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Plasma actuators have been proposed as a tool to produce hydrodynamical effects in the boundary layer of aerodynamical flows. We have analyzed some properties of these systems using suitable plasma diagnostics based on the emissivity characteristics of such plasmas. The direction and the velocity of propagation of the ionizing wave spreading on the dielectric surface were measured (in the 100–200 km/s range), and it was demonstrated that it behaves like a cathode-directed streamer. The averaged electron temperature (4–5 eV) and the reduced field strength (E/N ≈ 6 × 1019 V·m2) of the ionizing wave switching the discharges on were measured, too. [ABSTRACT FROM AUTHOR]

Low-angle grain boundaries (LAGBs) accommodate residual stress through the rearrangement and accumulation of dislocations during cold rolling. This study presents an electron wind force-based annealing approach to recover cold-rolling induced residual stress in FeCrAl alloy below 100 °C in 1 min. This is significantly lower than conventional thermal annealing, which typically requires temperatures around 750 °C for about 1.5 h. A key feature of our approach is the athermal electron wind force effect, which promotes dislocation movement and stress relief at significantly lower temperatures. The electron backscattered diffraction (EBSD) analysis reveals that the concentration of low-angle grain boundaries (LAGBs) is reduced from 82.4% in the cold-rolled state to a mere 47.5% following electropulsing. This level of defect recovery even surpasses the pristine material's initial state, which exhibited 54.8% LAGBs. This reduction in LAGB concentration was complemented by kernel average misorientation (KAM) maps and X-ray diffraction (XRD) Full Width at Half Maximum (FWHM) measurements, which further validated the microstructural enhancements. Nanoindentation tests revealed a slight increase in hardness despite the reduction in dislocation density, suggesting a balance between grain boundary refinement and dislocation dynamics. This proposed low-temperature technique, driven by athermal electron wind forces, presents a promising avenue for residual stress mitigation while minimizing undesirable thermal effects, paving the way for advancements in various material processing applications. [ABSTRACT FROM AUTHOR]

Recently, a novel approach of depositing metallic films with chemical vapor deposition (CVD), using plasma electrons as reducing agents, has been presented and is herein referred to as e-CVD. By applying a positive substrate bias to the substrate holder, plasma electrons are drawn to the surface of the substrate, where the film growth occurs. In this work, we have characterized the electron flux at the substrate position in terms of energy and number density as well as the plasma potential and floating potential when maintaining an unbiased and a positively biased substrate. The measurements were performed using a modified radio frequency Sobolewski probe to overcome issues due to the coating of conventional electrostatic probes. The plasma was generated using a DC hollow cathode plasma discharge at various discharge powers and operated with and without precursor gas. The results show that the electron density is typically around 1016 m−3 and increases with plasma power. With a precursor, an increase in the substrate bias shows a trend of increasing electron density. The electron temperature does not change much without precursor gas and is found in the range of 0.3–1.1 eV. Introducing a precursor gas to the vacuum chamber shows an increase in the electron temperature to a range of 1–5 eV and with a trend of decreasing electron temperature as a function of discharge power. From the values of the plasma potential and the substrate bias potential, we were able to calculate the potential difference between the plasma and the substrate, giving us insight into what charge carriers are expected at the substrate under different process conditions. [ABSTRACT FROM AUTHOR]

There are few reported cases in which the spatial distribution of spectral emission coefficients of plasmas from tomographic optical emission spectroscopy measurements is analyzed based on a collisional-radiative model to diagnose the spatial distribution electron temperature of T e and density N e . This study aimed at in situ diagnosis of process plasma. The spectral radiance of 18 lines-of-sight was measured simultaneously in argon inductively coupled plasma. The spatial distribution of the excited level number density distribution was calculated from the spatial distribution of spectral emission coefficients obtained from spectral tomography calculations. The three-dimensional distribution of T e and N e was analyzed using a collisional-radiative model from the obtained spatial distribution of the excited levels number density. The effects of power and pressure on the dependence of the spatial distribution of T e and N e were discussed. Furthermore, data processing methods for spectral tomographic measurements with coarse wavelength resolution were also discussed. [ABSTRACT FROM AUTHOR]

We present the first ground‐based measurements of daytime stable auroral red (SAR) arc using OI 630.0 nm emissions. SAR arc is a direct consequence of heat conduction from the inner‐magnetosphere to the ionospheric regions characterized by increased electron temperatures and low electron density in the region of mid‐latitude trough. So far, SAR arc emissions have only been reported for nighttime conditions. For the present study, daytime optical measurements were enabled using a high‐resolution imaging echelle spectrograph from Boston (42.36°N, 71.05°W, MLAT ≈ 53°). Simultaneous Millstone Hill Incoherent Scatter Radar and Defense Meteorological Satellite Program measurements of electron density and temperature confirm our findings. Forward modeling approach enabled estimation of daytime electron temperatures in 200–650 km altitude during this SAR arc event to be varying between 3,500 and 4,400 K. These observations open numerous possibilities of optical investigations of magnetospheric‐ionospheric interactions during daytime, when the upper atmosphere is dynamic with large gradients in ionospheric conductivities, temperatures, and winds. Plain Language Summary: A latitudinally narrow and zonally elongated channel consisting of enhanced red‐line emissions are known to be present, on occasions, in the optical measurements in the sub‐auroral latitudes and are referred to as the stable auroral red (SAR) arcs. These are now known to be caused by the conduction of heat from the Ring current region into the ionosphere. Earlier studies suggested an increased electron temperature (above ∼300 km altitude) collocated with the low electron density region of ionospheric trough. So far, observations of SAR arcs have only been reported for the night time. In the daytime, due to the presence of sunlight the atmospheric conditions are different, so also are the upper atmospheric dynamics. The measurements of SAR arcs in the daytime are also challenging as the background solar brightness is very large. In this work, by making use of high spectral resolution optical measurements in the daytime, we present the first measurements of daytime SAR arcs and perform model calculations to estimate the values of electron temperature in the 200–650 km altitude range to be varying in the range of 3,500–4400 K. Key Points: Ground‐based measurements of O(1D) dayglow showed enhancement in emissions on a geomagnetically disturbed day at a mid‐latitude locationComplementary data sets revealed the increase in optical emissions to be stable auroral red (SAR) arcs, which are associated with elevated electron temperaturesThis study presents the first ground‐based detection of daytime SAR arcs in OI 630.0 nm red‐line emissions [ABSTRACT FROM AUTHOR]

A fully kinetic 2D axisymmetric Particle-in-Cell (PIC) model is used to examine the effects of background facility pressure on the plasma transport and propulsive efficiency of magnetic nozzles. Simulations are performed for a low-power (150 W class) cathode-less radio-frequency (RF) plasma thruster, operating with xenon, between background pressures up to 1 0 − 2 Pa and average electron discharge temperatures of 4–16 eV. When the electron temperature within the near-plume region reaches 8 eV, a decisive reduction in performance occurs: at 1 0 − 2 Pa, in-plume power losses surpass 25% of the discharge energy flux. Given that the ionisation energy for Xe is 12 eV, the 8 eV threshold indicates that a consistent percentage of electrons has energy enough to trigger ionisation. On the other hand, when the temperature is below such threshold, the primary collisions are charge-exchange and inelastic ion scattering, and the power loss remains less than 10%. It is established that losses in the considered thruster are significant if the facility pressure is greater than 1 0 − 3 Pa, at absorbed powers larger than 130 W. At the nominal 150 W, this results in a 15% thrust reduction. When facility pressure is taken into consideration over ideal vacuum simulations, numerical error is reduced to < 30% when compared to experimental thrust measurements at 1 0 − 3 Pa. • Investigation of facility effects on cathode-less RF thruster performance. • Particle-in-Cell (PIC) simulation of magnetic nozzle expansion into background gas. • Up to 15% thrust reduction at 150 W beyond 1 0 − 3 Pa. • Electron inelastic collisions can cause up to 70% of total in-plume power losses. • Experimental results/setup should therefore take into account facility pressure. [ABSTRACT FROM AUTHOR]

In the framework of the ongoing project, aimed at the systematical studying galaxies in nearby voids, we conducted spectroscopy with the Southern African Large Telescope (SALT) of 62 objects from the Nearby Void Galaxy (NVG) sample. They include 8 remaining objects of the 60 pre-selected candidates to eXtremely Metal-Poor (XMP) dwarfs, two known void XMP dwarfs and 52 void dwarfs residing within the Local Volume. For 47 galaxies residing in the nearby voids, we obtained spectra of the diverse quality. For 42 of them, we detected the Hydrogen and Oxygen lines that allowed us to get estimates of O/H in the observed H  ii regions. For 12 of the 42 objects, we detected the faint line [O  iii ]λ4363, that allowed us to directly derive the electron temperature Te and obtain their gas O/H by the direct method. 14 objects with the undetected [O  iii ]λ4363 line fall to the lowest metallicities range (12+log(O/H) ≲ 7.5 dex). For them, we use a carefully checked new empirical 'Strong line' method of Izotov et al. For 14 other objects with only strong lines detected and with 12+log(O/H) of ∼7.5–8.0 dex, we used the modified version of 'semi-empirical' method of Izotov and Thuan. It accounts for effect of the excitation parameter O32 on Te. 16 new galaxies are found with parameter 12+log(O/H) ≲ 7.39 dex. Of them, four have 12+log(O/H) = 7.07–7.20 dex. Of the 60 observed NVG objects, 15 have mistaken radial velocities in HyperLEDA. They do not reside in the nearby voids. [ABSTRACT FROM AUTHOR]

A technique is proposed for reconstructing the electron temperature profile under conditions when the integral absorption coefficient of electron cyclotron emission (ECE) is less than unity. Numerical simulations of plasma ECE were performed for the L-2M stellarator in the ohmic heating regime. It is shown that the radiation temperature profiles recovered from the ECE diagnostics data in the ohmic heating regime require considerable correction. The profile width turns out to be smaller than the width of the true temperature profile, and the on-axis plasma temperature is underestimated by ~30%. A new method is proposed for the relative calibration of ECE diagnostics channels in the ohmic heating regime. The resulting calibration coefficients can be used to measure the plasma temperature in the electron cyclotron resonance heating regime. [ABSTRACT FROM AUTHOR]

Dual‐frequency (DF) dual‐antenna inductively coupled plasma (ICP) sources have been proposed as one of the methods to produce large‐area uniform plasma. In this study, a hybrid model, consisting of a fluid module and an electron Monte Carlo (eMC) module, is used to further investigate the modulation of the plasma characteristics (i.e., induced electric field, electron energy distribution, electron heating mechanism, electron temperature, and plasma density) by the low‐frequency (LF) and high‐frequency (HF) currents in a DF argon discharge. When the inner LF current increases from 12 to 22 A at a fixed outer HF current of 10 A, the induced electric field is strengthened near the LF coil and weakened near the HF coil. The fraction of high‐energy electrons at different spatial positions increases with the increase of LF current, which is caused by the sufficient collision heating in the skin layer of LF source, leading to an increase in electron temperature. When the outer HF current rises from 7 to 13 A with the inner LF current fixed at 17 A, the induced electric field is enhanced near the HF coil and weakened near the LF coil. The fraction of low‐energy electrons at different positions increases with the increase of HF current since the energetic electrons from the skin layer of HF source are cooled due to the ionization, excitation, and stepwise ionization collisions between electrons and neutral particles, as well as the weakened induced electric field near the LF coil. As a result, the electron temperature drops with the increase of HF current. Moreover, when the LF and HF currents increase, the plasma density increases, and the distribution of plasma density is also significantly modulated. [ABSTRACT FROM AUTHOR]

We report the first observation of global recycling coefficient R near 0.5 in the Lithium Tokamak eXperiment-β (LTX-β), significantly below the minimum R previously reported in other devices. In a series of experiments with varied Li wall conditioning, estimates of the recycling coefficient have been made using a Lyman-α array and DEGAS2 modeling. A progressive reduction in Lyman-α emission with increased lithium and an increase in edge electron temperature are observed. It is also observed that with increasing Li coating thickness, the effective particle confinement time τ p * is reduced and approaches TRANSP calculated energy confinement time (τE), with τ p * near τ E , TRANSP for the lowest recycling coefficients. Edge temperatures approaching core plasma temperatures, first reported in LTX, can now be directly connected to estimates of the recycling coefficient and qualitatively agree with previous UEDGE simulations. The particle flux to the limiting surfaces appears to be significantly reduced in comparison with fluid scrape-off layer (SOL) models, indicating that a large fraction of the SOL ions are mirror trapped. SOL collisionality drops more than an order of magnitude below the banana regime boundary, indicating the importance of kinetic effects. Full-f 1x2v gyrokinetic simulations of SOL field lines with the GKEYLL code indicate that the fraction of ions trapped along field lines increases as collisionality drops, as a result of increased lithium evaporation. [ABSTRACT FROM AUTHOR]

Collisionless trapped-electron mode (CTEM) turbulence is an important contributor to heat and particle transport in fusion devices. The ion-temperature gradient (ITG)/trapped-electron mode (TEM) fluid models are rarely treated analytically, due to the large number of transport channels involved, e.g., particle and ion/electron heat transport. The CTEM fluid model [Anderson et al., Plasma Phys. Controlled Fusion 48, 651 (2006)] provides a simplified model, in the regime where the density gradient drive (∇ n) is negligible compared to the electron temperature gradient drive (∇ T e ). This provides a starting point to study mechanisms associated with linear waves, such as crossphase dynamics, and its possible role in the formation of E × B staircase. Here, an extended CTEM fluid model (with both ∇ n and ∇ T e drive) is derived from the more general ITG/TEM model, using a simplified ion density response, and its linear dynamics is first analyzed and compared with CTEM gyrokinetic simulations with bounce-averaged kinetic electrons, while nonlinear analysis is left for future work. The wave action density is derived for this CTEM model. Comparisons of linear ITG spectrum are also made with other analytical models. [ABSTRACT FROM AUTHOR]

Featured Application: The obtained knowledge can be useful for understanding and optimizing various technologies with glass-forming materials under local fast laser excitations. The ability to control the temperature distribution T (t , r) and the rate of temperature change R t , r inside glasses is important for their microstructuring. The lattice temperature is considered at time t , exceeding the electron–phonon thermalization time, and at a distance r from the center of the model spherical heating zone. In order to describe thermal excitations, the heat capacity of glasses must be considered as a function of time due to its long-term relaxation. A method for the analytical calculation of T (t , r) and R (t , r) for glasses with dynamic heat capacity c d y n (t) is proposed. It is shown that during laser microstructuring, the local cooling rate − R (t , r) significantly depends on the time dispersion of c d y n (t) . It has been established that at the periphery of the model heating zone of the laser beam focus, the local cooling rate can reach more than 1011 K/s. Strong cooling rate gradients were found at the periphery of the heating zone, affecting the microstructure of the material. This effect is significantly enhanced by the time dispersion of c d y n (t) . The effect associated with this time dispersion is significant, even well above the glass transition temperature T g , since even short relaxation times of the dynamic heat capacity c d y n (t) are significant. [ABSTRACT FROM AUTHOR]

In low-temperature inductively coupled radio frequency (rf) plasmas, electrons and ions that gain energy from the electric field can transfer a portion of energy to neutral particles. The resulting radial variation of the neutral gas temperature T g can significantly influence the radial distributions of reaction rates and radical densities on the substrate, thus affecting the etching/film deposition uniformity. In this work, we perform an experimental study on the dependence of the neutral gas temperature T g on external parameters (i.e., rf power, pressure, and gas component) in inductively coupled Ar and Ar/O2 plasmas by using a fiber Bragg grating sensor. To analyze the correlation between T g and the plasma characteristics, a Langmuir probe is used to measure the electron density n e , effective electron temperature T e , and ion density n i under the same discharge conditions. It is found that in both Ar and Ar/O2 plasmas, neutral gas heating is sensitive to plasma density. As the plasma density increases with the pressure/power, the collisions of ions and electrons with neutral particles are enhanced so that T g increases monotonically. With the increase of O2 content, n e and n i are observed to decrease due to enhanced dissociation and excitation of O2, leading to a decrease in T g . The radial profile of T g exhibits a parabolic distribution in pure Ar discharges, whereas it evolves through a center-flat shape into a saddle shape with the increase of O2 content. The variation of T g with rf power during the E-to-H mode transition is also presented and discussed. [ABSTRACT FROM AUTHOR]

We present a theoretical investigation on the generation of Cerenkov emission of terahertz acoustic phonons in bilayer graphene (BLG) in the presence of a driving dc electric field. We have numerically and analytically studied the Cerenkov phonon emission spectrum, P s p e c t r u m (ω p , θ) , and phonon intensity, P i n t e n s i t y (θ) , dependence on the phonon frequency ω p , drift velocity v d , electron temperature T e , concentration n, and phonon emission angle θ in BLG with and without considering the chirality of the charge carriers. We find that the magnitude of P s p e c t r u m (ω p , θ) increases at larger drift velocities and applied electric fields with the peak of the spectrum shifting toward the higher frequency side. The spectrum magnitude in BLG is found to be much enhanced as compared to conventional 2D semiconductors and transition metal dichalcogenides, which makes it viable for SASER and other practical device applications. The chiral nature of carriers strongly influences the P s p e c t r u m (ω p , θ) behavior and sharpens the spectrum peak but with a decrease in the magnitude. The chirality favors the negative emission spectrum caused by the absorption of acoustic phonons. P s p e c t r u m (ω p , θ) and P i n t e n s i t y (θ) are found to be strongly dependent on temperature but independent of carrier concentration in the equipartition regime. The study is significant from the point of application of BLG as an acousto/optoelectronic device and high-frequency phonon spectrometers. [ABSTRACT FROM AUTHOR]

Subject and Purpose. In Part 2 of the current paper, we seek to analyze the observational results of decameter carbon radio recombination lines (RRLs) detected near the frequency 26 MHz through the UTR-2 radio telescope towards the S140 emission nebula and the GSH 139-03-69 super shell. These lines have proven themselves as a highly effective tool for cold, rarefied interstellar medium (ISM) diagnostics. The aim is to determine an association of line-forming regions (CII regions) with other ISM components and study physical conditions (electron temperature Te and electron density Ne) in these regions. Methods and Methodology. By iterative comparison of detected and modeled integral intensities of decameter carbon RRLs, we determine physical state ranges where recorded experimental data best fit the model values for various combinations of Te,Ne, and path lengths s. Results.It has been found that the characteristics of the detected decameter carbon RRLs are consistent with the higher-frequency data for both the S140 line of sight and other Galactic plane directions, including the GSH 139-03-69 direction. Ranges of physical conditions where recorded data and model values are in the best agreement have been determined, being Te = 50÷ 100 K, Ne = 0.01 cm–3, and s= 10 pc — for the S140 nebula direction and its vicinity and, also, Te = 50÷ 100 K, Ne =0.01 cm–3, and s = 5÷ 7 pc — for the GSH 139-03-69 super shell direction. Conclusions. The obtained results indicate that the detected decameter carbon RRLs originate from CII regions associated with clouds of diffuse neutral hydrogen HI in the Galactic plane. The lines are seen against a background Galactic radio emission whose brightness temperature increases as frequency decreases.

This study investigates the latitudinal characteristics of the nighttime electron temperature, as observed by the Defense Meteorological Satellite Program F16 satellite, and its dependence on solar and geomagnetic activities between 2013 and 2022 in the topside ionosphere, only for the winter hemispheres. The electron temperature in both hemispheres exhibited a low-temperature zone at the equator and a double high-temperature zone at the sub-auroral and auroral latitudes along the magnetic latitude. In addition, we further studied the temperature crest/trough positions in the temperature zone at different latitudes. As the solar activity intensity decreased (increased), the temperature trough position at the equator shifted from the Southern (Northern) to the Northern (Southern) Hemisphere, and the temperature double-crest positions at the sub-auroral and auroral latitudes gradually approached (moved away from) each other. Furthermore, during the geomagnetic disturbance time, the temperature double-crest positions both moved toward lower latitudes, but the temperature trough position was not sensitive to geomagnetic activity. Our analysis demonstrates that the values and correlations of the electron temperature and density varied in different temperature characteristic zones (the temperature crest/trough positions ±2°), possibly due to the different energy control factors of the electrons at different latitudes. This may also indirectly indicate the energy coupling process between the topside ionosphere and different regions at different latitudes.

Microdischarges (MDs) have attracted increasing attention recently due to their widespread applications. The electron beam injection as an external source can affect the formation and characteristics of microdischarges. Aimed at exploring the kinetic properties of the atmospheric-pressure microdischarges purely driven by electron beam injection without external voltage, the one-dimensional implicit particle-in-cell/Monte Carlo collision model is developed. The monoenergetic electron beam is injected from the left electrode with a current of 0.001–0.05 A and an emission energy of 20–80 eV. It is found that similar to voltage and current-driven MDs, electron beam driven MDs can sustain steady glow discharge with high density (10 21 – 10 22 m − 3 ) but has much lower plasma potential (∼ 0.15 − 0.30 V) and electron temperature (<1 eV) due to the absence of an external field. The electron energy distribution function is composed of a low-energy group with two-temperature distribution and a high-energy group with a discrete distribution. In addition, the injected electron beam current and energy can influence the plasma properties significantly, such as plasma density, electron temperature, plasma potential, etc. The characteristics of ion bombardment can also be modulated by the beam energy and current, resulting in achievement of low energy and high flux. By enlarging the gap between the electrodes, the parameter difference on both sides can be realized. [ABSTRACT FROM AUTHOR]

The electron energy probability function (EEPF) is experimentally identified in a miniature microwave discharge neutralizer over wide operating conditions. A tiny Langmuir probe coupled with the analog differentiation technique offers precise time-averaged EEPFs over about three orders of magnitude, including high-energy, low-density electrons. The non-Maxwellian, concave EEPFs are observed in all experimental conditions. They approach Maxwellian with higher gas pressure, where they deviate from Maxwellian with the absorbed microwave power. Analyzing the measured EEPFs by the generalized EEPF theory, the index that determines the shape of EEPFs (Maxwellian corresponds to 1) is found to be 0.7 ± 0.15. The ionization frequency is estimated using the measured non-Maxwellian EEPFs, and it is found that one would underestimate the ionization frequency with the Maxwellian approximation about up to ∼ 20 %, the value almost negatively correlating with the shape index. These results also suggest that the electron fluid model in microwave discharge neutralizers leads to the overestimation of the electron temperature and the Bohm velocity. [ABSTRACT FROM AUTHOR]

The performance of a recently proposed integrated graphene-bolometric photodetector is assessed. The responsivity of hundreds of A/W and speed on the scale of hundreds of GHz are predicted. The impressive performance is attributed to the small length over which the energy is absorbed by graphene. The short length leads to a highly enhanced energy density, which causes the increase of the electron temperature in graphene. The model has been validated against recently published experimental results from high-speed graphene photodetectors and found to be in good agreement. [ABSTRACT FROM AUTHOR]

A statistical analysis is conducted to identify which physically relevant non-dimensional parameters influence the total (neutral, ion, and electron) static pressure inside thermionic orificed hollow cathodes. It is critical to uncover and order the importance of the physical mechanisms that affect the pressure inside hollow cathodes because it influences the plasma attachment length, the electron temperature, and the sheath potential. These plasma parameters, in turn, affect the emitter lifetime. A principal component analysis of total pressure data obtained from the literature reveals that four non-dimensional variables can account for most of the variation in the total-to-magnetic pressure ratio over five orders of magnitude. The relevant variables are identified with a backward stepwise selection process and an exhaustive grid search and include, by order of importance: the gasdynamic-to-magnetic pressure ratio, the ratio of the mass flow rate to the discharge current, the orifice-to-insert diameter ratio, and the orifice Reynolds number. It is also shown, using various models and regression analyses, that empirical, Poiseuille, or isentropic flow models should not be used for predictive cathode design work. The data-driven study suggests that, while viscous effects may be important, the variation in those effects between cathodes is negligible compared to the effects of the modification of the gas constant due to the plasma, the transitional flow, the flux of heavy species on the orifice plate, and the Lorentz force. [ABSTRACT FROM AUTHOR]

Due to the raised interest in copper halides for optoelectronic applications, a wide range of plasma diagnostic tools based on Langmuir probe (LP) and optical emission spectroscopy (OES) were implemented to investigate the pulsed laser deposition (PLD) process of selected copper halides. This represents the first report of complete diagnostics of copper halide plasma generated by laser ablation. High plasma potential and electron temperature were observed by a time-resolved LP analysis, which affected the kinetic energy of the ejected ions during expansion. The effect of argon gas addition on the copper halide plasma dynamics was investigated. Angle-resolved measurements revealed a narrow cone plasma expansion with a dual peak charge particle distribution, which was affected only above 2 Pa of Ar atmosphere. Plasma potential, charge density, and electron excitation temperature were increasing with Ar pressure, while electron temperature and expansion velocities were decreasing. Using a semi-empirical model, the estimation of an ion acceleration field, neutral temperature, and densities were computed. Space- and time-resolved OES confirmed the plume splitting indicated by LP measurements and provided insight into the composition of the two-plasma structure. All the plasma parameters were investigated in conditions similar to those used for thin film growth, and the results were discussed with respect to the PLD technology. [ABSTRACT FROM AUTHOR]

This article reports on the characterization of a laboratory model 100 A-class hollow cathode with a sintered lanthanum hexaboride ( LaB 6) emitter for high-power Hall thrusters. The cathode has been fired up to 70 A with xenon as working gas. The cathode architecture, test setup, ignition procedure, and power consumption are described first. The second part of this contribution comments on the current–voltage characteristics and the discharge modes obtained for discharge currents in the 30–70 A range and flow rates in the 15–30 SCCM range. The cathode operates in a spot mode at high discharge currents and in a plume mode with large oscillations at low currents and low gas flow rate. Spectral analysis shows that most frequencies reside in the 10–200 kHz range with flat and sharp distributions in plume and spot modes, respectively. Finally, we present electron temperatures and densities measured in the cathode plasma plume by means of incoherent Thomson scattering. The two quantities decrease along the axis. The density is large (up to ∼ 10 19 m − 3 ) and increases with both the ion current and the gas flow rate. The electron temperature increases with the current and decreases with the gas flow rate. The temperature remains relatively low (<1.5 eV) in spite of large currents and applied powers. [ABSTRACT FROM AUTHOR]

We provide a measurement of the deficit in the Sunyaev–Zel'dovich Compton- y signal towards cosmic voids, by stacking a catalogue of 97 090 voids constructed with BOSS-DR12 data, on the y -maps built on data from the Atacama Cosmology Telescope (ACT) DR4 and the Planck satellite. We detect the void signal with a significance of |$7.3 \sigma$| with ACT and |$9.7\sigma$| with Planck , obtaining agreements in the associated void radial y -profiles extracted from both maps. The inner-void profile (for angular separations within the void angular radius) is reconstructed with significances of 4.7σ and 6.1σ with ACT and Planck , respectively; we model such profile using a simple model that assumes uniform gas (under)density and temperature, which enables us to place constraints on the product (−δv T e) of the void density contrast (negative) and the electron temperature. The best-fitting values from the two data sets are |$(-\delta _{\rm v}T_{\rm e})=(6.5\pm 2.3)\times 10^{5}\, \text{K}$| for ACT and |$(8.6 \pm 2.1)\times 10^{5}\, \text{K}$| for Planck [68 per cent confidence level (CL)], which are in good agreement under uncertainty. The data allow us to place lower limits on the expected void electron temperature at |$2.7\times 10^5\, \text{K}$| with ACT and |$5.1\times 10^5\, \text{K}$| with Planck (95 per cent CL); these results can transform into upper limits for the ratio between the void electron density and the cosmic mean as |$n^{\rm v}_{\rm e}/\bar{n}_{\rm e}\leqslant 0.73$| and 0.49 (95 per cent CL), respectively. Our findings prove the feasibility of using thermal Sunyaev–Zel'dovich observations to constrain the gas properties inside cosmic voids, and confirm that voids are under-pressured regions compared to their surroundings. [ABSTRACT FROM AUTHOR]

It is shown that the radial profile of the electron temperature in the Globus-M2 spherical tokamak is related to the radial profile of the electron density by a power law . An analytical model of the density attractor, assuming the dependence of on the specific poloidal volume v, previously tested on the TCV and JET tokamaks with a large aspect ratio, holds on the spherical tokamak, and the approximation of 162 experimental profiles has resulted in . The proposed model makes it possible to calculate the spatial distribution and according to a known magnetic configuration. [ABSTRACT FROM AUTHOR]

The microwave induced plasma jet (MIPJ) system was built using local materials based on a tapered waveguide. The parameters of this plasma were determined. The other characteristics, such as plasma frequency (fp), Debye length (λD), and quantity of particles in the Debye sphere (Nd), electron temperature Te, electron density ne, and others have been researched as well. The study was conducted at various Ar flow rates between (2.5-10) l/m and different discharge tube inner diameters between (2- 10) mm. The MIPJ spectra were used to determine each of these parameters. It was concluded that there is a good chance of influencing MIPJ's parameters by changing these parameters. [ABSTRACT FROM AUTHOR]

At atmospheric pressure and at a frequency of 9.1 kHz, a constructed magnetically stabilized tornado gliding arc discharge (MSGAD) system was utilized in this study to generate a non-thermal plasma with an alternating voltage source from 2,4,6,8 to 10 kV. Argon gas was used to generate the arc plasma with an adjustable flow rate using a flow meter regulator to stabilize the gas flow rate to 2 L/min. A gliding plasma discharge is achieved by a magnetic field for the purpose of a planned investigation. The influence of the magnetically stabilized tornado gliding arc discharge parameters such as magnetic field and applied voltage on microscopic tornado plasma parameters was studied. The electron temperature1was measured using a Boltzmann plot and the electron1density was1determined by the Stark1broadening method. The electron temperature ranged from 0.818 eV to 1.495 eV, and the electron density varied from 1.37 × 1018 cm-3 to 2.49 × 1018 cm-3 at a magnetic coil with 350 turns. Subsequently, the electron temperature increased to a range of 1.029 eV-1.794 eV, and the electron density reached a range of 1.53 × 1018 cm-3 to 2.89 × 1018 cm-3 at a magnetic coil with 500 turns. It can be observed that the plasma properties exhibit a rise as the number of turns of the coil and the applied voltage increase. [ABSTRACT FROM AUTHOR]

This theoretical study presents an investigation of the self-focusing of Gaussian laser beam under combined influence of electron temperature ramp and exponential plasma density ramp in plasma. Equation defining behaviour of the beam width parameter f with the dimensionless distance of propagation is derived under WKB and paraxial approximation. Our results reveal that the electron temperature and the exponential plasma density ramps are combinedly responsible for enhancement of self-focusing of the laser beam. Further, strong self-focusing is noticed with higher electron temperature for a given plasma density. [ABSTRACT FROM AUTHOR]

A chemical kinetics model was developed to characterise the gas‐phase dynamics of H2 production in nanosecond‐pulsed CH4 plasmas. Pulsed behaviour was observed in the calculated electric field, electron temperature and species densities at all pressures. The model agrees reasonably with experimental results, showing CH4 conversion at 30% and C2H2 and H2 as major products. The underlying mechanisms in CH4 dissociation and H2 formation were analysed, highlighting the large contribution of vibrationally excited CH4 and H2 to coupling energy from the plasma into gas‐phase heating, and revealing that H2 synthesis is not affected by applied pressure, with selectivity remaining unchanged at ~42% in the 1–5 bar range. [ABSTRACT FROM AUTHOR]

This study aims to investigate the aluminum (Al) arc plasma parameters generated through the explosive strip technique. The research involves the measurement of key plasma characteristics such as plasma frequency (fp), Debye length, and Debye number. The electron temperature (Te) and electron density (ne) of the plasma were calculated utilizing the Boltzmann plot and Stark expansion method. Analysis of the optical emission spectrum revealed distinctive peaks corresponding to oxygen, Al, and zinc oxide (ZnO) within the plasma. The outcomes of the study demonstrated a noteworthy correlation between the applied current and the electron temperature and density. Specifically, as the current increases, both electron temperature and density increase. The electron temperature of the Al plasma increased from the range of 0.852 eV to 0.92404 eV, accompanied by a corresponding elevation in electron density from 13.1x 1017 cm-3 to 15.2x 1017 cm-3. Furthermore, the detonation of the Al strip within a ZnO suspension led to even more pronounced changes. In this case, the electron temperature surged from 0.92885 eV to 1.1012 eV, and the electron density experienced an increase from 37.7 x 1017 cm-3 to 44.7 x 1017 cm-3. [ABSTRACT FROM AUTHOR]

In the present work, optical emission spectroscopy was used to diagnose the influence of A.C. power source frequency on the hollow magnetron sputtering discharge parameters (such as discharge emission, discharge current and voltage, glow discharge structure, temperature (Te) and electron number density (ne), Debye length (λD), and plasma parameter (ND) of constant pressure. The electron temperature and number density were determined using the Boltzmann plots and the Stark broadening methods, respectively. The results illustrate that the normal glow discharge structure is similar to the D.C. discharge mode. The magnetic field has no impact on the fundamental discharge parameter in both A.C. frequencies under study. On the other hand, the other discharge parameters (Te, ne, λD, and ND) increase with increasing the magnetic field in both discharge frequencies. In addition, the increase in the frequency of the A.C. source current led to an increase in the discharge intensity emission and the other discharge parameters being studied. In this case, in frequency 7 kHz, Te surged from 0.685 eV to 0.839 eV, and ne experienced an increase from 3.088 x 1018 m-3 to 4.902 x 1018 m-3. At a frequency of 9 kHz, the electron temperature surged from 0.711eV to 0.911 eV. ne experienced an increase from 3.615 x 1018 m-3 to 6.749 x 1018 m-3. [ABSTRACT FROM AUTHOR]

The plasma density and electron temperature are governed and influenced by the high-power pulsed magnetron sputtering parameters (e.g., operating voltage, pulse width, and working gas pressure), which are critical factors in determining the quality of high-power pulsed magnetron sputtering deposited films. This article proposes a vertical cylindrical magnetron sputtering plasma model based on the equivalent magnetic charge model to study the particle spatiotemporal and electron temperature distribution in high-power pulse magnetron sputtering. The results show that the electron converges in the highest magnetic field region in high-power pulsed magnetron sputtering during the increase of argon pressure from 3 to 7 Pa. The electron density distribution width ratio decreases from 80 to 64%, reducing target utilization. At the same time, for every 1 Pa increase in pressure, the average electron temperature in the discharge region is reduced by about 2 eV, which is inversely proportional to the pressure. As the voltage increases to 1000 V, the electric field intensity increases to 2 × 105 V/m, and the distribution of sputtered particles tends to be closer to the electrode, and the cathode dark zone changes from 2 to 1 mm. The increase in voltage has little effect on the shape of the plasma particle density distribution, but the electron temperature near the electrode increases to 19 eV at high voltages. The study reveals the change of plasma particles during the magnetron sputtering process, which is of guidance for magnetron sputtering. [ABSTRACT FROM AUTHOR]

We have recently incorporated the occupation probability formalism (OPF) in the simulation model [C. Stehlé and S. Jacquemot, Astron. Astrophys. 271, 348 (1993)] to have a smooth transition from discrete lines to continuum spectrum in the wavelength range near the Balmer series limit. We have analyzed spectra measured for the hydrogen pellet ablation cloud in the Large Helical Device with the revised model, and have found that the electron density in the ablation cloud has a close correlation with the electron temperature of the background plasma. This type of correlation is first confirmed in the present analysis and should give a new insight in the simulation studies of pellet ablation for the magnetically confined fusion plasma. [ABSTRACT FROM AUTHOR]

Observations of a quiet electrostatic auroral arc by the ALIS network on 5 March 2008 are used to infer a two‐dimensional map of the flux of precipitating energy. Among a family of numerical solutions of a stationary magnetosphere—ionosphere coupling model in which the origin of the arc is a magnetospheric generator interface, we find which generator interface properties best fit the observed precipitating energy flux. The procedure finds that the plasma populations in the generator are colder and more rarefied on one side of the interface and warmer and denser on the other side, similar to a transition between plasma trough and plasma sheet plasmas. The increase of the arc's brightness, the decrease of its thickness and its slight spatial undulation may be driven by an increase of plasma sheet electron temperature in the tailward direction, tangential to the interface, and a local spatial indentation in the dawn‐ward direction. Plain Language Summary: Optical observations of aurora provide information about the local electromagnetic and plasma conditions in the ionosphere where the impact of energetic electrons produces auroral light emissions. The electrons gain energy through acceleration by static or dynamic electric fields along their path from the magnetospheric source to the upper ionized atmosphere where they collide with various atomic species, like oxygen and nitrogen, which emit light at various wavelengths. In this paper we use optical observations of a steady electrostatic auroral arc to identify the conditions in the magnetospheric source that best fit these observations in the context of an electrostatic auroral acceleration model. This way, optical auroral observations from the ground are used as a remote sensing tool to probe the magnetospheric source of the arc. Key Points: A new application using tomographic imaging of electrostatic auroral arcs with ALIS estimates the magnetospheric generator stateThe generator of the arc observed by ALIS appears to be a plasma interface at the contact between trough and plasma sheet‐like plasmasThe arc's longitudinal changes are linked to a tailward increase of electron temperature and dawnward indentation of the generator interface [ABSTRACT FROM AUTHOR]

We report the first extragalactic detection of the higher-order millimeter hydrogen recombination lines (Δ n > 2). The γ -, ϵ -, and η -transitions have been detected toward the millimeter continuum source N 105–1 A in the star-forming region N 105 in the Large Magellanic Cloud with the Atacama Large Millimeter/submillimeter Array. We use the H40 α line, the brightest of the detected recombination lines (H40 α, H36 β, H50 β, H41 γ, H57 γ, H49 ϵ, H53 η, and H54 η), to determine the electron temperature and study ionized gas kinematics in the region, and the 3 mm free–free continuum emission to determine the physical parameters: the size, emission measure, and electron density. We compare the physical properties of N 105–1 A to a large sample of Galactic compact and ultracompact (UC) H ii regions and conclude that N 105–1 A is similar to the most luminous (L > 105 L ⊙) UC H ii regions in the Galaxy. N 105–1 A is ionized by an O5.5 V star; it is deeply embedded in its natal molecular clump, and likely associated with a (proto)cluster. We incorporate high-resolution molecular line data including CS, SO, SO2, and CH3OH (∼0.12 pc), and HCO+ and CO (∼0.087 pc) to explore the molecular environment of N 105–1 A. Based on the CO data, we find evidence for a cloud–cloud collision that likely triggered star formation in the region. We find no clear outflow signatures, but the presence of filaments and streamers indicates ongoing accretion onto the clump hosting the UC H ii region. Sulfur chemistry in N 105–1 A is consistent with the accretion shock model predictions. [ABSTRACT FROM AUTHOR]

The doping effect on the reservoir carrier temperature of the electron and hole in quantum dot optical amplifiers (QD SOAs) has been formalized and modeling, taking into account the most of carrier heating (CH) contributions such as; free carrier absorption, carrier heating time relaxation, interdot relaxation time, occupation probability of dot level, injected current and electron-hole interaction. The theoretical simulation shows the carrier temperature increasing straight forward with increasing the surface density of the donor and accepter which had not studied earlier as the best of our knowledge. It clears that, the surface carrier concentration of donor or acceptor atoms supplying more hot carriers for wetting layer (WL) which is leading an increasing the carrier temperature. In other word, the long life time of carriers from WL to Quantum Dot (QD) states is very high. Consequently, the collision of carriers and nonradiative relaxation are increasing the CH effect. Also, the majority of carrier is responsible on the increasing of electron or hole temperature, so the variation electron temperature in N-type is higher than hole in valence band, while the reverse is done with doping with P-type. [ABSTRACT FROM AUTHOR]

Technical solution were presented for a foil spectrometer installed on the Globus-M2 and TUMAN-3M tokamaks for measuring the electron plasma temperature. Measurements have been carried out of the time dependence of the plasma temperature in the central region of tokamaks. Using of integrated photodetectors and unique beryllium foils with a thickness of 14–80 μm made it possible to increase the sensitivity of the spectrometer. An important quality of the foils used were the increased values of strength, plasticity, homogeneity, and the absence of surface and internal defects. The combined use of the spectrometer with Thomson scattering diagnostics made it possible to carry out regular temperature measurements in the Globus-M2 tokamak with a high spatial and temporal resolution. The influence of impurities is estimated on the measurement of the electron temperature of the plasma. [ABSTRACT FROM AUTHOR]

The results of a study of the small-scale internal structure of a polarization jet/SAID (Subauroral Ion Drift) based on satellite data using the wavelet transform of ionospheric plasma parameters are presented. The minimum sizes of small-scale temperature and electron density irregularities are determined. Most likely, any polarization jet/SAID is stratified, as follows from the sample used in this work. It is shown that the wavelet transform is a convenient tool for studying the internal small-scale structure of the polarization jet/SAID, and the irregularities are better seen in the electron temperature power spectrograms than in the electron density spectrograms. [ABSTRACT FROM AUTHOR]

In general relativistic magnetohydrodynamic (GRMHD) simulations, accreted magnetic flux on the black hole horizon episodically decays, during which magnetic reconnection heats up the plasma near the horizon, potentially powering high-energy flares like those observed in M87* and Sgr A*. We study the mm observational counterparts of such flaring episodes in very high resolution GRMHD simulations. The change in 230 GHz flux during the expected high energy flares depends primarily on the efficiency of accelerating γ ≳ 100 (T e ≳ 1011 K) electrons. For models in which the electrons are heated to T e ∼ 1011 K during flares, the hot plasma produced by reconnection significantly enhances 230 GHz emission and increases the size of the 230 GHz image. By contrast, for models in which the electrons are heated to higher temperatures (which we argue are better motivated), the reconnection-heated plasma is too hot to produce significant 230 GHz synchrotron emission, and the 230 GHz flux decreases during high energy flares. We do not find a significant change in the mm polarization during flares as long as the emission is Faraday thin. We also present expectations for the ring-shaped image as observed by the Event Horizon Telescope during flares, as well as multiwavelength synchrotron spectra. Our results highlight several limitations of standard post-processing prescriptions for the electron temperature in GRMHD simulations. We also discuss the implications of our results for current and future observations of flares in Sgr A*, M87*, and related systems. Appendices contain detailed convergence studies with respect to resolution and plasma magnetization. [ABSTRACT FROM AUTHOR]

A double-sided electron energy analyzer is developed for studies of magnetic reconnection. It can measure electron energy distribution functions along two directions opposite to each other at the same time. Each side is composed of a floating reference grid, an energy selector grid, and a collector plate. The voltage of the selector grid is swept from −40 to 0 V with respect to the reference grid with a frequency of 1 MHz. This fast sweeping is required to resolve sub-Alfvénic changes in plasma quantities of the Magnetic Reconnection Experiment, where the typical Alfvénic time is a few microseconds. The reliability of the energy analyzer is checked in Maxwellian plasmas away from the reconnection region. In this case, the electron temperature computed from the electron energy distribution function agrees with measurements of a reference triple Langmuir probe. When it is located near the reconnection region, the temperatures of the tail electron population from both sides, facing into the electron flow and facing away from it, exceed the bulk electron temperature measured by the Langmuir probe by a factor of about 2. [ABSTRACT FROM AUTHOR]

Modelling of the plasma transport for inherently three-dimensional (3D) problems as in stellarators requires dedicated complex codes. FINDIF is a 3D multifluid plasma edge transport code that has been previously successfully used for the analysis of energy transport in the TEXTOR-DED tokamak [1], where 3D perturbations led to an ergodic structure of field lines in the plasma edge. The ongoing efforts to apply it meaningfully to Wendelstein 7-X (W7-X) plasma problems resulted in advancements in the main model and accompanying tools for mesh generation and post-processing. In order to verify the applicability of the code and to compare with the reported simulation (EMC3-EIRENE) and experimental (OP1.1) results, a series of simulations for varying plasma density, temperature and anomalous transport coefficients as well as for fixed input power were performed. The connection length pattern of FINDIF traced magnetic field lines on the limiter was reproduced and its impact on heat loads was confirmed. An increase in the peak heat load on the limiter with a rise in plasma density, temperature and anomalous plasma transport coefficients was observed. The decay lengths of density, electron temperature and heat flux did not change with density, and were decreasing with temperature and increasing with anomalous plasma transport coefficient, which was compared to the simple scrape-off layer (SOL) model. [ABSTRACT FROM AUTHOR]

The correlation between the bifurcation of resonant magnetic perturbations (RMPs) to the unshielded state and edge localized mode (ELM) suppression in ASDEX Upgrade is studied using a kinetic plasma response model numerically and analytically. For the numerical studies, the linear kinetic Maxwell solver KiLCA for cylindrical geometry and the quasilinear transport code QL-Balance are used in combination with the ideal MHD solver GPEC to account for realistic tokamak geometry. Based on this modelling, a numerical local bifurcation criterion is introduced which estimates the effect of RMP-induced temperature plateau formation in the resonant layer. Its analytical form is derived in constant-psi approximation. The kinetic model reproduces the known gyrocenter resonance, E r = 0 , and the electron fluid resonance. In contrast to MHD theory, the latter is located at the zero of the perpendicular electron fluid velocity computed only with half of the electron temperature gradient. The application of the criterion to experimental data shows a correlation between bifurcation and the ELM suppression phase. Moreover, an electron density limit is found resembling the one observed in experiments. [ABSTRACT FROM AUTHOR]

The experiments of pre‐ionized inert gas plasma MHD electrical power generation are conducted, and the performance and plasma behavior in the experimental generator are examined through time‐dependent r‐_ two‐dimensional numerical simulation. In the experiment, an enthalpy extraction ratio of 4.01% has been obtained with a disk‐shaped MHD generator with radio‐frequency pre‐ionization. In the numerical simulation, at an assumed inlet electron temperature around 5600 K (inlet ionization degree 0:10 × 10−4)_6600 K (1:36 × 10−4), the plasma structure is similar to the non‐uniform structure observed in the experiment. An enthalpy extraction ratio around 2_5% matches well with that in the experiment. At a suitable inlet electron temperature of 7000 K (3:15 × 10−4)_8000 K (1:79 × 10−3), although non‐uniform plasma structure still occurs, a high enthalpy extraction ratio over 10% is expected. [ABSTRACT FROM AUTHOR]

We present the first Thomson scattering (TS) measurements of electron temperature in the lower divertor of the Globus-M2 tokamak. The divertor TS diagnostics is designed for local measurements of the Te(z, t) in the range of 1–100 eV and ne(z, t) in the range of m–3. Parameters of the probing Nd:YAG laser are as follows 1064 nm/2 J/100 Hz/3 ns. The probing chord is launched vertically at R = 24 cm and covers areas of the inner leg, vicinity of separatrix and private flux region. Along probing chord of 110 mm, 9 spatial points were realized. Advanced filter polychromators were used to analyze Thomson scattering spectra. [ABSTRACT FROM AUTHOR]

Due to its particular geometry, stimulated Raman side-scattering (SRSS) drives scattered light emission in non-usually diagnosed directions, leading to scarce and complex experimental observations. Direct-irradiation campaigns at the SG-II Upgrade facility have measured the scattered light driven by SRSS over a wide range of angles. Typical interaction conditions were as follows: an overlapped laser intensity of 1.2 × 10 15 W cm−2 propagated into a plasma with a density scale length L n c / 4 ≈ 250 μm and an electron temperature T e ≈ 2.2 keV. It indicated an emission at large polar angles over a broad azimuthal range, sensitive to the plasma profile, resulting in a loss of about 5% of the total laser energy. Direct comparison with back-scattering measurement, both in the full-aperture back-scattered direction and sampled at smaller polar angles in the same azimuthal plane, has evidenced SRSS as the dominant Raman scattering process. The predominance of SRSS was confirmed by two-dimensional particle-in-cell simulations, and its angular spread has been corroborated by ray-tracing simulations. The main implication is that a complete characterization of the SRS instability and an accurate measurement of the energy losses require the collection of the scattered light in a broad range of directions. Otherwise, spatially limited measurement could lead to an underestimation of the energetic importance of stimulated Raman scattering. [ABSTRACT FROM AUTHOR]

In magnetohydrodynamics (MHD), a density perturbation perpendicular to an electron temperature gradient generates a magnetic field around itself that acts to increase the perturbation, which can lead to instability. An MHD dispersion relation is obtained for perturbations perpendicular to a fixed electron temperature gradient with an initial in-plane magnetic field, including resistivity, viscosity, and the electrothermal coefficient. Instability occurs for sufficiently small electron temperature-gradient scale lengths determined by the ion collisionless skin depth. Both viscosity and resistivity are required to prevent growth at arbitrarily small spatial scales and to give a physical result for the fastest growing mode. The perpendicular electrothermal coefficient is only significant for a narrow range of low electron Hall parameters, causing a modest reduction in magnetic field growth and modifying the criteria for instability in the presence of viscosity. If the definition of the Weibel instability [E. S. Weibel, Phys. Rev. Lett. 2, 83 (1959)] is extended to include all instabilities due to anisotropy in the electron velocity distribution, then this is a Weibel-like instability because an electron temperature gradient implies an anisotropic electron velocity distribution. The implications for the formation of filaments in laser-produced plasmas and for the verification of MHD codes are considered. [ABSTRACT FROM AUTHOR]