Plasma Temperature Research Articles

Effect of sample temperature and laser ablation angle on optical emission and acoustic signals from laser-induced zirconium plasma

A fiber-coupled, acoustic-wave-assisted (AW) microchip laser-induced breakdown spectroscopy (mLIBS) system was developed to analyze the elemental composition and surface imaging. In this study, we measured the dependence of sample temperature and laser ablation angle (LAA) on the laser-induced plasma–optical emission (LIP–OE) and LIP–acoustic signal (LIP–AS). The intensity of the LIP–OE and ablated mass at three different temperatures and eight different LAAs were estimated using a zirconium sample. Simultaneously, we investigated the LIP–AS amplitude, propagation speed, and shape by synchronizing the AW-mLIBS system with a high-speed camera. The results revealed that the LIP–OE increases with increasing temperature and is unaffected by LAA up to 40° because the amount of the ablated mass was similar to the plasma. Additionally, no considerable variation in plasma temperature was obtained using the Boltzmann method over the sample temperature. However, the propagation speed of the LIP–AS differs with temperature but has marginal angular dependence because the LIP–AS propagates as semispherical. Furthermore, no considerable changes were observed in the LIP–AS amplitude up to 100°C, and the LAA showed a similar tendency to that of the LIP–OE.

Effect of detachment on Magnum-PSI ELM-like pulses: direct observations and qualitative results

Abstract Conditions similar to those at the end of the divertor leg in a tokamak were replicated in the linear plasma machine Magnum-PSI. The neutral pressure in the target chamber is then increased to cause the target to transition from an attached to a detached state. Superimposed to this steady state regime, edge localised mode (ELM)-like pulses are reproduced, resulting in a sudden increase in plasma temperature and density, such that the heat flux increases transiently by half an order of magnitude. Visible light emission, target thermography, and Thomson scattering are used to demonstrate that the higher the neutral pressure the more energy is removed from the ELM-like pulse in the volume. If the neutral pressure is sufficiently high, the ELM-like pulse can be prevented from affecting the target and the plasma energy is fully dissipated in the volume instead (ID 4 in table 1). The visible light images allow the division of the ELM-plasma interaction process of ELM energy dissipation into 3 ‘stages’ ranging from no dissipation to full dissipation (the target plasma is detached). In the second publication related to this study, spectroscopic data is analysed with a Bayesian approach, to acquire insights into the significance of molecular processes in dissipating the plasma energy and particles.

Development of Numerical Analysis Method for Cathode Sheath Considering Electron Emission From Cathode in Vacuum Arc

ABSTRACTIt is imperative to develop the simulation of vacuum arcs as a tool to aid electrode design in vacuum circuit breakers. Although the development of electromagnetic thermo‐fluid simulations for vacuum arcs has been reported, most of them do not take cathode sheath phenomena into account and have not been able to reproduce vacuum arc phenomena, especially cathode spots. As the first step, the cathode sheath voltage, cathode surface electric field, and temperature and field (T‐F) electron emission current were analyzed numerically on the basis of the space charge in the cathode sheath. In this study, the cathode sheath was assumed to exist when the charge density induced on the cathode surface is positive, and the temperature and density of vacuum arc plasma and cathode temperature, which are physical quantities obtained by electromagnetic thermo‐fluid simulation, were used as parameters of the analysis. As a result, the cathode sheath voltage, electric field, and electron emission current density can be calculated from the vacuum arc plasma temperature, density, and cathode temperature. Numerical results show that the electron emission current density has a dominant effect on the presence or absence of the cathode sheath.

Theoretical investigation of iodine plasma through detailed electron impact excitation cross-section calculations and collisional-radiative model analysis

Abstract In the present study, we consider the electron impact excitation of neutral iodine and its application in developing a collisional-radiative model for plasma diagnostics of iodine plasma. Electron impact excitation cross- sections are calculated using fully relativistic distorted wave theory. The required atomic structure calculations for iodine are carried out using the relativistic multi-configuration Dirac-Fock method. The excitation energies obtained are reported and compared with values from the NIST database. The electron impact excitation cross-sections are calculated from the ground (5p5 2P3/2) and first- excited state (5p5 2P1/2) to the several upper fine structure levels. Our cross- section results align well with previous studies, reported by Ambalampitiya et al. [Atoms, 9, 103, 2021] using the Breit-Pauli B-spline R-matrix method. Further calculated cross-section results are incorporated into the collisional-radiative model. Our model also includes electron impact ionization, de-excitation, three- body recombination, and radiative decay. We validate our model using emission spectra from inductively coupled iodine plasma. For this purpose, we used the recorded intensities for the emission lines, 486.23 nm, 511.92 nm, 523.45 nm, 589.40 nm, and 608.24 nm are compared with those obtained from our model to calculate electron temperature and electron density of the iodine plasma.

Earthward‐Tailward Asymmetry of Plasma Temperature in Reconnection Outflow in Earth's Magnetotail

AbstractTo explore the asymmetry in ion and electron heating at Earth's magnetotail at mid‐tail distances ( −30 ), we analyze near‐simultaneous observations of reconnection outflows from two opposite sides of reconnection sites at those distances using Magnetospheric Multiscale (MMS) and Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) data. We report a pronounced temperature asymmetry between the earthward and tailward reconnection outflows. The asymmetry is more significant for electrons than for ions: Earthward moving ions are only three times hotter than tailward ones, but earthward moving electrons are 5–20 times hotter than tailward ones. The closed field‐line topology on the earthward side of the reconnection region, as opposed to the open topology on the tailward side, is likely a critical contributor to this asymmetry. These findings cast light on the underlying mechanisms of particle heating and energization in magnetotail reconnection, highlighting the significant role of Earth's dipolar magnetic field. This study offers insights for refining magnetic reconnection models, emphasizing the importance of incorporating realistic magnetic field topologies to accurately simulate the heating and energization processes observed in space plasma environments.

The impact of toroidal mode coupling on high-density discharges in J-TEXT

Density limit has long been a widely studied issue influencing the operating range of tokamaks. The rapid growth of the m/n = 2/1 (where m and n are poloidal and toroidal mode numbers, respectively) tearing mode is generally regarded as a primary precursor to the density limit disruption. In this experiment, the coupling of the m/n = 1/1 mode and the m/n = 2/1 mode in high-density plasma was observed. During a sawtooth cycle, the frequencies of the two modes gradually converge until they become equal. After that, toroidal coupling occurs between the 1/1 and 2/1 modes, resulting in a mutually fixed phase relationship. With the occurrence of toroidal coupling, the 2/1 mode is stabilized. Prior to the disruption, the cessation of the 1/1 and 2/1 mode coupling, along with the rapid growth in the amplitude of the 2/1 mode, can be observed. Additionally, under the same parameters, comparing discharges with or without the 1/1 mode, it is found that the presence of the 1/1 mode leads to higher plasma density and temperature parameters.

Spatially resolved plasma composition evolution in a solar flare – The effect of reconnection outflow

Context. Solar flares exhibit complex variations in elemental abundances compared to photospheric values. These abundance variations, characterized by the first ionization potential (FIP) bias, remain challenging to interpret. Aims. We aim to (1) examine the spatial and temporal evolution of coronal abundances in the X8.2 flare on 2017 September 10, and (2) provide a new scenario to interpret the often observed high FIP bias loop top, and provide further insight into differences between spatially resolved and Sun-as-a-star flare composition measurements. Methods. We analyzed 12 Hinode/Extreme-ultraviolet Imaging Spectrometer (EIS) raster scans spanning 3.5 hours, employing both Ca XIV 193.87 Å/Ar XIV 194.40 Å and Fe XVI 262.98 Å/S XIII 256.69 Å composition diagnostics to derive FIP bias values. We used the Markov Chain Monte Carlo (MCMC) differential emission measure (DEM) method to obtain the distribution of plasma temperatures, which forms the basis for the FIP bias calculations. Results. Both the Ca/Ar and Fe/S composition diagnostics consistently show that flare loop tops maintain high FIP bias values of > 2–6, with peak phase values exceeding 4, over the extended duration, while footpoints exhibit photospheric FIP bias of ∼1. The consistency between these two diagnostics forms the basis for our interpretation of the abundance variations. Conclusions. We propose that this variation arises from a combination of two distinct processes: high FIP bias plasma downflows from the plasma sheet confined to loop tops, and chromospheric evaporation filling the loop footpoints with low FIP bias plasma. Mixing between these two sources produces the observed gradient. Our observations show that the localized high FIP bias signature at loop tops is likely diluted by the bright footpoint emission in spatially averaged measurements. The spatially resolved spectroscopic observations enabled by EIS prove critical for revealing this complex abundance variation in loops. Furthermore, our observations show clear evidence that the origin of hot flare plasma in flaring loops consists of a combination of both directly heated plasma in the corona and from ablated chromospheric material; and our results provide valuable insights into the formation and composition of loop top brightenings, also known as EUV knots, which are a common feature at the tops of flare loops.

Assessment of a space and energy resolved diagnostic based on GEM technology on MAST-U

Abstract A Gas Electron Multiplier (GEM)-based detector was utilized for the first
time on a spherical tokamak, MAST-U, during the 2023 campaign to investigate Soft
X-Ray (SXR) radiation (1-20 keV) emitted from the plasma. GEM detectors, chosen
for their resilience to harsh fusion environments and their ability to provide energy-
resolved SXR emission images with sub-millisecond time resolution, are a relatively
new diagnostic compared to standard semiconductor diodes. In this study, the GEM
detector features a pinhole geometry outside the vacuum chamber and observes the
plasma through a beryllium window. Filled with an ArCO2 mixture, the detector
consists of an Aluminized Mylar cathode, three Aluminum-coated GEM foils, and an
anode made of a 16x16 matrix of 6mm2 pads for 2D readout. It employs custom
GEMINI ASICs (Application Specific Integrated Circuits) for signal readout, enabling
photon-counting techniques with Time over Threshold (ToT) analysis on each detector
channel, reaching a total maximum rate of 256 MHz.
Preliminary findings from the 2023 campaign demonstrate the effectiveness of the
GEM detector in complementing existing SXR camera data in terms of spatial and
temporal resolution. Case studies include the identification of Magnetohydrodynamic
(MHD) instabilities, such as the Snake instability, and the exploitation of energy
capabilities for plasma event energy characterization, as shown in the case of Internal
Reconnection Events. Additionally, the GEM detector allows for estimation of the
Electron Temperature of Maxwellian plasmas. These results underscore the potential
of the GEM-based diagnostic system in advancing tokamak research for comprehensive
plasma characterization and control.

Numerical study on wave attenuation via 1D fully kinetic electromagnetic particle-in-cell simulations

Abstract Electromagnetic wave-plasma interaction has drawn much attention recently due to numerous important technologies and applications, taking advantage of phenomena such as electromagnetic waves being reflected or absorbed in a plasma medium. The physics of wave-plasma interaction can be complicated, when non-uniform, non-equilibrium, or anisotropic plasmas are involved, in which numerical simulations can be used to fill the gaps between theoretical solutions and experimental measurements. Among many numerical methods, the particle-in-cell method, which can solve accurately both the electromagnetic fields and particle trajectories
self-consistently, would be the best choice to study wave-plasma interaction problems as long as the computational cost can be accepted. However, the applications of PIC on wave-plasma interaction remain rare, and the numerical effects of the PIC method on accurately evaluating the wave attenuation have not been studied in depth. In this paper, a number of numerical parameters and physical parameters are tested using a 1D electromagnetic PIC method plus Monte Carlo collision model. It is found that as long the as the basic PIC criterion is met, the PIC results can be trustable, and the numerical noise due to limited number of particles has a minor effect. The physical parameters of the EM wave frequency, amplitude, the plasma temperature, thickness, and collision type are studied, and their effects on the wave attenuation are presented. In addition, strategies on establishing simulation setup and evaluating the wave attenuation in terms of power or energy are discussed.

Distinctive features of measuring <I>T<SUB>e</SUB></I> and <I>n<SUB>e</SUB></I> spatial distributions in the Globus-M2 spherical tokamak using method of Thomson scattering of laser radiation

The results of measuring the electron temperature and density spatial distributions in plasma of the Globus-M2 tokamak using the Thomson scattering diagnostics are presented. The diagnostics provides measurements throughout the entire tokamak discharge, starting from time of gas breakdown. The Thomson scattering data were analyzed in order to determine the positions of the last closed flux surface, the plasma magnetic axis, and the radius of inversion during the saw-tooth oscillations. The results of measurements performed during the internal reconnection of magnetic field lines are presents, as well as the dynamics of spatial distributions of electron temperature, density and pressure during the plasma transition to the H-mode. The results of measuring the electron temperature distribution in the scrape-off layer using the Thomson scattering diagnostics are also presented for distances up to 4 cm outside the last closed flux surface.

Plasma Etch of IGZO Thin Film and IGZO/SiO2 Interface Diffusion in Inductively Coupled CH4/Ar Plasmas

ABSTRACTIn this work, the etching characteristics of InGaZnO4 (IGZO) thin films were systemically investigated in inductively coupled CH4/Ar plasmas with various gas ratios, bias voltages, and surface temperatures. The ion flux in the CH4/Ar plasmas was analyzed using bias power and voltage, whereas the relative densities of CH and H radicals were quantified through optical actinometry. The change in CH3 radical density was also estimated based on plasma kinetics analysis. The correlations between the plasma properties and IGZO etch rate were investigated. In CH4/Ar plasmas with CH4 ratios below 80%, the IGZO etch rate increases with a higher CH4 proportion, aligning with the ascending trend of CH3 radical density, which suggests that CH3 radical density acts as a limiting factor (radical‐limited regime). However, the IGZO etch rate decreases when the CH4 ratio exceeds 80%, corresponding to the reduction in ion flux, which indicates that ion flux becomes a limiting factor in this ion‐limited regime. The IGZO etch rate shows a linear relationship with bias voltage and follows the Arrhenius equation with varying surface temperature in plasmas without bias voltage. A spontaneous etch model was proposed based on these relationships. In this model, the IGZO etch rate depends on CH3 radical density and IGZO surface reactivity, where ion bombardment contributes more significantly to surface reactivity than high surface temperature. IGZO thin film was deposited on SiO2 during the fabrication of a 3D stacked ferroelectric field‐effect transistor (FeFET) memory device. The interaction between IGZO and SiO2 during CH4/Ar plasma processing was investigated using time‐of‐flight secondary ion mass spectrometry. The efficacy of removing IGZO atoms that had diffused into the SiO2 network was enhanced when subjected to plasma with a bias voltage, compared to the process without a bias voltage. However, exposure to CH4/Ar plasma resulted in a deeper diffusion of IGZO atoms into the SiO2 network, primarily attributed to ion bombardment rather than elevated surface temperature. A significant improvement in surface smoothness was achieved after IGZO and SiO2 etch by introducing BCl3 into the SiO2 etching chemistry.

Temperature measurement method with line and continuum emissions in Ar-N2 DC arc

Abstract This study discusses a technique for accurate temperature measurement of thermal plasmas with a high-speed camera. Temperature of thermal plasmas is important parameter for plasma processes. High-speed cameras are useful to measure plasma temperatures in two dimensions. Measurements of plasma emission with a high-speed camera and band-pass filter provide only the spectral intensity of the entire transmitted wavelength range. Temperature measurements with high-speed cameras by Boltzmann plot method or Fowler-Milne method are less accurate. Theoretical consideration of the line and continuum emissions has improved the accuracy of plasma temperature measurement. The measurement target was a free burning arc in an argon and nitrogen atmosphere. Temperature errors were estimated based on the deviation from the true emission coefficient. The calculation and measurement errors were discussed as the factors of the deviation. Error estimation provides important insight into the selection of the measurement wavelength.

Numerical and experimental study of TIG welding arc in high frequency longitudinal magnetic field

The phenomenon of arc compression in TIG welding with high-frequency longitudinal magnetic field (HF-LMF) has been observed. However, its mechanism remains unclear, and there is a lack of numerical investigation. This work presents a two-dimension axisymmetrical model of arc plasma in high-frequency longitudinal magnetic field based on the magnetohydrodynamics (MHD). The distributions of temperature, velocity and pressure of arc plasma in HF-LMF are investigated at different applied LMF frequencies ranging from 0 to 5000 Hz. In order to make the simulation results more convincing, the induced current and the electric force were considered. The results show that the HF-LMF could generate a circumferential electric field, causing particles rotating. However, since HF-LMF is variable, the direction of the electric field also changes, which causes the arc to rotate back and forth. When the frequency of HF-LMF reaches 2000 Hz, the negative pressure zone above the center of the anode disappeared and the arc was compressed. Thus, as the frequency of LMF increases, the distribution of current density, anodic heat flux, and arc pressure changes from a bimodal distribution to a unimodal distribution, and the peak value increases. The theoretical predictions were in good agreement with the experimental results.

Laser-induced plasma analysis of ammonia-oxygen and ammonia-oxygen-enriched-air flames at elevated pressures

This study employed Laser-induced breakdown spectroscopy (LIBS) to measure the fuel-oxidizer ratio (FOR) of ammonia combustion with oxygen-enriched air and pure oxygen flames at elevated pressures (100 - 300 kPa). The correlations between the spectral line intensity ratios of nitrogen (N), hydrogen (H), oxygen (O), and equivalence ratio were used to quantify the FOR of flames at various pressures. The effect of pressure on the stability and precision of the calibration profiles for the elemental intensity ratios in flames was investigated. It was observed that the H/O correlation decreases with pressure increase for both ammonia flames. N/O correlations decrease with elevated pressure for the ammonia-oxygen flame. Furthermore, the nitrogen (NII) spectral emission lines at 568 nm and 595 nm were used to estimate the plasma temperature, while the hydrogen (Hα) line at 656 nm was used for electron number density measurements.

Power handling in a highly-radiative negative triangularity pilot plant

Abstract This work explores detailed power handling solutions for a class of high-field, highly-radiative negative triangularity (NT) reactors based around the MANTA concept [Rutherford et al. (2024)]. The divertor design is kept as simple as possible, opting for a standard divertor with standard leg length. FreeGS is used to create an equilibrium for the boundary region, prioritizing a short outer leg length of only ∼50 cm (∼40% of the minor radius). The UEDGE code package is used for the boundary plasma solution, to track plasma temperatures and fluxes to the divertor targets. It is found that for PSOL = 25 MW and nsep = 0.96 × 1020 m−3, conditions consistent with initial core transport modeling, little additional power mitigation is necessary. For a fixed impurity fraction of just 0.13\% Ne in the plasma, the peak heat flux density at the more heavily loaded outer targets falls to 7.8 MW/m2, while the electron temperature, Te, remains just under 5 eV. Scans around the parameter space reveal that even at densities lower than in the primary operating scenario, PSOL can be increased up to 50 MW, so long as a slightly higher fraction of extrinsic radiator is used. With less than 1% neon (Ne) impurity content, the divertor still experiences less than 10 MW/m2 at the outer target. Design of the plasma-facing components includes a close-fitting vacuum vessel with a tungsten inner surface as well as FLiBe-carrying cooling channels fashioned into the VV wall directly behind the divertor targets. For the seeded heat flux profile, Ansys Fluent heat transfer simulations estimate that the outer target temperature remains at just below 1550◦C. Initial scoping of advanced divertor designs shows that for an X-divertor, detachment of the outer target becomes much simpler, and plasma fluxes to the targets drop considerably with only 0.01% Ne content.

N-changing population of Rydberg states by low-energy electron-Rydberg collisions.

Inelastic n-changing collisions play an important role in the evolution of Rydberg atoms into ultracold plasmas. However, for the initially intermediate n (n ∼ 40) Rydberg states, these collisions can hardly be observed due to the low electron temperature in ultracold plasmas. In this work, we designed an experimental scheme to facilitate collisions between free electrons at 1.5eV and intermediate n Rydberg atoms. Using the field ionization technique, we measured the state distributions resulting from the evolution of initially cold rubidium atoms in the 45P3/2 Rydberg state. The experimentally obtained probability of inelastic collisions excitation agrees well with the Monte Carlo simulation results. In addition, our experimental results indicate that the n-changing population induced by hot electrons is significant for lower nP Rydberg states. Our work plays a significant role in calculating the rates of electron-ion three-body recombination in ultracold plasmas.

Application of Laser-Induced Breakdown Spectroscopy to quantify the changes in plasma characteristics in calcite-precipitated soils

The changes in calcium carbonate precipitation of modified soil by Enzyme Induced Calcite Precipitation (EICP) were investigated using Laser-Induced Breakdown Spectroscopy (LIBS). This experiment enabled elemental composition analysis of the soil samples. The plasma electron density and temperature were also extracted from the collected spectra of distinct soil samples i.e., W1 and W2 treated with EICP. The type of the crystal of CaCO3 deposited during the treatment process was investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. This research was conducted by utilizing an Nd: YAG laser with a wavelength of 532 nm, a pulse duration of 6 ns, and an energy of 25 mJ, from where the plasma temperature and electron density of modified soil throughout several treatment cycles were analyzed. The spectra were collected from different locations within the sample and the spectral range considered for the study was 370 nm-800 nm. The plasma electron density and plasma temperature determined using LIBS spectral data increase with the increase in the treatment cycle. With the increase in the treatment cycle, the deposition of CaCO3 was found to increase and correspondingly plasma temperature increased by 220 % for soil W1 and 117.3 % for soil W2. A similar rise in plasma electron density was noticed at the highest cycle of the treatment process; plasma electron density is augmented by 106.4 % for W1 and 21.50 % for W2. This investigation of the LIBS spectral data information indicates a positive correlation between the number of treatment cycles and the plasma temperature, meaning that as the treatment cycles rise, the plasma temperature also increases indicating a larger deposition of CaCO3. The findings are valuable in the domain of geotechnical engineering, where lasers are extensively employed for the examination of the soil profile and can prove to be a useful method for the characterization of the modified soils.

Correlation of Plasma Temperature in Laser-Induced Breakdown Spectroscopy with the Hydrophobic Properties of Silicone Rubber Insulators

Correlation of Plasma Temperature in Laser-Induced Breakdown Spectroscopy with the Hydrophobic Properties of Silicone Rubber Insulators

A model for fast electron-driven high-density plasma in the double-cone ignition scheme

Abstract A model for fast electron-driven high-density plasma is proposed to describe the effect of injected fast electrons on the temperature and inner pressure of the plasma in the fast heating process of the double-cone ignition (DCI) scheme. Due to the collision of the two low-density plasmas, the density and volume of the high-density plasma vary. Therefore, the ignition temperature and energy requirement of the high-density plasma vary at different moments, and the required energy for hot electrons to heat the plasma also changes. In practical experiments, the energy input of hot electrons needs to be considered. To reduce the energy input of hot electrons, the optimal moment and the shortest time for injecting hot electrons with minimum energy are analyzed. In this paper, it is proposed to inject hot electrons for a short time to heat the high-density plasma to a relatively high temperature. Then, the alpha particles with the high heating rate and PdV work heat the plasma to the ignition temperature, further reducing the energy required to inject hot electrons. The study of the injection time of fast electrons can reduce the energy requirement of fast electrons for the high-density plasma and increase the probability of successful ignition of the high-density plasma.

A coupled plasma-thermal model for hollow cathode power decomposition and parametric analysis

Abstract A 2D axisymmetric transient coupled plasma-thermal model is developed to simulate the plasma behavior during the self-sustained discharge of hollow cathodes, which presents a complete hollow cathode structure and energy transfer processes in multiphysics fields. The model has been validated by quantitative agreement between the simulation results and experimental data on the plasma and emitter temperature at the NSTAR cathode. The effects of thermal protection design, operating conditions, and geometric design on the cathode performance are analysed through electric and thermal power decomposition. The parametric analysis shows that the optimal thermal protection design is to use a 1/3 thickness cathode tube with 4 layers of radiation shielding close to the tube, which reduces 43.7% conductive and 61.1% radiative heat dissipation, respectively. Increasing the inlet flow rate counter-intuitively reduces the emitter temperature due to the potential reversal in the diffusion electric field dominated region, revealing that the flow rate can be traded for the dual optimisation of lifetime and power consumption. Under high current conditions, the IAT effect dominates the plume resistance to increase the discharge voltage after an inflexion point, which is the main factor limiting the cathode performance. A large internal radius gives a uniform low emission and helps to prolong life, while the orifice length should be avoided to be longer than 4 times the orifice radius due to the significantly enhanced Joule heating in the narrow orifice. The orifice radius determines the power deposition due to electron and ion bombardment through potential penetration. For high-current discharger cathodes dominated by electron bombardment, large or through-orifice designs are preferred, while for low-current neutralizer cathodes dominated by electron bombardment, small-orifice designs are recommended.