Electron Density Fluctuations Research Articles

Electron Density Fluctuations and Phase Transition in α-Titanium

Electron Density Fluctuations and Phase Transition in α-Titanium

Deriving the bulk properties of solar wind electrons observed by Solar Orbiter

Context.We demonstrate the calculation of solar wind electron bulk parameters based on recent observations by Solar Wind Analyser – Electron Analyser System on board Solar Orbiter. We use our methods to derive the electron bulk parameters in a time interval spanning several hours. We attempt a preliminary examination of the polytropic behavior of the electrons by analyzing the derived electron density and temperature. Moreover, we discuss the challenges in analyzing the observations due to the spacecraft charging and photo-electron contamination in the energy range below 10 eV.Aims.We derived bulk parameters for thermal solar wind electrons by analyzing Solar Orbiter observations and we investigated whether there is any typical polytropic model that is applicable to the electron density and temperature fluctuations.Methods.We used the appropriate transformations to convert the observations to velocity distribution functions in the instrument frame. We then derived the electron bulk parameters by: (a) calculating the statistical moments of the constructed velocity distribution functions and (b) fitting the constructed distributions with analytical expressions. We first tested our methods by applying them to an artificial data set, which we produced by using the forward modeling technique.Results.The forward model validates the analysis techniques we use to derive the electron bulk parameters. The calculation of the statistical moments and the fitting method determines bulk parameters that are identical (within the uncertainty limits) to the input parameters that we use to simulate the plasma electrons in the first place. An application of our analysis technique to the data reveals a nearly isothermal electron “core”. The results are affected by the spacecraft potential and the photo-electron contamination, which should be characterized in detail as part of future analyses.

Simulation of transport in the FT-2 tokamak up to the electron scale with GENE

Prior experimental work on the FT-2 tokamak has observed electron density fluctuations at electron Larmor radius scales using the enhanced scattering (ES) diagnostic (Gusakov et al 2006 Plasma Phys. Control. Fusion 48 A371–6, Gurchenko and Gusakov 2010 Plasma Phys. Control. Fusion 52 124035). Gyrokinetic GENE simulations of conditions at the upper hybrid resonance layer probed by the ES diagnostic show the presence of the anticipated turbulence from the electron temperature gradient (ETG) driven instability in linear and nonlinear simulations. Ion-scale turbulence is responsible for majority of the transport via trapped electron modes, while impurities act to merge the spectrum of the ion and the electron scale instabilities into a continuum. The linear spectrum at electron scales is characterized by maximal growth rate at a significant ballooning angle θ 0, and at ion scales the turbulence is broad in the ballooning angle distribution. The neoclassical shearing rate obtained from GENE breaks symmetry in nonlinear simulations of ETG turbulence, which manifests itself as an asymmetric turbulence spectrum. The electron density fluctuation spectrum obtained with GENE corresponds well to the ES measurement at electron scales, as do the fluxes obtained from the ion-scale simulations.

Statistical Measurements of Dispersion Measure Fluctuations in Fast Radio Bursts

Abstract Extragalactic fast radio bursts (FRBs) have large dispersion measures (DMs) and are unique probes of intergalactic electron density fluctuations. By using the recently released First CHIME/FRB Catalog, we reexamined the structure function (SF) of DM fluctuations. It shows a large DM fluctuation similar to that previously reported in Xu & Zhang, but no clear correlation hinting toward large-scale turbulence is reproduced with this larger sample. To suppress the distortion effect from FRB distances and their host DMs, we focus on a subset of CHIME catalog with DM < 500 pc cm−3. A trend of nonconstant SF and nonzero correlation function (CF) at angular separations θ less than 10° is seen, but with large statistical uncertainties. The difference found between SF and that derived from CF at θ ≲ 10° can be ascribed to the large statistical uncertainties or the density inhomogeneities on scales on the order of 100 Mpc. The possible correlation of electron density fluctuations and inhomogeneities of density distribution should be tested when several thousands of FRBs are available.

Magnetoresistance anisotropy in ErB12 antiferromagnetic metal: The evidence for dynamic charge stripes

The nature of charge transport and magnetization anisotropy was investigated in the ErB12 antiferromagnetic metal with both cooperative Jahn-Teller distortions of the fcc crystal structure and electronic instability (dynamic charge stripes). A butterfly pattern of the H-φ magnetic phase diagram in the (1 1 0) plane was reconstructed, including a large number of different magnetic phases separated from each other by radial and circular boundaries. It is argued that fluctuations of electron density are responsible for the suppression of the indirect Ruderman-Kittel-Kasuya-Yoshida (RKKY) exchange between the nearest neighbored Er3+ ions located along the 〈110〉 directions producing the magnetic phase diversity in ErB12.

Linearized spectrum correlation analysis for thermal helium beam diagnostics.

We introduce a new correlation analysis technique for thermal helium beam (THB) diagnostics. Instead of directly evaluating line ratios from fluctuating time series, we apply arithmetic operations to all available He I lines and construct time series with desired dependencies on the plasma parameters. By cross-correlating those quantities and by evaluating ensemble averages, uncorrelated noise contributions can be removed. Through the synthetic data analysis, we demonstrate that the proposed analysis technique is capable of providing the power spectral densities of meaningful plasma parameters, such as the electron density and the electron temperature, even under low-photon-count conditions. In addition, we have applied this analysis technique to the experimental THB data obtained at the ASDEX Upgrade tokamak and successfully resolved the electron density and temperature fluctuations up to 90 kHz in a reactor relevant high power scenario.

Diagnostics of Es Layer Scintillation Observations Using FS3/COSMIC Data: Dependence on Sampling Spatial Scale

The basic theory and experimental results of amplitude scintillation from GPS/GNSS radio occultation (RO) observations on sporadic E (Es) layers are reported in this study. Considering an Es layer to be not a “thin” irregularity slab on limb viewing, we characterized the corresponding electron density fluctuations as a power-law function and applied the Ryton approximation to simulate spatial spectrum of amplitude fluctuations. The scintillation index S4 and normalized signal amplitude standard deviation S2 are calculated depending on the sampling spatial scale. The theoretical results show that both S4 and S2 values become saturated when the sampling spatial scale is less than the first Fresnel zone (FFZ), and S4 and S2 values could be underestimated and approximately proportional to the logarithm of sampled spatial wave numbers up to the FFZ wave number. This was verified by experimental analyses using the 50 Hz and de-sampled FormoSat-3/Constellation Observing System for Meteorology, Ionosphere and Climate (FS3/COSMIC) GPS RO data in the cases of weak, moderate, and strong scintillations. The results show that the measured S2 and S4 values have a very high correlation coefficient of >0.97 and a ratio of ~0.5 under both complete and undersampling conditions, and complete S4 and S2 values can be derived by dividing the measured undersampling S4 and S2 values by a factor of 0.8 when using 1-Hz RO data.

Impact of the mole fraction modulation on the RF/DC performance of GaAs1−xSbx FinFET

AbstractThe impact of mole fraction variation on the RF/DC performance of GaAs1−xSbx‐based FinFET has been examined in this study. Changing the Sb mole fraction has substantial effect on the electronic band parameters of GaAs, which directly affects the device performance. Electrical properties of the device including electron density and mobility fluctuation are investigated as a function of Sb mole fraction. Additionally, device DC performance parameters such as the ION/IOFF ratio, threshold voltage, transconductance, and device node capacitance, such as Cgg and Cds, are studied using a technology computer‐aided design (TCAD) simulator. The mole fraction dependence of the gate capacitance dictates the application of the proposed FinFET in the RF and high‐frequency domains. A detailed investigation of the figures of merits such as intrinsic gain, intrinsic delay, dynamic power dissipation, power delay product, energy dissipation, and unity gain bandwidth reveals that GaAsSb can be a potential material for realization of low‐power analog and digital circuits. The proper tuning of the mole fraction can help to optimize the device performance.

Constraining reionization with the first measurement of the cross-correlation between the CMB optical-depth fluctuations and the Compton y -map

We propose a new reionization probe that uses cosmic microwave background (CMB) observations; the cross-correlation between fluctuations in the CMB optical depth which probes the integrated electron density, $\delta\tau$, and the Compton $y$-map which probes the integrated electron pressure. This cross-correlation is much less contaminated than the $y$-map power spectrum by late-time cluster contributions. In addition, this cross-correlation can constrain the temperature of ionized bubbles while the optical-depth fluctuations and kinetic SZ effect can not. We measure this new observable using a Planck $y$-map as well as a map of optical-depth fluctuations that we reconstruct from Planck CMB temperature data. We use our measurements to derive a first CMB-only upper limit on the temperature inside ionized bubbles, $T_{\rm b}\lesssim 7.0\times10^5\,$K ($2\,\sigma$). We also present future forecasts, assuming a fiducial model with characteristic reionization bubble size $R_{\rm b}=5\,$Mpc and $T_{\rm b}=5\times10^4\,$K. The signal-to-noise ratio of the fiducial cross-correlation using a signal dominated PICO-like $y$-map becomes $\simeq7$ with CMB-S4 $\delta\tau$ and $\simeq13$ with CMB-HD $\delta\tau$. For the fiducial model, we predict that the CMB-HD $-$ PICO cross-correlation should achieve an accurate measurement of the reionization parameters; $T_{\rm b}\simeq 49800^{+4500}_{-5100}\,$K and $R_{\rm b}\simeq 5.09^{+0.66}_{-0.79}\,$Mpc. Since the power spectrum of the electron density fluctuations is constrained by the $\delta\tau$ auto spectrum, the temperature constraints should be only weakly model-dependent on the details of the electron distributions and should be statistically representative of the temperature in ionized bubbles during reionization. This cross-correlation could, therefore, become an important observable for future CMB experiments.

Scattering of ultrashort laser pulses on plasmons in a Maxwellian plasma

On the basis of equations obtained in the framework of second-order quantum-mechanical perturbation theory, the standard approach to the calculation of scattering radiation probability is extended to the case of ultrashort laser pulses. We investigate the mechanism of the appearance of plasmon peaks in the spectrum of the plasma form factor for different parameters of the problem. For the case in which scattering on plasmons dominates over scattering on electron density fluctuations caused by chaotic thermal motion, we derive analytical expressions describing the scattering probability of ultrashort laser pulses on plasmons. Together with this, we obtain a simple expression connecting the frequency of scattered radiation and the energy transmitted from the incident pulse to plasmon, and vice versa. In considering the scattering probability, our emphasis is on the dependence on the pulse duration. We assess in detail the trends of this dependence for various relations between pulse carrier frequency and plasmon energy.

An FFT overlap method for high bandwidth far-infrared laser Interferometer in HL-2A

A novel Real-Time High Bandwidth Phasemeter (RHBP) system has been developed for far-infrared laser interferometer in HL-2A tokamak. To meet the requirement of high-precision electron density fluctuation diagnostics, the system is based on the FFT overlap method, which can suppress the measurement error in high-bandwidth mode. The system consists of four Real-time Signal Conditioning (RSC) Modules and four RHBP Modules for high spatial resolution. Benefiting from the field-programmable gate array (FPGA) platform, the proposed method can be implemented with low noise and low cost. Experimental results suggest that the density resolution is 1.79× 1015/m-3 in high-bandwidth mode, which indicates that the proposed RHBP system achieves high performance for high-frequency fluctuation measurement.

Turbulence and Intermittency in the Winter Cusp Ionosphere Studied With the ICI Sounding Rockets

AbstractThe characteristics of turbulent plasma in the winter cusp ionosphere is studied based on in‐situ data from the Investigation of Cusp Irregularities (ICI) sounding rockets. The electron density fluctuations from ICI‐2 and ICI‐3 missions have been analyzed for the whole flight, using advanced time‐series analysis techniques. The analysis of the autocorrelation scale is indicative of the turbulence integral scale and marks the onset of the turbulent cascade from large to small scales in the power spectrum density of the rocket data. The power spectrum is typical for a turbulent field. The turbulent structures are persistent in the data, which are quantified by analyzing the Probability Distribution Functions (PDFs) and their deviations from the Gaussian distribution. The kurtosis analysis indicates the presence of intermittency. These results are compared with the Local Intermittence Measure ‐ LIM, which confirms the presence of small scale intermittent structures. The turbulence measured by rockets appears well developed and covers frequencies between 1 Hz and several hundred Hz. There is a good agreement with the previous results, suggesting that density fluctuations in the ionospheric cusp agree with the turbulence framework in which intermittent processes transfer energy across different scales.

On frequency-independent horn antenna design for plasma positioning reflectometers, from simulation to prototype testing

Using a new framework for horn antenna optimization, a first frequency-independent horn antenna for a plasma positioning reflectometer (PPR) is designed.This hardware optimization is a new approach aiming on lowering the computational complexity of PPR interpretative models able to extract profiles and fluctuations of electron density and temperature from reflectometry measurements. PPR measurements are a strong candidate to provide real-time feedback for plasma position control in long-discharge fusion tokamaks such as ITER and DEMO, which requires fast interpretative models. Reducing the computational complexity of these models is therefore critical.In this paper, ray tracing simulations in the poloidal plane are used to compare different radiation patterns and evaluate them on multiple performance criteria. An antenna shape leading to a frequency-independent far-field radiation diagram is found with the PROFUSION optimizer and a prototype of this antenna is tested against an unoptimized conical reference antenna.The ray tracing performance criteria indicate that fundamental Gaussian frequency-independent antennas perform well, albeit in general worse than same-sized frequency-dependent antennas. Furthermore, it is seen that the pyramidal ITER gap 6 antenna performs well given the spatial constraints and that more performant antennas could be used, when more space was available.The prototype testing reveals challenges in obtaining frequency-independent characteristics within a tokamak blanket environment, which is additionally complicated by misalignment risks.

Influence of magnetic shielding on electron dynamics characteristics of Penning ion source

The dynamic behaviors of electrons in a miniature Penning ion source model are analyzed by the particle in cell/Monte Carlo collision particle simulation method combined with the scalar magnetic potential finite-difference method. Mainly, the influence of magnetic shielding on the trajectory and spatial distribution of electrons in the discharge process is taken into consideration. The influence of magnetic shielding on the plasma impedance during the excitation discharge of the Penning source is further discussed. The calculated target current is in good agreement with the experimental value. The simulation results show that the addition of magnetic shielding can reduce the fluctuation of electron density, increase the uniformity of electron spatial distribution, and double the plasma impedance stabilization zone, which are beneficial to the stability of the discharge process in the source. However, the magnetic shielding can cause a decrease in the electron density, which limits the plasma ionization degree. The study on magnetic shielding helps to understand the electron dynamics characteristics of the Penning ion source and provides a reference for improving the source performance in the future.

Engineering of Interfacial Energy Bands for Synthesis of Photoluminescent 0D/2D Coupled MOF Heterostructure with Enhanced Selectivity toward the Proton-Exchange Membrane.

Engineering of the interface for tuning the structural, functional, and electronic properties of materials via the formation of heterostructure composites exhibits immense potential in the current research scenario. This study reports a novel ternary composite synthesized by decoration of zero-dimensional Pd nanoparticles (NPs) and two-dimensional (2D) graphite oxide (GO) sheets in the UiO-66 metal-organic framework (MOF). A mixed matrix membrane was fabricated by incorporating this composite in the SPEEK polymer matrix, which exhibited higher selectivity compared to commercial Nafion 117. The synthesized composite and fabricated membranes were thoroughly characterized in terms of their chemical structures, microstructural morphologies, physicochemical, thermal, photo-electrochemical, and optical properties, ion-exchange capacity, proton conductivity, and methanol permeability. As per our knowledge, this is the first study which explores the effect of noble metal NPs and carbon 2D material simultaneously on the electronic structure of the MOF, resulting in improved selectivity. The electron-accepting nature of GO and surface plasmon resonance effect of Pd alter the energy band positions and scavenge the electrons, improving the proton conduction of the composite. The introduction of oxygen vacancies in lattice leads to efficient charge separation. The formation of a Schottky junction results in the localized electric field effect due to electron density fluctuation which aids in ion transport. The current study opens up a new route to overcome the major challenge associated with direct methanol fuel cells (DMFCs), that is, high/low methanol crossover by improving the proton conduction.

Millimeter-wave beam scattering and induced broadening by plasma turbulence in the TCV tokamak

The scattering of millimeter-wave beams from electron density fluctuations and the associated beam broadening are experimentally demonstrated. Using a dedicated setup, instantaneous deflection and (de-)focusing of the beam due to density blobs on the beam path are shown to agree with full-wave simulations. The detected time-averaged wave power transmitted through the turbulent plasma is reproduced by the radiative-transfer model implemented in the WKBeam code, which predicts a ∼50% turbulence-induced broadening of the beam cross-section. The role of core turbulence for the considered geometry is highlighted.

Implementation and data processing of a five-channel microwave interferometer with high temporal resolution and low noise on Sino-UNIted Spherical Tokamak.

A five-channel microwave interferometer with high temporal resolution and high phase resolution has been developed for measuring electron density profiles and fluctuations on the Sino-UNIted Spherical Tokamak. A correction algorithm, based on the low signal amplitude detection, is proposed to eliminate the fringe jump errors. The correction algorithm achieves an accuracy of 92%. The density profile is reconstructed through the Park-matrix method, with the geometry of magnetic surfaces calculated by the equilibrium fitting. The reconstructed density profiles for discharges with supersonic molecular beam injection are in good agreement with the results of another 94GHz single-channel horizontal interferometer and the Langmuir probes. The temporal resolution of the system is 0.5 µs and the line-integrated electron density resolution is 1 × 1015m-2, which benefits from the single sideband modulation technique. Therefore, the multichannel interferometer system is capable of studying the details of the high-frequency (up to 200 kHz) density fluctuation such as that in the minor disruption event.

Design of microwave broadband CMOS transmitter and receiver circuits for MIR and ECEI plasma diagnostics.

To efficiently determine the plasma electron density fluctuations using the MIR diagnostic technique, a 55-75GHz 65 nm-CMOS transmitter has been developed where four separate intermediate frequency (IF) signals are up-converted, amplified, and then combined to generate an 8-tone RF output; a broadband 90 nm-CMOS receiver has also been constructed, which consists of an RF-low noise amplifier (LNA), mixer, and IF amplifier. The circuits and their corresponding modules will soon be deployed on the DIII-D and NSTX-U fusion devices. A 110-140GHz 65 nm-CMOS receiver has also been designed, which is suitable for measuring the deep-core temperature fluctuations in the DIII-D tokamak using the electron cyclotron emission imaging diagnostic system. In addition to the RF-LNA/balun, mixer, and IF amplifier, an LO balun/tripler and driving amplifier are now included in this highly integrated circuit chip. By adopting the microwave and millimeter-wave system-on-chip concept in the front-end system design, this paper demonstrates that compact transmitter and receiver modules can be easily built, which, in turn, facilitates array implementation and maintenance.

Looking for a proxy of the ionospheric turbulence with Swarm data

The present work focuses on the analysis of the scaling features of electron density fluctuations in the mid- and high-latitude topside ionosphere under different conditions of geomagnetic activity. The aim is to understand whether it is possible to identify a proxy that may provide information on the properties of electron density fluctuations and on the possible physical mechanisms at their origin, as for instance, turbulence phenomena. So, we selected about 4 years (April 2014–February 2018) of 1 Hz electron density measurements recorded on-board ESA Swarm A satellite. Using the Auroral Electrojet (AE) index, we identified two different geomagnetic conditions: quiet (AE < 50 nT) and active (AE > 300 nT). For both datasets, we evaluated the first- and second-order scaling exponents and an intermittency coefficient associated with the electron density fluctuations. Then, the joint probability distribution between each of these quantities and the rate of change of electron density index was also evaluated. We identified two families of plasma density fluctuations characterized by different mean values of both the scaling exponents and the considered ionospheric index, suggesting that different mechanisms (instabilities/turbulent processes) can be responsible for the observed scaling features. Furthermore, a clear different localization of the two families in the magnetic latitude—magnetic local time plane is found and its dependence on geomagnetic activity levels is analyzed. These results may well have a bearing about the capability of recognizing the turbulent character of irregularities using a typical ionospheric plasma irregularity index as a proxy.

Nonlocal effects in negative triangularity TCV plasmas

Global gradient driven gyrokinetic simulations performed with the Gyrokinetic Electromagnetic Numerical Experiment (GENE) code are used to investigate Tokamak à configuration variable (TCV) plasmas with negative triangularity. Considering limited L-mode plasmas, the numerical results are able to reproduce the actual transport level over a major fraction of the plasma minor radius for a plasma with and its equivalent with standard positive triangularity δ. For the same heat flux, a larger electron temperature gradient is sustained by , in turn resulting in an improved electron energy confinement. In agreement with the experiments, a reduction of the electron density fluctuations is also seen. Local flux-tube simulations are used to gauge the magnitude of nonlocal effects. Surprisingly, very little differences are found between local and global approaches for , while local results yield a strong overestimation of the heat fluxes when . Despite the high sensitivity of the turbulence level with respect to the input parameters, global effects appear to play a crucial role in the negative triangularity plasma and must be retained to reconcile simulations and experiments. Finally, a general stabilizing effect of negative triangularity, reducing fluxes and fluctuations by a factor dependent on the actual profiles, is recovered.