Radiative Condensation Instability Research Articles

Cavitating Bubbles in Condensing Gas as a Means of Forming Clumps, Chondrites, and Planetesimals

Vaporized metal, silicates, and ices on the verge of recondensing into solid or liquid particles appear in many contexts: behind shocks, in impact ejecta, and within the atmospheres and outflows of stars, disks, planets, and minor bodies. We speculate that a condensing gas might fragment, forming overdensities within relative voids, from a radiation–condensation instability. Seeded with small thermal fluctuations, a condensible gas will exhibit spatial variations in the density of particle condensates. Regions of higher particle density may radiate more, cooling faster. Faster cooling leads to still more condensation, lowering the local pressure. Regions undergoing runaway condensation may collapse under the pressure of their less condensed surroundings. Particle condensates will compactify with collapsing regions, potentially into macroscopic bodies (planetesimals). As a first step toward realizing this hypothetical instability, we calculate the evolution of a small volume of condensing silicate vapor—a spherical test “bubble” embedded in a background medium whose pressure and radiation field are assumed fixed for simplicity. Such a bubble condenses and collapses upon radiating its latent heat to the background, assuming that its energy loss is not stopped by background irradiation. Collapse speeds can range up to sonic, similar to cavitation in terrestrial settings. Adding a noncondensible gas like hydrogen to the bubble stalls the collapse. We discuss whether cavitation can provide a way for millimeter-sized chondrules and refractory solids to assemble into meteorite parent bodies, focusing on CB/CH chondrites whose constituent particles likely condensed from silicate/metal vapor released from the most energetic asteroid collisions.

Various edge low-frequency fluctuations during transition to a detached divertor in Experimental Advanced Superconducting Tokamak

Various edge low-frequency fluctuations with distinct characteristics exist in different detached divertor states. Three edge low-frequency fluctuations ( 10 kHz), namely low-frequency quasi-coherent fluctuation (LFCF), low-frequency broadband frequency fluctuation (LFBF), and low-n X-point mode (LNXM) on Experimental Advanced Superconducting Tokamak (EAST), are systematically assessed. The basic features of these fluctuations, such as spectral width, location, mode number, propagating direction, and particle transport capacities, are examined. LFCF occurs when the inner strike point is energy detached or nearly energy detached with 8–15 eV ( is the electron temperature of the inner strike point), and a large electron temperature gap between the inner and outer strike points 25 eV ( is the electron temperature gap between the inner and outer strike points) is essential for the occurrence of LFCF. By contrast, LFBF occurs when the inner strike point is energy detached with 8 eV, while the outer strike point is nearly energy detached or attached. The of LFBF is generally lower than that of LFCF, which is 25 eV. LNXM is related only to the radiative divertor with impurity seeding and considered to be excited by the geodesic acoustic mode proposed in earlier work (Sun 2021 Nucl. Fusion 61 014002; Diallo 2020 28th IAEA Fusion Energy Conf.), or the coupling of impurity radiation condensation instability and drift waves proposed in a previous work (Ye 2021 Nucl. Fusion 61 116032). In addition, the possible physical mechanisms of LFBF and LFCF are proposed, with LFBF being the purely growing rippling mode and LFCF being the mode formed by the coupling of the rippling mode to the drift waves. Related research may be beneficial to better clarify the various low-frequency fluctuations that occur during different divertor states.

Sustained edge-localized-modes suppression and radiative divertor with an impurity-driven instability in tokamak plasmas

Simultaneous control of the large edge localized modes (ELMs) and divertor heat fluxes in a metal wall environment is a critical issue for steady-state operation of a tokamak fusion reactors. Here we report a sustained ELM suppression scenario achieved in the EAST tokamak compatible with radiative divertor using different seeding impurity species over a wide range of conditions. A low-n mode appears, as manifested by the oscillations of a radiation front near the X-point. This mode appears to drive strong particle transport and tungsten exhaust, which is essential to the maintenance of the ELM-stable state. We have developed a model to explain the mode excitation, by coupling the impurity radiative condensation instability to drift waves, which could explain some characteristics of the low-n mode well. The low-n mode may offer a new ELM-stable scenario compatible with radiative divertor for future fusion reactors.

Analysis of radiative gravitational modes in magnetized dusty plasma with non-thermal ion distribution

The characteristics of radiative gravitational modes in non-thermal magnetized dusty plasma with charge fluctuation and the polarization force of dust particles are investigated. The electron species are assumed to be radiative and the ions are assumed to be non-thermal. A normal mode analysis is applied to derive the general dispersion relation for radiative magnetized self-gravitating dusty plasma. Modified radiative condensation and self-gravitational instability criteria for both perpendicular and parallel modes of propagation are obtained. Analytically, it is found that the presence of a non-thermal ion population significantly modified the usual radiative condensation instability criterion, and damped the growth rate of the radiative mode. The obtained analytical results are further discussed in the numerical result section. We investigate the fact that the non-thermal ion population acts as a stabilizing source for radiative condensation instability in magnetized self-gravitating dusty plasma fluid, including the dust polarization force and charge fluctuation. The thermal conductivity with non-thermal ion distribution quickly moves the system towards stability. The implications of the results in the region of the interstellar medium (ISM) are discussed.

Spontaneous Break of up–down Symmetry in a Symmetric Double-Null Divertor Configuration

A possibility of up–down asymmetry of the profiles of the edge plasma parameters in a symmetric double-null divertor configuration in the case of impurity seeding is found by computational modeling. The physical mechanism of such a symmetry violation, related to radiation-condensation instability, is proposed. This effect can reduce the would-be advantage of the double-null configuration in the power load spreading over a larger area, which is vital for fusion reactor projects.

Radiative condensation instability in partially ionized dusty plasma with polarization force

This paper studies the effect of polarization force on the radiative condensation (RC) instability of a partially ionized dusty medium both in the presence and absence of self-gravitation. The temperature and density dependent heat loss function is considered in the process of heating and radiative cooling. The linear-perturbation analysis is used to derive general dispersion relation and criteria for both the Jeans and RC instability. The condition of Jeans instability is modified due to the RC, polarization force, magnetic field and dust thermal speed, whereas in the case of RC instability the instability criterion is modified due to the presence of dust thermal speed, magnetic field and polarization force. The effects of various parameters have been numerically estimated on RC instability. It is clear from figure that the presence of polarization parameter and density dependent heat-loss function destabilize the system while the presence of temperature dependent heat-loss function, dust neutral collision frequency and ratio of neutral dust density stabilize the system. These findings are relevant for many areas of space and laboratory plasma research prime examples being the formation of dense molecular clouds in interstellar and intergalactic medium, condensations in planetary nebulae and in laboratory plasmas like tokamak edge plasma.

Influence of dust charge fluctuation and polarization force on radiative condensation instability of magnetized gravitating dusty plasma

The influence of dust charge fluctuation, thermal speed and polarization force due to massive charged dust grains is studied on the radiative condensation instability (RCI) of magnetized self-gravitating astrophysical dusty (complex) plasma. The dynamics of the charged dust and inertialess electrons are considered while the Boltzmann distributed ions are assumed to be thermal. The dusty fluid model is formulated and the general dispersion relations are derived analytically using the plane wave solutions under the long wavelength limits in both the presence and the absence of dust charge fluctuations. The combined effects of polarization force, dust thermal speed, dust charge fluctuation and dust cyclotron frequency are observed on the low frequency wave modes and radiative modified Jeans Instability. The classical criterion of RCI is also derived which remains unaffected due to the presence of these parameters. Numerical calculations have been performed to calculate the growth rate of the system and plotted graphically. We find that dust charge fluctuation, radiative cooling and polarization force have destabilizing while dust thermal speed and dust cyclotron frequency have stabilizing influence on the growth rate of Jeans instability. The results have been applied to understand the radiative cooling process in dusty molecular cloud when both the dust charging and polarization force are dominant.

Radiation−condensation instability in tokamaks with mixed impurities

Radiation−condensation instability (RCI) is one of the possible mechanisms behind the formation of microfaceted asymmetric radiation from the edge (MARFE) of a tokamak. It has been previously shown by the authors that RCI in carbon-seeded plasma can be stabilized using neon injection. Recently, beryllium- and tungsten-seeded plasmas became a subject of great interest. Therefore, in the present paper, RCI stability analysis of the edge plasma seeded with beryllium, tungsten, nitrogen, and carbon is performed. The influence of neutral hydrogen fluxes from the wall on the marginal stability limit is studied as well.

Radiative-condensation instability in gravitating strongly coupled dusty plasma with polarization force

The radiative-condensation instability (RCI) in self-gravitating strongly coupled dusty plasma (SCDP) is investigated considering the effects of dust thermal velocity and polarization force on the massive dust particulates. In particular, the outer core of the dense neutron star which is supposed to be strongly coupled in nature with temperature T∼107 K and number density n∼1.3×1030 cm−3 is analyzed. The modified generalized hydrodynamic (GH) equations and electron temperature perturbation equation with radiative effects are solved using the linear perturbation method. In the classical hydrodynamic limit, the modified condition of Jeans instability owing to radiative condensation, polarization force and dust thermal velocity is obtained. In the kinetic limit, velocity of compressional mode also modifies the condition of Jeans instability. The dust thermal velocity and viscoelastic effects have stabilizing whereas polarization force and radiative cooling have destabilizing influence on the growth rate of the Jeans instability. The radiative effects stabilize the growth rate of unstable radiative modes. In isobaric mode (short wavelength), the basic condition of radiative instability is obtained which is unaffected due to the presence of polarization force and viscoelastic effects. The radiative cooling time in the outer core of neutron star is estimated and compared with the gravitational free fall time, and it is found that the cooling takes place too fast for self-gravity to be important.

Stabilization of Radiation‐Condensation Instability by Light Impurity Injection

AbstractAs it has been shown in [1,2], Radiation‐Condensation Instability (RCI) may initiate Microfaceted Asymmetric Radiation from the Edge (MARFE) in tokamaks (see also review papers [3‐5]). Nevertheless, experiments demonstrate the stable regimes with strongly radiated edge plasmas after Ne injection [6‐8] or in siliconized discharges. Two effects destabilize radiative plasmas, the decrease of radiation losses Q with the electron temperature Te increase, and the increase of Q with electron and impurity densities rise. The finite relaxation time of impurity distribution over ionization states [6] as well as the thermal force acting on the growth rate doesn't shift the instability margin. Hence, one can examine the stability margin using the approximation of the coronal equilibrium. Radiation losses of intrinsic impurities like beryllium, carbon and nitrogen usually decrease with the temperature increase at the temperature range typical for the edge (see Fig. 1, curve 1). The situation may be significantly different for impurity mixtures. Radiation losses L ≡ Q /(nenI)normalized by electron and impurity densities ne and nI for the mixture of carbon and neon are shown in Fig. 1, curves 2‐5. One can see that ∂Q/∂T > 0 for practically any temperature at the edge if the concentration ratio nNe/nC ≥ 5. Hence, one can expect the stabilization of RCI by injection of additional impurity and achievement of stable regime with the strongly radiated edge plasmas. The stability of plasmas with few impurity mixtures is examined in the present paper numerically (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of dust temperature on radiative condensation instability of self-gravitating magnetized dusty plasma

The problem of radiative condensation instability of self-gravitating dusty plasma, including the effects of dust temperature and the magnetic field, is investigated. The medium consists of extremely massive, negatively charged hot dust grains and Boltzmann distributed ions where the electrostatic force is much smaller than the gravitational one. We assume a three-component plasma having electrons, ions and charged dust grains, in which ions are inertialess having infinite thermal conductivity and electrons are inertialess having finite thermal conductivity. Quasi-neutral equilibrium is considered in which there is no electric field and free energy due to the gravitation field of dust grains. The basic equations of the problem are constructed and linearized. A linear dispersion relation is obtained using the normal mode analysis. The Jeans criterion of instability is determined, which depends on dust temperature and radiative cooling effects. The presence of magnetic field has no effect on the condition of Jeans instability. Numerical calculations have been performed to show the effects of various parameters on the growth rate of radiative condensation instability. It is observed that radiation cooling, magnetic field and dust temperature increase the acoustic stabilization of Jeans instability. The presence of magnetic field and dust temperature stabilizes the growth rate of the system under consideration.

Radiation condensation instability in a plasma with ionization and recombination

In this work, we consider radiation (thermal) instability in a weakly ionized plasma with continuous ionization and recombination. The situation can be visualized in the case of envelopes of planetary nebulae, which are envelopes of ionized plasmas surrounding red giant stars. Various observations report continuous photoionization of these plasmas by the highly energetic streams of photons emanating from the parent star. Recently, it has been shown that thermal instability can be a probable candidate in such plasmas for the existence of small scale structures (viz., striations) whose kinematic age is much smaller than that of the parent nebula. We therefore report a systematic study of these plasmas with photoionization and determine the instability domain. We have shown that the continuous ionization and recombination may lead to modification of the underlying instability, which may limit the size of the small structures that are believed to form from these instabilities, and may thus provide an explanation of the physical processes responsible for the existence of these structures. We further show that in many cases the system bifurcates to an ovserstable (growing wave) state from a condensation instability (monotonic) and vice versa.

Radiation-condensation instability in a four-fluid dusty plasma

In this work, linear stability analysis of a four-fluid optically thin plasma consisting of electrons, ions, neutral atoms, and charged dust particles is performed with respect to the radiation-condensation (RC) instability. The energy budget of the plasma involves the input from heating through photoelectron emission by dust particles under external ultraviolet radiation as well as radiative losses in inelastic electron-neutral, electron-ion, and neutral-neutral collisions. It is shown that negatively charged particles stimulate the RC instability in the sense that the conditions for the instability to hold are wider than similar conditions in a single-fluid description.

Radiation condensation instability of compressional electromagnetic modes in magnetoplasmas containing charged dust impurities

We report on an investigation into the radiation condensation (RC) instability of low-frequency (in comparison with the electron gyrofrequency) compressional electromagnetic waves in a magnetized plasma containing charged dust impurities. By using a two-fluid model, supplemented by the Faraday and Ampère laws, we derive a new dispersion relation. The latter is numerically analysed to examine the role of charged dust grains on the growth rate of the RC instability. The relevance of our investigation to density condensation in the next generation tokamak edges and on solar prominences is discussed.

Radiative condensation and detachment in Wendelstein 7-AS stellarator

In the Wendelstein 7-AS stellarator (Renner et al 1989 Plasma Phys. Control. Fusion 31 1579), under particularly high plasma densities, a non-stationary radiation zone is observed to be formed on the inboard side of the torus. It causes a degradation of the diamagnetic energy of up to 50%. The configurational aspects of the magnetic field influence the development of the radiation zone as follows. The critical density is related to the connection length of the magnetic field, i.e. the observed degradation sets in at lower densities for magnetic configurations with large connection lengths. From camera observations, in conjunction with forward calculations, it is found that the radiation zone is located on closed field lines and forms a toroidal belt. Based on complementary observations, it is concluded that the radiation zone is caused by a radiative condensation instability (or multi-faceted asymmetric radiation from the edge). Fluctuations of the radiation zone were recorded using a fast framing camera with a time resolution of 25 µs. Temporal variations as well as spatial movements were observed. The fluctuations were found on various lines-of-sight around the torus with correlation and phase shifts compatible with a toroidal propagation.

Radiation-condensation instability in a self-gravitating dusty astrophysical plasma.

Properties of radiation-condensation instability in a partially-ionized self-gravitating dusty astrophysical plasmas are studied. For this purpose, new dispersion relations for coupled dusty plasma and condensation modes in both unmagnetized and magnetized plasmas are derived. The dispersion relations are numerically analyzed to investigate the interplay between self-gravitation and impurity losses, as well as to study the effects of the external magnetic field and finite plasma beta on instabilities we found.

Thermal condensation mode in a dusty plasma

In the present work, the radiative condensation instability is investigated in the presence of dust charge fluctuations. We find that the charge variability of the grain reduces the growth rate of radiative mode only for fluctuation wavelength smaller or of the order of the Debye length and this reduction is not very large. Far from the Debye sphere, radiative mode can damp due to thermal conduction of electrons and ions

Radiative Alfvén condensation instability

The coupling of magnetic perturbations to the radiative condensation instability has been investigated. It is shown that drift-like perturbations can couple the shear Alfvén waves to the radiative thermal mode and give rise to a radiative Alfvén condensation instability.

Radiation-condensation instability in a highly ionized dusty plasma

The dynamics of linear perturbations in a radiatively cooling dusty plasma is considered, with the charge of both dust (Zd) and plasma (Zp) components being allowed to vary with their densities. It is shown that in the long-wavelength limit corresponding to the characteristic cooling length, when the plasma can be treated as quasineutral, the presence of dust particles changes the criteria for radiation instability, regardless of the charging process of the dust particles. In particular, the condensation (isobaric) mode is shown to be stabilized (destabilized) if in the equilibrium, the relation between densities of the dust nd and plasma n under the quasineutrality condition, (d ln nd/d ln n)q<1 (>1) is satisfied, while the isentropic mode is stabilized (destabilized) when the opposite inequalities take place; the isochoric mode is unaltered. Numerical estimates show that these effects can be important in hot phases (T∼106 K) of the interstellar plasma, and in tokamak plasma near the walls.

Effect of edge turbulence on threshold of multifaceted asymmetric radiation from the edge instability in tokamaks

The radiative condensation instability believed to be responsible for the occurrence of multifaceted asymmetric radiation from the edge (MARFE) in tokamaks has been investigated in the presence of a background turbulence of saturated drift resistive ballooning modes (DRBM). These modes are a natural source for edge fluctuations in tokamaks. For the m=1 MARFE, it has been shown that a modest level of DRBM turbulence can significantly lower the threshold radiation rate required for excitation of MARFEs, enhance its growth rate, and introduce a real part to the mode frequency. Some of these results are consistent with observations of onset of MARFEs in recent experiments on Joint European Torus (JET) [Proceedings of the 17th European Conference on Controlled Fusion and Plasma Heating, Amsterdam (European Physical Society, Petit-Lancy, 1990), Vol. 14b-1, p. 339] and Tokamak Experiment for Technology Oriented Research (TEXTOR) [Phys. Rev. Lett. 71, 1549 (1993)].