ACCELERATOR FOR MULTI-PASS MASS SPECTROMETERS

Abstract

Improved pulsed ion sources and pulsed converters are proposed for multi-pass time-of-flight mass spectrometer, either multi-reflecting (MR) or multi-turn (MT) TOF. A wedge electrostatic field 45 is arranged within a region of small ion energy for electronically controlled tilting of ion packets 54 time front. Tilt angle γ of time front 54 is strongly amplified by a post-acceleration in a flat field 48. Electrostatic deflector 30 downstream of the post-acceleration 48 allows denser folding of ion trajectories, whereas the injection mechanism allows for electronically adjustable mutual compensation of the time front tilt angle, i.e. γ=0 for ion packet in location 55, for curvature of ion packets, and for the angular energy dispersion. The arrangement helps bypassing accelerator 40 rims, adjusting ion packets inclination angles α.sub.2, and what is most important, compensating for mechanical misalignments of the optical components.

Claims

1. A mass spectrometer having a pulsed ion accelerator, said pulsed ion accelerator comprising: a plurality of electrodes arranged and configured to generate an ion pulsing region, wherein the pulsed ion accelerator is configured such that ions entering the ion accelerator are initially received in the ion pulsing region; and a plurality of electrodes arranged and configured to generate a wedge-shaped electric field region downstream of said ion pulsing region; wherein the pulsed ion accelerator is configured to apply a pulsed voltage to at least one of said electrodes of the ion pulsing region for pulsing ions out of the ion accelerator, wherein the ions have a time front arranged in a first plane at the time the pulsed voltage is initiated, and wherein the ion accelerator is configured such that the pulsed ions pass through the wedge-shaped electric field region so as to cause the time front of the ions to be tilted at an angle to the first plane; wherein the ion accelerator further comprises a plurality of electrodes arranged and configured to generate an ion acceleration region downstream of the wedge-shaped electric field region for amplifying the time front tilt introduced by the wedge-shaped electric field; and wherein the at least one of said electrodes of the ion pulsing region for pulsing ions out of the ion accelerator is substantially parallel to said electrodes of the ion acceleration region.

2. The mass spectrometer of claim 1, wherein said plurality of electrodes for generating said ion acceleration region are a plurality of parallel electrodes.

3. The mass spectrometer of claim 1, wherein said electrodes for generating said wedge-shaped electric field region are arranged and configured for generating said wedge-shaped electric field region therebetween such that equipotential field lines in the wedge-shaped electric field region are angled to each other so as to form the wedge-shape.

4. The mass spectrometer of claim 1, wherein said electrodes for generating said wedge-shaped electric field region comprise one or more first electrode arranged in a first plane and one or more second electrode arranged in a second plane that is angled to the first plane so as to define the wedge-shaped electric field region between the one or more first electrode and one or more second electrode.

5. The mass spectrometer of claim 1, wherein said electrodes for generating said wedge-shaped electric field region comprise one or more first electrode arranged in a first plane and a plurality of second electrodes arranged in a second plane, wherein the ion accelerator is configured to apply different voltages to different ones of the second electrodes so as to define the wedge-shaped electric field region between the one or more first electrode and the second electrodes, wherein the second plane is parallel to the first plane.

6. The mass spectrometer of claim 5, wherein the pulsed ion accelerator comprises a printed circuit board which provides the second electrodes.

7. The mass spectrometer of claim 1, wherein the electrodes for generating said wedge-shaped electric field region are arranged so that equipotential field lines of the wedge-shaped electric field extend substantially in a first direction and the plurality of electrodes for generating an ion pulsing region are configured to pulse the ions through the wedge-shaped electric field substantially transverse to the equipotential field lines.

8. The mass spectrometer of claim 1, wherein the ion accelerator is arranged and configured to receive ions travelling in a first direction along a first axis that is substantially parallel to equipotential field lines of the wedge-shaped electric field.

9. The pulsed ion accelerator of claim 1, wherein said electrodes of the ion acceleration region are configured to apply a static electric field in the ion acceleration region for accelerating the ions.

10. The pulsed ion accelerator of claim 1, wherein said electrodes of the ion acceleration region are configured to apply an electric field in the ion acceleration region having parallel equipotential field lines for accelerating the ions.

11. The mass spectrometer of claim 1, comprising an ion optical component located downstream of the pulsed ion accelerator which deflects the average ion trajectory of the ions, thereby tilting the angle of the time front of the ions by the ion optical component; and wherein the wedge-shaped electric field region of the pulsed ion accelerator is configured to tilt the time front of the ions passing therethrough so as to at least partially counteract the tilting of the time front by the ion optical device.

12. The mass spectrometer claim 1, wherein said pulsed ion accelerator is one of: (i) a MALDI source; (ii) a SIMS source; (iii) a mapping or imaging ion source; (iv) an electron impact ion source; (v) a pulsed converter for converting a continuous or pseudo-continuous ion beam into ion pulses; (vi) an orthogonal accelerator; (vii) a pass-through orthogonal accelerator having an electrostatic ion guide; or (viii) a radio-frequency ion trap with pulsed ion ejection.

13. The mass spectrometer of claim 1, comprising: a multi-pass time-of-flight mass analyser or electrostatic ion trap having the pulsed ion accelerator, and electrodes arranged and configured so as to provide an ion drift region that is elongated in a drift direction (z-dimension) and to reflect or turn ions multiple times in an oscillating dimension (x-dimension) that is orthogonal to the drift direction.

14. The mass spectrometer of claim 13, wherein: (i) the multi-pass time-of-flight mass analyser is a multi-reflecting time of flight mass analyser having two ion mirrors that are elongated in the drift direction (z-dimension) and configured to reflect ions multiple times in the oscillation dimension (x-dimension), wherein the pulsed ion accelerator is arranged to receive ions and accelerate them into one of the ion mirrors; or (ii) the multi-pass time-of-flight mass analyser is a multi-turn time of flight mass analyser having at least two electric sectors configured to turn ions multiple times in the oscillation dimension (x-dimension), wherein the pulsed ion accelerator is arranged to receive ions and accelerate them into one of the sectors.

15. The mass spectrometer of claim 13, comprising an ion deflector located downstream of said pulsed ion accelerator, and that is configured to back-steer the average ion trajectory of the ions, in the drift direction, thereby tilting the angle of the time front of the ions received by the ion deflector.

16. The spectrometer of claim 15, wherein the wedge-shaped electric field region of the pulsed ion accelerator is configured to tilt the time front of the ions passing therethrough so as to at least partially counteract the tilting of the time front by the ion deflector.

17. The spectrometer of claim 15, wherein the ion deflector is configured to generate a quadrupolar field for controlling the spatial focusing of the ions in the drift direction.

18. The mass spectrometer of claim 1, wherein said electrodes of the ion pulsing region for pulsing ions out of the ion accelerator are substantially parallel to said electrodes of the ion acceleration region, and wherein said electrodes for generating said wedge-shaped electric field region comprises an intermediate electrode tilted at an angle to the electrodes of the ion pulsing and ion acceleration regions so as to define the wedge-shaped electric field.

19. The mass spectrometer of claim 1, wherein said electrodes of the ion pulsing region are configured for pulsing ions in a pulse direction, wherein said pulsed ion accelerator comprises a printed circuit board which provides said electrodes for generating said wedge-shaped electric field region, said electrodes for generating said wedge-shaped electric field region comprise multiple electrode segments (in the pulsing direction) that are interconnected via a resistive chain for generating said wedge-shaped electric field region.

20. A method of mass spectrometry comprising: providing the mass spectrometer as claimed in claim 1; applying the pulsed voltage to the plurality of electrodes for generating said ion pulsing region so as to pulse ions out of the ion accelerator, wherein the ions have a time front arranged in the first plane at the time the pulsed voltage is initiated, and wherein the ions pass through the wedge-shaped electric field region so as to cause the time front of the ions to be tilted at the angle to the first plane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0111] Various embodiments will now be described, by way of example only, and with reference to the accompanying drawings in which:

[0112] FIG. 1 shows prior art U.S. Pat. No. 6,717,132 planar multi-reflecting TOF with gridless orthogonal pulsed accelerator OA;

[0113] FIG. 2 illustrates problems of dense trajectory folding set by mechanical precision of the analyzer of FIG. 1;

[0114] FIG. 3 shows a novel deflector of an embodiment of the present invention, compensated by additional quadrupolar field for controlled spatial focusing;

[0115] FIG. 4 shows a novel wedge accelerator of an embodiment of the present invention, designed for flexible control over the tilt angle of ion packets' time front

[0116] FIG. 5 shows a balanced injection mechanism of an embodiment of the present invention employing the balanced deflector of FIG. 3 and wedge accelerator of FIG. 4 for controlling the inclination angle of ion packets while compensating the time-front tilt;

[0117] FIG. 6 shows numerical examples, illustrating ion packet spatial focusing within an MRTOF with the novel injection mechanism of FIG. 5, and presents a novel ion optical component of an embodiment of the present invention—a beam expander for bypassing detector rims, and demonstrates improved parameters of the exemplary compact MRTOF with resolution R>40,000;

[0118] FIG. 7 shows a numerical example with unintentional ion mirror misalignment—tilt of the ion mirror by 1 mrad, and illustrates how the novel injection mechanism of FIG. 5 helps compensating the misalignment with electrical adjustment of the instrument tuning;

[0119] FIG. 8 shows a sector MTTOF of an embodiment of the present invention with two improvements, one employing the compensated ion injection mechanism similar to FIG. 7, and the second employing a novel method the far-end ion packet steering with deflectors having quadrupolar focusing and defocusing fields of Matsuda plates; and

[0120] FIG. 9 shows alternative embodiments of pulsed ion sources and pulsed converters with novel amplifying wedge accelerating field.

DETAILED DESCRIPTION

[0121] Referring to FIG. 1, a prior art multi-reflecting TOF instrument 10 according to U.S. Pat. No. 6,717,132 is shown having an orthogonal accelerator (OA-MRTOF). The MRTOF instrument 10 comprises: an ion source 11 with a lens system 12 to form a substantially parallel ion beam 13; an orthogonal accelerator (OA) 14 with a storage gap to admit the beam 13; a pair of gridless ion mirrors 16, separated by field-free drift region, and a detector 17. Both OA 14 and mirrors 16 are formed with plate electrodes having slit openings, oriented in the Z-direction, thus forming a two dimensional electrostatic field, symmetric about the XZ symmetry plane (also denoted as s-plane). Accelerator 14, ion mirrors 16 and detector 17 are parallel to the Z-axis.

[0122] In operation, ion source 11 generates continuous ion beam. Commonly, ion sources 11 comprise gas-filled radio-frequency (RF) ion guides (not shown) for gaseous dampening of ion beams. Lens 12 forms a substantially parallel continuous ion beam 13, entering OA 14 along the Z-direction. Electrical pulse in OA 14 ejects ion packets 15. Packets 15 travel in the MRTOF analyser at a small inclination angle α to the x-axis, which is controlled by the ion source bias U.sub.Z.

[0123] Referring to FIG. 2, simulation examples 20 and 21 are shown that illustrate multiple problems of prior art MRTOF instruments 10, if pushing for higher resolutions and denser ion trajectory folding. Exemplary MRTOF parameters were used, including: D.sub.X=500 mm cap-cap distance; D.sub.Z=250 mm wide portion of non-distorted XY-field; acceleration potential is U.sub.X=8 kV, OA rim=10 mm and detector rim=5 mm.

[0124] In the Example 20, to fit 14 ion reflections (i.e. L=7m ion flight path) the source bias is set to U.sub.Z=9V. Parallel ion rays with an initial ion packet length in the z-dimension of Z.sub.0=10 mm and no angular spread Δα=0 start hitting rims of OA 14 and of detector 17. In Example 21, the top ion mirror is tilted by λ=1 mrad, representing realistic overall effective angle of mirror tilt, considering built up faults of stack assemblies, standard accuracy of machining and moderate electrode bend by internal stress at machining. Every “hard” ion reflection in the top ion mirror then changes the inclination angle α by 2 mrad. The inclination angle α grows from α.sub.1=27 mrad to α2=41 mard, gradually expanding central trajectory. To hit the detector after N=14 reflections, the source bias has to be reduced to U.sub.Z=6V. The angular divergence is amplified by mirror tilt and increase the ion packets width to ΔZ=18 mm, inducing ion losses on the rims. Obviously, slits in the drift space may be used to avoid trajectory overlaps and spectral confusion, however, at a cost of additional ionic losses.

[0125] In example 21, the inclination of ion mirror introduces yet another and much more serious problem. The time-front 15 of the ion packet becomes tilted by angle γ=14 mrad in front of the detector. The total ion packet spreading in the time-of-flight X-direction ΔX=ΔZ*γ=0.3 mm limits mass resolution to R<L/2ΔX=11,000 at L=7 m flight path, which is too low (for example compared to the desired R=80,000). To avoid the limitation, the electrode precision has to be brought to non-realistic level: λ<0.1 mrad, translated to better than 10 um accuracy and straightness of individual electrodes.

[0126] Summarizing problems of prior art MRTOF analysers, attempts of increasing flight path require much lower specific energies U.sub.Z of the continuous ion beam and cause larger angular divergences Δα of the ion packets, which induce ion losses on component rims and may produce spectral overlaps. Importantly, small mechanical imperfections strongly affect MRTOF resolution and require unreasonably high precision.

[0127] Referring to FIG. 3, there is proposed a compensated deflector 30 to steer ion rays while overcoming the over-focusing effects of conventional deflectors by incorporating a quadrupolar field (e.g. E.sub.Q=−2U.sub.Qz/H.sup.2) in addition to the ion deflection field (e.g. E.sub.Z=U/H). Conventional ion deflectors formed by opposing plate electrodes cause ions travelling at different positions between them to be deflected at different angles, causing angular dispersion of the ions and downstream over-focusing. The exemplary compensated deflector 30 according to embodiments of the present invention comprises a pair of deflection plates 32 spaced apart by distance H and having a potential difference U therebetween. The deflector 30 has side plates 33 at a different potential U.sub.Q, known as Matsuda plates (e.g. in electrostatic sector fields). The additional quadrupolar field provides the first order compensation for angular dispersion that would be otherwise caused by the deflection plates 32 (i.e. as is problematic with conventional deflectors). The compensated deflector 30 is capable of steering ions by the same angle ψ (relative to its trajectory when entering the deflector) regardless of the Z-coordinate of the ion in the deflector, tilts the time front 31 by angle γ=−ψ, is capable of compensating the over-focusing (e.g. F.fwdarw.∞) while avoiding bending of the time front (such bending being typical for conventional deflectors), or alternatively is capable of controlling the focal distance F independent of the steering angle ψ.

ψ=D/2H*U/K; γ=−ψ=const(z)  (Eq. 1)

[0128] Alternatively, compensated deflectors may be used that are trans-axial (TA) deflectors, e.g. formed by wedge electrodes such as those described herein in relation to the pulsed orthogonal accelerator. By “compensated”, it is meant that the angular dispersion of the ions caused by the ion deflection may be compensated for, e.g. by the quadrupolar field. Embodiments of the invention propose using a first order correction, produced by an additional curvature of TA-wedge. Controlled focusing/defocusing may also be generated by combination of the TA-wedge and TA-lens, arranged separately or combined into a single TA-device. For a narrower range of deflection angles, the compensated deflector may be arranged with a single potential while selecting the size of Matsuda plates or with a segment of toroidal sector.

[0129] Compensated deflectors perform well with MRTOF or MPTOF analysers. The quadrupolar field in the Z-direction generates an opposite focusing or defocusing field in the transverse Y-direction. Below simulations prove that the focal properties of MPTOF analyzers are sufficient to compensate for the Y-focusing of deflectors 30 without any significant TOF aberrations.

[0130] Again referring to FIG. 3, an embodiment 35 with a pair of compensated deflectors 36 and 37 each comprise: a single deflecting plate 32, a shield 38 at drift potential and Matsuda plate 33. Deflectors 36 and 37 may be spaced by one ion reflection from an ion mirror 16. In other words, the ions may undergo only a single ion mirror reflection between passing through deflector 36 and deflector 37. Since Matsuda plates allow achieving both focusing and defocusing, the pair of deflectors 36 and 37 may be arranged for telescopic compression of ion packets 31 to 39 with the factor of compression being given by ΔZ.sub.1/ΔZ.sub.2=C1, achieved at mutual compensation of the time front steering angle γ=0, equivalent to T|Z=0 if adjusting steering angles as ψ.sub.1=ψ.sub.2*C1. Preferably pair of deflectors 36 and 37 provide for parallel-to-parallel ray transformation, which provides for mutual compensation of the time-front curvature, equivalent to T|ZZ=0. Then the compression factor of the second deflector 37 may be considered as C2=1/C1.

γ=0 and T|Z=0 at ψ.sub.1=ψ.sub.2*C1  (Eq. 2)

T|ZZ=0, if C1*C2=1  (Eq. 3)

[0131] Thus, using transformation of the Z-width of ion packets by compensated deflectors 37,37 allows adjusting the overall time front tilt angle after passing through a set of deflectors independent of the summary deflecting angle induced by this set.

[0132] Referring to FIG. 4, a novel orthogonal accelerator (OA) 40 according to an embodiment of the present invention is proposed, incorporating a wedge ion accelerating field in the area of stagnated ion packets, combined with a flat (that is independent of Z coordinate) ion accelerating field, thus forming an “amplifying wedge field”. The amplifying wedge field allows electronically controlling the tilt angle γ of ion packets' time front whilst introducing only a small steering angle ϕ of ion rays (relative to the x-axis).

[0133] An exemplary orthogonal accelerator 40 comprises: a region of pulsed wedge field 45, arranged between a tilted push electrode 44 and ground plate 47 aligned with the Z-axis; and a flat DC accelerating field 48 formed by electrodes parallel to the Z-axis. Field 48 may have accelerating and decelerating regions for producing low time spread and spatial ion focusing of ion packets (e.g. in the XY-plane), however, all equi-potentials of field 48 may stay parallel to the Z-axis.

[0134] In operation, a continuous ion beam 41 enters along the Z-axis at specific ion energy U.sub.Z, e.g. defined by voltage bias of an upstream RF ion guide. Preferably ion beam angular divergence, spatial expansion and beam initial position are controlled by some radial confinement means that may be selected, for example, from the group of: (i) a radiofrequency rectilinear multipolar ion guide; (ii) an electrostatic quadrupolar ion guide with ion beam compression in the X-direction; (iii) an electrostatic periodic lens; and (iv) proposed in a co-pending application, an electrostatic ion guide with quadupolar field being spatially alternated along the Z-axis. An electrical pulse may be applied periodically to the push plate 44, ejecting a portion of the beam 41 through an aperture in electrode 47, thus forming an ion packet with starting time-front 42, which crosses a starting equipotential 46 that is tilted at the angle λ.sub.0 to the x-axis. Ions start with zero mean energy in the X-direction K=0, at the exit of wedge field 45 ions gain specific energy K.sub.1 and at the exit of DC field 48 gains the energy K.sub.0. Assuming small angles λ.sub.0 of equipotential 46 (in further examples 0.5 deg), beam thickness of at least ΔX>1 mm and moderate ion packet length (examples use Z.sub.0=10 mm), the λ.sub.0 tilt of starting equipotential 46 produces negligible corrections onto energy spread of ions in the x-direction ΔK of ion packet 49.

[0135] By applying trivial mathematics a non-expected and previously unknown result was arrived at: in accelerator 40 with amplifying wedge accelerating field, the time front tilt angle relative to the z-axis (γ) and the ion steering angle ϕ=introduced by the wedge field are controlled by the energy factor K.sub.0/K.sub.1 as:

γ=2λ*(K.sub.0/K.sub.1).sup.0.5=2λ*u.sub.0/u.sub.1  (Eq. 4)

ϕ=2λ/3*(K.sub.1/K.sub.0).sup.0.5=2λ/3*u.sub.1/u.sub.0  (Eq. 5)

i.e. γ/ϕ=3K.sub.0/K.sub.1>>1  (Eq. 6)

[0136] where K.sub.1 and K.sub.0 are mean ion kinetic energies at the exit of the wedge field 45 (index 1) and at the exit of flat field 48 (index 0) respectively, and u.sub.1 and u.sub.0 are the corresponding mean ion velocities.

[0137] Thus, novel accelerators with amplifying wedge field allow (i) operating with (e.g. continuous) ion beams introduced along the Z-axis, which allows convenient instrumental arrangements; (ii) tilting ion packets time front to a substantial angle γ, which may then be used for compensation of the time-front tilt in one or more ion deflector; (iii) controlling tilt angle electronically, either by adjusting the pulse potential or by minor steering of the (e.g. continuous) ion beam between various starting equipotential lines.

[0138] Again referring to FIG. 4, similar embodiment 40TR is proposed for an ion trap converter, having the same (as embodiment 40 OA) reference numbers for accelerator components. The trap 40TR may be arranged for ion through passage or for ion trapping in the Z-direction, where 41 is either an ion beam or an ion cloud correspondingly. In both cases one of the same (as in 40OA) means for radial ion confinement may be used, for example: (i) a radiofrequency rectilinear multipolar ion guide; (ii) an electrostatic quadrupolar ion guide with ion beam compression in the X-direction; (iii) an electrostatic periodic lens; or (iv) proposed in a co-pending application, an electrostatic ion guide with quadupolar field being spatially alternated along the Z-axis.

[0139] Ion injection into an MRTOF analysers may be improved by using higher energies of continuous ion beam for improving the ion beam admission into an orthogonal accelerator (OA) and for reducing angular divergence of ion packets in the MRTOF analyser. For higher MRTOF resolution, ion trajectories may be compact folded by using back steering of ion packets, achieved with a deflector. To compensate for the time front tilt produced by the deflector, it is proposed to use an amplifying wedge accelerating field such as that described above in the OA.

[0140] Referring to FIG. 5, embodiments 50 of the ion injection mechanism into the MRTOF analyser of embodiments of the present invention comprise: a planar ion mirror 53 with 2D XY-field, extended in the Z-direction; an orthogonal accelerator 40 with “flat” DC acceleration field 48 aligned with Z-axis and a wedge accelerating field 45 produced by tilted push plate 44; and a compensated deflector 30, located along the ion path and after first ion mirror reflection. Deflector 30 may correspond to the one of FIG. 3 and the accelerator 40 may correspond to one of those in FIG. 4.

[0141] The operation of embodiment 50 is illustrated by simulation example 51, showing time fronts 54 and 55 crossing ion rays. Continuous ion beam 41 at specific energy (e.g. U.sub.Z=57V) propagates along the Z-axis to cross starting (K=0) equipotential 46, which is tilted at the angle λ.sub.0 (e.g. λ.sub.0=0.5 deg) to the z-axis, with push plate 44 being tilted by 1 deg to the z-axis. Pulsed wedge field 45 accelerates ions to mean energy K.sub.1 (e.g. K.sub.1=800V), and flat field 48 to K.sub.0 (e.g. K.sub.0=8 kV), thus producing an amplifying factor K.sub.0/K.sub.1≅10. The amplifying wedge tilts the ion packets time front 54 at a large angle [e.g. γ=2λ.sub.0*(K.sub.0/K.sub.1).sup.0.5≅6λ.sub.0], while having a small deflection effect on the trajectory of the ion ray relative to the x-axis (as compared to if a conventional non-wedged and untilted OA was used). For example, the OA may result in an angle α.sub.1=α.sub.0−ϕ=4.7 deg (where ϕ≅0.2 deg is the deflection angle caused by the wedged field). In other words, the ion rays are inclined almost at natural inclination angle α.sub.0=(U.sub.Z/U.sub.X).sup.0.5=4.9 deg.

[0142] After the first ion mirror reflection, deflector 30 steers ion rays by angle ψ=−γ=−3.2 deg (in the x-z plane), thus reducing the inclination angle to the x-direction to α.sub.2=α.sub.1−ψ=1.5 deg, while aligning the ion packets time front 55 parallel with the Z-axis, i.e. γ=0. Much higher specific energies of the ion beam (e.g. U.sub.Z=57V as compared to 9V in the prior art) improves the ion admission into the OA and reduces the angular divergence Δα of ion packets, allowing denser folding of ion trajectories at smaller inclination angles, e.g. here at α.sub.2=α.sub.1−ψ=1.5 deg (as compared to the natural inclination angle α.sub.0=4.9 deg).

[0143] Table 1 below summarizes the equations for angles within the individual deflector 30 and wedge accelerator 40. Table 2 below presents conditions for compensation of the first order time-front tilt (T|Z=0) and of the chromatic spread of Z-velocity (α|K=0). It is of significant importance that both compensations are achieved simultaneously. This is a new finding by the inventor. The pair of wedge accelerator 40 and deflector 30 compensate multiple aberrations, including the first order time front tilt, the chromatic angular spread and, accounting focusing properties of gridless ion mirrors in example 51, the angular and spatial spreads of ion packets in the Y-direction.

TABLE-US-00001 TABLE 1 Chromatic dependence of Time-front Rays Steering Z-velocity Tilt Angle Angle d(Δw)/dδ Wedge Accelerator [00001]${\gamma }_0^{\left(OA\right)}=2{\lambda }_0\sqrt{\frac{K_0}{K_1}}$ [00002]${\phi }^{\left(\mathrm{OA}\right)}\approx +\frac{2{\lambda }_0}{3}\sqrt{\frac{K_1}{K_0}}$ [00003]${\lambda }_0{u}_0\sqrt{\frac{K_0}{K_1}}$ Deflector −ψ.sub.0 ψ.sub.0 [00004]$-\frac{1}{2}{u}_0{\psi }_0$

TABLE-US-00002 TABLE 2 Condition for the 1st order Time- Condition for Compensating front Tilt Compensation Chromatic Spread of Z-velocity Wedge Accelerator + Deflector [00005]$2\lambda \sqrt{\frac{K_0}{K_1}}={\psi }_0$ [00006]$2\lambda \sqrt{\frac{K_0}{K_1}}={\psi }_0$

[0144] Referring back to FIG. 5, an alternative embodiment 52 differs from embodiment 50 by tilting DC acceleration field 48 relative to the z-axis by angle λ.sub.0 for aligning ion beam 41 parallel with starting equi-potential 46. Although the angles are shifted, however, the above described compensations survive.

[0145] Referring to FIG. 6, the compensated mechanism 50 of ion injection into the MRTOF analyser has been verified in ion optical simulations 60, 62, 64 and 66. An exemplary MRTOF analyser comprises an ion mirrors 53 with cap-cap distance in the x-dimension of D.sub.X=450 mm and useful width in the z-dimension of D.sub.Z=250 mm, operating at acceleration potential in the x-dimension of U.sub.X=8 kV. Examples of FIG. 6 employ compensated deflector 30 with the Matsuda plates of FIG. 3, amplifying wedge accelerator 40 of FIG. 4, dual deflector 30D with Matsuda plates, and TOF detector 17, assumed having DET=1.5 ns Gaussian signal spread. Similar to example 51, continuous ion beam of μ=1000 amu with ΔX=1 mm width and 2 deg full angular divergence enters wedge OA at U.sub.Z=57V specific (per charge) energy and ΔU.sub.Z=0.5V energy spread.

[0146] Example 60 illustrates spatial focusing of ion rays 61 for ion packets having an initial width in the z-dimension of Z.sub.0=10 mm, while not accounting angular spread of ion packets Δα=0 at ΔU.sub.Z=0 and not accounting relative energy spread of ion packets δ=ΔK/K=0 at ΔX=0. The chosen position of deflector 30 improves the ion packets bypassing of the deflector 30. The Matsuda plate voltage of the deflector 30 is electrically adjusted for geometrical focusing of ion packets onto the detector, which allows a denser folding of ion rays in MRTOF at α.sub.2=1.5 deg.

[0147] Example 62 illustrates angular divergence of ion rays 63 at ΔU.sub.Z=0.5V, while not accounting ion packets width Z.sub.0=0 and energy spread δ=0. Dual compensated deflector 30D (another novel component for MRTOF) helps spreading ion rays in-front of the detector 17 for bypassing the detector rims (here 5 mm).

[0148] Example 64 illustrates the (predicted by Table 4) simultaneous compensation of chromatic angular spread α|δ=0 and of the first order time-front tilt γ=0 at δ=0.05, ΔU.sub.Z=0, and Z.sub.0=0. Dark areas along the ion trajectories show lengths of ion packets due to the energy spread at equally spaced time intervals, and in particular time focusing after each reflection and at the detector.

[0149] Example 66 illustrates overall mass resolution R.sub.M=47,000 achieved in a compact 450×250 mm analyzer while accounting all realistic spreads of ion beam and ion packets, so as DET=1.5 ns time spread. The embodiment satisfies a goal of R>40,000 for resolving major isobars for μ=m/z<500 in GC-MS instruments.

[0150] Apparently, the injection mechanism 50 has a built-in and not yet fully appreciated virtue—an ability to compensate for mechanical imperfections of the MRTOF analyser by electrical tuning of the instrument, including adjustment of ion beam energies U.sub.Z, the pulse voltage on push plate 44, deflector 30 steering, or steering of continuous ion beam 41 to fit different equi-potentials 46.

[0151] Referring to FIG. 7, there is presented a simulation example 70, employing the MRTOF analyzer of FIG. 6 with D.sub.X=450 mm, D.sub.Z=250 mm, and U.sub.X=8 kV. The example 70 is different from 60 by introducing a Φ=1 mrad tilt of the entire top mirror 71, representing a typical non intentional mechanical fault at manufacturing. If using the tuned settings of FIG. 6, resolution drops to 25,000 as shown in the graph 74. The resolution may be partially recovered to R=43,000 as shown in icon 75 by increasing the source bias and specific energy of continuous ion beam from U.sub.Z=57V to U.sub.Z=77V, and by retuning deflectors 30 and 30D. Example 70 shows ion rays after the compensation when accounting for all realistic ion beam and ion packet spreads, similar to FIG. 6. Thus, the proposed injection scheme 50 into a compact MRTOF allows compensating for moderate mechanical misalignments and recovering MRTOF resolution by electrical adjustments.

[0152] Referring to FIG. 8, an embodiment of a sector MTTOF analyser 80 of the present invention is shown, together with simulation examples 86, 87 and 88. The analyser comprises: sectors 82 and 83, separated by a drift space; an orthogonal accelerator 40 of FIG. 4, a compensated deflector 30 of FIG. 3; and a pair of compensated deflectors 84 and 85, similar to 30, however having different voltage settings of their Matsuda plates.

[0153] Electrodes of sectors 82 and 83 are extended in the Z-direction to form two-dimensional fields in the XY-plane, i.e. they do not have laminating fields of the prior art. Sectors 82 and 83 have different radii and are arranged for isochronous cycled trajectory 81 (well seen in the view 86) with at least second order time per energy focusing, as described in WO (RMS).

[0154] As shown in view 87, continuous ion beam 41 propagates along the Z-axis at elevated specific energy U.sub.Z (expected from 20 to 50V). A compensated ion injection mechanism into MTTOF 80 is arranged with a wedge accelerator 40 and compensated deflector 30, similar to injection mechanism 50, described in FIG. 5. Accelerator 40 with amplifying wedge accelerating field tilts the time front 89 of ion packets to compensate for the time front tilt of the downstream deflector 30, thus arranging dense trajectory folding at small inclination angles α.sub.2 while using relatively higher injection energies U.sub.Z. Ion packets bypass the OA 40 at larger angle α.sub.1 and then advance in the drift Z-direction within MTTOF along the spiral trajectory 81 at reduced inclination angle α.sub.2. Thus, a combination of wedge accelerator and of compensated deflector is well suitable for sector MTTOF analysers.

[0155] Embodiment 80 presents yet another novel ion optical solution—a compensated reversing of ion trajectories in the drift Z-direction. The idea of time front compensation after reversing is similar to that shown in arrangement 35 of FIG. 3. The reversing mechanism is arranged with a pair of focusing and defocusing deflectors 84 and 85, best seen and explained in simulation example 88, for clear view expanded in the Z-direction. Ion packets reach far Z-end of the sector analyzer at an inclination angle α.sub.2. Deflector 84 with Matsuda plates is set for increasing the inclination angle to α.sub.3 while focusing the packet Z-width within deflector 85. Deflector 85 is set to reverse ion trajectory with deflection for −2α.sub.3 angle and defocuses the packet from Z.sub.3 to Z.sub.2 by using Z-defocusing quadrupolar field of Matsuda plates in deflector 85. The focusing factor Z.sub.3/Z.sub.2 and deflection angles are arranged as 2Z.sub.3*α.sub.3=Z.sub.2(α.sub.3−α.sub.2) to mutually compensate for the time-front tilts, as illustrated with simulated dynamics of the time front 89. The proposed method of compensated reversing of ion trajectories is suitable for both MRTOF and MTTOF analyzers.

[0156] Referring to FIG. 9, exemplary embodiments 90, 92, 94, 96 and 98 of the present invention illustrate a variety of alternative pulsed ion sources and pulsed converters with amplifying wedge field 45, arranged for electronically adjustable tilt of time-fronts 54. All examples comprise a wedge field region 45, arranged within the region of small ion energy, and a flat post-acceleration field 48 for amplification of the tilt angle γ of time-front 54, preferably accompanied with notably smaller steering angle ϕ of ion trajectories. The time front tilt γ may be arranged for compensation of the time front steering associated with the downstream trajectory steering for angle ψ, about matching the angle γ for mutual compensation. Similar to previous drawings, ion starting equi-potentials are denoted as 46 and compensated deflectors are denoted by 30.

[0157] Deflectors 30 may be arranged anywhere downstream of the accelerator, which is illustrated by dashed ion rays between accelerator and deflector 30. However, to reduce the effect of ion packet angular divergence on compensation of time-front tilt, it is preferable to keep deflector 30 either immediately after the accelerator or after the first ion mirror reflection, or after the first electrostatic sector turn, or within the first full ion turn.

[0158] Example 90 presents an alternative spatial arrangement of the wedge accelerating field 45. An intermediate electrode 91 is tilted to produce the wedge at earlier stages of ion acceleration, though not immediately at ion starting point. Adjusting the potential of electrode 91 allows controlling the time front tilt angle γ electronically.

[0159] Example 92 presents an arrangement with an intermediate printed circuit board 93, having multiple electrode segments (in the x-direction) that are interconnected via a resistive chain for generating a wedge field structure similar to that in embodiment 90. The PCB embodiment 92 may provide a yet wider range of γ electronic tuning than 90.

[0160] Example 94 illustrates an application of the wedge accelerator to pulsed EI sources. Example 94 comprises an electron gun 95 and magnets B for controlling electron beam direction. Optionally, magnets may be tilted to align the electron beam with the tilted equipotential 46. Diverging electrodes within the EI source reduce the risk of electrode contamination by electron bombardment. Ions are produced by electron impact and are stored within the space charge field of the electron beam. Periodically electrical pulses are applied to tilted electrode 44. Example 94 provides compensated steering of ion rays past EI source, e.g. in order to bypass the accelerator and to adjust the inclination angle α of ion trajectories within an MRTOF or MTTOF analyser. The Matsuda plate potential in deflector 30 may be adjusted to control the ion packet spatial focusing.

[0161] Example 96 presents the application of the wedge accelerator to radio-frequency (RF) trap converters with radial ion ejection, known for their high (up to unity) duty cycle of pulsed conversion. The converter comprises side electrodes 97 at RF signal. The structure of electrodes 97 is better seen in the XY-plane. Ions are injected into the trap axially (in the x-direction) and are retained aligned with electrode 97 by the confining quadrupolar RF field of electrodes 97. In one (through) mode, the beam may propagate along equipotential 46 at small energy. In another (trapping) mode ions may be slowly dampened by gas at moderate mid-vacuum pressure (e.g. around 1 mTorr within several ms time). Ion packets are periodically ejected by energizing push plate 44. Tilting of push plate 44 controls the time-front tilt γ, which may be produced for compensating the downstream steering of time fronts by deflector 30. Example 96 provides compensated steering of ion rays past radial traps, e.g. in order to bypass the trap and to adjust the inclination angle α of ion trajectories within MRTOF or MTTOF analysers. The Matsuda plate potential in deflector 30 may be adjusted to control the ion packet spatial focusing. Note that to compensate T|ZZ aberrations at focusing in deflector 30 of substantially elongated ion packets, an additional compensating field curvature may be generated within accelerating field 45, either by curving electrode 97, or by curving of other trap electrodes, or by auxiliary fringing field, penetrating through or between trap electrodes.

[0162] Example 98 presents the application of the wedge accelerator to surface ionization methods, such as MALDI, SIMS, FAB, or particle bombardment, defined by the nature of primary beam 99—either photons, or pulsed packets of primary ions, or neutral particles or glow discharge or heavy particles or charged droplets. Electrode 44 may be energized static or pulsed, depending on the overall arrangement of prior art ionization methods. It is assumed that the exposed surface is relatively wide, either for imaging purposes or for improved sensitivity, so that ion packet width does affect the time-of-flight resolution, if ion packets are steered without compensation. Arranging wedge accelerator field 45, for example by tilting the target 44, is used here for compensating the time front tilt steering or for the spatial focusing of ion packets, or as a part of the surface imaging ion optics. Benefits of example 98 may be immediately seen by experts such as: (a) steering of ion packets allows the ion source bypassing and denser folding of ion trajectory in MPTOF analysers; (b) focusing by deflector 30 improves sensitivity; (c) unintentional tilt of the target 44 or some uneven topology of the sample on the target may be compensated electronically; (d) ion steering off the source axis allows an orthogonal arrangement of the impinging primary beam 99A; (e) compensated edge and curvature of accelerating field may be used for improving stigmatic properties of the overall imaging ion optics. Some further benefits are likely to be found, since the scheme allows fine and electronically adjustable control over the spatial focusing and the time-of-flight aberrations of the surface ionizing sources.

[0163] Annotations

[0164] Coordinates and Times:

x,y,z—Cartesian coordinates;
X Y, Z—directions, denoted as: X for time-of-flight, Z for drift, Y for transverse;
Z.sub.0—initial width of ion packets in the drift direction;
ΔZ—full width of ion packet on the detector;
D.sub.X and D.sub.Z—used height (e.g. cap-cap) and usable width of ion mirrors
L—overall flight path
N—number of ion reflections in mirror MRTOF or ion turns in sector MTTOF
u—x-component of ion velocity;
w—z-component of ion velocity;
T—ion flight time through TOF MS from accelerator to the detector;
ΔT—time spread of ion packet at the detector;

[0165] Potentials and Fields:

U—potentials or specific energy per charge;
U.sub.Z and ΔU.sub.Z—specific energy of continuous ion beam and its spread;
U.sub.X—acceleration potential for ion packets in TOF direction;
K and ΔK—ion energy in ion packets and its spread;
δ=ΔK/K—relative energy spread of ion packets;
E—x-component of accelerating field in the OA or in ion mirror around “turning” point;
μ—m/z—ions specific mass or mass-to-charge ratio;

[0166] Angles:

α—inclination angle of ion trajectory relative to X-axis;
Δα—angular divergence of ion packets;
γ—tilt angle of time front in ion packets relative to Z-axis
λ—tilt angle of “starting” equipotential to axis Z, where ions either start accelerating or are reflected within wedge fields of ion mirror
θ—tilt angle of the entire ion mirror (usually, unintentional);
φ—steering angle of ion trajectories or rays in various devices;
ψ— steering angle in deflectors
ε—spread in steering angle in conventional deflectors;

[0167] Aberration Coefficients [0168] T|Z, T|ZZ, T|δ, T|δδ, etc;

[0169] indexes are defined within the text

[0170] Although the present invention has been describing with reference to preferred embodiments, it will be apparent to those skilled in the art that various modifications in form and detail may be made without departing from the scope of the present invention as set forth in the accompanying claims.