Radiative Power Losses Research Articles

Radiative recombination data for low-charged tungsten ions: IV. W[formula omitted]W[formula omitted

The radiative recombination and photoionization cross sections as well as the radiative recombination rate coefficients and the radiated power loss rate coefficients are presented for the low-charged tungsten ions from W3+ to W13+. The data are essential to diagnostic and modeling the divertor plasmas impurities in the ITER tokamak because tungsten has been resolved to use as a plasma-facing material. Partial cross sections and rates are given for the ground and excited electron states with principal quantum numbers n≤10 and orbital momenta ℓ≤4 in the wide energy range. Relativistic calculations have been performed taking into account all significant multipoles of the radiative field. Electron wave functions have been found by the Dirac–Fock method. The relativistic Maxwell–Jüttner distribution of continuum electrons has been used in calculations of radiative recombination and radiated power loss rates. Photoionization cross sections have been fitted by an analytical expression with five fit parameters. Peculiarities of behavior of the cross sections and rates for low-charged ions as well as ensuing problems of the cross section fitting are considered. The radiative recombination rates are compared with other recent calculations for the low-charged tungsten ions.

Developments towards an ELM-free pedestal radiative cooling scenario using noble gas seeding in ASDEX Upgrade

Integrated edge-localized-mode (ELM)-free or small ELM scenarios for the demonstration fusion power plant (DEMO) are investigated in ASDEX Upgrade using argon seeding for radiative power removal mainly in the pedestal region. An important aspect is the modification of the electron pressure in the pedestal by the additional radiative power losses. Full ELM suppression could be achieved in a no-ELM H-mode scenario featuring an edge electromagnetic quasicoherent mode up to a heating power of 5 MW, where argon radiation allowed the extension of the heating power operational space. At higher powers up to 12 MW (reaching the beta limit), ELMs of reduced size prevail and detachment is obtained by the argon seeding. Control of the position of a radiating zone localized inside the X-point was found to be favorable compared to the control of the separatrix power for low /. Integration of pedestal cooling with Ar and ELM suppression by resonant magnetic perturbations (RMP) allowed an increase of the core radiation and a partial recovery of normalized confinement to H98 = 1. This favorable behavior is finally limited by the loss of the RMP density pump-out effect, followed by an ELM-free H-mode phase and re-occurrence of ELMs. For an active tailoring of the pedestal pressure profile, precise knowledge of the radiation profile is required. Modeling of the argon radiation profile with the STRAHL code showed good agreement with bolometry only if charge exchange of neutral deuterium with argon ions was taken into account, highlighting the importance of the neutral density in the pedestal region. In view of best integration of a no-ELM scenario with divertor detachment and high heating power, the divertor compression and enrichment of argon and neon were compared using dynamic gas puff experiments. Argon shows more than a factor of 3 higher divertor enrichment compared to neon, but the absolute values decrease with higher neutral deuterium pressure.

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.

Deeply understanding particle flux rollover with argon impurity injection and pumping effects in HL-2A by SOLPS

• The physical reason of particle flux rollover (PFR) is addressed by SOLPS. • This work uncovers the root/direct reason for PFR is the radiation loss. • The recombination loss is the indirect reason for PFR. • The radiation loss also could play a key role in inducing momentum loss. The physical reason and picture of particle flux rollover (PFR) are investigated by using SOLPS with the effects of argon impurity and pumping in this paper. This modeling work uncovers the root/direct reason for PFR is the radiation power loss from impurity and recycling particles (D and D2). The recombination particle loss is the indirect reason for PFR. Besides, the radiation power loss also could play a key role in inducing momentum loss. This work could unify the four factors ( recombination particle loss , impurity radiation power loss , power loss , momentum loss ) from P. C. Stangeby and Krasheninnikov.

Non-LTE radiation hydrodynamics in PLUTO

Context. Modeling the dynamics of most astrophysical structures requires an adequate description of the interaction of radiation and matter. Several numerical (magneto-) hydrodynamics codes were upgraded with a radiation module to fulfill this request. However, those that used either the flux-limited diffusion (FLD) or the M1 radiation moment approaches are restricted to local thermodynamic equilibrium (LTE). This assumption may not be valid in some astrophysical cases. Aims. We present an upgraded version of the LTE radiation-hydrodynamics (RHD) module implemented in the PLUTO code, which we have extended to handle non-LTE regimes. Methods. Starting from the general frequency-integrated comoving-frame equations of RHD, we have justified all the assumptions that were made to obtain the non-LTE equations that are implemented in the module under the FLD approximation. An operator-split method with two substeps was employed: the hydrodynamics part was solved with an explicit method by the solvers that are currently available in PLUTO, and the non-LTE radiation diffusion and energy exchange part was solved with an implicit method. The module was implemented in the PLUTO environment. It uses databases of radiative quantities that can be provided independently by the user: the radiative power loss, and the Planck and Rosseland mean opacities. In our case, these quantities were determined from a collisional-radiative steady-state model, and they are tabulated as functions of temperature and density. Results. Our implementation has been validated through different tests, in particular, radiative shock tests. The agreement with the semi-analytical solutions (when available) is good, with a maximum error of 7%. Moreover, we have proved that a non-LTE approach is of paramount importance to properly model accretion shock structures. Conclusion. Our radiation FLD module represents a step toward a general non-LTE RHD modeling.

First demonstration of radiative power exhaust with impurity seeding in the island divertor at Wendelstein 7-X

Radiative power exhaust by impurity seeding was demonstrated for the first time in island divertor configurations at the stellarator Wendelstein 7-X. Feasibility of stable plasma operation was shown during seeding with both neon (Ne) and nitrogen (N2). High radiative power losses (80%) were found to reduce the divertor heat loads globally by 2/3 with both seeding gases injected at a single toroidal location into one of five magnetic islands. Heat flux detachment was achieved for the price of a loss of (%) in the stored energy. Ne seeding allows for sustained enhancement of edge radiation with a very slow decay of line emission of several tens of seconds after the end of the injection indicating a high recycling of this noble gas at the carbon main plasma facing components. In N2 seeded discharges it is shown that a response of line emission and plasma parameters is in correlation to the puff duration which indicates a higher level of absorption of this seeding gas in the wall. Continuous N2 seeding results in global cooling of the scrape-off layer (SOL) and decay of radiation over several seconds after the injection. Damping of counter-streaming SOL flows, and divertor particle fluxes induced by Ne and N2 seeding have been measured and provide evidence for a reduction of the convective part of the divertor heat fluxes. Losses in density in response to seeding can be compensated by feedback controlled divertor fueling. The controlled reduction of heat fluxes within this complex 3D edge island geometry is a very promising finding concerning detachment control in a future all-metal divertor.

New Balance-Applications for Dual-Mode Ring Resonators in Planar Balanced Circuits (Application Notes)

Recently, 4G and 5G microwave communication circuits and systems have been undergoing rapid development [1], [2]. Signal crosstalk and high costs have seriously limited the fast development of microwave technology and multilayer integrated circuits [3], while radiation power loss of commonmode noise can be up to 25% of the input power in the Ka band (22-27 GHz) [4]. For the past 10 years, different balanced circuits with higher immunity to environmental noise, lower electromagnetic interference, and better dynamic range have attracted increasingly more attention [4], [5]. Balanced filters [6]-[15], balanced power dividers [16]-[22], and crossovers [23]-[27] are the most commonly used planar balanced circuits. In our opinion, for passive balanced circuits, some simple design objectives can be summarized as follows: 1) simpler balanced circuit structures, 2) high passband selectivity and wideband harmonic suppression for the differential mode, and 3) wideband and high-level commonmode suppression.

The role of particle, energy and momentum losses in 1D simulations of divertor detachment

A new 1D divertor plasma code, SD1D, has been used to examine the role of recombination, radiation, and momentum exchange in detachment. Neither momentum or power losses by themselves are found to be sufficient to produce a reduction in target ion flux in detachment (flux rollover); radiative power losses are required to (a) limit and reduce the ionisation source and (b) access low-target temperature, Ttarget, conditions for volumetric momentum losses. Recombination is found to play a small role at flux rollover, but as Ttarget drops to temperatures around 1 eV, it becomes a strong ion sink. In the case where radiative losses are dominated by hydrogen, the detachment threshold is identified as a minimum gradient of the energy cost per ionisation with respect to Ttarget. This is also linked to thresholds in Ttarget and in the ratio of upstream pressure to power flux. A system of determining the detached condition is developed such that the divertor solution at a given Ttarget (or lack of one) is determined by the simultaneous solution of two equations for target ion current—one dependent on power losses and the other on momentum. Depending on the detailed momentum and power loss dependence on temperature there are regions of Ttarget where there is no solution and the plasma ‘jumps’ from high to low Ttarget states. The novel analysis methods developed here provide an intuitive way to understand complex detachment phenomena, and can potentially be used to predict how changes in the seeding impurity used or recycling aspects of the divertor can be utilised to modify the development of detachment.

Effects of the gas puffing neutral on the plasma parameters in the end-cell of GAMMA 10/PDX by using the multi-fluid code “LINDA”

This research numerically investigates the behavior of plasma flow in GAMMA 10/PDX. The impact of impurity gases seeding into the divertor region on the plasma parameters and the energy loss processes has been investigated numerically by using the multi-fluid code “LINDA”. The neutral particles are injected into the bulk hydrogen plasma and the upstream plasma parameters on the z-axis are ni=1.0×1019m−3, Ti=100eV,Te=30eV. A reduction in the plasma temperature has been observed with the increasing H neutral injection. The ionization and Charge-exchange (CX) power loss increase almost linearly with the increasing H neutral density, which induce a reduction in the plasma temperature. During H seeding, Ar and Ne are seeded simultaneously to observe the influence of Ar and Ne on the electron and ion energy loss mechanism. In this study, the fraction of impurity density to upstream plasma density (nz/ni) is used to be 10%. A comparison between Ar and Ne shows that Ar is effective on the electron cooling. The radiation power loss of Ar is found to be higher than that of Ne. The radiation cooling effect and CX loss significantly reduces the electron and ion temperature, respectively. A slight influence of Ar and Ne seeding on the ion energy loss terms has been observed. The electron energy loss terms increase significantly during impurity gas Ar and Ne seeding. These outcomes represent the impact of gas seeding for reducing the plasma energy on the divertor target plates.

Radiation diagnostics for plasma current ramp-up and ramp-down research.

The plasma current ramp-up and ramp-down are the basic processes in the tokamak operation. In order to research these processes in SUNIST (Sino-UNIted Spherical Tokamak), some diagnostic systems that detect the plasma radiation ranging from hard X-rays to visible light are developed. CdZnTe and silicon drift detectors measure the energy spectrum of hard X-rays and soft X-rays coming from the plasma. A pinhole camera equipped with absolute extended ultraviolet array photodiodes has been installed on the top of SUNIST to observe the radiation power loss and the magneto-hydrodynamic activities with high temporal and spatial resolution. The spectrum of vacuum ultraviolet is acquired by using a CCD camera, and the intensity of the lines can be measured by using a photomultiplier tube with a scintillator. The full spectrum of the visible light can be acquired in every 3 ms, and the intensity of some lines, such as Hα, Hγ, can be measured by filter scopes with high time response. Additionally, a Doppler broadening measurement system is developed to measure the ion temperature of edge plasma.

A Diagnostic of Coronal Elemental Behavior during the Inverse FIP Effect in Solar Flares

Abstract The solar corona shows a distinctive pattern of elemental abundances that is different from that of the photosphere. Low first ionization potential (FIP) elements are enhanced by factors of several. A similar effect is seen in the atmospheres of some solar-like stars, while late-type M stars show an inverse FIP effect. This inverse effect was recently detected on the Sun during solar flares, potentially allowing a very detailed look at the spatial and temporal behavior that is not possible from stellar observations. A key question for interpreting these measurements is whether both effects act solely on low-FIP elements (a true inverse effect predicted by some models), or whether the inverse FIP effect arises because high-FIP elements are enhanced. Here we develop a new diagnostic that can discriminate between the two scenarios, based on modeling of the radiated power loss, and apply the models to a numerical hydrodynamic simulation of coronal loop cooling. We show that when low-/high-FIP elements are depleted/enhanced, there is a significant difference in the cooling lifetime of loops that is greatest at lower temperatures. We apply this diagnostic to a post X1.8 flare loop arcade and inverse FIP region, and show that for this event, low-FIP elements are depleted. We discuss the results in the context of stellar observations, and models of the FIP and inverse FIP effect. We also provide the radiated power-loss functions for the two inverse FIP effect scenarios in machine readable form to facilitate further modeling.

Net Emission Coefficient and Radiation Transfer Characteristics of Thermal Plasma Generated in Nitrogen-PTFE Vapor Mixture

The radiation characteristics of thermal plasma columns filled with N2-polytetrafluoroethylene vapor mixture has been studied for the first time. The net emission coefficient is first calculated for typical mixture concentrations. The discrete ordinate method (DOM), which has proven to be an approximate method of reasonable accuracy for radiation transfer in thermal plasmas, is then used to characterize the emission and absorption behavior of cylindrical plasma columns with typical temperature distributions. Results show that the radiative power loss per unit volume at the column center is not always proportional to the local gas pressure. The DOM12-9 configuration, i.e., considering 24 directions in the $r$ -plane of the calculation point and 18 directions crossing the $r$ -plane, produces remarkably accurate results. It is likely to recover the accurate emission and absorption profile by scaling the output from the DOM5-3 configuration with a scaling factor between 0.7 and 0.8. Furthermore, the DOM5-3 configuration accurately locates the absorption layer at the edge of the plasma column. Maximum absorption takes place at a radial location whose distance to the inner radius of the absorption layer is 30% of the layer thickness despite of the very different radial temperature profiles. Under the conditions studied 35%–60% of the radiation from the central part of the column is absorbed in the surrounding cooler gas.

Investigation of plasma behavior during noble gas injection in the end-cell of GAMMA 10/PDX by using the multi-fluid code ‘LINDA’

The linear divertor analysis with fluid model (LINDA) code has been developed in order to simulate plasma behavior in the end-cell of linear fusion device GAMMA 10/PDX. This paper presents the basic structure and simulated results of the LINDA code. The atomic processes of hydrogen and impurities have been included in the present model in order to investigate energy loss processes and mechanism of plasma detachment. A comparison among Ar, Kr and Xe shows that Xe is the most effective gas on the reduction of electron and ion temperature. Xe injection leads to strong reduction in the temperature of electron and ion. The energy loss terms for both the electron and the ion are enhanced significantly during Xe injection. It is shown that the major energy loss channels for ion and electron are charge-exchange loss and radiative power loss of the radiator gas, respectively. These outcomes indicate that Xe injection in the plasma edge region is effective for reducing plasma energy and generating detached plasma in linear device GAMMA 10/PDX.

Numerical simulation of detached plasma in the end-cell of GAMMA 10/PDX for divertor simulation study

This research investigates the effect of Argon (Ar) and Neon (Ne) injection on the plasma parameters in the end-cell of GAMMA 10/PDX numerically by using a multi-fluid code. Reduction in the temperature of the electrons and ions is observed according to the increment of impurity injection. The electron density and the particle flux show tendency of roll-over phenomena for Ar injection. Temperature reduction in the electrons and ions during Ar injection is higher than those of the Ne injection. It is also observed that the charge-exchange (CX) loss and radiative power loss for Ar injection is higher than that of the Ne injection. These outcomes indicate that Ar is more effective radiative gas for generating detached plasma.

Influence of atomic kinetics in the simulation of plasma microscopic properties and thermal instabilities for radiative bow shock experiments.

Numerical simulations of laboratory astrophysics experiments on plasma flows require plasma microscopic properties that are obtained by means of an atomic kinetic model. This fact implies a careful choice of the most suitable model for the experiment under analysis. Otherwise, the calculations could lead to inaccurate results and inappropriate conclusions. First, a study of the validity of the local thermodynamic equilibrium in the calculation of the average ionization, mean radiative properties, and cooling times of argon plasmas in a range of plasma conditions of interest in laboratory astrophysics experiments on radiative shocks is performed in this work. In the second part, we have made an analysis of the influence of the atomic kinetic model used to calculate plasma microscopic properties of experiments carried out on magpie on radiative bow shocks propagating in argon. The models considered were developed assuming both local and nonlocal thermodynamic equilibrium and, for the latter situation, we have considered in the kinetic model different effects such as external radiation field and plasma mixture. The microscopic properties studied were the average ionization, the charge state distributions, the monochromatic opacities and emissivities, the Planck mean opacity, and the radiative power loss. The microscopic study was made as a postprocess of a radiative-hydrodynamic simulation of the experiment. We have also performed a theoretical analysis of the influence of these atomic kinetic models in the criteria for the onset possibility of thermal instabilities due to radiative cooling in those experiments in which small structures were experimentally observed in the bow shock that could be due to this kind of instability.

Effect of Metal Vapours on the Radiation Properties of Thermal Plasmas

In metallurgic applications of thermal plasmas the presence of metal vapour, even in small proportion tends to increase the electron number density and to modify some basic properties such as the electrical conductivity and the radiation emission. In this paper we focus on the influence of these vapours on the radiation properties. After the definition of some necessary and basic functions and laws we briefly present the mechanisms responsible for emission and absorption of radiation in thermal plasmas. Then an important section is devoted to the role of metal vapours on the net emission coefficient which is the most popular parameter used to evaluate the radiation power losses in general models. It is shown that metal vapours increase the emission especially at low and intermediate temperatures (T < 12,000 K) and that their relative influence depends on the nature of the initial gas and of the metal itself. We list a rather important number of references presenting calculation of net emission in various gas–metal mixtures. Finally we show in a last section the influence of metal radiation on general plasma properties such as the energy transfer (other methods than the net emission coefficient), the cooling effect, the global energy balance and the heating of particulates injected in the plasma. The most spectacular effects are the increase of radiation losses in the energy balance and the complex role of the metal in the local cooling of the plasma.

Investigation of the plasma radiation power in the Globus-M tokamak by means of SPD silicon photodiodes

Radiation losses from the plasma of the Globus-M tokamak are studied by means of SPD silicon photodiodes developed at the Ioffe Institute, Russian Academy of Sciences. The results from measurements of radiation losses in regimes with ohmic and neutral beam injection heating of plasmas with different isotope compositions are presented. The dependence of the radiation loss power on the plasma current and plasma–wall distance is investigated. The radiation power in different spectral ranges is analyzed by means of an SPD spectrometric module. Results of measurements of radiation losses before and after tokamak vessel boronization are presented. The time evolution of the sensitivity of the SPD photodiode during its two-year exploitation in Globus-M is analyzed.

Impurity Seeding in ASDEX Upgrade Tokamak Modeled by COREDIV Code

AbstractThe self‐consistent COREDIV code is used to simulate discharges in a tokamak plasma, especially the influence of impurities during nitrogen and argon seeding on the key plasma parameters. The calculations are performed with and without taking into account the W prompt redeposition in the divertor area and are compared to the experimental results acquired on ASDEX Upgrade tokamak (shots #29254 and #29257).For both impurities the modeling shows a better agreement with the experiment in the case without prompt redeposition. It is attributed to higher average tungsten concentration, which on the other hand seriously exceeds the experimental value. By turning the prompt redeposition process on, the W concentration is lowered, what, in turn, results in underestimation of the radiative power losses. By analyzing the influence of the transport coefficients on the radiative power loss and average W concentration it is concluded that the way to compromise the opposing tendencies is to include the edge‐localized mode flushing mechanism into the code, which dominates the experimental particle and energy balance. Also performing the calculations with both anomalous and neoclassical diffusion transport mechanisms included is suggested.

Poynting flux in the neighbourhood of a point charge in arbitrary motion and radiative power losses

We examine the electromagnetic fields in the neighbourhood of a ‘point charge’ in arbitrary motion and thereby determine the Poynting flux across a spherical surface of vanishingly small radius surrounding the charge. We show that the radiative power losses from a point charge turn out to be proportional to the scalar product of the instantaneous velocity and the first time-derivative of the acceleration of the charge. This may seem to be discordant with the familiar Larmor formula where the instantaneous power radiated from a charge is proportional to the square of acceleration. However, it seems that the root cause of the discrepancy actually lies in Larmor’s formula, which is derived using the acceleration fields but without due consideration for the Poynting flux associated with the velocity-dependent self-fields ‘co-moving’ with the charge. Further, while deriving Larmor’s formula, one equates the Poynting flux through a surface at some later time to the radiation loss by the enclosed charge at the retarded time. Poynting’s theorem, on the other hand, relates the outgoing radiation flux from a closed surface to the rate of energy decrease within the enclosed volume, all calculated for the same given instant only. Here we explicitly show the absence of any Poynting flux in the neighbourhood of an instantly stationary point charge, implying no radiative losses from such a charge, which is in complete conformity with energy conservation. We further show how Larmor’s formula is still able to serve our purpose in the vast majority of cases. It is further shown that Larmor’s formula in general violates momentum conservation and, in the case of synchrotron radiation, leads to a potentially incorrect conclusion about the pitch angle changes of the radiating charges, and that only the radiation reaction formula yields a correct result, consistent with special relativity.

RETRACTED ARTICLE: Prevention of Plasma–Surface Interactions by Control of Plasma Equilibrium in Large Aspect Ratio Tokamaks

In tokamak plasma, impurities present a number of problems. One is the radiative power loss, principally due to line radiation from partially stripped ions. Another is fuel dilution. This arises because impurity atoms produce many electrons and, for a given plasma pressure, these electrons lake the place of fuel particles. At high concentrations impurities prevent the plasma being heated. This is particularly a problem during the plasma start-up phase since impurities radiate most strongly at low temperatures before they become highly ionized. Impurities can also lead to disruptions as a result of edge cooling and consequent current profile modification. On the other hand, these problems can be prevented by control of plasma equilibrium (which is defined by Grad–Shafranov (GS) equation). Numerous methods exist to solve the GS equation, describing the equilibrium of plasma confined by an axisymmetric magnetic field. In this paper, we have proposed a new numerical solution to the GS equation of an axisymmetric, transformed in cylindrical coordinates solved with the Chebyshev collocation method, when the source term (current density function) on the right hand side is linear. The Chebyshev collocation method is a method for computing highly accurate numerical solutions of deferential equations. We describe a circular cross section of tokamak and present numerical result of magnetic surfaces on the IR-T1 tokamak and then compare the results with an analytical solution.