Coulomb Heating Research Articles

Global Electron Thermodynamics in Radiatively Inefficient Accretion Flows

In the collisionless plasmas of radiatively inefficient accretion flows, heating and acceleration of ions and electrons are not well understood. Recent studies in the gyrokinetic limit revealed the importance of incorporating both the compressive and Alfvénic cascades when calculating the partition of dissipated energy between the plasma species. In this paper, we use a covariant analytic model of the accretion flow to explore the impact of compressive and Alfvénic heating, Coulomb collisions, compressional heating, and radiative cooling on the radial temperature profiles of ions and electrons. We show that, independent of the partition of heat between the plasma species, even a small fraction of turbulent energy dissipated to the electrons makes their temperature scale with a virial profile and the ion-to-electron temperature ratio smaller than in the case of pure Coulomb heating. In contrast, the presence of compressive cascades makes this ratio larger because compressive turbulent energy is channeled primarily into the ions. We calculate the ion-to-electron temperature in the inner accretion flow for a broad range of plasma properties, mass accretion rates, and black hole spins and show that it ranges between 5 ≲ T i /T e ≲ 40. We provide a physically motivated expression for this ratio that can be used to calculate observables from simulations of black hole accretion flows for a wide range of conditions.

Temperature-frequency wear mechanism maps for a heat-resistant austenitic stainless steel

A systematic experimental investigation is used to establish the influence of temperature and cycling frequency on the friction and wear behavior of the high-Cr, high-Ni heat-resistant austenitic stainless steel 310S (25%Cr–20%Ni) under gross slip fretting wear. The contact configuration is cylinder-on-flat using a like-on-like tribopair. Temperatures range from 20 °C to 700 °C and cycling frequencies range from 1 Hz to 50 Hz. A workflow to generate the wear maps with minimal number of tests, namely hierarchical probing and sampling strategy, is used to clearly establish the severe-to-mild wear transition associated with glaze layer formation. The critical temperatures related to this transition along with the number of cycles needed to establish effective glaze layer protection are obtained. A recent model reported in the literature that determines the number of cycles needed to establish effective glaze layer protection at different temperatures and frequencies gives good prediction if the temperature rise at the contact surface due to Coulomb heating is accounted for.

Space charge compensation of positive ion beams used in magnetic fusion applications

A model is presented for space charge neutralisation of positive ion beams. The model is used for the particular case of the beams used for magnetic based fusion applications. The beams consist, after a gas neutraliser, of ions and atoms at different energies. Account is taken of the contribution of all beam components to ionization of the background gas. Consideration is also given to not only beam heating of the plasma generated by the beam, due to Coulomb collisions, but also to Coulomb heating by fast electrons produced in ionization by all beam particles and stripping of the neutral components. Two approximations are considered for the motion of the secondary ions out of the beam potential; a drift approximation and a freefall approximation. All the beam plasma parameters can be calculated. The model is applied to a typical extracted beam of deuterium ions of 120 kV, 60 A. It is found that these beams are very highly compensated and that beam plasma heating by the electrons produced is generally greater than that due to the beam ions.

Space charge compensation of positive ion beams used in magnetic fusion applications

Abstract A model is presented for space charge neutralisation of positive ion beams. The model is used for the particular case of the beams used for magnetic based fusion applications. The beams consist, after a gas neutraliser, of ions and atoms at different energies. Account is taken of the contribution of all beam components to ionization of the background gas. Consideration is also given to not only beam heating of the plasma generated by the beam, due to Coulomb collisions, but also to Coulomb heating by fast electrons produced in ionization by all beam particles and stripping of the neutral components. Two approximations are considered for the motion of the secondary ions out of the beam potential; a drift approximation and a freefall approximation. All the beam plasma parameters can be calculated. The model is applied to a typical extracted beam of deuterium ions of 120kV,60A. It is found that these beams are very highly compensated and that beam plasma heating by the electrons produced is generally greater than that due to the beam ions.

Two-temperature GRRMHD Simulations of M87

Abstract We present axisymmetric two-temperature general relativistic radiation magnetohydrodynamic simulations of the inner region of the accretion flow onto the supermassive black hole M87. We address uncertainties from previous modeling efforts through inclusion of models for (1) self-consistent dissipative and Coulomb electron heating (2) radiation transport (3) frequency-dependent synchrotron emission, self-absorption, and Compton scattering. We adopt a distance D = 16.7 Mpc, an observer angle θ = 20°, and consider black hole masses and spins a ⋆ = (0.5, 0.9375) in a four-simulation suite. For each (M, a ⋆), we identify the accretion rate that recovers the 230 GHz flux from very long baseline interferometry measurements. We report on disk thermodynamics at these accretion rates ( ). The disk remains geometrically thick; cooling does not lead to a thin disk component. While electron heating is dominated by Coulomb rather than dissipation for r ≳ 10GM/c 2, the accretion disk remains two-temperature. Radiative cooling of electrons is not negligible, especially for r ≲ 10GM/c 2. The Compton y parameter is of order unity. We then compare derived and observed or inferred spectra, millimeter images, and jet powers. Simulations with M/M ⊙ = 3.3 × 109 are in conflict with observations. These simulations produce millimeter images that are too small, while the low-spin simulation also overproduces X-rays. For , both simulations agree with constraints on radio/IR/X-ray fluxes and millimeter image sizes. Simulation jet power is a factor 102–103 below inferred values, a possible consequence of the modest net magnetic flux in our models.

Cosmic-Ray Feedback Heating of the Intracluster Medium

Abstract Active galactic nuclei (AGNs) play a central role in solving the decades-old cooling-flow problem. Although there is consensus that AGNs provide the energy to prevent catastrophically large star formation, one major problem remains: How is the AGN energy thermalized in the intracluster medium (ICM)? We perform a suite of three-dimensional magnetohydrodynamical adaptive mesh refinement simulations of AGN feedback in a cool core cluster including cosmic rays (CRs). CRs are supplied to the ICM via collimated AGN jets and subsequently disperse in the magnetized ICM via streaming, and interact with the ICM via hadronic, Coulomb, and streaming instability heating. We find that CR transport is an essential model ingredient at least within the context of the physical model considered here. When streaming is included, (i) CRs come into contact with the ambient ICM and efficiently heat it, (ii) streaming instability heating dominates over Coulomb and hadronic heating, (iii) the AGN is variable and the atmosphere goes through low-/high-velocity dispersion cycles, and, importantly, (iv) CR pressure support in the cool core is very low and does not demonstrably violate observational constraints. However, when streaming is ignored, CR energy is not efficiently spent on the ICM heating and CR pressure builds up to a significant level, creating tension with the observations. Overall, we demonstrate that CR heating is a viable channel for the AGN energy thermalization in clusters and likely also in ellipticals, and that CRs play an important role in determining AGN intermittency and the dynamical state of cool cores.

Electron energetics in the Martian dayside ionosphere: Model comparisons with MAVEN data

AbstractThis paper presents a study of the energetics of the dayside ionosphere of Mars using models and data from several instruments on board the Mars Atmosphere and Volatile EvolutioN spacecraft. In particular, calculated photoelectron fluxes are compared with suprathermal electron fluxes measured by the Solar Wind Electron Analyzer, and calculated electron temperatures are compared with temperatures measured by the Langmuir Probe and Waves experiment. The major heat source for the thermal electrons is Coulomb heating from the suprathermal electron population, and cooling due to collisional rotational and vibrational CO2 dominates the energy loss. The models used in this study were largely able to reproduce the observed high topside ionosphere electron temperatures (e.g., 3000 K at 300 km altitude) without using a topside heat flux when magnetic field topologies consistent with the measured magnetic field were adopted. Magnetic topology affects both suprathermal electron transport and thermal electron heat conduction. The effects of using two different solar irradiance models were also investigated. In particular, photoelectron fluxes and electron temperatures found using the Heliospheric Environment Solar Spectrum Radiation irradiance were higher than those with the Flare Irradiance Spectrum Model‐Mars. The electron temperature is shown to affect the O2+ dissociative recombination rate coefficient, which in turn affects photochemical escape of oxygen from Mars.

The influence of the mean charge state on the Coulomb heating of fast diclusters through the Si〈1 1 1〉 direction

In the present work, we report a theoretical and experimental study of the Coulomb heating of H2+ and C2+ in Si〈111〉 channel, covering an energy range from 200keV/ion to 2200keV/ion. The experimental values for Coulomb heating were obtained by combining the Rutherford backscattering spectrometry (RBS) and the particle induced X-ray emission (PIXE) techniques under channeling conditions. Theoretical values were obtained by performing classical trajectory Monte-Carlo (CTMC) simulations of the ion paths inside the 〈111〉 Si channel, using Dirac–Hartree–Fock–Slater (DHFS) results for the interionic potential. As seen for the 〈110〉 case, it is shown that the use of a DHFS potential based on the ion mean charge states in amorphous targets leads to a disagreement between the Coulomb heating values and the expected potential energies stored in the dicluster prior to the Coulomb explosion. Therefore, a numerical procedure was used in order to calculate the mean charge state values for ions traveling in Si〈111〉. The use of the resulting charge states led to a linear relationship between the Coulomb heating values and the stored potential energy per ion of the diclusters. Finally, the Coulomb heating/stored potential energy ratio amounts to about 2/3, as expected from an isotropic Coulomb explosion.

Coulomb heating behavior of fast light diclusters channeled into Si (110) direction

Coulomb heating behavior of fast light diclusters channeled into Si (110) direction

Coulomb heating behavior of fast light diclusters thorough the Si ⟨ 110 ⟩ direction: influence of the mean charge state

In this work we report on the results for the Coulomb heating of H+ 2, B+ 2 and C+ 2 diclusters traveling in Si 〈 110 ⟩ direction covering an energy range from 200 keV/ion to 2400 keV/ion. Those results were obtained by combining the Rutherford backscattering spectrometry (RBS) and the particle induced X-ray emission (PIXE) techniques. By comparing the present results to those obtained previously for ions traveling in the narrower Si ⟨ 100 ⟩ channel, several common features are observed for the Coulomb heating values; especially, they follow a linear relationship as a function of the stored potential per ion. However, at variance with previous results, it is shown that the use of a Dirac-Hartree-Fock-Slater (DHFS) potential based on the ion mean charge states in amorphous targets leads to a considerable disagreement between the Coulomb heating values and the expected potential energies stored in the dicluster prior to the Coulomb explosion. In order to investigate this problem, a numerical procedure was developed in order to calculate the mean charge state values for ions traveling under channeling conditions. The use of the resulting charge states led to a linear relationship between the Coulomb heating values and the stored potential energy per ion of the diclusters. Moreover, the Coulomb heating/stored potential energy ratio amounts to about 2/3, which is in full agreement with those results obtained for the Si ⟨ 100 ⟩ direction.

THE DISK EVAPORATION MODEL FOR THE SPECTRAL FEATURES OF LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI

Observations show that the accretion flows in low-luminosity active galactic nuclei (LLAGNs) probably have a two-component structure with an inner ADAF and an outer truncated accretion disk. As shown by Taam et al. (2012), the truncation radius as a function of mass accretion rate is strongly affected by including the magnetic field within the framework of disk evaporation model, i.e., an increase of the magnetic field results in a smaller truncation radius of the accretion disk. In this work, we calculate the emergent spectrum of an inner ADAF + an outer truncated accretion disk around a supermassive black hole based on the prediction by Taam et al. (2012). It is found that an increase of the magnetic field from $\beta=0.8$ to $\beta=0.5$ (with magnetic pressure $p_{\rm m}=B^2/{8\pi}=(1-\beta)p_{\rm tot}$, $p_{\rm tot}=p_{\rm gas}+p_{\rm m}$) results in an increase of $\sim 8.7$ times of the luminosity from the truncated accretion disk. We found that the equipartition of gas pressure to magnetic pressure, i.e., $\beta=0.5$, failed to explain the observed anti-correlation between $L_{\rm 2-10 keV}/L_{\rm Edd}$ and the bolometric correction $\kappa_{\rm 2-10 keV}$ (with $\kappa_{\rm 2-10 keV} = L_{\rm bol}/L_{\rm 2-10 keV}$). The emergent spectra for larger value $\beta=0.8$ or $\beta=0.95$ can well explain the observed $L_{\rm 2-10 keV}/L_{\rm Edd}$-$\kappa_{\rm 2-10 keV}$ correlation. We argue that in the disk evaporation model, the electrons in the corona are assumed to be heated only by a transfer of energy from the ions to electrons via Coulomb collisions, which is reasonable for the accretion with a lower mass accretion rate. Coulomb heating is the dominated heating mechanism for the electrons only if the magnetic field is strongly sub-equipartition, which is roughly consistent with observations.

General relativistic model of hot accretion flows with global Compton cooling

We present a model of optically thin, two-temperature, accretion flows using an exact Monte Carlo treatment of global Comptonization, with seed photons from synchrotron and bremsstrahlung emission, as well as with a fully general relativistic description of both the radiative and hydrodynamic processes. We consider accretion rates for which the luminosities of the flows are between ~0.001 and 0.01 of the Eddington luminosity. The black hole spin parameter strongly affects the flow structure within the innermost 10 gravitational radii. The resulting large difference between the Coulomb heating in models with a non-rotating and a rapidly rotating black hole is, however, outweighed by a strong contribution of compression work, much less dependent on spin. The consequent reduction of effects related to the value of the black spin is more significant at smaller accretion rates. For a non-rotating black hole, the compressive heating of electrons dominates over their Coulomb heating, and results in an approximately constant radiative efficiency of approximately 0.4 per cent in the considered range of luminosities. For a rapidly rotating black hole, the Coulomb heating dominates, the radiative efficiency is ~1 per cent and it slightly increases (but less significantly than estimated in some previous works) with increasing accretion rate. We find an agreement between our model, in which the synchrotron emission is the main source of seed photons, and observations of black-hole binaries in their hard states and AGNs at low luminosities. In particular, our model predicts a hardening of the X-ray spectrum with increasing luminosity, as indeed observed below ~0.01 of the Eddington luminosity in both black-hole binaries and AGNs. Also, our model approximately reproduces the luminosity and the slope of the X-ray emission in Cen A.

X-ray impact on the protoplanetary disks around T Tauri stars

Context: T Tauri stars have X-ray luminosities ranging from L_X = 10^28-10^32 erg/s. These luminosities are similar to UV luminosities (L_UV 10^30-10^31 erg/s) and therefore X-rays are expected to affect the physics and chemistry of the upper layers of their surrounding protoplanetary disks. Aim: The effects and importance of X-rays on the chemical and hydrostatic structure of protoplanetary disks are investigated, species tracing X-ray irradiation (for L_X >= 10^29 erg/s) are identified and predictions for [OI], [CII] and [NII] fine structure line fluxes are provided. Methods: We have implemented X-ray physics and chemistry into the chemo-physical disk code ProDiMo. We include Coulomb heating and H2 ionization as heating processes and primary and secondary ionization due to X-rays in the chemistry. Results: X-rays heat up the gas causing it to expand in the optically thin surface layers. Neutral molecular species are not much affected in their abundance and spatial distribution, but charged species such as N+, OH+, H2O+ and H3O+ show enhanced abundances in the disk surface. Conclusions: Coulomb heating by X-rays changes the vertical structure of the disk, yielding temperatures of ~ 8000 K out to distances of 50 AU. The chemical structure is altered by the high electron abundance in the gas in the disk surface, causing an efficient ion-molecule chemistry. The products of this, OH+, H2O+ and H3O+, are of great interest for observations of low-mass young stellar objects with the Herschel Space Observatory. [OI] (at 63 and 145 mic) and [CII] (at 158 mic) fine structure emission are only affected for L_X > 10^30 erg/s.

Coulomb heating behavior of fast light diclusters

In this Brief Report we present data on the Coulomb heating induced by ${\text{B}}_{2}^{+}$ molecular beams channeling along $\text{Si}⟨100⟩$ direction in a large energy interval (800 up to 2200 keV/atom). The simultaneous detection of $\text{Si}\text{ }K\ensuremath{\alpha}$ x rays and backscattered particles established the necessary grounds for the calculation of the Coulomb heating, i.e., the molecular transversal energy due to the Coulomb explosion transferred to the target atoms. By combining the present results with those previously published for ${\text{H}}_{2}^{+}$ at 150 keV/atom and for ${\text{C}}_{2}^{+}$ at energies from 800 up to 2200 keV/atom, we were able to obtain two striking results. First, all the experimental values fall on a straight line when they are plotted as a function of the stored potential energy per ion, suggesting some kind of ``universal behavior.'' Second, the analysis of the whole set of experimental data shows that the Coulomb heating scales with 2/3 of the stored potential energy per ion, regardless the ion atomic number. This result is in agreement with theoretical predictions.

A compact pulsar wind nebula model of the γ-ray-loud binary LS I +61○303

We study a model of of LS I +61 303 in which its radio to TeV emission is due to interaction of a relativistic wind from a young pulsar with the wind from its companion Be star. We assume the fast polar wind is clumpy, which is typical for radiatively-driven winds. The clumpiness cause the two winds to mix. The relativistic electrons from the pulsar wind are retained in the moving clumps by inhomogeneities of the magnetic field, which explains the X-ray variability observed on time scales much shorter than the orbital period. We calculate detailed inhomogeneous spectral models reproducing the average broad-band spectrum from radio to TeVs. Given the uncertainties the form of the distribution of relativistic electrons, the X-ray spectrum could be dominated by either Compton or synchrotron emission. The recent Fermi observations constrain the high-energy cut-off in the electron distribution to be at the Lorentz factor of 2 10^4 or 10^8 in the former and latter model, respectively. We provide formulae comparing the losses of the relativistic electrons due to Compton, synchrotron and Coulomb processes vs. the distance from the Be star. We calculate the optical depth of the wind to free-free absorption, showing that it will suppress most of the radio emission within the orbit. We point out the importance of Compton and Coulomb heating of the stellar wind within and around the gamma-ray emitting region. Then, we find the most likely mechanism explaining the orbital modulation at TeV energies is anisotropy of emission.

A numerical study of energy transfer mechanisms in materials following irradiation by swift heavy ions

Swift heavy ions interact with electrons in materials and this may yield permanent atomic displacements; the energy transfer mechanisms that bring electronic excitations into atomic motion are not fully understood, and are generally discussed in terms of two theories, viz. Coulomb explosion and heat exchange between excited electrons and atoms, which is limited by electron-phonon coupling. We address this problem for a “generic” material using a semi-classical numerical approach where the dynamics of the evolving electron density is calculated by using molecular dynamics simulations applied to pseudo-electrons. The forces exerted on the nuclei are then used to calculated the trajectories of the nuclei. From the temporal evolution of the atomic kinetic energy, we find that the energy transfer between the electrons and the nuclei can be divided in two parts. First, a Coulomb heating starts the motion of the atoms by giving them a radial speed; this process differs from Coulomb explosion because the atoms are not displaced over interatomic distances. Second, a thermal energy transfer, as described in linear transport theory, takes place. Our study thus confirms the domination of thermal energy exchange mechanisms over Coulomb explosion models.

The Mechanisms of Particle Kinetics and Dynamics Leading to Seismic Emission and Sunquakes

In this paper the mechanisms responsible for observational features associated with sunquakes induced by different classes of solar flares are compared. The role of high-energy particle beams via Coulomb and Ohmic heating of the ambient plasma and nonthermal excitation and ionization is explored for different beam parameters at various atmospheric depths. On the one hand, only hard electron beams with high-energy fluxes are found producing extensive nonthermal hydrogen ionization, four orders of magnitude higher than in the quiet atmosphere. This excess ionization leads to the white-light flares associated with the seismic emission appearing simultaneously with hard X-ray emission and, consequently, to a strong increase of Ni-line emission observed as the seismic emission measured with the holographic technique. On the other hand, the ambient plasma hydrodynamic response to heating by such beam electrons forms hydrodynamic shocks just below the transition region, in the upper chromosphere, and they travel with supersonic velocity for up to five minutes before reaching the photosphere. These hydrodynamic responses caused by the beam electrons are maximized in the lower chromosphere for moderate electron beams because of their smaller Ohmic losses in the upper atmosphere compared to those for higher-energy electron beams whose bulk energy is deposited in the transition region. These shocks caused by electron beams can explain the observations of seismic emission by time – distance (TD) diagrams and the holographic method in M- and C-class flares, whereas to account for the quakes in X-class flares, high-energy quasi-thermal protons or power-law proton beams either by themselves or blended with electron beams are the most likely agents. Nonthermal ionization and excitation of lower atmospheric levels during the beam injection followed by thermo-conductive heating after the beam is stopped can contribute to the seismic signatures observed with the holographic technique caused by strong nonthermal ionization and back-warming heating occurring in the shock while it loses its energy by optically-thick radiation in the photospheric lines and continua.

Coulomb heating of channeledC+andC2+molecules in Si

is shown that this effect results from the Coulomb explosion of the molecule during the channeling motion. By combining the Rutherford backscattering channeling RBS-C and the x-ray results we were able to determine the value of the transverse energy transfer as a function of the beam energy due to the break up process Coulomb heating. This energy increases monotonically from 14 eV for 900 keV/atom up to 30 eV for 2200 keV/atom. In addition, we were able to predict the theoretical Coulomb heating values by combining calculations and simulations, the theoretical-experimental agreement, within the experimental errors, being quite reasonable.

A global 2.5-dimensional three fluid solar wind model with alpha particles

[1] A global 2.5-dimensional three fluid solar wind model is presented. Two ion species, namely protons and alpha particles, are heated by an empirical energy flux while electrons are heated by the classical heat flux and Coulomb coupling with ions. It is found that for a reasonable relative speed between alpha particles and protons at 1 AU to be achieved, the alphas need to be preferentially heated in the inner corona. No external heating is applied in the streamer base, the closed magnetic field region. A hot coronal boundary, the electron heat flux, and Coulomb coupling keep plasma species in equilibrium inside the streamer, and a nonisothermal streamer is found. The abundance of alpha particles varies within the streamer base. It is small in the streamer core compared with streamer legs, and alphas continuously drain out of the streamer core along magnetic field due to gravitational settling. The settling operates over a timescale of several days. Alpha particles in the slow wind have a smaller abundance than in the fast wind at 1 AU, in agreement with observations. This is mainly determined in the near-Sun region. For the coronal alpha abundances in the range 0.015-0.15, it is found that alpha particles play a negligible role in determining the magnetic field. In this sense, treating alphas as test particles is justified. However, alphas have an important impact on solar wind parameters. Coulomb collisions and heating drag alphas into the solar wind. The Coulomb friction with protons by itself is, however, unable to drive into the slow solar wind a flux of alphas flowing at roughly the same speed of protons as observed by in situ measurements at 1 AU.

The effect of Coulomb explosion ion heating in optical-field ionised nitrogen X-ray laser schemes

This paper examines the effect of Coulomb ion heating in various nitrogen targets produced by optical-field ionisation from plane polarised high intensity laser radiation. Methods for controlling the explosion, such that plasma suitable for recombination X-ray lasers may be produced are devised. A numerical model of breakdown by high intensity pulses is used to calculate optical-field ionisation, above-threshold ionisation and inverse bremsstrahlung electron heating, and Coulomb ion heating mechanisms. A 1D Lagrangian hydrodynamics and atomic kinetics model is used as a postprocessor to simulate the recombination phase. Both optimised nitrogen and nitrogen doped with hydrogen mixtures are examined. Electron temperatures are found to be significantly lower in mixtures, yielding higher gains. Single and double (pre- and main) pulses are investigated with double pulses found to give good control of the ion temperature resulting from the Coulomb ion repulsion. An optimised nitrogen hydrogen mixture ionised by a double pulse produce a gain of 60 cm −1 at 247 Å with a low saturation intensity of ∼1×10 7 W cm −2. A two-dimensional pulse propagation model, which solves the paraxial wave equation and includes optical-field ionisation, refraction and diffraction effects, is used to study nitrogen hydrogen mixtures with double pulse configurations. A loosely focused pre-pulse of vacuum peak intensity 4×10 14 W cm −2 is applied to produce a wide and 4 mm long channel of singly ionised dissociated gas mixture. The plasma is further ionised to the He-like N state by a tighter main pulse of peak intensity 6×10 16 W cm −2, which is suitable for achieving the gain referred to above.