Plasma Electron Density Research Articles

Decay characteristic of gas arc in C4F7N/N2 and C4F7N/CO2 gas mixture by Thomson scattering

Abstract C4F7N/N2 and C4F7N/CO2 gas mixtures are considered potential alternative gases to SF6, and it is of particular significance to investigate the plasma decay process in these mixtures for evaluating their circuit breaker breaking performance. To comprehend the decay process of electron density(ne) in arc plasma within C4F7N/N2 and C4F7N/CO2 gas mixtures, an arc-generating circuit and a Thomson scattering experiment platform were established. Through coherent Thomson scattering diagnosis of gas arc plasma under various gas mixture conditions, a series of electron density results over time and space were obtained. The findings suggest that the initial electron density of the arc plasma diminishes with an increase in the proportion of C4F7N, and electron density decay is further accelerated as the proportion of C4F7N increases. Moreover, it was observed that the electron density decay rate is higher in the C4F7N/N2 mixture compared to the C4F7N/CO2 mixture. Notably, the electron decay rate in a 50% C4F7N/N2 mixture closely resembles that observed in pure SF6.

Effects of discharge parameters on plasma acceleration and transmission characteristics of a coaxial gun operated in gas-prefilled mode

The effects of discharge parameters on the discharge process and plasma transport characteristics of a coaxial gun in the gas-prefilled mode are studied. The plasma optical intensity and ejection velocity are measured by photodiodes, the optical emission spectrum is taken by a spectroscopic system, and the plasma evolution in the transport process is captured by a high-speed camera. The plasma acceleration characteristics under different discharge parameters show that the velocity and electron density of the ejection plasma are mainly determined by the pre-filled pressure and discharge current, which is consistent with the snowplow model. The kinetic energy of ejection plasma can be significantly increased by reducing the outer loop inductance, which is conducive to increasing the energy utilization efficiency. The time-varying images of plasma radiation and the plasma density at different transport locations illuminate the transmission characteristics of coaxial gun discharge plasma. The results show that the snowplow effect continues to play a role in the plasma transport process, and the plasma accumulation is induced by the combination of shock wave compression. The current-driven magneto hydrodynamics instability occurs during the transport process, and the luminous signal of the plasma current sheet oscillates periodically. In addition, the plasma impact effect is obvious and the gas retarding effect is enhanced with the increase in the gas pressure. These results give us a more comprehensive view of the coaxial gun discharge process and plasma transport and provide a certain reference for optimizing the parameters selection and physical design of coaxial gun discharge plasma characteristics.

Observation of high frequency Alfvén eigenmodes excited by RF-accelerated minority hydrogen ions in the EAST tokamak

Abstract The paper presents the original observation of high frequency Alfvén eigenmode excited by fast minority hydrogen ions accelerated by ion cyclotron range of frequency waves in EAST. The frequency of high frequency Alfvén eigenmodes is around 0.75~8*Ω H, where Ω H is the cyclotron frequency of hydrogen ions evaluated at the low-field side plasma edge. It tracks the on-axis magnetic field B t and the edge plasma electron density n e via the Alfvenic relation ω~ B t *n e -1/2. The high frequency Alfvén eigenmodes are always accompanied by sub-cyclotron modes in several experiments at EAST, consistent with the high frequency Alfvén eigenmode detected on other conventional tokamaks, namely ASDEX Upgrade and DIII-D. Based on the previous study, these sub-cyclotron modes are consistent with the spectrum splitting produced by toroidal mode numbers[Nuclear Fusion 43, 228 (2003)]. We also found that the location of eigenmode excitation of high frequency Alfvén eigenmode driven by RF-accelerated minority hydrogen ions remains unchanged even though the cyclotron resonance location of hydrogen ions varies with B t.

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.

High precision phase difference calculation based on adaptive mixed-radix All-phase FFT for Tokamak plasma electron density measurement

In many Tokamak devices, laser interferometers, such as HCN, DCN, CO2, etc, are employed to measure the plasma electron density by calculating the phase difference between the reference signal and the detector signal. This paper proposes an adaptive All-phase fast Fourier transform (Ap-FFT) method in the electronic density of the plasma. And analyze the reasons why the multi-frequency measurement phase is inaccurate. The proposed method can reduce the accuracy of phase calculation by adjusting the conversion length and mixed-radix to reduce the spectrum leakage and grid effect. At the same time, the experimental data verifies the correctness of the calculation results of this method, and it shows that the measurement uncertainty of the method is 10% higher than the 1024-point Ap-FFT, and 15% higher than the 1024-point FFT. This method can be effectively applied to the measurement of the electronic density of an ionic plasma for plasma and provides a valuable reference for other phase detection systems and equipment.

Plasma electron density profile tomography for EAST based on integrated data analysis

Abstract Plasma electron density is a crucial parameter in plasma studies. Accurately inverting the plasma electron density profile is vital for plasma control experiments and the investigation of plasma physical mechanisms. This paper proposes an integrated data analysis (IDA) method based on Bayesian inference, which integrates polarimetric interferometry (POINT), hydrogen cyanide (HCN) laser
interferometer, and microwave reflectometer (RFL) diagnostics for inverting the plasma electron density profile. To enhance inversion accuracy, a Gaussian prior probability of the non-stationary hyperparameter is used. This prior probability effectively simulates
situations where there is a large plasma electron density gradient in the pedestal, especially under the condition of high-confinement mode discharge. Compared to the use of Gaussian prior probability for the stationary hyperparameter, the proposed IDA
method based on the non-stationary hyperparameter prior probability achieves higher inversion accuracy.

Overview of results from the 2023 DIII-D negative triangularity campaign

Abstract Negative triangularity (NT) is a potentially transformative configuration for tokamak-based fusion energy with its high-performance core, edge localized mode (ELM)-free edge, and low-field-side divertors that could readily scale to an integrated reactor solution. Previous NT work on the TCV and DIII-D tokamaks motivated the installation of graphite-tile armor on the low-field-side lower outer wall of DIII-D. A dedicated multiple-week experimental campaign was conducted to qualify the NT scenario for future reactors. During the DIII-D NT campaign, high confinement ( H 98 y , 2 ≳ 1), high current ( q 95 < 3), and high normalized pressure plasmas ( β N > 2.5) were simultaneously attained in strongly NT-shaped discharges with average triangularity δ avg = −0.5 that were stably controlled. Experiments covered a wide range of DIII-D operational space (plasma current, toroidal field, electron density and pressure) and did not trigger an ELM in a single discharge as long as sufficiently strong NT was maintained; in contrast, to other high-performance ELM-suppression scenarios that have narrower operating windows. These strong NT plasmas had a lower outer divertor X-point shape and maintained a non-ELMing edge with an electron temperature pedestal, exceeding that of typical L-mode plasmas. Also, the following was achieved during the campaign: high normalized density ( n e / n GW of at least 1.7), particle confinement comparable to energy confinement with Z eff ∼ 2 , a detached divertor without impurity seeding, and a mantle radiation scenario using extrinsic impurities. These results are promising for a NT fusion pilot plant but further questions on confinement extrapolation and core-edge integration remain, which motivate future NT studies on DIII-D and beyond.

Analysis of an induced Langmuir wave by ponderomotive forces and its applicability for plasma diagnostics

We present a numerical study on the electron and ion density perturbation in low-temperature plasmas driven by the frequency detuning of two intense laser beams. Our study is performed in the hydrodynamic regime, which becomes applicable when the plasma grating period induced by the beating of the laser beams is greater than the Debye length and collective processes such as plasma oscillations can be excited. Our findings show a resonance in electron density perturbation as the frequency detuning approaches a value consistent with the Bohm–Gross dispersion relation in low- and high-pressure plasmas. We discuss the potential of this resonance as a diagnostic tool for precisely measuring electron temperature and density in low-temperature plasmas through coherent scattering.

Characteristics of fluctuations in the equatorial and polar directions of a compact dipole plasma driven at steady state

The fluctuations in the plasma potential (Vs̃) and electron density (Nẽ) are measured in the steady-state dipole plasma confined in a spherical vacuum chamber using a single permanent dipole magnet. Measurements are made from a radial distance r = 0.5–17 cm, from the surface of the magnet in the equatorial (θ=90°) and polar (θ=180°) directions, using a 4-pin probe setup, and have been characterized by power spectra, cross-phase, cross-coherence, induced transport, and energy spectra. The fluctuations are stronger near the surface of the dipole magnet for θ=90°, thereafter their magnitude decreases gradually with the radial distance. However, a peaked profile of potential fluctuations with the peak around r = 9 cm is observed for θ=180°. The locations of strong fluctuations are around the locations of smaller values of the electron neutral collision frequency. Frequency-resolved power spectra show that the fluctuations in the dipole plasma, predominantly, belong to the very low-frequency range. The values of cross-phase (≤45°) and |Vs̃/Te|/|Nẽ/Ne|≤1 indicate the presence of drift wave instability in both planes, where Te and Ne are equilibrium values of the electron temperature and density. The radial variation of fluctuation-induced electron flux (Γr) verifies the “inward diffusion” of electrons in the equatorial plane.

Investigation of Partial Discharge Transformation Characteristics in Polyimide (PI) Insulations under High-Frequency Electric Stress.

This research delves into the primary issue of polyimide (PI) insulation failures in high-frequency power transformers (HFPTs) by scrutinizing partial discharge development under high-frequency electrical stress. This study employs an experimental approach coupled with a plasma simulation model for a ball-sphere electrode structure. The simulation model integrates the particle transport equation, Poisson equation, and complex chemical reactions to ascertain microscopic parameters, including plasma distribution, electric field, electron density, electron temperature, surface, and space charge distribution. The effect of the voltage polarity and electrical energy on the PD process is also discussed. The contact point plays a pivotal role in triggering partial discharges and culminating in the breakdown of PI insulation. Asymmetry phenomena were found between positive and negative half-cycles by analyzing the PD data stage by stage. A significant number of PDs increased at every stage and the PD amplitude was higher during the negative cycle at the initial stage, but in later stages, the PD amplitude was found to be higher in the positive half-cycle, and scanning electron microscopy (SEM) revealed that the maximum damage occurred near the contact point junction. The simulation results show that the plasma initially accumulates the electron density near the contact point junction. Under the action of the electric field, plasma starts traveling at the PI surface outward from the contact point. Before the PD activity, all parameters have higher values in the plasma head. The microscopic parameters reveal maximum values near the contact point junction, during PD activities where significant damage takes place. These parameter distributions exhibit a decreasing trend over time as when the PD activity ends. The model's predictions are consistent with the experimental data. The paper lays the foundation for future research in polymer insulation design under high-frequency electrical stress.

Statistics and Models of the Electron Plasma Density From the Van Allen Probes

AbstractWe use the full NASA Van Allen Probes mission (2012–2019) to extract the electron plasma density from the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) and Electric Field and Waves (EFW) instruments and discuss the evolution of the plasmasphere. We generate new statistics including mean and standard deviations of the plasma density with respect to L‐shell, magnetic local time (MLT), and various geomagnetic indices. These statistics are generated to be applied in radiation belt physics and space weather codes (with fits provided). The mean plasmasphere is circular around Earth with respect to MLT for Kp < 1. The mean 100 cm−3 level line is above L = 5 and mean 10 cm−3 level expands above the Van Allen Probes apogee for Kp < 1. The outer electron belt lies within the plasmasphere for 60% of all times. As activity increases (Kp > 2), a gradual MLT asymmetry forms with higher mean density in the afternoon sector due to plumes expanding outward. Conversely, the mean density decreases on the dawn and night sectors. The mean density is between ∼500 and ∼50 cm−3 between L ∼ 4 and L ∼ 6 during quiet and moderately active times (Kp < 3), representing ∼80% of all times. Statistics in regions of high density below L = 2 are underdefined for intense activity. The highest standard deviation of density represents a factor 2.5 to 3 times the mean above L = 5 and for active times. We find the percent difference between the EFW and EMFISIS densities is bounded by ±20% for quiet and moderate activity (Kp < 5) and goes up to ±100% for extreme activity.

Analysis of Monte-Carlo collision method with argon and helium background gases at different RF-powers and pressures in ELTRAP device

The impact of confined excited electron with argon and helium background gases is systematically studied using Monte-Carlo particle-in-cell simulations for various low powers (1.0–8.0 V) and pressures (1.50 × 10−8 Torr and 3.75 × 10−9 Torr) in ELTRAP device. The results of these numerical studies showed that the heating effect of the excited confined electron plasma density of 5 × 1014 m−3 within the Brillouin limit (ne≤ε0B22me=31.086×1019m-3) resulted a higher temperature (eV) and increased collision time in argon as a background gas as compared to helium gas. The axial temperature (eV) has a higher value than the radial temperature (eV) and increases with the increase in RF-Powers and pressures. The maximum kinetic energy of excited confined electrons occurred in the range of 0.03–0.04 m radially due to the maximum self-electric field intensity in simulation time up to 20 µs. The electric field decreases when the collision frequency is increased. The secondary electron production and ionization are higher than expected at a background pressure of 1.50 × 10−8 Torr as compared to 3.75 × 10−9 Torr. The remaining secondary electrons were always ejected from the symmetry axis of the device. It was observed that the production of secondary electrons is proportional to the ionization rate.

Machine learning-based prediction of the electron energy distribution function and electron density of argon plasma from the optical emission spectra

Machine learning-based prediction of the electron energy distribution function and electron density of argon plasma from the optical emission spectra

Mathematical simulation of ionospheric plasma diagnostics by electric current measurements using an insulated probe system

The goal of this work is to theoretically substantiate the possibility of determining the charged particle density in the ionospheric plasma by separately measuring the electric currents of an insulated probe system in the electron saturation region. The ionospheric plasma composition is modeled by two ion species with significantly different masses and electrons to keep the plasma quasi-neutrality. The probe system, which is electrically insulated from the spacecraft structure, consists of cylindrical electrodes: a probe and a reference electrode. The reference electrode to probe current-collecting area ratio can be significantly less than required by the single cylindrical probe theory. The electrodes are oriented transversely to a supersonic flow of a collisionless plasma. In addition to the main plasma with two ion species, a model plasma with a single ion species is considered. The mass of the model ions is such that the ion saturation current to the cylinder is the same for both plasma models. Based on a previously obtained asymptotic solution for the electron saturation current in a plasma with a single ion species, computational formulas are found for determining the ion mass composition and the electron density by probe current measurements. The errors of the formulas are estimated numerically and analytically as a function of the probe system geometry, the bias potential of the probe relative to the reference electrode, and the accuracy of potential and current measurements. It is shown that a proper choice of the probe system settings and the accuracy of probe measurements assures a reliable determination of the charged particle densities in a plasma with two ion species. A priori estimates are presented for the effect of the current bias potential measurement errors on the reliability of determining the ion mass composition and the electron density of the ionospheric plasma.

Electron density in a non-thermal atmospheric discharge in contact with water and the effect of water temperature on plasma-water interactions

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⋅1015 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.

A complete electrode model for plasma impedance probes

Plasma impedance probes measure the impedance spectrum of an antenna immersed in a plasma. The 1964 work of Balmain remains the standard method to interpret these data, using the peak in the magnitude at the upper-hybrid frequency to infer plasma electron density. The primary limitations of Balmain's model are the assumption of a homogenous plasma and a cylindrical dipole. This work presents a numerical model applicable to inhomogeneous plasma and arbitrary antenna geometry based on the cold, fluid approximation given by Balmain. This model solves Poisson's equation using the finite element method and accounts for the effects of the dipole using the plasma complete electrode model (PCEM). The PCEM is developed in this article and accounts for the voltage shunting effects of the dipole elements, the discrete current to the dipole, and the plasma sheath surrounding the dipole. The sheath is incorporated as a contact impedance between the dipole and the plasma in a manner analogous to the complete electrode model of electrical impedance tomography. The first portion of this paper presents the mathematical framework of the PCEM, starting from Maxwell's equations. The second part of the paper compares the output of this numerical method to Balmain's work and to data collected by an impedance probe in the Space Physics Simulation Chamber at the U.S. Naval Research Laboratory. The PCEM results agree with both the observed data and the prior modeling done by Balmain. An additional consequence of the numerical study is the observation that some second-order resonances not predicted by Balmain's model can be attributed to the presence of the plasma sheath.

Experimental investigation of PDI bifurcation of lower hybrid waves during electron density ramp-up in EAST

The effect of parametric decay instability (PDI) on the current drive efficiency of 4.6 GHz lower hybrid (LH) waves in EAST is investigated experimentally, showing the PDI channel bifurcation of LH waves for the first time in EAST. First, experiments with three platforms of LH power were performed, achieving the LH power required for the PDI occurrence. Second, PDI bifurcation experiments were further carried out by ramping up the plasma electron density. The loop voltage increases with an increase in density, implying a decrease in the current driven by the LH wave. PDI bifurcation during electron density ramp-up was studied by analyzing the parallel refractive index ( n∥ ) and the frequency spectrum broadening, which is measured with a radio frequency magnetic probe array recently installed close to the LH antenna. It is observed for the first time that they both first increase with density, then there is not much variation and a clear sideband in the frequency spectrum is also observed when the density is up to 4×1019 m−3 , suggesting a change in the PDI channel. Calculation of the mode growth rate driven by PDI shows that when the edge electron density is up to 1.9×1018 m−3 , the growth rate of the ion cyclotron quasi-mode (ICQM) will exceed that of the ion sound quasi-mode (ISQM), quantitively explaining that with an increase in density, the PDI channel partly transits from the ISQM to the ICQM channel. Studies provide a possible way to reduce the power deposition in the edge region and improve drive capability by means of mitigating PDI behavior.

OES diagnostics of atmospheric pressure argon plasma: Electron temperature and density assessment through visible bremsstrahlung inversion method and collisional-radiative model

This study determined the electron temperature and density in atmospheric pressure argon plasma using optical emission spectroscopy. The analysis combined continuum and line spectral data. Visible bremsstrahlung inversion was used to derive a partial electron energy probability function (EEPF) from the continuum spectrum. Subsequently, electron temperature was estimated assuming a two-temperature distribution based on the derived EEPF. Electron density was obtained by fitting a collisional-radiative (CR) model to the line spectrum, incorporating the obtained EEPF instead of assuming a Druyvesteynian EEPF. Comparative analysis revealed that the electron densities determined using the approach were approximately one order of magnitude lower than those derived from the CR model with the Druyvesteynian EEPF. However, they exhibited strong agreement with the results obtained by the CR model using a two-temperature distribution. This approach demonstrated favorable performance in reproducing both continuum and line spectra, revealing its high reliability and accuracy for atmospheric pressure argon plasma diagnosis.

Space-resolved electron density and temperature evaluation by x-ray pinhole camera method in an ECR plasma

X-ray emission characterization provides valuable insights about electron cyclotron resonance (ECR) plasmas. In principle, space-resolved spectroscopic techniques can be used to reveal spatial distributions of electron density and temperature. In the PANDORA (Plasma for Astrophysics, Nuclear Decay Observation, and Radiation for Archaeometry) project framework, and within the collaboration between the Atomki and INFN-LNS laboratories, we developed a high-resolution full-field x-ray pinhole setup. This setup incorporates advanced analysis techniques for single photon counted imaging in high dynamical range mode, enabling x-ray imaging and space-resolved spectroscopy at high spatial and energy resolution (560 μm and 242 eV @ 8.1 keV, respectively). Here, we introduce an innovative technique for quantitatively evaluating the local electron density and temperature of plasma, as the first application of such a method in an ECR setup. Specifically, we examine an argon plasma heated by 200 W microwave power at 14 GHz. Our analysis includes a retrospective comparison with past x-ray data collected from other ECR ion source setups. Our findings clearly reveal the formation of a plasmoid–halo structure within the plasma chamber, characterized by a dense and hot plasma almost totally enclosed inside the ECR magnetic iso-surface (the plasmoid). This plasmoid exhibits nearly uniform distribution of electron density and temperature, with only gentle gradients of both the parameters toward its edges. Inside the halo, x-ray emission is minimal or even negligible. Notably, cusp structures correspond to magnetic branches where deconfined electrons impinge upon the plasma chamber walls and endplates. The average values of temperature and density measured inside the plasmoid are 12.44±1.84 keV and (1.66±0.15)×1017 m−3, respectively.

Generation of low-energy abundant electron energy probability functions using a magnetized plasma source

The generation of low-energy electrons is essential for the plasma source of the charge neutralizer system within the ion implanter process of semiconductors and displays, owing to their exceptional capability of being effectively transported along their ion beams. In this study, we propose a method to produce non-Maxwellian electron energy probability functions (eepfs) characterized by low-energy-abundant electrons, specifically below 5 eV, across an electron extraction system. In the electron transport region with an axial magnetic field under conditions of high discharge voltage and gas flow rate, we observed a significant increase in low-energy electrons in eepfs. The simple global model proposed to analyze these results demonstrated that the wall loss of electrons can be reduced by an elevated plasma potential, which is influenced by the ionization rate in the transport region. These results are consistent with the experimentally measured plasma potential and electron density. Additionally, the reduction in wall losses and increased ionization rate within the transport region resulted in the relaxation of the plasma potential gradient. This phenomenon effectively inhibited the cutting of low-energy electrons within the eepfs, thereby facilitating their consequential transport to the target. This study emphasizes the significance of increasing the ionization rate and minimizing the potential gradient for the dual purposes of generating low-energy electrons and directing them towards the target.