Increase In Electron Temperature Research Articles

Analysis of the ECH effect on EPM/AE stability in Heliotron J plasma using a Landau closure model

The aim of the present study is to analyze the effect of the electron cyclotron heating (ECH) on the linear stability of Alfvén eigenmodes (AEs) and energetic particle modes (EPMs) triggered by energetic ions in Heliotron J plasma. The analysis is performed using the FAR3d code that solves a reduced MHD model to describe the thermal plasma coupled with a gyrofluid model for the energetic particle (EP) species. The simulations reproduce the AE/EPM stability trends observed in the experiments as the electron temperature (T e ) increases, modifying the thermal plasma β, EP β and EP slowing-down time. Particularly, the EPM and Global AE are stabilized in the low-bumpiness (LB) configuration due to an enhancement of the continuum, finite Larmor radius and e-i Landau damping effects as the thermal β increases. On the other hand, a larger ECH injection power cannot stabilize the AE/EPM in medium-bumpiness and high-bumpiness (HB) configurations because the damping effects are weaker compared to the LB case, unable to balance the further destabilization induced by an enhanced EP resonance as the EP slowing-down time and EP β increases with T e .

Laser induced breakdown spectroscopy of aluminum incorporated with metallic nanoparticles

Laser-Induced Breakdown Spectroscopy is a promising spectroscopic technique with a vast spectrum of applications in fields concerned with identification and detection of elements. But it faces some limitations due to self-absorption, noise due to matrix effect and line broadening resulting in low emission signal. This research proposes LIBS signal enhancement by incorporation of metal nanoparticles (Cu, Mg, Au) on Al surface and compares their effect. The successful optical emissions enhancement is achieved as the emission intensities of Al- and Na- lines of three coated samples are compared with those of uncoated Al. The Electron Temperature has been evaluated by Boltzmann plot and an increase in Electron Temperature has been observed with the incorporation of nanoparticles to the aluminum surface as compared to the untreated aluminum, due to more plasma emissions. The Electron Number Density of the aluminum plasma did not have much effect with the incorporation of Nanoparticles. The Local Thermal Equilibrium condition has been satisfied and checked by Mc Whirter’s Criterion. The incorporation of metal nanoparticles can be declared as an effective method not only for LIBS signal enhancement but also better detection of trace elements which were not observed without the use of Nanoparticles.

Electron density and electron temperature measurements in an atmospheric pressure plasma interacting with liquid anode

Plasma driven solution electrochemistry has received increasing attention during the last decade for a variety of applications including nanomaterial synthesis. We report the temporal and spatial resolved electron density and temperature for a negative pulsed DC discharge in helium with N2 shielding gas impinging on a liquid anode as measured by Thomson scattering spectroscopy. A stable radial plasma contraction and significant plasma-enhanced N2 mixing was found for the longest investigated pulse width (9 μs). It was found that the plasma enhanced N2 mixing significantly impacts the plasma morphology and electron properties. In addition, we observed a significant increase in electron temperature coinciding with a drop in electron density near the liquid anode surface, which is attributed to electron attachment and electron-water ion cluster recombination enhanced by plasma-induced water evaporation. This near anode surface phenomenon is argued to be responsible for the discharge stabilization by preventing the development of a thermal instability in spite of the significant gas heating. This increase in electron temperature near the anode suggests the presence of a significant flux of hot electrons into solution which might enable non-equilibrium electron-driven reactions in the liquid phase.

Study on characteristics of electron parameters on inert gas addition in a capacitively coupled SF6/O2 plasma

In this paper, characteristics of electron parameters of SF6/O2 and inert gas mixture in a capacitively coupled plasma were studied. Here, gases such as He, Ar, and Xe were added to SF6/O2 mixture and electron energy probability functions (EEPFs) were measured. The electron parameters were acquired, which agreed well with EEPF behaviors. Normally, the inert gas functioned as an electron source and the electron density tended to increase. When the inert gas ratio exceeded other gases, the effect of the mixture varied on each gas. He showed its unique behaviors with the increase in electron temperature. Ar and Xe showed consistent behaviors with increasing electron density and decreasing electron temperature as the inert gas proportion increases. Different behaviors of the electron parameters in inert gases can be explained by the complex contribution of electron attachment of SF6 and the ionization rate of each inert gas.

Enhancement of spectral line intensity and lifetime of femtosecond laser-induced Cu plasma in a cylindrical cavity

The spatial confinement effects in the femtosecond laser-induced Cu plasma contained within a cylindrical cavity are studied by optical emission spectroscopy. The Cu atomic emission intensity and spectral line lifetime are enhanced significantly when a cylindrical cavity with an inner diameter of 6 mm confined the femtosecond laser-induced Cu plasma. The enhancement factor of the emission intensity under the spatial confinement depends on the upper level energy of the spectral line, and the maximum enhancement factors is about 2.48 for the Cu I 529.3 nm spectral line. The spatial confinement can effectively prolong the lifetime of the femtosecond-induced Cu and the persistence time of the plasma is near to 7 μs. The enhancements of the spectral line intensity and lifetime are attributed to the increased electron temperature and density owing to the spatial confinement, and the mechanism for the enhancement effects with the cylindrical cavity are discussed in terms of the shockwave interactions.

Influence of air and water vapor on EEDF, plasma parameters, and the main RONS in atmospheric pressure low temperature helium plasmas: Global model approach

A zero-dimensional global model is developed with an aim to study the influence of air and water vapor on an electron energy distribution function, electron density, and temperature as well as on the chemical composition of atmospheric pressure helium plasmas, with special focus on the main reactive oxygen and nitrogen species important for applications of low temperature plasmas. The main channels for the production and consumption of electrons and electron energy gain and loss are examined by a global model based on a parametric study with variations of the mole fractions of air and water vapor. The calculations are done for 100, 1000, and 10 000 ppm of air in plasma, and for each of these values, the content of water vapor is taken to be 100, 1000, 2000, …, to 10 000 ppm. The variations of the most important production and consumption processes for reactive oxygen and nitrogen species are analyzed in detail. According to the results presented in this paper, water vapor highly contributes to electronegativity of the plasma through pronounced attachment of electrons, which then leads to an increase in electron temperature. For high water vapor content, vibrational excitations of water molecules are one of the main electron energy loss processes, leading to a further effect on the plasma composition. Water decreases concentrations of atomic oxygen, nitrogen, and ozone, while there is an increase in nitrogen oxide, OH, H2O2, and HO2 concentrations. Cross-sectional data for electron scattering on ground and excited state neutrals are mainly taken from the Quantemol-DB database.

Impact of Coulomb scattering on argon plasma based thermionic converter performance

Particle-in-cell (PIC) simulations were performed to study the impact of Coulomb scattering on the performance of argon plasma based thermionic converters. Using a simplified model, studies from the 1970’s concluded that plasma resistance resulting from Coulomb collisions shifts the IV-curves of thermionic converters that use plasmas to mitigate space charge, thereby strongly limiting their electricity generation capability. In this work the impact of Coulomb collisions in such devices were studied as a function of the relative electrical potential between the electrodes, with higher fidelity than earlier models, using a fully kinetic approach (PIC-MCC with grid based electron–ion scattering). This approach overcomes the incorrect assumption in earlier models that the electron temperature is equal to the cathode temperature in all operating conditions. The fully self-consistent results presented here showed an increase in electron temperature with an increase in gap distance or electrode bias, which decreases the plasma resistivity. It was consequently found that earlier reports overestimated the negative impact of Coulomb collisions at the maximum power point, suggesting the practical usefulness of such devices is higher than previously believed. Electronic conversion efficiency higher than 15% was shown to be feasible at 1200 °C cathode temperature with reasonable electrode work-functions.

Probing the charge and heat transfer channels in optically excited graphene — transition metal dichalcogenide hybrids using Johnson noise thermometry

Graphene (Gr)–transition metal dichalcogenide (TMDC) hybrids are promising platforms for achieving sensitive and ultra-fast photodetection. The process of photo-detection in such van der Waals hybrids is usually dictated by the formation of excitons followed by the transfer of charge and energy from the TMDC layer to graphene, but they have not been explored simultaneously in the same device before. In this work, we have investigated optically excited Gr–WS2 (tungsten disulfide) heterostructures using both standard electrical transport and Johnson noise thermometry. At large negative gate voltages, the experimentally observed photoresponse cannot be explained from conventional photogating but was found to host an increase in electron temperature as large as ∼4 K. Time dependence of the transport and the noise reveals that the change in temperature and photoresistance can originate from distinct microscopic processes. The findings can be exploited for the development of Gr–TMDC based ultra-fast bolometers.

Efficient ion acceleration by multistaged intense short laser pulses

We present a computational study of laser-driven ion acceleration that optimizes a combination of target transparency and extended field acceleration at moderate relativistic intensity. Our scheme applies two sequential laser pulses irradiating a thin target foil along the same direction: The first pulse drives a rapid expansion of the target, while the second one drives a quasistatic electric field in the expanding target with increasing electron temperature. In our particle-in-cell simulations we observe proton peak energies and numbers enhanced by factors of up to 3 compared with regular target-normal sheath acceleration.Received 6 October 2020Accepted 4 May 2022DOI:https://doi.org/10.1103/PhysRevResearch.4.L032003Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHigh-energy-density plasmasLaser driven ion accelerationAccelerators & BeamsPlasma PhysicsParticles & Fields

Electron Energization by High‐Amplitude Turbulent Electric Fields: A Possible Source of the Outer Radiation Belt

AbstractThe turbulent energy cascade that is characteristic of bursty bulk flow (BBF) braking regions in the Earth's magnetotail has been shown to be the energy source of large‐amplitude electric fields (>50 mV/m) which can, in turn, result in local energetic electron acceleration. These pre‐energized electrons can move inward to stronger magnetic fields being further accelerated and can eventually supply an energetic tail to electron distributions in the outer radiation belt. Using wave and plasma measurements from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites during four tail seasons from 2015 to 2019, we study the process of BBF magnetic and kinetic energy being transferred to electrons by turbulent electric fields from a statistical perspective. We identify turbulent BBF regions by the presence of high‐amplitude electric fields. We show that the high‐amplitude electric fields are associated with an increase in electron temperature by three times compared to quiet times and with a ten‐fold increase in temperature fluctuations. They are also associated with strong variations of energetic electron fluxes, indicative of local acceleration. We further discuss the implications of these findings and the role of this pre‐energized electron population in supplying the outer radiation belt.

Enhanced heating in plasma bulk due to electron cyclotron resonance in weakly magnetized capacitively coupled plasmas

An enhanced electron heating mechanism based on a resonance between the cyclotron motion of electrons and radio frequency (rf) electric field in the plasma bulk is reported in weakly magnetized capacitively coupled argon plasmas at low pressure. When the electron cyclotron frequency coincides with the applied power source frequency, the bulk electrons can continuously acquire energy from the background electric field within certain rf periods during the cyclotron motion, inducing overall distinct increase of excitation rate and electron temperature in the plasma bulk. This enhanced electron heating effect has been examined by a combination of kinetic particle simulations, experimental measurements, and an analytical model, and the dynamics of electrons are revealed at resonant conditions.

Experimental investigation of high velocity neutral flow interaction with a magnetized plasma

Plasma aerocapture is an orbit insertion method that leverages a magnetic dipole plasma to generate drag by ionizing, capturing, and deflecting atmospheric flow. Key physical assumptions about energy and momentum exchange during aerocapture are tested here by a novel experiment that characterizes the interaction between a high velocity free molecular flow and a magnetized plasma. A neutral beam source accelerates ions from a helicon plasma to a conductive plate, neutralizes them, and reflects them as a collimated flow. A hollow cathode plasma with an applied axial magnetic field of 1 kg acts as the target for the flow. It is found that interaction with the flow causes an increase in both density and temperature of the target plasma by up to a factor of two. The voltage required to operate the hollow cathode at a fixed current is reduced by up to 5% while the neutral beam is operating, suggesting power deposition by the flow. A 0D power balance model is invoked to show that flow kinetic energy is absorbed by the plasma at a rate of up to 50% of the hollow cathode power. The absorbed power correlates linearly with an electron temperature increase of up to 100%, indicative of electron heating by flow kinetic energy transfer. Deflection of the flow by the plasma is not resolved due to extraneous forces on the measurement device and uncertainties in plasma properties. Using the results found here, it is shown that the experiment can feasibly scale to demonstrate significantly higher energy and momentum transfer as required for a plasma aerocapture proof-of-concept.

Analysis of the reflection spectra of MAXI J1535-571 in the hard and intermediate states

ABSTRACT We report results on the joint-fit of the NuSTAR and HXMT data for the black hole X-ray binary candidate MAXI J1535-571. The observations were obtained in 2017 when the source evolved through the hard, hard-intermediate, and soft-intermediate states over the rising phase of the outburst. After subtracting continuum components, X-ray reflection signatures are clearly showed in those observations. By modelling the relativistic reflection in detail, we find that the inner radius Rin is relatively stable with Rin ≲ 1.55Rg during the three states, which implies that the inner radius likely extends to the innermost stable circular orbit even in the bright hard state. When adopting Rin = RISCO, the spin parameter is constrained to be $0.985_{-0.004}^{+0.002}$ at 90 per cent confidence (statistical only). The best-fitting results reveal that the inclination of the inner accretion disc is ∼70–74 deg, which notably conflicts with the apparent orientation of the ballistic jet (≤45 deg). In addition, both the photon index and the electron temperature increase during the transition from hard to soft state. It seems that the corona evolves from dense low-temperature in the low/hard state to tenuous high-temperature after the state transition, which indicates that the state transition is accompanied by the evolution of the coronal properties.

Kinetic‐Size Magnetic Holes in the Terrestrial Foreshock Region

AbstractKinetic‐size magnetic holes (KSMHs) can accelerate and heat the particles, resulting the energy dissipation in space plasmas. KSMHs in the terrestrial foreshock region are statistically investigated based on the Magnetospheric Multiscale data from October 2015 to December 2019. A total of 98 KSMHs are successfully selected, and most of them are accompanied by electron vortices. The fluxes of electrons at ∼90° of pitch angle enhance inside the magnetic holes, where the perpendicular and total electron temperature increase, and the parallel electron temperature slightly decreases inside these magnetic holes. Moreover, we reveal a novel phenomenon that a lot of the observed KSMHs are probably moving toward the Sun in the plasma flow frame. Such sunward propagating KSMHs are detected for the first time in the foreshock region. We propose that these observed KSMHs are probably generated in the foreshock region and then propagate to the Sun.

Dynamics of electron internal transport barrier formation at the H–L transition on EAST

The dynamics of electron-internal transport barrier (e-ITB) formation is studied in the hybrid plasma of neutral beam injection and lower hybrid wave heating on EAST. The e-ITB is observed to be repetitively formed at the H–L transition, where the relaxation process of core radiation triggers an increase in neutron yield and core electron temperature. A reversed q-profile is beneficial for generating the barrier, identified by the appearance of reversed shear Alfvén eigenmodes (RSAEs). The dimensionless parameter of the normalized Larmor radius is estimated to visualize the dynamic behavior of the e-ITB. It is found that the e-ITB forms once the electron exceeds 0.014, and the RSAEs are accompanied by the e-ITB formation. The barrier foot moves inwards until the L–H transition occurs, where the H-mode pedestal or type-I edge localized mode (ELM) strongly influences the e-ITB intensity. The results of thermal transport modeling show a significant reduction in the core thermal transport coefficient in the electron channel while maintaining a nearly unchanged ion transport level as the e-ITB evolves.

Spatial distribution and transport mechanism of electrons in large and powerful inductively coupled plasma sources with Faraday shield

A large and powerful radio frequency (RF) inductively coupled plasma (ICP) source with a Faraday shield (FS) has been investigated by a 3D fluid model, consisting of a plasma module and an electromagnetic field module. Effects of the structure of the FS, the RF current, and the gas pressure on the spatial distributions of plasma parameters including the electron density, electron temperature, and electron potential barrier are investigated systematically. The results show that the FS has a great influence on the spatial distribution and transport mechanism of electrons. The electron density has a maximum value at the center of the ICP source and declines sharply near the FS. Furthermore, it decreases obviously with the decreasing slit width, due to the electron transport mechanism, which is directly related to the electron potential barrier and electron temperature. In addition, the electron density increases with the RF current and gas pressure; it is noteworthy that the stronger induced electric field heating exists at the slit gap under high RF current that makes the electron temperature increase. The data obtained in this paper could lead to a deeper insight into the characteristics of ICP sources, which is extremely essential for optimizing the FS structure and designing large and powerful radio frequency ICPs in the future.

Influence of electron energy distribution on fluid models of a low-pressure inductively coupled plasma discharge

The aim of the present paper is to examine the influence of assumption on the electron energy distribution function on the relation between the plasma potential and the electron temperature for both electropositive (argon) and electronegative (chlorine) plasmas. A one-dimensional fluid model is used for simplicity although similar results were obtained using a self-consistent two-dimensional fluid model coupled with the Maxwell's equations for inductively coupled plasmas. We find that for electropositive plasma only a bi-Maxwellian electron energy distribution function provides reasonable results compared to measurements in low-pressure inductively coupled plasmas, namely, the increasing plasma potential for increasing electron temperature. For electronegative plasma, the plasma potential is an increasing function of the electron temperature for all electron distributions considered in the model. However, the scaling factors do not agree with the conventional plasma theory. We explain these results by the deviation of electrons from a Boltzmann distribution, which is due to non-equilibrium and non-local nature of plasma at the low-pressure conditions.

On electron temperature rise in divertor relevant recombining plasma along magnetic field line

The rise of electron temperature along the magnetic field line was clearly observed in divertor relevant recombining plasma, even though there was no additional electron heating source. Electron temperature obtained at recombination front was approximately 0.5 eV, whereas it increased up to greater than 1 eV at downstream of recombination front. Although this temperature rise is likely common in detached or recombining plasmas, the mechanism has not been understood yet. This report provides a reasonable interpretation of temperature rise along the magnetic field line, for the first time: depletion of low energy electrons due to volumetric recombination leads to deformation of electron energy distribution, resulting in an apparent increase in electron temperature. Our experiment supports this interpretation in that the experimentally observed electron temperature showed good agreement with calculated effective electron temperature.

Recent results from deuterium experiments on the large helical device and their contribution to fusion reactor development

In recent deuterium experiments on the large helical device (LHD), we succeeded in expanding the temperature domain to higher regions for both electron and ion temperatures. Suppression of the energetic particle driven resistive interchange mode (EIC) by a moderate electron temperature increase is a key technique to extend the high temperature domain of LHD plasmas. We found a clear isotope effect in the formation of the internal transport barrier in high temperature plasmas. A new technique to measure the hydrogen isotope fraction was developed in the LHD in order to investigate the behavior of the isotope mixing state. The technique revealed that the non-mixing and the mixing states of hydrogen isotopes can be realized in plasmas. In deuterium plasmas, we also succeeded in simultaneously realizing the formation of the edge transport barrier (ETB) and the divertor detachment. It is found that resonant magnetic perturbation plays an important role in the simultaneous formation of the ETB and the detachment. Contributions to fusion reactor development from the engineering point of view, i.e. negative-ion based neutral beam injector research and the mass balance study of tritium, are also discussed.

ELF/VLF Wave Radiation Experiment by Modulated Ionospheric Heating Based on Multi-Source Observations at EISCAT

Ground-based high-frequency modulated waves can periodically heat the ionosphere and create “virtual antennas”, which can radiate extremely low frequency (ELF, 0.3–3 kHz) or very low frequency (VLF, 3–30 kHz) waves for long-distance communication. Ionospheric X-mode and O-mode heating experiments using amplitude and beat-wave (BW) modulations were conducted on 21 November 2019. Experimental results were analyzed from multiple perspectives based on data from Dynasonde, a magnetometer, stimulated electromagnetic emissions, an ELF/VLF signal receiver, and ultra-high-frequency radar. The strongest excited ELF/VLF signals in previous BW modulation heating experiments were around 8–12 kHz; however, in this experiment, no signal excited in this frequency range was observed, and the signal with the highest signal/noise ratio was at the frequency of 3517 Hz, which will aid in understanding the best communication frequency under different ionospheric backgrounds. It is well-accepted that the electron temperature changes periodically with the modulation frequency. However, we noted that the electron temperature had insufficient cooling during the O-mode modulated heating process and then increased again, resulting in a continuous electron temperature increase. We found that this was related to the change in ion composition after analyzing ion-line spectra, which will be helpful in studying the effect of modulation heating on the ionosphere background.