Name: experimental methods of dust charging and mobilization on surfaces with exposure to ultraviolet radiation or plasmas
Uploaded: 2018-04-03T13:30:00.000+00:00
Duration: 7 min 54 s
Description: Watch this Scientific Journal Video about Experimental Methods of Dust Charging and Mobilization on Surfaces with Exposure to Ultraviolet Radiation or Plasmas at JoVE.com

This work was supported by the NASA/SSERVI&#39;s Institute for Modeling Plasma, Atmospheres and Cosmic Dust (IMPACT) and by the NASA Solar Systems Workings Program (Grant number: NNX16AO81G).

1. Vacuum chamber setup
<ol>
	<li>Place an insulating rubber sheet (0.2 cm thick, 5 cm in diameter) with a central hole 1.9 cm in diameter on an insulating plate (2 cm thick and 20 cm in diameter) (Figure 2a, b). Load insulating, irregularly-shaped dust particles (between 10 and 50 &#956;m in diameter) in the hole.</li>
	<li>Place the insulating plate on a metal plate standing in the middle of a vacuum chamber. Electrically isolate the metal plate from the chamber using ceramic standoffs.</li>
	<li>Turn on the vacuum pumps (a turbo pump backed by a mechanical roughing pump) to reach the base pressure of ~ 10-6 Torr. The demonstrating experiments are performed in a cylindrical stainless-steel vacuum chamber, 50 cm in diameter and 28 cm tall (Figure 2c).</li>
	<li>Record the dust movement and lofting with a video camera at a regular speed of 30 frames/s (fps) or a high-speed (&#62; 2000 fps) camera. Use an LED light with the maximum illumination equivalent to &#62; 500W incandesce light to produce enough lighting on the dust particles for good-quality video recording. 
	NOTE: Using the rubber is because of its dark color that minimizes the light reflection to the camera. Light-colored dust particles should be used for better photographing due to the color contrast to the dark rubber surface. The thick insulating plate is used for eliminating the effect of the electric field between the surface of the insulating plate and metal plate on the dust charging and mobilization. In this demonstration, Mars simulant (JSC-Mars-1, sieved to the mean diameter of 38-48 &#956;m, mass density of 1.9 g/cm-3 and major composition of SiO2 28) were used, which resembles the general regolith dust of airless bodies in the inner solar system. Various other types of insulating dust particles were also tested, such as lunar simulant (JSC-1), lunar simulant highland (LHT) and pure silica dust.</li>
</ol>
2. Exposure to thermal plasma with beam electrons
<ol>
	<li>Attach a thoriated tungsten filament (0.1 mm thick and ~ 3 cm long) to an electrode feedthrough and install it on the top of the chamber. Then pump the chamber down to the base pressure.</li>
	<li>Fill the vacuum chamber with argon gas to the pressure of ~ 0.5 mTorr.</li>
	<li>Turn on the power supplies and set the bias voltage -120 V to the filament.</li>
	<li>Increase the heating voltage to the heating current ~ 2A until the emission current reaches a desired value (a few mA). Energetic electrons with the energy of 120 eV will be emitted from the filament. 
	NOTE: These beam-like primary electrons impact neutral argon atoms, causing them to be ionized and creating a plasma with an electron temperature around 2 eV. A large fraction of the primary beam electrons directly reaches the dusty surface without collisions with neutral atoms. Dust particles are therefore exposed to both the thermal plasma and beam electrons.</li>
	<li>To show the role of energetic beam electrons in dust transport, use an alternative operation of creating a thermal plasma above dust particles.
	<ol>
		<li>Turn on an alternative filament in the bottom of the chamber with the bias voltage -40 V and emission current up to 400 mA (Figure 2a). The primary electrons emitted from the filament will be stopped by the metal plate below the insulting plate on which the dust particles rest (Figure 2a, b).</li>
		<li>Vary the emission current to change the electric field above the surface. Higher current creates higher plasma density, thinner sheath, and thus larger electric field.</li>
	</ol>
	</li>
</ol>
3. Exposure to beam electrons only
<ol>
	<li>Setup the experiment as described in the above experiment using the top filament.</li>
	<li>Turn on the top filament under the base pressure 10-6 Torr (i.e., no argon gas fed in the chamber). No plasma is created while only the 120 eV beam electrons emitted from the filament bombard the dust particles.</li>
	<li>Operate the filament in two different modes.
	<ol>
		<li>Set the bias voltage to -120 V, then increase the heating voltage until the emission current reaches a few mA.</li>
		<li>Increase the heating voltage to reach a desired heating current ~ 2 A, then increase the bias voltage from 0 V gradually to -120 V to emit electrons with an emission current of a few mA.</li>
	</ol>
	</li>
</ol>
4. Exposure to UV radiation only
<ol>
	<li>Replace the top filament with a UV lamp (Figure 2b) and pump down the chamber to the base pressure. Use a xenon excimer Osram lamp, which emits the UV light of 172 nm wavelength. The corresponding photon energy is 7.2 eV, larger than the work function of the dust surface (~ 5.5 eV) in order to emit photoelectrons. 
	NOTE: Shorter wavelength UV that radiates higher energy photons is expected to create more charges on the dust particles and therefore more mobilization, based on the patched charge model26,27.</li>
	<li>Turn on the UV lamp to radiate dust particles. In the demonstration, the photon irradiance is 40 mW/cm-2 at the UV source and ~ 16 mW/cm-2 at the dusty surface.</li>
</ol>

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The authors have nothing to disclose.

For decades, the problem of electrostatic dust transport on the regolith of airless bodies remained an open question how regolith dust particles gain sufficiently large charges to become mobilized or lofted. Recent laboratory studies26,27 have fundamentally advanced the understanding of this problem.
Here, it is demonstrated three recently developed experiments to show dust charging and mobilization in thermal plasma with beam electron...

Airless planetary bodies, such as the Moon and asteroids, are covered with fine dust particles called regolith. These airless bodies, unlike Earth, are directly exposed to solar wind plasma and solar ultraviolet (UV) radiation, causing the regolith dust to be charged. These charged dust particles may therefore be mobilized, lofted, transported, or even ejected and lost from the surface due to electrostatic forces. The first suggested evidence of this electrostatic process was the so-called &#34;lunar horizon glow&#34;, a distinct glow above the western horizon observed shortly after sunset by Surveyor 5, 6, and 7 spacecraft five decades ago (Figure 1a)1,2,3. It has been hypothesized that this glow was caused by sunlight scattered off from electrostatically lofted dust particles (5 &#956;m radius) to a height &#60; 1 m above the surface near the lunar terminator1,2,3. Electrostatically released fine dust was also suggested to be responsible for the ray-like streamers reaching a high altitude reported by the Apollo astronauts4,5.
Ever since these Apollo observations, a number of observations over other airless bodies were also linked to the mechanisms of electrostatic dust mobilization or lofting, such as the radial spokes in the Saturn&#39;s rings6,7,8, the dust ponds on asteroid Eros (Figure 1b)9 and comet 67P10, the porous surfaces indicated from the main-belt asteroid spectra11, the unusually smooth surface of Saturn&#39;s icy moon Atlas12, and the regolith at the lunar swirls13. In addition, the degradation of the laser retroreflectors on the lunar surface may be also caused by the accumulation of electrostatically lofted dust14.
Laboratory studies have been largely motivated by these unusual space observations in order to understand the physical processes of dust charging and transport. Dust mobilization has been observed in various plasma conditions, in which dust particles are shed off from a glass sphere surface15,16, levitated in plasma sheaths17, and recorded to move on both conducting and insulating surfaces18,19,20,21. However, how dust particles gain large enough charges to be lofted or mobilized remained poorly understood. The measurements of the charges on individual dust particles on a smooth surface22 and the average charge density on a dusty surface23 immersed in plasmas show that the charges are far too small for dust particles to be lofted or mobilized.
In the prior theories16,24,25, the charging was only considered to occur on the top surface layer that is directly exposed to UV or plasma. Charges are often considered to be distributed uniformly over the entire dusty surface, i.e., each individual dust particle acquires the same amount of charge, described by the so-called &#34;shared charge model&#34;16. However, the charges calculated from this model are much smaller than the gravitational force alone. A charge fluctuation theory that accounts for the stochastic process of the fluxes of electrons and ions to the surface16,24 shows a temporal enhancement in the electrostatic force, but it remains small in comparison to the gravitational force.
In this paper, electrostatic dust lofting and mobilization is demonstrated using three recently developed experiments26, which are important for understanding dust transport on the regolith of airless planetary bodies. These experiments are performed in the conditions of thermal plasma with beam electrons, beam electrons only or UV radiation only. These experiments demonstrate the validity of the recently developed &#34;patched charge model&#34;26,27, in which microcavities formed between neighboring dust particles below the surface can re-absorb the emitted photo and/or secondary electrons, generating large negative charges on the surfaces of the neighboring dust particles. The repulsive forces between these negative charges can become large enough to mobilize or lift off the dust particles.

<table><tbody><tr><td>Vacuum chamber</td><td>Any</td><td>NA</td><td></td></tr><tr><td>Vacuum electrode feedthrough</td><td>Lesker</td><td>EFT0113053</td><td></td></tr><tr><td>Tungsten filament (0.1 mm thick)</td><td>Goodfellow</td><td>W055250</td><td>Thoriated</td></tr><tr><td>Power supply #1 (0-8V, 3A)</td><td>Agilent</td><td>E3610A</td><td>Or equivalent</td></tr><tr><td>Power supply #2 (0-140V, 0.5A)</td><td>Agilent</td><td>E3612A</td><td>Or equivalent</td></tr><tr><td>UV lamp</td><td>Osram</td><td>XERADEX L40/120/SB-SX48/KF50HV</td><td>Or equivalent</td></tr><tr><td>Dust sample</td><td>Any</td><td>Mars or Lunar simulants or other types</td><td>Irregularly-shaped, sieved, insulating</td></tr><tr><td>Insulating plate</td><td>Any</td><td>NA</td><td>Thickness &gt; 1 cm</td></tr><tr><td>Rubber sheet</td><td>Any</td><td>NA</td><td>Thickness &gt; 1 mm</td></tr><tr><td>Metal plate</td><td>Any</td><td>NA</td><td></td></tr><tr><td>Ceramic stands</td><td>McMaster</td><td>94335A130</td><td>1/2&quot; diameter</td></tr><tr><td>Video camera (consumer)</td><td>Panasonic</td><td>HC-VX870</td><td>Or equivalent</td></tr><tr><td>Video camera (high-speed)</td><td>Phantom</td><td>V2512</td><td>&gt; 1000 fps</td></tr><tr><td>LED lamp</td><td>Any</td><td>NA</td><td>&gt; 500W Tungsten Equivalent</td></tr></tbody></table>

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.

A set of experiments were performed using the top or bottom filaments. With the top filament setup, the hopping of the dust particles was recorded (Figure 3a). In contrast, the dust particles remained at rest when using the bottom filament. It has been measured that the vertical electric field at the surface was approximately same (16 V/cm) in both experiments under the conditions described in Protocol step 226. These results indicate ...

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

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 ...

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Research

JoVE Journal

Environment

8.1K Views.  University of Colorado. Stof opladen en mobilisatie wordt gedemonstreerd in drie experimenten met blootstelling aan thermisch plasma met bundel elektronen, bundel elektronen alleen of ultraviolette (UV) straling alleen. Deze experimenten presenteren het gevorderde begrip van elektrostatische stof vervoer en haar rol in het vormgeven van de oppervlakken van airless planetaire lichamen.

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

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 ...

Engineering

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet (VUV) Synchrotron Radiation

Tunable soft ionization coupled to mass spectroscopy is a powerful method to investigate isolated molecules, complexes and clusters and their spectroscopy and dynamics1-4. Fundamental studies of photoionization processes of biomolecules provide information about the electronic structure of these systems. Furthermore determinations of ionization energies and other properties of biomolecules in the gas phase are not trivial, and these experiments provide a platform to generate these data. We have developed a thermal vaporization technique coupled with supersonic molecular beams that provides a gentle way to transport these species into the gas phase. Judicious combination of source gas and temperature allows for formation of dimers and higher clusters of the DNA bases. The focus of this particular work is on the effects of non-covalent interactions, i.e., hydrogen bonding, stacking, and electrostatic interactions, on the ionization energies and proton transfer of individual biomolecules, their complexes and upon micro-hydration by water1, 5-9.
We have performed experimental and theoretical characterization of the photoionization dynamics of gas-phase uracil and 1,3-dimethyluracil dimers using molecular beams coupled with synchrotron radiation at the Chemical Dynamics Beamline10 located at the Advanced Light Source and the experimental details are visualized here. This allowed us to observe the proton transfer in 1,3-dimethyluracil dimers, a system with pi stacking geometry and with no hydrogen bonds1. Molecular beams provide a very convenient and efficient way to isolate the sample of interest from environmental perturbations which in return allows accurate comparison with electronic structure calculations11, 12. By tuning the photon energy from the synchrotron, a photoionization efficiency (PIE) curve can be plotted which informs us about the cationic electronic states. These values can then be compared to theoretical models and calculations and in turn, explain in detail the electronic structure and dynamics of the investigated species 1, 3.

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet VUV Synchrotron Radiation

A molecular beam coupled to tunable vacuum ultraviolet photoionization mass spectrometer at a synchrotron provides a convenient tool to explore the electronic structure of isolated gas phase molecules and clusters. Proton transfer mechanisms in DNA base dimers were elucidated with this technique.

Tunable soft ionization coupled to mass spectroscopy is a powerful method to investigate isolated molecules, complexes and clusters and their spectroscopy ...

Activating Molecules, Ions, and Solid Particles with Acoustic Cavitation

The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species and to the emission of light, named sonoluminescence. In this manuscript, we describe the techniques allowing study of extreme intrabubble conditions and chemical reactivity of acoustic cavitation in solutions. The analysis of sonoluminescence spectra of water sparged with noble gases provides evidence for nonequilibrium plasma formation. The photons and the "hot" particles generated by cavitation bubbles enable to excite the non-volatile species in solutions increasing their chemical reactivity. For example the mechanism of ultrabright sonoluminescence of uranyl ions in acidic solutions varies with uranium concentration: sonophotoluminescence dominates in diluted solutions, and collisional excitation contributes at higher uranium concentration. Secondary sonochemical products may arise from chemically active species that are formed inside the bubble, but then diffuse into the liquid phase and react with solution precursors to form a variety of products. For instance, the sonochemical reduction of Pt(IV) in pure water provides an innovative synthetic route for monodispersed nanoparticles of metallic platinum without any templates or capping agents. Many studies reveal the advantages of ultrasound to activate the divided solids. In general, the mechanical effects of ultrasound strongly contribute in heterogeneous systems in addition to chemical effects. In particular, the sonolysis of PuO2 powder in pure water yields stable colloids of plutonium due to both effects.

Acoustic cavitation in liquids submitted to power ultrasound creates transient extreme conditions inside the collapsing bubbles, which are the origin of unusual chemical reactivity and light emission, known as sonoluminescence. In the presence of noble gases, nonequilibrium plasma is formed. The "hot" particles and the photons generated by collapsing bubbles are able to excite species in solution.

The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic ...

Chemistry

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 ...

Experimental Protocol to Investigate Particle Aerosolization of a Product Under Abrasion and Under Environmental Weathering

The present article presents an experimental protocol to investigate particle aerosolization of a product under abrasion and under environmental weathering, which is a fundamental element to the approach of nanosafety-by-design of nanostructured products for their durable development. This approach is basically a preemptive one in which the focus is put on minimizing the emission of engineered nanomaterials' aerosols during the usage phase of the product's life cycle. This can be attained by altering its material properties during its design phase without compromising with any of its added benefits. In this article, an experimental protocol is presented to investigate the nanosafety-by-design of three commercial nanostructured products with respect to their mechanical solicitation and environmental weathering. The means chosen for applying the mechanical solicitation is an abrasion process and for the environmental weathering, it is an accelerated UV exposure in the presence of humidity and heat. The eventual emission of engineered nanomaterials is studied in terms of their number concentration, size distribution, morphology and chemical composition. The purpose of the protocol is to study the emission for test samples and experimental conditions which are corresponding to real life situations. It was found that the application of the mechanical stresses alone emits the engineered nanomaterials' aerosols in which the engineered nanomaterial is always embedded inside the product matrix, thus, a representative product element. In such a case, the emitted aerosols comprise of both nanoparticles as well as microparticles. But if the mechanical stresses are coupled with the environmental weathering, the experimental protocol reveals then the eventual deterioration of the product, after a certain weathering duration, may lead to the emission of the free engineered nanomaterial aerosols too.

In this article, an experimental protocol to investigate particle aerosolization of a product under abrasion and under environmental weathering is presented. Results on the emission of engineered nanomaterials, in the form of aerosols are presented. The specific experimental set-up is described in detail.

The present article presents an experimental protocol to investigate particle aerosolization of a product under abrasion and under environmental ...

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 ...

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 ...

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

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