FOCAL PLANE DETECTOR

Abstract

A detection device for detecting charges particles. The active area of the detector extends along a principal direction over several centimeters and up to 1 meter or more. This allows for its use as a focal plane detector for a mass spectrometer device, allowing to record all mass-to-charge ratios provided by the spectrometer in parallel and within a reduced acquisition time.

Claims

1. A detection device for detecting charged particles or radiation, the detection device comprising a front area extending longitudinally along a principal direction, the front area comprising an arrangement of entry faces of at least two microchannel plate (MCP) assemblies, wherein each of the MCP assemblies is configured for receiving charged particles, neutral particles or electromagnetic radiation that impinge on their respective entry faces and for generating a corresponding amplified detection signal on a respective opposite exit face, the device further comprising at least one read-out anode for collecting said amplified detection signals; the anode being arranged at a distance to, and in parallel with the respective exit faces of said MCP assemblies, wherein the at least two MCP assemblies are arranged side by side along said principal direction, and wherein a gap of at most 1 mm separates the entry faces of any two adjacent MCP assemblies, wherein the detection device further comprises biasing means configured for applying a common electric potential to the respective exit faces of all of the MCP assemblies, and for applying individual electric potentials to the respective entry faces of each of the MCP assemblies.

2. The detection device according to claim 1, wherein the entry faces of the at least two MCP assemblies extend over an aggregated distance of at least 15 cm.

3. The detection device to claim 1, wherein the detection device comprises one dedicated read-out anode for each of the MCP assemblies, and wherein said read-out anode extends along the exit face of the respective MCP assembly.

4. The detection device according to claim 3, wherein the read-out anode of each of the MCP assemblies comprises at least one of delay-line anodes, pixelated anode arrays, resistive anodes, shaped anodes, and single anodes.

5. The detection device according to claim 3, wherein a gap of at most 1 mm width separates the respective exit faces of any two adjacent MCP assemblies.

6. The detection device according claim 5, wherein the gap separating any two adjacent read-out anodes has a same width as a gap separating the entry and exit faces of the corresponding two adjacent MCP assemblies.

7. The detection device according to claim 1, wherein all of the MCP assemblies have a same channel size and same amplification gain characteristics.

8. The detection device according to claim 1, wherein all of the MCP assemblies have a same width extending perpendicularly to said principal direction.

9. The detection device according to claim 1, wherein said front area consists of the entry faces of said MCP assemblies.

10. The detection device according to claim 1, wherein said biasing means are configured for applying an electric potential difference between the respective entry and exit faces of each of the MCP assemblies.

11. The detection device according to claim 10, wherein the biasing means are configured for applying a positive or negative floating electric potential to the front area.

12. The detection device according to claim 1, wherein the MCP assemblies comprise at least one of a stacked assembly of a plurality of multiple MCP devices, a chevron assembly, and a Z-stacked assembly.

13. The detection device according to claim 1, wherein said charged particles comprise ions.

14. The detection device according to claim 1, wherein said electromagnetic radiation comprises visible light.

15. A mass spectrometer for dispersing ions along a focal plane in accordance with their mass/charge ratio, the spectrometer comprising the detection device of claim 1 that is arranged on said focal plane so that said dispersed ions impinge on the front area of the detection device.

16. The mass spectrometer device according to claim 15, wherein the mass spectrometer device is a Mattauch-Herzog type device.

17. The mass spectrometer device according to claim 15, wherein the mass spectrometer device is configured for being used in a floating configuration.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Several embodiments of the present invention are illustrated by way of figures, which do not limit the scope of the invention, wherein:

[0031] FIG. 1 is a schematic illustration of a top view of a detection device in accordance with a preferred embodiment of the invention;

[0032] FIG. 2 is a schematic illustration of a front view of a detection device in accordance with a preferred embodiment of the invention;

[0033] FIG. 3a is a schematic illustration of a stacked chevron type microchannel plate assembly as used in a detection device in accordance with a preferred embodiment of the invention;

[0034] FIG. 3b is a schematic illustration of a stacked Z-type microchannel plate assembly as used in a detection device in accordance with a preferred embodiment of the invention;

[0035] FIG. 4 is a schematic illustration of a top view of a detection device in accordance with a preferred embodiment of the invention;

[0036] FIG. 5 is a schematic illustration of a mass spectrometer device in accordance with a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0037] This section describes features of the invention in further detail based on preferred embodiments and on the figures, without limiting the invention to the described embodiments. Unless otherwise stated, features described in the context of a specific embodiment may be combined with additional features of other described embodiments. Throughout the description, similar reference numerals will be used for similar or the same concept across different embodiments of the invention. For example, references 100 and 200 each describe a detection device in accordance with the invention, but in two respective embodiments thereof.

[0038] The description puts focus on those aspects of the proposed detector device that are relevant for understanding the invention. It will be clear to the skilled person that the device also comprises other commonly known aspects, such as for example an appropriately dimensioned power supply, or a mechanical holder frame for holding the various elements of the device in their respectively required positions, even if those aspects are not explicitly mentioned.

[0039] FIG. 1 shows a top view of a cut through a detection device 100 in accordance with a preferred embodiment of the invention. For the sake of explaining the various concepts, the illustrated dimensions are not at scale and some distances have been exaggerated for easier appreciation of the figure. The device comprises a front area 102 that extends along a principal direction A, defining the “single” direction along which the one-dimensional detection device 100 extends. The device further comprises a plurality of microchannel plate, MCP, assemblies 110 arranged side by side along the principal direction. The front faces 112 of the MCP assemblies make up the front area 102 of the device 100, save for the physical gaps or interstices G that separate the MCP assemblies. In the example shown, three MCP assemblies are used. Of course, other pluralities are possible without departing from the scope of the present invention. Depending on the available MCP sizes and on the desired total length L (e.g., from 15 to 100 cm) of the detection area, an appropriate number of MCP assemblies is integrated into the device 100. In the example of FIG. 1, two MCP assemblies extending over a common length L110 are arranged side by side, while a third MCP assembly extends over a shorter length 110′, thereby providing a shorter entry face. The depth H of each MCP assembly is preferably the same, so that the amplification characteristics are uniform along the length L of the detector. By way of a non-limiting example, the depth His typically of about 0.5 to 1 mm for a single MCP assemblies, 1-2 mm for a Chevron type stacked MCP assembly, and 1.5-3 mm for a Z-stacked type MCP assembly. Ideally, the gaps G are of neglectable size, but they should in practice not be larger than 1 mm. Indeed, a charged particle (i.e. ions, electrons) or neutral particle (i.e. atoms, molecules) or electromagnetic radiation (i.e. light, X-ray, etc. . . . ) 10 impinging on the front face 102 can only be detected if it hits a front face 112 of one of the MCPs, the gaps G forming dead spots in the detection range. Preferably, the gaps between any two adjacent MCP assemblies are of uniform size. Each impinging charged particle or photon generates a corresponding amplified signal at the exit face 114, 114′ of the MCP assembly whose entry face 112, 122′ it hit. The gap G extends to the respective exit faces of two adjacent MCP assemblies. In order to detect the amplified signals, at least one read-out anode 120 is arranged in parallel to the exit faces 114, 114′ of the MCP assemblies 110, at a distance d (typically but not limited to 2-5 mm) therefrom. The read-out anode(s) is/are operatively coupled to non-illustrated data processing means, which store the detection counts read by the anode(s), together with their position along the length L of the detector. By doing so, spectral data of the incoming charged particles, neutral particles or electromagnetic radiation 10 is produced. The spectral data is preferably stored in a memory element for further processing thereof, or for displaying the same on a display device. The processing means may for example comprise a data processor having read/write access to a memory element. While the data processor may comprise specific circuitry designed for reading out the anode(s) 120, it may alternatively comprise a programmable processor, programmed to perform this task by an appropriate software code. All described components are held in place by a holder frame 130 which may for example be a machined frame.

[0040] FIG. 2 provides a frontal view on the front area 102 and on the entry faces 112 of the MCP assemblies 110 of the device 100 as shown from the top on FIG. 1. It is appreciated that each MCP extends along a similar or equal width W in the direction that is perpendicular to the principal direction A of the device. The width W may range from millimetres to centimetres, for example from 3 mm to 15 cm.

[0041] A typical microchannel plate, MCP, is composed of 10.sup.4 to 10.sup.7 miniature electron multipliers whose typical diameters are in the range from 10 to 100 μm. Each channel acts as an individual electron multiplier, which can detect a single ion, electron, atom, molecule or photon. The MCP is typically fabricated from a high resistive material such as lead glass. The front side and rear side of the MCP are metallized electrodes to which a typical voltage difference of about 1000V is applied through appropriate biasing means, such as a source of electricity. When a single energetic particle hits a channel surface, it creates one or more secondary electrons, which are accelerated into an MCP channel by the applied voltage. Each of these secondary electrons can release two or more secondary electrons when hitting the channel wall again. This process is cascaded along the channel Therefore, a single energetic particle hitting a channel creates a cascade of electron emission along the channel, resulting in an electron cloud of at least 10.sup.4 electrons at the output of the channel. An anode placed behind the MCP can electronically detect the electron cloud to register each single event hitting the MCP. An MCP assembly 110 such as those depicted in FIG. 1 may comprise a single microchannel plate, or a stacked assembly thereof.

[0042] Each MCP typically provides an amplification gain of 10.sup.4. In most of the applications, a higher gain (10.sup.6-10.sup.7) is required. Several stacked MCPs can be used to achieve such a high gain. When using stacked MCPs, the channels of each MCP are tilted 8°-15° against the MCP normal. The channels of the following MCPs are tilted in the opposite directions in order to avoid the ion feedback from the successive MCPs. The combination of two MCPs 111, 111′ in an assembly 110 in this configuration is called the Chevron assembly, see FIG. 3a, while the combination of three MCPs 111, 111′, 111″ in an assembly 110 is called the Z-stack assembly, see FIG. 3b. The type of MCP assembly that is integrated to the device 100 depends on the required amplification gain. However, within one device 100, MCP assemblies of the same channel size and amplification gain are used to maintain uniform detection efficiency and spatial resolution along the entire detector.

[0043] Different types of anodes 120 may be considered for collecting the electrons leaving the MCP assemblies 110. The first type is a single anode, which is typically a single metal plate placed behind the MCP. This anode plate collects total number of electrons leaving the entire MCPs and therefore detects the total signal intensity hitting the MCPs (analog current or number of particles). The second type of anode is related to the position sensitive anode readouts, which can return both the position and the intensity of multiple events hitting the MCPs. Different types of position sensitive anode readout are currently used for the MCP-based detectors such as delay line, DL, anode, resistive anode, pixelated anode array, shaped anode, single anode, etc. . . . . Integrated array detectors, which are fabricated and coupled with the electronic circuits into a chip-type packaging for direct charge detection can also be used as read-out anodes in combination with the MCP assemblies. In this case, they are all referred as pixelated anode arrays. Several approaches to this type of detector have been developed including active pixel arrays, micro faraday cup arrays and micro faraday strip arrays.

[0044] FIG. 4 shows a top view of a cut through a detection device 200 in accordance with a preferred embodiment of the invention. For the sake of explaining the various concepts, the illustrated dimensions are not at scale and some distances have been exaggerated for easier appreciation of the figure. The device comprises a front area 202 that extends along a principal direction A. As in the previously described embodiment, the device further comprises a plurality of microchannel plate, MCP, assemblies 210 arranged side by side along the principal direction. The front faces 212 of the MCP assemblies make up the front area 202 of the device 200, save for the physical gaps or interstices G that separate the MCP assemblies. In the example shown, three MCP assemblies are used. Of course, other pluralities are possible without departing from the scope of the present invention. Depending on the available MCP sizes and on the desired total length L (e.g. from 15 to 100 cm) of the detection area, an appropriate number of MCP assemblies is integrated into the device 200. In the example of FIG. 4, two MCP assemblies extending over a common length L210 are arranged side by side, while a third MCP assembly extends over a shorter length 210′, thereby providing a shorter entry face. The depth H of each MCP assembly is preferably the same, so that the amplification characteristics are uniform along the length L of the detector. Ideally, the gaps G are of neglectable size, but they should in practice not be larger than 1 mm. Indeed, a charged particle (i.e. ions, electrons) or photon 10 impinging on the front face 202 can only be detected if it hits a front face 212 of one of the MCPs, the gaps G forming dead spots in the detection range. Preferably, the gaps between any two adjacent MCP assemblies are of uniform size. Each impinging charged particle or photon generates a corresponding amplified signal at the exit face 214, 214′ of the MCP assembly whose entry face 212, 222′ it hit. The gap G extends to the respective exit faces of two adjacent MCP assemblies. In order to detect the amplified signals, one dedicated read-out anode 220, 220′ for each MCP assembly 210, 210′ is arranged in parallel to the respective exit faces 214, 214′ of the MCP assemblies 210, in alignment therewith and at a distance d therefrom. All described components are held in place by a holder frame 130 which may for example be a machined frame.

[0045] Each MCP segment 210, 210′ combined with its anode 220, 220′ acts as an individual detector element. There are two main advantages of this configuration over the use of a single anode. Firstly, it helps to maximize the uniformity along the overall detector by adjusting the individual gain of each MCP to achieve the same detection efficiency of each anode. Secondly, it improves the overall dynamic range and count rate of the detector, which is typically limited by the anode readout. Here, the overall dynamic range and count rate are multiplied by the number of the anode readouts compared to those of each individual anode. Different anode types can be combined in one detector 200, including DL anode, resistive anode, pixelated anode array, single anode, etc. . . . . Each anode is selected in such a way that it is optimized for applications in its mass range. This allows for leveraging the strengths of different anode readout technologies in one detector device 200. For example, an integrated array like micro-faraday strip array can be selected for a mass range where high mass resolution (and therefore high spatial resolution of the detector (below 50 μm) is needed while high sensitivity is not required. On the other hand, the DL anode can be selected for the mass ranges where high sensitivity is needed with lower required spatial resolution.

[0046] In all the disclosed embodiments, the MCP assemblies are located close to each other, having a gap of at most 1 mm in between themselves along the main direction. If a common electric potential would be applied on the front/entry faces of each MCP assembly, and different electric potentials would be applied on the back/exit faces of MCPs, then a large field distortion would be generated around the gap separating the exit faces of neighbouring MCP assemblies, thereby creating a large detection dead-zone. Biasing a common potential on the exit faces of all MCP assemblies solves this issue. Therefore, in all the embodiments described herein, the biasing voltage differences between the entry and exit faces of the MCP assemblies can be independently regulated from each other in order to adjust their individual gain, so as to improve the uniformity and detection efficiency along the length L of the detector. Further, in all embodiments, the same electric potential U.sub.common is applied to all of the exit faces of the respective MCP assemblies arranged side by side along the principal direction. For achieving different biases between the respective entry and exit faces of an MCP assembly, the electric potentials U.sub.1, U.sub.2, . . . applied to the corresponding entry faces of the first, second, . . . MCP assemblies may in this case be different. The corresponding voltage differences (U.sub.common−U.sub.1, U.sub.common−U.sub.2, . . . ) applied to the respective MCP assemblies are typically chosen in the range from 800 to 1200 V for a single MCP configuration, 1600-2400V for a Chevron-type configuration and 2400-3600V for a Z-stack MCP configuration, without being limited to these examples. For a given type of MCP configuration, the range of potential differences that are applied to the series of MCP assemblies may preferably span 0 to 200V, each difference being chosen in order to adjust the individual gain of each MCP assembly for a particular application. This arrangement provides the advantage of generating a more uniform and homogeneous electrical field in the space that separate the MCP exit faces from the read-out anode(s), thereby smoothing rather than amplifying the effect of the gap that exists between any two adjacent MCP assemblies. This arrangement allows to limit the electrical field distortion around of the gap that separates the exit faces of any two adjacent MCP assemblies. Limiting this distortion also limits a detection dead-zone along the detection front that extends in the principal direction of the device, thereby improving the device's detection performance. Also, the detector device is able to be floated to a high voltage of up to 10 kV, while the floating potential may have either positive or negative polarity.

[0047] FIG. 5 illustrates components of a Mattauch-Herzog type spectrometer device in accordance with an aspect of the invention. The functioning of such spectrometers, which use an electrostatic sector 10 followed by a magnetic sector 30 for filtering an incoming ion beam 10 is well understood in the art and will not be explained in further details in the context of this description. The magnetic sector 30 comprises an exit plane 32 through which the ions comprised in the initial beam exit, spread along a principal direction in accordance with their respective mass-to-charge ratios. On the focal plane of the spectrometer, a detection device 100, 200 in accordance with any of the previously described embodiments is arranged, so that a full mass spectrum 40 may be obtained on the read-out anode(s) thereof, as previously described. The detection device is high vacuum/ultra-high vacuum, HV/UHV, compatible and covers the full focal plane of the Mattauch-Herzog mass spectrometer, which is typically from several centimetres to several tens of centimetres. It provides one-dimensional (horizontal) spatial resolution of better than 100 μm, a maximum overall count rate of better than 10.sup.7 cps, a dynamic range better than 10.sup.6, high sensitivity of better than 1 cps as well as both positive and negative ion detections.

[0048] Of course, the detection device may be used in other applications and in other spectrometers spreading an incoming ion beam along a focal plane without departing from the scope of the invention. The dimensions of the detector may be customized to provide a 1D focal plane detector having an active area (W×L100/L200) that fits into any mass spectrometer with a focal plane. The active width W can be ranged from few millimeters to several centimeters (<15 cm). The length L can be chosen from several centimetres to more than 100 cm (unlimited length in principle). The spatial resolution of the detector can be as high as 50 μm. There is a physical gap of less than 1 mm between the MCP assemblies. This physical gap results in a dead-zone in the mass spectrum at the region where the mass dispersion overlaps on the gap. The detector device with NMCP assemblies will create N−1 dead-zones in the acquired mass spectrum. The overall dynamic range and count rate of the detector are improved by using a separate anode readout for each MCP assembly. The detector with N MCP assemblies can approximately provide an overall dynamic range and count rate that are N times higher than those of a single MCP segment.

[0049] It should be understood that the detailed description of specific preferred embodiments is given by way of illustration only, since various changes and modifications within the scope of the invention will be apparent to the skilled person. The scope of protection is defined by the following set of claims.