Electron Density Measurements Research Articles

A new model for plasmapause locations derived from IMAGE RPI and Van Allen probe data

The outer boundary of the plasmasphere, the plasmapause, is characterized by a sharp electron density gradient that changes under varying space weather conditions. We developed a new model, called Neustrelitz/ESOC PlasmaPause Model (NEPPM), for providing plasmapause location in terms of -shell utilizing electron density measurements from the Van Allen probes from 2012 to 2018 and the IMAGE satellite data from 2001 to 2005. Both datasets were preprocessed, and algorithms were developed for automatic detection of plasmapause location. The suggested model provides a simple ellipse-based approach determined by the semi-major axis, the eccentricity, and the orientation angle of the semi-major axis. The modelled varies as a function of the index and magnetic local time . The NEPPM results are compared with the Global Core Plasma Model (GCPM). The plasmapause bulge in the evening hours follows the level of geomagnetic activity. The NEPPM will complete the NPSM (Neustrelitz PlasmaSphere Model), which was derived from dual-frequency GPS measurements on-board the CHAMP satellite mission.

The electron density at the midpoint of the plasmapause

The high density plasmasphere in the magnetosphere is often separated from a lower density region outside of the plasmasphere, called the plasmatrough, by a sharp gradient in electron density called the plasmapause. Here we use plasmapause events identified from electron density data from the ISEE, CRRES, Polar, and IMAGE missions, and the nonlinear genetic algorithm TuringBot, to find models for the electron density at the midpoint of the plasmapause, ne,pp. A good model for ne,pp should include dependence on L, which is the strongest dependence. But models can be improved by including weaker dependencies on the magnetic local time, MLT, the solar EUV index F10.7, and geomagnetic activity as indicated by averages of Kp and AE. The most complicated model that we present predicts ne,pp within a factor of 1.64, and is within the range of observed plasmapause densities for about 96% of our events. These models can be useful for separating plasma populations into plasmasphere-like and plasmatrough-like populations. We also make available our database of electron density measurements categorized into various populations.

Development of the interferometer control system on HFRC

The CO2 laser interferometer is an important diagnostic system in the HUST Field Reversed Configuration (HFRC) and can provide routine electron density measurement for plasma experiments. A commercial laser (λ = 10.6 μm) with a maximum output power of 20 watts is used as the laser source for the interferometer, which can pose a threat to the safety of experimenters and experimenters' experimental environment. Moreover, most of the components of the system are sensitive to the temperature and humidity of the environment. For the aim of safe and stable operation, it is necessary to develop a CO2 interferometer control system (CICS). A module was innovatively designed with a servo to regulate power according to commands and protect timely when a fault takes place. Additionally, a special device using a stepper motor can automatically regulate and release the laser according to the different stages of the experiment. The hardware design of the CO2 control system incorporates the ESP32 microcontroller, servo and stepper motor, which can automatically monitor, regulate and protect in case a fault takes place. The software implementation of the interaction is based on the OneNET platform and is first used on the CO2 interferometer, linking in the Internet based on Internet of Things (IoT) technologies to each sensor and device in the control system, which can achieve visualization monitoring and remote control. With the operation of CICS, the CO2 interferometer can run stably and be timely protected.

Real-Time Data Processing Method for CO2 Dispersion Interferometer on EAST

Abstract In this paper, a real-time data processing system is designed for the carbon dioxide dispersion interferometer (CO2-DI) on EAST to measure electron density and provide real-time feedback control. The system utilizes the parallel and pipelining capabilities of Field-Programmable Gate Array (FPGA) to digitize and process the intensity of signals from the detector. Finally, the real-time electron density signals are exported through a Digital-to-Analog Converter (DAC) module in the form of analog signals. The system has been successfully applied in the CO2-DI system to provide low-latency electron density data to the plasma control system on EAST. Experimental results of the latest campaign with long-pulse discharges on EAST (2022-2023) demonstrate that the system can respond effectively in the case of rapid density changes, which means it is reliable and accurate for future electron density calculation.

Electron density measurements in low-pressure plasmas using cutoff probes and comparison with hairpin and Langmuir probes

Electron density measurements in low-pressure plasmas using cutoff probes and comparison with hairpin and Langmuir probes

Two-dimensional Thomson scattering measurements of misaligned electron density and temperature gradients and associated Biermann battery produced fields

Two-dimensional Thomson scattering measurements of misaligned electron density and temperature gradients and associated Biermann battery produced fields

Spatio-temporal analysis of power deposition and vibrational excitation in pulsed N2 microwave discharges from 1D fluid modelling and experiments

Vibrational excitation of N2 beyond thermodynamic equilibrium enhances the reactivity of this molecule and the production of radicals. Experimentally measured temporal and spatial profiles of gas and vibrational temperature show that strong vibrational non-equilibrium is found in a pulsed microwave discharges at moderate pressure (25 mbar) in pure N2 outside the plasma core and as an effect of power pulsing. A one dimensional radial time-resolved self-consistent fluid model has been developed to study the mechanism of formation of vibrationally excited N2. In addition to the temperature maps, time-resolved measurements of spontaneous optical emission, electron density and electron temperature are used to validate the model and the choice of input power density. The model reveals two regions in the plasma: a core where chemistry is dominated by power deposition and where vibrational excitation starts within the first ∼10 µs and an outer region reliant on radial transport, where vibrational excitation is activated slowly during the whole length of the pulse (200 µs). The two regions are separated by a sharp gradient in the estimated deposited power density, which is revealed to be wider than the emission intensity profile used to estimate the plasma size. The low concentration of excited species outside the core prevents the gas from heating and the reduced quenching rates prevent the destruction of vibrationally excited N2, thereby maintaining the observed high non-equilibrium.

RF antenna helicity dependent particle heating in a helicon source

Experiments have demonstrated that ion phenomena, such as the lower hybrid resonance, play an important role in helicon source operation. Damping of the slow branch of the bounded whistler wave at the edge of a helicon source (i.e. the Trivelpiece-Gould mode) has been correlated with the creation of energetic electrons, heating of ions at the plasma edge, and anisotropic ion heating. Here we present ion velocity distribution function measurements, electron density and temperature measurements, and magnetic fluctuation measurements on both sides of an m=|1| helical antenna in a helicon source as a function of the driving frequency, magnetic field strength, and magnetic field orientation relative to the antenna helicity. Significant electron and ion heating (up to two times larger) occurs on the side of the antenna consistent with the launch of the m=+1 mode. The electron and ion heating occurs within one electron skin depth of the plasma edge, where slow wave damping is expected. The source parameters for enhanced particle heating are also consistent with lower hybrid resonance effects, which can only occur for Trivelpiece-Gould wave excitation.

An algorithm to enhance the capability of imaging Thomson scattering

Collective Thomson scattering (TS) is a powerful technique to accurately diagnose the parameters of laser-produced plasmas. However, when the scattering parameter α, which is inverse to the product of electron Debye length and wavenumber of plasma fluctuations, is significantly larger than 1, which of the conditions is easily satisfied in the experiment, the accuracy of electron density measurement is usually poor just with the single-wavenumber ion-acoustic wave feature of the TS spectrum. This situation can be greatly improved in the imaging TS experiment because the signal intensity is proportional to electron density. A novel algorithm is developed and validated for the data analysis of imaging TS through the combination of signal intensity and spectral profile. The results show that we can obtain the electron density with high confidence, as well as other plasma parameters like electron and ion temperatures.

Progress of CO2 Dispersion Interferometer on EAST

A CO2 Dispersion Interferometer (DI) system on the Experimental Advanced Superconducting Tokamak (EAST) was successfully operated, providing plasma electron density measurements. The DI system utilizes a continuous-wave 9.3 μm CO2 laser source to measure line-averaged electron densities. This offers significant advantages, including the ability to minimize fringe jumps and insensitivity to mechanical vibrations. These characteristics are well-suited for future high-density, long-pulse plasma discharges. The DI system provides a real-time density feedback signal to the plasma control system for routine density control during long-pulse operation. Experiments with EAST demonstrated good agreement between the density obtained by the DI system and the preset densities. The DI system also exhibited stability during long-pulse discharge. Moreover, the DI system was stable during rapid density changes and high-density pellet injections. In shot No. 120594, the DI system exhibited stable density feedback during continuous projectile injection lasting over 50 seconds; the line-averaged electron density is approximately 4×1019 m-3. In contrast to the long-wavelength source interferometer, which may deflect light from the detector owing to excessive refraction angles in larger density-gradient discharges, the DI ensured accurate density measurements. The DI system on EAST is dependable for accurately measuring the electron density.

Impact of ambient temperature on the filter polychromators performance and accuracy of thomson scattering diagnostics

Thomson scattering is one of the most important diagnostic methods for measuring plasma electron temperature (Te) and electron density (ne). In the diagnostic system, the polychromator is often used to analyze the spectral broadening and intensity of the detected scattered light. The performance of the avalanche photodiode (APD) used in the polychromator is greatly affected by the ambient temperature. The change of ambient temperature will seriously affect the accuracy of Thomson scattering diagnosis. Through experimental analysis, when the ambient temperature increases, the gain of APD will be significantly reduced, resulting in a significant deviation in electron density measurement. Taking the system response at an ambient temperature of 24.1 °C as reference, the deviation of electron density measurement varies from 43% to −16%, with the ambient temperature from 16.6 °C to 29.9 °C. However, the change of ambient temperature has little impact on the measurement of electron temperature. Detailed test of the polychromator shows that the estimated deviation of the electron temperature is within 3%. Due to the change of ambient temperature, the response of the detectors in each channel of the polychromator is inconsistent, which will cause random errors. The influence on electronic temperature calculation is analyzed by numerical simulation.

Novel approach for optimizing mechanical and damping performance of MABS composites reinforced with basalt fibers: An experimental study

The purpose of this research is to explore how basalt fibers, when compounded in specific proportions, impact the mechanical and damping attributes of methyl methacrylate acrylonitrile butadiene styrene (MABS). The fabrication process involved compounding basalt fibers in a twin-screw extruder at four distinct weight percentages: 5%, 10%, 15%, and 20%, with an MABS matrix. This study uniquely employs a comprehensive suite of characterization techniques including dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), X-ray microcomputed tomography (micro-CT), scanning electron microscopy (SEM), tensile tests, and density measurements to evaluate the composite's performance. The research significantly reveals that the integration of basalt fibers enhances the damping characteristics of MABS composites, as confirmed by DMA. Additionally, micro-CT scans provide unprecedented insights into the uniform distribution of basalt fibers within the MABS matrix, thereby elucidating the underlying mechanisms for the observed improvements. TGA data further bolsters the composite's thermal resilience, revealing its aptitude for high-temperature applications. Our findings establish a novel correlation between the basalt fiber weight percentage and the damping properties, revealing a non-monotonic relationship. This study thus not only augments the understanding of MABS based composites but also opens new avenues for the exploitation of basalt fibers in advanced composite materials, particularly in terms of their damping capabilities.

Метод эффективных вычитаний: работа с данными Иркутского радара некогерентного рассеяния

For incoherent scatter measurements, the effective subtraction technique is to alternate the duration of amplitude-modulated signals between a pair of consequently radiated pulses. The resulting gain of spatial resolution enables us to steadily assess the electron density profile by the Faraday rotation method. The paper describes the electron density measurement technique, which involves analyzing narrow-band signals from Irkutsk Incoherent Scatter Radar, and proposes an automated method of determining the electron density for the problem in which the convolution of the radiated signal waveform with backscatter signal cannot be neglected. The inverse problem of electron density recovery is considered as a standard nonlinear optimization problem, which is solved using the algorithms for global and local optimization applied consequently. We compare the electron density profiles obtained by analyzing different pulse waveforms and from Irkutsk ionosonde data.

Effective subtraction technique: implementation for Irkutsk Incoherent Scatter Radar

For incoherent scatter measurements, the effective subtraction technique is to alternate the duration of amplitude-modulated signals between a pair of consequently radiated pulses. The resulting gain of spatial resolution enables us to steadily assess the electron density profile by the Faraday rotation method. The paper describes the electron density measurement technique, which involves analyzing narrow-band signals from Irkutsk Incoherent Scatter Radar, and proposes an automated method of determining the electron density for the problem in which the convolution of the radiated signal waveform with backscatter signal cannot be neglected. The inverse problem of electron density recovery is considered as a standard nonlinear optimization problem, which is solved using the algorithms for global and local optimization applied consequently. We compare the electron density profiles obtained by analyzing different pulse waveforms and from Irkutsk ionosonde data.

Calibration of Swarm Ion Density, Drift, and Effective Mass Measurements

AbstractWe calibrate the Swarm Langmuir Probe Ion Drift, Density and Effective Mass (SLIDEM) products using the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC‐1) electron density measurements. SLIDEM combines electric current measurements from the Electric Field Instrument faceplate (situated on the ram‐facing side of the satellite) with ion admittance measurements from a spherical Langmuir probe to estimate ionospheric ion density, bulk ion drift parallel to the satellite trajectory in the polar regions, and effective ion mass at low and middle latitudes. SLIDEM processing includes an eight‐parameter empirical geometry model that expresses the corrections to the effective faceplate area and spherical probe radius arising from satellite‐plasma interactions. Validation of SLIDEM density by conjunctions with COSMIC density altitude profiles reveals systematic errors, with SLIDEM underestimating corresponding COSMIC data by around 10%. Using the same conjunctions to calibrate the SLIDEM density processor, a simple one‐parameter geometry model is obtained, which significantly reduces bias in ion density. This leads to reduced bias in the ion ram speed and in the effective mass, both of which are more consistent with empirical ionospheric models. We examined three models characterizing the variation of probe effective electrode current collection areas. Faceplate geometries are statistically indistinguishable from the physical faceplate cross section. Spherical Langmuir probe radius is effectively reduced by about 10% due to satellite‐plasma interactions. We recommend updating the SLIDEM processor to use a smaller value for the spherical probe's radius.

Electron density measurement by the three boundary channels of HCOOH laser interferometer on the HL-3 tokamak

Far-infrared (FIR) interferometer is widely used to measure the electron density in the magnetically confined fusion plasma devices. A new FIR laser interferometer with a total of 13 channels (8 horizontal channels and 5 oblique channels) is under development on the HL-3 tokamak by using the formic-acid laser (HCOOH, f = 694 GHz). In order to investigate the boundary electron density activity during the divertor discharge, three horizontal interferometry channels located at Z = −97, −76, 76.5 cm have been successfully developed on HL-3 in 2023, and put into operation in recent experimental campaign, with a time resolution of < 1.0 μs and line-integrated electron density resolution of ~ 7.0 × 1016 m−2. This paper mainly focuses on the optical design of the three-channel interferometry system, as well as optical elements and recent experimental result on HL-3.

Polarimeter–interferometer diagnostic using terahertz solid-state sources for fluctuation measurements on Keda Torus eXperiment (KTX)

A multi-channel polarimeter–interferometer has been developed on the Keda Torus eXperiment (KTX) for the study of equilibrium dynamics and internal magnetic fluctuations. A three-wave technique based on terahertz solid-state sources (~650 GHz) is applied for simultaneous measurements of electron density and Faraday rotation angle. The output power of the microwave source is 2 mW. Faraday rotation effect using a rotating wave plate is tested with phase noise less than 0.8°, and the density phase noise is less than 0.9°. Measurement of Faraday rotation angle and density for discharges on KTX have demonstrated high sensitivity to internal MHD activities.

Kinetic simulations of low-pressure inductively coupled plasma: an implicit electromagnetic PIC/MCC model with the ADI-FDTD method

Low-pressure inductively coupled plasma (ICP) is promising for space electric propulsion. For the first time, an implicit electromagnetic particle-in-cell Monte Carlo collision model based on the alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method is developed to investigate low-pressure xenon plasma characteristics of a miniature ICP source. The induced simulated electric field is well consistent with that calculated by the finite element method, indicating that this method can provide an accurate estimation of the electromagnetic field. The simulation time step used in the ADI-FDTD method is no longer restricted by the Courant–Friedrichs–Lewy constraints. Compared with the FDTD method, the ADI-FDTD method increases the size of the time step and significantly improves computational efficiency. The method is validated by comparing the simulated and measured electron density and plasma potential profile and reasonable agreement is reached. Therefore, the model is used to investigate the temporal and spatial distribution of plasma properties and the influence of the current amplitude of radio frequency (RF) coil, applied frequency of RF coil and neutral gas pressure on the plasma dynamics in the ionization chamber of a miniature gridded RF ion thruster. To explain the influence of the operating parameters, a concept called ‘the energy relaxation characteristics of electrons in response to the change of electric field’ is proposed and verified. The simulations also find that the oscillation frequency of plasma properties is twice the applied frequency of RF coil. The oscillation characteristics reveal the dynamic energy balance in the ICP. The experiment on the gridded RF ion thruster BHRIT-4 confirms the oscillation by measuring the plasma sheath potential.

Design and development of a single-laser 2D Thomson scattering measurement system for TS-6 merging tokamak/magnetic reconnection experiments

Nd:YAG Thomson scattering diagnostics is reliable measurement of electron temperature and density, but its 2D extension conventionally needs as many polychromators as measuring points and as many lasers as measuring paths. To reduce the numbers and costs, we designed and developed a single-laser 2D measurement system by use of multiple reflection and time-of-flight of laser light. A single laser pulse reflects between mirrors on both sides of the vacuum vessel and makes seven round trips, which enables measurement at m × 7 points with only m polychromators and a single laser. Here, we present the design to satisfy the resolution required for TS-6 merging tokamak and magnetic reconnection experiments and the system development, especially the time-separation of scattered light signals from different points with time-of-flight delays. The measured Thomson scattering signals from 7 × 2 points and the measured Raman scattered signals from points in four laser paths indicate the feasibility of Thomson scattering measurement at m × 4 points.

Validating the simulation of beam-ion charge exchange in MAST Upgrade

Simulation of the impact of charge-exchange (CX) reactions on beam ions in the Mega Amp Spherical Tokamak (MAST) Upgrade was compared to measurements carried out with a fission chamber (neutron fluxes) and a fast ion deuterium-alpha (FIDA) diagnostic. A simple model was developed to reconstruct the outer-midplane neutral density based on measurements of deuterium-alpha emission from edge neutrals, and on Thomson scattering measurements of electron density and temperature. The main computational tools used were the ASCOT orbit-following code and the FIDASIM code for producing synthetic FIDA signals. The neutral density reconstruction agrees qualitatively with SOLPS-ITER modelling and yields a synthetic passive FIDA signal that is consistent with measurement. When CX losses of beam ions are accounted for, predicted neutron emission rates are quantitatively more consistent with measurement. It was necessary to account for CX losses of beam ions in simulations to reproduce the measured passive FIDA signal quantitatively and qualitatively. The results suggest that the neutral density reconstruction is a good approximation, that CX with edge neutrals causes significant beam-ion losses in MAST Upgrade, typically 20% of beam power, and that the ASCOT fast-ion CX model can be used to accurately predict the redistribution and loss of beam ions due to CX.