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The evaluation of the Coulomb logarithm (CL) for different coupled plasma regimes is examined using generalized CL, effective CL, and conventional CL models. To find out the validity and scalability of these models for plasmas in appropriate evaluation of the CL, the classical plasma parameter $${{\Lambda }_{{{\text{cl}}}}}$$ (Coulomb logarithm) is employed. It is observed that the Coupled Gericke–Murillo–Schlanges (CGMS) model can cover better different coupled plasma regimes from weakly to strongly coupled plasmas. The CGMS model has also good agreement with the classical Molecular Dynamics (MD) model in the weakly coupled plasmas and with the generalized Khrapak CL (KH) model in the strongly coupled plasmas. Moreover, the electron–ion relaxation rates for plasmas with different coupling regimes are studied. It is found that the relaxation rates are substantially lower than the classical models predict for the strongly coupled plasmas. We show that the CGMS model is not only compatible with the other models in the weakly coupled plasmas but also almost fitted by the KH model, which is valid in the strongly coupled region.

A nonmagnetized collisional plasma parameter estimator from two frequency signal interrogation attenuation is developed. The plasma parameters that are estimated are the plasma frequency, electron neutral momentum collision frequency, and the plasma thickness. The plasma frequency and electron neutral momentum collision frequency are considered uniform across the plasma thickness. The relative permittivity is defined, and the complex index of refraction is developed. Using this definition and applying the plasma frequency, electron neutral momentum collision frequency, the radial propagation frequency, and plasma thickness, an attenuation is determined for known cases. The development of the estimator is discussed. The estimator uses a performance index where the minimum difference between the plasma frequencies and electron neutral momentum collision frequencies is determined for the two signal interrogation frequencies under the constraint of the same plasma thickness. The estimator was developed in three stages which include iterative, sequential, and adaptive. The setups of the iterative, sequential, and adaptive approaches are discussed. The impact of the interrogation frequency and the estimator setup is investigated. The estimator in the three development stages is compared with known cases and the plasma parameter estimator performance is quantified.

In this experiment, with the help of a Langmuir probe we estimated the plasma parameters at different axial positions inside a multi-dipole magnetic cage. At one end of the multi-dipole magnetic cage, a negatively biased mesh grid is placed. Important plasma parameter such as the electron density, plasma potential and electron temperature are seen to vary significantly towards the grid from the end of the magnetic filter.

The excitation temperature is a widely measured plasma parameter. In this article, the validity of an excitation temperature measurement is verified using a transition simulation between excited levels based on a collisional-radiative model. The collisional-radiative model calculation was validated by comparing it with the results of a spectroscopic measurement for a 2-kA peak vacuum arc ignited between the Cu100, Cu80Cr20, and Cu50Cr50 electrodes, whose diameter and gap length are 10 and 5 mm, respectively. As a result, the experimental result of the spectroscopy can be well simulated using the collisional-radiative model when the electron temperature and electron density are set to approximately 1.1–1.2 eV and 1.3– $2.1\times 10^{20}\,\,\text{m}^{-3}$ , respectively. It was found that the excitation temperature can be obtained from only two lines (510.6- and 515.3-nm lines) of the Cu I spectra with an accuracy comparable to that obtained from many line spectra of Cu neutrals. In addition, the relaxation times of the two lines are shorter than 100 ns. The excitation temperature, the electron temperature, and the electron density of the Cu100 electrodes were slightly higher than those of Cu50Cr50 electrodes. Such dependence on electrode material is caused by the difference in the density of the neutrals and ions. A comparison of the deposition ratio of Cu and Cr on the viewing port glass measured using energy-dispersive X-ray spectroscopy and a comparison of the cathode spot number suggest that the difference in the density of the neutrals and ions is caused by the difference in the cathode spot current.

The sputtering of tungsten divertor tiles at the JET ITER-like wall (ILW) during edge-localized modes (ELMs) is one of the main sources of tungsten impurity in the core plasma. The analytical approach for interpretation of the Langmuir probe (LP) measurements of ion flux at the divertor tile is elaborated to model the ELM ion parallel transport and to estimate the flux of sputtered tungsten atoms from the divertor under inter-ELM and intra-ELM conditions. Accounting for the pedestal temperature and density decrease at the pedestal crash during ELM allows obtaining the profiles of the particle and heat fluxes at the divertor tile corresponding to the measurements at the physically correct magnetic connection length. Estimates of the tungsten sputtered flux under intra-ELM and inter-ELM conditions show that first type ELMs contribute significantly (~85%) to the overall tungsten sputtering, which is in a good agreement with the divertor optical emission spectroscopy of the 400.9 nm atomic neutral tungsten line in JET discharges.

A cathode-less radio frequency (RF) thruster is a plasma-based system for space propulsion. It consists on a source for plasma generation driven by an RF antenna and a magnetic nozzle for the acceleration of the exhausted plasma stream. A parametric analysis has been conducted in order to evaluate the influence of some key design parameters on the performances of such a thruster. Specifically, the intensity and the topology of the magneto-static field, along with the antenna geometry have been varied. Their influence has been assessed on the plasma parameter profiles within the source (i.e., electron density, electron temperature, and power deposition), the antenna properties (i.e., impedance and current distribution), and the propulsive performances (i.e., thrust and specific impulse). The results presented in this work have been obtained with the validated code 3D-VIRTUS. The latter solves self-consistently both the electro-magnetic wave propagation and the plasma transport within a source driven by a RF antenna. An analytical model has been subsequently employed in order to solve the plasma dynamics in the plume and, in turn, to estimate the propulsive performances.

A multiple regression and machine learning approach is proposed to solve multiple plasma parameter inversion in complex systems. For an electromagnetic (EM) wave and plasma interaction system, it is common to retrieve plasma parameters based on the reflected or scattered EM field, whereas multiple parameter inversion becomes particularly challenging for anisotropic inhomogeneous plasma medium. Artificial neural network (ANN) is applied to retrieve the plasma density fluctuation in inhomogeneous medium. The method is computationally efficient and robust based solely on time series of data collected at a fixed number of spatial locations. The inversion algorithm opens venues and application for inhomogeneous plasma parameter inversion for EM wave and plasma interaction system at different frequencies.

A hollow cathode source is designed to generate multiple double layer (MDL) structures by the trapping of charged particles in the absence of any auxiliary plasma source or magnetic field, while the glow discharge switches between two distinctly different stable regimes. The generation and dynamics of localised and intensely luminous MDL formations are experimentally investigated in low-frequency sheath oscillation inhibited glow discharge by modified Langmuir probes in a linear vacuum vessel. The localised complex structures grow axially into visibly glowing coaxial formations along with structural changes in MDL formations, on increasing the applied voltage in nitrogen plasma at 0.1 mbar pressure. The discharge gradually expands to fill up the entire vessel through redistribution of energetic charged particles and formation of multiple sheaths on increasing the applied voltage across the electrodes. The present experimental study reveals interesting information about the formation of the sheath, stability of the plasma sheath and charged particle dynamics during the discharge transformations. The paper relates the plasma parameter variations with the nonlinear time series analysis of the discharge current and floating potential fluctuations through the reconstructed phase space in different discharge domains to analyse the dynamics of MDL formations and harmonic generation through sheath oscillations during the hollow cathode discharge regimes. The radial motion of the charged particles during the glow discharge between the semi-transparent gridded cylindrical cathode and the central anode might be useful for a better understanding of the underlying basic sheath physics related to particle acceleration in plasma as well as application in plasma sputtering.

As an important component of space environment, the ionospheric plasma is the main background environment for the operation of low-orbit spacecraft. The study of ionospheric plasma environment parameters and the enrichment of plasma environment data are beneficial to improve the reliability of low-orbit spacecraft operation. Langmuir probe is the most popular method for detecting the plasma parameter of ionospheric, however, it has some defects. In this paper, we design a plasma generator based on radio-frequency discharge to imitate the ionospheric plasma environment, and measure plasma parameter based on Thomson scattering by import a Nd: YAG laser oscillate in the plasma generator. The result demonstrates that the intensity of laser Thomson scattering signal is positively correlated with the change of plasma electron density. The electron density in the plasma generator is calculated according to the laser Thomson scattering signal intensity, and the error is less than 10% compared with that measured by the Langmuir probe.

Inductively coupled plasma sources driven by RF power at low-pressure regimes are well adopted for high-volume manufacturing of semiconductor devices. One vexing challenge to the utility of these plasma processing reactors is the existence of the E–H-mode transition. Industry notably avoids the process region associated with this transition, where plasma instabilities and bimodal power coupling prohibit reliable RF power delivery. One plasma instability detailed in this paper is associated with a hysteresis in coupled RF power (current) varying for the E-mode, or weakly capacitive coupling to the plasma, in comparison to the stronger current coupling in the H-mode, where inductive coupling is preferentially dominant. As a result, approximately two orders of magnitude of electron density is relinquished in this transition region from serving industrial manufacturing processes. We characterize the plasma parameter variation through the E-mode to H-mode with a time-resolved measurement of the electron density. Electronegative chemistries are incorporated into our experimental setup. The experimental scheme serves to evaluate RF power delivery and ameliorate its coupling through the transition region. We seek to extend this paper to adopt more efficient power coupling for toroidal plasma sources.

The core plasma confinement during detachment phase is investigated in the discharges with application of resonant magnetic perturbation (RMP) field in LHD. The RMP application creates a remnant magnetic island in the edge stochastic layer, which largely changes the plasma parameter profiles including impurity radiation. The electron temperature and pressure profiles are flattened at the island, while the electron density is slightly peaked at the edge of the island. The estimated impurity radiation profile is enhanced and fixed around the magnetic island during the detached phase, where the discharge is stably sustained with controlled level of radiation. Without RMP, the radiation penetrates the confinement region, leading to radiation collapse. It is found that in the case of the RMP application the plasma stored energy increases discontinuously at the detachment transition. In spite of the reduced effective plasma volume caused by the edge magnetic island and by the enhanced radiation there, the central plasma pressure finally exceeds the case without RMP. This is caused by the pressure profile peaking at the central region in the case with RMP. These results indicate clear change of core plasma confinement during the detached phase with RMP.

Impurity flow velocity measurements have been conducted for different magnetic field configurations in a wide plasma parameter range in the divertor leg region of LHD for understanding of the edge impurity transport. In all cases (densities, magnetic configurations, hydrogen (H) & deuterium (D) discharges), flows of several tens of km/s are observed. It is found that the flow in thick stochastic layer is faster than in thin stochastic layer configuration by a factor of 3. Different velocities of different charge states of carbon impurity are observed. The simulation with EMC3-EIRENE code shows similar trend as the experiments, but only qualitatively: faster flow in H compared to D discharges due to the mass effect, faster flow in the case of thick stochastic layer. However, synthetic spectra show discrepancy with experiments in the absolute Doppler shift, where the impurity velocity in the experiments is one order faster compared to the simulations. Keywords: Spectroscopy, Hydrogen, Deuterium, Carbon, Impurity transport, Edge plasma

Incoherent scatter (IS) radars are invaluable instruments for ionospheric physics, since they observe altitude profiles of electron density (Ne), electron temperature (Te), ion temperature (Ti) and line‐of‐sight plasma velocity (Vi) from ground. However, the temperatures can be fitted to the observed IS spectra only when the ion composition is known, and resolutions of the fitted plasma parameters are often insufficient for auroral electron precipitation, which requires high resolutions in both range and time. The problem of unknown ion composition has been addressed by means of the full‐profile analysis, which assumes that the plasma parameter profiles are smooth in altitude, or follow some predefined shape. In a similar manner, one could assume smooth time variations, but this option has not been used in IS analysis. We propose a plasma parameter fit technique based on Bayesian filtering, which we have implemented as an additional Bayesian Filtering Module (BAFIM) in the Grand Unified Incoherent Scatter Design and Analysis Package (GUISDAP). BAFIM allows us to control gradients in both time and range directions for each plasma parameter separately. With BAFIM we can fit F1 region ion composition together with Ne, Te, Ti and Vi, and we have reached 4 s/900 m time/range steps in four‐parameter fits of Ne, Te, Ti and Vi in E region observations of auroral electron precipitation.

59 pages, 24 ref.; We consider a homogeneous plasma composed of N particles of the same electric charge which interact through a Coulomb potential. In the large plasma parameter limit, classical kinetic theories justify that the empirical density is the solution of the Balescu-Guernsey-Lenard equation, at leading order. This is a law of large numbers. The Balescu-Guernsey-Lenard equation is approximated by the Landau equation for scales much smaller than the Debye length. In order to describe typical and rare fluctuations, we compute for the first time a large deviation principle for dynamical paths of the empirical density, within the Landau approximation. We obtain a large deviation Hamiltonian that describes fluctuations and rare excursions of the empirical density, in the large plasma parameter limit. We obtain this large deviation Hamiltonian either from the Boltzmann large deviation Hamiltonian in the grazing collision limit, or directly from the dynamics, extending the classical kinetic theory for plasmas within the Landau approximation. We also derive the large deviation Hamiltonian for the empirical density of N particles, each of which is governed by a Markov process, and coupled in a mean field way. We explain that the plasma large deviation Hamiltonian is not the one of N particles coupled in a mean-field way.

In the direct vicinity of plasma-facing surfaces, the incident plasma particles interact with surface-recombined neutrals. Remarkably high near-surface pressure losses were observed in the high-flux linear plasma generator Magnum-PSI. Combining the incoherent and coherent Thomson scattering diagnostics, we directly measured particle, momentum and energy fluxes down to 3 mm from the plasma target surface. At the surface, the particle and total heat flux were also measured, using respectively an in-target Langmuir probe and thermographic methods. The near-surface momentum and energy losses scale with density, and amount to at least 50 % and 20%, respectively, at ne=8centerdot1020m-3. These losses are attributed to the efficient exchange of charge, momentum and energy between incident plasma and surface-recombined neutrals. In low-temperature plasmas with sufficient density, incident particles go through several cycles of interaction and surface deposition before leaving the plasma, thereby providing an effective alternative dissipation channel to the incident plasma. Parallel plasma parameter profiles exhibit a transition with increasing plasma density. In low-density conditions, the plasma temperature is constant and near-surface ion acceleration is observed, attributed to the ambipolar electric field. Conversely, deceleration and plasma cooling are observed in dense conditions. These results are explained by the combined effect of ion-neutral friction and electron-ion thermal equilibration in the so-called thermalized collisional pre-sheath. The energy available for ambipolar acceleration is thus reduced, as well as the upstream flow velocity. In the ITER divertor, enhanced near-surface p-n interaction is expected as well, given the overlap in plasma conditions. Including these effects in finite-element scrape-off layer models requires a near-surface resolution smaller than the neutral mean free path. This amounts to 1 mm in Magnum-PSI, and possibly an order of magnitude smaller in ITER.

International audience; In low temperature magnetized plasma, Langmuir probe measurements must be corrected because of the electron diffusion through the sheath which is formed around the probe collector. The correction factor which is called the electron diffusion or electron sink parameter depends on many other parameters like the probe geometry, the electron diffusion coefficient, the sheath thickness or the potential profile through the sheath. Based on a previous work, we determine the values of this parameter under different experimental conditions and we study the effect of the electron energy, of the probe biased voltage and of the magnetic field intensity on this parameter. The results are compared with theoretical models published in literature. An empirical equation is determined to fit the diffusion parameter value versus magnetic field intensity.

An investigation has been done to study the effects of κ-distributed electrons on the waves with arbitrary amplitude of magnetized plasma in the presence of warm ions and negatively charged dust particles. The kappa distribution (κ > 3/2), which represents a velocity distribution, contains high energy tail but nears to the Maxwell–Boltzmann distribution as κ → ∞. In this work, by using the non-perturbation technique (i.e., Sagdeev pseudopotential analysis), a suitable mathematical expression for the arbitrary amplitude double layers in dust kinetic Alfven waves is formulated. Using the standard numerical values for different plasma parameter related to it, the Sagdeev Potential (SP) has been calculated for the plasma waves. It is observed that the spatial index κ plays a substantial role in finding the size and shape of double layers. Depth of double layers increases with decreasing kz, keeping ω fixed. For this parameter set, the double layer does not exist when M ≤ 1.1. This theoretical study may be helpful for explaining some of recent in situ observations (e.g., Freja, Cassini) in space plasmas, where one of its constituents is kappa distributed electron.

The propagation of nonlinear magnetosonic waves in electron–ion–dust (complex) plasmas has been studied by considering the effects of Bohm potential in the presence of an external magnetic field. By using the quantum hydrodynamic model and applying the reductive perturbation method, the Kadomtsev–Petviashvili (KP) equation is obtained. The compressive structures of magnetosonic solitary waves and periodic travelling waves are studied. The effects of the electron to dust density ratio, the quantum plasma parameter, and the dust equilibrium density on the nonlinear magnetosonic periodic travelling waves are discussed. It is observed that the wave structure is more sensitive to the changes in the ratio of electron to dust densities, as compared to the changes in other physical parameters. The obtained results may be useful for a better understanding of obliquely nonlinear magnetosonic travelling waves of localized structures with a small amplitude in dense magnetized quantum dusty plasmas. Publisher's Version

Simultaneous measurement of negative ion source plasma and extracted beam is carried out in order to clarify a key plasma parameter governing the meniscus formation in negative ion sources for fusion. The plasma discharge is performed with various discharge powers at different bias voltages in order to vary the plasma parameters. It is shown that the beam width changes along the same curve with respect to the negative ion density at any bias voltage while it varies along different curves with other plasma parameters depending on the bias voltage. This implies that the mechanism of meniscus formation in negative ion sources could be described along the similar manner as positive ion sources.

International audience; A new fluid model describing backward stimulated Raman scattering (SRS) is presented based on parametric three-wave coupling in multidimensional geometry. It takes into account kinetic effects in the description of the plasma wave via a non linear frequency shift due to trapped electrons. The model is valid in the regime of hot and weakly inhomogeneous plasmas under conditions relevant for inertial confinement fusion with the plasma parameter k L λ De 0.25 (k L standing for the plasma wave number and λ De for the Debye length). Benchmarks of the model have been performed against the Maxwell-particle-in-cell (PIC) code Emi2D in order to calibrate the adjustable parameters controlling the non linear frequency shift. Two major configurations have been tested, one in a homogeneous plasma, with the onset of laser pump depletion and the other in an inhomogeneous plasma, producing auto-resonant growth. Good agreement between fluid and PIC simulations has been found for both configurations, in particular for the growth of SRS, and further on in time for the average backscatter level. The model is a promising tool to be implemented in multi-dimensional laser-plasma interaction packages coupled to hydrodynamics codes in order to compute SRS in mm-size volumes, usually inaccessible with PIC codes.

In a laser-irradiated plasma, the Langdon effect makes the electron energy distribution function (EEDF) tend to a super-Gaussian distribution, which has important influences on laser plasma instabilities. In this work, the influences of a super-Gaussian EEDF on the convective stimulated backward Raman scattering (SRS) and stimulated backward Brillouin scattering (SBS) are studied systematically for a wide range of typical plasma parameters in the inertial confinement fusion (ICF). Distinct behaviors are found for SRS and SBS in the variation trend of the peak spatial growth rate and the corresponding wavelength of the scattered light. Especially, the Langdon effect on the SBS in plasmas with different ion species and isotopes is analyzed in detail, and the parameter boundary for judging the variation trend of the peak spatial growth rate of SBS with the superGaussian exponent is presented for the first time. In certain plasma parameter region, it is found that the Langdon effect could enhance SBS in mixed plasma, which may attenuate the improvement in suppressing SBS by mixing low-Z ions into the high-Z plasma. These comprehension of Langdon effect on LPIs would contribute to a better understanding of SRS and SBS in experiments., Comment: 15 figures

The optical emission study of aluminum (Al) plasma generated by a $Q$ -switched Nd:YAG laser has been presented. The plasma parameter, such as electron temperature ( $T_{e}$ ) and electron number density ( $N_{e}$ ), has been estimated. The electron temperature has been estimated by four different methods and $N_{e}$ was estimated by Stark broadening of spectral lines and the Saha–Boltzmann equation. The laser-generated Al plasma was optically thin and also fulfills the conditions of local thermodynamical equilibrium. The emission spectrum used for determination of the branching fraction and thus transition probabilities of all allowed transitions. The measured values are good in agreement with the literature.

This paper presents the application of a theoretically developed method that provides plasma parameter solution space information from measured RF attenuation that occurs during reentry. The purpose is to provide reentry plasma parameter information from the communication signal attenuation. The theoretical development centers around the attenuation and the complex index of refraction. The methodology uses an imaginary index of the refraction matching algorithm with a tolerance to find suitable solutions that satisfy the theory. The imaginary matching terms are then used to determine the real index of refraction resulting in the complex index of refraction. Then a filter is used to reject nonphysical solutions. Signal attenuation-based plasma parameter properties investigated include the complex index of refraction, plasma frequency, electron density, collision frequency, propagation constant, attenuation constant, phase constant, complex plasma conductivity, and electron mobility. RF plasma thickness attenuation is investigated and compared to the literature. Similar plasma thickness for a specific signal attenuation can have different plasma properties.

In this paper, the spatial-temporal evolution of the anode temperature in the vacuum arc during the formation of an anode spot is investigated by numerical simulation and experiments. A transient self-consistent model is established to calculate the arc parameters and the anode temperature. The simulations predict that the maximum anode temperature always occurs after the current peak. Ion density and atom density at the anode side increase significantly during the formation of the anode spot. In the anode spot mode, more evaporated anode material comes into the arc column, leading to higher plasma temperature around the spot. The anode vapor can reduce the energy flux from the plasma to the anode center, providing more uniform anode temperature distribution and correspondingly smoother plasma parameter distributions in the vicinity of the anode center. In addition, a higher Cr fraction in the electrodes can result in a higher anode temperature. Near-infrared spectroscopy and high-speed camera thermography are used to study the anode temperature experimentally in order to verify the simulation results. A reasonable agreement was found.

The basis of plasma stealth technology is the attenuation of electromagnetic waves by plasma. In this study, the calculation principle of the finite-difference time-domain (FDTD) method is introduced and a FDTD time–space coupling model of electromagnetic wave propagation in plasma is established. The time-domain variation characteristics of electromagnetic waves entering the plasma are analyzed. The plasma parameter distribution under different conditions obtained using the COMSOL fluid mechanics model is introduced into the FDTD model. The plasma reflectivity measurement experiment was carried out in a microwave anechoic chamber, and the influence of different experimental conditions on the plasma reflectivity was analyzed. The variation of reflectivity under different plasma parameter distributions is obtained. The results show that increasing electron density and plasma thickness and enhanced plasma distribution uniformity are beneficial for improving the attenuation effect of plasma on electromagnetic waves. These results provide a reference for the inductively coupled plasma parameter distribution in a closed quartz cavity, which provides a basis for the plasma to attenuate the electromagnetic waves.

Adding electronegative gas to the inert gas is an important means of adjusting the plasma parameter distribution. In this paper, a fluid model of the Ar/O 2 inductivly coupled plasma (ICP) is used to investigate the parameter distribution, while the electron energy distribution function (EEDF) and the transport coefficients are obtained by the Boltzmann equation solver module to improve the accuracy. The spatial-temporal evolution of the electron density and the electron temperature of the ICP are obtained and the influence of the discharge power and the oxygen mole ratio on the distribution of the ICP parameters is compared. Additionally, the physical mechanism is researched using the diffusion-transport theory of the plasma. In order to verify the reliability of the model results, an experiment is carried out to diagnose the discharge parameters. The results of the simulation and the experiment are performed for different power and oxygen mole ratios and a good qualitative and numerical agreement is obtained, indicating that the inclusion of the simulation results in a high accuracy.

With the advent of more than Moore’s law era, control of plasma etch process is expected to become inevitable. Given that highly complex plasma is a medium of etch processes, plasma parameters are key factors to be controlled. In addition, highly interactive plasma characteristics require multivariate control schemes. In this paper, we design a multi-loop controller which controls effective plasma parameters in Ar plasma conditions. The effective plasma parameters obtained by optical emission spectroscopy are paired with plasma reactor instrumental variables through relative gain array and singular value decomposition. Each single input-single output (SISO) system based on the pairing result shows successful disturbance rejection performance but interactions between SISO controllers occur. In order to handle the interactions, 2 × 2 multiple input-multiple output (MIMO) controllers with and without decouplers are simulated to track set point change. Based on the simulations, a MIMO controller with decouplers is implemented in a capacitively coupled plasma reactor and show feasible control performance without interaction. Hopefully, the results introduced in this paper contribute to making progress in plasma parameter control.

The plasma parameters in the 2.45 GHz electron cyclotron resonance (ECR) proton ion source have been measured and optimized at low pressures. These parameters are important as they are related to the beam parameters of the ion source. A detailed plasma characterization study has been conducted using hydrogen as a working gas in the operating pressure and power range $10^{-4}$ – $10^{-3}$ mbar, 400–1000 W of the ion source, respectively. The plasma parameters have been measured in the ECR zone of the plasma chamber. An automatic Langmuir probe and data acquisition system has been used to measure these parameters. In the above-mentioned power and pressure range, the plasma density, plasma electron temperature, and plasma potential measured are in the range $4 \times 10^{11}$ – $6.5 \times 10^{11}$ cm $^{-3}$ , 4–11 eV, and 30–40 V, respectively. The variation of plasma parameters with neutral gas pressure is studied for different microwave powers. A 0-D (global) model has been developed to compare the measured plasma parameter data with the calculated ones. The ion species content in the plasma was measured after extraction using a magnetic mass analyzer and a Faraday cup. A plasma-based model has been developed to compare the measured ion species fraction data with the calculated ones by taking the measured ECR plasma parameters as input.

The collisions of weakly nonlinear structures in an electronegative plasma consisting of Boltzmann electrons, Boltzmann negative ions, and cold mobile positive ions are investigated depending on experimental data. Our attention is focused on the study of the face-to-face soliton collisions, i.e. head-on soliton collisions. To do this, the extended Poincare–Lighthill–Kuo (PLK) reductive perturbation method is used. The present study is split into two parts: the first one, called generic case. In this case, the two-coupled Korteweg–de Vries (KdV) equations and the analytical phase shifts after the head-on collision of the two-KdV solitons are obtained. Our numerical calculations, showed that both compressive and rarefactive solitons can exist in such plasma, depending on the relevant physical plasma parameters, namely the electrons-to-negative ion temperature ratio and the negative ion concentration. It is found that the phase shift has a positive sign for compressive solitary structures and negative sign for rarefactive solitary structures. At the critical value of the temperature ratio, the two-coupled modified Kortwege–de Vries (mKdV) equations are used to study the soliton collision rather than the two-KdV equations and the analytical phase shifts after the collision are derived. In the latter case (called special case), the combinations of negative and positive soliton collision can occur, contrary to the generic case, where both soliton collisions necessarily have the same polarity. The plasma parameter values for laboratory experiment are taken for discussion.

We study the optical properties of the Kehagias-Sfetsos (KS) compact objects, characterized by the "Ho\v{r}ava" parameter $\omega_{_{KS}}$, in the presence of plasma, considering its homogeneous or power-law density distribution. The strong effects of both "Ho\v{r}ava" parameter $\omega_{_{KS}}$ and plasma on the shadow cast by the KS compact objects are demonstrated. Using the weak field approximation, we investigate the gravitational lensing effect. Strong dependence of the deflection angle of the light on both the "Ho\v{r}ava" and plasma parameter is explicitly shown. The magnification of image source due to the weak gravitational lensing is given for both the homogeneous and inhomogeneous plasma., Comment: 15 pages, 10 figures

In the present study, the machine learning algorithm is utilized for the first time to improve the probe diagnosis. Machine learning methods are utilized to improve the Langmuir probe diagnostic accuracy and the diagnosable plasma parameter range without changing the probe structure based on the Langmuir probe. They provide a new way for experimentally obtaining electron density. A DC glow discharge simulation model and experimental equipment are established. Utilizing the discharge pressure and voltage as independent variables, the simulation and experimental electron densities are collected, the simulation and experimental data are utilized for training, and the plasma electron density outside of the pressure and voltage range of the training data is predicted, thereby achieving the prediction. Simultaneously, when the data amount is large enough, even without experimental measurement, the electron density can be obtained directly through the input parameters, without relying on the plasma physical model.

By using the equation of the state of P = α d + β d T d, we studied a shock wave propagation in a strongly coupled complex plasma. A Korteweg-de Vries–Burgers equation is obtained to describe a shock wave in strongly coupled complex plasma. Dependence of the shock wave speed on the piston velocity and the plasma parameters such as the screening parameter of the strongly coupled complex plasma are given analytically for a weak shock wave. It is in good agreement with previous results. It shows in the present paper that there are density oscillations in the postshock region which is similar to that found in the previous works. Dependence of the length between two first peaks of the density oscillation on the piston velocity and the plasma parameter are also given analytically which is also in agreement qualitatively with previous results.

In the current experimental device of TAE Technologies, C-2W (also called "Norman"), record breaking advanced beam-driven field-reversed configuration (FRC) plasmas are produced and sustained in steady state utilizing variable energy neutral beams (15-40 keV, total power up to 20 MW), advanced divertors, bias electrodes, and an active plasma control system. This fully operational experiment is coupled with a fully operational suite of advanced diagnostic systems. The suite consists of 60+ individual systems spanning 20 categories, including magnetic sensors, Thomson scattering, interferometry/polarimetry, spectroscopy, fast imaging, bolometry, reflectometry, charged and neutral particle analysis, fusion product detection, and electric probes. Recently, measurements of main ion temperatures via a diagnostic neutral beam, axial profiles of energy flux from an array of bolometers, and divertor and edge plasma parameters via an extensive set of electric probes, interferometers, and spectrometers have all been made available. All the diagnostics work together to provide a complete picture of the FRC, fast-ion inventory, and edge plasma details enabling tomographic reconstruction of plasma parameter profiles and real-time plasma control.

Microtearing mode (MTM) real frequency, growth rate, magnetic fluctuation amplitude, and resulting electron thermal transport are studied in systematic NSTX scans of relevant plasma parameters. The dependency of the MTM real frequency and growth rate on plasma parameters, suitable for low and high collision NSTX discharges, is obtained by using the reduced MTM transport model [T. Rafiq et al., Phys. Plasmas 23, 062507 (2016)]. The plasma parameter dependencies are compared and found to be consistent with the results obtained from MTM using the gyrokinetic GYRO code. The scaling trend of collision frequency and plasma beta is found to be consistent with the global energy confinement trend observed in the NSTX experiment. The strength of the magnetic fluctuation is found to be consistent with the gyrokinetic estimate. In earlier studies, it was found that the version of the multi-mode (MM) anomalous transport model, which did not contain the effect of MTMs, provided an appropriate description of the electron temperature profiles in standard tokamak discharges and not in spherical tokamaks. When the MM model, which involves transport associated with MTMs, is incorporated in the TRANSP code and is used in the study of electron thermal transport in NSTX discharges, it is observed that the agreement with the experimental electron temperature profile is substantially improved.

A large-area high-power radio-frequency (RF) driven ion source was developed for positive and negative neutral beam injectors at the Korea Atomic Energy Research Institute (KAERI). The RF ion source consists of a driver region, including a helical antenna and a discharge chamber, and an expansion region. RF power can be transferred at up to 10 kW with a fixed frequency of 2 MHz through an optimized RF matching system. An actively water-cooled Faraday shield is located inside the driver region of the ion source for the stable and steady-state operations of high-power RF discharge. Plasma ignition of the ion source is initiated by the injection of argon-gas without a starter-filament heating, and the argon-gas is then slowly exchanged by the injection of hydrogen-gas to produce pure hydrogen plasmas. The uniformities of the plasma parameter, such as a plasma density and an electron temperature, are measured at the lowest area of the driver region using two RF-compensated electrostatic probes along the direction of the short-and long-dimensions of the driver region. The plasma parameters will be compared with those obtained at the lowest area of the expansion bucket to analyze the plasma expansion properties from the driver region to the expansion region.

We investigate the effects of Lorentzian astrophysical plasmas on resonant Compton scattering of photons by the helium ground and excited states. The bound-excited states energies in the plasma environments are obtained by using highly correlated exponential wave functions in the framework of Ritz variational method. The resonance Compton scattering cross sections in Lorentzian plasmas between the $$\hbox {1s}^{2}{\,}^{1}\hbox {S}$$ and 1s2p $$^{1}\hbox {P}$$ , 1s2s $$^{1}\hbox {S}$$ and 1s3p $$^{1}\hbox {P}$$ , 1s3s $$^{1}\hbox {S}$$ and 1s3d $$^{1}\hbox {D}$$ states are reported as a function of the spectral index and plasma parameter. The nonthermal character of the Lorentzian plasmas shows interesting features on the resonant Compton scattering cross sections.

The quantum magnetohydrodynamic (QMHD) model is applied in investigating the propagation of linear waves in quantum magnetoplasmas. Using the QMHD model, the dispersion equation for quantum magnetoplasmas and the dispersion relations of linear waves are deduced. Results show that quantum effects affect the propagation of electron plasma waves and extraordinary waves (X waves). When we select the plasma parameters of the laser-based plasma compression (LBPC) schemes for calculation, the quantum correction cannot be neglected. Meanwhile, the corrections produced by the Fermi degeneracy pressure and Bohm potential are compared under different plasma parameter conditions.

An experimental technique for the determination of electric conductivity and temperature of plasma is presented. The technique is based on comparing the signals that are produced by a pulsed magnetic field in the circuits of two probes located within the studied plasma and outside of it. The proposed technique for the measurement of plasma parameters was tested experimentally in the context of measuring the electric conductivity and temperature of plasma flux formed in cathode spots of a high-current pulsed vacuum arc with a magnesium cathode.

We have implemented laser Thomson scattering for local plasma measurement of electron and ion temperatures, electron density, flow velocity, and charge state. The electron density increases by two times in the interaction of two plasma flows, indicating collisionless interaction. The density and velocity show fluctuations only at t = 40 ns, and the density suddenly decreases, indicating the plasma ejection from the interaction region, which can be explained by a magnetic reconnection. The electron temperature in the double-flow is larger than that in the single flow. This may be explained by the energy transfer from the plasma kinetic energy to thermal energy. The ion temperature is much larger than electron temperature in the double-flow, and this may be explained by collisional effects between two plasmas, and/or possibly interpreted as a thermalization due to magnetic reconnection.

The particles transport and optical emission of tungsten plasma in magnetic field are two of the prime aspects for the diagnosis of plasma wall interaction process in nuclear devices such as EAST tokamak. In this work, the effect of the magnetic field (1.1 T) on the laser produced tungsten plasma plume dynamics and its optical emission produced by laser in vacuum (~4 × 10−3 Pa) were investigated. Fast imaging results presented that magnetic field confined the plasma and affected the plasma geometry. Temporal evolution of the optical emission showed that the continuum radiation at early stage (>100 ns) was not affected by the magnetic field while the tungsten ionic and atomic lines were significantly enhanced at later delay times (>200 ns, >400 ns, respectively). The negligible influence on the early continuum radiation was due to the laser-plasma pressure was far higher than the magnetic pressure as the plasma was hot and dense at early times. The higher electron temperature (Te) and electron density (ne) at later delay times were also observed in the magnetic field. The time-dependent plume dynamics in the magnetic field was correlated to the temporal variation of the plasma parameter β (the ratio of plasma pressure to magnetic pressure) and the electron collision frequency (ve), and electron cyclotron frequency (ωce) were also discussed. Moreover, the information including plasma evolution, plasma velocity, electron temperature electron density, ionic and atomic velocities with and without magnetic field were obtained.

The dynamics of coupled ion-acoustic waves is investigated in an electronegative plasma made of Boltzmann negative ions, cold mobile positive ions and Boltzmann electrons. Using the reductive perturbation method, it is shown that the system can fully be described by a set of two coupled nonlinear Schrodinger equations. The parametric analysis of modulational instability reveals the existence of regions of instability that are sensitive to changes in plasma parameters such as the negative ion concentration ratio and the electron-to-negative ion temperature ratio. The analytical results are confronted to numerical simulations, where we examine the long-time dynamics of modulated waves in the electronegative plasma. One obtains the generation of nonlinear modulated waves that are sensitive to the negative-ion concentration ratio. Exact solutions for individual modes are discussed and one finally derives the coupled solution. The response of the latter to the plasma parameter variations is also addressed.

The foreshock plasma exhibits large-amplitude disturbance in the plasma density and the magnetic field. The question of the density response to the magnetic field fluctuation is addressed and studied observationally and statistically using the in situ Cluster spacecraft data of the foreshock plasma. Three major findings are obtained. First, the density response is unique to the magnetic field fluctuation and is of the fast magnetosonic mode type. Second, the density response to the total magnetic energy density (simply subtracting by the mean field) exhibits a clear scaling to the beta-tilde parameter defined as the squared ratio of the sound speed to the Alfvén speed. We interpret that the total fluctuations mostly represent linear-mode waves, and the scaling law has a potential application to estimate the plasma parameter beta using the fluctuation data of the density and the magnetic field only. Third, the density response to the nonlinear (or large-amplitude) magnetic field fluctuation has a weak agreement with the theoretical expectation from the quasi-static balance with a larger degree of scattering in the data. We conclude that the foreshock plasma overall exhibits the linear-mode waves (fast mode) and a moderate degree of nonlinear fluctuations. The concept of the quasi-static balance is partly justified and applicable in the foreshock plasma.

We numerically study magnetic reconnection on different spatial scales and at different heights in the weakly ionized plasma of the low solar atmosphere (around $300-800$~km above the solar surface) within a reactive 2.5 D multi-fluid plasma-neutral model. We consider a strongly magnetized plasma ($\beta \sim 6\% $) evolving from a force-free magnetic configuration and perturbed to initialize formation of a reconnection current sheet. On large scales, the resulting current sheets are observed to undergo a secondary 'plasmoid' instability. A series of simulations at different scales demonstrate a cascading current sheet formation process that terminates for current sheets with width of ~2m and length of $\sim100$~m, corresponding to the critical current sheet aspect ratio of $\sim50$. We also observe that the plasmoid instability is the primary physical mechanism accelerating the magnetic reconnection in this plasma parameter regime. After plasmoid instabilities appear, the reconnection rate sharply increases to a value of $\sim$ 0.035, observed to be independent of the Lundquist number. These characteristics are very similar to magnetic reconnection in fully ionized plasmas. In this low $\beta$ guide field reconnection regime, both the recombination and collisionless effects are observed to have a small contribution to the reconnection rate. The simulations show that it is difficult to heat the dense weakly ionized photospheric plasmas to above $2\times10^4$~K during the magnetic reconnection process. However, the plasmas in the low solar chromosphere can be heated above $3\times10^4$~K with reconnection magnetic fields of $500$~G or stronger.

The beam-plasma mechanism, based on the Langmuir decay process, has been proposed to explain naturally enhanced ion-acoustic lines (NEIALs), which are spectral distortions in incoherent scatter radar (ISR) data frequently observed in the vicinity of auroral arcs. In this work the effect of the Langmuir decay process on the ISR spectrum is studied and compared with an analytical model for different plasma parameters by using an electrostatic parallel particle-in-cell (EPPIC) code. Simulations show that the code is working in accordance with theory for a wide range of beam and plasma values and that the features of the spectrum are sensitive to changes of those values. These results suggest that the EPPIC code might be used to build a spectrum-plasma parameter model which will allow estimation of beam and plasma parameters from observed spectra. Simulations also confirm that background electron density (ne) plays an important role in determining the maximum detectable wavenumber of the enhancement. Specifically, results demonstrate that an increase in ne makes the enhancements of the ion acoustic more likely line at large wavenumbers, a finding consistent with statistical studies showing more frequent NEIAL occurrence near solar maximum. Finally, the simulations expose some inaccuracies of the current theoretical model in quantifying the energy passed from the beam to the Langmuir waves as well as with the range of enhanced wavenumbers. These differences may be attributable to the weak Langmuir turbulent regime assumption used in the theory.

Inductively Coupled Plasma sources driven by RF power at low pressure regimes are well adopted for high-volume manufacturing of semiconductor devices. The vexing challenge to the utility of these plasma processing reactors is the existence of the E-H mode transition1. Industry notably avoids the process region associated with this transition, where plasma instabilities prohibit reliable RF power delivery. The plasma instability is associated with a hysteresis in coupled RF power (current) varying for the E-Mode, or weakly capacitive coupling to the plasma, in comparison to the stronger current coupling in the H-Mode, where inductive coupling is preferentially dominant. As a result, approximately two orders of magnitude of electron density is relinquished in this transition region from serving industrial manufacturing processes. We characterize the plasma parameter variation through the E to H-mode with a time-resolved measurement of the electron density. Electropositive and electronegative chemistries are incorporated into our experimental setup. The experimental scheme serves to evaluate RF power delivery and ameliorate its coupling through the transition region. The work is further extended to adopt more efficient power coupling to toroidal plasma sources.

The impedance probe is a measurement device to measure plasma parameters, such as electron density. It consists of one electrode connected to a network analyzer via a coaxial cable and is immersed into a plasma. A bias potential superposed with an alternating potential is applied to the electrode and the response of the plasma is measured. Its dynamical interaction with the plasma in an electrostatic, kinetic description can be modeled in an abstract notation based on functional analytic methods. These methods provide the opportunity to derive a general solution, which is given as the response function of the probe–plasma system. It is defined by the matrix elements of the resolvent of an appropriate dynamical operator. Based on the general solution, a residual damping for vanishing pressure can be predicted and can only be explained by kinetic effects. In this paper, an explicit response function of the spherical impedance probe is derived. Therefore, the resolvent is determined by its algebraic representation based on an expansion in orthogonal basis functions. This allows one to compute an approximated response function and its corresponding spectra. These spectra show additional damping due to kinetic effects and are in good agreement with former kinetically determined spectra.

International audience; The simultaneous control of the density and particle number of non-neutral plasmas confined in Penning-Malmberg traps is demonstrated. Control is achieved by setting the plasma’s density by applying a rotating electric field while simultaneously fixing its axial potential via evaporative cooling. This novel method is particularly useful for stabilizing positron plasmas, as the procedures used to collect positrons from radioactive sources typically yield plasmas with variable densities and particle numbers; it also simplifies optimization studies that require plasma parameter scans. The reproducibility achieved by applying this technique to the positron and electron plasmas used by the ALPHA antihydrogen experiment at CERN, combined with other developments, contributed to a 10-fold increase in the antiatom trapping rate.

This paper presents measurements of the electron temperature in Wendelstein 7-X (W7-X) stellarator plasmas heated by electron-cyclotron-resonance (ECRH) during the first operational phase (OP1.1). The analysis of the slope of the observed X-ray continuum emission (in a semi-logarithmic plot) measured by the use of the Pulse Height Analysis (PHA) system, provides the information about the electron temperature (Te) of the hydrogen plasma. The determination of this fundamental plasma parameter is based on the exponential dependence of the continuum radiation (Bremsstrahlung) on photon energy assuming Maxwellian distribution. In this paper, some experimental results of the estimated electron temperature are presented and compared to the results obtained from the simulations of X-ray spectrum and other diagnostic like the Thomson Scattering (TS) system.

The dynamics of the population of excited states of atoms in metastable states and nonstationary optical emission and transmission spectra of nanosecond discharges in plasma waveguides filled with inert gases in a wide range of variation of external conditions are studied experimentally. Estimates of the energy of electrons accelerated at the edge of the high-velocity ionization wave are given, and the effect of high-energy electrons on the dynamics of the development of nanosecond discharge in shielded dielectric tubes is analyzed. The results of the experimental study of the processes of formation of the transverse plasma parameter distribution are presented, and their role during the formation of the transmission spectra of nonuniform plasma of nanosecond discharges near narrow spectral absorption lines is determined. For the first time, the formation of transmission spectra of the dispersion type near spectral absorption lines of neon atoms is discovered and studied in experiments outside the resonator.

The Plasma Liner Experiment-ALPHA (PLX-α) is investigating the merging of supersonic plasma jets into a spherically imploding plasma liner as a driver for use in magneto-inertial fusion (MIF) architectures. 1 The present work is focused on characterizing the merging of six and/or seven plasma jets, converging in a cone of solid angle $0.4 \pi $ over a distance of 1.3 meters. Results from high-speed imaging, photodiode arrays, self-emission visible survey spectroscopy, and self-emission visible high-resolution spectroscopy will be presented, yielding measurements of plasma velocity, number density, electron/ ion temperatures, and mean ionization state pre- and post-merge. Anticipated plasma parameter regimes are $\mathrm {n}\sim 10 ^{15}-10 ^{17}$ cm$^{-3}$, $\mathrm {T}\sim 1-10$ eV, and $\mathrm {v}\sim 50$ km/s, with gas species varied among argon, nitrogen, neon, krypton, and xenon. Images and spectra will be compared with synthetic data generated from 3D fronttracking and smooth-particle-hydrodynamic simulations coupled with atomic physics / opacity analysis codes. Results will inform questions of liner-Mach-number and lineruniformity evolution throughout the jet-merging and subsequent liner-convergence process.