The transferred arc twin torch system has attracted significant attention in fields such as coal gasification, metallurgy, and solid waste treatment due to its superior characteristics, including high temperature, high enthalpy, and high energy density. However, compared with the traditional axial-arc plasma torch, the large-area exposed arc of the transferred arc twin torch system renders the maintenance of stable discharge more complex. This work focuses on the DC transferred arc twin torch system and investigates the effects of nozzle structural parameters and discharge operating parameters on arc stability. The correlation between arc characteristics and both structural and operating parameters is established. Research shows that both straight-channel nozzles and backward-facing stepped nozzles are effective in stabilizing the arc. In contrast, the backward-facing stepped nozzle exhibits lower gas flow limits for discharge stability, weaker arc rigidity, a longer restrike period, as well as lower average discharge voltage and power. An increase in nozzle length or a decrease in nozzle diameter can enhance the constraint strength of the arc, increasing its rigidity, average length, and restrike frequency. This is beneficial for increasing the average voltage and reducing voltage fluctuations, but it also raises the minimum gas flow rate required for stable discharge. In addition, as the current increases, the rigidity of the arc also improves. Emission spectroscopy results indicate that the DC transferred arc twin torch system generated plasma with extremely high temperature. At a current of 140 A, the electron temperature could reach up to 1.88 eV, while the heavy particle temperature was approximately 21000 K, which makes the system suitable for high-temperature and high-enthalpy applications.

Abstract This study experimentally and numerically investigates the electrohydrodynamic (EHD) interaction induced by a surface dielectric barrier discharge (SDBD) actuator at atmospheric pressure. The EHD effect, driven by non-thermal plasma in a dielectric barrier discharge (DBD), generates ionic wind, which is characterized here for a symmetric annular-type DBD actuator. A symmetric annular-type DBD actuator, consisting of concentric ring–disk electrodes that generate a predominantly vertical ionic wind rather than a tangential jet. Despite extensive studies on linear and tangential SDBD actuators, the influence of annular electrode geometry on vertically induced ionic wind and associated ozone generation remains insufficiently explored. We analyze the induced wind velocity perpendicular to the electrode plane, focusing on the influence of geometric parameters—electrode diameter (D) and thickness (δ)—on performance. Experimental results reveal a maximum wind velocity of 3.42 m/s ± 1% for an optimized configuration (D = 32 mm, δ = 0.06 mm), corroborated by numerical simulations. The simulations further elucidate the velocity profile, volumetric force, electron temperature, and gas pressure distribution within the plasma region. Complementary diagnostics, including O3 concentration measurements and Schlieren imaging, demonstrate that larger electrode diameters (e.g., 32 mm and 22 mm) enhance vertical flow height but concurrently increase ozone production. These findings provide actionable insights for designing DBD-based systems in applications such as plasma flow control, air purification, and biomedical plasma technologies.

Abstract Two-dimensional (2D) electron temperature and density profiles were obtained for a cylindrical Hall thruster plasma by incorporating optical emission tomography and a collisional–radiative (CR) model. Using an inverse Radon transform-based tomographic reconstruction of 1350 lines of sight, 2D profiles of Xe neutral optical emission intensities of 10 distinct wavelengths (992.3, 979.9, 916.2, 904.5, 895.2, 881.9, 834.6, 828.0, 823.1, and 788.7 nm) were obtained at 4 mm from the thruster channel exit. Local electron temperatures and densities were subsequently derived using the CR model. The developed CR model, combined with tomographically reconstructed optical emission spectroscopy, demonstrated electron parameters comparable to those measured using a double Langmuir probe. This study highlights the essential role of optical emission tomographic reconstruction in accurately capturing the localized electron parameters for Xe-based Hall thruster plasmas.

Abstract Low-temperature plasmas (LTPs) are essential to both fundamental scientific research and critical industrial applications. As in many areas of science, numerical simulations have become a vital tool for uncovering new physical phenomena and guiding technological development. Code benchmarking remains crucial for verifying implementations and evaluating performance. This work continues the Landmark benchmark initiative, a series specifically designed to support the verification of LTP codes. In this study, seventeen simulation codes from a collaborative community of nineteen international institutions modeled a partially magnetized E × B Penning discharge. The emergence of large scale coherent structures, or rotating plasma spokes, endows this configuration with an enormous range of time scales, making it particularly challenging to simulate. The codes showed excellent agreement on the rotation frequency of the spoke as well as key plasma properties, including time-averaged ion density, plasma potential, and electron temperature profiles. Achieving this level of agreement came with challenges, and we share lessons learned on how to conduct future benchmarking campaigns. Comparing code implementations, computational hardware, and simulation runtimes also revealed interesting trends, which are summarized with the aim of guiding future plasma simulation software development.

Abstract State parameter profiles in the equatorial topside ionosphere were measured in June, 2023, and late July and early August, 2025, at the Jicamarca Radio Observatory. The measurements combined multiple radar pulsing schemes and analysis methods. In 2025, for the first time, plasma drifts were measured concurrently with electron densities, electron and ion temperatures, and ion composition by exploiting a new electronic beam steering capability. Significant quiet‐time day‐to‐day variability is evident across all measurements. In this study, variability in the vertical drifts is considered as a source of variability in the other plasma state parameters. Topside temperatures and the midday temperature depression in particular are examined for sensitivity to vertical drifts. While predictions obtained from the SAMI2‐PE model, which includes energetic electron transport, exhibit reasonable agreement with observations overall, they do not account for topside variability. Some limitations of the measurements and the model along with strategies for improvement and further study are discussed.

Local shot noise spectroscopy with scanning tunneling microscopy (STM) has proven to be a powerful technique to investigate the electronic properties of quantum materials. It provides direct and non-invasive insight into the tunneling charge quanta or dynamics at the atomic scale. Due to the typically weak noise signal and the presence of low frequency spurious noise, local noise experiments require a high-resolution measurement amplifier. Here, we present a newly developed high-resolution noise amplifier that we implemented in three different STMs. Compared to our previous generation, we obtain more than a 20-fold improvement in the noise resolution, allowing us to resolve values of the effective charge as small as 0.01e. Our amplifier opens new possibilities for studying electronic properties in novel materials such as d-wave superconductors. In addition to this, it can give direct information about the local electron temperature in STM experiments.

In indirect-drive inertial confinement fusion research, precise diagnostics of ablator electron temperature evolution are essential for understanding radiative ablation behavior. Using silicon-traced CH samples with point-projection backlighting, we measured time-resolved backlight spectra and silicon plasma absorption spectra at different times, deriving transmission spectra. Radiation temperature on sample was determined via the 3D view-factor code IRAD3D, while radiation-hydrodynamic simulations provided the evolution of electron temperature and density in the silicon plasma. By comparing experimentally measured transmission spectra with theoretically calculated spectra at varying electron temperatures, we inferred the electron temperature of the silicon plasma. Results reveal a rise-then-fall electron temperature trend in the silicon layer, with agreement between experiment and simulation during the temperature decline phase but discrepancies in the rise phase due to ionization-state complexities. This work elucidates electron temperature evolution and transport mechanisms during radiative heat wave propagation in low-Z materials.

Abstract Strong electron–neutral collisions in atmospheric-pressure plasma jets constrain the electron energy distribution, which governs plasma chemistry. Here, we demonstrate phase-resolved EEDF measurements in a dual-frequency atmospheric-pressure plasma jet (DF-APPJ) using laser Thomson scattering spectroscopy combined with Bayesian inference. The plasma jet sustained by a continuous 5 MHz sinusoidal power is modulated using a counter electrode, onto which the plasma impinges, with a 50 kHz bipolar square-wave bias. Nanosecond-resolved, incoherent TS spectra were analysed to determine not only electron density and temperature but also the electron energy distribution function, which quantifies deviations from Maxwellian energy distributions. We observe phase dependent transitions in the EEDF, shifting toward a Maxwellian-like shape during negative voltage transitions and exhibiting weakly Druyvesteyn-like features during positive transitions of the applied low-frequency waveform. This study establishes a quantitative framework for time-resolved electron kinetics in dual-frequency APPJs and highlights the potential of Bayesian-enhanced TS for kinetic analysis in highly collisional plasmas.

Abstract Ion beams enable direct printing of materials without external heat sources and have a large potential in applications such as electronic circuit direct writing and microfabrication. However, high-density ion beams generally suffer from divergence effects and electron interferences, thus posing challenges for high-precision beam focusing. In this study, a divergent ion beam is considered as a set of numerous parallel ion microbeams. A two-stage focusing scheme incorporating a micro-lens arc array, a deep-hole electrode, and a substrate electrode is proposed, and the focusing properties are studied theoretically by simulation. Based on an ion beam density of 1×1019 m-3 and average electron temperature of 3 eV, the results show that the plasma sheaths in the micro-lens can overlap when the potential is -100 V, inner diameter is 0.29 mm, and spacing is 0.05 mm, consequently enabling complete electron filtering while maintaining maximal ion transmission (>77.4%). Under the optimal focusing conditions of the arc array curvature of 14.3 m-1, electrode diameter of 20 mm, electrode spacing of 105 mm, and potential difference of 1400 V, the ion beam can be compressed from 140 mm to 1.50 mm, resulting in a central density of 4.70×1020 m-3 and ion utilization of 65.3%. To uniformize the output ion beam, the deep-hole electrode is studied, and the optimal parameters are: 1.5 mm diameter × 2.0 mm depth, 0.5 mm electrode spacing, and 4,500 V potential difference. In this case, the space-charge repulsion between central ions and convergence arising from the peripheral electric field can be balanced. Therefore, not only can the beam diameter be further reduced to 0.78 mm to produce an average ion density of 2.88×1020 m-3 and an ion utilization rate of 57.3%, but also the ion density fluctuation is only ±5.8% with a variation coefficient of only 4.8%.

A Comprehensive Model of the K-coronal Spectrum for the Inference of Electron Temperature and Bulk Flow Velocity in the Corona

We investigated the physics of black hole accretion flows, particularly focusing on phenomena like magnetic reconnection and plasmoid formation, which are believed to be responsible for energetic events such as flares observed from astrophysical black holes. We aim to understand the influence of radiative cooling on plasmoid formation within black hole accretion flows that are threaded by multi-loop magnetic field configurations. We conducted 2D and 3D two-temperature general relativistic magnetohydrodynamic simulations. By varying the magnetic loop sizes and the mass accretion rate, we explored how radiative cooling alters the accretion dynamics, disk structure, and properties of reconnection-driven plasmoid chains. Our results demonstrate that radiative cooling suppresses the transition to the magnetically arrested disk state by reducing magnetic flux accumulation near the horizon. It significantly modifies the disk morphology by lowering the electron temperature and compressing the disk, which leads to increased density at the equatorial plane and decreased magnetization. Within the current sheets, radiative cooling triggers layer compression and the collapse of plasmoids, shortening their lifetime and reducing their size, while the frequency of plasmoid events increases. Moreover, we observe enhanced negative energy-at-infinity density in plasmoids near the ergosphere, with its peaks corresponding to plasmoid formation events. Radiative cooling plays a critical role in shaping both macroscopic accretion flow properties and microscopic reconnection phenomena near black holes. This suggests that radiative cooling modulates black hole energy extraction through reconnection-driven Penrose processes, highlighting its importance in models of astrophysical black holes.

Abstract The effect of different D 2 fueling locations and divertor closure on MAST-U is studied in detail with the SOLPS-ITER code to gain insights into detachment physics of H-mode plasma experiments in conventional divertor configuration. The SOLPS-ITER simulations reveals that changing D 2 fueling location significantly impacts divertor conditions: Under lower divertor (LD) fueling, the total power loss at the lower outer divertor (LOD) is higher compared to the midplane fueling scenario for the same electron density at the outboard midplane side ( n e , sep OMP ). With LD fueling in closed configuration, the analysis demonstrates substantial reductions on the peak heat flux and electron temperature at the LOD, facilitating the detachment onset due to an increased D neutral density and enhanced radiation, while suppressing carbon (C) sputtering. The closed divertor shows higher neutral trapping capability under both midplane and LD fueling. With LD fueling, the peak plasma temperature ( T e ) show greater reduction in the closed divertor compared to the open divertor and the roll over of main ion flux ( Γ i ) happens at ∼ 40 % lower n e , sep OMP in the closed divertor. These differences between divertor closure diminish when the midplane fueling is used. The analysis of all four scenarios (midplane/LD fueling in closed/open divertor) show that divertor closure and localized fueling work in synergy to create the optimized neutral trapping and energy dissipation, promoting detachment onset at lower n e , sep OMP . This work demonstrates that divertor closure and localized fueling can facilitate detachment onset at lower n e , sep OMP , highlighting the importance of an integrated approach to divertor optimization.

Abstract Quasi-thermal noise is an important diagnostic tool for measuring electron density and temperature in space plasmas, with its low-frequency range being dominated by electron shot noise. However, previous missions have shown that conventional shot noise models often yield poor fits in the low frequency ( f < f p ) , limiting the accurate characterization of electron parameters. To address this issue, we introduce an effective sheath resistance into the previous model, thereby establishing a calibrated shot noise model that improves measurements of electron parameters in the inner heliosphere. Methodologically, we applied the steep-descent and Levenberg–Marquardt method algorithm to determine the electron density and temperature above the plasma frequency; we then isolate the pure shot noise by subtracting other noise sources; and finally, we derive the antenna impedance using measurements below the plasma frequency ( f p ). Based on Parker Solar Probe (PSP) observations during PSP Encounter 4 ∼ 8 (with unbiased antennas operating in the dipole regime), we obtain an effective antenna capacitance of 8.30 ± 0.21 pF and an effective resistance in the range of 0.5 ∼ 4 MΩ, with their radial of the capacitances and resistances of r − 0.072 ± 0.001 and r 2.57 ± 0.02 , respectively.

Abstract We introduce genesis-metallicity , a gas-phase metallicity measurement P ython software employing the direct and strong-line methods depending on the available oxygen lines. The nonparametric strong-line estimator is calibrated based on a kernel density estimate in the four-dimensional space of O2 = [O ii ] λλ 3727,29/H β ; O3 = [O iii ] λ 5007/H β ; H β equivalent width EW(H β ); and gas-phase metallicity 12 + log ( O/H) . We use a calibration sample of 1510 galaxies at 0 < z < 10 with direct-method metallicity measurements, compiled from the JWST/NIRSpec and ground-based observations. In particular, we report 122 new NIRSpec direct-method metallicity measurements at z > 1. We show that the O2, O3, and EW(H β ) measurements are sufficient for a gas-phase metallicity estimate that is more accurate than 0.09 dex. Our calibration is universal, meaning that its accuracy does not depend on the target redshift. Furthermore, the direct-method module employs a nonparametric T e (O ii ) electron temperature estimator based on a kernel density estimate in the five-dimensional space of O2, O3, EW(H β ), T e (O ii ), and T e (O iii ). This T e (O ii ) estimator is calibrated based on 1004 spectra with detections of both [O iii ] λ 4363 and [O ii ] λλ 7320,30, notably reporting 20 new NIRSpec detections of the [O ii ] λλ 7320,30 doublet. We make genesis-metallicity and its calibration data publicly available and commit to keeping both up to date in light of the incoming data.

ABSTRACT Planetary nebulae represent a late evolutionary phase of low‐ to intermediate‐mass stars. In this article, we present the serendipitous discovery of a previously unknown, faint potential Galactic planetary nebula (PN) in the constellation Camelopardalis, identified during a survey‐inspection, aiming at the detection of dwarf companions of the spiral galaxy NGC 2403. Narrow‐band imaging and spectroscopic observations of the nebula and its potential central star were obtained using a combination of amateur and professional telescopes. Our observations revealed a compact, dense, triangular structure—hereafter referred to as the Triangle Nebula—embedded within a broader elliptical region, which we call the Cam Nebula. Both are enclosed by an even fainter, nearly circular outer shell detectable only in deep, long‐exposure images. This Shell Nebula and the Cam Nebula may be superpositions by chance, but we will assume they are connected. We designate the entire complex as TBG‐N1. This is the first TBG nebula to avoid confusion with previously discovered TBG‐DWs (dwarf galaxies). A candidate for the central star was identified near the geometric centre of the outer shell. Spectroscopic analysis provided estimates of the nebular electron temperature and density. The combined evidence from imaging, spectroscopy, and the photometric properties of the central star candidate supports the classification of TBG‐N1 as a planetary nebula located at a distance of approximately 1 kpc. This discovery highlights the important role that collaborations between amateur and professional astronomers can play in uncovering and characterizing previously unrecognized celestial objects.

Abstract Fast ions have been observed to be accelerated in the presence of Edge Localised Modes (ELMs) and MHD activity on the Tokamak à Configuration Variable (TCV). The acceleration time, velocity-space and frequency dynamics have been resolved by analysing the fast-ion losses measured using a unique Fast Ion Loss Detector (FILD) that allows microsecond velocity-space mapping. The findings presented herein complement and extend previous studies done at the Asdex Upgrade Tokamak (AUG) and show a decorrelation between the acceleration and the ELM crash. The experimental scenario is a high-confinement mode (H-mode) plasma, characterised by low density, high electron temperature and, hence, long slowing down times of the fast-ion population. Significant MHD activity has been observed in the inter-ELM-crash period with frequencies ranging from 50 to 250 kHz. These modes exhibit strong down-chirping and burst signatures. The empirical dependence of the modes’ frequency upon the plasma density identifies them as Alfvén Eigenmodes (AEs) and locates them in the outer region of the plasma, where the resonance conditions between the fast ions and modes are fulfilled. Their resonant interaction with the fast-ion, generated using a Neutral Beam Injector (NBI) changes during the ELM cycle according to the changes in the plasma parameters, such as density and temperature. The fast-ion losses are also identified using orbit following simulations, allowing us to distinguish the different contributions to the FILD signal. The pre-ELM AEs’ frequencies and the velocity-space of the MHD-induced fast-ion losses are preserved on the FILD signal during the first ∼800 microseconds of the ELM crash, suggesting a complex interaction between AEs, fast ions and ELMs.

This research outlines a simulation-based analysis of dual-gate semiconducting graphene field-effect transistors (GFETs) constructed using vertically aligned synthesized graphene via plasma-enhanced chemical vapor deposition (PECVD) technique. Using SILVACO TCAD software, the study investigates the impact of varying plasma parameters-specifically electron and ion temperatures, and densities-each associated with different graphene channel thicknesses. Distinct combinations of plasma electron/ion temperature and density were investigated; each linked to a specific graphene channel thickness. The study focused on the electrical properties of the dual gate semiconducting GFET, comparing them with the existing experimental observations and correlating these properties with the plasma processing parameters. It was seen that the values of these properties, like drain current,Ion/Ioff current ratio, transconductancegm, cutoff frequencyfc, etc., increased on decreasing the plasma parameters of the PECVD process involved. The relations developed can be used to modulate the properties of plasma-grown GFETs, by scaling them down for industrial use in several concerned sectors of high-frequency circuits, solar cells, supercapacitors and biosensing technologies. These findings provide a theoretical framework to support future experimental validation and process optimization.

Abstract In order to test the robustness and reliability of the new generation spectral-line identifier PyEMILI, as initially introduced in Paper I, in line identification and establish a reference/benchmark dataset for future spectroscopic studies, we run the code on the line lists of a selected sample of emission-line nebulae, including planetary nebulae (PNe), H ii regions, and Herbig–Haro objects with deep high-dispersion spectroscopic observations published over the past two decades. The automated line identifications by PyEMILI demonstrate significant improvements in both completeness and accuracy compared to the previous manual identifications in the literature. Since our last report of PyEMILI, the atomic transition database used by the code has been further expanded by crossmatching the Kurucz line lists. Moreover, to aid the PyEMILI identification of numerous faint optical recombination lines (ORLs) of C ii , N ii , O ii , and Ne ii , we compiled a new dataset of effective recombination coefficients for these nebular lines, and created a new subroutine in the code to generate theoretical spectra of heavy-element ORLs at various electron temperature and density cases; these theoretical spectra can be used to fit the observed recombination spectrum of a PN to obtain the electron temperature, density, and ionic abundances using the Markov Chain Monte Carlo (MCMC) method. We present MCMC-derived parameters for a sample of PNe. This work establishes PyEMILI as a robust and versatile tool for both line identification and plasma diagnostics in deep spectroscopy of gaseous nebulae.

Abstract Understanding and quantifying particle and energy transport at the plasma edge region is crucial for magnetic confinement fusion. For this purpose, a new polychromator system with 1 µs time resolution was installed for the thermal helium beam diagnostic in the island divertor of the stellarator W7-X. The time resolution is four orders of magnitude faster than the spectrometer-based system. This allows for the first time access to turbulence-relevant time scales, enabling the investigation of plasma edge dynamics such as modes and instabilities. Their connection to averaged plasma profiles is likewise accessible with this diagnostic. Furthermore, the diagnostic system measures in two magnetically connected divertors, which enables the study of long-range correlation of fluctuations. Utilising a collisional-radiative model, the diagnostic can reconstruct fast electron density and temperature variations with an effective resolution of 10 kHz, associated with plasma modes and bursts. Additionally, it provides high temporal resolution measurements of the detachment process in the divertor. Since it simultaneously measures at an upper and lower divertor, it is the first edge diagnostic at W7-X capable of measuring the up-down asymmetry of turbulence. This article presents the design and implementation of the diagnostic as well as an analysis of the signal quality. It also looks at the influence of diagnostic gas puffs on the plasma in detail. To present the potential of the diagnostic, this work briefly shows a long-range correlation analysis of an edge mode between two divertors that are magnetically connected as well as the electron temperature and density calculation for this mode. Furthermore, a detachment process measured with high time resolution is presented.

Temperature rise of qubits due to heating is a critical issue in large-scale quantum computers based on quantum-dot (QD) arrays. This leads to shorter coherence times, induced readout errors, and increased charge noise. Here, we propose a simple thermal circuit model to describe the heating effect on silicon QD array structures. Noting that the QD array is a periodic structure, we represent it as a thermal distributed-element circuit, forming a thermal transmission line. We validate this model by measuring the electron temperature in a QD array device using Coulomb blockade thermometry, finding that the model effectively reproduces experimental results. This simple and scalable model can be used to develop the thermal design of large-scale silicon-based quantum computers.