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Probe measurements were conducted in the middle cross-section of an inductive, low-pressure xenon plasma using a straight cylindrical Langmuir probe with a bare metal shield that protected the probe from radio frequency interference. As a result, reliable radial distributions of the plasma parameters were obtained. Subsequent analyses of these measurements revealed that the electron energy distribution function (EEDF) deviated substantially from the Maxwellian functions and that this deviation depended on the length of the probe shield. To evaluate the shield's influence on the measurement results, in addition to the probe (which was moved radially as its shield length varied in the range of lsh1 = lmax–0), an additional L-shaped probe was inserted at a different location. This probe was moved differently from the first probe and provided confirmational measurements in the common special position where lsh1 = 0 and lsh2 ≠ 0. In this position, the second shield decreased all the plasma parameters. A comparison of the probe datasets identified the principles of the relationships between measurement errors and EEDF distortions caused by the bare probe shields. This dependence was used to correct the measurements performed using the first probe by eliminating the influence of its shield. Physical analyses based on earlier studies showed that these peculiarities are caused by a short-circuited double-probe effect that occurs in bare metal probe protective shields. [ABSTRACT FROM AUTHOR]

This paper presents two kinds of regular features revealed from the observations of the Langmuir probe (LAP) onboard the low-earth polar orbit satellite - China Seismo-Electromagnetic Satellite (CSES). The first feature behaves as a sudden drop (SD) in the plasma potential (Vp) and floating potential (Vf) data, while the second one appears as a spike (SP) in the dayside Vp and Vf data. The SD structure occurs at geo-latitudes from 40°N to 65°N, roughly from mid-March to mid-September months but with an apparent yearly growth of its amplitude. The SD is caused by the satellite-current system adjustment at the terminator transition zone. The SP feature predominately appears at geo-latitudes from 10°S to 40°N, showing annual recurrence and growing amplitude. Simulation suggests that the SP is caused by instantaneous illumination changes of probe surface when the boom of the electric field detector in the windward panel shades the LAP. According to the analysis of I-V curves both inside and outside the SD and SP structures, we exclude the possibility of probe contamination and confirm that the scientific data of CSES LAP are reliable. These two regular features depend on the solar illumination conditions and the corresponding adjustment of the satellite-current system equilibrium. This study provides a valuable reference for validating and pre-calibrating data from LAP in-situ measurements onboard similar low-earth polar orbit satellites. [ABSTRACT FROM AUTHOR]

The subject of this paper is a comparative analysis of the plasma parameters inferred from the classical Langmuir probe procedure, from different theories of the ion current to the probe, and from measured electron energy distribution function (EEDF) obtained by double differentiation of the probe characteristic. We concluded that the plasma parameters inferred from the classical Langmuir procedure can be subjected to significant inaccuracy due to the non-Maxwellian EEDF, uncertainty of locating the plasma potential, and the arbitrariness of the ion current approximation. The plasma densities derived from the ion part of the probe characteristics diverge by as much as an order of magnitude from the density calculated according to Langmuir procedure or calculated as corresponding integral of the measured EEDF. The electron temperature extracted from the ion part is always subjected to uncertainty. Such inaccuracy is attributed to modification of the EEDF for fast electrons due to inelastic electron collisions, and to deficiencies in the existing ion current theories; i.e., unrealistic assumptions about Maxwellian EEDFs, underestimation of the ion collisions and the ion ambipolar drift, and discounting deformation of the one-dimensional structure of the region perturbed by the probe. We concluded that EEDF measurement is the single reliable probe diagnostics for the basic research and industrial applications of highly non-equilibrium gas discharge plasmas. Examples of EEDF measurements point up importance of examining the probe current derivatives in real time and reiterate significance of the equipment technical characteristics, such as high energy resolution and wide dynamic range. [ABSTRACT FROM AUTHOR]

The Floating Potential Measurement Unit (FPMU) has been operational on board the International Space Station (ISS) since 2006. One of the instruments in the FPMU suite is a spherical wide‐sweeping Langmuir probe, referred to as the WLP, which is sampled at a temporal cadence of 1 s giving in‐situ measurements of the plasma density and electron temperature. In this study we present our refinements to the Langmuir probe analysis algorithm that address the uncertainties associated with photoelectron emission current from the metal probe. We also derive the fraction of O+ ions as a secondary data product, which shows decrease in O+ abundance in the post‐midnight sector during solar minimum. The derived plasma parameters are compared and validated with an independent in‐situ measurement technique, overlapping ground‐based incoherent scatter radar measurements, as well as International Reference Ionosphere model output. The reduced data set spans the entire solar cycle 24 and shows the F‐region ionosphere variance at ISS altitudes. Key Points: Langmuir probe measurements of plasma parameters in Earth's F‐region ionosphere over Solar Cycle 24Reduced parameters include plasma density, electron temperature, and O+ fraction which are validated using plasma impedance probe and Incoherent Scatter Radar observationsAlgorithm details of analyzing a Langmuir probe IV curve in ionospheric space plasma are provided [ABSTRACT FROM AUTHOR]

This work reports investigation of the Al-doped ZnO (AZO) film deposition process, at different working pressures, in a conventional magnetron sputtering system. The primary goal of this study is to investigate the plasma formation and deposition process using various diagnostic tools, by utilizing low-temperature deposition process. In addition, this paper also presents a systematic Langmuir probe (LP) analysis procedure to determine the maximum information about plasma parameters. For the present study, we have extensively used LP method to characterize the deposition process for the control of plasma parameters. Along with the LP method, we have also used optical emission spectroscopy diagnostic to examine the favorable deposition condition for the fabrication of conductive AZO film. Utilizing diagnostics, this also reports measurements of ion current density, substrate temperature, and deposition rates to fabricate low resistivity films of ~3mΩ cm. [ABSTRACT FROM AUTHOR]

This work presents a systematic plasma diagnostic approach for plasma processing using radio frequency (RF) and RF/UHF (ultra high frequency) hybrid plasmas. The present work also studies the influence of frequency on the deposition of Hydrogenated silicon nitride (SiNx: H) film using N2/SiH4/NH3 discharges. Analysis of data reveals that the UHF power addition to RF is quite effective in the plasma and radicals formation in different operating conditions. For the diagnostics, we have used optical emission spectroscopy, vacuum ultraviolet absorption spectroscopy, and RF compensated Langmuir probe. The presented diagnostic method directly exploits the optimized condition for fabricating high-quality silicon rich nitride (SiNx: H) thin film, at low temperature. With the help of hybrid plasmas, it is possible to fabricate SiNx: H film with high transparency ∼90%. [ABSTRACT FROM AUTHOR]

Strong turbulent waves (nn ∼0.5, f ∼5-40 kHz) are observed in the upgraded Large Plasma Device W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991) on density gradients produced by an annular obstacle. Energetic lithium ions (E fast / T i 300, fast / s ∼ 10) orbit through the turbulent region. Scans with a collimated analyzer and with probes give detailed profiles of the fast ion spatial distribution and of the fluctuating wave fields. The characteristics of the fluctuations are modified by changing the plasma species from helium to neon and by modifying the bias on the obstacle. Different spatial structure sizes (L s) and correlation lengths (Lcorr) of the wave potential fields alter the fast ion transport. The effects of electrostatic fluctuations are reduced due to gyro-averaging, which explains the difference in the fast-ion transport. A transition from super-diffusive to sub-diffusive transport is observed when the fast ion interacts with the waves for most of a wave period, which agrees with theoretical predictions. © 2011 American Institute of Physics.

A CH3F:O2 (50%:50%) inductively coupled discharge, sustained in a compact plasma reactor, was investigated as a function of power (20-400 W) and pressure (9-30 mTorr), using optical emission spectroscopy and Langmuir probe measurements. The electron density increased linearly with power but only weakly with pressure. The effective electron temperature was nearly independent of power and pressure. The gas temperature, obtained from the rotational structure of N2 (C → B) optical emission, increased from 400 to 900 K as a function of inductive mode power between 75 and 400 W at 10 mTorr. For constant feed gas flow, the absolute H, F, and O atom densities, estimated by optical emission rare gas actinometry, increased linearly with power. The absolute number density ratios H/Ar, F/Ar, and O/Ar, increased, decreased, and remained constant, respectively, with pressure. The H-atom density was estimated to be 5.4 × 1013 cm-3 at 400 W and 10 mTorr (gas temperature = 900 K), implying a high degree of dissociation of the CH3F feedstock gas. The F and O atom number densities were much lower (8.3 × 1012 cm-3 and 5.9 × 1012 cm-3, respectively) for the same conditions, suggesting that most of the fluorine and oxygen is contained in reaction products HF, CO, CO2, H2O, and OH. The relative number densities of HF, CO, and CO2 were observed to first rapidly increase with power, and then reach a plateau or decay slightly at higher power. Reaction mechanisms were proposed to explain the observed behavior of the number density of F and HF vs. power and pressure. [ABSTRACT FROM AUTHOR]

In this study, we present a technique to analyze side wall passivation layers formed on silicon sidewalls after plasma processing. The thickness and chemical composition are derived from angle resolved x-ray photoelectron spectroscopy analyses. It is a non-destructive, quasi in situ method to determine profiles of the thickness and the chemical composition of passivation layers in trenches up to an aspect ratio of about 3. The performance of this technique to quantify the passivation layer thickness is compared to a standard technique using secondary electron microscopy images with respect to two different samples and is found to be at least equivalent. The possible uncertainties and limitations of this technique are discussed as well. [ABSTRACT FROM AUTHOR]

This paper investigates the radial distributions of potential and electron density in free expansion plasma induced by an electron beam irradiating on the plate. The region of plasma production is assumed to be cylindrical, and the plasma expansion is assumed to be from a cylindrical source. Therefore, the one-dimensional model in cylindrical coordinates is employed in order to analyze the radial distributions of the potential and electron density. The Runge-Kutta method and the perturbation method are utilized in order to obtain the numerical and approximate solutions, respectively. The results reveal that the decrease in the initial ion energy makes most of the ions gather near the plasma production region and reduces the distribution of the average positive potential, electron, and ion density along the radial direction. The oscillation of steady-state plasma along the radial direction is also presented in this paper. The ions induce a larger amplitude of oscillation along the radial direction than do electrons because the electrons oscillate around slowly moving ions due to a far smaller electron mass than ion mass. The radial distributions of the positive potential and electron density predicted from this study are compared with the available experimental data. [ABSTRACT FROM AUTHOR]

This study investigates the mechanism of H2/N2 plasma ashing damage of porous SiOCH films. Porous SiOCH films were treated by a H2/N2 plasma using a 100-MHz capacitively coupled plasma etcher. The impact of ions, radicals, and vacuum ultraviolet radiation on the porous SiOCH films was investigated using in situ bulk analysis techniques such as spectroscopic ellipsometry and Fourier-transform infrared spectroscopy and ex situ film characterization techniques such as dynamic secondary ion mass spectrometry and x-ray photoelectron spectroscopy. In addition, plasma analysis including vacuum ultraviolet absorption spectroscopy was performed. The film characterization and plasma analysis show that the extraction of methyl by H radicals was enhanced by light while N radicals were responsible for inhibit the extraction of Si-CH3 bonds by forming nitride layer. The H2/N2 plasma damage mechanism is discussed based on characterization of the film and plasma diagnostics. [ABSTRACT FROM AUTHOR]

Atomic radicals such as hydrogen (H) and oxygen (O) play important roles in process plasmas. In a previous study, we developed a system for measuring the absolute density of H, O, nitrogen, and carbon atoms in plasmas using vacuum ultraviolet absorption spectroscopy (VUVAS) with a compact light source using an atmospheric pressure microplasma [microdischarge hollow cathode lamp (MHCL)]. In this study, we developed a monitoring probe for atomic radicals employing the VUVAS with the MHCL. The probe size was 2.7 mm in diameter. Using this probe, only a single port needs to be accessed for radical density measurements. We successfully measured the spatial distribution of the absolute densities of H and O atomic radicals in a radical-based plasma processing system by moving the probe along the radial direction of the chamber. This probe allows convenient analysis of atomic radical densities to be carried out for any type of process plasma at any time. We refer to this probe as a ubiquitous monitoring probe for atomic radicals. [ABSTRACT FROM AUTHOR]

The triple probe technique has been used to study the parameters of flowing plasma plume formed by laser-blow-off (LBO) of a multicomponent LiF–C target. The advantages of triple Langmuir probe over the single probe have been discussed with regard to the present study. Our results show that triple probe is better suited for parametric measurements close to the target. The spatiotemporal evolutions of electron density and temperature were measured in different ambient environments and for various laser fluences. The angular distribution of electron density and temperature was also measured. It was found that the presence of ambient gas drastically affects the electron density and temperature of the LBO plume. Large enhancement in ne and Te at intermediate pressures (10-2 Torr) is expected due to increase in collisional processes. On the other hand, laser fluence does not affect the observed ne and Te significantly. In vacuum, a new phenomenon, i.e., an oscillation in the trailing portion of the plasma plume at a closer distance from the target, is also reported. [ABSTRACT FROM AUTHOR]

The field emission characteristics of amorphous carbon (a-C) films are studied before and after H plasma treatment. It is found that H plasma treatment lowered the turn-on field and improved the field emission uniformity. Surface sp2/sp3 ratio, work function, and topography of the a-C films before and after H plasma treatment are studied using Raman spectroscopy, Kelvin probe, and atomic force microscopy, respectively. The results show that the etching effect of H plasma on a-C film is obvious, which is different from those of diamond and tetrahedral amorphous carbon (ta-C) films. We suggest that the surface component change and nanostructure of treated a-C films cause electron injection from sp2 sites to surface sp3 sites which are responsible for low macroelectrical field emission. [ABSTRACT FROM AUTHOR]

The cylindrical Hall thruster (CHT) is an attractive approach to achieve a long lifetime thruster operation especially in low power space applications. Because of the larger volume-to-surface ratio than conventional coaxial Hall thrusters, the cylindrical Hall thrusters are characterized by a reduced heating of the thruster parts and potential lower erosion. Existing CHTs can feature a short coaxial channel in order to sustain a high ionization in the thruster discharge. A 5.6 cm diameter cylindrical Hall thruster was developed and operated with and without a short coaxial region of the thruster channel, in the power range of 70–300 W. It is shown that the CHT without coaxial region can operate stable and achieve higher thrust efficiency, 22%–32% more than that with a coaxial region. Plasma probe measurements inside the thruster channel and ion energy measurements in the plasma plume suggest that the ionization/acceleration region in the CHT is located near the anode region where a radial magnetic field is stronger. [ABSTRACT FROM AUTHOR]

A cylindrical Langmuir probe in a low-density, collisionless plasma (density ~108 cm-3, electron temperature 0.2 eV) has been scanned radially through the presheath region to determine the effect of distance from the axis on the current-voltage characteristic. In the ion part of the probe characteristic, the collected ion current decreases with distance from the axis as a consequence of ion acceleration by the presheath. The part of the ion current from charge-exchange collisions remains relatively constant. In the electron part of the probe characteristic, the collected current decreases with distance from the axis, consistent with the existence of a small potential barrier from the presheath between the axis and the probe. The electron temperature from the slope of the probe characteristic is nearly constant across the presheath region. The plasma potential from the Langmuir probe characteristic is also nearly constant, indicating that the probe analysis finds the plasma potential on the axis, even when the probe is not on the axis. The plasma potential from an emissive probe shows an approximately parabolic profile. The plasma potential from the emissive probe and the Boltzmann relation give nearly the same density profile in the presheath that is obtained from the Langmuir probe data. [ABSTRACT FROM AUTHOR]

The excitation mechanisms of the lower lying excited levels in a low-ionized, low-pressure, argon plasma are modeled and studied in order to characterize the plasma through optical emission spectroscopy. It is found that the lower lying excited states of argon play an important role in the excitation and that they must be taken explicitly into account for an accurate determination of the excitation rates. The possible influence of radiative cascades from upper argon excited states, which are not included in the model, has been studied by introducing an effective level in the description and studying its influence on the results. The model has been used to calculate the electron density and electron temperature in an argon magnetron sputtering plasma produced at different electromagnetic powers and gas pressures, as a function of the intensity of the optical emission lines λ1=750.38 nm and λ2=696.54 nm. The results obtained from the model have been compared with Langmuir probe measurements, showing a good agreement. It is hereby demonstrated that optical emission spectroscopy can be used to monitor the plasma properties during the deposition process when applying a nonlinear model. [ABSTRACT FROM AUTHOR]

A floating-type probe and its driving circuit using the nonlinear characteristics of the probe sheath was developed and the electron temperature and the plasma density which is found from the ion part of the probe characteristic (ion density) were measured in inductively coupled plasmas. The floating-type probe was compared with a single Langmuir probe and it turned out that the floating-type probe agrees closely with the single probe at various rf powers and pressures. The ion density and electron temperature by the floating-type probe were measured with a film on the probe tip coated in CF4 plasma. It is found that the ion density and electron temperature by the floating-type probe were almost the same regardless of the coating on the probe tip while a single Langmuir probe does not work. Because the floating-type probe is hardly affected by the deposition on the probe tip, it is expected to be applied to plasma diagnostics for plasma processing such as deposition or etching. [ABSTRACT FROM AUTHOR]

The surface pressure of monolayers of insoluble diblock copolymers has been measured. One of the blocks is made of poly(t-butyl acrylate) (PtBA), and the other one by polystyrene (PS). The interface is a good solvent for PtBA, while it is a poor solvent for PS. For the sake of comparison, monolayers of a PtBA homopolymer (good solvent conditions) and of poly(4-hydroxy styrene) (P4HS) (poor solvent conditions) have been also measured. It has been found that the relative length of the blocks plays an important role on the shape of the surface pressure Π versus surface concentration Γ curves and also on the shape of the equilibrium compressibility versus Γ curves. However, it does not affect the maximum value of Π reached at high Γ’s. Surprisingly, the ellipsometric thickness of the copolymer monolayers is almost independent of the relative length of the blocks. The dynamics of the monolayers has been studied by step compression and by surface-light scattering techniques. When Mw,PtBA>Mw,PS single exponential relaxations are observed. However, stretched exponentials are obtained for Mw,PS>=Mw,PtBA. The relaxation times decrease with increasing Γ for all the copolymers studied. This is the behavior usually found for poor solvent conditions (P4HS) and opposite to that found for homopolymers under good solvent conditions [PtBA, poly(vinylacetate)]. This means that the solvent quality of the interface does not determine the pressure dependence of τ. The elasticity modulus of the monolayers in the kilohertz range takes values that are similar to those of the high-frequency limit of the relaxation experiments. This means that the relaxation processes have characteristic frequencies below 1 Hz. [ABSTRACT FROM AUTHOR]

Rate constants were measured for electron attachment to MoF6, ReF6, and WF6 in 133 Pa of helium gas using a flowing-afterglow Langmuir-probe apparatus. The experiment is a thorny one because the molecules tend to form oxide impurities on feedline surfaces and because of thermal decomposition of MoF6 on surfaces as the gas temperature is increased. The electron attachment rate constant for MoF6 is (2.3±0.8)×10-9 cm3 s-1 at 297 K; only MoF6- is formed in the temperature range of 297–385 K. The rate constant increases with temperature up to the point where decomposition becomes apparent. Electron attachment to ReF6 occurs with a rate constant of (2.4±0.8)×10-9 cm3 s-1 at 297 K; only ReF6- is produced. MoF6- reacts with ReF6 to form ReF6- on essentially every collision, showing definitively that the electron affinity of ReF6 is greater than that of MoF6. A rate constant of (5.0±1.3)×10-10 cm3 s-1 was measured for this ion-molecule reaction at 304 K. The reverse reaction is not observed. The reaction of Ar+ with MoF6 was found to produce MoF5++F, with a rate constant of (1.8±0.5)×10-9 cm3 s-1. WF6 attaches electrons so slowly at room temperature that the attachment rate was below detection level (<=10-12 cm3 s-1). By 552 K, the attachment rate constant reaches a value of (2±1)×10-10 cm3 s-1. [ABSTRACT FROM AUTHOR]

Rate constants were measured for electron attachment to MoF6, ReF6, and WF6 in 133 Pa of helium gas using a flowing-afterglow Langmuir-probe apparatus. The experiment is a thorny one because the molecules tend to form oxide impurities on feedline surfaces and because of thermal decomposition of MoF6 on surfaces as the gas temperature is increased. The electron attachment rate constant for MoF6 is (2.3±0.8)×10-9 cm3 s-1 at 297 K; only MoF6- is formed in the temperature range of 297–385 K. The rate constant increases with temperature up to the point where decomposition becomes apparent. Electron attachment to ReF6 occurs with a rate constant of (2.4±0.8)×10-9 cm3 s-1 at 297 K; only ReF6- is produced. MoF6- reacts with ReF6 to form ReF6- on essentially every collision, showing definitively that the electron affinity of ReF6 is greater than that of MoF6. A rate constant of (5.0±1.3)×10-10 cm3 s-1 was measured for this ion-molecule reaction at 304 K. The reverse reaction is not observed. The reaction of Ar+ with MoF6 was found to produce MoF5++F, with a rate constant of (1.8±0.5)×10-9 cm3 s-1. WF6 attaches electrons so slowly at room temperature that the attachment rate was below detection level (<=10-12 cm3 s-1). By 552 K, the attachment rate constant reaches a value of (2±1)×10-10 cm3 s-1. [ABSTRACT FROM AUTHOR]

This paper developes a theoretical model for the sheath that surrounds cylindrical and spherical Langmuir probes immersed in an electronegative plasma. The model allows the electric potential profile surrounding the negatively polarized probe, the densities of the different charged particles within the sheath, and the I-V characteristic curves to be determined for several negative ion density and temperature values. These curves are fitted analytically, permitting expressions to be obtained for the potential profile, the floating potential, and the sheath edge. [ABSTRACT FROM AUTHOR]

This article deals with an extension of the radial model for the sheath that surrounds a cylindrical or spherical Langmuir probe immersed in a plasma in which positive ion thermal motion is taken into account. The dependence of the electric potential profile and of the I–V characteristic on the positive ion temperature is obtained. Moreover, a different parameterization is established from a numerical fit of the I–V characteristic as a function of the probe radius, the biasing potential, and the ratio between the positive ion temperature and the electron temperature. This parameterization allows us to obtain an analytical approximation to the potential profile and the sheath edge. Finally, it also gives us a means of justifying under what conditions the radial model can be applied in plasmas with finite positive ion temperature. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Conventional annular Hall thrusters become inefficient when scaled to low power. Their lifetime decreases significantly due to the channel wall erosion. Cylindrical Hall thrusters, which have lower surface-to-volume ratio and, thus, seem to be more promising for scaling down, exhibit performance comparable with conventional annular Hall thrusters of the similar size. Plasma potential, ion density, and electron temperature profiles were measured inside the 2.6 cm cylindrical Hall thruster with the use of stationary and slow movable emissive and biased Langmuir probes. Potential drop in the 2.6 cm cylindrical Hall thruster is localized mainly in the cylindrical part of the channel and in the plume, which suggests that the thruster should suffer lower erosion of the channel walls due to fast ion bombardment. Plasma density has a maximum of about (2.6–3.8)×10[sup 12] cm[sup -3] at the thruster axis. At the discharge voltage of 300 V, the maximum electron temperature is about 21 eV, which is not enough to produce multiple ionization in the accelerated flux of Xe[sup +] ions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A global plasma model for an ionized physical vapor deposition (IPVD) system is described. The model predicts the density of electrons, excited state, Ar and N[sub 2], ironized Ar, N[sub 2], and Ti, the density of atomic N and N[sup +], and the electron temperature. The computed results are compared to experimental measurements of a titanium nitride IPVD reactor to confirm the validity of the model. The reactor consists of an inductively coupled plasma source that is fed by argon, nitrogen, and sputtered titanium. The dissociation of nitrogen in the discharge is typically found to be in the range of 10%-30%. The electron temperature is 1.8 eV, and the ion density is between 2 × 10[sup 11] and 6 × 10[sup 11] cm[sup -3]. The ion density is found to decrease as nitrogen is added to the Ar discharge due to collisional losses associated with molecular states. In the metal mode of operation, the atomic nitrogen density is suppressed by the Ti-rich reactor walls. As the nitrogen flow rate is increased, the target and walls become nitrided and the density of N increases an order of magnitude to 2-4 × 10[sup 12] cm[sup -3]. The ionization fraction for the depositing flux of titanium is typically 0.4-0.7. The model is easily adapted to other technologically relevant diffusion barrier layer materials such as WN and TaN. [ABSTRACT FROM AUTHOR]

Determines the radio-frequency plasma potential in a stove top inductively coupled plasma source by a capacitive probe. Comparison of results to a circuit model; Terms of the capacitive coupling model; Relevance of the measured ion energy spectrum.

• New design of the Divertor Thomson Scattering is presented. • Electromagnetic and contact analyses are conducted. • Conclusions about the obtained stresses and construction survivability are made. This article reports the results of the assessment performed on the ITER Divertor Thomson Scattering (DTS). It is designed to provide an instrument capable of measuring the electron temperature and the related density profiles in the outer divertor plasma, relying on Thomson scattering method. The DTS main components are front rack, back rack, neutron shielding and diagnostic mirrors. Current DTS design has been modified compared to the one described in the previous article dedicated to this object. The most significant changes are: • Upper neutron shielding has been removed. It is now not connected directly with the DTS system. It helped to reduce total weight of the construction; • Dielectric insertions were added in order to reduce influence of the ponderomotive forces on construction strength; • DTS supports were redesigned. Connections of the DTS with radial rails on which the construction is mounted on the sides were explored. Corresponding contact problem was solved and the structure integrity in this area was assessed. Mirrors made of SiC material are the DTS diagnostic elements. They are installed into front and back diagnostic racks. Other elements of the DTS are made of 316L(N)-IG steel. The contact pads on the radial rails are made of 660 steel. The whole Divertor Thomson Scattering system has to withstand all the loads (thermal, mechanical, electromagnetic and seismic) acting on the in-vessel region in which it is located without compromising its integrity. Its design layout is being modified and optimized according to the outcome of the structural assessment. Every step of the design update brings the construction closer to satisfying all of the criterions of structural integrity. This paper describes some important steps that really help moving forward to the DTS implementation. [ABSTRACT FROM AUTHOR]

Presents information on a study that determined the plasma distribution using a cathodic arc plasma source with and without magnetic macroparticle filter by depositing on a transparent plastic substrate and measuring the film absorption. Introduction to cathodic arc deposition; Cathodic arc deposition systems; Plasma distribution for cathodic arc source.

Plasma probes are simple and inexpensive diagnostic tools for fast measurements of relevant plasma parameters. While in earlier times being employed mainly in relatively cold laboratory plasmas, plasma probes are now routinely used even in toroidal magnetic fusion experiments, albeit only in the edge region, i.e., the so-called scrape-off layer (SOL), where temperature and density of the plasma are lower. To further avoid overheating and other damages, in medium-size tokamak (MST) probes are inserted only momentarily by probe manipulators, with usually no more than a 0.1 s per insertion during an average MST discharge of a few seconds. However, in such hot and high-density plasmas, their usage is limited due to the strong particle fluxes onto the probes and their casing which can damage the probes by sputtering and heating and by possible chemical reactions between plasma particles and the probe material. In an attempt to make probes more resilient against these detrimental effects, we tested two graphite probe heads (i.e., probe casings with probes inserted) coated with a layer of electrically isolating ultra-nano-crystalline diamond (UNCD) in the edge plasma region of the Experimental Advanced Superconducting Tokamak (EAST) in Hefei, People’s Republic of China. The probe heads, equipped with various graphite probe pins, were inserted frequently even into the deep SOL up to a distance of 15 mm inside the last closed flux surface (LCFS) in low- and high-confinement regimes (L-mode and H-mode). Here, we concentrate on results most relevant for the ability to protect the graphite probe casings by UNCD against harmful effects from the plasma. We found that the UNCD coating also prevented almost completely the sputtering of graphite from the probe casings and thereby the subsequent risk of re-deposition on the boron nitride isolations between probe pins and probe casings by a layer of conductive graphite. After numerous insertions into the SOL, first signs of detachment of the UNCD layer were noticed.

The character of ammonia-oxygen (NH3-O2) plasma-treated polysulfone (PSF) membrane was studied in this work. The time effect of the plasma-treated PSF membrane was checked with energy-dispersive X-ray (EDX) detector, attenuated total reflection Fourier transform infrared (ATR-FTIR), membrane contact angle, and filtration property. EDX detector and ATR-FTIR spectra have shown that the surface oxygen content of the modified membrane increased in the form of peroxy, hydroxyl, and aromatic carboxide groups. However, nitrogen was not observed in the NH3-O2 plasma-treated membrane surface. The peroxy group disappeared and hydroxyl and aromatic carboxide groups were reduced 3 months later. However, the plasma-treated membrane still shown great hydrophilicity, and the contact angle decreased to 0 within 11 s despite the time effect. During the two rounds of 80 min of bovine serum albumin buffer solution filtration process, the fluxes of newly plasma-treated membrane and that of the membrane 3 months later decreased to 78 L m−2 h−1 and 54 L m−2 h−1, respectively, whereas the flux of the pristine membrane decreased to 12 L m−2 h−1. [ABSTRACT FROM AUTHOR]

We report upon the picosecond plasma dynamics at the rear surface of a thin aluminium foil (of either 5.5 μm or 12 μm thickness) excited by high contrast (picosecond intensity contrast of 10−10), 800 nm, femtosecond pulses at an intensity of 3 × 1019 W/cm2. We employ ultrafast pump-probe reflectometry using a second harmonic probe (400 nm) interacting with the rear surface of the target. A rise in the probe reflectivity 30 ps after the pump pulse interaction reveals the breakout of a shock wave at the target rear surface which reflects the 400 nm probe pulse. Simulations using the ZEPHYROS hybrid particle-in-cell code were performed to understand the heating of the target under the influence of the high intensity laser pulse, and the temperature profile was then passed to the radiation-hydrodynamic simulation code HYADES in order to model the shock wave propagation in the target. A good agreement was found between the calculations and experimental results. [ABSTRACT FROM AUTHOR]

Multi-needle Langmuir probe is a fairly new instrument technique that has been flown on several recent sounding rockets and is slated to fly on a subset of QB50 CubeSat constellation. This paper takes a fundamental look into the data analysis procedures used for this instrument to derive absolute electron density. Our calculations suggest that while the technique remains promising, the current data analysis procedures could easily result in errors of 50% or more. We present a simple data analysis adjustment that can reduce errors by at least a factor of five in typical operation. [ABSTRACT FROM AUTHOR]

The introduction of ambient ionization at atmospheric pressure for mass spectrometry (AI-MS) attracted the interest of many researchers in the field and various ionization techniques have been described in recent years that allow a quick and easy-to-handle analysis of samples under ambient conditions without or with only minor sample preparation. Among those, plasma-based techniques including the low-temperature plasma probe require very little resources thereby providing great potential for implementation in mobile analytical devices. However, systematic studies on signal responsiveness with this technique, such as the influence of the analyte and matrix characteristics on relative signal intensity, are still rare. Therefore, we used a low-temperature plasma source based on dielectric barrier discharge with helium as process gas to assess influencing factors on signal intensity in mass spectrometry. Among 12 tested molecular descriptors, in particular a low vaporization enthalpy and a large molecular nonpolar surface area improve the relative signal intensity. In addition, we show that the impact of compound characteristics strongly outperforms the influence of simple sample matrices such as different organic solvents and water, with a weak trend that volatile solvents tend to decrease the signal responsiveness of the analytes. However, several specific solvent-analyte interactions occurred, which have to be considered in targeted applications of this method. Our results will help further in improving the implementation and standardization of low-temperature plasma ionization for ambient mass spectrometry and understanding the requirements and selectivity of this technique.Influencing factors (analyte and matrix characteristics) on signal intensity in dielectric-barrier discharge plasma for ionization in mass spectrometry. [ABSTRACT FROM AUTHOR]

The plasma physics of dielectric barrier discharges (DBD) for carrying out ion implantation in insulators is investigated. A hollow cathode DBD excited by high-voltage pulses is suitable for ion bombardment of the surfaces of insulating tubing, porous material, particles and sheets. Plasma immersion ion implantation of insulating surfaces is useful for many applications in medicine and engineering. The ion bombardment of glass is useful for cleaning and surface modification. The ion implantation of polymers creates radicals that are able to bind molecules to their surfaces for applications in medical procedures and diagnostics. A wire diagnostic probe and optical emission spectroscopy are used for experimental work. A theory based on mutual capacitance is developed to convert data from the probe to give implanted charge as a function of pressure, voltage and pulse duration. We find the operating conditions that allow for charge to be implanted and those that achieve the highest implanted charge. [ABSTRACT FROM AUTHOR]

This paper presents the design and development of a trigger with a high repetition rate, low jitter, and compact structure for the pseudospark switch (PSS), which includes an improved Marx generator based on avalanche transistors and a corona-plasma trigger unit. The generator adopted a novel 3 × 12-stage Marx circuit based on avalanche transistors in which the failure rate of transistors in the first and second stages was significantly reduced by connecting the parallel capacitors compared to the previous similar generator. The reason for the improved performance was also discussed. The main parameters of output pulses were an amplitude of −7 kV, rise time of 6 ns, jitter of 0.2 ns, and repetition rate of 2 kHz. The corona-plasma trigger unit adopted BaTiO3 ceramics with high εr as the dielectric and was arranged in the hollow cathode of the PSS. The experiments of triggering a PSS prototype were conducted. The influence of anode voltage and pressure on the trigger delay and jitter was studied, and the minimum trigger jitter achieved <1 ns. This trigger worked for 107 shots at the repetition rate of 2 kHz continuously without obvious performance degradation and any failure of the generator. The main advantage of this trigger is the simultaneous combination of the high repetition rate, low jitter, long lifetime, and great simplicity in a compact structure. [ABSTRACT FROM AUTHOR]

We present two microwave probe stations with motorized rotary stages for adjusting the magnitude and angle of the applied magnetic field. In the first system, the magnetic field is provided by an electromagnet and can be adjusted from 0 to ∼1.4 T while its polar angle (θ) can be varied from 0° to 360°. In the second system, the magnetic field is provided by a Halbach array permanent magnet, which can be rotated and translated to cover the full range of polar (θ) and azimuthal (φ) angles with a tunable field magnitude up to ∼1 T. Both systems are equipped with microwave probes, bias-Ts, amplifiers, and spectrum analyzers to allow for microwave characterization up to 40 GHz, as well as software to automatically perform continuous large sets of electrical and microwave measurements. [ABSTRACT FROM AUTHOR]

Many surfaces found on the Moon, asteroids, Mars, moons, and other planetary bodies are covered in a fine granular material known as regolith. Increased knowledge of the physical properties of extraterrestrial regolith surfaces will help advance the scientific knowledge of these bodies as well as the development of exploration (e.g., instrument and robotic) and in situ resource utilization (ISRU) systems. The Center for Space Resources at the Colorado School of Mines as part of the Institute for Modeling Plasma, Atmospheres, and Cosmic Dust of NASA’s Solar System Exploration Research Virtual Institute has developed a novel system, called the ISRU Experimental Probe (IEP) that can support studies of dry and icy regolith from −196 to 150 °C and pressure from laboratory ambient pressure to 10−7 Torr. The IEP system and proof-of-concept results are presented in this paper. [ABSTRACT FROM AUTHOR]

An insertable probe head called high resolution probe (HRP) has been developed at Consorzio reversed field experiment in the framework of the EUROfusion S1 work program and in collaboration with IPP Greifswald, to study the electrostatic and electromagnetic features of turbulence in the edge region of Wendelstein 7-X using the multipurpose manipulator. This paper reports the design development of the HRP diagnostic head, from the choice of the sensors to the engineering design. The assumptions and evaluations supporting the main design choices, together with the R&D tests carried out to check the most critical parts, are described in detail. [ABSTRACT FROM AUTHOR]

One of the main challenges in X-mode reflectometry is the correct determination of the group delay measurement used for density profile reconstruction. The X-mode upper cutoff group delay measurement can be used to reconstruct the electron density profiles from the near zero density. However, due to the broad operational conditions of experimental fusion devices, the start of the upper cutoff region can occur at any probing frequency. The first fringe (FF) of the interference signal measured by reflectometry that corresponds to the start of the upper cutoff reflection is used together with the magnetic field profile to determine vacuum distance between the reflectometer antenna and the start of the plasma. An incorrect estimation of the FF probing frequency not only introduces a radial error but also a group delay error, affecting the shape of the resulting density profile. In this paper, we present the new developments in the automatic FF estimation required for the reliable reconstruction of density profiles, used in the multichannel X-mode density profile reflectometry diagnostic recently installed on ASDEX Upgrade. An improved algorithm to estimate and track the frequency of the FF along a discharge is introduced. Tests show that it is able to correctly determine the FF for most discharges. However, for a number of unanticipated cases, the algorithm provides jitter and imprecise results, introducing errors in the reconstructed density profiles. We also present a novel neural network (NN) approach for the first time for the estimation of the FF frequency. A comprehensive training set was carefully selected by experienced reflectometry diagnosticians and used to train the NN model using the open source software libraries TensorFlow and Keras. The resulting NN is able to provide more precise FF estimations than the previous algorithm. The reconstructed density profiles, using both algorithms, are presented and compared. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to decolorize the effluents of textile Reactive Orange 5 and Reactive Red 195 dyes by using cationized sugarcane bagasse.Design/methodology/approach Cationized sugarcane bagasse was prepared and used as an adsorbent for both reactive and hydrolyzed reactive dyes. Characterization of the sugarcane bagasse structure resulted by cationization was monitored using Fourier transform–infrared, while morphologically was detected using scanning electron microscopy and X-ray powder diffraction.Findings The maximum adsorption capacities are 805, 1,664, 1,772 and 1,596 mg/g for Hydrolyzed Red 195, Hydrolyzed Orange 5, Reactive Red 195 and Reactive Orange 5 dyes, respectively.Research limitations/implications Factors affecting the percentage of dye removal were optimized on different parameters such as adsorbent dose and treatment time. The data were discussed using the Langmuir and Freundlich Models of adsorption.Practical implications The reuse of hydrolyzed reactive dyebaths gives reasonably good fastness properties on nylon fabrics.Social implications The study has enabled the production of an eco-friendly and less expensive method of reactive dye effluent decolorization.Originality/value The study provides a potentially simple approach to decolorize dye effluents of Reactive Orange 5, Red 195 dyes and also the reuse of hydrolyzed reactive dyebaths for dyeing nylon. [ABSTRACT FROM AUTHOR]

In this work, two new possibilities for standard probe diagnostics are described. The first one can be used to study isotropic, collisionless low-pressure plasma in which the electron energy distribution function is close to a Maxwellian one. In such plasmas, the Boltzmann law, Bohm effect, and 3/2 power law are valid. Use of corresponding system of equations for cylindrical Langmuir probes allowed for measurements of probe sheath thicknesses and the mean ion mass. The solution of this task was provided by accurate probe diagnostics of inductive xenon plasma at pressure p = 2 mTorr that resulted in the determination of the Bohm coefficient CBCyl = 1.22. The second possibility of probe diagnostics includes a method and device for evaluation of ion current density to a wall under a floating potential using a radially movable plane wall Langmuir probe simulator. This measurement in the same xenon plasma served as the basis for development of an ion source in which the given wall was represented by an ion extracting electrode of the ion extraction grid system. [ABSTRACT FROM AUTHOR]

An array of exchange biased spin-valve giant-magnetoresistance nanopillars was fabricated and the current I dependence of the resistance R was investigated using an electrically conducting atomic-force microscope (AFM) probe contact at room temperature. We observed current induced switching in a MnIr/CoFe/Cu/CoFe/NiFe nanopillar using the AFM probe contact. Current-driven switching using nanoprobe contact is a powerful method for developing nonvolatile and rewritable magnetic memory with high density. [ABSTRACT FROM AUTHOR]

Developing substrates that enable both reproducible and highly sensitive Raman detection of trace amounts of molecules in aqueous systems remains a challenge, although these substrates are crucial in biomedicine and environmental sciences. To address this issue, we report spatially uniform plasmonic nanowrinkles formed by intimate contact between plasmonic nanograins on the surface of colloidal crystal monolayers. The Au or Ag nanograin layers coated on hydrogel colloidal crystal monolayers can reversibly wrinkle and unwrinkle according to changes in the water temperature. The reversible switches are directed by surface structural changes in the colloidal crystal monolayers, while the colloids repeat the hydration-dehydration process. The Au and Ag nanowrinkles are obtained upon hydration, thus enabling the highly reproducible detection of Raman probes in water at the nano- and picomolar levels, respectively, throughout the entire substrate area. Additionally, the reversible switching of the nanostructures in the plasmonic nanograin layers causes reversible dynamic changes in the corresponding Raman signals upon varying the water temperature. [ABSTRACT FROM AUTHOR]

The notion of weak measurement in quantum mechanics has gained a significant and wide interest in realizing apparently counterintuitive quantum effects. In recent times, several theoretical and experimental works have been reported for demonstrating the joint weak value of two observables where the coupling strength is restricted to the second order. In this paper, we extend such a formulation by providing a complete treatment of joint weak measurement scenario for all-order-coupling for the observable satisfying A = 핀 and A = A, which allows us to reveal several hitherto unexplored features. By considering the probe state to be discrete as well as continuous variable, we demonstrate how the joint weak value can be inferred for any given strength of the coupling. A particularly interesting result we pointed out that even if the initial pointer state is uncorrelated, the single pointer displacement can provide the information about the joint weak value, if at least third order of the coupling is taken into account. As an application of our scheme, we provide an all-order-coupling treatment of the well-known Hardy paradox by considering the continuous as well as discrete meter states and show how the negative joint weak probabilities emerge in the quantum paradoxes at the weak coupling limit. Graphical abstract: [ABSTRACT FROM AUTHOR]

In this paper, we address the question of whether spacecraft potential depends on the ambient electron density. In Maxwellian space plasmas, the onset of spacecraft charging does not depend on the ambient electron density. The balance of electron currents causes the incoming electrons to balance with the outgoing secondary electrons. The onset is controlled by the critical or anticritical temperature of the ambient electrons, but not the electron density. Above the critical temperature, charging to negative potential occurs. If the energy of the incoming electrons increases to well beyond the second crossing point of the secondary electron yield (SEY), the value of SEY decreases to well below unity. When the secondary electron current is negligible compared with the primary electron current, the spacecraft potential is governed solely by the balance of the incoming electrons and the sum of the currents of the repelled electrons and the attracted ions. In neutral space plasma, the electron and ion charges cancel each other. But if the space plasma deviates from being neutral, then the densities can have effect on the spacecraft potential. If the ambient plasma deviates significantly from equilibrium, a non-Maxwellian electron distribution may result. For a kappa distribution, one can show that the spacecraft charging level is independent of the ambient electron density. For a double Maxwellian distribution, the spacecraft charging level depends on the electron densities. For a conducting spacecraft charging in sunlight, the charging level is low and positive. It also depends on the ambient electron density. For a dielectric spacecraft in sunlight, the high-level negative-voltage charging on the shadowed side may extend to the sunlit side and block the photoelectrons trying to escape from the sunlit side. In this case, the charging level does not depend on ambient electron density. Using coordinated environmental and spacecraft charging data obtained from the Los Alamos National Laboratory geosynchronous satellites, we showed some results confirming that spacecraft potential is indeed often independent of the ambient electron density. [ABSTRACT FROM AUTHOR]

Illumination-assisted droplet spray ionization (IA-DSI) mass spectrometry was developed for in situ analysis and real-time monitoring of photolysis reactions. In IA-DSI, a photolysis reaction occurs on a corner of a cover slip positioned in front of a mass spectrometer, and the generated reaction intermediates are ionized via the corner and are directed to the inlet and analyzed by a mass spectrometer. IA-DSI is contaminant-free, low-cost and simple, and was demonstrated for in situ analysis and real-time monitoring of the degradation of Cu(II)-EDTA in H 2 O 2 /UV. The reaction times varied from seconds to minutes, and three new reaction intermediates were detected and identified by tandem mass spectrometry. More importantly, the proposed initiation site of Cu(II)-EDTA at the carboxyl group by ∙OH attack was verified for the first time. The degradation of Cu(II)-EDTA occurred through its chemical bonds broken at the carboxyl group, at the amino group, and between EDTA and Cu(II). By sampling in situ and monitoring in real time, IA-DSI provides advantages in simplifying the analysis process for photolysis reaction intermediates and products, and can detect photolysis reaction intermediates and products in less than a second. [ABSTRACT FROM AUTHOR]

The Langmuir probe is used to characterize the plasma produced by fs-laser ablation from pure metallic targets. Time dependence of the probe current and the total collected charge is discussed in terms of a shifted Maxwell-Boltzmann distribution function, and from probe characteristics the plasma temperature and average charge state are calculated. Target materials of various physical properties (atomic mass, thermal constants) are used to find possible correlations with resulting plasma parameters. By positively biasing the probe, the collected charge -probe voltage characteristic is in general vertically shifted, and for low negative probe potentials an effect consisting in an abnormal decrease of the ion current is observed. Periodic falls of the total collected charge vs. probe voltage are experimentally recorded, the effect being more significant at high background pressure. They are tentatively attributed to secondary ionization. [ABSTRACT FROM AUTHOR]

Dielectric barrier discharge (DBD)-based analytical applications have experienced rapid development in recent years. DBD designs and parameters and the application they are used for can vary considerably. This leads to a diverse field with many apparently unique systems that are all based on the same physical principle. The most significant changes among DBDs used for chemical analysis are in how the discharge electrodes are separated from the ignited discharge gas. While the official definition of a DBD states that at least one electrode has to be covered by a dielectric to be considered a DBD, configurations with both electrodes covered by dielectric layers can also be realized. The electrode surface plays a major role in several plasma-related technical fields, surface treatment or sputtering processes, for example, and has hence been studied in great detail. Analytical DBDs are often operated at low power and atmospheric pressure, making a direct transfer of insight and know-how gained from the aforementioned well-studied fields complicated. This work focuses on comparing two DBD configurations: the low temperature plasma probe (LTP) and the dielectric barrier discharge for soft ionization (DBDI). The LTP is representative of a DBD with one covered electrode and the DBDI of a design in which both electrodes are covered. These two configurations are well suited for a systematic comparison due to their similar geometric designs based on a dielectric capillary. [ABSTRACT FROM AUTHOR]