Search

Noninvasive measurements of electron properties in a Hall effect thruster (HET) are needed to understand the physical processes in the acceleration region and to validate simulations. This paper presents spatially resolved laser Thomson scattering (LTS) measurements across the entire acceleration region of a HET. The test article is the H9, a 9 kW class magnetically shielded HET. The H9 is operated on krypton at a facility pressure of 1.2 × 10−5 Torr Kr (1.6 mPa). The thruster is operated at three discharge conditions: 171 V, 35 A, an inner coil current (Iic) of 4.11 A, and an outer coil current (Ioc) of 2.27 A as the baseline 6 kW condition; 154 V, 34.8 A, an Iic of 4.11 A, and an Ioc of 2.27 A to vary the discharge voltage; and 171 V, 34.4 A, an Iic of 4.52 A, and an Ioc of 2.5 A to vary the magnetic field strength. At each discharge condition, we measured axial profiles of electron density and electron temperature along the channel centerline from 5% to 95% of a channel length downstream of the channel exit plane. At the baseline condition, we also measure the axial profile of the azimuthal electron drift velocity. We measure a minimum electron density of 1.3 × 1017 m−3, peak electron temperatures around 40 eV, and a peak azimuthal electron drift velocity around 680 km/s. The results suggest the presence of anomalous electron heating and demonstrate that low discharge voltages allow LTS to access the entire acceleration region of a HET. [ABSTRACT FROM AUTHOR]

This paper established a three-dimensional transient MHD model of a high-current multi-component vacuum arc under a transverse magnetic field (TMF) to simulate the dynamic characteristics of plasma parameters in the uniform motion mode of a contracted arc under lower TMF. The model considered the ionization–recombination process among the multi-components and used the P1 model to calculate the thermal radiation losses. The simulation results show that the ion number density of The TMF arc is on the order 1024 m−3, and when the plasma temperature reaches 4.3 eV, the effects of thermal radiation cannot be ignored. The majority of the plasma from the cathode and anode undergo acceleration and then deceleration before finally intersecting at the center of the arc, creating an extreme value of the density and the pressure, where a large amount of kinetic energy is converted into internal energy. The arc will be bent and deflected under the action of the ampere force, and the deflection of Cu3+ is especially obvious. The TMF affects the collision strength of the jet in the intersection area and, thus, affects the ion density, in which the change of Cu2+ is dominant. The ionization–recombination process of ions is mainly determined by the electron temperature, which is affected by the arc current. As the current decreases, Cu1+ increases and Cu2+ and Cu3+ decrease, and the change in ionization rate is the main reason for the change in the proportion of each ionic component; the heat flux density to the anode and cathode is on the order of 1010 W/m2, which heats the front of the arc and ensures the stable movement of the arc. Meanwhile, due to the high ion number density, the ion heat flux accounts for the main part of the heat flux, and the anode exhibits a higher proportion of ion heat flux. [ABSTRACT FROM AUTHOR]

We develop an analytical model for estimating the equilibrium quantities, such as electron temperature and number density, in an electron beam–plasma interaction system. This model provides a convenient way to calculate the effective electron temperature and density by considering the energy balance of the bulk cold electrons. Six energy sources/losses terms relevant to the cold electrons are accounted for, where quasi-linear theory is applied for estimating wave heating at equilibrium. We compare this calculation with the particle-in-cell (PIC) simulation results and find good agreement. Based on these results, we then consider two situations where we can simplify our model. The first is dominated by the balance between electron–electron Coulomb collisions and loss to the anode, which is mostly relevant to the conduction phase of plasma switches. The second is dominated by wave heating balanced by the anode loss, relevant to the electron beam–plasma discharge systems. We then couple our simplified energy balance model with the ion diffusion model and solve both the number density and the electron temperature as functions of the current density, electrode distance, pressure, and applied voltage, where a nice agreement is also obtained when comparing to PIC simulations. [ABSTRACT FROM AUTHOR]

A reduced pressure glow discharge is produced by passing a high-power pulsed DC source of 0–500 W with a frequency of 50 Hz across two parallel disk electrodes. A hydrogen peroxide aqueous solution is used as a flowing gas for discharge generation. Optical emission spectroscopy is employed to diagnose the discharge generated at a reduced pressure of 0.2 mbar with an electrode gap of 4 cm. The spectra are recorded at a power density of 9.4 mW/cm3 and typically lie in the visible wavelength range of 380–880 nm. The spectra are analyzed using the line intensity ratio method to estimate electron temperature and density. The results indicated that the electron temperature and density are, respectively, 0.87 eV and 6.4 × 1014 cm−3. [ABSTRACT FROM AUTHOR]

We investigated the magnetic properties of Sendust (Fe-Al-Si) alloys not only at 0 K but also at finite temperatures by means of the first-principles calculations assuming A2, B2, and D 0 3 structures. We confirmed that the itinerant characteristics of 3 d electrons of Fe are not negligible and a significantly small exchange stiffness constant exists at zero temperature in a B2 structure. However, the calculated Curie temperatures are in the same order for all structures; this indicates that the Curie temperature cannot be determined only by the exchange interactions at zero temperature in itinerant electron systems. Temperature dependence of the exchange interaction, namely, spin configuration dependence, also might be important for determining it. In addition, this property might also be related to the unique behavior of the temperature dependence of the exchange stiffness constant for the B2 structure, which does not decrease monotonically as temperatures increase, contrary to the behavior expected from the Heisenberg model. In addition, we investigated composition dependence on the exchange stiffness constant at zero temperature and confirmed that the substitution of Si with Al could improve the amplitude of the exchange stiffness constant at zero temperature for all structures. [ABSTRACT FROM AUTHOR]

Density Functional Theory (DFT) has become a cornerstone in the modeling of metals. However, accurately simulating metals, particularly under extreme conditions, presents two significant challenges. First, simulating complex metallic systems at low electron temperatures is difficult due to their highly delocalized density matrix. Second, modeling metallic warm-dense materials at very high electron temperatures is challenging because it requires the computation of a large number of partially occupied orbitals. This study demonstrates that both challenges can be effectively addressed using the latest advances in linear-scaling stochastic DFT methodologies. Despite the inherent introduction of noise into all computed properties by stochastic DFT, this research evaluates the efficacy of various noise reduction techniques under different thermal conditions. Our observations indicate that the effectiveness of noise reduction strategies varies significantly with the electron temperature. Furthermore, we provide evidence that the computational cost of stochastic DFT methods scales linearly with system size for metal systems, regardless of the electron temperature regime. [ABSTRACT FROM AUTHOR]

The unstable plume mode of hollow cathodes should be avoided in practical applications because it severely degrades the overall cathode lifetime. In this study, we investigate the spot-plume transition and plasma stability characteristics of an unused segmented lanthanum hexaboride emitter. The expansion of the unstable plume mode region is observed during a discharge experiment. Subsequently, the segmented emitter is retrieved, the inner surface of the emitter is observed, and the work function on the surface is measured at room temperature. The emitter surface exhibits color variations with oxygen and carbon detection. The downstream edge shows the original purple color and almost no degradation in the work function. The high temperature in this region promotes the desorption of carbon and oxygen. In the spot mode, this region mainly contributes to thermionic electron emission; therefore, the discharge voltage in the spot mode does not change during the discharge experiment. Carbon or carbide is detected in the middle of the axial direction on the emitter surface, where the surface temperature is not sufficiently high to desorb carbon during discharge. Based on the surface analysis results, the dominant substance in the region where carbon is detected was lanthanum carbide. An increase in the work function is indicated in the region, which appears to increase the plasma instability. According to previous studies, an increase in the work function results in a rise in the potential in the emitter, and an increase in the electron temperature in the outside plume region induces the plasma instability. Further investigation is needed to understand the mechanism connecting the rise in the work function and the rise in the electron temperature in the plume region. [ABSTRACT FROM AUTHOR]

We use a 2.5D hybrid simulation to study the breathing mode (BM) dynamics in Hall thrusters (HTs). This involves a 1D Euler fluid simulation for neutral dynamics in the axial direction, coupled with a 2D axial–azimuthal Particle-in-Cell (PIC) simulation for charged species. The simulation also includes an out-of-plane virtual dimension for wall losses. This setup allows us to replicate the BM's macroscopic features observed in experiments. A comprehensive analysis of plasma parameters in BM's phases divides it into two growth and two decay sub-phases. Examining 1D axial profiles of electron temperature, gas and plasma densities, and particle creation rate shows that an increase in electron temperature alone cannot sustain ionization. Ionization seems to be influenced by the spatial correlation between electron and gas densities and the ionization rate coefficient. Investigating ion back-flow reveals its impact on modulating neutral flux entering the ionization region. The hybrid simulation's outcomes let us assess the usual 0D predator–prey model's validity and identify its limitations. The ionization and ion convection term approximations hold, but the gas convective term approximation does not. Introducing an alternative gas convective term approximation involving constant density ejection from the ionization region constructs an unstable BM model consistent with simulation results. In addition, this paper explores how varying the imposed voltage and mass flow rate impacts the BM. The BM frequency increases with imposed voltage, aligning with theoretical predictions. The mass flow rate variation has a limited effect on BM frequency, following the theoretical model's trend. [ABSTRACT FROM AUTHOR]

We report the first ever measurements of the thermalization length of low-energy electrons injected into solid para-hydrogen at a temperature T ≈ 2.8 K. The use of the pulsed Townsend photoinjection technique has allowed us to investigate the behavior of quasi-free electrons rather than of massive, slow negative charges, as reported in all previous literature. We have found an average thermalization length ⟨z0⟩ = 26.1 nm, which is three to five times longer than that in liquid helium at the same temperature. [ABSTRACT FROM AUTHOR]

Electron-piezoelectric phonon interaction provides a significant extrinsic channel for energy relaxation in a graphene sheet placed on a polar substrate. We report in this paper our analytical and numerical investigations on energy relaxation rate and power loss density in graphene sheet on a polar substrate considering the electron-piezoelectric phonon scattering channel in the Boltzmann transport approach. We overcome the earlier crude approximations made to achieve the reported analytical results and compare the obtained results for their compliance with the numerical findings for the graphene sheet on the GaAs substrate. The obtained analytical expression for energy relaxation rate is valid for all temperatures and electron energies. The analytical result for power loss density limits its validity for low electron densities (< 1 0 1 2 cm − 2). It is observed that the relaxation rate due to surface piezoelectric phonons in graphene on GaAs substrate is directly proportional to temperatures above ∼ 1 0 K , below which temperature independence is seen. Also, it is observed that the relaxation rate is linearly dependent on electron energy, E k at low temperatures, and E k independent at high temperatures. Moreover, the relaxation rate is electron density-independent for all (low to high) temperatures. The seemingly odd (from earlier reported behavior) temperature-independent, linearly dependent E k and n independent relaxation rate behavior for low temperatures is attributed to the approximation used so far in the phononic statistical occupation factor in deriving the relaxation rate in the low-temperature Bloch-Gruneisen (BG) regime. In undoped graphene, we have found that the power loss behavior follows a crossover from T e 5 to T e 4 behavior while moving from low (∼ 2 0 K) to high (∼ 1 0 0 0 K) electron temperature. This behavior contradicts the study by Zhang et al. [Phys. Rev. B 87, 075443 (2013)] and M. Ansari [Physica E: Low Dimens. Syst. Nanostruct. 131, 114722 (2021)] which reported low-temperature BG behavior of T e 3 . This behavior is again attributed to using BG regime approximation for statistical occupation factors. Our findings are in agreement with the experimental work by Chen et al. [Nature Nanotechnol.  3, 206 (2008)] and You et al. [Appl. Phys. Lett. 115, 043104 (2019)]. [ABSTRACT FROM AUTHOR]

Electron–ion coupling is a fundamental process in nonequilibrium Warm Dense Matter. It also plays a central role in governing the states resulting from the interaction of high-intensity ultrafast lasers and free-electron-lasers with matter, an area that is of growing interest. Our inadequate understanding of the process was revealed in 1992 by the discovery of much weaker than expected electron–ion coupling in the nonequilibrium state at a shock front in Si where energy was transferred from hot ions to cold electrons. This necessarily raised questions about the behavior of electron–ion coupling in states with hot electrons and cold ions. It became a new focus of the field with the discovery of apparently constant electron–ion coupling in f s -laser heated Au, prompting a wide range of experimental and theoretical investigations of non-equilibrium warm dense Au as well as Cu for almost two decades. Fueling the pursuit were the findings of both constant and temperature-dependent coupling from subsequent experiments while the results of theoretical models were revealing reduced electron temperature dependence of electron–ion coupling. The goal of this review is to provide a concise historical account of the reported investigations, focussing on the salient characteristics of the experiments and models and how the diverse findings may be reconciled. Surprisingly, with alternative interpretations of some of the experimental results, a consistent behavior of weak electron–ion coupling has now emerged for f s -laser heated Au and Cu for electron temperature up to 20,000 K, corroborated by the evolution of theoretical predictions towards weak coupling. This is a significant progress. It will incentivize new research to gain further understanding of electron–ion coupling in nonequilibrium Warm Dense Matter. [ABSTRACT FROM AUTHOR]

We studied the ionized gas in the inner region (⁠|$\sim$| |$680\times 470$| pc2) of the galaxy NGC 6868 using Gemini/GMOS (Gemini Multi-Object Spectrograph) integral field unit observations. Channel maps reveal complex kinematics and morphology, indicating multiple processes at work in NGC 6868. Through emission-line fitting, we identified two ubiquitous components in our data: a narrow (⁠|$\sigma \sim 110$| km s |$^{-1}$|⁠) tracing an ionized gas disc and a broad component (⁠|$\sigma \sim 300$| km s |$^{-1}$|⁠) mainly associated with inflowing/outflowing gas. The derived V -band reddening shows a spatial distribution consistent with that obtained from stellar population synthesis, although with generally higher values. For the first time, we measured the electron temperature in NGC 6868, finding values ranging from |$\sim$| 14 000 K in the central region to |$\gtrsim 20000$| K with an outward increasing temperature gradient. The electron density map exhibits an inverse relationship, with central values reaching |$N_e\sim 4000$| cm–3 for the broad component decreasing to |$N_e\sim 100$| cm–3 towards the edges of the field of view. Using BPT diagrams, we found that all spaxels are consistent with both active galactic nucleus (AGN) and shock ionization. However, when this information is combined with our kinematic and temperature findings, and further supported by the WHAN diagram, we argue that an AGN is the dominant ionization mechanism in the central region of NGC 6868, while the extended outer component is ionized by a combination of hot low-mass evolved stars and shocks. According to our findings, shocks play a significant role in the ionization balance of this galaxy. [ABSTRACT FROM AUTHOR]

The dynamical behavior of the capacitively coupled Ar plasma driven by four frequencies (54, 80, 94 and 100 MHz) at fixed pressure are simulated by the particle-in-cell/Monte-Carlo collisions (PIC/MCC) model based on the electromagnetic field. The magnetic field is generated by plasma current itself. The results show that the electron density, charge density, and electron temperature increase with the frequency increase when radio frequency (RF) power is 40 W. The electron heating rate and argon ion heating rate near the sheath increase with the frequency increase. The high-energy electron density (> 3 0   eV) varies nonlinearly with the frequency increase. The high-energy electron density is highest at 80 MHz among the four frequencies. The electron density, charge density, and high-energy electron density increase with RF power (30, 45, 60, and 75 W) increase at 80 MHz. The electron temperature decreases with RF power increase at 80 MHz. The electron heating rate and argon ion heating rate near the sheath have no change with RF power increase at 80 MHz. The electron energy probability distributions (EEPF) show that the number of high-energy electrons (> 3 0   eV) is highest at 80 MHz. The reason may be the electron resonant heating that occurs in the plasma when the electron cyclotron frequency equals source frequency at 80 MHz. The electron dynamics of capacitively coupled plasma is important for microelectronics etching and membrane deposition. [ABSTRACT FROM AUTHOR]

Air plasma induced by ultrafast laser pulses is an extraordinary source of electromagnetic waves, emitting microwave, terahertz (THz) radiation, and cavityless lasing in the near‐infrared and visible ranges. The temporal dynamics of the electron density have been revealed by optical pump‐probe techniques, while the evolution of the electron temperature remains elusive due to a lack of suitable methods. Here, it is demonstrated that the intense THz‐field‐enhanced fluorescence emission from the excited molecules of nitrogen is a novel tool that allows to explore the complex dynamics of the plasma density and electron temperature simultaneously. Two relaxation times of electrons in air plasma are observed and interpreted as a competition between the excitation of a triplet state by laser or THz‐field‐heated electrons and the dissociative recombination of nitrogen molecular ions. Based on the theoretical simulations, the tens of picoseconds relaxation process is attributed to the ultrafast temperature decrease, while the longer relaxation in the range of hundreds of picoseconds is ascribed to the decay of electron density. The temporal relaxation of both the electron density and temperature revealed by applying an intense THz field provides further insights into the laser‐air plasma interaction and will benefit the engineering of this exceptional source. [ABSTRACT FROM AUTHOR]

We present a first-principles-based electron-temperature model that can be used in atomistic calculations. The electron–phonon coupling coefficient in the model is derived from the density of states as a function of electron temperature, and the thermal conductivity of tungsten from our model shows significant improvement over the baseline atomistic calculations in which only ion-thermal contribution to the thermal conductivity is available. The correction to the thermal conductivity also changes damage cascades as cascades cool down more rapidly within our model. The mobility of defects is consequently reduced, leaving more residual damage than the predictions without an electron-temperature model. [ABSTRACT FROM AUTHOR]

In this study the electron density of an atmospheric plasma generated between a pin electrode and a water surface is measured by determining the Stark broadening of H α and H β emission lines. Comparable values for the electron density are achieved using the H α and H β broadening obtained in separate measurements. During the temporally evolving system, increasing electron densities are measured of 0.5 − 3 ⋅ 10 15 cm−3 during the plasma treatment of 5–10 min. The effect of the water temperature on plasma-water interaction is investigated by heating the water to ≈ 70 ∘ C prior to the measurements. This resulted in higher gas temperatures during the discharge up to 2500 K and 4000 K for positively and negatively pulsed discharge, respectively. Furthermore, an earlier increase of electron density and conductivity of the water is measured for the preheated experiments. The humidity of the gas is likely to be an important parameter causing the observed results. [ABSTRACT FROM AUTHOR]

Introduction: This work explores the use of eXplainable artificial intelligence (XAI) to analyze a convolutional neural network (CNN) trained for disruption prediction in tokamak devices and fed with inputs composed of different physical quantities. Methods: This work focuses on a reduced dataset containing disruptions that follow patterns which are distinguishable based on their impact on the electron temperature profile. Our objective is to demonstrate that the CNN, without explicit training for these specific mechanisms, has implicitly learned to differentiate between these two disruption paths. With this purpose, two XAI algorithms have been implemented: occlusion and saliency maps. Results: The main outcome of this paper comes from the temperature profile analysis, which evaluates whether the CNN prioritizes the outer and inner regions. Discussion: The result of this investigation reveals a consistent shift in the CNN's output sensitivity depending on whether the inner or outer part of the temperature profile is perturbed, reflecting the underlying physical phenomena occurring in the plasma. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper examines the impact of different L−π$$ L-\pi $$ type external matching networks on the discharge characteristics of dual‐frequency capacitively coupled plasma. A nonlinear global model is employed to analyze the discharge of dual‐frequency capacitively coupled argon plasma, with a low frequency of 8 MHz and 60 W and a high frequency of 100 MHz at 10–80 W. Discharge voltage waveforms, current waveforms, and emission spectra of the plasma were measured, while electron density and electron temperature were determined using the Boltzmann method. The electron density and electron temperature are utilized as input parameters for the nonlinear global model, while the plasma discharge is simulated with a fixed low‐frequency radio frequency (RF) source power (60 W) and a varied high‐frequency RF source power ranging from 10 to 80 W. The results indicate that the plasma discharge current, sheath capacitance, plasma resistance, plasma inductance, and the ratio of stochastic heating to Ohmic heating increase, while the sheath thickness decreases with increasing power. It is also found that the fundamental frequency current as well as 12th and 13th harmonic currents in the plasma are caused by the matching network and the nonlinear interaction between the sheath and the plasma. An optimal matching network can be designed to eliminate the effects of the harmonics and to meet industrial requirements for discharge uniformity. [ABSTRACT FROM AUTHOR]

This paper presents the results of spectroscopic measurements of plasma in a linear simulator of a plasma-beam installation (PBI) for conducting materials science research. For the first time, non-contact optical diagnostic methods were employed to measure the plasma parameters in the PBI. These measurements were allowed for the clarification of the PBI plasma parameters and the identification of transition zones in different operational modes. Analysis of the plasma emission spectrum enabled the identification of impurity spectral lines and the estimation of key plasma parameters under varying experimental conditions. The spectra were recorded using two optical spectrometers covering a wavelength range of 200–800 nm. The experimental conditions varied in terms of electron beam accelerating voltage (1–5 kV), working gas pressure (1–6 mTorr), and target bias voltage (from −500 to −100 V). The Boltzmann plot method and Stark broadening of the Balmer lines were used to estimate electron temperature and density. Based on the obtained spectroscopic data, the electron density and the electron temperature were determined. The methods described in this study are applicable to linear plasma devices. [ABSTRACT FROM AUTHOR]

This research explores the use of laser-induced breakdown spectroscopy to detect elements in water residue. This research focuses on inducing plasma on pelletized water residue samples via a pulsed Neodymium-doped yttrium aluminum garnet (Nd:YAG) nanosecond laser with a wavelength of 1064 nm and energy of 100 mJ. The LIBS measurements were performed without and with a magnetic field of 0.8 T. Magnetic discs were used to create a magnetic field of 0.8 T. The presence of different elements (Ca, Mg, Fe, Cr, Mn, As, C, Li, Sr, Ba, Ti, K, O, N, and Si) was confirmed by examining the plasma emission spectra obtained from LIBS analysis. The results show that LIBS successfully detected toxic and heavy metals in water residues. Notably, the presence of a magnetic field affects the plasma properties such that the electron temperature and electron number density increase with increasing magnetic field. The Joule heating effect and the magnetic confinement effect are responsible for the increase in the plasma properties. The improved spectroscopic outcomes are associated with the magnetic confinement of water residue plasma, supported by the affirmation of thermal beta βt, which is less than one for all samples. [ABSTRACT FROM AUTHOR]

We describe the design of a Thomson scattering (TS) diagnostic to be used on the SMall Aspect Ratio Tokamak (SMART). SMART is a spherical tokamak being commissioned in Spain that aims to explore positive triangularity and negative triangularity plasma scenarios at a low aspect ratio. The SMART TS diagnostic is designed to operate at high spatial resolution, 6 mm scattering length in the low-field side and 9 mm in the high-field side regions, and a wide dynamic range, electron temperature from 1 eV to 1 keV and density from 5 × 1 0 18 m − 3 to 1 × 1 0 20 m − 3 , to resolve large gradients formed at the plasma edge and in the scrape-off layer (SOL) under different triangularities and low aspect ratios. A 2 J @ 1064 nm laser will be used that is capable of operating in the burst mode at 1, 2, and 4 kHz to investigate fast phenomena and at 30 Hz to study 1 s (or more) long discharges. The scattered light will be collected over an angular range of 60 ° – 120 ° from 28 spatial points in the midplane covering the entire plasma width and the outer midplane SOL. Each scattering signal will be spectrally resolved on five wavelength channels of a polychromator to obtain the electron temperature measurement. We will also present a method to monitor in situ laser alignment in the core during calibrations and plasma operations. [ABSTRACT FROM AUTHOR]

Laser-collisional induced fluorescence is used to study the plasma generated by a split-ring resonator discharge under an external cusp shaped magnetic field created by permanent magnets. The electron density and electron temperature are measured for a helium plasma at different pressures, powers, and magnet field strengths. It is found that the magnetic fields produce higher electron temperatures with peak temperatures of ∼3 eV, while the no magnet case has peak temperatures of ∼0.8 eV. Conversely, the peak electron density is obtained in the no magnet case at a value of ∼1.9 × 1011 cm−3. This indicates that the cusp-field did magnetize the electrons, but contrary to expectations, it resulted in a decrease in electron density. This is believed to be due to the magnetic field having negative effects on the resonance of the plasma source. [ABSTRACT FROM AUTHOR]

A semi-empirical global model for a nitrogen discharge in a strong magnetic field is developed. The model is based upon experimental data from high-resolution Doppler and extreme-ultraviolet vacuum spectroscopy, which establish the plasma composition, discharge parameters, and, most importantly, electronic transitions. This allows the number of required molecular systems and atomic/ionic states to be reduced, thereby retaining only the essential plasma chemistry reactions. The set of 35 stiff non-linear ordinary differential equations is numerically integrated using an unconditionally stable adaptive method. Simulations show the existence of two solution branches with low and high electron temperature, respectively. A distinct hysteresis is exhibited by the discharge and illustrated for three typical N2 mass flow rates. The dependencies of the plasma parameters on the applied power are presented and discussed in detail, including in the vicinity of the bifurcation points. The efficiency of operation in the opposing limits of N2 discharge behavior as either a source of plasma or light emission is examined, with special emphasis on electric propulsion capabilities. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate the transition of fast electron generation mechanism from J × B heating to stochastic heating by varying preplasma scale length in the interaction of ultrashort (∼25 fs) high intensity (∼3–4 × 1019 W/cm2) laser with thin foil. At sharp plasma density laser interaction (contrast ∼2 × 10−10 at 1 ns, L/λ ≪ 1), fast electrons were observed along the laser propagation direction demonstrating J × B heating. Interestingly, fast electron temperature in this case was less than ponderomotive scaling. The reasons were identified to be the small excursion length of electron compared to laser wavelength in sharp density interaction along with energy loss while escaping through the rear surface. A simplistic model has been proposed to understand the energy loss mechanism from the rear surface. Next, preplasma was introduced gradually by varying the amplified spontaneous emission contrast and additional picosecond prepulse at different delays. It resulted in an increase in the energy and temperature of fast electrons. Most importantly, at larger scale length (L/λ ≫ 1), fast electron temperature beyond the ponderomotive limit was observed. The temperature scales with scale length as T ∝ L 0.59 and shows a saturation effect at longer scale length. The results indicate a gradual change in the fast electron generation mechanism to stochastic heating producing superponderomotive energy. Particle-in-cell simulation also very well reproduces our experimental findings. [ABSTRACT FROM AUTHOR]

While the electron transport barrier remains in its final form before an edge-localized mode crash, edge turbulence manifests as fluctuations in electron temperature. Because edge turbulence is closely related to the evolution and collapse of pedestal, the microscopic spatial structure and dynamics of electron temperature fluctuations during the electron temperature pedestal evolution phase are studied using broadband electron cyclotron emission measurements. The cross phase between the electron temperature and potential fluctuations is evaluated using a velocimetry technique to identify the nature of turbulence. A comprehensive comparison of the properties of various instabilities confirms that the micro-tearing mode is a leading candidate associated with the electron temperature pedestal evolution and collapse. The quadratic transfer function reveals that the energy within the pedestal is nonlinearly transferred to the interior of the electron temperature pedestal before the pedestal collapse, resulting in radial change in the mode structure and dynamics. [ABSTRACT FROM AUTHOR]

An experimental study is conducted on macro- and microscopic characteristics of low to high (LH) transition acquired by electron cyclotron resonance heating (ECRH) in KSTAR. A scan of pre-transition density demonstrates the existence of the characteristic minimum density, which requires minimum power to make LH transition. The minimum density in KSTAR shows a tendency to be lower than that evaluated from an empirical scaling law proposed by Ryter et al. [Nucl. Fusion 54, 083003 (2014)]. A comprehensive study of the evolution of low wavenumber electron temperature fluctuations is carried out using electron cyclotron emission imaging diagnostics. An analysis of the fluctuation amplitude in L-mode in terms of the electron collisionality and the electron temperature scaling length suggests that the dissipative trapped electron mode is likely to be a dominant instability before the LH transition. The fluctuation amplitude reduces first as the transition starts. A coherent mode that chirps down from 60 to 20 kHz emerges when the transition further develops. This coherent mode is then shown to revive turbulence that has been reduced significantly during the initial stage of the LH transition. The revival of turbulence could be a possible origin of the absence of the large edge localized mode when the coherent mode is persistent in ECRH-induced H-mode plasmas. [ABSTRACT FROM AUTHOR]

Results from a laboratory experiment are presented in which, for the first time, a shear Alfvén wave is launched using an antenna in a current-carrying plasma column that is tailored to be either stable or unstable to the kink oscillation. As the plasma is driven kink unstable, the frequency power spectrum of the Alfvén wave evolves from a single peak to a peak with multiple sidebands separated by integer multiples of the kink frequency. The main sidebands (one on either side of the launched wave peak in the power spectrum) are analyzed using azimuthal wavenumber matching, perpendicular and parallel wavenumber decomposition, and bispectral time series analysis. The dispersion relation and three-wave matching conditions are satisfied, given each sideband is a propagating Alfvén wave that results from the interaction of the pump Alfvén wave and the co-propagating component of a half-wavelength, standing kink mode. The interaction is shown to generate smaller perpendicular wavelength Alfvén waves that drive energy transport to scales that will approach the dissipation scale of k ⊥ ρ s = 1 , with k ⊥ being the perpendicular wavenumber and ρs being the ion gyroradius at the electron temperature. [ABSTRACT FROM AUTHOR]

Magnetic field configurations extending over macroscopic scale distances are shown to be generated in rarefied collisionless plasmas when non-thermal and spatially inhomogeneous electron distributions in phase space emerge. The analyzed representative case is where, in the presence of a significant spatial gradient of the electron pressure and of a sheared magnetic field configuration, an alternating magnetic field reconnection process can develop associated with the anisotropy of the fluctuating electron temperature. The relevant process is intrinsically different from that known as the "Biermann Battery," which does not involve magnetic reconnection and requires that the unperturbed spatial gradient of the (isotropic) electron temperature be misaligned relative to that of the density gradient. [ABSTRACT FROM AUTHOR]

Head-on collision of the two small-amplitude electron-acoustic (EA) solitons is studied in an unmagnetized collisionless plasma in the presence of superthermal (hot) trapped electrons. For this purpose, using a well-known extended Poincare–Lighthill–Kuo (PLK) method, a pair of the trapped Korteweg–de Vries (tKdV) equations is derived to investigate the soliton trajectories and phase shifts. The latter are found dependent on amplitudes of the interacting solitons, effectively altering with hot-electron superthermality and plasma parameters. Typical parameters for the electron diffusion region (EDR) and day-side auroral zone have been selected to examine the impact of hot-electron superthermality, trapping parameter, hot-to-cold electron number density ratio, and cold-to-hot electron temperature ratio on the profiles of potential excitations and phase shifts of interacting solitons. It is found that phase speed of the EA waves becomes altered by varying the κ – parameter, strongly modifying the nonlinearity and dispersive coefficients in a superthermal trapped plasma. However, particle trapping phenomenon does not affect the linear phase speed but introduces a fractional nonlinearity in the tKdV equations of two interacting solitons. The impact of the adiabatic and isothermal pressures is also highlighted to show new modifications in the propagation characteristics of two interacting solitons. [ABSTRACT FROM AUTHOR]

In hypersonic computational fluid dynamics, the two-temperature (2-T) model is widely used to simulate thermochemical nonequilibrium. The 2-T model incorporates translational-rotational and electron-electronic-vibrational energies, assuming that the integrated energies have the equivalent temperature. In this study, multi-T models are constructed to accurately predict the effects on heat flux and free electrons due to the separation of energy modes under hypersonic environments. The three-temperature (3-T) model separates the electron-electronic energy from the electron-electronic-vibrational energy of the 2-T model. The 3-T model can accurately predict the distribution and temperature of free electrons by separating the energy of free electrons, which has different characteristics from heavy particles. The four-temperature model treats rotational energy as a nonequilibrium energy mode, distinct from translational-rotational energy. While the rotational temperature reaches equilibrium rapidly at low temperatures, at high-temperature regime rotational temperature shows a relaxation time similar to that of vibrational temperature, which cannot be ignored. To develop multi-T models, electron-vibrational relaxation and translational-rotational relaxation, which are omitted in the 2-T model, are considered. Various flight test and ground facility conditions are analyzed to verify the effects of electron and heat flux under circumstances that include shock, expansion, and shock wave boundary layer interaction. The results of the multi-T models show significant differences in electron temperature and distribution caused by electron-electronic nonequilibrium. Additionally, rotational nonequilibrium increases the shock standoff distance and alters the electron distribution at high altitudes. The heat flux difference across multi-T models is found to be negligible, except in the high degree of ionization condition. [ABSTRACT FROM AUTHOR]

In the present theoretical analysis, a new scheme of terahertz (THz) generation is proposed by beating of the two dark hollow laser beams (DHLBs) in the magnetized plasma under the influence of a D.C. electric field. The D.C. electric and static magnetic fields are applied mutually perpendicular to each other as well as to the direction of propagation of DHLBs. The nonlinear current density becomes strong due to the coupling between the nonlinear density and D.C. drift velocity of the electrons of magnetized plasma which is further responsible for THz generation. The normalized THz amplitude shows enhancement with the increase of D.C. electric and static magnetic fields. The dark-size parameter and beam order also play a significant role in the enhancement of the THz generation. The present scheme is capable of generating THz radiation at laser intensities 10 14 W / cm 2 , the magnetic field 38 kG , D.C. electric field 45 kV / cm , and electron temperature 6 keV. We have also considered the mutual interactions between the DHLBs and emitted THz radiation with magnetized plasma to provide more practical and accurate results. This scheme can be proved to be very effective and helpful in developing a proper tunable THz source for the investigation of histopathological samples, Bessel cell carcinoma tissues, and the treatment of tumors. [ABSTRACT FROM AUTHOR]

For the first time, a calibration between the He  i |$\lambda 5876$| /H  |$\beta$| emission line ratio and the helium abundance y = 12 + log(He/H) for Narrow line regions of Seyfert 2 Active Galactic Nuclei is proposed. In this context, observational data (taken from the SDSS-DR15 and from the literature) and direct abundance estimates (via the |$T_{\rm e}$| -method) for a sample of 65 local (⁠|$z \: \lt \: 0.2$|⁠) Seyfert 2 nuclei are considered. The resulting calibration estimates the y abundance with an average uncertainty of 0.02 dex. Applying our calibration to spectroscopic data containing only strong emission lines, it yields a helium abundance distribution similar to that obtained via the |$T_{\rm e}$| -method. Some cautions must be considered to apply our calibration for Seyfert 2 nuclei with high values of electron temperature (⁠|${\gtrsim} 20\, 000$|  K) or ionization parameter (⁠|$\log U \ \gt\ {-}2.0$|⁠). [ABSTRACT FROM AUTHOR]

Experiments performed during strongly-shaped high-power diverted negative triangularity (NT) experiments in DIII-D achieved detached divertor conditions and a transient-free edge, showcasing the potential for application of NT to a core-edge integrated reactor-like scenario and providing the first characterization of the parametric dependencies for detachment onset. Detached divertor conditions will be required in future devices to mitigate divertor heat fluxes. Access to dissipative divertor conditions was investigated via an increase in upstream density. Detachment onset at the outer strike point was achieved with H-mode level confinement H 98 − y 2 ∼ 1 and reactor-relevant normalized pressures β N ∼ 2 . Confinement degradation was observed with deeper detachment, associated with the loss of an electron temperature pedestal. Differences in geometry, radial transport, impact of cross field drifts are discussed to explain differences in access to detachment in NT discharges. Higher normalized densities, with respect to equivalent discharges in positive triangularity, were necessary to achieve detachment, partially explained by the shorter parallel connection length to the targets. The effect of cross-field particle drifts (E × B, B × ∇ B) on access to detachment was demonstrated by the lower upstream density needed to access detachment with ion B × ∇ B drift directed outside of the active divertor (Greenwald fraction f Gw ∼ 0.9–1.0 vs f Gw ∼ 1.3). The upstream density at detachment onset was observed to increase linearly with plasma current with ion B × ∇ B drift into the divertor, consistent with the observed narrowing of the scrape-off layer heat flux width λ q . Edge fluid simulations capture separatrix densities needed to achieve detachment in NT plasma and their dependence on drift direction. The ability to reproduce detachment dynamics in NT plasma increases the confidence in future design studies for NT divertors. [ABSTRACT FROM AUTHOR]

In the present study, we have investigated the time evolution of molecular LIBS (MLIBS) and nanoparticle enhanced molecular LIBS (NEMLIBS) of graphite samples using 10 nm gold nanoparticles for delays up to 100 μs. A systematic study of signal enhancement observed in the CN violet band (B²Σ+ → X ²Σ+) and C2 Swan band (d³Πg → a³Πu) was carried out. For acquisition delays of a few μs to tens μs, we have observed typically 1--2 orders of optical signal enhancement in these molecular bands of the graphite target using Au NPs. We have studied the mechanism of signal enhancement in the context of lifetime and plasma parameters viz., rotational and vibrational temperature of molecular bands as well as electron number density. The relative enhancement observed in C2 and CN bands, which are produced through different routes/mechanisms, has been explained through our analysis. The enhancements observed in NEMLIBS at higher delays are due to the increase of atomic species in the plasma which are antecedent of the molecules formed. This is evident through higher electron number density and slightly lower vibrational temperature in the case of NEMLIBS as observed in our analysis. [ABSTRACT FROM AUTHOR]

In this study, we investigate the impacts of the 17 March 2013 strong geomagnetic storm on the wholly coupled Solar Wind‐Magnetosphere‐Ionosphere‐Thermosphere system‐of‐systems. Obtained from multipoint observations, our new results show (1) the solar‐wind Alfven waves propagating antisunward in the sheath region and (2) oscillating solar wind interplanetary magnetic field (IMF) and electric (E) field (IEF EY) that powered (3) rigorous dayside and nightside flux transfer events (FTEs) when (4) the nightside‐reconnection‐related short circuiting led to fast‐time Subauroral Ion Drifts (SAID) and Subauroral Polarization Streams (SAPS) E field development across the inner‐magnetosphere plasmapause where the solar‐wind Alfven waves (4) transitioned into kinetic Alfven waves (5) fueling the hot zone. Also, the antisunward solar‐wind Alfven waves (6) drove enhanced large‐scale region‐1 field‐aligned currents creating (7) undershielding conditions (8) allowing the dawn‐to‐dusk convection E field's earthward penetration, and (9) generated increased solar‐wind kinetic energy, which became deposited (10) to the ionosphere increasing the ionospheric electron temperature (by the downward flowing suprathermal electron fluxes) and (11) to the thermosphere oscillating the neutral winds and increasing the neutral temperature, and finally leading to (12) the development of bright stable auroral red (SAR) arcs in (13) the enhanced SAID/SAPS flow channels (FCs) developed during FTEs, (14) demonstrated with FC‐2 and FC‐3 events, in the enhanced polar convection that (15) the Rice Convection Model could reproduce. Finally, we conclude the antisunward‐propagating large‐amplitude solar‐wind Alfven waves' ultimate significant role in creating the favorable conditions for the various phenomena documented with the new observational results (1–14). Plain Language Summary: We investigate the wholly coupled Solar Wind‐Magnetosphere‐Ionosphere‐Thermosphere (SW‐M‐I‐T) system‐of‐systems operational during the 17 March 2013 strong geomagnetic storm. Results show the development of two significant phenomena in the coupled SW‐M system: (a) the region 1 field‐aligned currents and (b) the antisunward solar‐wind Alfven waves. While (a) created undershielding conditions allowing the dawn‐to‐dusk electric field (Edd) earthward propagation, (b) drove (B field, E field, wind) oscillations and generated kinetic energy (up to ∼400 TW) that became deposited (up to ∼5 TW) into the magnetosphere efficiently (up to ∼2.5%). In the coupled M‐I system, the kinetic energy drove reconnection events while the Edd convected the plasma in a two‐cell pattern. During nightside reconnection, the earthward injected ring current (RC) protons led to the development of the hot zone and conjugate large‐scale E fields near/across the plasmapause, while the downward heat flux channeled into the ionosphere elevated the electron temperature (Te). In the coupled I‐T system, the elevated Te increased the thermospheric neutral temperature (Tn) and both (Te and Tn) ignited the stable auroral red arc while the thermospheric neutral winds became oscillatory because of the antisunward solar‐wind Alfven waves that acted as the ultimate driver of the wholly coupled SW‐M‐I‐T system‐of‐systems operational. Key Points: Solar‐wind Alfven waves led to SAID/SAPS development via reconnection and transitioned into kinetic Alfven waves fueling the hot zoneEnhanced R1 FACs led to undershielding permitting the dawn‐to‐dusk convection E field's earthward penetration (to L ≈ 6 RE) on the nightsideOscillating thermospheric neutral winds and neutral temperature increase led to the development of bright SAR arcs [ABSTRACT FROM AUTHOR]

Copyright of Baghdad Science Journal is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to study the coupling mechanism of the process parameters during the double-glow discharge process, and thus to enhance the theoretical study of double-glow plasma surface metallurgical technology, in this paper, a two-dimensional fluid model is established using COMSOL simulation software. The effects of key processing factors on the distribution of electrons and excited argon ions, potential and electron temperature in the coupling process of double-glow discharge were investigated. The results indicated that the electron density between the two electrode plates increases as the voltage difference increases. The optimal working pressure was kept between 0.14 Torr and 0.29 Torr. The optimal electrode spacing was between 15 mm and 30 mm and decreased with the increase in pressure. Compared with the actual plasma surface alloying process experiment, the simulation results were consistent with the experiments. The research can guide experiments by combining simulation and theory, and the predictability and accuracy of double-glow surface metallurgy technology have been improved. [ABSTRACT FROM AUTHOR]

The selectivity of the reactive ion etching of silicon using a negative electron resist AR-N 7520 mask was investigated. The selectivity dependencies on the fraction of SF6 in the feeding gas and bias voltage were obtained. To understand the kinetics of passivation film formation and etching, the type and concentration of neutral particles were evaluated and identified using plasma optical emission spectroscopy. Electron temperature and electron density were measured by the Langmuir probe method to interpret the optical emission spectroscopy data. A high etching selectivity of 8.0 ± 1.8 was obtained for the etching process. The optimum electron beam exposure dose for defining the mask was 8200 pC/m at 30 keV. [ABSTRACT FROM AUTHOR]

Non-thermal plasma as an emergent technology has received considerable attention for its wide range of applications in agriculture, material synthesis, and the biomedical field due to its low cost and portability. It has promising antimicrobial properties, making it a powerful tool for bacterial decontamination. However, traditional techniques for producing non-thermal plasma frequently rely on radiofrequency (RF) devices, despite their effectiveness, are intricate and expensive. This study focuses on generating Ar-O2 capacitively coupled plasma under vacuum conditions, utilizing a low-frequency alternating current (AC) power supply, to evaluate the system's antimicrobial efficacy. A single Langmuir probe diagnostic was used to assess the key plasma parameters such as electron density (ne), electron temperature (Te), and electron energy distribution function (EEDF). Experimental results showed that ne increases (7 × 1015 m−3 to 1.5 × 1016 m−3) with a rise in pressure and AC power. Similarly, the EEDF modified into a bi-Maxwellian distribution with an increase in AC power, showing a higher population of low-energy electrons at higher power. Finally, the generated plasma was tested for antimicrobial treatment of Xanthomonas campestris pv. Vesicatoria. It is noted that the plasma generated by the AC power supply, at a pressure of 0.5 mbar and power of 400 W for 180 s, has 75% killing efficiency. This promising result highlights the capability of the suggested approach, which may be a budget-friendly and effective technique for eliminating microbes with promising applications in agriculture, biomedicine, and food processing. [ABSTRACT FROM AUTHOR]

C5F10O-Air mixtures have a great potential to replace SF6 in medium-voltage power equipment. However, during the partial overheating or arc discharge, C5F10O-Air mixtures are inevitably to decompose to form various byproducts. The local chemical non-equilibrium and local thermal non-equilibrium appears due to the finite reaction rates and insufficient energy change between species. This paper establishes a chemical kinetic model to calculate the decomposition byproducts of C5F10O-Air mixtures from 500 K to 3500 K by taking into account the local thermal non-equilibrium and local chemical non-equilibrium simultaneously. The chemical kinetic model contains 50 species and 249 reactions. All the reactions are assumed to be reversible except the reactions producing photos. The local thermal non-equilibrium is characterized by the difference of the electron temperature (Te) and the temperature of heavy species (Th). In this work, the ratio of Te to Th is determined to be a function of the electron number density. Therefore, the value varies with electron number density. The temperature dependent decomposition composition of C5F10O-Air mixtures with C5F10O content to be 5%, 10% and 15% are obtained. In order to investigate the effects of Air on the decomposition of C5F10O, the decomposition products of pure C5F10O from 500 K to 3500 K are also investigated. In addition, the main chemical processes in 0.1C5F10O-0.9Air mixture are investigated by capturing the main reaction pathways. The main reaction pathways can help interpret the formation mechanism of the decomposition products. [ABSTRACT FROM AUTHOR]

We have revisited recent results on the ideal ignition of H11B fuel, in the light of the latest available reactivity, an alternative self-consistent calculation of the electron temperature, an increased extent of the suprathermal effects and the impact of plasma density. At high density, we find that the ideal ignition temperature is appreciably relaxed (e.g., T,· 150 keV for n,· ~ 1026 cm-3 and an optimal UB/H concentration ε = 0.15) and burn becomes substantial. We have then investigated central hot-spot ignition in both isobaric and isochoric inertial confinement configurations. Although implosion-driven ignition appears to be unfeasible, the isochoric self-heating conditions foster favourable preliminary conclusions on the utilization of proton fast ignition. In the isochoric case, we find a broad minimum in the ignition energy at pR 8.5g/cm2 and 220 < T,· < 340 keV (80 < Te < 95 keV), for ε = 0.15. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The coupling of transport code SOLPS with the turbulence code BOUT++ was reported in Reference [D. R. Zhang et al., Phys. Plasmas 26, 012508 (2019)], while the grids of SOLPS and BOUT++ are not completely consistent with each other, especially in the divertor region. In the present work, a method of replacing the grids of BOUT++ with the grids of SOLPS is proposed to make the simulation region fully consistent with each other for the SOLPS/BOUT++ coupling. A SOLPS grid file is generated with an MHD equilibrium and used in BOUT++ code to simulate the profiles of plasma density, ion temperature, and electron temperature with the six‐field two‐fluid model. The profiles of the main plasma parameters simulated with the SOLPS grids are similar with the profiles simulated with the BOUT++ grids at the midplane, while the profiles are deformed compared with the profiles simulated with the BOUT++ grids at the outer divertor target because of the differences of the distributions of SOLPS grids and BOUT++ grids in the divertor region. The radial particle transport coefficient and heat transport coefficients are also calculated by using the BOUT++ code with the two grids, and the comparisons of the radial particle transport coefficient and heat transport coefficients simulated with the two grids at the midplane and outer divertor target plate are discussed. [ABSTRACT FROM AUTHOR]

Predictions of the scrape‐off layer (SOL) plasma conditions from the 2D multi‐fluid code EDGE2D‐EIRENE are compared to the OEDGE 1D fluid code for JET low‐confinement mode (L‐mode) plasmas. In the low‐recycling divertor conditions (divertor target plasma collisionality νe≈30$$ {\nu}_e\approx 30 $$), OEDGE and EDGE2D‐EIRENE agree on the electron temperature, the ion temperature, and the electron density within 10% in the low‐field side (LFS) divertor X‐point region (divertor SOL) and within 25% in the LFS midplane region. In high‐recycling conditions (νe≈55,000$$ {\nu}_e\approx 55,000 $$), the predictions of both codes agree on the electron temperature within 20%, while differences in the ion temperature and electron density increase to as high as 50% in the divertor SOL. [ABSTRACT FROM AUTHOR]

The trajectories and the ablation positions of boron dust particles dropped from an impurity powder dropper in the peripheral plasma in the Large Helical Device (LHD) were calculated using a three‐dimensional edge plasma simulation code (EMC3‐EIRENE) and a dust transport simulation code (DUSTT). The simulation shows that the trajectory of the boron dust particles is deflected at the upper divertor leg due to the effect of the hydrogen plasma flow, and the ablation positions of the dust particles in an ergodic layer change toward the outboard side of the torus for higher plasma densities. The effect of the boron ion flow in the divertor leg on the deflection is investigated by coupling the two codes self‐consistently. The simulation predicts that the boron ions in the divertor leg, which are produced by sputtering on the divertor plates, which do not affect the change in the ablation positions. It also shows that the ablation positions move toward the inboard side and approach the Last Closed Flux Surface (LCFS) in case of increased boron dust drop rates, which is caused by the lowered plasma flow in the upper divertor leg due to the lowered electron temperature by radiation cooling by the dropped dust particles. [ABSTRACT FROM AUTHOR]

Cryogenic confocal microscopy is a powerful method for studying solid state quantum devices such as single photon sources and optically controlled qubits. While the vast majority of such studies have been conducted at temperatures of a few Kelvin, experiments involving fragile quantum effects often require lower operating temperatures. To also allow for electrical dynamic control, microwave connectivity is required. For polarization-sensitive studies, free space optical access is advantageous compared to fiber coupling. Here we present a confocal microscope in a dilution refrigerator providing all the above features at temperatures below 100 mK. The installed high frequency cabling meets the requirements for state-of-the-art spin qubit experiments. As another unique advantage of our system, the sample fitting inside a large puck can be exchanged while keeping the cryostat cold with minimal realignment. Assessing the performance of the instrument, we demonstrate confocal imaging, sub-nanosecond modulation of the emission wavelength of a suitable sample, and an electron temperature of 76 mK. While the instrument was constructed primarily with the development of optical interfaces to electrically controlled qubits in mind, it can be used for many experiments involving quantum transport, solid state quantum optics, and microwave-optical transducers. [ABSTRACT FROM AUTHOR]

A pioneering 4-channel, high-k poloidal, millimeter-wave collective scattering system has been successfully developed for the Experimental Advanced Superconducting Tokamak (EAST). Engineered to explore high-k electron density fluctuations, this innovative system deploys a 270 GHz mm-wave probe beam launched from Port K and directed toward Port P (both ports lie on the midplane and are 110° part), where large aperture optics capture radiation across four simultaneous scattering angles. Tailored to measure density fluctuations with a poloidal wavenumber of up to 20 cm−1, this high-k scattering system underwent rigorous laboratory testing in 2023, and the installation is currently being carried out on EAST. Its primary purpose lies in scrutinizing ion and electron-scale instabilities, such as the electron temperature gradient (ETG) mode, by furnishing measurements of the kθ (poloidal wavenumber) spectrum. This advancement significantly bolsters the capacity to probe high-k electron density fluctuations within the framework of EAST. Beam tracing and data interpretation modules developed for both EAST and NSTX-U high-k scattering diagnostics are described. [ABSTRACT FROM AUTHOR]

The mission of the JT-60SA project is to complement ITER's capabilities by addressing the fundamental physics and engineering challenges necessary to develop a practical and reliable fusion power plant. Diagnostics play a pivotal role in achieving this mission, especially the Thomson Scattering (TS) diagnostic systems developed by a collaborative Japan–EU team. The edge Thomson scattering of JT-60SA is tailored to measure the low field side outer region of the plasma, in particular, to resolve the electron temperature Te and density ne. The collection optics of the edge TS system have a critical role in meeting the required field of view and spatial resolution despite the limited space. This work presents a comprehensive optomechanical design of the optics assembly, whose main features are telecentricity and compactness, highlighting its capabilities. The tests undertaken to verify its performance: focal plane identification, thermal cycle, and magnification, are described. [ABSTRACT FROM AUTHOR]

The Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak is capable of operating at a wide range of toroidal magnetic fields up to 3.5 T at the major radius. The electron cyclotron emission (ECE) diagnostic on KSTAR is required to cover a broad frequency range for electron temperature profile measurements in both the low and high field sides. To meet these broadband requirements, the ECE system consists of W-band (78–110 GHz) and D-band (110–162 GHz) heterodyne radiometers. The two radiometers are connected to 28 and 48 detection channels, respectively. However, since the absolute ECE calibration based on the hot–cold calibration has been very challenging, an alternative method of calibration was performed using Thomson scattering measurements and varying toroidal magnetic fields. As the toroidal magnetic field is scanned from 1.6 to 3.2 T in steps of 0.2 T, most of the 76 ECE channels are calibrated relatively by the electron temperature values of Thomson scattering in a narrow region (0.2 < r/a <0.6). In this article, the methodological details of the ECE calibration are described. In addition, to demonstrate the robustness of the ECE calibration factors, the calibrated electron temperature profiles from ECE measurements are compared with the ion temperature profiles in terms of the plasma position as the plasma positon shifts outward. [ABSTRACT FROM AUTHOR]

A set of new millimeter-wave diagnostics will deliver unique measurement capabilities for National Spherical Torus Experiment-Upgrade to address a variety of plasma instabilities believed to be important in determining thermal and particle transport, such as micro-tearing, global Alfvén eigenmodes, kinetic ballooning, trapped electron, and electron temperature gradient modes. These diagnostics include a new integrated intermediate-k Doppler backscattering (DBS) and cross-polarization scattering (CPS) system (four channels, 82.5–87 GHz) to measure density and magnetic fluctuations, respectively. The system can access reasonably large normalized wavenumbers kθρs ranging from ≤0.5 to 15 (where ion sound gyroradius ρs = 1 cm and kθ is the binormal density turbulence wavenumber). The system addresses the challenges for making useful DBS/CPS measurements with a remote control of launch polarization (X- or O-mode), probed wavenumber, polarization match of the launch beam with the edge magnetic field pitch angle, and beam steering of the launched beam for wave-vector alignment. In addition, a low-k DBS system consisting of eight fixed frequencies (34–52 GHz) and four tunable frequencies (55–75 GHz) for low-k density turbulence and fast ion physics will be located at a nearby port location. The combined systems cover the near LCFS and pedestal regions (34–52 GHz), the pedestal or mid-radius (50–75 GHz), and core plasmas (82.5–87 GHz). [ABSTRACT FROM AUTHOR]