Radiative Loss Rates Research Articles

CHIANTI—An Atomic Database for Emission Lines—Paper. XVIII. Version 11, Advanced Ionization Equilibrium Models: Density and Charge Transfer Effects

Version 11 of the chianti database and software package is presented. Advanced ionization equilibrium models have been added for low charge states of seven elements (C, N, O, Ne, Mg, Si, and S), and represent a significant improvement especially when modeling the solar transition region. The models include the effects of higher electron density and charge transfer on ionization and recombination rates. As an illustration of the difference these models make, a synthetic spectrum is calculated for an electron pressure of 7 × 1015 cm−3 K and compared with an active region observation from HRTS. Increases are seen in factors of 2–5 in the predicted radiances of the strongest lines in the UV from Si iv, C iv, and N v, compared to the previous modeling using the coronal approximation. Much better agreement (within 20%) with the observations is found for the majority of the lines. The new atomic models better equip both those who are studying the transition region and those who are interpreting the emission from higher-density astrophysical and laboratory plasma. In addition to the advanced models, several ion data sets have been added or updated, and data for the radiative recombination energy loss rate have been updated.

Radiation induced non-linear oscillations in ITER baseline scenario plasmas in DIII-D

This work shows how the radiation brought about by metals or metal-equivalent radiators such as Kr and Xe produces non-linear dynamics on otherwise stationary β N flattops of DIII-D ITER Baseline Scenario demonstration discharges. The Kr and Xe gases are used to reproduce the radiative loss rates of W in present machines that operate at core temperatures much lower than the expected ITER temperature. Experiments on DIII-D with injection of Kr and Xe, as well as with sources of intrinsic metals reach the range of radiated fraction values expected in the ITER core and experience slow oscillations in temperature and radiated power. In many cases of high radiated fraction, the core temperature decreases enough for the safety factor profile to rise above the 1/1 rational surface, naturally eliminating sawteeth and occasionally producing a persistent helical core. The oscillations can be reproduced by a modified Lotka–Volterra system for temperature and radiated fraction if diffusion and noise are included, which indicates that the interplay between temperature and radiation can be the main cause of the cyclic nature of the system. A new physics based model which includes equations for temperature, density and input power can also reproduce the oscillations observed in the experiments. The present results suggest that the non-linearity of the system can be increased by the inclusion of the inherently non-linear alpha heating term, which is proportional to ∼n e 2 T i 2, and obtains oscillations in the model when added to an otherwise more stationary system.

First tungsten radiation studies in DIII-D’s ITER baseline demonstration discharges

ITER Baseline Scenario plasmas were studied in DIII-D using krypton and xenon gases as a proxy for the tungsten that will be present in ITER. These impurities were chosen for having the same radiative loss rate Lz as tungsten would exhibit in the hotter ITER core. Results show that the scenario with these core radiators spans the range of impurity concentration and W radiated fraction expected for ITER, and up to 50% higher values, explored at zero injected torque, as well as 1 Nm and full co-torque injection with T ∼ 3 Nm. Stationary discharges with duration >2–4 τR are achieved with f rad ⩾ 30% leading to a reduction in confinement of ∼10%, and a comparison with real metal radiators in the same range of f rad shows that the higher Lz at the lower temperatures in these plasmas yields too pessimistic results on the survivability and performance of this scenario in ITER. Simulations of ITER power balance including W radiation show that with concentration up to three times higher than in the DIII-D plasmas the scenario can be stationary, remaining at acceptable core radiated fraction values.

Lunar Mare Lava Flow Dynamics and Emplacement: Predictions of Non-Newtonian Flow Dynamics, Syn- and Post-emplacement Cooling and Volatile Release Patterns, and Vertical and Lateral Flow Structure Development

We apply basic principles of magma ascent from deep source regions and its eruption into a low-gravity vacuum environment to develop a theoretical treatment of the fluid dynamics and thermodynamics of mare basalt lava flow emplacement and evolution on the Moon. The vacuum conditions influenced the release of volatiles in magma passing through lava fountains, thus controlling the syn- and post-emplacement vesicularity of the resulting deposits. To explain observed lengths and volumes of Mare Imbrium–type flows, high (106–105 m3 s−1) initial magma eruption rates were needed. Combined with low lunar magma viscosity, these caused flows to be initially turbulent. Resulting high radiative heat loss and consequent high crystallization rates caused rapid non-Newtonian rheological evolution and suppression of turbulence at tens of kilometers from vents. Slower cooling rates in the subsequent laminar parts of flows imply distinctive crystal growth rate histories. In a four-phase sequence, (i) initial transient dike-tip gas release followed by (ii) Hawaiian fire fountain activity with efficient volatile loss (iii) transitioned to (iv) Strombolian explosions in a lava lake. Late-stage lava now able to retain volatiles intruded and inflated existing flow deposits after flow front advance ceased. Volatiles forced out of solution by second boiling as lava cooled caused additional inflation. Low gravity and lack of atmospheric pressure commonly produced very vesicular lava. Escape of such lava through cracks in flow crusts is a possible source of ring-moat dome structures; collapse of such lava may explain irregular mare patches.

Experimental study and numerical analysis of radiative losses of single-channel solar chimney

Solar chimneys provide natural ventilation for buildings, reducing the energy consumption of mechanical systems. Therefore, analyzing energy losses through solar chimney components and inlet/outlet of air channel is critical to develop a suitable design for this passive ventilation system. In this study, the performance and energy losses analysis of a single-channel solar chimney (SC-SOCH) is described; a parametric study under laboratory conditions was conducted regarding the air gap (0.10, 0.15, and 0.20 m) and heat flux of absorber plate (100, 200, 300, 400, and 500 Wm−2). The energy losses were analyzed with temperature sensors, heat flow transducers, and a net radiation transfer model. The parametric study results showed that between 10% and 15% of the total energy supplied to the absorber plate was dissipated to the laboratory environment through the glass cover. Furthermore, combining the different thermal insulation layers on the backside of the absorber plate and sidewalls of the air channel permitted only energy losses below 8% of the total energy supplied. The highest energy losses occurred due to radiative exchange; the radiative losses through the inlet and outlet of the air channel were between 9.38% and 25.78% of the total energy supplied. However, the radiative energy loss rate decreased as airflow increased; the volumetric flow rate was from 34.11 to 94.92 m3h−1, which was enough to satisfy the requirements of total ventilation rate for spaces of 9, 18, and 36 m2 according to ASHRAE 62.2–2019. Therefore, solar chimney designs must be optimized to minimize energy losses and increase airflow for natural ventilation.

Strong coupling between quasi-bound states in the continuum and molecular vibrations in the mid-infrared

Abstract Strong light–matter coupling is of much interest for both fundamental research and technological applications. The recently studied bound state in the continuum (BIC) phenomenon in photonics with controlled radiation loss rate significantly facilitates the realization of the strong coupling effect. In this work, we report the experimental observation of room temperature strong coupling between quasi-BIC resonances supported by a zigzag metasurface array of germanium elliptical disks and the vibrational resonance of polymethyl methacrylate (PMMA) molecules in the mid-infrared. Based on the approach of tuning the quasi-BIC resonance by changing the thickness of the coated PMMA layer, we can easily observe the strong coupling phenomenon, manifested by significant spectral splitting and typical anti-crossing behaviors in the transmission spectrum, with the spectral distance between the two hybrid photon-vibration resonances significantly larger than the bandwidth of both the quasi-BIC resonance and the PMMA absorption line. Our results demonstrate that the use of quasi-BIC resonance in all-dielectric nanostructures provides an effective and convenient approach for the realization of strong coupling effect.

Numerical simulation for wire X-pinch plasma on 2D/3D geometry

This paper investigates wire X-pinch (WXP) evolutions by the Eulerian resistive magneto-hydrodynamic code, STHENO, on 2D/3D geometry. A single-fluid two-temperature model is applied to pinch plasmas in local thermal equilibrium. The equation of state based on the Thomas–Fermi model is used to determine the ionization degree of the plasma. Electron internal energy is determined by the local density, temperature, and ionization potential with the average ion charge state. Lee–More–Desjarlais transport models are employed to obtain the thermal conductivities and resistivity for a non-ideal plasma. The radiation loss rate is calculated by the Bremsstrahlung and recombination emissivity within the ionization balance. The crossing point, which is the central part of the X-pinch, is assumed to be an axisymmetric configuration on a small computational domain in the RZ plane. The 2D simulation demonstrates that the micrometer size plasma column is elongated axially with the onset of the neck cascading structure. The radiation power is calculated and compared with the measured x-ray power from a modular X-pinch device (120-kA in 650-ns) at Seoul National University. The time evolution of the radiation power reproduces the trend of the measured x ray. 3D analyses are performed for the aluminum WXP configurations by varying wire numbers and cross-angles. The relation between the radiation performance and the numbers of wires reveals that the current density, rather than the line density, determines the central pinching condition. In addition, the multiple plasma instabilities (m = 0) near the central regions are found to degrade the radiation performance on the small cross-angle WXP.

Mechanical Properties and Gamma Radiation Transmission Rate of Heavyweight Concrete Containing Barite Aggregates.

The primary objective of this research was to study the transmission of gamma radiation from heavyweight concrete containing barite aggregates. For this purpose, cylindrical and cubic specimens were produced for 10 mix designs. The mix designs containing different percentages of barite aggregates were calculated; five mix designs were also calculated for the compressive strength of 25 MPa, while five of them were designed for the compressive strength of 35 MPa to study the influence of the compressive strength rate on the reduction in gamma radiation transmission. The results indicated that both compressive and tensile strength was decreased by increasing the ratio of barite aggregates. The rate in reduction of compressive strength and especially tensile strength in concrete C35 was less than in concrete C25. The use of barite aggregates increased the attenuation coefficient of concrete. The attenuation coefficient in C35 concrete increased more than that in C25 upon increasing the amount of barite aggregate. By increasing the thickness of concrete with different percentages of barite, the rate of radiation loss in different samples was closer. The difference in the rate of radiation loss at a thickness of 150 mm was not much different from that at a thickness of 100 mm, whereas it was considerably decreased at a thickness of 300 mm. The test results indicated that the reduction in the gamma transmission rate is significantly dependent on the density of concrete.

A fast multi-dimensional magnetohydrodynamic formulation of the transition region adaptive conduction (TRAC) method

We have demonstrated that the transition region adaptive conduction (TRAC) method permits fast and accurate numerical solutions of the field-aligned hydrodynamic equations, successfully removing the influence of numerical resolution on the coronal density response to impulsive heating. This is achieved by adjusting the parallel thermal conductivity, radiative loss, and heating rates to broaden the transition region (TR), below a global cutoff temperature, so that the steep gradients are spatially resolved even when using coarse numerical grids. Implementing the original 1D formulation of TRAC in multi-dimensional magnetohydrodynamic (MHD) models would require tracing a large number of magnetic field lines at every time step in order to prescribe a global cutoff temperature to each field line. In this paper, we present a highly efficient formulation of the TRAC method for use in multi-dimensional MHD simulations, which does not rely on field line tracing. In the TR, adaptive local cutoff temperatures are used instead of global cutoff temperatures to broaden any unresolved parts of the atmosphere. These local cutoff temperatures are calculated using only local grid cell quantities, enabling the MHD extension of TRAC to efficiently account for the magnetic field evolution, without tracing field lines. Consistent with analytical predictions, we show that this approach successfully preserves the properties of the original TRAC method. In particular, the total radiative losses and heating remain conserved under the MHD formulation. Results from 2D MHD simulations of impulsive heating in unsheared and sheared arcades of coronal loops are also presented. These simulations benchmark the MHD TRAC method against a series of 1D models and demonstrate the versatility and robustness of the method in multi-dimensional magnetic fields. We show, for the first time, that pressure differences, generated during the evaporation phase of impulsive heating events, can produce current layers that are significantly narrower than the transverse energy deposition.

Excitation relaxation in a molecular chain and energy transfer at steady state.

We consider the reduced dynamics of a molecular chain weakly coupled to a phonon bath. With a small and constant inhomogeneity in the coupling, the excitation relaxation rates are obtained in closed form. They are dominated by transitions between exciton modes lying next to each other in the energy spectrum. The rates are quadratic in the number of sites in a long chain. Consequently, the evolution of site occupation numbers exhibits longer coherence lifetime for short chains only. When external source and sink are added, the rate equations of exciton occupation numbers are similar to those obtained earlier by Fröhlich to explain energy storage and energy transfer in biological systems. There is a clear separation of timescale into a faster one pertaining to internal influence of the chain and phonon bath, and a slower one determined by external influence, such as the pumping rate of the source, the absorption rate of the sink, and the rate of radiation loss. The energy transfer efficiency at steady state depends strongly on these external parameters and is robust against a change in the internal parameters, such as temperature and inhomogeneity. Excitations are predicted to concentrate to the lowest energy mode when the source power is sufficiently high. In the site basis, this implies that when sustained by a high power source, a sink positioned at the center of the chain is more efficient in trapping energy than a sink placed at its end. Analytic expressions of energy transfer efficiency are obtained in the high power and low-power source limit. Parameters of a photosynthetic system are used as examples to illustrate the results.

Numerical Simulation on the Formation and Pinching Plasma in X-pinch Wires on 2-D Geometry

This paper deals with the computational work to characterize the formation and pinching of a plasma in an X-pinch configuration. A resistive magnetohydrodynamic model of a single fluid and two temperature is adopted assuming a hollow conical structure in the (r,z) domain. The model includes the thermodynamic parameter of tungsten from the corrected Thomas-Fermi EOS(equation of state), determining the average ionization charge, pressure, and internal energy. The transport coefficients, resistivity and thermal conductivity, are obtained by the corrected Lee & More model and a simple radiation loss rate by recombination process is considered in the simulation. The simulation demonstrated the formation of a core-corona plasma and intense compression process near the central region which agrees with the experimental observation in the X-pinch device at Seoul National University. In addition, it confirmed the increase in radiation loss rate with the density and temperature of the core plasma. Keywords: X-pinch, Magnetohydrodynamics, Exploding Wires Keywords: 엑스핀치, ìžê¸°ìœ ì²´ì—­í•™, ì„¸ì„ í­ë°œ

Hot Electron Plasmon-Resonant Grating Structures for Enhanced Photochemistry: A Theoretical Study

Metallic grating structures have been shown to provide an effective platform for generating hot electrons and driving electrochemical reactions. Here, we present a systematic theoretical study of the surface plasmon resonance in different corrugated metallic grating structures using computational electromagnetic tools (i.e., the finite difference time domain (FDTD) method). We identify the corrugation parameters that produce maximum resonant field enhancement at commonly used wavelengths for photocatalytic applications (633 nm and 785 nm) in different material systems, including Ag, Au, Cu, Al, and Pt. The absorption spectra of each grating structure have been fitted with the analytical equation obtained from Coupled Mode Theory. We then extracted the absorptive and radiative loss rates. The field enhancement can be maximized by matching the absorption and radiation losses via tuning the geometric parameters. We could improve the average field enhancement of 633 nm and 785 nm modes by a factor of 1.8× and 3.8× for Ag, 1.4× and 3.6× for Au, and 1.2× and 2.6× for Cu. The optimum structures are found to be shallower for Ag, Au, and Cu; deeper for Pt; and to almost remain the same for Al. The gratings become flat for all the metals for increasing the average field enhancement. Overall, Ag and Au were found to be the best in terms of overall field enhancement while Pt had the worst performance.

Superradiant Ensembles of Terahertz Polaritonic Meta-Atoms

We experimentally demonstrate the robustness of strong light-matter interaction in an ensemble of terahertz cavities with variable radiation loss. Each cavity in the form of a planar metallic resonator is strongly coupled to intersubband transitions of semiconductor quantum wells. The polariton spectra, measured by time-domain spectroscopy, do not diminish when the cavity ensemble is brought to the superradiant regime with a radiative loss rate increased by a factor of three. In contrast, the splitting of the polariton frequencies gets larger, and indicates an increased vacuum Rabi frequency. We attribute the observed phenomenon to this well-known many-body effect in quantum electrodynamics, but here associated to an ensemble of otherwise independent polariton systems.

Fire behaviors of fuels with different sootiness levels in hot and humid conditions

The behaviors of fires fueled by materials that produce different levels of soot (diesel and alcohol) were studied under hot and humid conditions with natural ventilation. Experimental tests were performed under different initial ambient temperatures (20 °C and 30 °C) and relative humidity levels (50 % and 90 %), and flame temperature, thermal radiation and mass loss rate were measured. A theoretical flame radiation model was established and verified. The fire development index (FDI) was defined as the ratio of the peak flame temperature, Tp, to the duration, tp, during initial fire development stage, and the fire severity index (FSI) was defined as the product of the flame thermal radiation, Rav, and the duration, td, during fully developed stage. The results validated the reasonableness of the established theoretical model. During initial fire development stage, increasing the initial ambient temperature increased the FDI, while increasing the relative humidity decreased it. During fully developed stage, increasing the initial ambient temperature or humidity resulted in a decrease in the FSI under limited-fuel conditions, and the ambient temperature more significantly affected the pool fires fueled by alcohol than those that consumed diesel. Additionally, under conditions of high temperature and high humidity, both the indices were reduced.

High quality factor phase gradient metasurfaces.

Dielectric microcavities with quality factors (Q-factors) in the thousands to billions markedly enhance light-matter interactions, with applications spanning high-efficiency on-chip lasing, frequency comb generation and modulation and sensitive molecular detection. However, as the dimensions of dielectric cavities are reduced to subwavelength scales, their resonant modes begin to scatter light into many spatial channels. Such enhanced scattering is a powerful tool for light manipulation, but also leads to high radiative loss rates and commensurately low Q-factors, generally of order ten. Here, we describe and experimentally demonstrate a strategy for the generation of high Q-factor resonances in subwavelength-thick phase gradient metasurfaces. By including subtle structural perturbations in individual metasurface elements, resonances are created that weakly couple free-space light into otherwise bound and spatially localized modes. Our metasurface can achieve Q-factors >2,500 while beam steering light to particular directions. High-Q beam splitters are also demonstrated. With high-Q metasurfaces, the optical transfer function, near-field intensity and resonant line shape can all be rationally designed, providing a foundation for efficient, free-space-reconfigurable and nonlinear nanophotonics.

An Observational Test of Solar Plasma Heating by Magnetic Flux Cancellation

Abstract Recent observations suggest that magnetic flux cancellation may play a crucial role in heating the Sun’s upper atmosphere (chromosphere, transition region, corona). Here, we intended to validate an analytic model for magnetic reconnection and consequent coronal heating, driven by a pair of converging and canceling magnetic flux sources of opposite polarities. For this test, we analyzed photospheric magnetic field and multiwavelength ultraviolet/extreme ultraviolet (EUV) observations of a small-scale flux cancellation event in a quiet-Sun internetwork region over a target interval of 5.2 hr. The observed cancellation event exhibits a converging motion of two opposite-polarity magnetic patches on the photosphere and redshifted Doppler velocities (downflows) therein consistently over the target interval, with a decrease in magnetic flux of both polarities at a rate of 1015 Mx s−1. Several impulsive EUV brightenings, with differential emission measure values peaked at 1.6–2.0 MK, are also observed in the shape of arcades with their two footpoints anchored in the two patches. The rate of magnetic energy released as heat at the flux cancellation region is estimated to be in the range of (0.2–1) × 1024 erg s−1 over the target interval, which can satisfy the requirement of previously reported heating rates for the quiet-Sun corona. Finally, both short-term (a few to several tens of minutes) variations and long-term (a few hours) trends in the magnetic energy release rate are clearly shown in the estimated rate of radiative energy loss of electrons at temperatures above 2.0 MK. All these observational findings support the validity of the investigated reconnection model for plasma heating in the upper solar atmosphere by flux cancellation.

Impact of a minority relativistic electron tail interacting with a thermal plasma containing high-atomic-number impurities

A minority relativistic electron component can arise in both laboratory and naturally occurring plasmas. In the presence of high-atomic-number ion species, the ion charge state distribution at a low bulk electron temperature can be dominated by relativistic electrons, even though their density is orders of magnitude lower. This is due to the relativistic enhancement of the collisional excitation and ionization cross sections. The resulting charge state effect can dramatically impact the radiative power loss rate and the related Bethe stopping power of relativistic electrons in a dilute plasma.

Coronal Cooling as a Result of Mixing by the Nonlinear Kelvin–Helmholtz Instability

Abstract Recent observations show cool, oscillating prominence threads fading when observed in cool spectral lines and appearing in warm spectral lines. A proposed mechanism to explain the observed temperature evolution is that the threads were heated by turbulence driven by the Kelvin–Helmholtz instability that developed as a result of wave-driven shear flows on the surface of the thread. As the Kelvin–Helmholtz instability is an instability that works to mix the two fluids on either side of the velocity shear layer, in the solar corona it can be expected to work by mixing the cool prominence material with that of the hot corona to form a warm boundary layer. In this paper, we develop a simple phenomenological model of nonlinear Kelvin–Helmholtz mixing, using it to determine the characteristic density and temperature of the mixing layer. For the case under study, with constant pressure across the two fluids, these quantities are and . One result from the model is that it provides an accurate—as determined by comparison with simulation results—determination of the kinetic energy in the mean velocity field. A consequence of this is that the magnitude of turbulence—and with it, the energy that can be dissipated on fast timescales—as driven by this instability can be determined. For the prominence–corona system, the mean temperature rise possible from turbulent heating is estimated to be less than 1% of the characteristic temperature (which is found to be T mixed = 105 K). These results highlight that mixing, and not heating, is likely to be the cause of the observed transition between cool to warm material. One consequence of this result is that the mixing creates a region with higher radiative loss rates on average than either of the original fluids, meaning that this instability could contribute a net loss of thermal energy from the corona, i.e., coronal cooling.

The Influence of Low-$Z$ Impurities on the Ignition Parameters in p6Li Inertial Fusion Plasma

The presence of impurities in a high-temperature plasma is one of the major challenges in an inertial fusion reactor. In addition to radiation losses, the impurities affect the ignition parameters of the fusion plasma in the reactor. In this article, the effect of the arbitrary concentration of impurity nuclei carbon, beryllium, and lithium on the ignition properties of the p6Li fusion plasma is investigated. The results show that by increasing the concentration of impurities, the reaction rate decreases and the rate of energy loss self-radiation increases in the p6Li plasma. This effect is considerably stronger than the weak positive effect of reducing the energy lost for matter acceleration and electron heat conduction. With 20% impurity concentration of carbon, beryllium, and lithium, the reaction rate decreases 3.4, 2.7, and 2.2 times, respectively, and the radiation loss rate increases 6.7, 3.5, and 2.4 times, respectively, by more than a factor in comparison to pure p6Li plasma. The factors of energy losses related to material acceleration and electron heat conduction reduce only to 1.1–1.2 in comparison to pure p6Li plasma. The ignition is impossible at any values of the ignition parameter, areal density. The results show that the minimum ignition temperature from 800 keV increases to 1250, 950, and 840 keV with 20% impurity concentration of carbon, beryllium, and lithium, respectively. Also, both areal density and ignition energy parameters increase by increasing the concentration of these impurities. The conclusions show gain decreases in the p6Li plasma due to a decrease in the fusion reaction rate.

Bandwidth bounds of coherent perfect absorber in resonant metasurfaces.

Coherent perfect absorber (CPA), a resonator with critical losses that can perfectly absorb all incident light, has been observed at various frequency regimes (from microwave to visible light). Besides the functional frequency, the bandwidth is also an important parameter in characterizing the performance of CPA. Here, we explore the bandwidth of CPA in a kind of weakly-coupled-resonance metasurfaces with 4κ2-γs2<0, where κ is the near-field coupling between the radiative and non-radiative resonant modes, and γsis the scattering loss rate of the radiative resonant mode. Based on the coupled mode theory, we analytically derive the upper and lower bounds of the bandwidth, and show that they are determined by the dissipation loss rates of the composed modes. To narrow the bandwidth, it is better to increase the radiative loss rate when designing a weakly coupled resonator. We also show that CPA is associated with a robust phase singularity with a winding number of ± 1. The conclusions are numerically verified in a designed resonant metasurface and could perform as a guideline for designing CPA in various resonant systems.