Name: How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters (Video) | JoVE Journal
Uploaded: 2015-04-16T15:00:00.000+00:00
Duration: 8 min 42 s
Description: Learn to ignite an atmospheric pressure microwave plasma torch without additional igniters using frequency-matched resonance and three-stub tuner optimization. This method enables stable, continuous plasma operation for industrial applications.

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5 minutes

The authors would like to thank the Arbeitsgemeinschaft industrieller Forschungsvereinigungen &#8222;Otto von Guericke&#8220; e.V., AiF (German Federation of Industrial Research Associations) and the Deutsche Forschungsgemeinschaft, DFG (German Research Foundation) for partly funding the presented work under contract number 14248 and STR 662/4-1, respectively.

1. Measurement of the Magnetron
Note: The schematic of the experimental setup for measuring the magnetron is depicted in Figure 1A.
<ol>
	<li>Connect the magnetron to an insulator consisting of a circulator and a water load with 10 screws.</li>
	<li>Connect the insulator to a directional coupler with 10 screws.</li>
	<li>Connect the directional coupler to a second water load with 10 screws.</li>
	<li>Supply all water loads with water.</li>
	<li>Calibrate the spectrum analyzer with its calibration function according to manufacturer&#8217;s protocol.</li>
	<li>Connect a 20 dB attenuator to the spectrum analyzer by plugging the 20 dB attenuator to the spectrum analyzer. 
	Note: The 20 dB attenuator is used to protect the spectrum analyzer from too high powers above 1 W.</li>
	<li>Connect the 20 dB attenuator equipped spectrum analyzer to the end of the coaxial cable equipped with a BNC connector by plugging the coaxial cable into the 20 dB attenuator.</li>
	<li>Connect the end of the coaxial cable equipped with an N connector to the directional coupler by plugging the coaxial cable to the directional cable.</li>
	<li>Switch on the magnetron via the power supply and the spectrum of the emitted microwave is displayed on the spectrum analyzer.</li>
	<li>If necessary, adjust the displayed abscissa, ordinate and their resolution according to the manual of the spectrum analyzer.</li>
	<li>To measure the frequency of the output microwave in dependence of the microwave power, increase the microwave power from 10% to the maximum of the output power in 5% to 10% steps and for every step determine the frequency of the maximal amplitude of the spectrum displayed by the spectrum analyzer. 
	Note: Usually, the frequency spectrum of a magnetron below 10% of its maximum output power is very broad, exhibits many different peaks and therefore is not usable.</li>
</ol>
2. Adjustment of the Resonance Frequency
Note: The schematic of the experimental setup for measuring and adjusting the resonance frequency is depicted in Figure 2A.
<ol>
	<li>Calibrate the network analyzer with the calibration kit for S11 operation (according to manufacturer&#8217;s protocol).</li>
	<li>Connect the coaxial cable via the N-connector to the coaxial part of a coaxial-to-rectangular-wave guide transition by plugging the coaxial cable to the coaxial-to-wave-guide-transition.</li>
	<li>Connect the rectangular part of the coaxial-to-rectangular-wave guide transition to a three stub tuner with 10 screws.</li>
	<li>Connect the three stub tuner to the microwave plasma torch assembly with 10 screws.</li>
	<li>In the network analyzer menu switch to S11 operation.</li>
	<li>In the network analyzer menu switch to VSWR mode or to log mode.</li>
	<li>Iteratively adjust the resonance frequency of the microwave plasma torch assembly to the measured frequency of the magnetron at an output power of 25%&#8211; 60% of the maximum output power by moving the nozzle up and down. The resonance frequency of the microwave plasma torch assembly is given by the dip of the S11 parameter measurement as depicted in Figure 2B. Adjust this dip by moving the nozzle up and down to the recommended frequency.</li>
	<li>When the resonance frequency is adjusted, lock the position of the nozzle with the locking nut.</li>
	<li>Increase the forward microwave power iteratively by adjusting the three stubs of the three stub tuner by moving the stubs up and down. The microwave power absorbed by the microwave plasma torch assembly is given by the depth of the dip of the S11 parameter. Thus, maximize this dip by adjusting the stubs of the three stub tuner. Commonly, it is sufficient that two of the three stubs are used.</li>
</ol>
3. Ignition of the Plasma
<ol>
	<li>Wear UV protection glasses since the plasma emits UV radiation. Operate the plasma torch under local gas ventilation since the plasma produces nitride oxides.</li>
	<li>Connect the microwave plasma torch assembly with the adjusted coaxial resonator (nozzle is locked) and the adjusted three stub tuner to the magnetron equipped with an insulator consisting of a circulator connected to a water load.</li>
	<li>Connect the gas supply to the microwave plasma torch.</li>
	<li>Turn on the gas supply to 5 to 20 slm.</li>
	<li>Since microwave radiation in higher doses is harmful especially for the eyes, check that there are no microwave leakages.
	<ol>
		<li>To do so, turn on the microwave at a very low power of 10% to 12% and check all microwave connections with a microwave meter for leakages.</li>
		<li>If there are any leakages remove them completely before increasing the microwave power or operating the microwave plasma torch.</li>
	</ol>
	</li>
	<li>If there are no leakages turn on the microwave starting with low powers of 10% and increase the microwave power slowly within 10 to 60 sec until the plasma ignites in the quartz tube of the microwave plasma torch.</li>
	<li>Carefully observe if and where the plasma ignites but be careful with possibly radiated microwaves. Preferably use a mirror for the observation of the plasma ignition.</li>
	<li>If no plasma ignites, switch off the microwave power and carefully check if the microwave power is properly coupled into the coaxial resonator and not misguided to other components heating them up or even harming them. Check if some components are getting heated up.
	<ol>
		<li>If any component gets heated up &#8212; i.e., the microwave power is misguided &#8212; move all stubs of the three stub tuner out of the waveguide and adjust them to maximize the microwave coupling into the plasma torch assembly as described in step 2.9. Then start again with step 3.1.</li>
		<li>Adjust the resonance frequency of the coaxial resonator of the plasma torch to the sending frequency of the magnetron at a high enough microwave power output of 25% to 60% of the maximum output power with the network analyzer as described in step 2. To improve the ignition, adjust the resonance frequency of the coaxial resonator as described in step 2 to a higher output power. Then start again with step 3.1.</li>
	</ol>
	</li>
	<li>If the plasma ignites somewhere in the plasma torch and does not automatically switch to the coaxial or cylindrical mode, vary the supplied microwave power and gas flow until it burns in the cylindrical mode.</li>
	<li>When the plasma burns in the cylindrical mode, iteratively adjust the stubs of the three stub tuner by moving them up and down so that all of the supplied microwave power is absorbed by the plasma and the reflected microwave power becomes zero. 
	Note: If a microwave diode is connected to the water load and to the corresponding input of the control unit, the reflected microwave power is displayed at the control unit of the microwave power supply. How to do this is described in the manual of the microwave power supply.</li>
	<li>When higher microwave powers of 1.5 kW or more and low gas flows of less than 15 slm are used, check carefully that the plasma does not touch the walls of the quartz tube. The quartz tube must not glow anywhere.</li>
	<li>If the quartz tube glows red, decrease the microwave power or increase the gas flow until it vanishes completely.</li>
	<li>Since microwaves can be radiated by the plasma due to the conductivity of the plasma, check with a microwave meter that the radiated microwave power is below the threshold.</li>
	<li>If the radiated microwave power is above the threshold, shield the plasma with a metallic mesh where the mesh size is much smaller than half of the used microwave wave length.</li>
</ol>
4. High-speed Camera Movie of the Plasma Ignition
Note: Since the ignition of the plasma and its transition to the cylindrical mode is in the range of some hundred milliseconds, this process can best be investigated by means of a high speed camera. However, it is not necessary to observe the ignition process by means of a high speed camera each time the plasma is ignited.
<ol>
	<li>Place the lens of the high speed camera in front of the microwave plasma torch looking through the diagnostic slit at the front of the plasma torch.</li>
	<li>Adjust until the camera is pointing into the coaxial resonator at the tip of the metallic nozzle.</li>
	<li>Focus the camera on the tip of the metallic nozzle.</li>
	<li>Start the recording with 1,000&#160;fps (frames per second) of the high speed camera.</li>
	<li>Ignite the plasma as described in section 3.</li>
</ol>
5. Stable and Continuous Plasma Operation
Note: When the plasma has been ignited in the cylindrical mode and the three stub tuner has been adjusted to maximize the absorption of the microwave power by the plasma a stable and continuous operation of the plasma torch is possible.
<ol>
	<li>Adjust the dimension &#8212; the radial and axial extension &#8212; of the plasma to the desired dimension by varying the supplied microwave power between 10% and the maximum output power and the gas flow between 10 and 70 slm. Keep the radial dimension limited to the diameter of the quartz tube. The plasma must not touch the wall of the quartz tube which means that the quartz tube must not glow.</li>
	<li>To shape the plasma to different shapes, use a short quartz tube which only confines the plasma inside of the cylindrical resonator and place one orifice on the top of the plasma torch assembly.</li>
	<li>If necessary, fasten the orifices with some screws.</li>
</ol>

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<li>Moisan, M., Pelletier, J. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aMoisan%2C+M+%22Microwave+Excited+Plasmas%22">Microwave Excited Plasmas</a>. , Elsevier. New York. (1992).</li>
<li>Moisan, M., Sauvé, G., Zakrzewski, Z., Hubert, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((An+atmospheric+pressure+waveguide+fed+microwave+plasma+torch%3A+the+TIA+design%5BTitle%5D)+AND+%22Plasma.+Sources+Sci.+Technol%22%5BJournal%5D)">An atmospheric pressure waveguide fed microwave plasma torch: the TIA design.</a> Plasma. Sources Sci. Technol. 3, 584-592 (1994).</li>
<li>Jin, Q., Zhu, C., Borer, M. W., Hieftje, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+microwave+plasma+torch+assembly+for+atomic+emission+spectrometry%5BTitle%5D)+AND+%22Spectorchim.+Acta+Part+B%22%5BJournal%5D)">A microwave plasma torch assembly for atomic emission spectrometry.</a> Spectorchim. Acta Part B. 46, 417-430 (1991).</li>
<li>Baeva, M., Pott, A., Uhlenbusch, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Modelling+of+NOx+removal+by+a+pulsed+microwave+discharge%5BTitle%5D)+AND+%22Plasma+Sources+Sci.+Technol%22%5BJournal%5D)">Modelling of NOx removal by a pulsed microwave discharge.</a> Plasma Sources Sci. Technol. 11, 135-141 (2002).</li>
<li>Korzec, D., Werner, F., Winter, R., Engemann, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Scaling+of+microwave+slot+antenna+%28SLAN%29%3A+a+concept+for+efficient+plasma+generation%5BTitle%5D)+AND+%22Plasma+Sources+Sci.+Technol%22%5BJournal%5D)">Scaling of microwave slot antenna (SLAN): a concept for efficient plasma generation.</a> Plasma Sources Sci. Technol. 5, 216-234 (1996).</li>
<li>Tendero, C., Tixier, C., Tristant, P., Desmaison, J., Leprince, P. h <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Atmospheric+pressure+plasmas%3A+A+review%5BTitle%5D)+AND+%22Spectorchimica+Acta+Part+B%22%5BJournal%5D)">Atmospheric pressure plasmas: A review.</a> Spectorchimica Acta Part B. 61, 2-30 (2006).</li>
<li>Ehlbeck, J., Ohl, A., Maaß, M., Krohmann, U., Neumann, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Moving+atmospheric+microwave+plasma+for+surface+and+volume+treatment%5BTitle%5D)+AND+%22Surface+and+Coatings+Technology%22%5BJournal%5D)">Moving atmospheric microwave plasma for surface and volume treatment.</a> Surface and Coatings Technology. 174-175, 493-497 (2003).</li>
<li>Pipa, A. V., Andrasch, M., Rackow, K., Ehlbeck, J., Weltmann, K. -D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Observation+of+microwave+volume+plasma+ignition+in+ambient+air%5BTitle%5D)+AND+%22Plasma+Sources+Sci.+Technol%22%5BJournal%5D)">Observation of microwave volume plasma ignition in ambient air.</a> Plasma Sources Sci. Technol. 21 (3), 035009(2012).</li>
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<li>Rackow, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Microwave-based+characterization+of+an+athmospheric+pressure+microwave-driven+plasma+source+for+surface+treatment%5BTitle%5D)+AND+%22Plasma+Sources+Sci.+Technol%22%5BJournal%5D)">Microwave-based characterization of an athmospheric pressure microwave-driven plasma source for surface treatment.</a> Plasma Sources Sci. Technol. 20, 1-9 (2011).</li>
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</ol>

The authors have nothing to disclose.

The presented movie explains how an ignition of an atmospheric pressure microwave plasma without any additional igniters can be realized, the basic principles of this microwave plasma torch, its adjustment, the ignition process of the plasma and its stable and continuous operation. As described in the introduction, there are already different kinds of microwave plasma torches but none of those provide an ignition of the plasma without any additional igniters as well as stable and continuous plasma operation.
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Atmospheric pressure microwave plasma torches offer a variety of different applications. On one hand they can be used for chemical volume processes and on the other hand their afterglow plasma can be applied for the treatment of surfaces. As surface treatment processes the treatment to increase the adhesion of glue, paint or lacquer or the decontamination or sterilization of surfaces can be named. The hot and reactive plasma itself can be used for volume processes like the decomposition of waste gases 1&#8211;7. These waste gases are harmful, contribute to the global warming and can hardly be degraded conventionally. However, they are needed in growing industrial sectors such as the semiconductor branch. Other applications are chemical synthesis like the dissociation of CO2 to CO and O2 or CH4 to carbon and hydrogen 8,9. Surplus electrical energy from renewable energy sources can be used to dissociate CO2 into CO and O2. The CO can be processed further to higher hydrocarbons which can be used as synthetic fuels for transportation, as platform chemicals for the chemical industry or as chemical storage.
There are some microwave plasma torches but most of them have disadvantages: They only have very small plasma volumes, need additional igniters, need cooling of the plasma reactor or can only be operated in pulsed mode 10&#8211;18. The microwave plasma torch presented in this movie offers an ignition of the plasma solely with the provided microwave power with no additional igniters as well as a stable and continuous operation without any cooling of the plasma reactor for a broad range of operation parameters and can be used for all of the above mentioned applications. The microwave plasma torch is based on a combination of two resonators: a coaxial one and a cylindrical one. The cylindrical resonator has a low quality and is operated in the well-known E010-mode with the highest electrical field in its center. The coaxial resonator is located below the cylindrical resonator and consists of a movable metallic nozzle in combination with a tangential gas supply. The high quality of the coaxial resonator exhibits a very narrow but deep resonance curve. Due to the high quality of the coaxial resonator a high electrical field can be reached which is required for the ignition of the plasma. However, the high quality of the coaxial resonator is associated with a very narrow resonance curve and therefore the resonance frequency has to perfectly match the frequency of the supplied microwave. Since the resonance frequency shifts after ignition of the plasma due to the permittivity of the plasma, the microwave can no longer penetrate into the coaxial resonator. For the continuous operation of the plasma the cylindrical resonator with a low quality and a broad resonance curve is needed.
An additional axial gas supply via the metallic nozzle of the coaxial resonator is possible. The plasma is ignited and confined in a microwave-transparent tube, for example a quartz tube. The permittivity of the quartz tube also affects the resonance frequency. Since the quartz has a permittivity of &#62; 1, the volume of the cylindrical resonator is virtually enlarged which leads to a lower resonance frequency. This phenomenon has to be considered when the dimensions of the cylindrical resonator are designed. A detailed discussion about how the resonance frequency is affected by the inserted quartz tube can be found in Reference 23. If a long and extended quartz tube is used, this can also act as the reaction chamber for the volume processes. However, for surface treatments the plasma can also be shaped differently by different kind of orifices. The microwave is supplied via a rectangular waveguide from the magnetron. To avoid noise nuisance the use of a low ripple magnetron is recommended. The magnetron which is used in the movie is a low ripple one.
For the ignition of the plasma the high quality coaxial resonator is used while a stable and continuous operation is provided by the cylindrical resonator. To achieve the ignition of the plasma by the high quality coaxial resonator the resonance frequency of this resonator has to perfectly match the frequency of the microwave provided by the used magnetron. Since all magnetrons do not emit their microwave frequency at exactly the nominal frequency and since the frequency is dependent on the output power, the magnetron has to be measured with a spectrum analyzer. The resonance frequency of the coaxial resonator can be adjusted by moving the metallic nozzle up and down. This resonance frequency can be measured and thereby also adjusted to the sending frequency of the used magnetron with a network analyzer. To reach the high electrical field at the tip of the nozzle, required for the ignition of the plasma, a three stub tuner is needed in addition. This three stub tuner is a commonly used microwave component. The three stub tuner is mounted between the microwave plasma torch and the magnetron. After the resonance frequency of the coaxial resonator is adjusted, the forward power is maximized and the reflected power minimized by iteratively adjusting the stubs of the three stub tuner.
After having adjusted the resonance frequency of the coaxial resonator as well as having maximized the forward powers by means of the three stub tuner, the plasma of the microwave plasma torch can be ignited when the microwave plasma torch is connected to a magnetron. For the ignition of the plasma a minimum microwave power of about 0.3 to 1 kW is sufficient. The plasma ignites in the coaxial resonator. After the ignition of the plasma the resonance frequency of the coaxial resonator is shifted due to the dielectric permittivity of the plasma and the microwave can no longer penetrate into the coaxial resonator. Thus, the plasma switches from the coaxial mode into its much more extended cylindrical mode burning freely-standing above the metallic nozzle in the center of the cylindrical resonator. Since the quality of the cylindrical mode is very low and therefore exhibits a broad resonance curve, the microwave can still penetrate into the cylindrical resonator despite of the shift of the resonance frequency due to the dielectric permittivity of the plasma. Thus, a continuous and stable operation of the plasma in the cylindrical mode is provided by the microwave plasma torch. However, to reach a complete absorption of the supplied microwave power, the stubs of the three stub tuner have to be readjusted. Otherwise the supplied microwave power is not completely absorbed by the plasma but some percentage of the provided microwave is reflected and absorbed by the water load.
To examine the ignition of the plasma in the coaxial mode and then its transition into the extended cylindrical mode, the plasma ignition is observed by a high speed camera.
The presented movie will show how the frequency dependence of the magnetron is measured, the resonance frequency of the coaxial resonator is adjusted, how the forward power is maximized and how the plasma is ignited by the supplied microwave power. The high speed camera recording is shown as well.

<table><tbody><tr><td>2 kW magnetron</td><td>Muegge&amp;nbsp;</td><td>MH2000S 211BA</td><td></td></tr><tr><td>2 kW power supply</td><td>Muegge&amp;nbsp;</td><td>ML2000D-111TC</td><td></td></tr><tr><td>insulator - circulator with water load</td><td>Muegge&amp;nbsp;</td><td>MW1003A-210EC</td><td></td></tr><tr><td>water load</td><td>Muegge&amp;nbsp;</td><td>MW1002E-260EC</td><td></td></tr><tr><td>three stub tuner</td><td>Muegge&amp;nbsp;</td><td>MW2009A-260ED</td><td></td></tr><tr><td>orifices</td><td>homemade</td><td></td><td></td></tr><tr><td>microwave plasma torch</td><td>homemade</td><td></td><td></td></tr><tr><td>spectrum analyzer</td><td>Agilent</td><td>E4402B</td><td></td></tr><tr><td>network analyzer</td><td>Anritsu</td><td>MS4662A</td><td></td></tr><tr><td>calibration kit</td><td>Anritsu</td><td>model 3753</td><td></td></tr><tr><td>directional coupler</td><td>homemade</td><td></td><td></td></tr><tr><td>20 dB attenuator</td><td>Weinschee engineering</td><td>20 dB AA57u8</td><td></td></tr><tr><td>coaxial to rectangular wave guide transition</td><td>Muegge&amp;nbsp;</td><td>MW5002A-260YD</td><td></td></tr><tr><td>adaptor 7-16 to N connector</td><td>Teleg&amp;auml;rtner</td><td>7-16/N Adaptor</td><td></td></tr><tr><td>coaxial cable</td><td>Rosenberger Hochfrequenztechnik</td><td>LU7_070_800</td><td></td></tr><tr><td>high speed camera</td><td>Photron</td><td>fastcam SA5</td><td></td></tr><tr><td>lens</td><td>Revueflex</td><td>makro revuenon 1:3.5/28mm</td><td></td></tr><tr><td>local gas ventilation</td><td>Industrievertrieb Henning</td><td>ACD220</td><td></td></tr><tr><td>UV protection glasses</td><td>uvex</td><td>HC-F9178265</td><td></td></tr><tr><td>microwave leakage tester</td><td>conrad electronic</td><td>not available</td><td></td></tr><tr><td>microwave survey meter</td><td>Holaday industries inc.</td><td>81273</td><td></td></tr></tbody></table>

how to ignite an atmospheric pressure microwave plasma torch without any additional igniters

How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a stable and continuous operation of the plasma is possible and the plasma torch can be used for many different applications. On one hand, the hot (3,600 K gas temperature) plasma can be used for chemical processes and on the other hand the cold afterglow (temperatures down to almost RT) can be applied for surface processes. For example chemical syntheses are interesting volume processes. Here the microwave plasma torch can be used for the decomposition of waste gases which are harmful and contribute to the global warming but are needed as etching gases in growing industry sectors like the semiconductor branch. Another application is the dissociation of CO2. Surplus electrical energy from renewable energy sources can be used to dissociate CO2 to CO and O2. The CO can be further processed to gaseous or liquid higher hydrocarbons thereby providing chemical storage of the energy, synthetic fuels or platform chemicals for the chemical industry. Applications of the afterglow of the plasma torch are the treatment of surfaces to increase the adhesion of lacquer, glue or paint, and the sterilization or decontamination of different kind of surfaces. The movie will explain how to ignite the plasma solely by microwave power without any additional igniters, e.g., electric sparks. The microwave plasma torch is based on a combination of two resonators &#8212; a coaxial one which provides the ignition of the plasma and a cylindrical one which guarantees a continuous and stable operation of the plasma after ignition. The plasma can be operated in a long microwave transparent tube for volume processes or shaped by orifices for surface treatment purposes.

To provide a plasma ignition without any additional igniters as well as a stable and continuous plasma operation a high quality coaxial resonator with an adjustable resonance frequency was combined with a low quality cylindrical resonator to a microwave plasma torch. The schematic of this plasma torch is presented in Figure 3. The plasma is confined into a microwave-transparent tube, here a quartz tube. This tube can act as a reaction chamber for volume plasma processes or a plasma brush for surface trea...

This movie shows how an atmospheric plasma torch can be ignited by microwaves with no additional igniters and provides a stable and continuous plasma operation suitable for plenty of applications.

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a ...

The overall goal of this procedure is to obtain a microwave plasma torch, which provides ignition without any additional igniters, as well as stable and continuous operation. This is accomplished by first measuring the frequency dependence of the magnetron. The second step is to adjust the resonance frequency of the coaxial resonator of the microwave plasma torch to the sending frequency of the magnetron.Next, maximize the forward microwave power by adjusting the stubs of the three stub tuner. The final step is to mount the adjusted microwave plasma torch system to the priorly measured magnetron. Ultimately, when the microwave power is supplied, the plasma ignites and can be operated stably and continuously.This method provides insight into the ignition process and operation of a microwave plasma torch. It can also be applied to other systems such as microwave micro plasma jets. Begin by preparing the magnetron.This video begins with the magnetron connected to an insulator with a circulator and a water load. The insulator is connected to a directional coupler, which is connected to a second water load before proceeding supply all water loads with water. Next, turn attention to the spectrum analyzer.Connect a 20 decibel attenuator to protect the analyzer. When power exceeds one watt, then get a coaxial cable. The cable should have a BNC connector at one end and an end connector at the other.Connect the BNC end to the attenuator and extend the cable to the directional coupler. Connect the end connector of the coaxial cable to the directional coupler. This schematic provides an overview of the equipment connections at this point.Now switch on the magnetron and view the spectrum on the spectrum analyzer Display. Proceed to measure the frequency of the output as a function of the microwave power. Do this by increasing the microwave power from 10%to 100%of its maximum output power in increments of five to 10%of maximum power.For every step, determine the frequency of the maximum amplitude displayed on the spectrum analyzer. The measured frequency dependence of the magnetron is given in this diagram. After completing the measurement, shut off the power and the water supply.Then remove the directional coupler and the second water load, leaving the magnetron and insulator connected. Once the spectrum of the magnetron has been measured, begin working with the microwave plasma torch assembly and the network analyzer. The plasma torch assembly is connected to a three stub tuner, which is connected to a coaxial rectangular transition.Use a network analyzer with an appropriate measuring cable equipped on one end and an end connector on the other. Connect the analyzer via the end connector to the coaxial rectangular waveguide transition. This schematic gives the final configuration of the equipment for adjusting the resonance frequency and the forward power.Switch the network analyzer to VSWR or log mode and S one one operation. To monitor the resonance frequency, observe the dip of the S one one parameter, which marks the resonance frequency of the microwave plasma torch assembly. Prepare to adjust the dip position by moving the nozzle of the plasma torch assembly.Make iterative adjustments to the nozzle to set the resonance frequency. Set the resonance frequency to the measured frequency of the magnetron at 25 to 60%of its maximum output power. Then lock the position of the nozzle with the locking nut.Next work to increase the forward microwave power by iteratively adjusting the stubs of the three stub tuner. Use the depth of the S one one parameter for feedback. The aim is to maximize its depth for safety.Perform plasma ignition under local gas ventilation and wear UV glasses. The apparatus for the experiment is located on the right. For the experiment.The microwave plasma torch assembly and the three stub tuner are connected to the circulator and magnetron. As in this schematic, the gas supply is being connected to the microwave plasma torch. The magnetron and insulator are located in the back, but not pictured.Here.Turn on the gas supply to five to 20 standard liters. Air per minute, turn on the microwave to 10%of maximum power, and then and ensure that there are no microwave leaks. Hold a mirror to monitor plasma ignition in the quartz tube and begin to slowly increase the power while monitoring the ignition of the plasma.Stop increasing the power when ignition has occurred. When the plasma burns in the cylindrical mode, adjust the tuner so that all of the microwave power is absorbed by the plasma. Now adjust the extent of the plasma by varying the microwave power.Note, the plasma must not touch the quartz tube. A camera at 1000 frames per second captured images of microwave plasma ignition through the diagnostic slit portions of the coaxial resonator nozzle tip and the cylindrical resonator before ignition are labeled for orientation. The microwave power is one kilowatt and the gas flow is 15 standard liter air per minute.The plasma ignites in the coaxial resonator. The plasma then winds up the metallic nozzle to its tip and begins to burn straight in the coaxial mode. As time goes on, the intensity of the plasma grows until there is a shift in the resonant frequency due to the burning plasma in the coaxial resonator.At this point, the plasma starts to break away from the nozzle tip. After complete breakaway, the plasma burns freely above the metallic nozzle. In cylindrical mode, the stubs of the three stub tuner are readjusted to the complete power absorption by the plasma.The dimensions of the plasma depend on the supplied microwave power and the gas flow. As this comparison demonstrates for the same microwave power, an increase in gas flow leads to a decrease in plasma asthma for the same gas flow. An increase in microwave power leads to an increase of plasma.After watching this video, you should have a good understanding of how the ignition and operation after presented microwave plasma touch works.

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Learn to ignite an atmospheric pressure microwave plasma torch without additional igniters using frequency-matched resonance and three-stub tuner optimization. This method enables stable, continuous plasma operation for industrial applications.

How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters

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