The authors thank Chris Mortimer, Chris Rhodes (Department of Chemistry workshops) and Kari Niemi (York Plasma Institute) for their help with the equipment. The work was supported by the Leverhulme Trust (grant No. RPG-2013-079) and EPSRC (EP/H003797/1 &amp; EP/K018388/1).

1. Shielding the Plasma Setup
<ol>
	<li>Position all parts of the electric environment inside the cage: power supply, voltage/current meter, power cable, plasma electrodes, plasma jet, etc.</li>
	<li>Make sure that the space within the cage is sufficient so that the live electrode, the ground electrode and respective cables are not in contact with each other or the metal mesh.</li>
	<li>Equip the cage with an interlock connected to the plasma power supply to avoid the risk of electric shock from the high voltage electrode during the plasma operation.</li>
	<li>Place the voltage and frequency controls on the outer surface of the cage to allow changing of the parameters without interrupting the plasma operation.</li>
	<li>Ground all metal supports inside the mesh cage and the cage itself by wiring them to an earth bonding plug.</li>
</ol>
2. Discharge Parameters
<ol>
	<li>Position the live electrode below the ground electrode on the glass tube (i.e., closer to the tube nozzle).</li>
	<li>Connect the voltage probe to the plasma power supply to measure the operating voltage, and pass the ground electrode through the circular current probe to monitor the return current.</li>
	<li>Connect both the voltage and the current probe to an oscilloscope, monitoring the current, the voltage and the plasma operating frequency (determined by either the current or the voltage probe).</li>
	<li>Set the flow of gas through the glass tube to 2 slm using the mass flow controllers (MFCs).</li>
	<li>Ignite the plasma in a glass tube with the feed gas helium passing through it by turning on the plasma power supply. Using the readings from the probes, set the voltage and frequency of the discharge to 18 kV and 25 kHz, respectively. 
	NOTE: Parameter variations are carried out to determine the minimal voltage and frequency at which the discharge is occurring with the highest molecular content of all the experiments. The increased molecular content requires higher voltage for the plasma to be ignited. Note that elevated voltages can result in significant gas temperature increase of the plasma, thus leading to increased evaporation of the liquid sample.</li>
	<li>Keep the voltage constant in all experiments.</li>
</ol>
3. Introducing Admixtures to the Feed Gas
<ol>
	<li>Connect the second MFC to the main feed gas tubing using a T-connector.</li>
	<li>To add the water vapor to the feed gas, direct an MFC-regulated flow of helium through a Drechsel flask filled with water and positioned outside (on top or on the side) of the mesh cage.</li>
	<li>Obtain a desired level of saturation by splitting the flow of the feed gas. Direct 10% of the gas flow (200 sccm) through the Drechsel flask with water (H216O) to achieve a 10% saturation of the feed gas.</li>
	<li>Using the T-connector, combine this fully water vapor-saturated gas with the 90% (1,800 sccm) of the dry gas flow.</li>
</ol>
4. The Reactor
<ol>
	<li>Prepare a glass reactor consisting of two parts, upper and lower. Equip the lower part of the with an exhaust tube.</li>
	<li>Position the glass reactor at the nozzle of the plasma jet.</li>
	<li>Insert the plasma jet nozzle into a rubber grommet inside the opening in the upper part of the reactor.</li>
	<li>Prepare the container consisting of a well-like reservoir on top of a stand. Make both the stand and the well from a dielectric material (e.g., glass, quartz glass).</li>
	<li>Place the sample container inside the reactor so that it is exposed to the plasma effluent from the nozzle of the jet.</li>
	<li>Put a liquid H217O sample inside the sample container. For the detection of the hydroxyl radicals, use a solution of the 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) spin trap (see 5.1). 
	NOTE: The choice of the spin trap as well as the choice of the liquid sample components depends on the specific species investigated. For example, the source of the &#8226;OH radical is studied using H216O/H217O and DMPO spin trap. The source of &#8226;H radical requires the use of an H2O/D2O (gas and liquid). N-tert-Butyl-&#945;-phenylnitrone (PBN) should be used for the detection of the &#8226;H radical. In the case of He plasma with H2O vapor, it was shown to predominantly trap hydrogen radical, while DMPO formed mostly DMPO-OH adduct15.</li>
	<li>Connect the two reactor parts via the ground glass surfaces contact.</li>
</ol>
5. Spin Trapping of Radical Species
<ol>
	<li>Prepare the solutions of the chosen spin trap with the required concentration. For aqueous solutions, use de-ionized water. For nitrone spin traps (such as DMPO), use a 100 mM concentration.</li>
	<li>Pre-flush the reactor with the feed gas (2 slm) for 30 sec.</li>
	<li>Ignite the plasma (see 2.5) and expose the liquid sample to the plasma effluent for a set period of time (e.g., 60 sec).</li>
	<li>After a required exposure time, switch off the plasma power supply and open the reactor. Remove the sample container from the reactor.</li>
	<li>Collect the sample and analyze it using the electron paramagnetic resonance spectroscopy (EPR)15.</li>
</ol>

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R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> CRC Handbook of Chemistry and Physics. , (1992).</li><li>Tsuchiya, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nitric+oxide-forming+reactions+of+the+water-soluble+nitric+oxide+spin-trapping+agent,+MGD.">Nitric oxide-forming reactions of the water-soluble nitric oxide spin-trapping agent, MGD.</a> Free Radic. Biol. Med. 27, 347-355 (1999).</li><li>Robert, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rare+gas+flow+structuration+in+plasma+jet+experiments.">Rare gas flow structuration in plasma jet experiments.</a> Plasma Sources Sci. Technol. 23, 012003 (2014).</li><li>Allen, T. 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The authors have nothing to disclose.

Here, we demonstrate the use of an in-house built atmospheric pressure plasma setup. The metal mesh cage helps to achieve reproducible plasma conditions with minimized interference from external fields, at the same time protecting nearby sensitive equipment from possible interference and/or damage by any plasma-induced fields. The shielding (caging) of the setup depends on the type of operated plasma and its electrical characteristics. The aim is to ensure the absence of external interference on the plasma operation and avoid the plasma fields interfering with surrounding equipment. In this case the mesh size is 22 mm, however, reduced mesh size may be required for different plasmas. The plasma operation parameters were controlled using a voltage and a current probe connected to an oscilloscope. The introduction of the high voltage probe significantly changes the electric environment, and therefore the probe must become part of the electrical system and be positioned the same way throughout all of the experiments.
The use of the glass reactor encapsulating the sample and the plasma jet allows exclusion of the ambient atmosphere of often unknown composition from the reaction system. In the presented results (vide supra), it was used to determine the source of the plasma-induced reactive oxygen species in the aqueous sample exposed to the plasma effluent. Such investigation is possible if the molecules of the liquid water and the water in the feed gas (vapor) can be differentiated. To determine whether the hydroxyl radicals were formed in the gas phase or from the liquid water molecules, isotopically labelled water was introduced: H217O as the liquid medium, H216O vapor in the feed gas. If a hypothetical experiment was conducted in an open atmosphere, distinguishing between the two phases would have been hampered by the presence of the water vapor in the surrounding air. An alternative method to minimize the influence of the surrounding atmosphere was demonstrated in the literature, in which the diffusion of the species from the atmosphere into the plasma effluent was prevented using a shielding gas17. The shielding gas (N2 or O2) creates a gas curtain with a known composition18. The reactor presented in this manuscript is a simple way to remove the influence of the ambient air components (such as water vapor), and can be used with different plasma jets without the introduction of the additional gas flow. Similar to the &#8226;OH radical, the source of the &#8226;H radical can be determined by employing a D2O/H2O system. The inexpensive D2O can also be introduced into the feed gas as a vapor as described above.
The saturation of the gas with H2O vapor was determined by weighing the Drechsel flask before and after bubbling the gas flow through it. The relative humidity (i.e., saturation) of the gas is calculated by the amount of the water evaporated and the volume of gas passed through.
Note that in prolonged experiments, the temperature of the liquid in the Drechsel flask may decrease due to the evaporation. The relative humidity is calculated for a specific temperature. The calculated values are further compared with those in literature19 to determine the relative humidity of the feed gas. We have empirically discovered that a flow of up to 2 slm of He through a water-filled Drechsel flask fully saturates the gas with water vapor. However, elevated flow rates may not allow sufficient residence time of the gas in the liquid for full saturation. Other saturation techniques may be required.
Another challenging task is ensuring that no surrounding air is present in the system. The reactor is pre-flushed with the feed gas to remove the residual air. The time required for pre-flushing will depend on the volume of the reactor and the flow of the feed gas. The absence of external ambient air diffusion and entrainment into the system such as a helium feed gas plasma system can be tested using an &#8226;NO radical trapping reaction. Nitric oxide generated by plasma from N2 and O2 molecules of air can be detected by EPR as a radical adduct of the (MGD)2Fe2+ complex20 (MGD = N-methyl-D-glucamine dithiocarbamate). In the case of the complete absence of air, the EPR signal of the adduct is not observed. The absence of external water molecules in the reactor can be demonstrated by the following experiment. A liquid sample of D2O is exposed to a dry feed gas plasma. The NMR analysis of the post-exposure sample reveals the amount of H2O brought into the liquid during the exposure. This allows to estimate the amount of the residual H2O in the tubing used for the feed gas15 in the experiment.
The sample container design is crucial in the experimental work. Initially, we have attempted using plastic and glass microcentrifuge tubes. Together with relatively high plasma feed gas flow, the small diameter of the opening does not let the surrounding air penetrate the microcentrifuge tube. However, this has many disadvantages. The plasma exhibited arching and large temperature increase near the edges of the microcentrifuge tube. The delivery of the species from the gas phase into the liquid was also significantly less efficient due to the different gas phase dynamics and the low surface area (and large volume) of the liquid sample. Thus, the surface area of the liquid sample is crucial for the delivery of the reactive species from the gas phase to the liquid sample. This is especially important for the short-lived radicals. The liquid sample container must therefore be designed to allow the exposed liquid to have high surface area for efficient diffusion. The sample should also have low depth to minimize the convection-related limitations of the liquid sample. It must be taken into account that elevated gas flows and especially with ignited plasma create significant disturbances at the surface of the liquid sample21. Therefore, the sample container has a well-like shape with diameter and depth required for the specific experiment. The height of the stand on which the well is positioned can be adjusted to experimental needs. The rubber grommet through which the plasma jet is inserted into the reactor makes it possible to change the contact angle of the effluent with the liquid.
The presented method allows investigation of the source of the reactive species (&#8226;OH, &#8226;H, etc.) induced in the liquid by a kHz frequency parallel field plasma jet. The method employing a glass reactor surrounding the jet is not limited to the described conditions, and can be used with other atmospheric pressure plasmas. The method allows introduction of any admixtures to the feed gas: vapor, O2, N2, etc. Among its other advantages is the possibility of conducting optical measurements inside it, although in this case optical quality quartz glass must be used as a reactor material. The exhaust tube in the lower part of the reactor allows using the plasma jet in virtually any lab: the exhaust can be connected via plastic tubing to a remote extraction hood. The reactor concept is versatile and can be used in research of different plasmas where controlled atmosphere is required. For example, polymerization of styrene is inhibited by the oxygen species22, but can be observed in the reactor when liquid styrene is exposed to the helium feed gas plasma.

Low-temperature atmospheric pressure plasmas (LTPs) have attracted increased attention in recent years due to their vast potential for biomedical applications1-3. Upon contact with ambient atmosphere, LTP reacts with molecular content of air (N2, O2, H2O vapor), generating a variety of reactive oxygen and nitrogen species (RONS)2,4. Among these are relatively stable species (such as hydrogen peroxide, ozone, nitrite and nitrate anions) and highly reactive radicals (&#8226;OH, &#8226;OOH/O2&#8226;-, &#8226;H, &#8226;NO, etc.). These species, initially generated in the gas phase, are further delivered by the plasma to the biological substrate5. RONS interact with substrates and thus define the antimicrobial, anticancer and antiviral effects of LTP6-8.
The development of LTP therapies requires complex modelling of the reactions of RONS9. Water is an essential part of the biological milieu, and the reactions in the aqueous phase increase the complexity of the system dramatically. The investigation of the gas-phase plasma is widely performed using various analytical techniques, including optical emission spectroscopy, laser induced fluorescence, infrared spectroscopy, mass spectrometry (MS), etc.10-12. At the same time, detailed investigations of the species detected in the liquid phase are still scarce. Available reports describe the use of various analytical methods such as UV and electron paramagnetic resonance (EPR) spectroscopy, cytometry, etc. for the detection of RONS in aqueous solutions13,14. EPR is one of the most direct methods for radical detection in the liquid. However, many radical species cannot be detected by EPR due to their short life time. In these cases, spin trapping is often used. Spin trapping a technique involving a compound (spin trap) which rapidly and selectively reacts with the radical to yield a more persistent radical adduct (e.g., DMPO reacts with the hydroxyl radical, forming DMPO-OH adduct).
The common challenges in plasma-liquid interaction studies are the inability to control the ambient atmosphere around the plasma effluent and other interfering factors (external fields, environment-sensitive power supply parts, etc.). Here, we demonstrate the use of a setup comprising of a metal mesh case containing the operated plasma and an in-house built reactor around the plasma jet nozzle. The metal mesh serves as the Faraday cage, allowing significantly improved reproducibility and general operability of the plasma jet. The glass reactor encapsulates both the plasma jet and the liquid sample, excluding the surrounding atmosphere from the system.
This method can be employed for any atmospheric pressure plasma jet in contact with liquid solutions. For example, we have recently presented an investigation of the source of the reactive oxygen species detected in an aqueous sample exposed to plasma. Isotopically labelled water was used to distinguish between the species formed in the liquid and in the gas phase of the plasma jet-liquid solution system15.

<table><tbody><tr><td>Plasma Resonant and Dielectric Barrier Corona Driver power supply&amp;nbsp;</td><td>Information Unlimited</td><td></td><td>PVM500&amp;nbsp;</td></tr><tr><td>Mass flow controller (MFC)</td><td>Brooks Instruments&amp;nbsp;</td><td></td><td>2 slm (He calib.)</td></tr><tr><td>MFC</td><td>Brooks Instruments&amp;nbsp;</td><td></td><td>5 slm (He calib.)</td></tr><tr><td>Microcomputer controller for MFCs</td><td>Brooks Instruments&amp;nbsp;</td><td></td><td>0254</td></tr><tr><td>H&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;17&lt;/sup&gt;O</td><td>Icon Isotopes</td><td>IO 6245</td><td></td></tr><tr><td>5,5-dimethyl-1-pyrroline &lt;em&gt;N&lt;/em&gt;-oxide</td><td>Dojindo Molecular Technologies, Inc.&amp;nbsp;</td><td>D048-10</td><td>&amp;ge;99%</td></tr><tr><td>2,2,6,6-tetramethylpiperidine 1-oxyl&amp;nbsp;</td><td>Sigma-Aldrich</td><td>214000</td><td>98%</td></tr><tr><td>Helium</td><td>BOC UK</td><td>110745-V</td><td>99.996%</td></tr><tr><td>High voltage probe</td><td>Tektronix&amp;nbsp;</td><td></td><td>P6015A</td></tr><tr><td>Current probe</td><td>Ion Physics Corporation&amp;nbsp;</td><td></td><td>CM-100-L</td></tr><tr><td>Oscilloscope</td><td>Teledyne LeCroy</td><td></td><td>WaveJet 354A&amp;nbsp;</td></tr></tbody></table>

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.

Using the method and equipment described above, we have investigated the origin of the reactive oxygen species in the LTP system in contact with water. The plasma operating frequency and voltage were 25 kHz and 18 kV (peak-to-peak), respectively (Figure 1).
For example, the source of the hydroxyl radical was determined using the isotopically labelled water. This enabled distinguishing between the water molecules in the feed gas from those in the liquid sample. For that, H216O was introduced in the feed gas (as vapor). A liquid sample of H217O with the dissolved spin trap DMPO was positioned in a sample container. The reactor was pre-flushed for 30 sec with the feed gas. Importantly, in this case longer pre-flushing time may result in substantial amount of H216O delivered to the liquid H217O sample. Then, the plasma was ignited and the sample was exposed to the effluent for 60 sec. The post-exposure solution was analyzed by EPR. Two DMPO-OH radical adducts (DMPO-17OH and DMPO-16OH) were detected (Figure 2). The ratio of the adducts formed was determined via further analysis of the EPR data. The MS analysis of the liquid phase composition showed the ratio of H216O (diffused into the liquid from the gas phase) to H217O (Table 1). The comparison of the two suggested that the hydroxyl radicals detected in the liquid were, in fact, originating in the gas phase, and not in the liquid.
Similar studies can be performed by using other systems, such as a D2O/H2O system to detect the source of the &#8226;H (&#8226;D) radical15.
<img alt="Figure 1" src="/files/ftp_upload/54765/54765fig1.jpg" /> 
Figure 1. Setup used for the investigation of the source of reactive oxygen species. The plasma was generated in a quartz glass tube (4 mm internal diameter, 1 mm wall thickness) with the helium feed gas. The feed gas flow was 2 slm. The feed gas contained H2O vapor introduced as stated above. <a href="https://www.jove.com/files/ftp_upload/54765/54765fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/54765/54765fig2.jpg" /> 
Figure 2. An EPR spectrum of the mixture of DMPO-H, DMPO-16OH and DMPO-17OH radical adducts induced in the solution of DMPO in H217O exposed to plasma. The analysis was performed using the spectra simulation software using the hyperfine values available in literature16. <a href="https://www.jove.com/files/ftp_upload/54765/54765fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Table 1" src="/files/ftp_upload/54765/54765tbl1.jpg" /> 
Table 1. Concentration of the DMPO-16OH and DMPO-17OH radical adducts and the amount of H216O in the liquid H217O sample after the plasma exposure. The absolute quantities of adducts concentrations were obtained using the EPR calibration with the stable radical 2,2,6,6-Tetramethylpiperidine 1-oxyl (TEMPO). In the case of no added water vapor (entry 1), a residual humidity was present in the feed gas. The relative amounts of H217O and H216O in the liquid sample were determined using a hydrolysis reaction of cinnamoyl chloride yielding a mixture 16O- and 17O-cinnamic acids upon reaction with the post-plasma exposure solution. The resulting mixture was analyzed by high resolution mass spectrometry as described elsewhere15.

Watch this Scientific Journal Video about An Atmospheric Pressure Plasma Setup to Investigate the Reactive Species Formation at JoVE.com

An Atmospheric Pressure Plasma Setup to Investigate the Reactive Species Formation

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. ...

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9.8K Views.  University of York. 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. 

Video: An Atmospheric Pressure Plasma Setup to Investigate the Reactive Species Formation

Encapsulation and Permeability Characteristics of Plasma Polymerized Hollow Particles

In this protocol, core-shell nanostructures are synthesized by plasma enhanced chemical vapor deposition. We produce an amorphous barrier by plasma polymerization of isopropanol on various solid substrates, including silica and potassium chloride. This versatile technique is used to treat nanoparticles and nanopowders with sizes ranging from 37 nm to 1 micron, by depositing films whose thickness can be anywhere from 1 nm to upwards of 100 nm. Dissolution of the core allows us to study the rate of permeation through the film. In these experiments, we determine the diffusion coefficient of KCl through the barrier film by coating KCL nanocrystals and subsequently monitoring the ionic conductivity of the coated particles suspended in water. The primary interest in this process is the encapsulation and delayed release of solutes. The thickness of the shell is one of the independent variables by which we control the rate of release. It has a strong effect on the rate of release, which increases from a six-hour release (shell thickness is 20 nm) to a long-term release over 30 days (shell thickness is 95 nm). The release profile shows a characteristic behavior: a fast release (35% of the final materials) during the first five minutes after the beginning of the dissolution, and a slower release till all of the core materials come out.

We have used plasma enhanced chemical vapor deposition to deposit thin films ranging from a few nm to several 100 nm on nano-sized particles of various materials. We subsequently etch the core material to produce hollow nanoshells whose permeability is controlled by the thickness of the shell. We characterize the permeability of these coatings to small solutes and demonstrate that these barriers can provide sustained release of the core material over several days.

In this protocol, core-shell nanostructures are synthesized by plasma enhanced chemical vapor deposition. We produce an amorphous barrier by plasma ...

Synthesis and Microdiffraction at Extreme Pressures and Temperatures

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary interiors, design materials with novel properties, understand the mechanical behavior of materials exposed to very high stresses as in explosions or impacts. Synthesis and structural analysis of materials at extreme conditions of pressure and temperature entails remarkable technical challenges. In the laser heated diamond anvil cell (LH-DAC), very high pressure is generated between the tips of two opposing diamond anvils forced against each other; focused infrared laser beams, shined through the diamonds, allow to reach very high temperatures on samples absorbing the laser radiation. When the LH-DAC is installed in a synchrotron beamline that provides extremely brilliant x-ray radiation, the structure of materials under extreme conditions can be probed in situ. LH-DAC samples, although very small, can show highly variable grain size, phase and chemical composition. In order to obtain the high resolution structural analysis and the most comprehensive characterization of a sample, we collect diffraction data in 2D grids and combine powder, single crystal and multigrain diffraction techniques. Representative results obtained in the synthesis of a new iron oxide, Fe4O5 1 will be shown.

The laser heated diamond anvil cell combined with synchrotron micro-diffraction techniques allows researchers to explore the nature and properties of new phases of matter at extreme pressure and temperature (PT) conditions. Heterogeneous samples can be characterized in situ under high pressure by 2D mapping and combined powder, single-crystal and multigrain diffraction approaches.

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary ...

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.

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 ...

Basic Research in Plasma Medicine - A Throughput Approach from Liquids to Cells

In plasma medicine, ionized gases with temperatures close to that of vertebrate systems are applied to cells and tissues. Cold plasmas generate reactive species known to redox regulate biological processes in health and disease. Pre-clinical and clinical evidence points to beneficial effects of plasma treatment in the healing of chronic ulcer of the skin. Other emerging topics, such as plasma cancer treatment, are receiving increasing attention. Plasma medical research requires interdisciplinary expertise in physics, chemistry, and biomedicine. One goal of plasma research is to characterize plasma-treated cells in a variety of specific applications. This includes, for example, cell count and viability, cellular oxidation, mitochondrial activity, cytotoxicity and mode of cell death, cell cycle analysis, cell surface marker expression, and cytokine release. This study describes the essential equipment and workflows required for such research in plasma biomedicine. It describes the proper operation of an atmospheric pressure argon plasma jet, specifically monitoring its basic emission spectra and feed gas settings to modulate reactive species output. Using a high-precision xyz-table and computer software, the jet is hovered in millisecond-precision over the cavities of 96-well plates in micrometer-precision for maximal reproducibility. Downstream assays for liquid analysis of redox-active molecules are shown, and target cells are plasma-treated. Specifically, melanoma cells are analyzed in an efficient sequence of different consecutive assays but using the same cells: measurement of metabolic activity, total cell area, and surface marker expression of calreticulin, a molecule important for the immunogenic cell death of cancer cells. These assays retrieve content-rich biological information about plasma effects from a single plate. Altogether, this study describes the essential steps and protocols for plasma medical research.

A high-throughput cold physical plasma treatment protocol of liquids and cells is shown. It involves setting up different feed gas compositions for plasma ignition, measuring the plasma&#39;s emission spectra, and the subsequent analysis of liquids and cellular activity after plasma treatment.

In plasma medicine, ionized gases with temperatures close to that of vertebrate systems are applied to cells and tissues. Cold plasmas generate reactive ...

Environment

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 ...

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

Total Internal Reflection Absorption Spectroscopy (TIRAS) for the Detection of Solvated Electrons at a Plasma-liquid Interface

The total internal reflection absorption spectroscopy (TIRAS) method presented in this article uses an inexpensive diode laser to detect solvated electrons produced by a low-temperature plasma in contact with an aqueous solution. Solvated electrons are powerful reducing agents, and it has been postulated that they play an important role in the interfacial chemistry between a gaseous plasma or discharge and a conductive liquid. However, due to the high local concentrations of reactive species at the interface, they have a short average lifetime (~1 &#181;s), which makes them extremely difficult to detect. The TIRAS technique uses a unique total internal reflection geometry combined with amplitude-modulated lock-in amplification to distinguish solvated electrons&#39; absorbance signal from other spurious noise sources. This enables the in situ detection of short-lived intermediates in the interfacial region, as opposed to the bulk measurement of stable products in the solution. This approach is especially attractive for the field of plasma electrochemistry, where much of the important chemistry is driven by short-lived free radicals. This experimental method has been used to analyze the reduction of nitrite (NO2-(aq)), nitrate (NO3-(aq)), hydrogen peroxide (H2O2(aq)), and dissolved carbon dioxide (CO2(aq)) by plasma-solvated electrons and deduce effective rate constants. Limitations of the method may arise in the presence of unintended parallel reactions, such as air contamination in the plasma, and absorbance measurements may also be hindered by the precipitation of reduced electrochemical products. Overall, the TIRAS method can be a powerful tool for studying the plasma-liquid interface, but its effectiveness depends on the particular system and reaction chemistry under study.

Total Internal Reflection Absorption Spectroscopy TIRAS for the Detection of Solvated Electrons at a Plasma-liquid Interface

This article presents a total internal reflection absorption spectroscopy (TIRAS) method for measuring short-lived free radicals at a plasma-liquid interface. In particular, TIRAS is used to identify solvated electrons based on their optical absorbance of red light near 700 nm.

The total internal reflection absorption spectroscopy (TIRAS) method presented in this article uses an inexpensive diode laser to detect solvated ...

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) ...