Apparatus for controlling plasma components

Abstract

The present application discloses an apparatus for controlling plasma composition, comprising a pair of electrodes having a dielectric barrier therebetween, the apparatus further comprising: a temperature control unit in thermal contact with one of the electrodes or the dielectric barrier; a sensor configured to measure a temperature of one of the electrodes or the dielectric barrier; a detector configured to determine a concentration of a main chemical form of the plasma; and a processor configured to control the temperature control unit based on the measured temperature and the determined concentration.

Description

Technical Field

[0001] The present invention relates to a device for controlling the composition of a plasma and a method for controlling the composition of a plasma. Background Art

[0002] Plasma technology is widely used in numerous industries. For example, its applications range from automotive manufacturing to medicine. A variety of variables determine whether a plasma is suitable for a particular application. For example, the composition, electron and ion temperatures, and electron and ion densities all influence the usefulness of a plasma in a particular application. However, controlling the composition of a plasma remains unclear.

[0003] Therefore, there is a need for a device for controlling the composition of a plasma. Similarly, there is a need for a device for promoting the generation of different chemical states in a plasma. In summary, there is a need for a device and method for controlling the generation of plasma morphology. Summary of the Invention

[0004] An object of the present invention is to provide an apparatus for controlling the composition of a plasma that at least partially obviates or mitigates at least some of the disadvantages of the prior art, whether identified herein or elsewhere, or provides an alternative approach. According to the present invention, an apparatus for controlling the composition of a plasma and a method for controlling the composition of a plasma are provided, as set forth in the independent claims. Further aspects of the invention are set forth in the dependent claims and in the description.

[0005] According to a first aspect of the present invention, there is provided an apparatus for controlling plasma composition, comprising a pair of electrodes with a dielectric barrier therebetween, the apparatus further comprising: a temperature control unit in thermal contact with one of the electrodes or the dielectric barrier; a sensor configured to measure the temperature of one of the electrodes or the dielectric barrier; a detector configured to determine a concentration of a major chemical species of the plasma; and a processor configured to control the temperature control unit based on the measured temperature and the determined concentration.

[0006] In one embodiment, a power source for attachment to the pair of electrodes is electrically isolated from the temperature control unit.

[0007] In one embodiment, in a first mode: the processor is configured to determine whether the concentration is above a first predetermined threshold, the first predetermined threshold being zero, and the processor is configured to control the temperature control unit only if the concentration is above the first predetermined threshold.

[0008] In one embodiment, in the second mode: the processor is configured to determine whether the concentration is above a second predetermined threshold, the second predetermined threshold being non-zero, and the processor is configured to control the temperature control unit only if the concentration is above the second predetermined threshold.

[0009] In one embodiment, the apparatus is switchable between the first mode and the second mode.

[0010] In one embodiment, the primary chemical species is reactive nitrogen.

[0011] In one embodiment, the detector is configured to detect nitrogen dioxide.

[0012] In one embodiment, the predominant chemical species is reactive oxygen species.

[0013] In one embodiment, the detector is configured to detect ozone.

[0014] In one embodiment, the detector comprises at least one of an ultraviolet spectrometer and an infrared spectrometer.

[0015] In one embodiment, the sensor comprises a thermocouple.

[0016] In one embodiment, the temperature control unit is attachable to an electrode or the dielectric barrier via a thermal interface material.

[0017] In one embodiment, the temperature control unit is one of a thermoelectric module or a temperature controlled fluid system.

[0018] In one embodiment, the dielectric material includes at least one of alumina and quartz.

[0019] In one embodiment, the device is arranged in a surface barrier discharge, SBD configuration or a dielectric barrier discharge, DBD configuration.

[0020] According to a second aspect of the present invention, there is provided a method of controlling the composition of a plasma generated by a pair of electrodes with a dielectric barrier therebetween, the method comprising: providing a temperature control unit in thermal contact with one of the electrodes or the dielectric barrier; measuring the temperature of one of the electrodes or the dielectric barrier using a sensor; determining the concentration of a major chemical species of the plasma using a detector; and controlling the temperature control unit based on the measured temperature and the determined concentration.

[0021] According to a third aspect, there is provided a transitory or non-transitory computer-readable medium comprising instructions, which, when executed by a computer, cause the computer to perform the steps of the method of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] For a better understanding of the invention and to show how exemplary embodiments of the invention may be practiced, reference will now be made, by way of example only, to the accompanying drawings, in which: Figure 1A and 1B An apparatus for controlling plasma composition according to an embodiment is shown respectively; and Figure 2A and 2B The relationship between temperature and plasma composition is shown.

[0023] Figure 3 A method of controlling plasma composition according to one embodiment is shown. DETAILED DESCRIPTION

[0024] Figure 1A and 1B 1 and 2 show an apparatus for controlling plasma composition at atmospheric pressure according to an embodiment. Figure 1A and 1B In each of the figures, the device is shown in use with a first electrode 101 and a second electrode 102 , the electrodes 101 , 102 being coupled to a power source 110 . Figure 1A The device is shown as part of a surface barrier discharge (SBD) configuration, while Figure 1B The device is shown as part of a dielectric barrier discharge (DBD) configuration.

[0025] like Figure 1A As shown, the SBD configuration generally includes a sheet-like first electrode 101 and a second electrode 102, with the second electrode including gaps (e.g., depressions or grooves) at intervals. A first dielectric barrier 121 is located between the first electrode 101 and the second electrode 102. By applying a time-varying electric field across the electrodes 101 and 102, plasma is generated from the gas present between the gaps spaced apart along the second electrode 102.

[0026] like Figure 1B As shown, a DBD configuration generally includes two sheet-like electrodes 101 and 102. A first dielectric barrier 121 is connected (e.g., attached) to the first electrode 101. A second dielectric barrier 122 is optionally connected (e.g., attached) to the second electrode 102. A power supply 110 is coupled to the first and second electrodes 101, 102. A gap 202 exists between the first dielectric barrier 121 and the second electrode 102, or, if the second dielectric barrier 122 is connected to the second electrode 102, between the first and second dielectric barriers 121, 122. When a time-varying electric field is applied across the electrodes 101 and 102, a plasma forms in the gap 202.

[0027] The first dielectric barrier 121 and, in the case of a DBD configuration, the second dielectric barrier 122 may comprise at least one of alumina and quartz. Advantageously, alumina / quartz has relatively high thermal conductivity and low dielectric loss tangent, thereby allowing efficient heating / cooling of the plasma contact / generation surface.

[0028] like Figure 1A and 1B As shown, the apparatus includes a temperature control unit 130 attachable to the first electrode 101. The temperature control unit 130 is capable of controlling the temperature of the first electrode 101. Traditionally, the only temperature control performed on the electrode during plasma generation has been related to electrode cooling, as it was assumed that any changes in the composition of the generated plasma were a result of electrode heating. However, it has been found that at atmospheric pressure, there is no direct correlation between increased temperature and the decomposition of certain plasma molecules (e.g., ozone). In other words, for controlling the plasma composition, it is not just electrode cooling that is important, but rather both electrode heating and cooling. Furthermore, it has been found that dynamically heating and cooling the electrode results in well-controlled morphology generation.

[0029] Figure 2A and Figure 2B The relationship between temperature and composition of plasma generated at atmospheric pressure is shown. Figure 2A shows the relationship between temperature (solid line) and parts per million in ozone plasma (dashed line) as a function of time. Figure 2B The temperature (solid line) and the parts per million (dashed line) in the nitrogen dioxide plasma are shown as a function of time. Figure 2A and 2B It can be seen that the relationship between temperature and plasma composition is not a simple linear relationship, and precise electrode temperature control (heating and cooling) is very important for controlling the plasma composition.

[0030] Advantageously, the temperature control unit 130 allows cooling and heating of the first electrode 101 or the dielectrics 121, 122. It has been found that by controlling the temperature of at least one electrode and the dielectric, a better control of the entire system can be achieved. In practice, given that, for example, the electrode 101 and the dielectric 121 are in close proximity, e.g. Figure 1A and 1BAs shown, controlling the temperature of one element also changes the temperature of the other. Preferably, the temperature control unit is a thermoelectric module (Peltier module). Advantageously, thermoelectric modules allow for rapid switching between cooling and heating, which is crucial for maintaining plasma generation with a specific desired composition. Furthermore, using thermoelectric modules facilitates dynamic cooling and heating of the first electrode 101 in a short period of time, compared to, for example, water cooling / heating, although this could be a viable alternative using a suitable fluid-based system. Another advantage of thermoelectric modules is their ease of combination, meaning that multiple thermoelectric modules can be used to expand or reduce the area where plasma is generated. Therefore, depending on the arrangement of multiple thermoelectric modules, plasma can be processed over a larger surface area or generated at a higher density.

[0031] The temperature control unit 130 can be attached to the first electrode 101 by a thermal interface material such as a pad or paste (e.g., glue, resin, adhesive, cement). Advantageously, the thermal interface material allows for efficient heat transfer from the temperature control unit 130 to the first electrode 101. The temperature control unit 130 is typically attached to the ground side of the device.

[0032] Another form of temperature control that can be utilized involves the use of a heated or cooled fluid. A suitable fluid is water, but other fluids can be used as desired. In certain embodiments, mineral oil can be used because it has suitable thermal properties and is an electrical insulator, which is important in systems using high voltages. In such a system, the temperature-control fluid is delivered through a tube in thermal contact with the first electrode 101, in much the same manner as in the Peltier device described above. That is, the tube carrying the fluid is attached to the first electrode via a thermal interface material to ensure good thermal contact between the tube and the first electrode.

[0033] In another embodiment, a temperature-control fluid is passed through the body of the electrode or dielectric via embedded pipes or channels. This arrangement allows for excellent heat transfer between the electrode / dielectric and the fluid, enabling better and faster temperature control. In larger systems, this arrangement may be more energy-efficient and economical than a Peltier-based system, although both have advantages and can be used.

[0034] The fluid-based temperature control system can still provide rapid temperature control and can be installed and operated over a larger surface area of ​​the first electrode, which may be desirable in certain use cases, such as the processing of food, pharmaceutical compounds, or other relatively delicate materials.

[0035] A fluid-based temperature control system may include a container of a suitable fluid (e.g., water or mineral oil) placed in close proximity and thermal contact with the first electrode via a conduit. The fluid is circulated from the container using a suitable pump. A temperature control unit, connected in series with the conduit, includes a heater and a cooler that can be used to raise or lower the temperature of the fluid in the conduit, thereby correspondingly raising or lowering the temperature of the first electrode or dielectric. The ratings of the heater and cooler are selected based on the desired rate of change in the fluid temperature, and thus the electrode / dielectric temperature. This will largely depend on the size of the electrode / dielectric and the device in which it is mounted.

[0036] It is worth noting that if the temperature control unit 130 is attached to the electrode, the temperature control unit 130 is thermally connected to the first electrode 101, but otherwise the temperature control unit 130 is electrically isolated from the first electrode 101. In some embodiments, the potential difference between the first electrode 101 and the second electrode 102 can be in the range of 1-30 kV, or more typically in the range of 5-15 kV. It should be noted that this should not be a DC voltage, but should be time-varying, such as AC or pulsed in some manner.

[0037] In most embodiments of the present invention, it is important to ensure that arcing does not occur, so the temperature of the first electrode 101 should be controlled under conditions that ensure good thermal contact while ensuring no electrical contact. Known prior art systems utilize a Peltier temperature control element as one of the electrodes. This poses a risk that electrical interference generated by plasma generation could interfere with surrounding electronic systems such as the temperature control unit 130 and sensors 140 and 150. Embodiments of the present invention electrically isolate the voltage 110 used for plasma generation from any electronics or signals associated with operating the temperature control unit 130, whether Peltier-based or fluid-based.

[0038] By controlling the temperature of the first electrode / dielectric, better and more precise control of the device can be achieved. In particular, the desired morphology can be better controlled than, for example, controlling the temperature of the surrounding environment.

[0039] Although described as controlling the temperature of the first electrode, it is noted that the same effect can be achieved by controlling the temperature of the second electrode or the first and second electrodes and the dielectric. In some aspects, controlling the temperature of the electrode is a substitute for controlling the temperature of the dielectric.

[0040] like Figure 1A and 1B As shown, the device includes a sensor 140. Preferably, the sensor 140 includes a thermocouple. The sensor may also include a thermal imager, and / or an infrared pyrometer. Figure 1A and 1BIn FIG, the sensor 140 is configured to measure the temperature of the first dielectric barrier 121. However, the sensor 140 may be configured to measure the temperature of one of the first electrode 101, the second electrode 102, the first dielectric barrier 121, or the second dielectric barrier 122.

[0041] like Figure 1A and 1B As shown, the apparatus includes a detector 150. Detector 150 is configured to determine the concentration of the primary chemical species in the plasma. As previously mentioned, the primary chemical species can be reactive nitrogen or reactive oxygen. If the primary chemical species is reactive nitrogen, detector 150 is configured to detect nitrogen dioxide (NO2). If the primary chemical species is reactive oxygen, detector 150 is configured to detect ozone (O3). Advantageously, nitrogen dioxide and ozone are indicative of reactive nitrogen and reactive oxygen, respectively. Advantageously, controlling reactive nitrogen is important for controlling water toxicity, while controlling reactive oxygen is important for effective bacterial destruction.

[0042] Detector 150 may include one or more of an ultraviolet spectrometer, an infrared spectrometer, a Fourier transform infrared spectrometer, a direct reading spectrometer, a mass spectrometer, an absorption spectrometer, a cavity ring-down spectrometer, and a laser-induced fluorescence spectrometer. For example, detector 150 may include an ultraviolet / infrared spectrometer coupled to ultraviolet light for quantifying ozone. Fourier transform infrared spectroscopy can be used to detect nitrogen dioxide and ozone.

[0043] like Figure 1A and 1B As shown, the apparatus includes a processor 160. The processor may represent a microprocessor or a computer. More specifically, the processor 160 may be a proportional-integral-derivative controller or a bang-bang controller. The processor 160 may utilize predictive control and machine learning methods, for example, to facilitate automated control of plasma composition.

[0044] The processor 160 is configured to control the temperature control unit 130 based on the measured temperature and the determined concentration. To this end, the processor 160 communicates with the temperature control unit 130, the sensor 140, and the detector 150. The processor 160 may communicate with the temperature control unit 130, the sensor 140, and the detector 150 wirelessly.

[0045] The processor 160 may be configured to adjust the power provided by the power supply 110 to the temperature control unit 130 to control the temperature of the first electrode 101. For example, the processor 160 may be configured to increase the power provided by the power supply 110 to the temperature control unit 130 to increase the temperature of the first electrode 101, or to decrease the power provided by the power supply 110 to the temperature control unit 130 to decrease the temperature of the first electrode 101.

[0046] In a first mode (i.e., a first chemical state), processor 160 can be configured to determine whether the concentration is above a first predetermined threshold, which is zero (or near zero, e.g., <1%, <5%, <10%), and to control temperature control unit 130 only when the concentration is above the first predetermined threshold. In this way, a plasma comprising 100% (or near 100%, e.g., >99%, >95%, >90%) of the desired species can be generated. For example, in the case of reactive nitrogen and reactive oxygen species, the transition between generating a plasma comprising reactive oxygen species and generating a plasma comprising reactive nitrogen species is an irreversible, runaway process. By detecting the early formation of reactive nitrogen species before runaway (i.e., when the concentration is above the predetermined threshold of zero) and applying appropriate levels of cooling / heating, the plasma composition can be manipulated to maintain 100% reactive oxygen species.

[0047] In the second mode (i.e., the second chemical state), the processor 160 can be configured to determine whether the concentration is above a second predetermined threshold, which is non-zero, and the processor 160 can be configured to control the temperature control unit 130 only when the concentration is above the second predetermined threshold. For example, when the first electrode 101 is at a specific temperature, a desired plasma containing equal concentrations of reactive nitrogen and reactive oxygen occurs. Therefore, by adjusting the power supplied to the first electrode 101 in response to the concentration of one of the reactive nitrogen and reactive oxygen being above 50%, the generation of a plasma containing equal concentrations of reactive nitrogen and reactive oxygen can be maintained.

[0048] The device is switchable between a first mode and a second mode. Thus, the device can operate in a mode where the generated plasma comprises 100% reactive nitrogen or 100% reactive oxygen, as well as in a mode where the generated plasma comprises a mixture of reactive nitrogen and reactive oxygen. Advantageously, the device facilitates different modes of plasma generation, allowing the device to be used in a range of applications with varying requirements for the composition of the generated plasma.

[0049] The device may be powered by a dedicated power source (ie a power source different from that coupled to the first electrode) to enable extended use. Alternatively, the device may include batteries to enable use without the need for, for example, mains power.

[0050] Figure 3 A method for controlling plasma composition according to one embodiment is shown. The method includes attaching (S1) a temperature control unit 130 to a first electrode 101; measuring (S2) the temperature of the first electrode 101, the second electrode 102, the first dielectric barrier 121, or the second dielectric barrier 122 using a sensor 140; determining (S3) the concentration of a major chemical species of the plasma using a detector 150; and controlling (S4) the temperature control unit 130 based on the measured temperature and the determined concentration.

[0051] The method may include controlling the temperature control unit 130 to be in a first mode and a second mode and to switch between these modes, as described above with respect to Figure 1A and 1B Similarly, the primary chemical form may be reactive nitrogen (e.g., nitrogen dioxide) or reactive oxygen (e.g., ozone), as described above with respect to Figure 1A 、 1B and mentioned in 2.

[0052] In summary, the present invention provides a device for controlling plasma composition and a method for controlling plasma composition, which can achieve plasma generation in different modes, thereby accurately controlling the plasma composition and enabling plasma technology to be applied in a range of fields and industries.

[0053] The optional features described herein may be used individually or, where appropriate, in combination with each other, particularly in the combinations described in the appended claims. Optional features described herein for each aspect or exemplary embodiment of the invention may, where appropriate, also be applicable to all other aspects or exemplary embodiments of the invention. In other words, a skilled reader of this specification should consider the optional features of each aspect or exemplary embodiment of the invention to be interchangeable and combinable between different aspects and exemplary embodiments.

[0054] All features disclosed in this specification (including any accompanying claims and drawings), and / or all steps of any disclosed method or process, may be combined in any combination, except combinations where at most some of such features and / or steps are mutually exclusive.

[0055] While preferred embodiments have been shown and described, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the appended claims and described above.

Claims

1. An apparatus for controlling plasma composition, comprising a pair of electrodes with a dielectric barrier therebetween, the apparatus further comprising: a temperature control unit in thermal contact with one of the electrodes or the dielectric barrier; a sensor configured to measure a temperature of one of the electrodes or the dielectric barrier; a detector configured to determine a concentration of a major chemical species of the plasma; and A processor is configured to control the temperature control unit based on the measured temperature and the determined concentration. 2 . The device according to claim 1 , wherein a power source for attachment to the pair of electrodes is electrically insulated from the temperature control unit.

3. The device according to claim 1 or 2, wherein: In the first mode: The processor is configured to determine whether the concentration is above a first predetermined threshold, the first predetermined threshold being zero, and the processor is configured to control the temperature control unit only when the concentration is above the first predetermined threshold.

4. The device according to claim 1 or 2, wherein: In the second mode: The processor is configured to determine whether the concentration is above a second predetermined threshold, the second predetermined threshold being non-zero, and the processor is configured to control the temperature control unit only if the concentration is above the second predetermined threshold. The device of claim 4 , wherein the device is switchable between the first mode and the second mode.

6. The device of any one of the preceding claims, wherein the predominant chemical species is reactive nitrogen. The apparatus of claim 6 , wherein the detector is configured to detect nitrogen dioxide.

8. The device of any one of claims 1 to 5, wherein the predominant chemical species is reactive oxygen species.

9. The apparatus of claim 8, wherein the detector is configured to detect ozone.

10. The apparatus of claim 9, wherein the detector comprises at least one of an ultraviolet spectrometer and an infrared spectrometer.

11. The apparatus of any preceding claim, wherein the sensor comprises a thermocouple.

12. The device of any of the preceding claims, wherein the temperature control unit is attachable to the electrode or the dielectric barrier by a thermal interface material.

13. The apparatus of any preceding claim, wherein the temperature control unit is one of a thermoelectric module or a temperature-controlled fluid system.

14. The apparatus of any preceding claim, wherein the dielectric material comprises at least one of alumina and quartz.

15. An apparatus according to any preceding claim, arranged in a surface barrier discharge, SBD, configuration or a dielectric barrier discharge, DBD, configuration.

16. A method of controlling the composition of a plasma generated by a pair of electrodes with a dielectric barrier therebetween, the method comprising: providing a temperature control unit in thermal contact with one of the electrodes or the dielectric barrier; measuring the temperature of one of the electrodes or the dielectric barrier using a sensor; determining the concentration of a major chemical species in the plasma using a detector; and The temperature control unit is controlled based on the measured temperature and the determined concentration.

17. A transitory or non-transitory computer-readable medium comprising instructions, which, when executed by a computer, cause the computer to perform the steps of the method of claim 14.

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