] In this way, compared with a conventional Paul trap, the maximum ion charge of the ion trap can be increased to more than 5 times or more than 10 times. In addition, an ion trap with a disk-shaped ring electrode can be manufactured in a simple manner. The spatial ring storage of ions in the ring ion storage unit also makes it possible to significantly reduce the space charge density in an effective manner by appropriately enlarging the ring of the ion storage unit , to solve the space charge problem. By appropriately driving the ion trap designed as described above, the non-linear field section in the ion storage unit can be suppressed at the same time, so that high-quality resolution or sensitivity of the ion trap can be achieved.

[0021] In the case of one embodiment, the inner ring electrode and the outer ring electrode are arranged at a constant radial distance from each other. Therefore, the ion storage unit extends in the radial direction between the minimum radius determined by the radially outer end face of the inner ring electrode and the maximum radius determined by the radially inner end face of the outer ring electrode. In this way, the ions circulate in the ion trap in a "cold, cooled" state on an orbit whose radius is in the middle between the maximum radius and the minimum radius of the ion storage unit. Among them, the inner ring electrode and the outer ring electrode are separated by the ion storage unit.

[0022] In the case of another embodiment, the radial distance between the inner ring electrode and the outer ring electrode is less than the radius of the ring end cap electrode. The ring end cap electrode generally has a hyperbolic geometry. The radius of the end cap electrode is understood as the average value between the maximum and minimum extensions of the end cap electrode in the radial direction.

[0023] This radius should at least correspond to the generally constant radial distance between the inner ring electrode and the outer ring electrode.

[0024] In the case of another embodiment, in each case, the inner ring electrode and the outer ring electrode are arranged in a common plane perpendicular to the axial direction. The planes in which the pairs of ring electrodes are arranged are parallel and aligned with each other, and are stacked on top of each other, and are spaced apart from each other in the axial direction.

[0025] In the case of one embodiment, in each case, the inner ring electrode and the outer ring electrode, that is, a pair of ring electrodes, are conductively connected to each other. The ring electrodes conductively connected to each other have the same electric potential. Each pair of ring electrodes is preferably arranged in the above-mentioned common plane.

[0026] In the case of another embodiment, for the width b of the respective first or second annular electrode in the radial direction and the distance d between two adjacent first or second annular electrodes in the axial direction, respectively, the following applies: d / b < 1 / 4. The distance d between adjacent annular electrodes can be, for example, between approximately 100 μm and approximately 1 mm. Thus, the width b in the radial direction is between approximately 400 μm and 4 mm. Due to the open mechanical architecture of the ion trap (as free as possible of "enclosed" spaces), since the disk-shaped annular electrodes are spaced apart from each other ("discrete") to create a potential well for the ions, a higher vacuum conductance of the ion trap can be ensured compared to a conventional ion trap with solid annular electrodes.

[0027] In the case of another embodiment, the ion trap has a number N of radially inner annular electrodes and a number N of radially outer annular electrodes, for which the following applies: 10 < N < 200.

[0028] It has been shown that even a relatively small number N of annular electrodes is sufficient to allow the ions to circulate in a stable orbit in the ion storage unit in a "cold, cooled" state.

[0029] In the case of another embodiment, the first end cap electrode and / or the second end cap electrode is divided into at least two annular segments in the circumferential direction. Two or more segments typically extend at the same angular interval in the circumferential direction: If the respective end cap electrode is divided into two segments in the circumferential direction, these two segments extend at an angle of approximately 180° in the circumferential direction and are electrically isolated from each other by a gap. Thus, in each case, three segments extend at approximately 120°, in each case, four segments extend at approximately 90° in the circumferential direction, etc. In the case where both end cap electrodes are segmented, these segments typically extend over the same angular range in the circumferential direction. Due to the segmentation, in time-division multiplexing operation, the end cap electrodes can optionally be used as excitation or detection or measurement electrodes. In this way, all conventional Fourier transform measurement tools can be used for the case of the ion trap, such as for a conventional FT ion trap (e.g., ion filtering during ionization or storage, separation of ions, and non-destructive detection).

[0030] In the case of another embodiment, the ion trap further includes an injection device for injecting an ion and / or electron beam preferably tangentially, in particular pulsed, into the annular ion storage unit. The ions can be generated in an (external) ion source and introduced into the annular ion storage unit through the injection device. Typically, the injection of the ions occurs in a pulsed manner, i.e., by a pulsed supply, which can, for example, have a controllable valve.

[0031] The injection device may have an ion lens or the like in order to inject or emit ions into the toroidal ion storage unit on a straight track, and the lens is preferably oriented tangentially to the average radius of the toroidal ion storage unit. Preferably, the ions are injected into the toroidal ion storage unit in the gap between two outer toroidal electrodes spaced apart in the axial direction. The injection is preferably carried out in a plane perpendicular to the axial direction, i.e., parallel to the toroidal electrodes.

[0032] The injection device can also be used to inject an electron beam into the toroidal ion storage unit in order to directly generate ions in the ion trap by means of collisional ionization. In this case, the gas to be analyzed can be guided into the ion storage unit by means of the injection device before ions are generated by means of the electron beam.

[0033] Another aspect of the present invention relates to a mass spectrometer, comprising: an ion trap designed as described above, and (electronic) control means, which are designed to actuate the disk-shaped toroidal electrodes and end cap electrodes of the ion trap for storage, selection, excitation and / or detection of ions in the toroidal ion storage unit. The generation of the HF storage field (see below) and the generation of the necessary signals for excitation, selection / separation and for detection of ions are achieved by means of the electronic control means. For this purpose, the control means can comprise suitable hardware, such as electronic circuits, and / or software. Generally, the signals for excitation, selection and detection are applied to or tapped at the end cap electrodes. However, in order to excite the ions, the control means can also provide an excitation signal at the toroidal electrodes.

[0034] For excitation, as described above, at least one selective SWIFT ("Stored Waveform Inverse Fourier Transform") excitation depending on the ion mass-to-charge ratio can be carried out, or possibly broadband excitation.

[0035] In the case of one embodiment, the control means are at least partially arranged in the volume region surrounded by the toroidal ion storage unit. The control means are preferably arranged in the center of the ion trap or the toroidal ion storage unit. The control means can for example be arranged in a separate vacuum region, which is separated from the toroidal ion storage unit, for example by means of seals, by differential pumping or by a housing. However, the control means do not necessarily have to be arranged in the center of the ion trap; on the contrary, the control means or the components of the ion trap required for actuating the ion trap can also be arranged elsewhere in the vicinity of the ion trap.

[0036] In the case of another embodiment, the control device is designed to actuate a disk-shaped annular electrode to generate a corresponding HF storage voltage for storing ions in the ion storage unit. For this purpose, the HF potential generated by the HF generator can be separated in a suitable manner on the individual annular electrodes. Preferably, each inner annular electrode is at a different potential. Similarly, each outer annular electrode is at a different potential. Preferably, the corresponding inner annular electrode and outer annular electrode are at the same potential, and the potential , for example operating with the square of i, can be applied to the i-th annular electrode; starting from the HF potential , for example a harmonic potential , for example which is defined as follows:

[0037]

[0038] where the following applies to i: , that is, there are a total of 2N + 1 inner annular electrodes and 2N + 1 outer annular electrodes available, which are arranged equidistantly from each other in the axial direction (in the Z direction); also refer to the article by M. Aliman and A. Glasmachers cited at the beginning.

[0039] It should be understood that the annular electrodes do not have to be arranged equidistantly, and the HF voltage applied to a corresponding pair of inner and outer annular electrodes does not have to be distributed according to equation (2). The application of voltage to the corresponding annular electrodes can occur by means of a matching network and a voltage divider network, which, for example, has resistors and capacitors with parallel switches, as described in the article by M. Aliman and A. Glasmachers cited at the beginning, the entire content of which is incorporated herein by reference. By means of the HF storage field of the annular electrodes, spatial annular ion storage can be achieved, where the ions move along an annular orbit in a "cold, cooled" state. Such an HF storage field has only relatively small non-linear field segments and can therefore enable ion detection with high mass resolution.

[0040] In the case of one embodiment, the control device is designed to determine the time-dependent diffusion of ions injected into the ion storage unit in pulsed manner, based on ion signals recorded at different segments of the end cap electrodes. When ions are injected into the annular ion storage unit in pulsed manner, that is, in the form of an ion packet and are thus initially excited, it is possible to determine how the ion diffusion progresses as the storage time increases (more mobile ions move faster) based on the recorded ion signals. It has proven advantageous here that individual ion signals can be recorded at each segment of the (one or more) end cap electrodes.

[0041] In this way, conclusions can be drawn, for example, about the spatial distribution of the ion swarm and about pressure-related processes in the ion trap. To obtain conclusions about the ion mobility, cooling with a time-limited braking gas (such as helium) can be introduced.

[0042] In the case of one embodiment, the control device is designed to deflect an electron beam injected tangentially along a circular trajectory into an annular ion storage unit. As has been further described above, for flexible ion generation and ion storage, at least one (pulsed) electron beam can be injected into the ion storage unit. Furthermore, since electrons (with an elementary charge e ; velocity V e ) are at least three to four orders of magnitude lighter than the ions to be detected, the electron beam can actually be deflected separately, such that by generating a sufficiently small, time-limited induction B , when the Lorentz force F acts on the electron beam according to the following equation, it moves on a circular orbit and, in doing so, travels through all sections of the annular ion storage unit:

[0043]

[0044] By forcing the electron beam onto a circular path, particularly efficient electron ionization can be achieved, and the flexibility of ion generation, storage, and injection can be increased.

[0045] Other features and advantages of the present invention result from the following description of exemplary embodiments of the present invention, from the illustrations based on the drawings, and from the claims, which show important details of the present invention. In variants of the present invention, in each case, the individual features can be implemented individually or in any desired combination as a plurality. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Exemplary embodiments are shown in schematic diagrams and are explained in the following description. In the drawings,

[0047] Figure 1 a schematic representation of a cross-section of a mass spectrometer with an ion trap having an annular ion storage unit is shown,

[0048] Figure 2 shows Figure 1 a top view of the annular ion storage unit having segmented end cap electrodes, and

[0049] Figure 3 a detailed representation of a number of outer disk-shaped annular electrodes and inner disk-shaped annular electrodes that radially delimit the storage unit is shown.

[0050] In the following description of the drawings, the same reference numerals are used to denote the same or functionally identical components. Detailed Description of the Invention

[0051] Figure 1 A schematic cross-sectional view of a mass spectrometer 1 is shown, which has an ion trap 2 and an electronic control device 3. The ion trap 2 includes a first annular end cap electrode 4a located at the top in the axial direction Z of the XYZ coordinate system, and a second annular end cap electrode 4b located at the bottom in the axial direction Z, between which an annular ion storage unit 5 is formed. The two end cap electrodes 4a, 4b each have a hyperbolic curved surface facing the ion storage unit 5, as is common in the case of an ion trap in the form of a Paul trap.

[0052] The annular ion storage unit 5 extends radially symmetrically about the axial direction Z of the XYZ coordinate system. In Figure 1 the cross-sectional view, the radial direction corresponds to the X direction of the XYZ coordinate system. In the radial direction X, the ion storage unit 5 is bounded internally by a plurality or number N of radially inner disk-shaped annular electrodes and externally by a plurality or number N of radially outer disk-shaped annular electrodes . The N radially inner annular electrodes are arranged one above the other in the axial direction Z. Thus, the N radially outer annular electrodes are also arranged one above the other in the axial direction Z.

[0053] The annular ion storage unit 5 has a constant extension in the radial direction X, which corresponds to the distance between the inner annular electrode and the outer annular electrode . The radial distance between the inner annular electrode and the outer annular electrode is here less than the radius R of the two end cap electrodes 4a, 4b. The radius R of the end cap electrodes 4a, 4b corresponds to the average radius R of the ion storage unit 5 and extends centrally in the radial direction X through the two end cap electrodes 4a, 4b.

[0054] The ion storage unit 5 extends in the radial direction X between a minimum radius determined by the radially outer end face of the inner annular electrode and a maximum radius determined by the radially inner end face of the outer annular electrode . The ion storage unit 5 extends between the inner annular electrode , by the constant distance , so that ions 6 in the "cold, cooled" state can circulate in the ion trap 2 in an orbit corresponding to the average radius R of the toroidal ion storage unit 5.

[0055] In the example shown, the number N of the inner toroidal electrodes corresponds to the number N of the outer toroidal electrodes .

[0056] For the number N, the following applies in the example shown: 10 < N < 200. It has been shown that even a relatively small number N of toroidal electrodes , is sufficient to allow ions 6 in the "cold, cooled" state to circulate in a stable orbit in the toroidal ion storage unit 5.

[0057] As Figure 1 and Figure 3 can be seen, the toroidal electrodes , are arranged in pairs in a common plane X,Y perpendicular to the axial direction Z. In each case, the two toroidal electrodes arranged in the common plane X,Y , are connected to each other by electrical leads or electrical contacts not shown in the figure, i.e., they are at the same electrical potential. Electrical contact can also be achieved via the control device 3. For the corresponding disk-shaped first toroidal electrode the width b in the radial direction X and in the axial direction Z between two adjacent first toroidal electrodes , respectively, the following applies: d / b < 1 / 4. Thus, for the (same) width b of the second toroidal electrode and for the distance d in the axial direction Z between two adjacent second toroidal electrodes , respectively, the following also applies: d / b < 1 / 4.

[0058] The distance d between adjacent toroidal electrodes , or , can be, for example, between approximately 100 μm and approximately 1 mm. Thus, the width b in the radial direction X is between approximately 400 μm and 4 mm. Due to the open mechanical architecture of the ion trap 2 resulting from the disk-shaped toroidal electrodes being spaced apart from each other ("discrete") to generate a potential well for ions 6, a higher vacuum conductance of the ion trap 2 compared to conventional ion traps is ensured using solid toroidal electrodes.

[0059] As Figure 2As can be seen, the first end cap electrode 4a is divided into four annular segments Q1, Q2, Q3, Q4 in the circumferential direction, each of which extends through an angle of 90° in the circumferential direction in each case.

[0060] Accordingly, the second end cap electrode 4b is also divided into four annular segments Q1, Q2, Q3, Q4 (not shown in the figure). Due to the segmentation, in the time-division multiplex operation of the control device 3, the end cap electrodes 4a, 4b can be optionally used as excitation, filtering, or measurement electrodes.

[0061] The control device 3 is signal-connected to each of the four segments Q1, Q2, Q3, Q4 of the first end cap electrode 4a and to each of the four segments Q1, Q2, Q3, Q4 of the second end cap electrode 4b in order to transmit excitation signals and receive ion signals or measurement signals. By way of example, Figure 1 two such measurement signals S1, S2 are shown, which are generated by the mirror charge of the excited ions 6 stored in the ion storage unit 5 and which originate from the respective first segment Q1 of the first or second end cap electrode 4a, 4b. Based on these ion signals S1, S2, which are usually evaluated differentially, and based on additional ion signals recorded at the second to fourth segments Q2, Q3, Q4, it is possible to establish the time-dependent diffusion of the ions 6 injected into the ring-shaped ion storage unit 5 in pulsed manner (more mobile ions advance faster).

[0062] As well as in the case of using non-segmented end cap electrodes 4a, 4b, it is also possible in the case of the ion trap 2 to apply all conventional Fourier transform measurement tools, such as those used in conventional FT ion traps, for example ion filtering, ion separation, and non-destructive detection during ionization or storage. In particular, in the ion trap 2, SWIFT excitation can also be carried out, for example, in the manner described in US 10,141,174B4, the entire content of US 10,141,174B4 being incorporated herein by reference.

[0063] As has been further described above, the control device 3 generally actuates the end cap electrodes 4a, 4b or the respective segments Q1, Q2, Q3, Q4 of the end cap electrodes 4a, 4b in order to select, excite, and detect the ions 6 in the ion storage unit 5.

[0064] The control device 3 is also designed to store ions 6 in the ion storage unit 5. For this purpose, the control device 3 has an HF generator 8 and a resistor network in order to actuate the disc-shaped ring electrodes to generate the corresponding HF storage voltage or to apply the corresponding HF storage voltage to them. At the respective ring electrodes or a given storage voltage of, for example, a harmonic HF on the corresponding electrode pair The splitting of can be carried out, for example, in the manner described in the article by M. Aliman and A. Glasmachers cited above (in this case, or if equation (2) is used, the following applies to i: -N / 2 < i < N / 2). It is understood that the splitting of the HF storage voltage into the respective HF storage voltages of the individual toroidal electrodes can also occur in a manner different from that described here. into the respective HF storage voltages of the individual toroidal electrodes can also occur in a manner different from that described here. .

[0065] In the case of the example shown in Figure 1 and Figure 2 , the control device 3 is arranged entirely within the volume region 7 surrounded by the toroidal ion storage unit 5. The control device 3 is arranged in the center of the ion trap 2 or the toroidal ion storage unit 5 and does not protrude in the axial direction Z beyond the toroidal ion storage unit 5. The control device 3 can, for example, be arranged in a separate vacuum region which is separated from the toroidal ion storage unit 5, for example, by a seal, by differential pumping or by a housing. By this arrangement of the control device 3, a particularly compact mass spectrometer 1 can be achieved.

[0066] The control device 3 is also designed to actuate Figure 2 the injection device 9 shown in Figure 2 , which, in the example shown, is used to inject the ions 6 tangentially, typically in pulses, into the toroidal ion storage unit 5. The injection device 9 can have a controllable, in particular pulsed, inlet or inlet system, for example a controllable valve, in order to inject the ions 6 of the gas to be analyzed, which are generated by an (external) ion source not shown in the figure, into the mass spectrometer 1 or the toroidal ion storage unit 5. For this purpose, the injection device 9 can in particular have an ion lens not shown in the figure, which injects the ions 6 into the toroidal ion storage unit 5 on a straight trajectory tangentially aligned with the mean radius R of the toroidal ion storage unit 5, as can be seen in Figure 2 Figure 2 .

[0067] In the example shown, the ions 6 are injected centrally between the end cap electrodes 4a, 4b in the plane X, Y perpendicular to the axial direction Z and in the axial direction Z, such that the ions 6 move on a circular trajectory 11 in the middle of the ion storage unit 5 in a non-excited state.

[0068] In the example shown here, the distance d between adjacent outer toroidal electrodes is chosen to be large enough to inject the ions 6 between two adjacent toroidal electrodes into the toroidal ion storage unit 5, i.e., no additional inlet for injecting 6 into the toroidal ion storage unit 5 has to be provided.

[0069] The mass spectrometer 1 and in particular the toroidal ion storage unit 5 are arranged in a housing, not shown in the figures, which separates the mass spectrometer 1 from its surroundings, for example from a processing chamber with the gas to be analyzed.

[0070] By means of a vacuum pump not shown in the figures, a vacuum is produced in the ion trap 2 and in particular in the ion storage unit 5. Thus, in addition to the ions 6 of the gas to be analyzed, only background gas with a generally very low pressure is present in the ion storage unit 5.

[0071] In the example shown here, in addition to injecting the ions 6, the injection device 9 is also designed to generate an electron beam 10 and inject it into the toroidal ion storage unit 5. The electron beam 10 is also fed tangentially to the ion storage unit 5, as Figure 2 can be seen. The control device 3 actuates the end cap electrodes 4a, 4b in order to generate a Lorentz force on the electron beam 10 according to the above equation (3) and deflect it onto a circular trajectory 11 in the ion storage unit 5. The electron beam 10 is used to directly generate ions 6 in the ion storage unit 5 by means of collision ionization. The generation of ions 6 in the ion storage unit 5 can occur on the neutral gas to be analyzed before the ions 6 of the gas to be analyzed are generated in situ in the ion storage unit 5 by means of the electron beam 10, and the neutral gas to be analyzed is supplied to the ion storage unit 5 via the injection device 9 or possibly via another inlet.

[0072] In summary, by means of the above-mentioned toroidal or circular ion trap 2, the available ion storage unit 5 can be significantly enlarged without significantly enlarging the construction space of the ion trap 2. By means of the electronic control device 3, a circular ion storage in space can also be forced, in which the ions 6 move in a painted-like manner in a circular orbit. In this way, a circular enlargement of the ion storage unit 5 is achieved, the space charge problem is minimized, and thus the measurement resolution is improved compared to a conventional FT ion trap.

Claims

1. A mass spectrometer, comprising: An ion trap (2), the ion trap comprising: A first annular end cap electrode (4a) and a second annular end cap electrode (4b), between which an annular ion storage unit (5) is formed, Characterized in that, Define a plurality (N) of radially inner disk-shaped toroidal electrodes (E 1，i ) and a plurality (N) of radially outer disk-shaped toroidal electrodes (E 2，i ) that define the toroidal ion storage cell (5). Wherein, the first annular end cap electrode (4a) and / or the second annular end cap electrode (4b) are divided into at least two annular segments (Q1, Q2, Q3, Q4) in the circumferential direction; and The mass spectrometer further comprises a control device (3), which is designed to actuate the radially inner disc-shaped ring electrode (E 1，i ) and / or the radially outer disc-shaped ring electrode (E 2，i ) and the first ring end cap electrode (4a) and / or the second ring end cap electrode (4b) for storing, selecting, exciting and / or detecting ions (6) in the ring ion storage unit (5), and the control device (3) is designed to determine the time-dependent diffusion of the ions (6) injected in a pulsed manner into the ring ion storage unit (5) based on ion signals (S1, S2) recorded at different segments (Q1, Q2, Q3, Q4) of the first ring end cap electrode (4a) and / or the second ring end cap electrode (4b).

2. The mass spectrometer according to claim 1, wherein in the ion trap, the radially inner disk-shaped ring electrode (E 1，i ) and the radially outer disk-shaped ring electrode (E 2，i ) are arranged at a constant radial distance (2r0) from each other.

3. The mass spectrometer according to claim 1 or 2, wherein, in the ion trap, the radial distance (2r0) between the radially inner disc-shaped ring electrode (E 1，i ) and the radially outer disc-shaped ring electrode (E 2,i ) is less than the radius (R) of the first annular end cap electrode (4a) and the second annular end cap electrode (4b).

4. The mass spectrometer according to claim 1 or 2, wherein in the ion trap, in each case, a radially inner disk-shaped ring electrode (E 1，i ) and a radially outer disk-shaped ring electrode (E 2，i ) are arranged in a common plane (X, Y) perpendicular to the axial direction (Z).

5. The mass spectrometer according to claim 1 or 2, wherein In the ion trap, in each case, the radially inner disk-shaped ring electrode (E 1,i ) and the radially outer disk-shaped ring electrode (E 2,i ) are conductively connected to each other.

6. The mass spectrometer according to claim 1 or 2, wherein, Each of the radially inner disk-shaped annular electrodes and also each of the radially outer disk-shaped annular electrodes are separated from each other to be able to apply different electric potentials to each disk-shaped annular electrode.

7. The mass spectrometer according to claim 1 or 2, wherein in the ion trap, for the width b of the corresponding radially inner disk-shaped ring electrode (E 1,i ) or the radially outer disk-shaped ring electrode (E 2,i ), and the distance d in the axial direction (Z) between two adjacent radially inner disk-shaped ring electrodes or two adjacent radially outer disk-shaped ring electrodes (E 1,i , E 1,i+1 ; E 2,i , E 2,i+1 ), the following applies: d / b < 1 / 4.

8. The mass spectrometer according to claim 1 or 2, wherein the ion trap has a number N of radially inner disk-shaped ring electrodes (E 1，i ) and a number N of radially outer disk-shaped ring electrodes (E 2，i ), for which the following applies: 10 < N < 200.

9. The mass spectrometer according to claim 1 or 2, wherein the ion trap further comprises: At least one injection device (9) for injecting ions (6) and / or an electron beam (10) into the annular ion storage unit (5).

10. The mass spectrometer according to claim 9, wherein, The at least one injection device (9) is configured to inject ions (6) and / or an electron beam (10) tangentially into the annular ion storage unit (5).

11. The mass spectrometer according to claim 10, wherein, The at least one injection device (9) is configured to inject ions (6) and / or an electron beam (10) tangentially and pulsed into the annular ion storage unit (5).

12. The mass spectrometer according to claim 1, wherein in the mass spectrometer, the control device (3) is at least partially arranged in a volume region (7) surrounded by the annular ion storage unit (5).

13. The mass spectrometer according to claim 1 or 12, wherein in the mass spectrometer, the control device (3) is designed to actuate the radially inner disk-shaped ring electrode (E 1，i ) and / or the radially outer disk-shaped ring electrode (E 2，i ) to generate a corresponding HF storage voltage (V RF，i ) for storing ions (6) in the ring ion storage unit (5).

14. The mass spectrometer according to claim 1 or 12, wherein in the mass spectrometer, the control device (3) is designed to turn an electron beam (10) injected tangentially into the annular ion storage unit (5) along a circular trajectory (11).

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