Increase In Electron Temperature Research Articles

Development of the MiXI Thruster with the ARCH Discharge

The Miniature Xenon Ion (MiXI) thruster with the Axial Ring-Cusp Hybrid ‘MiXI(ARCH)’ discharge was developed and operated with beam extraction at 1 kV. The thruster achieved 59% cathode-free total discharge efficiency at 23.7 mA xenon beam current with filament cathodes and low temperature operation, corresponding to a discharge loss of 226 W/A and propellant utilization of 72%. Thruster efficiency was observed to increase with increasing flow rate and decrease with increasing temperature up to thermal steady state. At thermal steady state, the thruster anode reached ∼320 °C due to the thermal isolation of the thruster head. Reducing the discharge chamber aspect ratio from 0.5 to 0.4 increased thermal steady state efficiency from 46% to 57% but required slow ramping of beam voltage and was limited to stable operation to above 0.5 sccm discharge propellant flow. In contrast to the 3-ring cusp configuration, MiXI(3-Ring), the performance is generally higher but is not able to achieve lower thrust levels and requires more complex start-up for stable operation. An analytical single-cell model was developed and applied to investigate internal processes of the MiXI(ARCH) discharge. The model emulated the effect of increasing flow on performance, indicating that the dominant loss mechanism is plasma electron current to the anode, in contrast to the 3-Ring geometry, which is dominated by primary electron losses. This model also matched trends reported in previous works of strongly increasing electron temperature and primary density with propellant utilization. Through this effort, the MiXI thruster’s highest achievable total efficiency has been increased, and several mechanisms for further improved efficiency have been identified.

Simulation of Discharge Characteristics for the Plasma Etching of Large Area SiO2 Substrates

The electron density distribution and average electron temperature distribution in reactive ion etching (RIE) chamber are of great significance for the ionization and excitation reaction rate. The uniformity of radial distributions of the electron density and average electron temperature in the discharge chamber greatly affects the uniformity of the etching, especially the plasma etching of large area SiO2 substrates. We study the effects of discharge conditions (including power and pressure) on the electron density and average electron temperature of plasma-etched 400 mm SiO2 substrates in the reactive ion etching chamber; the simulation results show that the allowable major discharge conditions strongly affect the characteristics of plasma in the large area reactive ion etching chamber. Specifically, with increase in the power both the electron density and average electron temperature increase, being accompanied by deteriorating uniformity of their radial distributions. As the pressure increases, the electron density increases but average electron temperature decreases, being accompanied by deteriorating uniformity of their radial distributions. These methods and conclusions can provide reference for the improvement of cavity structure and large area RIE equipment designing and selection of the process parameters.

Magnetospheric Multiscale (MMS) Observations of Magnetic Reconnection in Foreshock Transients

AbstractMagnetic reconnection is a fundamental process of energy conversion in plasmas between electromagnetic fields and particles. Magnetic reconnection has been observed directly in a variety of plasmas in the solar wind and Earth's magnetosphere. Most recently, electron magnetic reconnection without ion coupling was observed for the first time in the turbulent magnetosheath and within the transition region of Earth's bow shock. In the ion foreshock upstream of Earth's bow shock, there may also be magnetic reconnection especially around foreshock transients that are very turbulent and dynamic. With observations from the National Aeronautics and Space Administration's Magnetospheric Multiscale mission inside foreshock transients, we report two events of magnetic reconnection with and without a strong guide field, respectively. In both events, a super‐ion‐Alfvénic electron jet was observed within a current sheet with thickness less than or comparable to one ion inertial length. In both events, energy was converted from the magnetic field to electrons, manifested as an increase in electron temperature. Weak or no ion coupling was observed in either event. Results from particle‐in‐cell simulations of magnetic reconnection with and without a strong guide field are qualitatively consistent with observations. Our results imply that magnetic reconnection is another electron acceleration/heating process inside foreshock transients and could play an important role in shock dynamics.

Direct Observations of a Polar Cap Patch Formation Associated With Dayside Reconnection Driven Fast Flow

AbstractDayside solar‐produced concentrated F region plasma can be transported from the midlatitude region into the polar cap during geomagnetically disturbed period, creating plasma density irregularities like polar cap patches, which can cause scintillation and degrade performance of satellite communication and navigation at polar latitudes. In this paper, we observed and investigated a dynamic formation process of a polar cap patch during the 13 October 2016 intense geomagnetic storm. During the storm main phase, storm‐enhanced density (SED) was formed within an extended period of strong southward interplanetary magnetic field (IMF) Bz condition. Total electron content (TEC) map shows that a polar cap patch was segmented from the SED plume. The Sondrestrom Incoherent Scatter Radar (ISR) was right underneath the segmentation region and captured the dynamic process. It shows that the patch segmentation was related with a sudden northeastward flow enhancement reaching ~2 km/s near the dayside cusp inflow region. The flow surge was observed along with abrupt E region electron temperature increase, F region ion temperature increase, and density decrease. The upstream solar wind and IMF observations suggest that the flow enhancement was associated with dayside magnetic reconnection triggered by a sudden and short period of IMF By negative excursion. Quantitative estimation suggests that plasma density loss due to enhanced frictional heating was insufficient for the patch segmentation because the elevated F region density peaking at ~500 km made dissociative recombination inefficient. Instead, the patch was segmented from the SED by low‐density plasma transported by the fast flow channel from earlier local time.

Numerical study on the influence of electron temperature on void formation in dusty plasma

In the past, experiments have proven that the electron temperature in the void is lower than that in the dust cloud. Based on this point, the influence of the spatial distribution of the electron temperature on the void is studied by calculating the fluid equation with explicit ionization, and the images of the circular void and the ring void are obtained by simulation. It is found that when the electron temperature is greater than the threshold value, a stable circular void is generated, and as the electron temperature increases, the time required for the circular void to reach a steady state decreases and its size decreases. This law is not affected by electron temperature spatial distribution set in the center. Combined with the studies of circular void, we speculate that the electron temperature in the ring void is also lower than that in the dust cloud. Through the assumption of the spatial distribution of electron temperature, the simulation results in a ring-shaped void. And the influence of the intensity of the spatial variation of the electron temperature on the ring void is verified. The results show that when the electron temperature change is severe enough, a ring void is generated. And as the intensity increases, the time required for the ring void to reach a steady state decreases, and the size increases slightly.

Effect of two temperature electrons in a collisional magnetized plasma sheath

A collisional magnetized plasma consisting of two temperature electrons has been investigated numerically to study the sheath structure and the ion flux to the wall. The low-temperature electrons are described by Maxwellian distribution, and the high-temperature electrons are described by truncated Maxwellian distribution. It has been observed that sheath width and ion flux to the wall are non monotonous functions of collision frequency as well as hot electron concentration. A sheath formation criterion has been analytically derived and is used to find the ion velocity at the sheath edge. The sheath edge velocity is found to decrease with the increase of hot electron concentration and hot electron temperature. The study of such a system can help in understanding of plasma surface interaction.

Study of the transition from self-organised to homogeneous plasma distribution in chromium HiPIMS discharge

The self-organised plasma patterns, known as spokes or ionisation zones in magnetron sputtering discharges, were observed in a wide range of power densities, from low power direct current magnetron sputtering (dcMS) discharge to high power impulse magnetron sputtering (HiPIMS) discharge. For some target materials and non-reactive gases, it was observed that at very high power densities (>) the plasma exhibits a transition from a regime where spokes are observed to a homogeneous plasma regime. In this contribution, we present a comparison of plasma properties: plasma emission (optical emission spectroscopy) and flux of argon and chromium ions (mass spectrometry), measured both in the spoke regime and in the homogeneous plasma regime, aimed to expand the understanding of the plasma transition between the two modes. A simple biased flat probe was used to distinguish between the spoke regime and the homogeneous plasma regime. It was found that the flux of multiply charged ions (Ar2+ , Cr2+ , Cr3+ , Cr4+) increases abruptly at the transition between the spoke regime and the homogeneous plasma regime. Similarly, the emission from Cr+ ions exhibits a strong increase of about 50% when the plasma torus becomes homogeneous. These observations are interpreted as an increase in electron temperature and a change in the electron heating mode, from a combination of secondary electron heating and Ohmic heating towards pure Ohmic heating. The transition to the homogeneous plasma regime and pure Ohmic heating is only observed in non-reactive HiPIMS discharges for target atoms with the second ionisation potential higher than the first ionisation potential of Ar (15.76 eV), and a self-sputter yield larger than 1.

Electrons in the Young Solar Wind: First Results from the Parker Solar Probe

Abstract The Solar Wind Electrons Alphas and Protons experiment on the Parker Solar Probe (PSP) mission measures the three-dimensional electron velocity distribution function. We derive the parameters of the core, halo, and strahl populations utilizing a combination of fitting to model distributions and numerical integration for ∼100,000 electron distributions measured near the Sun on the first two PSP orbits, which reached heliocentric distances as small as ∼0.17 au. As expected, the electron core density and temperature increase with decreasing heliocentric distance, while the ratio of electron thermal pressure to magnetic pressure (β e ) decreases. These quantities have radial scaling consistent with previous observations farther from the Sun, with superposed variations associated with different solar wind streams. The density in the strahl also increases; however, the density of the halo plateaus and even decreases at perihelion, leading to a large strahl/halo ratio near the Sun. As at greater heliocentric distances, the core has a sunward drift relative to the proton frame, which balances the current carried by the strahl, satisfying the zero-current condition necessary to maintain quasi-neutrality. Many characteristics of the electron distributions near perihelion have trends with solar wind flow speed, β e , and/or collisional age. Near the Sun, some trends not clearly seen at 1 au become apparent, including anticorrelations between wind speed and both electron temperature and heat flux. These trends help us understand the mechanisms that shape the solar wind electron distributions at an early stage of their evolution.

Morning Overshoot of Electron Temperature as Observed by the Swarm Constellation and the International Space Station

AbstractThe rapid increase of electron temperature in the early morning hours at low latitudes is a well‐known ionospheric phenomenon called morning overshoot. In this study, we extensively investigate the dependence of morning overshoot on local time, season, latitude/longitude/altitude, and magnetic activity. The electron temperature and density data set used in this study are obtained from (1) the Swarm constellation at two different altitudes of 470 and 520 km with identical payloads and (2) the Floating Potential Measurement Unit onboard International Space Station at an altitude of 400 km. Based on the data between 2014 and 2019, the main findings of this study are as follows: (1) on a global average, morning overshoot generally weakens with decreasing altitudes. (2) Morning overshoot is stronger around the dip equator than at midlatitude regions. As latitude increases, the overshoot decreases gradually and shifts to later local times. (3) In off‐equatorial regions the overshoot is stronger in the winter than in the summer hemisphere, especially at higher altitudes. (4) Lastly, the morning overshoot shows multiday oscillations, which are negatively correlated with plasma density and affected by geomagnetic activity.

Estimation of tungsten production from the upper divertor in EAST during edge localized modes**Project supported by the National Key R&D Program of China (Grant Nos. 2017YFE0300400 and 2017YFE0301300), the National Natural Science Foundation of China (Grant Nos. 11475223 and 11775257), the National Magnetic Confinement Fusion Science Program of China (Grant No. 2015GB101003), and also partly supported by AHNSF of China

During edge localized modes (ELMs), the sheath evolution in front of the Experimental Advanced Superconducting Tokamak (EAST) upper divertor is studied to estimate the sputtered tungsten (W) atoms from the divertor target. A large potential drop across the sheath is formed during ELMs by compared with inter-ELMs, and the maximum of sheath potential drop can exceed one thousand of eV in current EAST operation. Due to the enhancement of the sheath potential drop during ELMs, the W physical sputtering yield from the deuterium (D) ions and the impurity ions on the upper divertor target is found to be significant. It is established that the sputtered W yield during ELMs is at least higher by an order of magnitude than inter-ELMs, and D ions and carbon (C) ions are the main ions governing the W production for the current H-mode with ELMs discharges. With increase in the pedestal electron temperature, the maximum of the D and C ion impact energy during ELMs shows a nearly linear increase, and the D ions have sufficient impact energy to cause the strong W physical sputtering. As a consequence, the D ions may dominate the sputtered W flux from the divertor target when the C concentration is controlled less than one percent for the higher heating power H-mode with ELM discharges in near future.

Centre-to-Limb Brightness Variations from the Atacama Large Millimeter-Submillimeter Array (ALMA) Full-Disk Solar Images

Science Verification (SV) data of solar observations with the Atacama Large Millimeter-submillimeter Array (ALMA) telescope have been released to the scientific community. Understanding the centre-to-limb brightness function is necessary to compare features in full-disk images. Our goals are to find the empirical centre-to-limb brightness functions in two available spectral bands and create flattened images with centre-to-limb brightness variations removed. We used a second-order polynomial fit of the cosine of incidence angle to data points as a function of radial distance to the centre of the solar disk. The method also includes iterative removal of outliers based on the inter-quartile range. Fitting functions for all available images proved to describe the data adequately with comparatively small errors in the fitting coefficients. In both bands we found brightening towards the limb, which is a consequence of the increase in electron temperature with radial distance in this region of the solar atmosphere. This study found that the brightness temperature $[T_{\mathrm{b}}]$ of an active region has about 180 K difference between estimates with and without the limb brightening at radial distance ${\approx}\,0.75~\mbox{R}_{\odot }$ in Band 6. We also made flattened images with limb brightening removed. The limb-brightening effect in ALMA images is significant enough (of the order of 10% for Band 3 and about 15% in Band 6) that it cannot be neglected in further analyses. Since the effect of the side lobes was not included in this study, these values probably represent the lower limit of the limb brightening. The shape of the limb-brightening function can also be used to constrain electron densities and temperatures in various layers of the solar atmosphere.

Case studies: A possible mechanism for F2-lacuna formation

Two cases of F2-lacuna and their simultaneous ionospheric convection and TEC variations were presented to further understand F2-lacuna formation mechanism. Both cases of F2-lacuna are accompanied by decreased electron density and increased plasma flow. Through analyzing the role of convection electric field in the formation of F2-lacuna, an explanation for F2-lacuna formation was provided. The joule heating and frictional heating ascribed to the strengthened electric field causes the increase of electron and ion temperature, which subsequently, causes the enhancements of the recombination rate and the upflow of the O+ density resulting in decreased O+ density in F2 region.

Investigation of multi-component magnetized plasma interaction with the carbon surface

The proper understanding of magnetized plasma wall-interaction is important in various plasma applications such as surface modifications, sputtering and etching. A multi-component plasma interacting with carbon surface in presence of an oblique magnetic field has been investigated using three-fluids model. In the present case, the plasma is assumed to consist of two species of positive ions (H+ and He+) and electrons. The governing equations are solved numerically for given initial and boundary conditions. The results show that the magnitude of sheath potential increases with the increase in electron temperature and it affects velocity of both ion species, which is crucial in the understanding of plasma wall-transition mechanism. The reflection coefficients of lighter and heavier ions for the carbon surface decrease with the increase in ion velocity and in reduced energy; however the lighter ions are reflected more than the heavier ions. Hence, the absorption coefficients of both the ions increase for the increase in ion velocity and reduced energy as well. Furthermore, the reflection coefficient of hydrogen ions is about 20% more in magnitude than that of helium ions for the carbon surface.

Characteristics of the Ionospheric Mid-Latitude Trough Measured by Topside Sounders in 1960–70s

The ionospheric mid-latitude trough (IMT) is the electron density depletion phenomenon in the F region during nighttime. It has been suggested that the IMT is the result of complex plasma processes coupled to the magnetosphere. In order to statistically investigate the characteristics of the IMT, we analyze topside sounding data from Alouette and ISIS satellites in 1960s and 1970s. The IMT position is almost constant for seasons and solar activities whereas the IMT depth ratio and the IMT feature are stronger and clearer in the winter hemisphere under solar minimum condition. We also calculated transition heights at which the densities of oxygen ions and hydrogen/helium ions are equal. Transition heights are generally higher in daytime and lower in nighttime, but the opposite aspects are seen in the IMT region. Utilizing the Incoherent Scatter Radar (ISR) electron temperature measurements, we find that the electron temperature in the IMT region is enhanced at night during winter. The increase of electron temperature may cause fast transport of the ionospheric plasma to the magnetosphere via ambipolar diffusion, resulting in the IMT depletion. This mechanism of the IMT may work in addition to the simply prolonged recombination of ions proposed by the traditional stagnation model.

Spectroscopic study the plasma parameters for SnO2 doped ZnO prepared by pulse Nd:YAG laser deposition

In this work, plasma parameters such as (electron temperature (Te), electron density (ne), plasma frequency (fp) and Debye length (λD)) were studied using spectral analysis techniques. The spectrum of the plasma was recorded with different energy values, SnO2 and ZnO anesthetized at a different ratio (X = 0.2, 0.4 and 0.6) were recorded. Spectral study of this mixing in the air. The results showed electron density and electron temperature increase in zinc oxide: tin oxide alloy targets. It was located that The intensity of the lines increases in different laser peak powers when the laser peak power increases and then decreases when the force continues to increase.

The local nature of the plasma response to cold pulses with electron and ion heating at ASDEX Upgrade

In low density Ohmic heated tokamak plasmas a fast increase of the central electron temperature is regularly observed in response to a drop at the edge produced by the cold pulse of an impurity ablation. This observation has challenged the physical understanding and the theory-based local transport modelling for several decades. Recent experimental results in C-Mod and related modelling (Rodriguez-Fernandez et al 2018 Phys. Rev. Lett. 120 075001) have for the first time provided an explanation for this phenomenology, which results from the stabilization of trapped electron mode turbulence caused by the sudden flattening of the electron density profile as a consequence of the impurity ablation. Starting from this breakthrough result, recent cold pulse experiments in ASDEX Upgrade produced by laser ablation of carbon in deuterium plasmas demonstrate that the fast increase of the central electron temperature is only observed in the presence of dominant electron heating, whereas no fast increase is observed in dominantly ion heated plasmas, even at the same low density. The measured fast flattening of the density profile is shown to be large enough to produce a strong stabilization of the trapped electron mode turbulence in the case where the electron temperature largely exceeds the ion temperature, allowing the fast increase of the central electron temperature, consistent with the C-Mod modelling results. In contrast, it produces a destabilization of the electron temperature gradient modes when the electron and ion temperatures are closer, preventing the increase of the central electron temperature. Finally, modelling which also includes the dynamical evolution of the density profile with a local theory-based transport model shows that the impurity penetration transiently modifies the local turbulence causing a fast penetration of the particles, which explains the observation of a very fast flattening of the electron density profile. By this, the complex density and temperature behaviours in response to a cold pulse are demonstrated to be fully explained by multi-channel interactions within a local model.

Terahertz wave generation by photo mixing of radially polarized hollow sinh super-Gaussian lasers in hot plasma

An analytical model for forward emission of radially polarized terahertz (THz) wave emission by photo mixing of two-color, radially polarized lasers having hollow sinh super-Gaussian envelopes in hot plasma with periodic density is developed. THz field distribution is optimized with the help of laser envelope parameters. Numerical investigations show that THz field amplitude is maximum at (resonant excitation). Our investigations show that THz field amplitude increases with electron temperature without affecting resonance condition. The position of THz field peaks shifts with laser parameters (i.e., orders of hollow sinh and super-Gaussian, respectively) but not with electron temperature. It is also found that THz conversion efficiency increases manifold with the increase in electron temperature.

Predict-first experiments and modeling of perturbative cold pulses in the DIII-D tokamak

Cold pulses are introduced in Ohmic DIII-D tokamak plasmas via injection of impurities with a laser blow-off system, revealing for the first time in this machine a quick increase in core electron temperature shortly after the edge cold-pulse injection at low collisionality. The experimental results are consistent with predict-first simulations of heat transport enabled by the Trapped Gyro-Landau-Fluid transport model. Measurements of electron density evolution during the cold-pulse propagation are enabled by a high time resolution density profile reflectometer. The density evolution reveals the quick propagation of a pulse from edge to core, which is a mechanism to transiently increase core temperature in low-collisionality plasmas. Local transport simulations with measured density evolution demonstrate that the core temperature response can indeed be explained by the stabilization of Trapped Electron Mode turbulence at low collisionality, thus providing confidence that local transport modeling is enough to explain cold-pulse propagation and associated phenomenology.

Effect of Nitrogen Addition on Electron Density and Temperature of Cascaded Arc Argon Discharge Plasma Diagnosed by Laser Thomson Scattering

The electron density and electron temperature of the recombining argon plasma from a cascaded arc discharge source were measured by the laser Thomson scattering approach. In this paper, a small amount of nitrogen gas was introduced into the argon discharge source. The addition of the nitrogen gas was applied to investigate the change of the plasma parameters in terms of electron density and temperature. The measurements showed that the electron density dropped by 2 orders of magnitude at 10% nitrogen gas addition compared with no nitrogen addition. The dissociative recombination following the charge transfer between atomic ions and nitrogen molecules was responsible for the decrease of electron density. In addition, with the increase of nitrogen gas addition, the measurements indicated that the electron temperature first increased to a maximum and then decreased. This was due to that the superelastic collision between the electrons and the highly excited vibrational nitrogen molecules could heat the electrons leading to the increase of electron temperature while the electron-vibrational energy transfer by electron–nitrogen molecules impact excitation resulted in that electron temperature decreased due to electrons’ kinetic energy losing processes.

Atomic modeling of photoionization fronts in nitrogen gas

Photoionization fronts play a dominant role in many astrophysical environments but remain difficult to achieve in a laboratory experiment. Recent papers have suggested that experiments using a nitrogen medium held at ten atmospheres of pressure which is irradiated by a source with a radiation temperature of TR ∼ 100 eV can produce viable photoionization fronts. We present a suite of one-dimensional numerical simulations using the Helios multimaterial radiation hydrodynamics code that models these conditions and the formation of a photoionization front. We study the effects of varying the atomic kinetics and radiative transfer model on the hydrodynamics and ionization state of the nitrogen gas, finding that more sophisticated physics, in particular, a multi-angle long characteristic radiative transfer model and a collisional-radiative atomics model, dramatically changes the atomic kinetic evolution of the gas. A photoionization front is identified by computing the ratios between the photoionization rate, the electron impact ionization rate, and the total recombination rate. We find that due to the increased electron temperatures found using more advanced physics that photoionization fronts are likely to form in our nominal model. We report the results of several parameter studies. In one of these, the nitrogen pressure is fixed at ten atmospheres and the source radiation temperature is varied, while in another, the temperature is fixed at 100 eV and the nitrogen pressure is varied. Lower nitrogen pressures increase the likelihood of generating a photoionization front while varying the peak source temperature has little effect.