Ionized Gases

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Egil Leer - One of the best experts on this subject based on the ideXlab platform.

  • describing the flow of fully Ionized magnetized Gases improved gyrotropic transport equations
    Journal of Plasma Physics, 2005
    Co-Authors: A M Janse, Oystein Liesvendsen, Egil Leer
    Abstract:

    We have developed a new set of transport equations for magnetized, fully Ionized Gases designed to cover the entire regime from collision-dominated to collisionless flow. The equations are based on a skewed bi-Maxwellian velocity distribution function and describe number density, $n$ , flow velocity, ${\vek u}$ , parallel and perpendicular temperature, $T_{\parallel}$ and $T_{\perp}$ , and heat flow, $\mathbf q$ . We choose a velocity distribution function $f(\vek v) = f^{\mathrm{bM}}(1+\phi)$ where $f^{\mathrm{bM}}$ is a bi-Maxwellian and the ‘skewness’, $\phi$ , is proportional to $c^3$ instead of the more commonly used $\phi\propto c \ (c \equiv |\vek v-\vek u|)$ . We find transport coefficients (heat flux and thermal force) in the collision-dominated limit that are in good agreement with results from classical transport theory. The equations also describe, reasonably well, the flow of collisionless, Ionized Gases, and should therefore be well suited to describe the transition region–corona–solar wind system and other fully Ionized, expanding stellar atmospheres.

  • improved transport equations for fully Ionized Gases
    The Astrophysical Journal, 2004
    Co-Authors: Mari Anne Killie, A M Janse, Oystein Liesvendsen, Egil Leer
    Abstract:

    We have developed fluid transport equations for fully Ionized Gases that improve the description of Coulomb collisions. The aim has been to develop simple and versatile equations that can easily be implemented in numerical models and thus be applied to a large variety of space plasmas, while they still accurately describe thermal forces and energy flows in collision-dominated plasmas. Based on exact solutions to the Boltzmann equation in the collision-dominated limit, the correction term to the velocity distribution function that account for particle flows is assumed to be proportional to the third power of the velocity, leading to a near isotropic core distribution. Applying the fluid equations derived from this new velocity distribution to a collision-dominated electron-proton plasma with a small temperature gradient, the resulting electron heat flux, as well as the thermal force between electrons and protons, deviate less than 25% from the exact results of classical transport theory. The new equations predict a factor of 4 reduction in the thermal force acting on heavy, minor ions caused by an imposed heat flux, compared with fluid equations that are in common use today. The improved description of thermal forces is expected to be important for modeling the composition of stellar atmospheres.

Ellen G Zweibel - One of the best experts on this subject based on the ideXlab platform.

  • onset of fast magnetic reconnection in partially Ionized Gases
    The Astrophysical Journal, 2011
    Co-Authors: Leonid Malyshkin, Ellen G Zweibel
    Abstract:

    We consider quasi-stationary two-dimensional magnetic reconnection in a partially Ionized incompressible plasma. We find that when the plasma is weakly Ionized and the collisions between the ions and the neutral particles are significant, the transition to fast collisionless reconnection due to the Hall effect in the generalized Ohm's law is expected to occur at much lower values of the Lundquist number, as compared to a fully Ionized plasma case. We estimate that these conditions for fast reconnection are satisfied in molecular clouds and in protostellar disks.

  • fast dynamos in weakly Ionized Gases
    The Astrophysical Journal, 2008
    Co-Authors: Ellen G Zweibel, Fabian Heitsch
    Abstract:

    The turnover of interstellar gas on ~109 yr timescales argues for the continuous operation of a galactic dynamo. The conductivity of interstellar gas is so high that the dynamo must be "fast"; i.e., the magnetic field must be amplified at a rate nearly independent of the magnetic diffusivity. Yet all the fast dynamos so far known, and all direct numerical simulations of interstellar dynamos, yield magnetic power spectra that peak at the resistive scale, while galactic magnetic fields have substantial power on large scales. In this paper we show that in weakly Ionized gas the limiting scale may be the ion-neutral decoupling scale, which, although still small, is many orders of magnitude larger than the resistive scale.

P Bletzinger - One of the best experts on this subject based on the ideXlab platform.

  • shock wave propagation in neutral and Ionized Gases
    Journal of Applied Physics, 2008
    Co-Authors: N K Podder, R B Wilson, P Bletzinger
    Abstract:

    Preliminary measurements on a recently built shock tube are presented. Planar shock waves are excited by the spark discharge of a capacitor, and launched into the neutral argon or nitrogen gas as well as its Ionized glow discharge in the pressure region 1–17 Torr. For the shock wave propagation in the neutral argon at fixed capacitor charging voltage, the shock wave velocity is found to increase nonlinearly at the lower pressures, reach a maximum at an intermediate pressure, and then decrease almost linearly at the higher pressures, whereas the shock wave strength continues to increase at a nonlinear rate over the entire range of pressure. However, at fixed gas pressure the shock wave velocity increases almost monotonically as the capacitor charging voltage is increased. For the shock wave propagation in the Ionized argon glow, the shock wave is found to be most influenced by the glow discharge plasma current. As the plasma current is increased, both the shock wave propagation velocity and the dispersion ...

Oystein Liesvendsen - One of the best experts on this subject based on the ideXlab platform.

  • describing the flow of fully Ionized magnetized Gases improved gyrotropic transport equations
    Journal of Plasma Physics, 2005
    Co-Authors: A M Janse, Oystein Liesvendsen, Egil Leer
    Abstract:

    We have developed a new set of transport equations for magnetized, fully Ionized Gases designed to cover the entire regime from collision-dominated to collisionless flow. The equations are based on a skewed bi-Maxwellian velocity distribution function and describe number density, $n$ , flow velocity, ${\vek u}$ , parallel and perpendicular temperature, $T_{\parallel}$ and $T_{\perp}$ , and heat flow, $\mathbf q$ . We choose a velocity distribution function $f(\vek v) = f^{\mathrm{bM}}(1+\phi)$ where $f^{\mathrm{bM}}$ is a bi-Maxwellian and the ‘skewness’, $\phi$ , is proportional to $c^3$ instead of the more commonly used $\phi\propto c \ (c \equiv |\vek v-\vek u|)$ . We find transport coefficients (heat flux and thermal force) in the collision-dominated limit that are in good agreement with results from classical transport theory. The equations also describe, reasonably well, the flow of collisionless, Ionized Gases, and should therefore be well suited to describe the transition region–corona–solar wind system and other fully Ionized, expanding stellar atmospheres.

  • improved transport equations for fully Ionized Gases
    The Astrophysical Journal, 2004
    Co-Authors: Mari Anne Killie, A M Janse, Oystein Liesvendsen, Egil Leer
    Abstract:

    We have developed fluid transport equations for fully Ionized Gases that improve the description of Coulomb collisions. The aim has been to develop simple and versatile equations that can easily be implemented in numerical models and thus be applied to a large variety of space plasmas, while they still accurately describe thermal forces and energy flows in collision-dominated plasmas. Based on exact solutions to the Boltzmann equation in the collision-dominated limit, the correction term to the velocity distribution function that account for particle flows is assumed to be proportional to the third power of the velocity, leading to a near isotropic core distribution. Applying the fluid equations derived from this new velocity distribution to a collision-dominated electron-proton plasma with a small temperature gradient, the resulting electron heat flux, as well as the thermal force between electrons and protons, deviate less than 25% from the exact results of classical transport theory. The new equations predict a factor of 4 reduction in the thermal force acting on heavy, minor ions caused by an imposed heat flux, compared with fluid equations that are in common use today. The improved description of thermal forces is expected to be important for modeling the composition of stellar atmospheres.

L Berge - One of the best experts on this subject based on the ideXlab platform.

  • boosting terahertz generation in laser field Ionized Gases using a sawtooth wave shape
    Physical Review Letters, 2015
    Co-Authors: Gonzalez P De Alaiza Martinez, L Berge, I Babushkin, Stefan Skupin, E Cabreragranado, C Kohler, Uwe Morgner, A Husakou, J Herrmann
    Abstract:

    Broadband ultrashort terahertz (THz) pulses can be produced using plasma generation in a noble gas Ionized by femtosecond two-color pulses. Here we demonstrate that, by using multiple-frequency laser pulses, one can obtain a waveform which optimizes the free electron trajectories in such a way that they acquire the largest drift velocity. This allows us to increase the THz conversion efficiency to 2%, an unprecedented performance for THz generation in Gases. In addition to the analytical study of THz generation using a local current model, we perform comprehensive 3D simulations accounting for propagation effects which confirm this prediction. Our results show that THz conversion via tunnel ionization can be greatly improved with well-designed multicolor pulses.

  • nonlinear propagation of self guided ultra short pulses in Ionized Gases
    Physics of Plasmas, 2000
    Co-Authors: L Berge, A Couairon
    Abstract:

    The nonlinear propagation regimes of femtosecond pulses in noble Gases and air are analyzed from an extended nonlinear Schrodinger equation coupled with the inertial response of an electron plasma created by multiphoton process and avalanche ionization. By means of integral relations supplemented by two variational approaches, it is shown that the electron density produced by photo-ionization defocuses the beam and arrests the self-focusing promoted by the Kerr response of the gas, so that a balance between both these effects can be realized for incident pulses with sufficiently high input power. Theoretical descriptions of self-guided beams emphasize the distortions caused by multiphoton sources in the temporal pulse profiles and they are confronted with direct numerical simulations. Dissipative effects as multiphoton absorption and the delayed Kerr response induced by air are finally discussed.