Comment on the paper 'Two-fluid model of the solar corona' by J. W. Knight, C. E. Newman, and P. A. Sturrock
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Billings, D. E.↗
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Transition region, corona, and solar wind in coronal holes - Some two-fluid models
A model is presented which treats the heating of the corona and the heating and acceleration of the solar wind as a single process, namely, the turbulent dissipation of solar-generated Alfven waves at the Kolmogorov rate. This model is similar to that described by Hollweg (1986), except that the electron temperature and the proton temperature are allowed to have different values. It is found that, similar to the findings of Hollweg, solutions which yield base pressures in the observed range lead to solar wind flows which are much too slow at 1 AU; a new feature is the appearance of proton temperature peak near 3-4 solar radii. Thus, this model seems to be also unsatisfactory. Several possible resolutions are discussed.
Hollweg, Joseph V.↗
Nonthermal heating in the two-fluid solar wind model
Simple two fluid solar wind speed and proton temperature model, discussing nonthermal energy dissipation
Barnes, A.↗
Solitary waves in mantle plumes
Numerical calculations in two dimensions show that solitary wave disturbances can propagate along thermal plumes in a homogeneous, viscous fluid with a thermally activated rheology similar to the mantle. Comparison of the numerical results with analytic results from an idealized two-fluid model indicates that the two-fluid model can be applied to solitary waves in the thermally activated plume. A two-fluid model of solitary waves on cylindrical conduits is accordingly applied to mantle plumes to estimate the propagation speeds, time durations, and pulse lengths of solitary waves in mantle plumes as a function of background mantle viscosity, plume flux, plume density deficit, plume viscosity, and the volume of material transported by the solitary wave. It is inferred that mantle plumes may be eposodic via solitary waves and that these disturbances might account for observed 0(10 m.y.) variations in the durations and spacings of episodes of enhanced hotspot volcanic activity. Solitary waves in mantle plumes could be generated by interactions among plumes and between plumes and the large-scale, time-dependent mantle circulation.
Schubert, G.↗
Effects of plasma squareness on RMP response in MAST-U
The effect of the squareness of the plasma boundary shape on the plasma response to the applied n = 2 (n is the toroidal mode number) resonant magnetic perturbation, and consequently on controlling the edge-localized mode (ELM) in MAST-U in the double-null configuration, is numerically systematically investigated. The modeling is performed utilizing three different plasma response models: the single-fluid model, the two-fluid model and the magnetohydrodynamic-kinetic hybrid model. The effect of the plasma squareness on ELM control is found to depend on the equilbrium kinetic profiles. Fixing the equilibrium radial profiles to that from a recent MAST-U discharge, the experimental plasma shape is found to be close to optimal for ELM control in terms of squareness. The optimal coil phasing does not significantly vary with varying plasma squareness. These findings robustly hold with (i) two figures of merit (FoMs) defined for predicting the ELM control feasibility, and (ii) three plasma response models employed for evaluating these FoMs.
MAST-U↗
A reexamination of two-fluid solar wind models
The two-fluid solar-wind equations have been solved by a method which is approximately 50 times faster than any previously developed, through the use of asymptotic expansions which are self-consistently iterated upon to find a solution that passes through the critical point. The energy assumptions in two-fluid solar-wind models are reexamined, and the conclusions are as follows: (1) proton thermal conduction may not be neglected, (2) the Coulomb logarithm must be calculated as a function of radius, and (3) the electron and proton temperatures at the base need not be equal, even when the time scale for energy exchange between the species is an order of magnitude smaller than the expansion time at the base. It is possible to reproduce reasonable quiet-time solar-wind parameters at 1 AU, but only if the proton temperature is approximately twice the electron temperature at 1 solar radius. This may indicate that extended proton heating is important in the outer solar corona. Winds with velocities at 1 AU of 450 km/s are generated without nonthermal energy deposition but require high proton temperatures as well as very low densities at the base. Higher-velocity solutions are not possible in a spherically symmetric geometry for reasonable particle fluxes at 1 AU, and it is suggested that these higher-velocity states probably require additional heating, acceleration mechanisms, or nonradial flow.
Nerney, S.↗
High temperature superconductors applications in telecommunications
The purpose of this paper is twofold: (1) to discuss high temperature superconductors with specific reference to their employment in telecommunications applications; and (2) to discuss a few of the limitations of the normally employed two-fluid model. While the debate on the actual usage of high temperature superconductors in the design of electronic and telecommunications devices - obvious advantages versus practical difficulties - needs to be settled in the near future, it is of great interest to investigate the parameters and the assumptions that will be employed in such designs. This paper deals with the issue of providing the microwave design engineer with performance data for such superconducting waveguides. The values of conductivity and surface resistance, which are the primary determining factors of a waveguide performance, are computed based on the two-fluid model. A comparison between two models - a theoretical one in terms of microscopic parameters (termed Model A) and an experimental fit in terms of macroscopic parameters (termed Model B) - shows the limitations and the resulting ambiguities of the two-fluid model at high frequencies and at temperatures close to the transition temperature. The validity of the two-fluid model is then discussed. Our preliminary results show that the electrical transport description in the normal and superconducting phases as they are formulated in the two-fluid model needs to be modified to incorporate the new and special features of high temperature superconductors. Parameters describing the waveguide performance - conductivity, surface resistance and attenuation constant - will be computed. Potential applications in communications networks and large scale integrated circuits will be discussed. Some of the ongoing work will be reported. In particular, a brief proposal is made to investigate of the effects of electromagnetic interference and the concomitant notion of electromagnetic compatibility (EMI/EMC) of high T(sub c) superconductors.
Kumar, A. Anil↗
A two-fluid solar wind model with anisotropic proton temperature
Two fluid model of solar wind with anisotropic proton temperature and allowing for extended coronal proton heating
Leer, E.↗
Two-fluid physical modeling of superconducting resonators in the ARTEMIS framework
In this work, we implement a new London equation module for superconductivity in the GPU-enabled ARTEMIS framework, and couple it to a finite-difference time-domain solver for Maxwell's equations. We apply this two-fluid approach to model a superconducting coplanar waveguide (CPW) resonator. We validate our implementation by verifying that the theoretical skin depth and reflection coefficients can be obtained for several superconductive materials, with different London penetration depths, over a range of frequencies. Our convergence studies show that the algorithm is second-order accurate in both space and time, except at superconducting interfaces where the approach is spatially first-order. In our CPW simulations, we leverage the GPU scalability of our code to compare the two-fluid model to more traditional approaches that approximate superconducting behavior and demonstrate that superconducting physics can show comparable performance to the assumption of quasi-infinite conductivity as measured by the Q-factor.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
A Plasma Modeling Hierarchy and Verification Approach
This report reviews a hierarchy of formal mathematical models for describing plasma phenomena. Starting with the Boltzmann equation, a sequence of approximations and modeling assumptions can be made that progressively reduce to the equations for magnetohydrodynamics. Understanding the assumptions behind each of these models and their mathematical form is essential to appropriate use of each level of the hierarchy. A sequence of moment models of the Boltzmann equation are presented, then focused into a generalized three-fluid model for neutral species, electrons, and ions. This model is then further reduced to a two-fluid model, for which Braginskii described a useful closure. Further reduction of the two-fluid model yields a Generalized Ohm's Law model, which provides a connection to magnetohydrodynamic approaches. A verification approach based on linear plasma waves is presented alongside the model hierarchy, which is intended as an initial and necessary but not sufficient step for verification of plasma models within this hierarchy.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Optical Efficiency and R(T,I) Measurements of ACTPol TESes Using Time Domain Multiplexing Electronics
We present new data on feedhorn-coupled transition-edge sensor devices fabricated for the second-generation receiver (ACTPol) for the Atacama cosmology telescope (ACT). First, we describe optical efficiency measurements of the latest ACTPol detector wafer, which has a 86±15% average optical efficiency. Next, we discuss measurements of the TES resistance as a function of temperature and bias current ( R(T,I) ) using the ACTPol time-domain multiplexing electronics. Qualitative agreement between R(T,I) data at low bias current and the two-fluid model prediction is shown. Using the two-fluid model and low bias current R(T,I) data, α and β at our operating bias current are calculated.
Atacama cosmology telescope (ACT)↗
A Two-Fluid, MHD Coronal Model
We describe first results from a numerical two-fluid MHD model of the global structure of the solar corona. The model is two-fluid in the sense that it accounts for the collisional energy exchange between protons and electrons. As in our single-fluid model, volumetric heat and momentum sources are required to produce high speed wind from coronal holes, low speed wind above streamers, and mass fluxes similar to the empirical solar wind. By specifying different proton and electron heating functions we obtain a high proton temperature in the coronal hole and a relatively low proton temperature in the streamer (in comparison with the electron temperature). This is consistent with inferences from SOHO/UVCS, and with the Ulysses/SWOOPS proton and electron temperature measurements which we show from the fast latitude scan. The density in the coronal hole between 2 solar radii and 5 solar radii (2RS and 5RS) is similar to the density reported from SPARTAN 201-01 measurements by Fisher and Guhathakurta. The proton mass flux scaled to 1 AU is 2.4 x 10(exp 8)/sq cm s, which is consistent with Ulysses observations. Inside the closed field region, the density is sufficiently high so that the simulation gives equal proton and electron temperatures due to the high collision rate. In open field regions (in the coronal hole and above the streamer) the proton and electron temperatures differ by varying amounts. In the streamer, the temperature and density are similar to those reported empirically by Li et al and the plasma beta is larger than unity everywhere above approx. 1.5 R(sub s), as it is in all other MHD coronal streamer models.
Suess, Steven T.↗
A Two-Fluid, MHD Coronal Model
We describe first results from a numerical two-fluid MHD model of the global structure of the solar Corona. The model is two-fluid in the sense that it accounts for the collisional energy exchange between protons and electrons. As in our single-fluid model, volumetric heat and Momentum sources are required to produce high speed wind from Corona] holes, low speed wind above streamers, and mass fluxes similar to the empirical solar wind. By specifying different proton and electron heating functions we obtain a high proton temperature in the coronal hole and a relatively low proton temperature above the streamer (in comparison with the electron temperature). This is consistent with inferences from SOHO/UltraViolet Coronagraph Spectrometer instrument (UVCS), and with the Ulysses/Solar Wind Observations Over the Poles of the Sun instrument (SWOOPS) proton and electron temperature measurements which we show from the fast latitude scan. The density in the coronal hole between 2 and 5 solar radii (2 and 5 R(sub S)) is similar to the density reported from SPARTAN 201.-01 measurements by Fisher and Guhathakurta [19941. The proton mass flux scaled to 1 AU is 2.4 x 10(exp 8)/sq cm s, which is consistent with Ulysses observations. Inside the closed field region, the density is sufficiently high so that the simulation gives equal proton and electron temperatures due to the high collision rate. In open field regions (in the coronal hole and above the streamer) the proton and electron temperatures differ by varying amounts. In the streamer the temperature and density are similar to those reported empirically by Li et al. [1998], and the plasma beta is larger than unity everywhere above approx. 1.5 R(sub S), as it is in all other MHD coronal streamer models [e.g., Steinolfson et al., 1982; also G. A. Gary and D. Alexander, Constructing the coronal magnetic field, submitted to Solar Physics, 1998].
Suess, S. T.↗
Polarization and Compressibility of Oblique Kinetic Alfven Waves
Even though solar wind, as a collisionless plasma, is properly described by the kineticMaxwell-Vlasov description, it can be argued that much of our understanding of solar wind observational data comes from an interpretation and numerical modeling which is based on a fluid description of magnetohydrodynamics. In recent years, there has been a significant interest in better understanding the importance of kinetic effects, i.e. the differences between the kinetic and usual fluid descriptions. Here we concentrate on physical properties of oblique kinetic Alfvn waves (KAWs), which are often recognized as one of the key ingredients in the solar wind turbulence cascade. We use three different fluid models with various degrees of complexity and calculate polarization and magnetic compressibility of oblique KAWs (propagation angle q = 88), which we compare to solutions derived from linear kinetic theory. We explore a wide range of possible proton plasma b = [0.1,10.0] and a wide range of length scales krL = [0.001,10.0]. It is shown that the classical isotropic two-fluid model is very compressible in comparison with kinetic theory and that the largest discrepancy occurs at scales larger than the proton gyroscale. We also show that the two-fluid model contains a large error in the polarization of electric field, even at scales krL 1. Furthermore, to understand these discrepancies between the two-fluid model and the kinetic theory, we employ two versions of the Landau fluid model that incorporate linear low-frequency kinetic effects such as Landau damping and finite Larmor radius (FLR) corrections into the fluid description. It is shown that Landau damping significantly reduces the magnetic compressibility and that FLR corrections (i.e. nongyrotropic contributions) are required to correctly capture the polarization.We also show that, in addition to Landau damping, FLR corrections are necessary to accurately describe the damping rate of KAWs. We conclude that kinetic effects are important even at scales which are significantly larger than the proton gyroscale krL 1.
Turbulence↗
Observations and physical interpretations of the solar wind flow properties as obtained from white light coronagraph aboard SPARTAN 201-01
The solar corona was observed with an externally occulted White Light Coronagraph (WLC) carried on the SPARTAN 201-1 spacecraft on 11-12 Apr. 1993. With observations from WLC and the ground based Mauna Loa White Light Coronagraph, a large number of polar plumes both in the north and south polar holes were traced from 1.16 to 5.5 Rs. Flow properties of the solar wind in coronal holes have been determined (Habbal et al., 1995) by using a two fluid model constrained by density profiles and scale height temperatures from the white light observations, and interplanetary measurements of the flow speed and proton mass flux from Ulysses' south polar passage. Provisions for acceleration by Alfven waves, as well as electron and proton heating, are included in the momentum and the energy equations respectively. The model computations fit remarkably well the empirical constraints of the two different density structures (plumes and coronal holes) for a range of input parameters. In this study we investigate the physical nature of the heating function used in the two-fluid model. Alfven waves have been suggested as the possible source of heating that accelerates the solar wind (Ofman and Davila, 1995). We utilize the density contrast observed in WLC data in the plume and ambient coronal hole region to estimate the Alfven wave frequencies responsible for heating these structures. The source heating function utilized in the two fluid model of the solar wind acceleration will be compared with the resonant Alfven wave heating function.
Guhathakurta, Madhulika↗
On rotational discontinuities in both two-fluid and hybrid models
Rotational discontinuities are studied in a two-fluid model that includes finite ion inertia dispersion and in a hybrid model in which the full ion dynamics is retained while the electrons are treated as a massless fluid. It is shown that as in previous dissipative MHD studies, a rotational discontinuity is unstable in both models and evolves to a 2-3 intermediate shock, a slow rarefaction wave, and other waves. In addition, it is shown that the so-called Walen relation, which holds exactly for rotational discontinuities, can also be well satisfied by tran-Alfvenic intermediate shocks. Thus intermediate shocks can be candidates for those observed structures that satisfy the Walen relation.
Wu, C. C.↗
Formation of intermediate shocks in both two-fluid and hybrid models
Intermediate shocks are studied in a two-fluid model that includes finite ion inertia dispersion and in a hybrid model in which the full ion dynamics is retained while the electrons are treated as a massless fluid. It is shown that in both models intermediate shocks can be formed through wave steepening, meaning that they are stable and possess shock structures.
Wu, C. C.↗
A two-fluid single-column model of turbulent shallow convection, Part III: Results and parameter sensitivity
Two-fluid modelling has recently emerged as a promising approach to representing cumulus convection in weather and climate models. This study applies the two-fluid model described in Part II Thuburn et al., 2021b to a shallow cumulus convection case study over land (ARM). Large eddy simulation data is used to tune the majority of the closures that determine the properties of entrained and detrained air. The two-fluid model is generally able to reproduce the profiles of the mean and turbulent quantities over all stages of the diurnal cycle. As such, the initiation of shallow convection and the evolution of the cloud layer are well captured. The robustness of the two-fluid model is further verified using a steady-state test case (BOMEX), in which the cloud properties are also well modelled.
54 ENVIRONMENTAL SCIENCES↗