Device for controlling plasma composition

Abstract

An apparatus for controlling the composition of a plasma is disclosed, 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 the temperature of the one of the electrodes or the dielectric barrier, a detector configured to calculate the concentration of a major chemical species in the plasma, and a processor configured to control the temperature control unit based on the measured temperature and the calculated concentration.

Description

[Technical Field]

[0001] The present invention relates to an apparatus for controlling the composition of a plasma and a method for controlling the composition of a plasma. [Background technology]

[0002] Plasma technology is used in a wide range of industries. For example, plasma technology has applications in fields ranging from automotive manufacturing to medicine. The suitability of plasma for a particular application depends on several variables. For example, the composition of the plasma, the temperature of the electrons and ions, and the density of the electrons and ions each affect the usefulness of the plasma for a particular application. However, methods for controlling the composition of the plasma are not yet fully understood.

[0003] Therefore, there is a need for an apparatus that controls the composition of the plasma. Similarly, there is a need for an apparatus that can easily achieve various chemical states for plasma generation. Overall, it is desirable to provide an apparatus and method for controlling the generation of plasma species. Summary of the Invention [Problem to be solved by the invention]

[0004] One object of the present invention is, inter alia, to provide an apparatus for controlling the composition of a plasma, or to provide an alternative approach, which at least partially overcomes or mitigates at least some of the disadvantages of the prior art identified herein or elsewhere. According to the present invention, there is provided an apparatus for controlling the composition of a plasma and a method for controlling the composition of a plasma as set out in the independent claims. Further aspects of the invention are set out in the dependent claims and in the description. [Means for solving the problem]

[0005] According to a first aspect of the present invention, there is provided an apparatus for controlling the composition of a plasma 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 the temperature of the one of the electrodes or the dielectric barrier, a detector configured to calculate the concentration of a major chemical species in the plasma, and a processor configured to control the temperature control unit based on the measured temperature and the calculated concentration.

[0006] In one embodiment, the power supply attached to the pair of electrodes is electrically isolated from the temperature control unit.

[0007] In one embodiment, in the first mode, the processor is configured to determine whether the concentration exceeds 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 exceeds the first predetermined threshold.

[0008] In one embodiment, in the second mode, the processor is configured to determine whether the concentration exceeds 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 exceeds the second predetermined threshold.

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

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

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

[0012] In one embodiment, the primary species is a 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 a UV spectrometer and an IR spectrometer.

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

[0016] In one embodiment, the temperature control unit can be attached to one of the electrodes or the dielectric barrier via a thermally conductive material.

[0017] In one embodiment, the temperature control unit is either 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 configured in either 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 having 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 the one of the electrodes or the dielectric barrier using a sensor, calculating the concentration of a major chemical species in the plasma using a detector, and controlling the temperature control unit based on the measured temperature and the calculated concentration.

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

[0022] For a better understanding of the present invention, and to show how exemplary embodiments thereof may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: [Brief explanation of the drawings]

[0023] [Figure 1A] FIG. 1 illustrates an apparatus for controlling the composition of a plasma according to one embodiment. [Figure 1B] FIG. 1 illustrates an apparatus for controlling the composition of a plasma according to one embodiment. [Figure 2A] 1 is a graph showing the relationship between temperature and plasma composition. [Figure 2B] 1 is a graph showing the relationship between temperature and plasma composition. [Figure 3] FIG. 1 illustrates a method for controlling the composition of a plasma according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] Figures 1A and 1B each show an apparatus for controlling the composition of a plasma at atmospheric pressure according to one embodiment. In both Figures 1A and 1B, the apparatus is shown in use with a first electrode 101 and a second electrode 102, which are connected to a power supply 110. Figure 1A shows the apparatus as part of a surface barrier discharge (SBD) configuration, and Figure 1B shows the apparatus as part of a dielectric barrier discharge (DBD) configuration.

[0025] 1A includes a first electrode 101, typically in the form of a plate, and a second electrode 102, the second electrode having a spaced-apart gap (e.g., a recess or groove). A first dielectric barrier 121 is located between the first electrode 101 and the second electrode 102. By applying a time-varying electric field between the electrodes 101 and 102, a plasma is generated from a gas present in the spaced-apart gap along the second electrode 102.

[0026] 1B , a DBD configuration typically includes two plate-like electrodes 101, 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 source 110 is coupled to the first electrode 101 and the second electrode 102. A gap 202 exists between the first dielectric barrier 121 and the second electrode 102, or between the first dielectric barrier 121 and the second dielectric barrier 122 if the second dielectric barrier 122 is connected to the second electrode 102. A plasma is formed in the gap 202 when a time-varying electric field is applied between the electrodes 101, 102.

[0027] The first dielectric barrier 121, and in the case of a DBD configuration, the second dielectric barrier 122, may comprise alumina and / or quartz, which are advantageous in that they have relatively high thermal conductivity and low dielectric loss tangent, allowing for effective heating / cooling of the plasma contact / generation surface.

[0028] As shown in Figures 1A and 1B, the present apparatus includes a temperature control unit 130 that can be attached to the first electrode 101. The temperature control unit 130 is capable of controlling the temperature of the first electrode 101. Traditionally, it has been assumed that changes in the composition of the generated plasma are due to electrode heating, and therefore, only electrode temperature control during plasma generation is related to electrode cooling. However, it has been found that under atmospheric pressure, there is no direct relationship between temperature increase and the decomposition of specific molecules in the plasma (e.g., ozone). In other words, it is the heating and cooling of the electrode, not simply the cooling of the electrode, that is important for controlling the plasma composition. Furthermore, it has been found that dynamic heating and cooling of the electrode results in well-controlled species generation.

[0029] Figures 2A and 2B show the relationship between the composition and temperature of plasma generated at atmospheric pressure. Figure 2A shows the relationship between temperature (solid line) and ppm (dashed line) in ozone plasma over time, and Figure 2B shows the relationship between temperature (solid line) and ppm (dashed line) in nitrogen dioxide plasma over time. As can be seen from Figures 2A and 2B, the relationship between temperature and plasma composition is not a simple linear relationship, and precise temperature control (heating and cooling) of the electrodes is important for controlling the plasma composition.

[0030] The temperature control unit 130 advantageously performs both cooling and heating of the first electrode 101 or the dielectrics 121 and 122. It has been found that controlling the temperature of at least one of the electrodes and the dielectric can achieve good control of the entire system. In fact, for example, when the electrode 101 and the dielectric 121 are in close proximity, as shown in Figures 1A and 1B, controlling the temperature of one element will also change the temperature of the other element. The temperature control unit is preferably a thermoelectric (Peltier) module. The use of a thermoelectric module advantageously allows for rapid switching between cooling and heating, which is essential for maintaining the generation of a plasma with a specific desired composition. Furthermore, compared to, for example, water cooling / heating, the use of a thermoelectric module facilitates dynamic cooling and heating of the first electrode 101 in a short time, which may be a viable alternative with an appropriate fluid-based system. Another advantage of thermoelectric modules is that they can be easily combined. This means that multiple thermoelectric modules may be used to expand or contract the plasma generation region. Thus, depending on how the multiple thermoelectric modules are arranged, plasma can be generated at a larger surface area or at a higher density.

[0031] The temperature control unit 130 may be attachable to the first electrode 101 via a thermally conductive material such as a pad or paste (e.g., glue, resin, adhesive, cement). The thermally conductive material is advantageous in that it allows 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, although other fluids may be utilized as needed. In certain embodiments, mineral oil may be used because it has good thermal properties and is an electrical insulator, which can be important in systems such as the present system that utilize high voltages. In such systems, the temperature-controlled fluid is plumbed in thermal contact with the first electrode 101 in much the same manner as the Peltier device described above. That is, the tubing carrying the fluid is attached to the first electrode via a thermally conductive material to ensure good thermal contact between the tubing and the first electrode.

[0033] In another embodiment, the temperature-controlled fluid flows through the body of the electrodes or dielectric in embedded pipes or channels. This configuration allows for better heat transfer between the electrodes / dielectric and the fluid, allowing for more accurate and rapid temperature control. In large-scale systems, such configurations can be more energy-efficient and cost-effective than Peltier-based systems, but both have their advantages and can be used.

[0034] Fluidic temperature control systems 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 processing food ingredients, pharmaceutical compounds, or other more sensitive materials.

[0035] The fluidic temperature control system may include a reservoir of a suitable fluid (e.g., water or mineral oil) plumbed adjacent to and in thermal contact with the first electrode. The fluid flows from the reservoir using a suitable pump. The line containing the piping includes a temperature control unit including a heater and a cooler operable to raise or lower the temperature of the fluid in the piping, thereby similarly raising or lowering the temperature of the first electrode or dielectric. The heater and cooler ratings are selected according to the rate required to change the temperature of the fluid, and thereby the temperature of the electrode / dielectric. This is largely dependent on the dimensions of the electrode / dielectric and the equipment in which it is installed.

[0036] It is important to note that the temperature control unit 130, when attached to the electrode, is thermally connected to the first electrode 101 but electrically isolated from it. In certain embodiments, the potential difference between the first electrode 101 and the second electrode 102 may be in the range of 1-30 KV, or more typically 5-15 KV. Note that this should not be a DC voltage, but rather a time-varying voltage (e.g., an AC voltage) or pulsed in some way.

[0037] In most embodiments of the present invention, it is important to avoid arcing, so the temperature of the first electrode 101 must be controlled to ensure good thermal contact but no electrical contact. Prior art systems are known that use a Peltier temperature control element as one of the electrodes. This approach risks electrical interference from plasma generation harming the temperature control unit 130 and surrounding electronic systems, such as sensors 140 and 150. In embodiments of the present invention, the voltage 110 applied for plasma generation, whether Peltier or fluidic, is electrically isolated from any electronic components or signals involved in the operation of the temperature control unit 130.

[0038] It has been found that controlling the temperature of the first electrode / dielectric allows for better and more precise control of the device, particularly of the desired species, than, for example, controlling the temperature of the ambient environment.

[0039] It should be noted that although we have mentioned temperature control of the first electrode, the same effect can be achieved by temperature control of the second electrode, or both the first and second electrodes and the dielectric. In a sense, temperature control of the electrodes is a substitute for temperature control of the dielectric.

[0040] As shown in Figures 1A and 1B, the apparatus includes a sensor 140. Preferably, the sensor 140 includes a thermocouple. The sensor may also include a thermal imager and / or an infrared pyrometer. In Figures 1A and 1B, 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 any of the first electrode 101, the second electrode 102, the first dielectric barrier 121, or the second dielectric barrier 122.

[0041] As shown in FIGS. 1A and 1B, the apparatus includes a detector 150. The detector 150 is configured to calculate the concentration of a primary chemical species in the plasma. As previously mentioned, the primary chemical species may be a reactive nitrogen species or a reactive oxygen species. If the primary chemical species is a reactive nitrogen species, the detector 150 is configured to detect nitrogen dioxide (NO). If the primary chemical species is a reactive oxygen species, the detector 150 is configured to detect ozone (O). Advantageously, nitrogen dioxide represents a reactive nitrogen species, and ozone represents a reactive oxygen species. Advantageously, control of reactive nitrogen species is important for controlling water toxicity, and control of reactive oxygen species is important for effective use in destroying bacteria.

[0042] Detector 150 may include one or more of a UV spectrometer, an IR spectrometer, an FTIR spectrometer, an optical emission spectrometer, a mass spectrometer, an optical absorption spectrometer, a cavity ring-down spectrometer, and a laser-induced fluorescence spectrometer. For example, detector 150 may include a UV / IR spectrometer coupled with UV light for ozone quantification. FTIR spectroscopy can be used to detect both nitrogen dioxide and ozone.

[0043] 1A and 1B, the apparatus includes a processor 160. The processor may refer to 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 techniques to facilitate automatic control of the plasma composition, for example.

[0044] The processor 160 is configured to control the temperature control unit 130 based on the measured temperature and the calculated concentration. To that end, the processor 160 is in communication with the temperature control unit 130, the sensor 140, and the detector 150. The processor 160 may be in wireless communication with the temperature control unit 130, the sensor 140, and the detector 150.

[0045] The processor 160 may be configured to adjust the power supplied 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 supplied 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 supplied 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), the processor 160 may be configured to determine whether the concentration exceeds a first predetermined threshold, where the first predetermined threshold is zero (or a value close to zero, e.g., <1%, <5%, <10%), and the processor 160 may be configured to control the temperature control unit 130 only if the concentration exceeds the first predetermined threshold. In this manner, a plasma containing 100% (or a value close to 100%, e.g., >99%, >95%, >90%) of the desired species may be generated. For example, in the case of reactive nitrogen and reactive oxygen species, the transition between generating a plasma containing reactive oxygen species and generating a plasma containing reactive nitrogen species is an irreversible runaway process. By detecting the early formation of reactive nitrogen species before runaway (i.e., when the concentration exceeds the predetermined threshold of zero) and applying an appropriate level of cooling / heating, the composition of the plasma can be manipulated to maintain 100% reactive oxygen species.

[0047] In the second mode (i.e., the second chemical state), the processor 160 may be configured to determine whether the concentration exceeds a second predetermined threshold, where the second predetermined threshold is non-zero, and the processor 160 may be configured to control the temperature control unit 130 only if the concentration exceeds the second predetermined threshold. For example, when the first electrode 101 is at a particular temperature, a desired plasma is generated in which the concentration of reactive nitrogen species and the concentration of reactive oxygen species are equal. Therefore, by adjusting the power supplied to the first electrode 101 in response to the concentration of either the reactive nitrogen species or the reactive oxygen species exceeding 50%, the generation of a plasma in which the concentration of reactive nitrogen species and the concentration of reactive oxygen species are equal can be maintained.

[0048] The apparatus may be switchable between a first mode and a second mode, such that the apparatus may operate in a mode in which the generated plasma contains 100% reactive nitrogen species or 100% reactive oxygen species, or in a mode in which the generated plasma contains a mixture of reactive nitrogen species and reactive oxygen species. Therefore, the apparatus has the advantage that different plasma generation modes can be easily realized, making it useful for a variety of applications with different requirements regarding the composition of the generated plasma.

[0049] The device may be powered from a dedicated power source (i.e., a separate power source from that connected to the first electrode) to allow for extended use, or the device may be equipped with a battery, for example, to allow use without the need for mains power.

[0050] 3 illustrates a method for controlling the composition of a plasma according to one embodiment, which includes attaching a temperature control unit 130 to the first electrode 101 (S1), measuring 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 (S2), calculating the concentration of a major chemical species in the plasma using a detector 150 (S3), and controlling the temperature control unit 130 based on the measured temperature and the calculated concentration (S4).

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

[0052] In summary, the present invention provides an apparatus and method for controlling the composition of a plasma, facilitates different modes of plasma generation so that the plasma composition can be precisely controlled, and makes plasma technology applicable across a wide range of fields and industries.

[0053] The optional features described herein may be used individually or in combination with each other, as appropriate, particularly in the combinations set forth in the appended claims. As described herein, optional features of each aspect or exemplary embodiment of the present invention may also be applied to any other aspect or exemplary embodiment of the present invention, as appropriate. In other words, those skilled in the art who read this specification should consider optional features of each aspect or exemplary embodiment of the present invention to be interchangeable and combinable between different aspects and exemplary embodiments.

[0054] Any and all features disclosed in this specification (including the accompanying claims and drawings), and / or any and all method or process steps disclosed in this specification, may be combined in any combination, except combinations in which 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 therein without departing from the scope of the invention as defined in the appended claims and as described above.

Claims

1. 1. An apparatus for controlling a composition of a plasma, comprising a pair of electrodes having a dielectric barrier therebetween, the apparatus 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 calculate a concentration of a major chemical species in the plasma; and a processor configured to control the temperature control unit based on the measured temperature and the calculated concentration. Device.

2. 2. The apparatus of claim 1, wherein a power supply attached to the pair of electrodes is electrically isolated from the temperature control unit.

3. In the first mode, the processor is configured to determine whether the concentration exceeds a first predetermined threshold, the first predetermined threshold being zero; 3. The apparatus of claim 1, wherein the processor is configured to control the temperature control unit only if the concentration exceeds the first predetermined threshold.

4. In the second mode, The processor is configured to determine whether the concentration exceeds a second predetermined threshold, the second predetermined threshold being non-zero; 3. The apparatus of claim 1, wherein the processor is configured to control the temperature control unit only if the concentration exceeds the second predetermined threshold.

5. 5. The device of claim 4, wherein the device is switchable between the first mode and the second mode.

6. 6. Apparatus according to any one of claims 1 to 5, characterized in that the predominant species is a reactive nitrogen species.

7. 7. The apparatus of claim 6, wherein the detector is configured to detect nitrogen dioxide.

8. The device according to any one of claims 1 to 5, characterized in that the predominant chemical species are reactive oxygen species.

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

10. 10. The apparatus of claim 9, wherein the detector comprises at least one of a UV spectrometer and an IR spectrometer.

11. A device according to any one of the preceding claims, characterized in that the sensor comprises a thermocouple.

12. The device according to any one of claims 1 to 11, characterized in that the temperature control unit is attachable to one of the electrodes or the dielectric barrier via a thermally conductive material.

13. The device according to any one of claims 1 to 12, characterized in that the temperature control unit is either a thermoelectric module or a temperature-controlled fluid system.

14. The device according to any one of claims 1 to 13, characterized in that the dielectric material comprises at least one of alumina and quartz.

15. 15. The apparatus of any one of claims 1 to 14, configured in either a surface barrier discharge (SBD) configuration or a dielectric barrier discharge (DBD) configuration.

16. 1. A method of controlling the composition of a plasma generated by a pair of electrodes having a dielectric barrier between the electrodes, the method comprising: providing a temperature control unit in thermal contact with one of said electrodes or said dielectric barrier; measuring the temperature of one of the electrodes or the dielectric barrier using a sensor; calculating the concentration of a major chemical species in the plasma using a detector; and controlling the temperature control unit based on the measured temperature and the calculated concentration. method.

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

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