Name: how to ignite an atmospheric pressure microwave plasma torch without any additional igniters
Uploaded: 2015-04-16T15:00:00.000+00:00
Duration: 8 min 42 s
Description: Watch this Scientific Journal Video about How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters at JoVE.com

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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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

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...

Watch this Scientific Journal Video about How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters at JoVE.com

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

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 ...

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Engineering

19.5K Views.  University of Stuttgart. 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. 

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

Flame Experiments at the Advanced Light Source: New Insights into Soot Formation Processes

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics Beamline of the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory1-4. This video demonstrates how the complex chemical structures of laboratory-based model flames are analyzed using flame-sampling mass spectrometry with tunable synchrotron-generated vacuum-ultraviolet (VUV) radiation. This experimental approach combines isomer-resolving capabilities with high sensitivity and a large dynamic range5,6. The first part of the video describes experiments involving burner-stabilized, reduced-pressure (20-80 mbar) laminar premixed flames. A small hydrocarbon fuel was used for the selected flame to demonstrate the general experimental approach. It is shown how species&#8217; profiles are acquired as a function of distance from the burner surface and how the tunability of the VUV photon energy is used advantageously to identify many combustion intermediates based on their ionization energies. For example, this technique has been used to study gas-phase aspects of the soot-formation processes, and the video shows how the resonance-stabilized radicals, such as C3H3, C3H5, and i-C4H5, are identified as important intermediates7. The work has been focused on soot formation processes, and, from the chemical point of view, this process is very intriguing because chemical structures containing millions of carbon atoms are assembled from a fuel molecule possessing only a few carbon atoms in just milliseconds. The second part of the video highlights a new experiment, in which an opposed-flow diffusion flame and synchrotron-based aerosol mass spectrometry are used to study the chemical composition of the combustion-generated soot particles4. The experimental results indicate that the widely accepted H-abstraction-C2H2-addition (HACA) mechanism is not the sole molecular growth process responsible for the formation of the observed large polycyclic aromatic hydrocarbons (PAHs).

Gas sampling from laboratory-scale flames with online analysis of all species by mass spectrometry is a powerful method to investigate the complex mixture of chemical compounds occurring during combustion processes. Coupled with tunable soft ionization via synchrotron-generated vacuum-ultraviolet radiation, this technique provides isomer-resolved information and potentially fragment-free mass spectra.

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics ...

Simultaneous Synthesis of Single-walled Carbon Nanotubes and Graphene in a Magnetically-enhanced Arc Plasma

Carbon nanostructures such as single-walled carbon nanotubes (SWCNT) and graphene attract a deluge of interest of scholars nowadays due to their very promising application for molecular sensors, field effect transistor and super thin and flexible electronic devices1-4. Anodic arc discharge supported by the erosion of the anode material is one of the most practical and efficient methods, which can provide specific non-equilibrium processes and a high influx of carbon material to the developing structures at relatively higher temperature, and consequently the as-synthesized products have few structural defects and better crystallinity.
 To further improve the controllability and flexibility of the synthesis of carbon nanostructures in arc discharge, magnetic fields can be applied during the synthesis process according to the strong magnetic responses of arc plasmas. It was demonstrated that the magnetically-enhanced arc discharge can increase the average length of SWCNT 5, narrow the diameter distribution of metallic catalyst particles and carbon nanotubes 6, and change the ratio of metallic and semiconducting carbon nanotubes 7, as well as lead to graphene synthesis 8. 
 Furthermore, it is worthwhile to remark that when we introduce a non-uniform magnetic field with the component normal to the current in arc, the Lorentz force along the J&times;B direction can generate the plasmas jet and make effective delivery of carbon ion particles and heat flux to samples. As a result, large-scale graphene flakes and high-purity single-walled carbon nanotubes were simultaneously generated by such new magnetically-enhanced anodic arc method. Arc imaging, scanning electron microscope (SEM), transmission electron microscope (TEM) and Raman spectroscopy were employed to analyze the characterization of carbon nanostructures. These findings indicate a wide spectrum of opportunities to manipulate with the properties of nanostructures produced in plasmas by means of controlling the arc conditions.

Anodic arc discharge is one of the most practical and efficient methods to synthesize various carbon nanostructures. To increase the arc controllability and flexibility, a non-uniform magnetic field was introduced to process the one-step synthesis of large-scale graphene flakes and high-purity single-walled carbon nanotubes.

Carbon nanostructures such as single-walled carbon nanotubes (SWCNT) and graphene attract a deluge of interest of scholars nowadays due to their very ...

Bioengineering

Experimental Methods of Dust Charging and Mobilization on Surfaces with Exposure to Ultraviolet Radiation or Plasmas

Electrostatic dust transport has been hypothesized to explain a number of observations of unusual planetary phenomena. Here, it is demonstrated using three recently developed experiments in which dust particles are exposed to thermal plasma with beam electrons, beam electrons only, or ultraviolet (UV) radiation only. The UV light source has a narrow bandwidth in wavelength centered at 172 nm. The beam electrons with the energy of 120 eV are created with a negatively biased hot filament. When the vacuum chamber is filled with the argon gas, a thermal plasma is created in addition to the electron beam. Insulating dust particles of a few tens of microns in diameter are used in the experiments. Dust particles are recorded to be lofted to a height up to a few centimeters with a launch speed up to 1 m/s. These experiments demonstrate that photo and/or secondary electron emission from a dusty surface changes the charging mechanism of dust particles. According to the recently developed &#34;patched charge model&#34;, the emitted electrons can be re-absorbed inside microcavities between neighboring dust particles below the surface, causing the accumulation of enhanced negative charges on the surrounding dust particles. The repulsive forces between these negatively charged particles may be large enough to mobilize and lift them off the surface. These experiments present the advanced understanding of dust charging and transport on dusty surfaces, and laid a foundation for future investigations of its role in the surface evolution of airless planetary bodies.

Dust charging and mobilization is demonstrated in three experiments with exposure to thermal plasma with beam electrons, beam electrons only, or ultraviolet (UV) radiation only. These experiments present the advanced understanding of electrostatic dust transport and its role in shaping the surfaces of airless planetary bodies.

Electrostatic dust transport has been hypothesized to explain a number of observations of unusual planetary phenomena. Here, it is demonstrated using ...

Environment

Emission Spectroscopic Boundary Layer Investigation during Ablative Material Testing in Plasmatron

Ablative Thermal Protection Systems (TPS) allowed the first humans to safely return to Earth from the moon and are still considered as the only solution for future high-speed reentry missions. But despite the advancements made since Apollo, heat flux prediction remains an imperfect science and engineers resort to safety factors to determine the TPS thickness. This goes at the expense of embarked payload, hampering, for example, sample return missions. 
Ground testing in plasma wind-tunnels is currently the only affordable possibility for both material qualification and validation of material response codes. The subsonic 1.2MW Inductively Coupled Plasmatron facility at the von Karman Institute for Fluid Dynamics is able to reproduce a wide range of reentry environments. This protocol describes a procedure for the study of the gas/surface interaction on ablative materials in high enthalpy flows and presents sample results of a non-pyrolyzing, ablating carbon fiber precursor. With this publication, the authors envisage the definition of a standard procedure, facilitating comparison with other laboratories and contributing to ongoing efforts to improve heat shield reliability and reduce design uncertainties.
The described core techniques are non-intrusive methods to track the material recession with a high-speed camera along with the chemistry in the reactive boundary layer, probed by emission spectroscopy. Although optical emission spectroscopy is limited to line-of-sight measurements and is further constrained to electronically excited atoms and molecules, its simplicity and broad applicability still make it the technique of choice for analysis of the reactive boundary layer. Recession of the ablating sample further requires that the distance of the measurement location with respect to the surface is known at all times during the experiment. Calibration of the optical system of the applied three spectrometers allowed quantitative comparison. At the fiber scale, results from a post-test microscopy analysis are presented.

Development of new ablative materials and their numerical modeling requires extensive experimental investigation. This protocol describes procedures for material response characterization in plasma flows with the core techniques being non-intrusive methods to track the material recession along with the chemistry in the reactive boundary layer by emission spectroscopy.

Ablative Thermal Protection Systems (TPS) allowed the first humans to safely return to Earth from the moon and are still considered as the only solution ...

Non-equilibrium Microwave Plasma for Efficient High Temperature Chemistry

A flowing microwave plasma based methodology for converting electric energy into internal and/or translational modes of stable molecules with the purpose of efficiently driving non-equilibrium chemistry is discussed. The advantage of a flowing plasma reactor is that continuous chemical processes can be driven with the flexibility of startup times in the seconds timescale. The plasma approach is generically suitable for conversion/activation of stable molecules such as CO2, N2 and CH4. Here the reduction of CO2 to CO is used as a model system: the complementary diagnostics illustrate how a baseline thermodynamic equilibrium conversion can be exceeded by the intrinsic non-equilibrium from high vibrational excitation. Laser (Rayleigh) scattering is used to measure the reactor temperature and Fourier Transform Infrared Spectroscopy (FTIR) to characterize in situ internal (vibrational) excitation as well as the effluent composition to monitor conversion and selectivity.

This article describes a flowing microwave reactor that is used to drive efficient non-equilibrium chemistry for the application of conversion/activation of stable molecules such as CO2, N2 and CH4. The goal of the procedure described here is to measure the in situ gas temperature and gas conversion.

A flowing microwave plasma based methodology for converting electric energy into internal and/or translational modes of stable molecules with the purpose ...

Chemistry

An Atmospheric Pressure Plasma Setup to Investigate the Reactive Species Formation

Non-thermal atmospheric pressure (&#39;cold&#39;) plasmas have received increased attention in recent years due to their significant biomedical potential. The reactions of cold plasma with the surrounding atmosphere yield a variety of reactive species, which can define its effectiveness. While efficient development of cold plasma therapy requires kinetic models, model benchmarking needs empirical data. Experimental studies of the source of reactive species detected in aqueous solutions exposed to plasma are still scarce. Biomedical plasma is often operated with He or Ar feed gas, and a specific interest lies in investigation of the reactive species generated by plasma with various gas admixtures (O2, N2, air, H2O vapor, etc.) Such investigations are very complex due to difficulties in controlling the ambient atmosphere in contact with the plasma effluent. In this work, we addressed common issues of &#39;high&#39; voltage kHz frequency driven plasma jet experimental studies. A reactor was developed allowing the exclusion of ambient atmosphere from the plasma-liquid system. The system thus comprised the feed gas with admixtures and the components of the liquid sample. This controlled atmosphere allowed the investigation of the source of the reactive oxygen species induced in aqueous solutions by He-water vapor plasma. The use of isotopically labelled water allowed distinguishing between the species originating in the gas phase and those formed in the liquid. The plasma equipment was contained inside a Faraday cage to eliminate possible influence of any external field. The setup is versatile and can aid in further understanding the cold plasma-liquid interactions chemistry.

An experimental setup was created for the helium-operated kHz frequency plasma jet. The setup includes a cage for the plasma power supply and jet and an in-house built reactor to monitor plasma-induced reactive species without the interference of the ambient atmosphere.

Non-thermal atmospheric pressure (&#39;cold&#39;) plasmas have received increased attention in recent years due to their significant biomedical potential. ...

Treating Surfaces with a Cold Atmospheric Pressure Plasma using the COST-Jet

In recent years, non-thermal atmospheric pressure plasmas have been used extensively for surface treatments, in particular, due to their potential in biological applications. However, the scientific results often suffer from reproducibility problems due to unreliable plasma conditions as well as complex treatment procedures. To address this issue and provide a stable and reproducible plasma source, the COST-Jet reference source was developed.
In this work, we propose a detailed protocol to perform reliable and reproducible surface treatments using the COST reference microplasma jet (COST-Jet). Common issues and pitfalls are discussed, as well as the peculiarities of the COST-Jet compared to other devices and its advantageous remote character. A detailed description of both solid and liquid surface treatment is provided. The described methods are versatile and can be adapted for other types of atmospheric pressure plasma devices.

This protocol is presented to characterize the setup, handling, and application of the COST-Jet for the treatment of diverse surfaces such as solids and liquids.

In recent years, non-thermal atmospheric pressure plasmas have been used extensively for surface treatments, in particular, due to their potential in ...

Building Langmuir Probes and Emissive Probes for Plasma Potential Measurements in Low Pressure, Low Temperature Plasmas

Langmuir probes have long been used in experimental plasma physics research as the primary diagnostic for particle fluxes (i.e., electron and ion fluxes) and their local spatial concentrations, for electron temperatures, and for electrostatic plasma potential measurements, since its invention by Langmuir in the early 1920s. Emissive probes are used for measuring plasma potentials. The protocols exhibited in this work serve to demonstrate how these probes may be built for use in a vacuum chamber in which a plasma discharge may be confined and sustained. This involves vacuum techniques for building what is essentially an electrical feedthrough, one that is rotatable and translatable. Certainly, complete Langmuir probe systems may be purchased, but they can also be built by the user at considerable cost savings, and at the same time be more directly adapted to their use in a particular experiment. We describe the use of Langmuir probes and emissive probes in mapping the electrostatic plasma potential from the body of the plasma up to the sheath region of a plasma boundary, which in these experiments&#160;is created by a negatively biased electrode immersed within the plasma, in order to compare the two diagnostic techniques and assess their relative advantages and weaknesses. Although Langmuir probes have the advantage of measuring the plasma density and electron temperature most accurately, emissive probes can measure electrostatic plasma potentials more accurately throughout the plasma, up to and including the sheath region.

The main goal of this work is to make it easier for research groups unfamiliar with Langmuir probes and emissive probes to use them as plasma diagnostics, especially near plasma boundaries. We do this by demonstrating how to build the probes from readily available materials and supplies.

Langmuir probes have long been used in experimental plasma physics research as the primary diagnostic for particle fluxes (i.e., electron and ion fluxes) ...

Inductively Coupled Plasma Atomic Emission Spectroscopy: Principle

Inductively coupled plasma (ICP) is the most widely used plasma source in atomic emission spectroscopy (AES), also known as Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The ICP source, or torch, consists of three concentric quartz tubes with argon gas flowing through them. A spark from a Tesla coil initiates the ionization of argon, generating a high-temperature plasma.
The ions and electrons produced interact with the fluctuating magnetic field created by a water-cooled induction coil powered by a radio-frequency generator. This interaction leads to ohmic heating, forming a high-temperature plasma and providing an optimal environment for elemental analysis. Sample introduction in ICP-AES can be achieved using different methods, such as a concentric glass nebulizer or electrothermal vaporization. In the former, the sample is transported by the Bernoulli effect with the help of high-velocity argon gas, forming fine droplets that enter the plasma. In the latter, the sample is vaporized in a furnace before being introduced into the plasma via a stream of argon.
Configurations for ICP spectrometers include radial or axial viewing. Horizontally oriented, axially viewed plasma is ideal for high-sensitivity analyses. It features a unique cooled cone interface (CCI) that prevents the optics from considering the cooler plasma tail, reducing interferences and improving the system&#39;s tolerance to high dissolved solids. Vertically oriented, radially viewed plasma is suitable for challenging applications, such as the analysis of oils, organic solvents, geological/metal digests, and high total dissolved solids (TDS) solutions.
Isothermal contours depict the range of temperatures experienced by sample atoms in the plasma during their residence time before reaching the observation point. This results in more complete atomization and fewer chemical interferences. The ICP source in AES offers numerous advantages, including chemically inert atomization, uniform temperature distribution, linear calibration curves over a wide range of concentrations, and significant ionization, making it an excellent choice for ICP-MS applications.

Inductively coupled plasma (ICP) is the most widely used plasma source in atomic emission spectroscopy (AES), also known as Inductively Coupled Plasma ...

Education

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Analytical Chemistry

Unit 1

Atomic Spectroscopy

KEY TERMS AND CONCEPTS

Flame Photometry: Overview

Flame photometry, also known as flame emission spectrometry, is a technique used for the qualitative and quantitative analysis of elements present in a sample using a flame as the source of excitation energy. The concept of flame photometry was realized in the early 1860s by Kirchhoff and Bunsen, who discovered that specific elements emit characteristic radiation when excited in flames. The first instrument developed for this purpose was used to measure sodium (Na) in plant ash using a Bunsen flame. However, the challenge lay in finding the most effective way to introduce the sample into the flame. It wasn&#39;t until 1929, when Lundegardh introduced a nebulizer, that a significant breakthrough was made, allowing a reproducible introduction of the sample into the flame.
In flame emission spectrometry, the nebulizer converts a liquid sample into a fine mist or aerosol. This is achieved by passing a high-pressure gas stream over the end of a capillary tube containing the sample and aspirating it into a spray chamber. The aerosol produced is then passed to the burner, where flame heat desolvates it, forming dry particles that volatilize and produce free atoms for analysis.
Early instruments utilized quartz prism spectrographs and photographic recording to disperse and capture atomic emission lines. However, advancements in optical filters and electrical photodetectors replaced these components, improving precision and convenience.
Flame photometry involves introducing the sample solution into a nebulizer, which converts it into a fine mist or aerosol. The atomized sample then enters the flame, along with air or oxygen and a fuel gas such as propane or acetylene. The flame provides the thermal excitation necessary to energize the atoms in the sample. As these excited atoms relax, their emitted radiation is detected by a photocell or photomultiplier.
Flame photometry is particularly effective in measuring sodium, potassium, lithium, and calcium elements. The flame used in flame photometry is typically a propane-air flame with a temperature range of 1900-2000 &#176;C, although alternative flames like butane-air or natural gas-air can also be used. Flame photometry has some limitations that can be overcome by using higher temperatures and more reducing flames, such as air-acetylene, along with higher-resolution spectrometric detection. However, these approaches are not cost-competitive compared to the more broadly applicable flame atomic absorption spectrometry or AAS technique.

Flame photometry, also known as flame emission spectrometry, is a technique used for the qualitative and quantitative analysis of elements present in a ...