Wide Range Of Plasma Conditions Research Articles

Exact stark analytical function for Hα line based on the FFM model related with plasma parameters

Optical Emission Spectroscopy is a widely used technique for plasma diagnosis, with particular interest in hydrogen atomic emission due to its prevalence in plasmas. However, accurately determining plasma parameters like electron density, electron temperature, and gas temperature starting from the experimental profiles remains a challenge. This paper introduces a comprehensive model for Stark broadening of the Hα line in a wide range of plasma conditions, addressing the limitations of existing analytical expressions for line shapes. The proposed model encompasses the full splitting of the transition into fifteen Lorentzian profiles and electric micro-field fluctuations surrounding the emitting atoms due to collisions with charged particles. Starting from accurate spectral data obtained from realistic computer simulations, fitting parameters of the model, have been obtained by using an optimization method based on a genetic algorithm. The set of parameters of the model are reported for a wide range of plasma conditions. The behavior of these parameters is analyzed to understand their dependence in terms of the electron density and temperature and gas density of the plasma. The model parameters here obtained constitute a useful tool in plasma diagnosis to obtaining the values of the physical parameters of the plasma starting from the experimental profiles.

The STAG code: A fully relativistic super transition array calculation using Green’s functions

Calculating opacities for a wide range of plasma conditions (i.e. temperature, density, element) requires detailed knowledge of the plasma configuration space and electronic structure. For plasmas composed of heavier elements, relativistic effects are important in both the electronic structure and the details of opacity spectra. We extend our previously described superconfiguration and super transition array capabilities (Gill et al., 2023) to include a fully relativistic formalism. The use of hybrid bound-continuum supershells in our superconfigurations demonstrates the importance of a consistent treatment of bound and continuum electrons in dense plasma opacities, and we expand the discussion of these consequences to include issues associated with equation of state and electron correlations between bound and continuum electrons.

Temperature relaxation and generalized Coulomb logarithm in two-temperature dense plasmas relevant to inertial confinement fusion implosions

Detailed knowledge of energy exchange between electrons and ions is of fundamental importance for the description of temperature relaxation and also other nonequilibrium physics in Inertial Confinement Fusion (ICF). We present a theoretical model for the temperature relaxation rate and the related generalized Coulomb logarithm based on the Quantum Lenard–Balescu (QLB) kinetic equation, where no special cutoffs are needed to be introduced. To describe the collective modes characterizing the ionic acoustic waves, a single-pole approximation is introduced for the ionic dielectric response. The proposed model for the generalized Coulomb logarithm is examined over a wide range of plasma conditions for electron temperatures between 102 and 105 eV and electron densities between 1022 and . The values of the generalized Coulomb logarithm are demonstrated to be in excellent agreement with the ones evaluated using the original QLB kinetic approach but with much less computational cost. Comparisons with molecular dynamics simulations and other theoretical approaches are presented. For further applications of our model, we present results for the recently measured experimental Coulomb logarithm. Compared to other widely applied models such as the Landau–Spitzer Coulomb logarithm, our model provides more consistent descriptions for the results of molecular dynamics simulations and also for the experimental outcomes. Our model for the generalized Coulomb logarithm is easy to calculate and can benefit efficient and reliable simulations for the ICF implosions.

Theoretical study of electron-impact broadening for highly charged Ar XV ion lines

Spectral line widths produced by collisions between charged particles and emitters are of special interest for precise plasma spectroscopy. The highly charged Ar XV ion is demonstrated to have strong intrashell electron interactions, which manifest as an atomic system with many resonance structures, due to the quasi-degeneracy of orbital energies. In this paper we use the relativistic R-matrix method to investigate the electron-impact broadening of highly charged Ar XV ion spectral lines under the impact approximation. It is found that the results considering resonance structures are significantly different from those of the distorted wave approach. Furthermore, we propose a new empirical formula with a correction term to take into account the effect of resonances for electron-impact widths over a relatively wide range of plasma conditions. The corresponding fitting parameters of the new empirical formula for all 47 calculated transitions are also given with an estimated accuracy within 1%, which should be convenient for practical applications. The dataset that supported the findings of this study is available in Science Data Bank, with the link https://doi.org/10.57760/sciencedb.j00113.00101.

Nonthermal effects on hydrogen Stark profiles

Plasma waves in nonthermal conditions can be strongly amplified by instabilities. We consider plasma conditions where a velocity-space instability amplifies the oscillating electric field magnitude of electron plasma waves up to several times the average plasma microfield. For a wide range of plasma conditions, the first Lyman and Balmer lines of hydrogen are then affected by both the dynamic plasma microfield and the oscillating field. We present computer simulations of line shapes showing the changes expected in such nonthermal conditions.

Predicted performance of a tangential viewing hard x-ray camera for the DIII-D high field side lower hybrid current drive experiment.

High field side launch of lower hybrid current drive (LHCD) has improved accessibility and penetration over low field side launch on DIII-D. Simulations predict single pass absorption under a wide range of plasma conditions. Hard x-ray (HXR) measurement of LHCD generated fast electron bremsstrahlung (50-250keV) will validate wave propagation and absorption. Emissivity profiles are recovered from one-dimensional inversion of HXR brightness to determine LH damping location, fast electron slowing down time, and some indication of the fast electron energy. The camera will be implemented by populating 32 tangential sightlines of the existing Gamma Ray Imager with Kromek SPEARTM Cadmium Zinc Telluride (CZT) detectors sensitive to 10-1000keV photons with 10keV energy resolution. Expected count rates allow for <0.5ms time resolution. Pulses are processed using 50ns shaping time Cremat CR-200 Gaussian shaping modules and are digitized by 25MHz D-TACQ ACQ216 digitizers. The performance of the HXR camera is evaluated by comparing predicted fast electron density profiles and inverted synthetic brightnesses obtained from the ray-tracing/Fokker-Planck codes GENRAY/CQL3D. Inversions closely matched predicted fast electron profiles for a range of experimental parameters.

Hollow cathode enhanced capacitively coupled plasmas in Ar/N2/H2 mixtures and implications for plasma enhanced ALD

Plasma enhanced atomic layer deposition (PEALD) is a cyclic atomic layer deposition process that incorporates plasma-generated species into one of the cycle substeps. The addition of plasma is advantageous as it generally provides unique gas-phase chemistries and a substantially reduced growth temperature compared to thermal approaches. However, the inclusion of plasma, coupled with the increasing variety of plasma sources used in PEALD, can make these systems challenging to understand and control. This work focuses on the use of plasma diagnostics to examine the plasma characteristics of a hollow cathode enhanced capacitively coupled plasma (HC-CCP) source, a type of plasma source that has seen increasing attention in recent years for PEALD. Ultraviolet to near-infrared spectroscopy as well as spatially resolved Langmuir probe and emissive probe measurements are employed to characterize an HC-CCP plasma source using nitrogen based gas chemistries typical of nitride PEALD processes. Spectroscopy is used to characterize the relative concentrations of important reactive and energetic neutral species generated in HC-CCP systems as a function of applied RF power, gas chemistry, and pressure. In addition, the electron energy distribution function, electron temperature, plasma potential, and plasma density for the same process parameters are examined using an RF compensated Langmuir probe and emissive probe. These measurements indicated that electron temperature (Te), electron density (ne), and plasma potential (Vp) varied significantly over the operating conditions examined with Te varying from 1.5 to 8 eV, Vp varying from 30 to 90 V, and ne varying between 1015 and low 1016 m−3. This wide range of plasma conditions is mediated by a mode transition from a low Te, high ne mode of operation at low pressure (&amp;lt;100 mTorr) to a high Te, low ne mode at higher pressures (&amp;gt;100 mTorr). These operational modes appear analogous to the classical γ and α modes of traditional capacitively coupled plasmas. Atomic N and H densities also vary significantly over the operating conditions examined.

Analysis of the ion collisional contribution over the Stark profile in Hα line

Laboratory plasmas can be characterized by Optical Emission Spectroscopy techniques by using Hydrogen Balmer series lines. The line shape is the result of the convolution of the several internal process occuring in plasma. The Stark effect over the Hydrogen emitter atom has been studied in a limited range of plasma parameters, obtaining a profile which is the result of a sum of a given number of Lorentzian functions for the Hα and Hβ line. In this paper, we have extended this analysis to cover a wide range of plasma conditions for the Hα line. The number of Lorentzian functions depends on the contribution of ion collisions around the Hydrogen emitter atom and their mobility in comparison with that of electrons.

High performance simulations of a single X-pinch

The dynamics of plasmas produced by low current X-pinch devices are explored. This comprehensive computational study is the first step in the preparation of an experimental campaign aiming to understand the formation of plasma jets in table-top pulsed power X-pinch devices. Two state-of-the-art magneto-hydro-dynamic codes, GORGON and PLUTO, are used to simulate the evolution of the plasma and describe its key dynamic features. GORGON and PLUTO are built on different approximation schemes and the simulation results obtained are discussed and analyzed in relation to the physics adopted by each code. Both codes manage to accurately handle the numerical demands of the X-pinch plasma evolution and provide precise details on the mechanisms of the plasma expansion, the jet-formation, and the pinch generation. Furthermore, the influence of electrical resistivity, radiation transport and optically thin losses on the dynamic behaviour of the simulated X-pinch produced plasma is studied in PLUTO. Our findings highlight the capabilities of the GORGON and PLUTO codes in simulating the wide range of plasma conditions found in X-pinch experiments, enabling a direct comparison to the scheduled experiments.

Beam-driven ECH waves: A parametric study

Electron cyclotron harmonic (ECH) waves play a significant role in driving the diffuse aurora, which constitutes more than 75% of the particle energy input into the ionosphere. ECH waves in magnetospheric plasmas have long been thought to be excited predominantly by the loss cone anisotropy (velocity–space gradients) that arises naturally in a planetary dipole field. Recent THEMIS observations, however, indicate that an electron beam can also excite such waves in Earth's magnetotail. The ambient and beam plasma conditions under which electron beam excitation can take place are unknown. Knowledge of such conditions would allow us to further explore the relative contribution of this excitation mechanism to ECH wave scattering of magnetospheric electrons at Earth and the outer planets. Using the hot plasma dispersion relation, we address the nature of beam-driven ECH waves and conduct a comprehensive parametric survey of this instability. We find that growth is provided by beam electron cyclotron resonances of both first and higher orders. We also find that these waves are unstable under a wide range of plasma conditions. The growth rate increases with beam density, beam velocity, and hot electron temperature; it decreases with increasing beam temperature and beam temperature anisotropy (T⊥/T∥), hot electron density, and cold electron density and temperature. Such conditions abound in Earth's magnetotail, where magnetospheric electrons heated by earthward convection and magnetic reconnection coexist with colder ionospheric electrons.

Opacity calculation for aluminum, iron, and gold plasmas using FLYCHK code

The opacity information of a finite-temperature plasma is an important property and requires the population distribution of a given plasma condition. A population kinetic code for plasma spectroscopy, FLYCHK, has been widely used by researchers to study the spectroscopic properties of high-energy-density plasmas under a wide range of conditions. In this study, the FLYCHK calculation of the Planck and Rosseland mean opacities of low- to high-Z elements, such as aluminum (Z = 13), iron (Z = 26), and gold (Z = 79), under a wide temperature and density range (T = 10−3–102 keV, ρ = 10−6–102 g/cc) is reported. This study mainly focused on the quantitative comparisons of FLYCHK opacities with commonly used opacities: ATOMIC and PROPACEOS. Comparisons show that the FLYCHK mean opacities are comparable to other results over a wide range of plasma conditions. Aluminum opacities were analyzed in detail to understand the characteristics of FLYCHK opacity simulations.

Density peaking in JET—determined by fuelling or transport?

Core density profile peaking and electron particle transport have been extensively studied by performing several dimensionless collisionality (υ*) scans with other matched dimensionless profiles in various plasma operation scenarios on the Joint European Torus (JET). This is the first time when electron particle transport coefficients in the H-mode have been measured on JET with high resolution diagnostics, and therefore we are in a position to distinguish between the neutral beam injection (NBI) source and inward electron particle pinch in contributing to core density peaking. The NBI particle source is found to contribute typically 50%–60% to the electron density peaking in JET H-mode plasmas where Te/Ti ~ 1 or smaller and at υ* = 0.1–0.5 (averaged between r/a = 0.3–0.8), and being independent of υ* within that range. In these H-mode plasmas, the electron particle transport coefficients, De and ve, are small, thus giving rise to the large influence of NBI fueling with respect to transport effect on peaking. In L-mode plasma conditions, the role of the NBI source is small, typically 10%–20%, and the electron particle transport coefficients are large. These dimensionless υ* scans give the best possible data for model validation. TGLF simulations are in good agreement with the experimental results with respect to the role of NBI particle source versus inward pinch in affecting density peaking, both for the H-mode and L-mode υ* scans. It predicts, similarly to experimental results, that typically about half of the peaking originates from the NBI fuelling in the H-mode and 10%–20% in the L-mode. GENE simulation results also support the key role of NBI fuelling in causing a peaked density profile in JET H-mode plasma (Te/Ti ~ 1 and υ* = 0.1–0.5) and, in fact, give an even higher weight on NBI fuelling than that experimentally observed or predicted by TGLF. For the non-fuelled H-mode plasma at higher Te/Ti = 1.5 and lower βN and υ*, both TGLF and GENE predict peaked density profiles, therefore agreeing well with experimental steady-state density peaking. Overall, the various modelling results give a fairly good confidence in using TGLF and GENE in predicting density peaking in quite a wide range of plasma conditions in JET.

Analysis of radiative opacities for optically thin and thick astrophysical plasmas

The resolution of the radiative transfer equation in radiation-hydrodynamic simulations of astrophysical plasmas require radiative opacities. In this work, an analysis of the monochromatic and multigroup opacities of an astrophysical plasma mixture has been carried out. The study has been made in ranges of electron temperatures and densities of 1−1000 eV and 1011−1020 cm−3, respectively, a wide range of plasma conditions that can be found in several astrophysical scenarios where local and non-local thermodynamic regimes are attained. Collisional-radiative calculations were performed to obtain the plasma level populations and the monochromatic opacities in that range of plasma conditions, covering both thermodynamic regimes. Since the astrophysical mixture includes chemical elements from hydrogen to iron, their contribution to the total opacity will depend on the plasma conditions and we have made a characterization of their contribution as a function of the electron density and temperature and also of the photon frequency. Multigroup and gray approaches are commonly used in the radiative transfer equation in radiation-hydrodynamic calculations. We have analyzed the influence of the number of the groups in the accuracy of the multigroup opacities and we have showed that, for a given plasma condition, the opacity of the multicomponent plasma in the gray approach may be considerably influenced by only some of the contributing elements, due to the influence of the weighting function in the mean, which can lead to great differences with respect to the monochromatic opacity. Finally, since there are situations in which the self-absorption of the plasma radiation becomes relevant due to the dimensions of the plasma, we have performed an analysis of the influence of the radiation trapping in the monochromatic and multigroup opacities in terms of the plasma conditions and the width of the plasma slab, assuming the plasma with planar geometry and we have also studied the departures of the local thermodynamic regime.

Implementation of an inelastic collision operator into KIPP‐SOLPS coupling and its effects on electron parallel transport in the scrape‐off layer plasmas

This paper develops an inelastic collision operator for the Kinetic Code for Plasma Periphery (KIPP) code to investigate the kinetic effects of electron cooling due to inelastic collisions. It is fully tested based on the self‐consistent KIPP‐SOLPS coupling algorithm by being compared to the ADAS database. The collisional radiative rate coefficients from the ADAS database for deuterium atomic physics can be recovered using the inelastic collision operator with assuming Maxwellian electrons, which shows that the inelastic collision operator works well for various plasma conditions. Across a wide range of plasma conditions in the scrape‐off layer, KIPP‐SOLPS coupling simulation results with the implementation of an inelastic collision operator are not significantly different from results using a simpler uniform cooling scheme. The uniform scheme is thus recommended rather than including computationally intensive inelastic collision physics.

The Hβ line dip shift measurements in wide range of plasma electron density

In this paper, we present experimental shift results of the dip of the Balmer Hβ line emitted from three plasma sources. The use of different sources enabled the measurements to be carried out under a wide range of plasma conditions. The electron density was in the range of (0.17–6.56) × 1023 m−3 and electron temperature in the range of 10,100–33,000 K. For higher electron densities, the measured dip shift shows a nonlinear dependence on the electron density. It is shown that this nonlinearity is the consequence of the asymmetry of the Hβ line. The correlation between the measured dip shift and Hβ line halfwidths shows that the dip shift can be used for plasma electron density determination. This can be useful in cases when the Hβ spectrum cannot be fully covered by the spectral apparatus.

Incorporating kinetic effects on Nernst advection in inertial fusion simulations

We present a simple method to incorporate nonlocal effects on the Nernst advection of magnetic fields down steep temperature gradients, and demonstrate its effectiveness in a number of inertial fusion scenarios. This is based on assuming that the relationship between the Nernst velocity and the heat flow velocity is unaffected by nonlocality. The validity of this assumption is confirmed over a wide range of plasma conditions by comparing Vlasov–Fokker–Planck and flux-limited classical transport simulations. Additionally, we observe that the Righi–Leduc heat flow is more severely affected by nonlocality due to its dependence on high velocity moments of the electron distribution function, but are unable to suggest a reliable method of accounting for this in fluid simulations.

Poloidal asymmetries of flows in the Tore Supra tokamak

Simultaneous measurements of binormal velocity of density fluctuations using two separate Doppler backscattering systems at the low field side and at the top of the plasma show significant poloidal asymmetry. The measurements are performed in the core region between the radii 0.7 &amp;lt; ρ &amp;lt; 0.95, over a limited number of L-mode discharges covering a wide range of plasma conditions in the Tore Supra tokamak. A possible generation mechanism by the ballooned structure of the underlying turbulence, in the form of convective cells, is proposed for explaining the observation of these poloidally asymmetric mean flows.

Isolating and quantifying cross-beam energy transfer in direct-drive implosions on OMEGA and the National Ignition Facility

The angularly resolved mass ablation rates and ablation-front trajectories for Si-coated CH targets were measured in direct-drive inertial confinement fusion experiments to quantify cross-beam energy transfer (CBET) while constraining the hydrodynamic coupling. A polar-direct-drive laser configuration, where the equatorial laser beams were dropped and the polar beams were repointed from a symmetric direct-drive configuration, was used to limit CBET at the pole while allowing it to persist at the equator. The combination of low- and high-CBET conditions observed in the same implosion allowed for the effects of CBET on the ablation rate and ablation pressure to be determined. Hydrodynamic simulations performed without CBET agreed with the measured ablation rate and ablation-front trajectory at the pole of the target, confirming that the CBET effects on the pole are small. The simulated mass ablation rates and ablation-front trajectories were in excellent agreement with the measurements at all angles when a CBET model based on Randall's equations [C. J. Randall et al., Phys. Fluids 24, 1474 (1981)] was included into the simulations with a multiplier on the CBET gain factor. These measurements were performed on OMEGA and at the National Ignition Facility to access a wide range of plasma conditions, laser intensities, and laser beam geometries. The presence of the CBET gain multiplier required to match the data in all of the configurations tested suggests that additional physics effects, such as intensity variations caused by diffraction, polarization effects, or shortcomings of extending the 1-D Randall model to 3-D, should be explored to explain the differences in observed and predicted drive.

First-principles investigations on ionization and thermal conductivity of polystyrene for inertial confinement fusion applications

Using quantum molecular-dynamics (QMD) methods based on the density functional theory, we have performed first-principles investigations of the ionization and thermal conductivity of polystyrene (CH) over a wide range of plasma conditions (ρ = 0.5 to 100 g/cm3 and T = 15 625 to 500 000 K). The ionization data from orbital-free molecular-dynamics calculations have been fitted with a “Saha-type” model as a function of the CH plasma density and temperature, which gives an increasing ionization as the CH density increases even at low temperatures (T &amp;lt; 50 eV). The orbital-free molecular dynamics method is only used to gauge the average ionization behavior of CH under the average-atom model in conjunction with the pressure-matching mixing rule. The thermal conductivities (κQMD) of CH, derived directly from the Kohn–Sham molecular-dynamics calculations, are then analytically fitted with a generalized Coulomb logarithm [(lnΛ)QMD] over a wide range of plasma conditions. When compared with the traditional ionization and thermal conductivity models used in radiation–hydrodynamics codes for inertial confinement fusion simulations, the QMD results show a large difference in the low-temperature regime in which strong coupling and electron degeneracy play an essential role in determining plasma properties. Hydrodynamic simulations of cryogenic deuterium–tritium targets with CH ablators on OMEGA and the National Ignition Facility using the QMD-derived ionization and thermal conductivity of CH have predicted ∼20% variation in target performance in terms of hot-spot pressure and neutron yield (gain) with respect to traditional model simulations.

First-principles equation of state of polystyrene and its effect on inertial confinement fusion implosions

Obtaining an accurate equation of state (EOS) of polystyrene (CH) is crucial to reliably design inertial confinement fusion (ICF) capsules using CH/CH-based ablators. With first-principles calculations, we have investigated the extended EOS of CH over a wide range of plasma conditions (ρ=0.1to100g/cm(3) and T=1000 to 4,000,000 K). When compared with the widely used SESAME-EOS table, the first-principles equation of state (FPEOS) of CH has shown significant differences in the low-temperature regime, in which strong coupling and electron degeneracy play an essential role in determining plasma properties. Hydrodynamic simulations of cryogenic target implosions on OMEGA using the FPEOS table of CH have predicted ∼30% decrease in neutron yield in comparison with the usual SESAME simulations. This is attributed to the ∼5% reduction in implosion velocity that is caused by the ∼10% lower mass ablation rate of CH predicted by FPEOS. Simulations using CH-FPEOS show better agreement with measurements of Hugoniot temperature and scattered light from ICF implosions.