Lyman Series Research Articles

Lyman line opacities in tokamak divertor plasmas under high-recycling and detached conditions

Radiation transport simulations of the deuterium Lyman series using EIRENE predict a factor of 2 increase of Balmer-α emission in the JET-ILW low confinement divertor plasmas in high-recycling and detached conditions caused by the re-absorption of Lyman-β emission. The photon tracing model in the EIRENE code is applied to SOLPS-ITER pure deuterium plasma solutions of JET-ILW to evaluate the contribution of Lyman-β capture towards the population density of D(p=3) and consequently the Balmer-α emission. The local population escape factors of Lyman-α and Lyman-β lines in the JET-ILW divertor show steep spatial gradients and indicate local regions with high opacity in high-recycling and detached conditions. The relative contribution of Lyman-β capture towards the population density of D(p=3) is significant in high-recycling and detached conditions. This observation is further corroborated by line-integrated calculations using Balmer-α diagnostic line-of-sights.

He II line intensity measurements in the JET tokamak

Abstract An understanding of the behaviour of the D or He fuel used in tokamak discharges is essential in analyses such as modelling edge and divertor transport and the erosion of the vessel walls. However, poor agreement is found between measurements made on the JET tokamak and collisional-radiative models used to predict the hydrogen-like D and He line intensities. The range of temperatures of the plasmas emitting the radiation is also limited, in contrast to that for many impurities for which a wide range is possible. This is particularly so for He II whose line intensities tend to have the same near-constant ratios in most pulses, suggesting that the emission originates in plasma regions with very similar electron temperatures. To gain understanding and to allow quantitative comparisons with theoretical models, extensive observations of the VUV Lyman series have been made, for all discharge scenarios run during three He campaigns. Those for He discharges in both JET ITER-like wall (JET-ILW) and JET C (JET-C) campaigns are presented here. He discharges have the advantage of fewer impurities resulting in less complex spectra than when D is used as the fuel. However, the characteristics of the observed discrepancies are similar in both species, allowing He to be used as a proxy for D in order to gain understanding of the discrepancy. In addition, the study of He avoids the complication of molecular species contributing to the level populations. Opacity effects are also expected to be less severe in He discharges. Nevertheless, so as to ensure that the measurements are not unduly affected by opacity, comparisons have also been made with emission from Balmer and Paschen series members. Measurements of both line intensities and their ratios are presented for all-pulse surveys and for individual pulses. In exceptional cases in which the He emission is intense a dependence on the He II line intensity is demonstrated. The discrepancy between these measurements and the theoretical models is illustrated.

A Markovian description of the multi-level source function and its application to the Lyman series in the Sun

Aims. We introduce a new method to calculate and interpret indirect transition rates populating atomic levels using Markov chain theory. Indirect transition rates are essential to evaluate interlocking in a multi-level source function, which quantifies all the processes that add and remove photons from a spectral line. A better understanding of the multi-level source function is central to interpret optically thick spectral line formation in stellar atmospheres, especially outside local thermodynamical equilibrium (LTE). Methods. We compute the level populations from a hydrogen model atom in statistical equilibrium, using the solar FALC model, a 1D static atmosphere. From the transition rates, we reconstruct the multi-level source function using our new method and compare it with existing methods to build the source function. We focus on the Lyman series lines and analyze the different contributions to the source functions and synthetic spectra. Results. Absorbing Markov chains can represent the level-ratio solution of the statistical equilibrium equation and can therefore be used to calculate the indirect transition rates between the upper and lower levels of an atomic transition. Our description of the multi-level source function allows a more physical interpretation of its individual terms, particularly a quantitative view of interlocking. For the Lyman lines in the FALC atmosphere, we find that interlocking becomes increasingly important with order in the series, with Ly-α showing very little, but Ly-β nearly 50% and Ly-γ about 60% contribution coming from interlocking. In some cases, this view seems opposed to the conventional wisdom that these lines are mostly scattering, and we discuss the reasons why. Conclusions. Our formalism to describe the multi-level source function is general and can provide more physical insight into the processes that set the line source function in a multi-level atom. The effects of interlocking for lines formed in the solar chromosphere can be more important than previously thought, and our method provides the basis for further exploration.

Impact of Helium ii Resonant Absorption on the Ultraviolet Background Modeled in Three Dimensions

We implement a treatment of helium ii absorption and reemission into the Technicolor Dawn cosmological simulations to study its impact on the metagalactic ultraviolet background (UVB) in three dimensions. By comparing simulations with and without He ii reprocessing, we show that it weakens the mean UVB by ∼3 dex from z = 10–5 between 3.5 and 4 Ryd, where the He ii Lyman series resonance occurs. In overdense regions, the overall UVB amplitude is higher, and the impact of He ii reprocessing is weaker, qualitatively indicating an early start to He ii reionization near galaxies. Comparing our simulations to two popular one-dimensional UV models, we find good agreement up to 3 Ryd at z = 5. At higher energies, our simulation shows significantly greater He ii absorption because it accounts for He ii arising both in diffuse regions and in Lyman limit systems. By contrast, the comparison models account only for He ii in Lyman limit systems, which are subdominant prior to the completion of He ii reionization. The H i and He ii reionization histories are nearly unaffected by He ii reprocessing, although the cosmic star formation rate density is altered by up to 4%. The cosmic mass density of C iv is reduced by ∼2 dex when He ii is accounted for, while Si iv, C ii, Mg ii, Si ii, and O i are unaffected.

The diversity of spectral shapes of hydrogen Lyman lines and Mg II lines in a quiescent prominence

Context. Broad sets of spectroscopic observations comprising multiple lines represent an excellent opportunity for diagnostics of the properties of the prominence plasma and the dynamics of their fine structures. However, they also bring significant challenges when they are compared with synthetic spectra provided by radiative transfer modeling. Aims. In this work, we provide a statistical spectroscopic analysis of a unique dataset of coordinated prominence observations in the Lyman lines (Lyα to Lyδ) and the Mg II k and h lines. The observed data were obtained by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrograph on board of the Solar and Heliospheric Observatory (SoHO) satellite and the Interface Region Imaging Spectrograph (IRIS) on 22 October 2013. Only a few similar coordinated datasets of Lyman and Mg II k and h observations have ever been obtained in prominences and we present here the first analysis using these two sets of spectral lines. Moreover, for the first time, we assess the influence of noise on the statistical properties of the studied profile characteristics. Methods. We focus on the following profile characteristics: the shape of the observed line profiles based on the number of distinct peaks, the integrated line intensity, the center-to-peak ratio describing the depth of the reversal of two-peaked profiles, and the asymmetry of these peaks. Results. We show that the presence of noise has a negligible effect on the integrated intensity of all observed lines, but it significantly affects the classification of spectral profiles using the number of distinct peaks, the reversal depth, and also the peak asymmetry. We also demonstrate that by taking the influence of noise into account, we can assess which profile characteristics in which spectral lines are suitable for diagnostics of different properties of the observed prominence. For example, we show that the subordinate peaks (peaks below error bars) in the Lyman line profiles are mostly caused by noise, which means that only the dominant peaks should be used for statistical analyses or comparisons with synthetic spectra. On the other hand, in the Mg II k and h profiles, the key role in the distinction between the multi-peaked profiles with low peaks and the profiles with deep reversals is played by the dynamics of multiple fine structures located along a line of sight. The complex, multi-peaked profiles are observed in places where multiple fine structures with different line-of-sight velocities are crossing the line of sight, while the profiles with deep reversals likely correspond to instances when we observe single fine structures or more fine structures but with similar line-of-sight velocities. Conclusions. This study allows us to conclude that if we are interested in the diagnostics of the dynamics of prominence fine structures, the best approach is to use a combination of profile asymmetry in the Lyman lines together with the complex profiles of Mg II k and h lines. On the other hand, if we want to diagnose the temperature and pressure properties of individual prominence fine structures, we need to focus on the deeply reversed Mg II k and h lines in combination with the Lyman lines and to analyze the depth of the central reversal and the integrated intensities.

The Search for the Origin of the Quantum Conditions under the Paradigm of Absolute Space

This study deals with the physical (not the mathematical) origin of the quantum conditions. The assumption of an absolute space together with the speed of 369.5 km/s of the sun leads to cycloidal or helical orbits of the electron around the proton. This kind of orbits is a previously unnoticed fact and not compatible with the model of a closed circular standing wave. It is the aim of this study to search for alternative models. The Alternating Field model (AFM) assumes the existence of alternating fields for both the proton and the electron. The Higgs-field provides the energy requirements. By Puthoff’s effect, adapted for the electrostatic field, the electron changes its Compton frequency according to its position in the field. The interference of the alternating fields of the proton and the electron causes beats that are integer multiples of the orbital frequencies when the electron moves on Bohr’s orbits. Important results of this study are: The electrostatic Schwarzschild-radius is exactly half the value of the classical electron radius. Bohr’s first three principal quantum numbers, 1, 2, 3, are reproduced as 1.000052, 2.000214, and 3.000685. A two-dimensional simulation shows that the AFM causes orbits with ribbon shape. A formula, using only the orbital frequencies of the two innermost circular orbits, can predict the shortest wavelength of the Lyman series. The AFM is still incomplete. E.g., it does not prevent illegal orbits, but only indicates them. Also, the AFM does not use the magnetic core field of the proton. On the other hand, the model has produced results showing that Newton’s absolute space and the QM are compatible.

Source of High-Efficiency Radiation in the Lyman and Werner Bands of a Pulse Discharge in Mixtures of Hydrogen and Helium

Source of High-Efficiency Radiation in the Lyman and Werner Bands of a Pulse Discharge in Mixtures of Hydrogen and Helium

An extremely metal-poor star complex in the reionization era: Approaching Population III stars with JWST

We present JWST/Near Infrared Spectrograph (NIRSpec) integral field spectroscopy (IFS) of a lensed Population III candidate stellar complex (dubbed Lensed And Pristine 1, LAP1), with a lensing-corrected stellar mass of ≲104 M⊙ and an absolute luminosity of MUV > −11.2 (mUV > 35.6), confirmed at redshift 6.639 ± 0.004. The system is strongly amplified (μ ≳ 100) by straddling a critical line of the Hubble Frontier Field galaxy cluster MACS J0416. Although the stellar continuum is currently not detected in the Hubble and JWST/Near Infrared Camera (NIRCam) and Near Infrared Imager and Slitless Spectrograph (NIRISS) imaging, arclet-like shapes of Lyman and Balmer lines, Lyα, Hγ, Hβ and Hα are detected with NIRSpec IFS with signal-to-noise ratios (S/N) of approximately 5 − 13 and large equivalent widths (> 300 − 2000 Å), along with a remarkably weak [O III]λλ4959, 5007 at S/N ≃ 4. LAP1 shows a large ionizing photon production efficiency, log(ξion[erg Hz−1]) > 26. From the metallicity indexes R23 = ([O III] + [O II])/Hβ ≲ 0.74 and R3 = ([O III]/Hβ) = 0.55 ± 0.14, we derive an oxygen abundance of 12 + log(O/H)≲6.3. Intriguingly, the Hα emission is also measured in mirrored subcomponents where no [O III] is detected, providing even more stringent upper limits on the metallicity if in situ star formation is ongoing in this region (12 + log(O/H) < 6). The formal stellar mass limit of the subcomponents would correspond to ∼103 M⊙ or MUV fainter than −10. Alternatively, this metal-free, pure line-emitting region could be the first case of a fluorescing H I gas region induced by transverse escaping ionizing radiation from a nearby star complex. The presence of large equivalent-width hydrogen lines and the deficiency of metal lines in such a small region make LAP1 the most metal-poor star-forming region currently known in the reionization era and a promising site that may host isolated, pristine stars.

VUV lasing in diffuse discharges formed by runaway electrons

The parameters of stimulated emission in diffuse discharges formed in a sharply inhomogeneous electric field by runaway electrons in mixtures of rare gases with the addition of H2 and F2 at pressures up to 10 atm are studied. Efficient VUV lasing was obtained at wavelengths from 148 to 193 nm on the transitions of H2, F2 and exciplex ArF* molecules. It was shown that the addition of He buffer gas increases the pulse duration, while Ne addition improves the output energy of the VUV laser on the H2 Lyman band. A laser pulse duration over 10 ns and an output of 0.12 mJ were obtained. The diffuse discharge in mixtures of He with F2 was found to form as a result of successive ionization waves. It was shown that the laser pulse at 157 nm has three peaks, which correspond to the maxima of the diffuse discharge current. Therewith, the first or second peak of the laser radiation has the maximum intensity, depending on the amplitude of the conduction current in the primary ionization wave. A maximal F2* laser electrical efficiency of η 0 = 0.18% and an output of Q 157 = 3.8 mJ were obtained in a He–F2 gas mixture at pressure of 10 atm, which exceeds the efficiency of lasers of this type pumped by transverse volume discharges with UV preionization. Long-pulse operation of the ArF* laser was achieved in a He–Ne–Ar–F2 gas mixture. Lasing at 193 nm continued during two periods of the diffuse discharge current. The total duration of the laser pulse was as long as 40 ns, and the radiation energy at 193 nm was as high as 2 mJ from an active volume of 20 cm3.

Formation of Hε in the solar atmosphere

Context. In the solar spectrum, the Balmer series line Hε is a weak blend on the wing of Ca II H. Recent high-resolution Hε spectroheliograms reveal a reversed granulation pattern and in some cases, even unique structures. It is apparent that Hε could potentially be a useful diagnostic tool for the lower solar atmosphere. Aims. Our aim is to understand how Hε is formed in the quiet Sun. In particular, we consider the particular physical mechanism that sets its source function and extinction, how it is formed in different solar structures, and why it is sometimes observed in emission. Methods. We used a 3D radiative magnetohydrodynamic (MHD) simulation that accounts for non-equilibrium hydrogen ionization, run with the Bifrost code. To synthesize Hε and Ca II H spectra, we made use of the RH code, which was modified to take into account the non-equilibrium hydrogen ionization. To determine the dominant terms in the Hε source function, we adopted a multi-level description of the source function. Making use of the synthetic spectra and simulation, we studied the contribution function to the relative line absorption or emission and compared it with atmospheric quantities at different locations. Results. Our multi-level source function description suggests that the Hε source function is dominated by interlocking, with the dominant interlocking transition being through the ground level, populating the upper level of Hε via the Lyman series. This makes the Hε source function partly sensitive to temperature. The Hε extinction is set by Lyman-α. In some cases, this temperature dependence gives rise to Hε emission, indicating heating. The typical absorption profiles show reversed granulation and the Hε line core reflects mostly the Ca II H background radiation. Conclusions. Synthetic Hε spectra can reproduce quiet Sun observations quite well. High-resolution observations reveal that Hε is not just a weak absorption line. Regions with Hε in emission are especially interesting to detect small-scale heating events in the lower solar atmosphere, such as Ellerman bombs. Thus, Hε can be an important new diagnostic tool for studies of heating in the solar atmosphere, augmenting the diagnostic potential of Ca II H when observed simultaneously.

Comparison of Different Detection Scenarios of Lyman-α

After the first galaxies formed in the universe, the energy they produced causes the cosmic reionization. Galaxies at high redshift are so faint that it will be extremely difficult to obtain their data. The Ly-α line becomes an excellent target for spectroscopic redshift determinations to gain the data because it is among the strongest lines emitted by high-redshift galaxies. This paper reviews recently observation and simulation relating to Ly-α: J2129.4 and the Sherwood simulations. Lyman-alpha line is a spectral line of hydrogen in the Lyman series among the strongest lines emitted by high-redshift galaxies. This review concludes the Keck DEIMOS and HST Grism Data. It indicates the gravitational lensing may be the most efficient method of galaxy detection, even in the era of the James Webb Space Telescope and conclude. This paper also summarizes the results of the Sherwood simulation, which shows that the simulations are perfectly corresponding to high resolution, high signal-to-noise observations of the Ly α forest over the redshift range 2 ≤ z ≤ 5 although there are some discrepancies. This paper can help people have a picture of recent observation and simulations as well as shed light on guiding further exploration of Ly-α.

Caught in the Act: A Metal-rich High-velocity Cloud in the Inner Galaxy

We characterize the chemical and physical conditions in an outflowing high-velocity cloud (HVC) in the inner Galaxy. We report a supersolar metallicity of [O/H] = +0.36 ± 0.12 for the HVC at v LSR = 125.6 km s−1 toward the star HD 156359 (l = 328.°7, b = −14.°5, d = 9 kpc, z = −2.3 kpc). Using archival observations from the Far-Ultraviolet Spectroscopic Explorer (FUSE), the Hubble Space Telescope Imaging Spectrograph, and the European Southern Observatory Fiber-fed Extended Range Optical Spectrograph we measure high-velocity absorption in H i, O i, C ii, N ii, Si ii, Ca ii, Si iii, Fe iii, C iv, Si iv, N v, and O vi. We measure a low H i column density of log N(H i) = 15.54 ± 0.05 in the HVC from multiple unsaturated H i Lyman series lines in the FUSE data. We determine a low dust depletion level in the HVC from the relative strength of silicon, iron, and calcium absorption relative to oxygen, with [Si/O] = −0.33 ± 0.14, [Fe/O] = −0.30 ± 0.20, and [Ca/O] = −0.56 ± 0.16. Analysis of the high-ion absorption using collisional ionization models indicates that the hot plasma is multiphase, with the C iv and Si iv tracing 104.9 K gas and N v and O vi tracing 105.4 K gas. The cloud’s metallicity, dust content, kinematics, and close proximity to the disk are all consistent with a Galactic wind origin. As the HD 156359 line of sight probes the inner Galaxy, the HVC appears to be a young cloud caught in the act of being entrained in a multiphase Galactic outflow and driven out into the halo.

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.

R-matrix Electron-impact Excitation Data for the H- and He-like Ions with Z = 6−30

Abstract Plasma models built on extensive atomic data are essential to interpreting observed cosmic spectra. H-like Lyman series and He-like triplets observable in the X-ray band are powerful diagnostic lines to measure the physical properties of various types of astrophysical plasmas. Electron-impact excitation is a fundamental atomic process for the formation of H-like and He-like key diagnostic lines. Electron-impact excitation data adopted by the widely used plasma codes (AtomDB, CHIANTI, and SPEX) do not necessarily agree with each other. Here we present a systematic calculation of electron-impact excitation data of H-like and He-like ions with the atomic number Z = 6–30 (i.e., C to Zn). A radiation-damped R-matrix intermediate-coupling frame transformation calculation was performed for each ion with configurations up to n = 6. We compare the present work with the above three plasma codes and the literature to assess the quality of the new data, which are relevant for current and future high-resolution X-ray spectrometers.

Real-time VUV radiation monitoring in low-pressure hydrogen plasma based on fluorescence of sodium salicylate

Recently, vacuum ultra-violet (VUV) radiation emitted from plasmas has been of particular interest in semiconductor device fabrication because of the effects of its high-energy photons, such as induced damage or curing on low-k materials. Due to the difficulty of implementing conventional spectroscopic methods to monitor VUV radiation with high accuracy and time resolution in current plasma processing equipment, novel monitoring methods must be investigated. Therefore, in this work, we developed a compact VUV radiation monitoring system based on a scintillator, i.e. sodium salicylate (NaSal), for real-time VUV measurements. Compared to conventional VUV spectrometers, the system shows considerable implementation potential thanks to its compact size, higher detection accuracy and high time resolution. VUV radiation emitted by continuous and pulsed hydrogen plasmas generated at low pressure was investigated using the developed system. Using various filters, we were able to compare the VUV photon intensity in different wavelength ranges. It was found that the VUV photon intensity between 115 and 250 nm was about 2.5 times higher than in the region below 115 nm due to intense Lyman-α and molecular radiation, such as Lyman and Werner bands observed in low-pressure hydrogen plasmas.

Formula omitted] cooling in the jovian aurora: Juno remote sensing observations and modeling

Cooling of Jupiter's auroral thermosphere by H3+ radiation to space is one of the processes controlling the energy balance in the auroral upper atmosphere. The UltraViolet Spectrograph (UVS) and the Jupiter InfraRed Auroral Mapper (JIRAM) on board Juno have observed the Jovian polar aurora from its polar orbit since August 2016. The UVS instrument measures the H2 Lyman and Werner bands whose brightness is a proxy of the precipitated auroral electron flux. The 3.3–3.6 μm spectral window of the JIRAM L-band imager maps the H3+ thermal radiance with unprecedented spatial resolution. Comparison of concurrent observations indicates that the morphological features are similar in the two spectral regions but differences are also observed in the spatial intensity contrast. We compare the total (direct and indirect) particle heating rate and the cooling by H3+ radiation derived from four pairs of simultaneous UVS and JIRAM images. The total auroral cooling power H3+ is in the range 2–4 terawatts in both hemispheres. In all cases, the H3+ cooling in the aurora is found to range between 0.45 and 0.67 time less than the particle collisional heating. In a second step, we use the ultraviolet H2 brightness and FUV color ratio to derive the characteristics of the electron precipitation and model the H3+ radiance for each UVS map pixel. The comparison of the H3+ modeled radiance map with the JIRAM observations shows general good agreement with some local differences. The four spatially integrated H3+ cooling power from the model are in very good agreement with the JIRAM values. These results are important constraints for global magnetosphere-ionosphere-atmosphere models.

Detection Feasibility of H2 in Ultra-hot Jupiter Atmospheres

Ultra-hot Jupiters (UHJs) have recently been the focus of several atmospheric studies due to their extreme properties. While molecular hydrogen (H2) plays a key role in UHJ atmospheres, it has not been directly detected on an exoplanet. To determine the feasibility of H2 detection via transmission spectroscopy of the Lyman and Werner bands, we modeled UHJ atmospheres with H2 rotational temperatures varying from 2000 to 4000 K orbiting A-type stars ranging from T eff = 8500 K to T eff = 10,300 K. We present simulated transmission spectra for each planet-star temperature combination while adding Poisson noise varying in magnitude from 0.5% to 2.0%. Finally, we cross-correlated the spectra with expected atmospheric H2 absorption templates for each temperature combination. Our results suggest that H2 detection with current facilities, namely the Hubble Space Telescope, is not possible. However, direct atmospheric transmission spectroscopy of H2 may be viable with future UV-capable flagship missions.

A complex multiphase DLA associated with a compact group at z = 2.431 traces accretion, outflows, and tidal streams

ABSTRACT As part of our program to identify host galaxies of known z = 2–3 Mg ii absorbers with the Keck Cosmic Web Imager (KCWI), we discovered a compact group giving rise to a z = 2.431 DLA with ultrastrong Mg ii absorption in quasar field J234628+124859. The group consists of four star-forming galaxies within 8–28 kpc and v ∼ 40–340 km s−1 of each other, where tidal streams are weakly visible in deep HST imaging. The group geometric centre is D = 25 kpc from the quasar (D = 20–40 kpc for each galaxy). Galaxy G1 dominates the group (1.66L*, SFRFUV = 11.6 M⊙ yr−1) while G2, G3, and G4 are less massive (0.1–0.3L*, SFRFUV = 1.4–2.0 M⊙ yr−1). Using a VLT/UVES quasar spectrum covering the H i Lyman series and metal lines such as Mg ii, Si iii, and C iv, we characterized the kinematic structure and physical conditions along the line of sight with cloud-by-cloud multiphase Bayesian modelling. The absorption system has a total $\log (N({{{\rm H}\,\rm{\small I}}})/{\rm cm}^{-2})=20.53$ and an $N({{{\rm H}\,\rm{\small I}}})$-weighted mean metallicity of log (Z/Z⊙) = −0.68, with a very large Mg ii linewidth of Δv ∼ 700 km s−1. The highly kinematically complex profile is well modelled with 30 clouds across low- and intermediate-ionization phases with values ${13\lesssim \log (N({{{\rm H}\,\rm{\small I}}})/{\rm cm}^{-2})\lesssim 20}$ and −3 ≲ log (Z/Z⊙) ≲ 1. Comparing these properties to the galaxy properties, we infer a wide range of gaseous environments, including metal-rich outflows, metal-poor IGM accretion, and tidal streams from galaxy–galaxy interactions. This diversity of structures forms the intragroup medium around a complex compact group environment at the epoch of peak star formation activity. Surveys of low-redshift compact groups would benefit from obtaining a more complete census of this medium for characterizing evolutionary pathways.

X-ray emission associated with radiative recombination for Pb82+ ions at threshold energies

For decelerated bare lead ions at a low beam energy of 10 MeV/u, the x-ray emission associated with radiative recombination (RR) at threshold energies has been studied at the electron cooler of CRYRING@ESR at GSI, Darmstadt. In our experiment, we observed the full x-ray emission pattern by utilizing dedicated x-ray detection chambers installed at 0∘ and 180∘ observation geometry. Most remarkably, no line distortion effects due to delayed emission are present in the well-defined x-ray spectra, spanning a wide range of x-ray energies (from about 5 to 100 keV), which enables us to identify fine-structure resolved Lyman, Balmer, and Paschen x-ray lines along with the RR transitions into the K, L, and M shells of the ions. For comparison with theory, an elaborate theoretical model is established taking into account the initial population distribution via RR for all atomic levels up to Rydberg states with principal quantum number n=165 in combination with time-dependent feeding transitions. Within the statistical accuracy, the experimental data are in very good agreement with the results of rigorous relativistic predictions. Most notably, this comparison sheds light on the contribution of prompt and delayed x-ray emission (up to 70 ns) to the observed x-ray spectra, originating in particular from yrast transitions into inner shells.2 MoreReceived 19 January 2022Accepted 31 March 2022DOI:https://doi.org/10.1103/PhysRevA.105.052804Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAtomic & molecular collisionsAtomic spectraElectronic transitionsTechniquesEnergy-dispersive x-ray spectroscopyAtomic, Molecular & OpticalAccelerators & Beams

Modeling of deuterium and carbon radiation transport in MAST-U tokamak advanced divertors

Modest effects of deuterium and carbon radiation opacity in the Super-X and snowflake divertor plasmas are predicted for MAST Upgrade tokamak with core plasma input power 2.5–5 MW and plasma current 1 MA. The radiation transport modeling is based on the SOLPS-EIRENE and UEDGE code divertor plasma predictions. Two radiation transport models are used: one is based on a full radiation transport equation implemented in the radiation transport and collisional-radiative code CRETIN (without feedback on the background plasma), and another is an internal self-consistent UEDGE model with ionization, recombination, and heating rates corrected for Ly α line trapping based on the escape probability model implemented in CRETIN. In MAST-U, the Super-X and snowflake divertor plasmas are predicted to reach detached regimes at lower upstream densities than the standard divertor, and the conclusion still holds with radiation transport effects included. At neutral densities m−3, modest Ly α deuterium line trapping with optical depths 10–15 is predicted in the Super-X divertor. Divertor plasmas are optically thin to other Lyman and Balmer lines, as well as to strong C III and C IV lines that are responsible for most of divertor radiated power. Insignificant changes (within a few percent) to divertor deuterium ionization and recombination rates are found. Radiation fluxes on outer divertor target are modified within a factor of 2–3 when the radiation transport is accounted for, and a similar variation is found due to the line shape models that define the absorption and emission line profiles in the radiation transport modeling. The predicted Lyman and Balmer spectral intensities are significantly modified due to radiation trapping. A measurement of divertor radiation transport effects is discussed using the Ly β /Ba α line ratio. In the snowflake divertor configuration, divertor plasmas are found to be optically thin to Lyman series lines within a large range of parameter variations that include upstream density, divertor transport coefficients, and magnetic configurations. Modest radiation transport effects are only found in a few cases with strongest divertor transport and magnetic configurations closest to the ideal snowflake configuration, however, the plasma background models that were used are yet to be validated with an experiment.