FILTER STACK FOR A THOMSON PARABOLA SPECTROMETER

Abstract

A filter stack for a Thomson Parabola spectrometer, the filter stack having at least one filter foil of a filter material, wherein the filter foil is shaped to have stripes of a respective stripe size made of the filter material and gaps of a respective controlled gap size free of the filter material between the stripes or without gaps.

Claims

1. A filter stack for a Thomson Parabola spectrometer, the filter stack having at least one filter foil of a filter material, wherein the filter foil is shaped to have stripes of a respective stripe size made of the filter material, with gaps of a respective controlled gap size free of the filter material between the stripes or without gaps.

2. The filter stack according to claim 1, wherein: the stripes are parallel, or the stripes are curved and have a constant width, or the stripes are curved and have a varying width.

3. The filter stack according to claim 1, wherein the gaps are enclosed on at least three sides by the filter material.

4. The filter stack according to claim 1, wherein the stripe sizes and the gap sizes of the filter foil are configured to result in selectively filtering and not filtering at least one type of particle of a potential beam of particles with equal charge-over-mass ratio to be analyzed.

5. The filter stack according to claim 1, wherein the filter thickness in certain regions of the filter stack is changed to adjust the attenuation of the particle beam.

6. The filter stack according to claim 1, wherein the gaps are cut[A1] into the filter foil for the filter foil to be shaped to have the stripes and gaps.

7. The filter stack according to claim 1, wherein the filter stack further comprises a frame, the frame comprising at least one guiding pin, and the filter foil[A2] is configured to be assembled onto the frame, wherein the filter foil comprises at least one guiding opening for receiving the at least one guiding pin.

8. The filter stack according to claim 1, wherein the filter foil is made of a high voltage (HV)-compatible material.

9. A method of manufacturing a filter stack for a Thomson Parabola spectrometer according to claim 1, the method comprising the step of cutting a filter foil, so that the filter foil is shaped to have stripes of a respective stripe size made of the filter material and gaps of a respective controlled gap size free of the filter material between the stripes.

10. The method according to claim 9, wherein one or more additional holes are manufactured into the filter foils to be used for alignment purposes.

11. The method according to claim 9, wherein the cutting of the filter foil is a laser-cutting of the filter foil.

12. The method according to claim 9, further comprising determining the stripe sizes, stripe shapes and positions of the stripes, and gap sizes, gap shapes and positions of the gaps based on at least one of two types of charged particles with equal charge-over-mass ratio to be analyzed by the Thomson Parabola spectrometer, stopping ranges of the elements, and parameters of the Thomson Parabola spectrometer.

13. The method according to claim 12, wherein the stripe sizes, stripe shapes and the positions of the stripes, and gap sizes, gap shapes and the positions of the gaps are determined such that, according to the stopping ranges of the two types of charged particles with equal charge-over-mass ratio to be measured and the parameters of the Thomson Parabola spectrometer, the filter stack used with the Thomson Parabola spectrometer filters at least one of the elements to be measured.

14. The method according to claim 12, wherein the determining of the stripe sizes, the stripe shapes and positions of the stripes, and the gap sizes, gap shapes and positions of the gaps further includes considering a distribution of the stripes and gaps to be balanced regarding filtering and non-filtering parts of the filter based on an energy-position dispersion of the Thomson Parabola spectrometer.

15. A Thomson parabola method for analyzing a beam of particles, the beam comprising two types of charged particles with equal charge-over-mass ratio, using a Thomson Parabola spectrometer, the method comprising the steps of: filtering the beam of particles using a filter stack according to claim 1, and analyzing the beam of particles using a detector plate.

16. The filter stack according to claim 5, wherein the filter thickness of the filter stack is changed in the regions of the filter stack for filtering neutral particles.

17. The filter stack according to claim 6, wherein the gaps are laser-cut into the filter foil.

18. The filter stack according to claim 7, wherein the filter foil is a plurality of the filter foils, and each of the filter foils comprises at least one guiding opening for receiving the at least one guiding pin.

19. The filter stack according to claim 8, wherein the filter foil is made of a polymer.

20. The filter stack according to claim 19, wherein the filter foil is made of a thermoset polymer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Embodiments of the present disclosure, which are presented for better understanding the disclosed concepts, but which are not to be seen as limiting the claims, will now be described with reference to the figures in which:

[0009] FIGS. 1A and 1B show a schematic overview of a Thomson Parabola spectrometer and a filter stack according to an embodiment of the present disclosure used therein, as well as a schematic result of a measurement on a detector plate;

[0010] FIG. 2 shows a schematic filter foil of the filter stack according to an embodiment of the present disclosure;

[0011] FIG. 3 shows a schematic spectrum recovered from a filter stack according to an embodiment of the present disclosure;

[0012] FIGS. 4A, 4B, 4C, and 4D show a schematic overview of considerations involved in determining the parameters of the filter stack according to an embodiment of the present disclosure;

[0013] FIG. 5 shows a schematic view of a front view of an assembled filter stack according to an embodiment of the present disclosure;

[0014] FIG. 6 shows a schematic explosion view of a plurality of filter foils within a filter stack and the support frame according to an embodiment of the present disclosure;

[0015] FIG. 7 shows an assembled filter stack according to an embodiment of the present disclosure and the manufacturing process; and

[0016] FIG. 8 shows a photograph of an assembled filter stack according to the present disclosure.

DETAILED DESCRIPTION

[0017] FIGS. 1A and 1B show a schematic overview of a Thomson Parabola spectrometer and a filter stack 1 according to an embodiment of the present disclosure used therein, as well as a schematic result of a measurement on a detector plate.

[0018] In particular, FIGS. 1A and 1B demonstrate the schematics of a Thomson Parabola spectrometer, as well as the schematics of an example measurement. A pinhole at the entrance of the instrument selects a bundled beam of particles from the expanding plasma. This beam then passes through a magnetic and an electric field, before arriving at a detector plate. Typically, the magnetic field and the electric field are kept constant and uniform such that the deflecting forces acting on the particles are the same for the entire beam of particles. The uncharged particles are not affected by the fields, propagate straight through, and thus appear as a dot on the detector (bottom left corner in FIG. 1B). Different from that, the charged particles are deflected by the fields due to the Lorentz force deflecting the particles in parabolic lines depending on their properties (charge, mass and energy). Analyzing the brightness along the parabolas allows to extract the aforementioned spectra. As discussed elsewhere in this document, a conventional TPS, that is, a TPS without a filter stack 1 according to an embodiment of the present disclosure resolves different particles only by their charge-over-mass ratio, conventionally expressed as q/m. In a case where the composition of the beam of particles is known or a scenario in which the occurrence of two (or more) types of particles with the same charge-over-mass ratio can be excluded, this is a powerful tool. If this is not the case, different particles overlap on the same parabolic line and accordingly the analysis is hindered.

[0019] A filter stack 1 according to embodiments of the present disclosure resolves this complication by allowing to filter the different particles with same charge-over-mass ratio such that the ambiguity can be resolved, thus allowing a TPS to be used also in such scenarios to provide reliable and detailed information about the different types of particles, for example, about the spectra. In other words, the filter stack 1 allows to resolve the “blindness” of the instrument to different ions with same charge-over-mass ratio. In very general terms, this is achieved since different particles with the same charge-over-mass ratio have different masses and accordingly are stopped by matter, i.e., the filter, differently. Therefore, the filter stack 1 can stop certain particle types while not stopping the other particle types, thereby differentiating between the particles. Furthermore, more than one filter stack 1 may be used in combination to extend this concept to more than two types of particles with the same charge-over-mass ratio. Such a scenario could be achieved by having a first filter stack 1 configured to transmit the two lightest ion species from the plasma mixture and a second filter stack 1 after the first stack, for example right behind it, that filter only the lightest ion species. In this way, three different curves could be measured and interpolated individually.

[0020] FIG. 2 shows a schematic example of a filter foil 10 of the filter stack 1 according to an embodiment of the present disclosure. In this example, the filter foil 10 has stripes 101 of a filter material and gaps 102 between the stripes 101. In other words, the filter foil 10 has alternating stripes. The stripes 101 and gaps 102 are enclosed by the filter material providing the filter foil 10 as a whole. As depicted, the filter foil 10 may have guiding holes 103 at the end for placing and fixating the filter foil 10 as a part of the filter stack 1 and/or filter stack 1 as a whole.

[0021] That is, the filter stack 1 for a Thomson Parabola spectrometer may have at least one filter foil 10 of a filter material, wherein the filter foil 10 is shaped to have stripes 101 of a respective stripe size made of the filter material and gaps 102 of a respective controlled gap size free of the filter material between the stripes 101 or without gaps.

[0022] The sizes of the stripes 101 and the gaps 102 may be controlled in view of the goal to separate two types of particles with same charge-over-mass ratio as discussed elsewhere in this document.

[0023] In line with FIG. 2, in a filter stack 1 according to the present disclosure, the stripes 101 are parallel. Alternative embodiments of the present disclosure may cover stripes 101 that are, for example, trapezoidal, curved, or have a different shape. Accordingly, the stripes 101 can have a constant width or varying width along their main extension direction. The shape has an influence of the filtering done. Referring to FIG. 1B, the choice of type of stripes 101, for example, parallel or curved and having a constant width or a varying width, has an influence according to which parameters the filtering is performed. For example, apart from parallel stripes 101, stripes 101 coming out from the focal point of the parabola and following, perpendicular to it, its curvature, or shapes following a line of equal energy or equal velocity or equal momentum between different charge states may prove to be useful for specific experiments. For instance, stripes 101 crossing the parabola perpendicularly, instead of, for example, vertically, may result in an improved energy resolution of the TPS. Furthermore, more complex curved shapes 101 may allow achieving a desired filtering for multiple parabolas simultaneously, whereby each corresponds to a mixture of particles with different charge-over-mass ratios.

[0024] As described above, the filter stack 1 according to an embodiment of the present disclosure may contain gaps 102 that are enclosed on at least three sides, preferably enclosed on all sides, by the filter material. More preferably, the gaps 102 are rectangularly shaped.

[0025] Regarding the manufacturing, the gaps 102 of a filter stack 1 according to an embodiment of the present disclosure are cut into the filter foil 10 for it to be shaped to have the stripes 101 and gaps 102. In particular, the use of a thermoset polymer as a foil material allows to use laser cutting. This allows for an easy and variable but also very precise production of the individual filter foils 10 and in consequence the filter stack 1 as a whole.

[0026] Moreover, the manufacturing method allows to position alignment holes 104 which can be used to precisely position the assembled filter stack 1 relative to the TPS, in particular using an alignment laser beam.

[0027] Moreover, the manufacturing method allows to make a conventional differential filter, i.e., with a stair-step thickness profile and with no gaps.

[0028] Moreover, the filter foil 10 may be made of a HV-compatible material, in particular of a polymer. Here, HV refers to high voltage; that is, the filter foil may be made of a high voltage compatible material. This may be particularly advantageous in scenarios of high voltages when compared to conventional filter using metals. Polymers are HV-compatible since they show little-to-no interaction with high voltages and thus are not affected by high voltages. An example for such a polymer is polyimide. A further advantage of using a polymer as filter material is that it can easily be used in laser-cutting, thus allowing for high precision manufacturing. High precision manufacturing may be particularly advantageous in small TPS instruments.

[0029] Furthermore and in line with the above, the present disclosure also provides a Thomson parabola method for analyzing a beam of particles, the beam comprising two types of charged particles with equal charge-over-mass ratio, using a Thomson Parabola spectrometer. The method comprises the steps of filtering the beam of particles using a filter stack 1 according to an embodiment of the present disclosure, and analyzing the beam of particles using a detector plate. As discussed above, the filter stack 1 can be used to resolve the “blindness” beyond charge-over-mass ratio and thus provide, for example, more resolved spectra.

[0030] FIG. 3 shows a schematic spectrum recovered from a filter stack 1 according to an embodiment of the present disclosure.

[0031] FIG. 3 shows a spectrum, that is the signal intensity (here in arbitrary units) as a function of the energy (here in units of MeV). The grey stripes indicate the parts in which the filter stack 1 according to the present disclosure has stripes 101 while the remaining parts (the white parts) indicate the parts with gaps 102 (that is, without filtering). The measured data for the unfiltered parts is represented by a solid line while a dashed line shows the measured data for the filtered parts. Clearly, the intensity of the filtered data is lower than the intensity of the unfiltered data as the unfiltered data includes the filtered data. Moreover, due to the positions and the sizes of the stripes 101, it is evident that the curves of the filtered and unfiltered data can easily be interpolated over the whole energy range, thus leading to a complete spectrum of the unfiltered and the filtered data, i.e., a reconstruction of the missing data. This is in particular due to the slow change of the spectrum as a function of the energy.

[0032] In line with the above, the stripe sizes and the gap sizes of the filter foil 10 of a filter stack 1 according to an embodiment of the present disclosure are configured to result in selectively filtering and not filtering at least one type of particle of a potential beam of particles with equal charge-over-mass ratio to be analyzed.

[0033] In the case that the beam of particles also contains neutral particles that are not deflected by the magnetic field or the electric field of the TPS, these neutral particles are also part of the measured data. In some scenarios, this may lead to a very bright spot on the detector plane which might influence the quality of the measurement results. Accordingly, if this data is not of particular interest, it may be appropriate to filter it out. Accordingly, in an embodiment of the present disclosure, the filter thickness in certain regions of the filter stack 1 is changed to adjust the attenuation of the particle beam, preferably in the regions of the filter stack 1 filtering neutral particles. In other words, by providing a filter foil 10 with high thickness where the neutral particles are expected, the flux of these neutral particles may be adjusted before reaching the detector plate. Moreover, this may also filter out X-ray radiation, which may be a relevant background radiation as well.

[0034] FIGS. 4A, 4B, 4C, and 4D show a schematic overview of considerations involved in determining the parameters of the filter stack 1 according to an embodiment of the present disclosure.

[0035] More specifically, FIG. 4A shows an image of a parabola on the detector for an incoming particle with charge-over-mass ratio of ½, more specifically an alpha particle. The x-axis shows the deflection due to the magnetic field (here abbreviated as ‘B-deflection’) in units of millimeter on the detector. The y-axis shows the deflection due to the electric field (here abbreviated as ‘E-deflection’) in units of millimeter on the detector. The grey scale decodes the incoming energy in units of MeV, wherein particles with higher energy are darker: the fast particles pierce through the electric field and the magnetic field with very little deflection, while the slower ones are subject to the field for a longer time and thus drift away further from the particle beam axis.

[0036] Furthermore, FIG. 4B shows the mapping of the energy in units of MeV to the deflection due to the magnetic field in units of millimeter, i.e., the dispersion (or energy-position dispersion) of the instrument, i.e., the TPS. This curve depends both on general physics laws such as the Lorentz force but also on the specific parameters of the TPS.

[0037] Next, FIG. 4C shows a sample calculation of the stopping ranges and a possible filter stack configuration in energy space. The vertical scale on the left represents the stopping range in units of micrometer, in this case for boron ions (diamond) and alpha particles (squares). The grey bars represent the position, width, and thickness of the filter stripes 101. In this example, this is chosen in increments of commercially available foils. This is also indicated by the vertical scale on the right representing layer thickness in units of micrometer. This is further indicated by the dashed line aligning with the grey bars between the alpha particle line and the boron ions line. As can be seen from the image, the thickness and position and size of the filter stack 1 is determined such that it separates alpha particles from boron ions: While the thickness of each stripe 101 is bigger than the stopping range of the boron ions, it is lower than the stopping range of the alpha particles, leading to a separation of the two types of particles over the whole energy range.

[0038] This configuration shown in FIG. 4C has to be transferred from energy space into position to manufacture the filter stack. The corresponding calculation and configuration are shown in FIG. 4D. This image shows the same situation as the bottom left image with the difference that the x-axis represents the position in units of millimeter. Accordingly, the grey bars indicate the position and size of the stripes, their heights indicating the thickness. It is noted that the more equidistant and balanced distribution of the stripes from the energy space stretches and shrinks while mapped into real space, according to the dispersion of the instrument shown in FIG. 4B. This can be understood as a consequence of the non-linear dispersion of the instrument.

[0039] From this, it can be understood that in an embodiment of the present disclosure the method of analyzing the beam further comprises determining the shapes, sizes and positions of the stripes 101 and the shapes, sizes and positions of the gaps 102 based on at least one of two types of charged particles with equal charge-over-mass ratio to be analyzed by the Thomson Parabola spectrometer, stopping ranges of the elements, and parameters of the Thomson Parabola spectrometer.

[0040] Moreover, according to a further embodiment of the present disclosure in the method of analyzing the beam the stripe sizes and the positions of the stripes 101 and the gap sizes and the positions of the gaps 102 may be determined such that, according to the stopping ranges of the two types of charged particles with equal charge-over-mass ratio to be measured and the parameters of the Thomson Parabola spectrometer, the filter stack 1 used with the Thomson Parabola spectrometer filters at least one of the elements to be measured.

[0041] In addition, in a further embodiment of the present disclosure, the determination of the stripe sizes and positions of the stripes 101 and the determination of the gap sizes and positions of the gaps 102 may further include considering a distribution of the stripes 101 and gaps 102 to be balanced regarding filtering and non-filtering parts of the filter based on the energy-position dispersion of the Thomson Parabola spectrometer.

[0042] It is clear that this procedure described in the context of the above FIGS. 4A to 4D can be implemented by means of software, i.e., a computer program. Such a computer program may receive as an input the parameters of the TPS as well as the (expected) particle types in the beam of particles, in particular those having the same charge-over-mass ratio. Further, an input may be which of these particles should be filtered and which aspects of the different quantities are of specific interest. Then, based on stopping range calculations for the particles types of interest, a stripes-and-gaps configuration in terms of width, position and thickness may be determined (calculated) and provided as output. This output may be then directed to a manufacturing process. Furthermore, the program may also include a step of optimization of the configuration of the stripes 101 and gaps 102 such that the information gained by using the filter stack 1 is a balance between filtered and non-filtered information allowing faithful reconstruction of the entire information. This step may be supported by data provided from experiments done without a filter, i.e., supported by data about the typical unfiltered spectrum.

[0043] FIG. 5 shows a schematic view of a front view of an assembled filter stack 1 according to an embodiment of the present disclosure.

[0044] FIG. 5 shows the assembled filter stack 1 including a round frame 11 (support frame 11) with six guiding openings 112 (one top left, top center, top right, bottom left, bottom center and bottom right each, see FIG. 6) as well as the filter foils 10 in the center of the of the assembled filter stack 1. The different grey scales indicate the different thickness of the resulting stripes 101. The guiding openings 112 may both facilitate the manufacturing as it allows several filter foils to be arranged together in a precise manner using guiding pins 111, but may also allow the filter stack to be fixated precisely in the overall measurement setup of the TPS.

[0045] Accordingly, in a filter stack 1 according to the present disclosure, the filter stack 1 further comprises a frame 11, the frame preferably comprising at least one guiding pin 111, and the filter foil 10, preferably a plurality of the filter foils 10, is configured to be assembled onto the frame 11, in particular in that each of the filter foils 10 comprises at least one guiding opening 112 for receiving the at least one guiding pin 111.

[0046] FIG. 6 shows a schematic explosion view of a plurality of filter foils 10 and the support frame 11 according to an embodiment of the present disclosure. In detail, FIG. 6 shows, from left to right, a back of the round frame 11 with six guiding pins 111 and a rectangular opening, a plurality of filter foils 10, each with different stripes 101 and gaps 102 and a front of the round frame 11 with six guiding openings 112 corresponding to the six guiding pins 111. The stacking of filter foils 10 allows for a flexible manufacture of the filter stack 1 as each filter foil 10 may have the same thickness and the resulting profile of varying thickness over the width of the filter stack 1 can thus be obtained by the different filter foils 10 with different stripes 101 and gaps 102.

[0047] Accordingly, the present disclosure also comprises a method of manufacturing a filter stack 1 for a Thomson Parabola spectrometer, in particular according to any of the filter stacks 1 discussed elsewhere in this document, the method comprising the step of cutting a filter foil 10, so that the filter foil 10 is shaped to have stripes 101 of a respective stripe size made of the filter material and gaps 102 of a respective controlled gap size free of the filter material between the stripes. Moreover, the cutting of the filter foil 10 may be a laser-cutting of the filter foil 10.

[0048] FIG. 7 shows an assembled filter stack 1 according to the present disclosure with a stair-step profile, that is, with no gaps 102 between regions of different thickness but instead a gap after the regions of different thickness. This front view on a filter stack 1 shows the six guiding pins 111 of one part of the frame 11 engaged in the six guiding openings 112 in the other part of the frame 11 and the assembled filter foils 10 in between. As can be seen from FIG. 7, the structure of the frame 11 can also be rectangular, i.e., is not limited to a round form and is in particular not limited at all. Moreover, in the lower left corner of the filter stack 1 there is a hole (alignment hole) 113 which is positioned so as to coincide with the axis of the TPS and is intended to be used for alignment of the filter stack 1 assembly to the TPS, preferably using an alignment laser beam. This may be advantageous in cases in which an alignment laser is used to position the TPS in the experiment as the hole in the filter stack may then be used by the alignment laser for aligning the filter stack 1.

[0049] FIG. 8 shows a photo of an assembled filter stack 1 according to an embodiment of the present disclosure with a pattern of 5 parallel stripes 101 and an alignment hole 113 in the bottom left corner of the filter stack 1.

[0050] Although detailed embodiments have been described, these only serve to provide a better understanding of the present disclosure and are not to be seen as limiting to the claims.

[0051] The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.