Radial Profiles Of Electron Temperature Research Articles

Total electron temperature derived from quasi-thermal noise spectroscopy in the pristine solar wind from Parker Solar Probe observations

Aims. We applied the quasi-thermal noise (QTN) method to Parker Solar Probe (PSP) observations to derive the total electron temperature (Te). We combined a set of encounters to make up a 12-day period of observations around each perihelion from encounter one (E01) to ten (E10), with E08 not included. Here, the heliocentric distance varies from about 13 to 60 solar radii (R⊙). Methods. The QTN technique is a reliable tool to yield accurate measurements of the electron parameters in the solar wind. We obtained Te from the linear fit of the high-frequency part of the QTN spectra acquired by the RFS/FIELDS instrument. Then, we provided the mean radial electron temperature profile, and examined the electron temperature gradients for different solar wind populations (i.e. classified by the proton bulk speed, Vp, and the solar wind mass flux). Results. We find that the total electron temperature decreases with the distance as ∼R−0.66, which is much slower than adiabatic. The extrapolated Te based on PSP observations is consistent with the exospheric solar wind model prediction at ∼10 R⊙, Helios observations at ∼0.3 AU, and Wind observations at 1 AU. Also, Te, extrapolated back to 10 R⊙, is almost the same as the Strahl electron temperature, Ts (measured by SPAN-E), which is considered to be closely related to or even almost equal to the coronal electron temperature. Furthermore, the radial Te profiles in the slower solar wind (or flux tube with larger mass flux) are steeper than those in the faster solar wind (or flux tube with smaller mass flux). The more pronounced anticorrelation of Vp–Te is observed when the solar wind is slower and located closer to the Sun.

High resolution Thomson scattering diagnostic for measurements of radial profiles of electron temperature and density in the gas dynamic trap.

The incoherent Thomson scattering diagnostic with multiple lines of sight is installed at the gas dynamic trap (GDT) for measurements of radial profiles of the plasma electron temperature and density. The diagnostic is built on the Nd:YAG laser operating at 1064nm. The laser input beamline is provided with an automatic system for alignment status monitoring and correction. The collecting lens uses ∼90° scattering geometry having 11 lines of sight in total. Presently, six of them (covering the full plasma radius from the axis to the limiter) are equipped with high etendue (f/2.4) interference filter spectrometers. The design of the spectrometer's data acquisition system based on the "time stretch" principle allowed for the 12 bits vertical resolution with a sampling rate of 5 GSample/s and a maximum sustainable measurement repetition frequency of 40kHz. The repetition frequency is the crucial parameter for the study of plasma dynamics with a new pulse burst laser to be started in early 2023. Results of the diagnostic operation in several GDT campaigns show that radial profiles are routinely delivered with the typical observation error of 2%-3% for Te ⩾ 20eV in a single pulse. After Raman scattering calibration, the diagnostic is capable to measure the electron density profile with the resolution ne (min)≃4⋅1018m-3 and error bars of 5%.

Effect of neutral pressure on the blue core in Ar helicon plasma under an inhomogeneous magnetic field

The effect of neutral pressure on the blue core in Ar helicon plasma under an inhomogeneous magnetic field was investigated in this work. The neutral pressure was set to 0.08 Pa, 0.36 Pa, and 0.68 Pa. A Nikon camera, intensified charge-coupled device (ICCD), optical emission spectrometer (OES), and Langmuir probe were used to diagnose the blue core in helicon plasma. Helicon plasma discharges experienced density jumps from the E mode, H mode to W mode before power just rose to 200 W. The plasma density increased and maintained a central peak with the increase of neutral pressure. However, the brightness of the blue core gradually decreased. It is demonstrated that the relative intensity of Ar II spectral lines and the ionization rate in the central area were reduced. Radial electron temperature profiles were flattened and became hollow as neutral pressure increased. It is demonstrated that increasing the neutral pressure weakened the central heating efficiency dominated by the helicon wave and strengthened the edge heating efficiency governed by the TG wave and skin effect. Therefore, the present experiment successfully reveals how the neutral pressure affects the heating mechanism of helicon plasma in an inhomogeneous magnetic field.

ASTI: Data assimilation system for particle and heat transport in toroidal plasmas

ASTI, a data assimilation system for integrated transport simulation of fusion plasma, has been developed to predict and control the fusion plasma behavior. ASTI employs the ensemble Kalman filter (EnKF) and smoother (EnKS) as data assimilation methods and the integrated transport simulation code for helical fusion plasma, TASK3D, as the system model. ASTI assimilates the time-series data of measured temperature and density radial profiles into the particle and heat transport simulation. In this study, we consider the uncertainties included in the density, temperature, transport model, neutral beam injection (NBI) heating model, and particle source model. We apply ASTI to 12 experimental data sets of the NBI-heated plasma in Large Helical Device (LHD) and investigate the validity of estimation and the prediction performance of ASTI. The obtained radial profile and time evolution of density, electron temperature, and ion temperature agree well with the experimental data sets. Faster and more accurate integrated transport simulation is realized byASTI than the previous integrated simulation of fusion plasmas.

Radial profile measurement with an improved 1 kHz Thomson scattering system on Versatile Experiment Spherical Torus.

A Thomson scattering (TS) system has been utilized to measure the electron temperature and density of the core region of Versatile Experiment Spherical Torus (VEST). Recently, the laser injection system is successfully upgraded adopting the burst laser with the repetition rate of 1 kHz and the energy of 2J. Furthermore, improved collection optics with additional polychromators and a 32-channel fast digitizer are prepared to observe the fast time evolution of radial profiles. This improvement is essential to study fast phenomena such as internal reconnection event (IRE). We increase the TS signal and reduce the stray light by introducing new filters having better optical properties such as high optical density at 1064nm, transmission, and reflectance. Moreover, the optimum reverse bias voltages are newly set to make the system operational independent of the background radiation. As a result, 1 kHz radial profiles of the core electron temperature and density are measured for the first time, showing characteristics of IREs in VEST.

Evidence for electron energization accompanying spontaneous formation of ion acceleration regions in expanding plasmas

We report experiments conducted in an expanding argon plasma generated in the inductive mode of a helicon source in the Hot hELIcon eXperiment–Large Experiment on Instabilities and Anisotropies facility. As the neutral gas pressure increases, the supersonic ion acceleration weakens. Increasing neutral pressure also alters the radial profile of electron temperature, density, and plasma potential upstream of the plasma expansion region. Langmuir probe measurements of the electron energy probability function (EEPF) show that heating of electrons at the plasma edge by RF fields diminishes with increasing gas pressure, yielding a plasma with a centrally peaked electron temperature, and flat potential profiles at higher neutral pressures. For neutral pressures at which ion acceleration regions develop in the expanding plasma plume, EEPFs reveal electrons with two temperature components.

Radial control of electron temperature gradient with optimized operational configuration of double plasma device

A double plasma device (DPD) is tested for different operational configurations to identify suitable control for plasma parameters in a weakly ionized, unmagnetized plasma discharge. A separation grid is installed between the two chambers of DPD, which allows filtering of plasma from the first to the second chamber. Investigations are carried out to control the plasma parameters, especially the electron temperature by exploring the role of the grid. The grid bias is varied between −25–0 V and 0–30 V to reflect cooling and heating of plasma. The electron heating and cooling is prominent for the maximum ratio of n source/n target. The electron energy distribution function (EEDF) is obtained to describe the role of grid biasing in controlling the electron temperature in the second chamber. We demonstrated control on the radial profile of electron temperature by charging different radial cross-sections of plasma differently by using a multi-grid assembly system (MGAS). We have also identified the suitable operational regime for DPD where exercising a radial control on electron temperature is possible. Such plasmas can facilitate investigations on electron temperature control for applications in plasma processing, cold–plasma material interaction, etc where low energy electrons are desired.

Estimation of plasma density perturbation from dusty plasma injection by laser irradiation on tungsten target in DiPS

To investigate the interaction of dusty plasma with magnetized plasmas at divertor plasma simulator, radial profiles of plasma density (ne) and electron temperature were measured in terms of plasma discharge currents and magnetic flux intensity by using a fast scanning probes system with triple tips. Dusty plasma with dusts (a generation rate of 3 μg s−1 and a size of 1–10 μm) was produced via interactions between a high-power laser beam and a full tungsten target. As ne increases, the scale of the effects of dusty plasma injection on magnetized plasmas was decreased. Also, the duration of transient fluctuation was reduced. For numerical estimation of plasma density perturbation due to dusty plasma injection, the result was ∼10% at a core region of the magnetized plasma with ne of (2–5) × 1011 cm−3 at steady state condition.

Comparison between Theoretical and Experimental Radial Electron Temperature Profiles in a Low Density Weakly Ionized Plasma

Experimental and theoretical studies of the radial distribution function of the electron temperature (RDFT) in a low-density plasma and weakly ionized gas for the abnormal glow region are presented. Experimentally, the electron temperatures and densities are measured by a Langmuir probe moved radially from the center to the edge of the cathode electrode for helium gas at different pressures in the low-pressure glow discharge. The comparison of the final experimental data for the radial distribution of electron temperatures and densities for different low pressures ranging from 0.2 to 1.2 torr, with the final proved equation of RDFT confirms that the electron temperatures decrease with increasing product of radial distance and gas pressures, showing a radial decrement dependence of the electron temperature from the center to the edge of the electrode. This is attributed to the increase of the number of electron-atom collisions at higher gas pressures and consequently of the rate of ionization. For the axial distance (L) from the tip of the probe to cathode electrode and the cathode electrode radius (R), a theoretical and experimental comparison for the two conditions L R, for both cases the produced plasma temperatures decrease and densities increase. It is concluded that the RDFT accurately shows a dramatic decrease for L R similar as for conditions of magnetized and unmagnetized effect for DC plasma. This means that the rate of plasma loss by diffusion decreased for L < R, agrees well with the applied of magnetic field behavior

A model for the basic plasma parameter profiles and the force exerted by fireballs with non-isothermal electrons

As discovered in recent work, plasma fireballs have the ability to exert considerable force onto ions and neutrals and, hence, induce macroscopic gas flows. This property makes them interesting objects for fundamental scientific research. Furthermore, there are also the possibilities for applications in the field space propulsion. As there is a lack of fundamental understanding of these plasma phenomena, this article aims to enhance the physical knowledge of fireballs by presenting a mathematical model for the calculation of the force that can be provided by them. It will be shown that all the main plasma parameters such as the plasma potential and the electron density can be derived completely with the knowledge of the potential of the electrode and the radial electron temperature profile. The calculations show very good agreement with the experimental data if two species of electrons (i.e., fast and slow) are considered. Both electron populations have different temperature profiles as is shown with measurements. Furthermore, it will be demonstrated that the potential drop throughout the fireball is much larger than previously thought and that this larger potential drop can considerably contribute to the acceleration of ions in the double layer. This mechanism makes it more likely that the force exerted by the fireball is rather caused by heating of the neutrals via collisions with those accelerated ions and the high energetic ions themselves than by collisions between fast electrons and neutrals.

A Scanning SXR Spectrometer Used in Experiments on ECR Plasma Heating at the L-2M Stellarator

Abstract—A diagnostic complex that is based on a scanning soft X-ray spectrometer has been developed at the Prokhorov General Physics Institute. The diagnostic complex is intended to measure the radial profiles of the plasma electron temperature in the L-2M stellarator. The maximum counting rate of the spectrometer is 2.0 × 105 pulses/s. It allows measuring of SXR spectra in the energy range of γ-photons of 1–80 keV. The spectral resolution of the spectrometer measured using a source of radioactive radiation with energy of E = 5.89 keV (55Fe) was ΔE = 320 eV (FWHM). The scanning system makes it possible to measure SXR spectra along the chords lying in the angular range from –13.5° to +26.5°. Negative and positive angles correspond to chords below and above the equatorial plane of the facility, respectively. The radial resolution of the spectrometer at the plasma axis is ~1.7 cm. The first results of spectral measurements in experiments at electron cyclotron resonance plasma heating at the L-2M stellarator are presented.

Feasibility experiment of physics-based global electron temperature profile control in KSTAR

KSTAR experiments have been conducted aiming at establishing a real-time control system that uses multiple actuators (NBI and ECH) to control the plasma profiles (Te and q profiles) and validating an applied physics-based plasma profile response model. Toward establishing the multiple plasma profile control system, the control experiment of the electron temperature profile has been performed in KSTAR as a first step. Although the plasma profile control system was in the commissioning phase, the electron temperature was feedback controlled successfully in real-time while the normalized radial profile of electron temperature remained nearly constant. In the circumstance, the implemented physics-based response model was successfully validated against control experiments with a step variation on the control target and an application of multiple actuators. The robustness of the controller is examined against an external disturbance in which a static version of the control matrix was used.

Influence of neutral beam attenuation on beam emission spectroscopy and charge exchange recombination spectroscopy.

Neutral beam attenuation is simulated by means of consulting the ADAS (Atomic Data and Analysis Structure) database based on experimentally diagnosed radial plasma density and electron temperature profiles on the Experimental Advanced Superconducting Tokamak (EAST). Two-dimensional distributions of beam emission and charge exchange recombination photon flux are simulated, taking neutral beam attenuation into account, together with comparison with experimental results of Beam Emission Spectroscopy (BES) and Charge eXchange Recombination Spectroscopy (CXRS). A photon number which is over 1014 promises a sufficient photon flux for typical detectors of BES, CXRS, and UltraFast-CXRS (UF-CXRS) diagnostics. Evidence shows that the ADAS database overvalues neutral beam injection effective stopping coefficient on the EAST tokamak. The joint diagnostic of BES and UF-CXRS which is under development to measure plasma pressure with a high temporal resolution of 1 μs will have strong signals in a radial range of 0.6 < ρ < 0.8. The steep gradients of plasma density and C6+ density at ρ ∼ 1 bring great difficulty to edge plasma investigation by this joint diagnostic.

Argon impurity transport studies at Wendelstein 7-X using x-ray imaging spectrometer measurements

In the first operational phase of the stellarator Wendelstein 7-X (W7-X), the x-ray imaging crystal spectrometer (XICS) system has been commissioned for measuring radial profiles of ion and electron temperature, T i and T e, plasma rotation velocities, v P, and selected impurity densities, n Z . This paper shows the first measurements of the spectrometer and gives an initial calculation of impurity transport parameters derived from an Ar impurity transport study. Using Bayesian analysis, the temporal evolution of Ar impurity density profiles after an Ar gas puff could be observed with a time resolution of up to 5 ms, yielding a maximum value for the diffusion coefficient of D = 1.5 m2 s−1 at ρ ~ 0.5 and small pinch velocities in the inner plasma region.

Cross-field transport of electrons at the magnetic throat in an annular plasma reactor

Cross-field transport of electrons has been studied at the magnetic throat of the annular Chi-Kung reactor. This annular configuration allows the creation of a low pressure argon plasma with two distinct electron heating locations by independently operating a radio-frequency antenna surrounding the outer source tube, or an antenna housed inside the inner source tube. The two antenna cases show opposite variation trends in radial profiles of electron energy probability function, electron density, plasma potential and electron temperature. The momentum and energy transport coefficients are obtained from the electron energy probability functions, and the related electron fluxes follow the path of electron cooling across the magnetic throat.

The charge imbalance in ultracold plasmas

Ultracold plasmas are regarded as quasineutral but not strictly neutral. The results of charge imbalance in the expansion of ultracold plasmas are reported. The calculations are performed by a full molecular-dynamics simulation. The details of the electron velocity distributions are calculated without the assumption of electron global thermal equilibrium and Boltzmann distribution. Spontaneous evolutions of the charge imbalance from the initial states with perfect neutrality are given in the simulations. The expansion of outer plasma slows down with the charge imbalance. The influences of plasma size and parameters on the charge imbalance are discussed. The radial profiles of electron temperature are given for the first time, and the self-similar expansion can still occur even if there is no global thermal equilibrium. The electron disorder induced heating is also found in the simulation.

Edge profile analysis of Joint European Torus (JET) Thomson scattering data: Quantifying the systematic error due to edge localised mode synchronisation.

The Joint European Torus (JET) high resolution Thomson scattering (HRTS) system measures radial electron temperature and density profiles. One of the key capabilities of this diagnostic is measuring the steep pressure gradient, termed the pedestal, at the edge of JET plasmas. The pedestal is susceptible to limiting instabilities, such as Edge Localised Modes (ELMs), characterised by a periodic collapse of the steep gradient region. A common method to extract the pedestal width, gradient, and height, used on numerous machines, is by performing a modified hyperbolic tangent (mtanh) fit to overlaid profiles selected from the same region of the ELM cycle. This process of overlaying profiles, termed ELM synchronisation, maximises the number of data points defining the pedestal region for a given phase of the ELM cycle. When fitting to HRTS profiles, it is necessary to incorporate the diagnostic radial instrument function, particularly important when considering the pedestal width. A deconvolved fit is determined by a forward convolution method requiring knowledge of only the instrument function and profiles. The systematic error due to the deconvolution technique incorporated into the JET pedestal fitting tool has been documented by Frassinetti et al. [Rev. Sci. Instrum. 83, 013506 (2012)]. This paper seeks to understand and quantify the systematic error introduced to the pedestal width due to ELM synchronisation. Synthetic profiles, generated with error bars and point-to-point variation characteristic of real HRTS profiles, are used to evaluate the deviation from the underlying pedestal width. We find on JET that the ELM synchronisation systematic error is negligible in comparison to the statistical error when assuming ten overlaid profiles (typical for a pre-ELM fit to HRTS profiles). This confirms that fitting a mtanh to ELM synchronised profiles is a robust and practical technique for extracting the pedestal structure.

Fast Thermal Helium Beam diagnostic for measurements of edge electron profiles and fluctuations.

The edge of fusion experiments is a region where strong gradients develop, together with the presence of strong fluctuations due to turbulence. The thermal helium beam diagnostic developed for the RFX-mod experiment allows the measurements with a single diagnostic of both low frequency time evolution of the edge radial profiles of electron density and temperature (tens of hertz), and the high frequency fluctuations (hundreds of kHz). To maximize the collected light, the three HeI lines necessary to be measured for the evaluation of n(e) and T(e) are separated with a spectrograph, and multianode photomultipliers are used as light detectors. The paper describes the diagnostic setup, with the interface hardware with the machine and the optical layout, and the characterization of its performances.

Radial Electron Temperature and Density Measurements Using Thomson Scattering System in GAMMA 10/PDX

A Thomson scattering (TS) system in GAMMA 10/PDX has been developed for the measurement of radial profiles of electron temperature and density in a single plasma and laser shot. The TS system has a large solid angle optical collection system and high-sensitivity signal detection system. The TS signals are obtained using four-channel high-speed digital oscilloscopes controlled by a Windows PC. We designed the acquisition program for six oscilloscopes to obtain 10-Hz TS signals in a single plasma shot, following which the time-dependent electron temperatures and densities can be determined. Moreover, in order to obtain larger TS signal intensity in the edge region, we added a second collection mirror. The radial electron temperatures and densities at six radial positions in GAMMA 10/PDX were successfully obtained.

Properties of Argon–Nitrogen Atmospheric Pressure DC Arc Plasma

The effect of nitrogen addition (1–20 %) on atmospheric argon DC arc plasma parameters was investigated. Nitrogen was added to three initial plasma gas compositions: pure argon gas, argon gas with water aerosol, and argon gas with water aerosol containing 0.5 % KCl. Admixtures of nitrogen from 1 up to 10 % (in the case of Ar–N2–water aerosol plasma) or up to 5 % (in the presence of 0.5 % KCl) produced a more contracted discharge, with larger gradients of electron number density and temperature, as compared to plasma without molecular gas addition. The opposite effect was observed in gas mixtures with 20 % of nitrogen. In that case, the arc core was expanded, and the radial profile of electron density and temperature became flatter as compared to the case of pure argon plasma. The changes in the radial structure of the discharge could be explained by increased thermal conductivity of mixed gas plasma and the presence of molecular ions. Increasing nitrogen content brings plasma closer to thermal equilibrium. To evaluate the effect of nitrogen upon analytic performance of the arc source, limits of detection (LODs) were measured for Zn, Cu, Li, and Rb. In plasma without KCl, the addition of nitrogen resulted in lowering of LODs for Cu, Li and Rb, while the opposite was observed for Zn. In the presence of KCl the addition of nitrogen had little or no effect on LODs for Cu, Li and Rb, while detection limits for Zn were increased.