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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Absolute light yield of the EJ-204 plastic scintillator

The absolute light yield of a scintillator, defined as the number of scintillation photons produced per unit energy deposited, is a useful quantity for scintillator development, research, and applications. Yet, literature data on the absolute light yield of organic scintillators are limited. The goal of this work is to assess the suitability of the EJ-204 plastic scintillator from Eljen Technology to serve as a reference standard for measurements of the absolute light yield of organic scintillators. Four EJ-204 samples were examined: two manufactured approximately four months prior and stored in high-purity nitrogen, and two aged approximately eleven years and stored in ambient air. The scintillator response was measured using a large-area avalanche photodiode calibrated using low energy $γ$-ray and X-ray sources. The product of the quantum efficiency of the photodetector and light collection efficiency of the housing was characterized using an experimentally-benchmarked optical photon simulation. The average absolute light yield of the fresh samples, 9100 ± 400 photons per MeV, is lower than the manufacturer-reported value of 10400 photons per MeV. Moreover, the aged samples demonstrated significantly lower light yields, deviating from the manufacturer specification by as much as 26%. These results are consistent with recent work showcasing environmental aging in plastic scintillators and suggest that experimenters should use caution when deploying plastic scintillators in photon counting applications.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Determination of the Raman polarizability tensor in the optically anisotropic crystal potassium dihydrogen phosphate and its deuterated analog

Abstract The Raman tensor of the dominant A 1 modes of the nonlinear optical crystalline material potassium dihydrogen phosphate and its 70% deuterated analog have been ascertained. Challenges in determining the A 1 mode tensor element values based on previous reports have been resolved using a specially designed experimental setup that makes use of spherical crystal samples. This novel experimental design enabled the determination of measurement artifacts, including polarization rotation of the pump and/or scattered light propagating through the sample and the contribution of additional overlapping phonon modes, which have hindered previous efforts. Results confirmed that the polarization tensor is diagonal, and matrix elements were determined with high accuracy.

36 MATERIALS SCIENCE↗
DOE OSTI2022

A method and tool to determine the colorimetric and photobiological properties of light transmitted through glass and other optical materials

Here we describe a framework and provides a computational tool to characterize the color quality and biological potential of light that is transmitted through glass and other optical materials. The IES TM-30 framework and Excel computation tool were adapted to evaluate color quality, with measures from CIE S 026, UL 24480, and the WELL Building Standard v2 added to evaluate biological potential. The user selects a pre-transmittance spectral power distribution (SPD), such as for a CIE D-Series Illuminant, Planckian radiation, electric lamp, or measurement of daylight at a building site. The tool allows a user to populate a database with spectral data for glazing or other optical materials, comprising spectral transmission and the spectral reflectance of both sides. The user creates a unit with one, two, or three panes of glazing or other optical materials, and the tool calculates the composite spectral transmittance accounting for reflections between materials. The tool computes the transmitted SPD, then determines colorimetric and photobiological outputs using the transmitted SPD as the test source. Glass, window, and skylight manufacturers can employ the tool to optimize glazing spectral transmission to achieve intentional colorimetric and photobiological performance with transmitted light. Electric lighting manufacturers, designers, and researchers can use the tool to evaluate the impact of glazing units and other optical materials on the color quality and biological potential of transmitted light.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Optical reflectance imaging reveals interlayer coupling in mechanically stacked MoS 2 and WS 2 bilayers

Optical reflectance imaging is a popular technique for characterizing 2D materials, thanks to its simplicity and speed of data acquisition. The use of this method for studying interlayer phenomena in stacked 2D layers has, however, remained limited. Here we demonstrate that optical imaging can reveal the nature of interlayer coupling in stacked MoS 2 and WS 2 bilayers through their observed reflectance contrast versus the substrate. Successful determination of interlayer coupling requires co-optimization of the illumination wavelength and the thickness of an underlying SiO 2 film. Our observations are supported by multilayer optical calculations together with an analysis of the effect of any interlayer gap. This approach promises quick characterization of constructed 2D material systems.

Nguyen, Vu↗
DOE OSTI2023

Influence of NaCl concentration on the optical scattering properties of water-based aerosols

We present the characterization of several atmospheric aerosol analogs in a tabletop chamber and an analysis of how the concentration of NaCl present in these aerosols influences their bulk optical properties. Atmospheric aerosols (e.g., fog and haze) degrade optical signal via light–aerosol interactions causing scattering and absorption, which can be described by Mie theory. This attenuation is a function of the size distribution and number concentration of droplets in the light path. These properties are influenced by ambient conditions and the droplet’s composition, as described by Köhler theory. It is therefore possible to tune the wavelength-dependent bulk optical properties of an aerosol by controlling droplet composition. We present experimentation wherein we generated multiple microphysically and optically distinct atmospheric aerosol analogs using salt water solutions with varying concentrations of NaCl. The results demonstrate that changing the NaCl concentration has a clear and predictable impact on the microphysical and optical properties of the aerosol.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Computational Imaging for Intelligence in Highly Scattering Aerosols (Final Report)

Natural and man-made degraded visual environments pose major threats to national security. The random scattering and absorption of light by tiny particles suspended in the air reduces situational awareness and causes unacceptable down-time for critical systems and operations. To improve the situation, we have developed several approaches to interpret the information contained within scattered light to enhance sensing and imaging in scattering media. These approaches were tested at the Sandia National Laboratory Fog Chamber facility and with tabletop fog chambers. Computationally efficient light transport models were developed and leveraged for computational sensing. The models are based on a weak angular dependence approximation to the Boltzmann or radiative transfer equation that appears to be applicable in both the moderate and highly scattering regimes. After the new model was experimentally validated, statistical approaches for detection, localization, and imaging of objects hidden in fog were developed and demonstrated. A binary hypothesis test and the Neyman-Pearson lemma provided the highest theoretically possible probability of detection for a specified false alarm rate and signal-to-noise ratio. Maximum likelihood estimation allowed estimation of the fog optical properties as well as the position, size, and reflection coefficient of an object in fog. A computational dehazing approach was implemented to reduce the effects of scatter on images, making object features more readily discernible. We have developed, characterized, and deployed a new Tabletop Fog Chamber capable of repeatably generating multiple unique fog-analogues for optical testing in degraded visual environments. We characterized this chamber using both optical and microphysical techniques. In doing so we have explored the ability of droplet nucleation theory to describe the aerosols generated within the chamber, as well as Mie scattering theory to describe the attenuation of light by said aerosols, and correlated the aerosol microphysics to optical properties such as transmission and meteorological optical range (MOR). This chamber has proved highly valuable and has supported multiple efforts inclusive to and exclusive of this LDRD project to test optics in degraded visual environments. Circularly polarized light has been found to maintain its polarization state better than linearly polarized light when propagating through fog. This was demonstrated experimentally in both the visible and short-wave infrared (SWIR) by imaging targets made of different commercially available retroreflective films. It was found that active circularly polarized imaging can increase contrast and range compared to linearly polarized imaging. We have completed an initial investigation of the capability for machine learning methods to reduce the effects of light scattering when imaging through fog. Previously acquired experimental long-wave images were used to train an autoencoder denoising architecture. Overfitting was found to be a problem because of lack of variability in the object type in this data set. The lessons learned were used to collect a well labeled dataset with much more variability using the Tabletop Fog Chamber that will be available for future studies. We have developed several new sensing methods using speckle intensity correlations. First, the ability to image moving objects in fog was shown, establishing that our unique speckle imaging method can be implemented in dynamic scattering media. Second, the speckle decorrelation over time was found to be sensitive to fog composition, implying extensions to fog characterization. Third, the ability to distinguish macroscopically identical objects on a far-subwavelength scale was demonstrated, suggesting numerous applications ranging from nanoscale defect detection to security. Fourth, we have shown the capability to simultaneously image and localize hidden objects, allowing the speckle imaging method to be effective without prior object positional information. Finally, an interferometric effect was presented that illustrates a new approach for analyzing speckle intensity correlations that may lead to more effective ways to localize and image moving objects. All of these results represent significant developments that challenge the limits of the application of speckle imaging and open important application spaces. A theory was developed and simulations were performed to assess the potential transverse resolution benefit of relative motion in structured illumination for radar systems. Results for a simplified radar system model indicate that significant resolution benefits are possible using data from scanning a structured beam over the target, with the use of appropriate signal processing.

58 GEOSCIENCES↗
DOE OSTI2021

Processable High Electron Mobility {pi}-Copolymers via Mesoscale Backbone Conformational Ordering

The synthesis and experimental/theoretical characterization of a new series of electron-transporting copolymers based on the naphthalene bis(4,8-diamino-1,5-dicarboxyl)amide (NBA) building block are reported. Comonomers are designed to test the emergent effects of manipulating backbone torsional characteristics, and density functional theory (DFT) analysis reveals the key role of backbone conformation in optimizing electronic delocalization and transport. The NBA copolymer conformational and electronic properties are characterized using a broad array of molecular/macromolecular, thermal, optical, electrochemical, and charge transport techniques. All NBA copolymers exhibit strongly aggregated morphologies with significant nanoscale order. Copolymer charge transport properties are investigated in thin-film transistors and exhibit excellent electron mobilities ranging from 0.4 to 4.5 cm(2) V-1 s(-1). Importantly, the electron transport efficiency correlates with the film mesoscale order, which emerges from comonomer-dependent backbone planarity and extension. These results illuminate the key NBA building block structure-morphology-bulk property design relationships essential for processable, electronics-applicable high-performance polymeric semiconductors.

n‐↗
DOE OSTI2024

Inverse Design of Photonic Surfaces via High throughput Femtosecond Laser Processing and Tandem Neural Networks

Abstract This work demonstrates a method to design photonic surfaces by combining femtosecond laser processing with the inverse design capabilities of tandem neural networks that directly link laser fabrication parameters to their resulting textured substrate optical properties. High throughput fabrication and characterization platforms are developed that generate a dataset comprising 35280 unique microtextured surfaces on stainless steel with corresponding measured spectral emissivities. The trained model utilizes the nonlinear one‐to‐many mapping between spectral emissivity and laser parameters. Consequently, it generates predominantly novel designs, which reproduce the full range of spectral emissivities (average root‐mean‐squared‐error < 2.5%) using only a compact region of laser parameter space 25 times smaller than what is represented in the training data. Finally, the inverse design model is experimentally validated on a thermophotovoltaic emitter design application. By synergizing laser‐matter interactions with neural network capabilities, the approach offers insights into accelerating the discovery of photonic surfaces, advancing energy harvesting technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Transport and Assembly of Magnetic Surface Rotors**

This minireview focuses on recent advances with surface magnetic rotors, namely field-responsive spherical or anisotropic microparticles that translate close to, or are embedded in a confining surface. The application of external magnetic modulations allows these microscopic wheels to be remotely spun and steered while also tuning their interactions and inducing assembly from a collection of disordered, moving units. With optical microscopy one can observe and characterize the complex collective phenomena that emerge in dissipative colloidal systems driven far from equilibrium by external fields. From a technological point of view, magnetic surface rotors envisage implementation into microfluidic devices, and can be used for drug delivery, mixing as well as a model system for biological active matter.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Long-range transported North American wildfire aerosols observed in marine boundary layer of eastern North Atlantic

Wildfire is a major source of biomass burning aerosols, which greatly impact Earth climate. Tree species in North America (NA) boreal forests can support high-intensity crown fires, resulting in elevated injection height and longer lifetime (on the order of months) of the wildfire aerosols. Given the long lifetime, the properties of aged NA wildfire aerosols are required to understand and quantify their effects on radiation and climate. Here we present comprehensive characterization of climatically relevant properties, including optical properties and cloud condensation nuclei (CCN) activities of aged NA wildfire aerosols, emitted from the record-breaking Canadian wildfires in August 2017. Despite the extreme injection height of ~12 km, some of the wildfire plumes descended into the marine boundary layer in the eastern North Atlantic over a period of ~2 weeks, owing to the dry intrusions behind mid-latitude cyclones. The aged wildfire aerosols have high single scattering albedos at 529 nm (ω 529 ; 0.92–0.95) while low absorption Ångström exponents (Å abs ) at 464 nm/648 nm (0.7–0.9). In comparison, Å abs of fresh/slightly aged ones are typically 1.4–3.5. This low Å abs 529 and low Å abs ~110 nm diameter) with thick non-absorbing coatings. The accelerated descent of the wildfire plume also led to strong increase of CCN concentration at the supersaturation levels representative of marine low clouds. The hygroscopicity parameter, κ CCN , of the aged wildfire aerosols varies from 0.2 to 0.4, substantially lower than that of background marine boundary layer aerosols. However, the high fraction of particles with large diameter (i.e., within accumulation size ranges, ~100–250 nm) compensates for the low values of κ, and as a result, the aged NA wildfire aerosols contribute more efficiently to CCN population. These results provide direct evidence that the long-range transported NA wildfires can strongly influence CCN concentration in remote marine boundary layer, therefore the radiative properties of marine low clouds. Given the expected increases of NA wildfire intensity and frequency and regular occurrence of dry intrusion following mid-latitude cyclones, the influence of NA wildfire aerosols on CCN and clouds in remote marine environment need to be further examined.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Weather aging effects on modified asphalt with rubber-polyethylene composites

Weather aging may cause more severe degradation on asphalt than thermal-oxidative aging due to the synergistic effect among oxygen, heat, ultraviolet (UV) radiation, and moisture. This study aimed to investigate weather aging effects and anti-aging mechanisms on asphalt modified with rubber-polyethylene (PE) composites. The modified binder blends and asphalt mixtures were subjected to outdoor weather aging. Dynamic shear rheometer (DSR), Fourier transform infrared spectroscopy (FTIR), Gel permeation chromatography (GPC), and optical microscopy tests were adopted to characterize the rheological properties, aging resistance, polymer degradation, and anti-aging mechanisms of modified binder blends, respectively. Mixture performance tests including Asphalt Pavement Analyzer (APA) and Ideal-CT tests were used to evaluate rutting and cracking resistance of asphalt mixtures. Results showed that weather aging can cause more severe aging to asphalt binders than pressure aging vessel (PAV) due to the severe degradation of PE particles. Rubber-PE composites alloyed with an extruder proved to stabilize PE particles in asphalt and significantly improve the aging resistance of modified binder blends. Furthermore, the enhanced aging resistance is attributed to the dispersion of PE particles and carbon black released by soluble rubbers.

Aging resistance↗
DOE OSTI2022

Monofluorination of Naphthyls Promotes the Cofacial π–π Stacking and Increases the Electron Mobility of Non-Planar Zinc(II) Complexes of Di(naphthylethynyl)azadipyrromethene

The homoleptic zinc(II) complex of [2,8-di(1-naphthylethynyl) 3,7-diphenyl 1,9-(4-hexylphenyl)azadipyrromethene (ZnL2) 2 ] is a promising non-planar non-fullerene acceptor for organic photovoltaic applications, but it has a relatively low electron mobility that may limit its performance. Here, we explored the fluorination of peripheral aryl groups to increase intermolecular cofacial π–π stacking interactions, which are desirable for electron transport. Here complexes with fluorine on the distal phenyls [Zn(1F-L2) 2 ], on the naphthyls [Zn(2F-L2) 2 ], and on both [Zn(3F-L2) 2 ] were synthesized and characterized. All three complexes had similar optical and electrochemical properties. The crystal packing structure of Zn(2F-L2) 2 and Zn(3F-L2) 2 revealed cofacial parallel-displaced π–π stacking between the fluorinated 1-naphthylethynyl groups. Such a cofacial orientation was not observed in Zn(L2) 2 crystals, suggesting that fluorination of the naphthyl groups promotes the cofacial π–π stacking orientation. The hole mobility increased from 1.0 × 10 –4 cm 2 V –1 s –1 for Zn(L2) 2 to 0.8–1.0 × 10 –3 cm 2 V –1 s –1 for the fluorinated complexes. Fluorination on the naphthyl groups increased the electron mobility from 4.2 × 10 –5 cm 2 V –1 s –1 for Zn(L2) 2 and Zn(1F-L2) 2 to 2.0 × 10 –4 cm 2 V –1 s –1 for Zn(2F-L2) 2 and Zn(3F-L2) 2 , consistent with cofacial π–π stacking being favorable for electron transport. The three complexes were tested in OPVs using regioregular poly(3-hexylthiophene) (P3HT) as the p-type material, and the best power conversion efficiencies were 5.2, 5.4, and 5.8% for Zn(2F-L2) 2 , Zn(1F-L2) 2 , and Zn(3F-L2) 2 , respectively, compared to 5.5% for Zn(L2) 2 . The fluorination combination found in Zn(3F-L2) 2 resulted in the best device performance. This study points to a viable strategy to increase the electron mobility and performance of non-planar zinc(II) complexes of azadipyrromethene.

36 MATERIALS SCIENCE↗
DOE OSTI2024

High Density Two-Component Glasses of Organic Semiconductors Prepared by Physical Vapor Deposition

Physical Vapor Deposition (PVD) is widely utilized for the production of organic semiconductor devices due to its ability to form thin layers with exceptional properties. Although the layers in the device usually consist of two or more components, there is limited understanding about the fundamental characteristics of such multi-component vapor-deposited glasses. Here, spectroscopic ellipsometry was employed to characterize the densities, thermal stabilities and optical properties of co-vapor deposited NPD and TPD glasses across the entire range of composition. We find that co-deposited NPD and TPD form high density glasses with enhanced thermal stability. The dependences of density and stability upon substrate temperature are correlated, and the birefringence of the co-deposited glasses is determined by the reduced substrate temperature of mixtures. Additionally, we observe that the transformation of a highly stable and dense two-component glass into its supercooled liquid initiates from the free surface and propagates into the bulk at constant velocity, like single component PVD glasses. As a result, all these features are consistent with the surface equilibration mechanism.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Engineering Surface Architectures for Improved Durability in III–V Photocathodes

GaInP2 has shown promise as the wide bandgap top junction in tandem absorber photoelectrochemical (PEC) water splitting devices. Among previously reported dual-junction PEC devices with a GaInP 2 top cell, those with the highest performance incorporate an AlInP 2 window layer (WL) to reduce surface recombination and a thin GaInP2 capping layer (CL) to protect the WL from corrosion in electrolytes. However, the stability of these III-V systems is limited, and durability continues to be a major challenge broadly in the field of PEC water splitting. This work provides a systematic investigation into the durability of GaInP 2 systems, examining the impacts of the window layer and capping layer among single junction pn-GaInP 2 photocathodes coated with an MoS 2 catalytic and protective layer. The photocathode with both a CL and WL demonstrates the highest PEC performance and longest lifetime, producing a significant current for >125 h. In situ optical imaging and post-test characterization illustrate the progression of macroscopic degradation and chemical state. The surface architecture combining an MoS 2 catalyst, CL, and WL can be translated to dual-junction PEC devices with GaInP 2 or other III-V top junctions to enable more efficient and stable PEC systems.

08 HYDROGEN↗
DOE OSTI2025

Efficient Measurement of Length Distribution of 1D Nanoparticles in Solution via Optical Polarimetry

The efficient measurement of the length distribution of nanotubes, nanowires, and other one-dimensional (1D) nanoparticles in solution is important to enable their incorporation into materials and devices and to optimize their processing for properties of interest, such as thermal/electrical conductivity or mechanical strength, in suspensions and composites. We report an electric-field (E-field)-assisted optical-polarimetry technique to measure the length distribution of ensembles of high-aspect-ratio particles in dilute suspension. The degree of alignment of polarizable 1D particles suspended in a fluid under Brownian motion explicitly depends on the E-field strength and the particle length. We show that it is possible to extract the length distribution of 1D nanoparticles suspended in an insulating fluid by applying a range of E-fields and using optical polarimetry to measure the corresponding alignment order parameter. Notably, the method is relatively insensitive to the diameter of the 1D particles, which can be poorly known or vary within a sample. The technique is validated with silver nanowires and carbon nanotubes of known lengths, as well as polymer-depletion-length-separated single-wall carbon nanotube samples with length distributions independently measured with analytical ultracentrifugation. Finally, we demonstrate the ability of the optical-polarimetry technique to quantify changes in the length distribution of ultranarrow, sub-nanometer-diameter single-wall carbon nanotubes under different types and durations of ultrasonication. Within its range of applicability (polarizable 1D nanoparticles in the 0.5 to 15 μm length range, constrained by the voltage stability of the media and the suspended particles), the E-field-assisted optical-polarimetry method is a particularly efficient and accurate method to measure the length distribution of nanowires and nanotubes in suspension.

1D nanoparticles↗
DOE OSTI2022

Nano-spectroscopy of excitons in atomically thin transition metal dichalcogenides

Abstract Excitons play a dominant role in the optoelectronic properties of atomically thin van der Waals (vdW) semiconductors. These excitons are amenable to on-demand engineering with diverse control knobs, including dielectric screening, interlayer hybridization, and moiré potentials. However, external stimuli frequently yield heterogeneous excitonic responses at the nano- and meso-scales, making their spatial characterization with conventional diffraction-limited optics a formidable task. Here, we use a scattering-type scanning near-field optical microscope (s-SNOM) to acquire exciton spectra in atomically thin transition metal dichalcogenide microcrystals with previously unattainable 20 nm resolution. Our nano-optical data revealed material- and stacking-dependent exciton spectra of MoSe 2 , WSe 2 , and their heterostructures. Furthermore, we extracted the complex dielectric function of these prototypical vdW semiconductors. s-SNOM hyperspectral images uncovered how the dielectric screening modifies excitons at length scales as short as few nanometers. This work paves the way towards understanding and manipulation of excitons in atomically thin layers at the nanoscale.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

High-throughput micro-scale bandgap mapping for perovskite-inspired materials with complex composition space

Abstract To realize the full promise of high-throughput experimental workflows, the rate of sample synthesis must be matched by that of characterization. Of growing interest are contactless optical techniques that can rapidly measure material homogeneity and properties. Here, we present a hyperspectral imaging method to measure local optical bandgap distributions within samples, utilizing spatially-resolved reflectance spectra coupled with automated data analysis. We collect approximately one million optical bandgap data across the compositional space of Cs 3 (Bi x Sb 1-x ) 2 (Br y I 1-y ) 9 perovskite-inspired materials. Our results show non-monotonic bandgap variations (i.e., bandgap bowing) along six composition gradient sequences, in addition to identifying samples with multiple bandgaps in statistics. High-throughput transient absorption spectroscopy reveals that within these compositions, the depletion of the ground state carriers to excited states occurred at discrete energy levels with independent carrier dynamics, consistent with the bandgap observation and indicative of phase separation. This work demonstrates the potential for rapid optical measurements to assess material quality and homogeneity in a high-throughput experimental setting, supporting screening and recipe optimization of optoelectronic material candidates with desired carrier dynamics and optical properties.

Science & Technology - Other Topics↗
DOE OSTI2020

Characterization of an RF-driven argon plasma at atmospheric pressure using broadband absorption and optical emission spectroscopy

Atmospheric pressure plasmas in argon are of particular interest due to the production of highly excited and reactive species enabling numerous plasma-aided applications. In this contribution, we report on absolute optical emission and absorption spectroscopy of a radio frequency (RF) driven capacitively coupled argon glow discharge operated in a parallel-plate configuration. This enabled the study of all key parameters including electron density and temperature, gas temperature, and absolute densities of atoms in highly electronically excited states. The space and time-averaged electron density and temperature were determined from the measurement of the absolute intensity of the electron-atom bremsstrahlung in the visible range. Considering the non-Maxwellian electron energy distribution function, an electron temperature (T e ) of 2.1 eV and an electron density (n e ) of 1.1 × 10 19 m –3 were obtained. The time-averaged and spatially resolved absolute densities of atoms in the metastable (1s 5 and 1s 3 ) and resonant (1s 4 and 1s 2 ) states of argon in pure Ar and Ar/He mixture were obtained by broadband absorption spectroscopy. The 1s 5 metastable atoms had the largest density near the sheath region with a maximum value of 8 × 10 17 m –3 , while all other 1s states had densities of at most 2 × 10 17 m –3 . Here, the dominant production and loss mechanisms of these atoms were discussed, in particular, the role of radiation trapping. We conclude with a comparison of the plasma properties of the argon RF glow discharges with the more common He equivalent and highlight their differences.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗