Reply to Comment by J. C. Byrne on "Ambipolar Drift, Deformation, and Diffusion of a Plasma in a Magnetic Field"

1974 ◽  
Vol 52 (1) ◽  
pp. 95-95
Author(s):  
R. L. Monroe
Keyword(s):  
Magnetic Field ◽  
Ambipolar Drift ◽  
And Diffusion

Ambipolar Drift, Deformation, and Diffusion of a Plasma in a Magnetic Field

1973 ◽  
Vol 51 (5) ◽  
pp. 564-573 ◽  
Author(s):  
Richard L. Monroe
Keyword(s):  
Magnetic Field ◽  
Diffusion Coefficient ◽  
Effective Magnetic Field ◽  
Theoretical Problem ◽  
Direction Parallel ◽  
Transverse Diffusion ◽  
Weakly Ionized ◽  
Plasma Diffusion ◽  
Ambipolar Drift ◽  
And Diffusion

The theoretical problem of a weakly ionized, constant temperature, three particle plasma in an externally generated magnetic field is reformulated by transforming the set of 14 macroscopic plasma equations (continuity and momentum equations for ions and electrons plus Maxwell's equations) in 14 unknowns (ion and electron number densities and velocities plus the effective electric and magnetic fields) into an equivalent set of 4 integral equations in 4 unknowns. In the course of this transformation, it is shown that the plasma behavior can be interpreted in terms of three ambipolar processes : drift, deformation, and diffusion. Plasma diffusion is characterized by two diffusion coefficients : the usual Schottky formula applying in the direction parallel to the effective magnetic field and a new expression for the ambipolar transverse diffusion coefficient applying in directions perpendicular to the effective magnetic field. The new ambipolar coefficient differs markedly from the familiar ambipolar coefficient associated with the names of Bickerton, Lehnert, Holway, Allis, and Buchsbaum; and, in general, it gives values for the transverse diffusion coefficient which are two orders of magnitude larger than those given by the latter. It is concluded that ambipolar diffusion can produce a transverse diffusion coefficient large enough to account for the diffusion rates measured by Bohm, Burhop, Massey, and Williams in argon arc discharges.

A Comment on "Ambipolar Drift, Deformation, and Diffusion of a Plasma in a Magnetic Field" by Richard L. Monroe

1974 ◽  
Vol 52 (1) ◽  
pp. 95-95
Author(s):  
J. C. Byrne
Keyword(s):  
Magnetic Field ◽  
Electric Fields ◽  
Maxwell’S Equations ◽  
Additional Assumption ◽  
Maxwell's Equations ◽  
Displacement Current ◽  
Charge Neutrality ◽  
Ambipolar Drift ◽  
And Diffusion

When the displacement current is negligible in Maxwell's equations an additional assumption of charge neutrality is not a redundant assumption, as was recently claimed by Monroe, for a plasma in a magnetic field when there are no externally maintained electric fields.

Fast (non-)diffusive Quasi-Geostrophic Magneto-Coriolis Modes in the Earth's core

2021 ◽  
Author(s):  
Felix Gerick ◽  
Dominique Jault ◽  
Jerome Noir
Keyword(s):  
Magnetic Field ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Outer Core ◽  
Equatorial Region ◽  
Earth’S Core ◽  
Earth's Core ◽  
Strong Focusing ◽  
Geomagnetic Observations ◽  
And Diffusion

<p> Fast changes of Earth's magnetic field could be explained by inviscid and diffusion-less quasi-geostrophic (QG) Magneto-Coriolis modes. We present a hybrid QG model with columnar flows and three-dimensional magnetic fields and find modes with periods of a few years at parameters relevant to Earth's core. These fast Magneto-Coriolis modes show strong focusing of their kinetic and magnetic energy in the equatorial region, while maintaining a relatively large spatial structure along the azimuthal direction. Their properties agree with some of the observations and inferred core flows. We find additionally, in contrast to what has been assumed previously, that these modes are not affected significantly by magnetic diffusion. The model opens a new way of inverting geomagnetic observations to the flow and magnetic field deep within the Earth's outer core.</p>

scholarly journals Constraint on ion–neutral drift velocity in the Class 0 protostar B335 from ALMA observations

2018 ◽  
Vol 615 ◽  
pp. A58 ◽  
Author(s):  
Hsi-Wei Yen ◽  
Bo Zhao ◽  
Patrick M. Koch ◽  
Ruben Krasnopolsky ◽  
Zhi-Yun Li ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Drift Velocity ◽  
Large Scale ◽  
Ambipolar Diffusion ◽  
Neutral Drift ◽  
Neutral Gas ◽  
Mhd Simulations ◽  
Ambipolar Drift ◽  
Velocity Drift ◽  
The Magnetic Field

Aims. Ambipolar diffusion can cause a velocity drift between ions and neutrals. This is one of the non-ideal magnetohydrodynamics (MHD) effects proposed to enable the formation of large-scale Keplerian disks with sizes of tens of au. To observationally study ambipolar diffusion in collapsing protostellar envelopes, we compare here gas kinematics traced by ionized and neutral molecular lines and discuss the implication on ambipolar diffusion. Methods. We analyzed the data of the H13CO+ (3–2) and C18O (2–1) emission in the Class 0 protostar B335 obtained with our ALMA observations. We constructed kinematical models to fit the velocity structures observed in the H13CO+ and C18O emission and to measure the infalling velocities of the ionized and neutral gas on a 100 au scale in B335. Results. A central compact (~1′′–2′′) component that is elongated perpendicular to the outflow direction and exhibits a clear velocity gradient along the outflow direction is observed in both lines and most likely traces the infalling flattened envelope. With our kinematical models, the infalling velocities in the H13CO+ and C18O emission are both measured to be 0.85 ± 0.2 km s−1 at a radius of 100 au, suggesting that the velocity drift between the ionized and neutral gas is at most 0.3 km s−1 at a radius of 100 au in B335. Conclusions. The Hall parameter for H13CO+ is estimated to be ≫1 on a 100 au scale in B335, so that H13CO+ is expected to be attached to the magnetic field. Our non-detection or upper limit of the velocity drift between the ionized and neutral gas could suggest that the magnetic field remains rather well coupled to the bulk neutral material on a 100 au scale in this source, and that any significant field-matter decoupling, if present, likely occurs only on a smaller scale, leading to an accumulation of magnetic flux and thus efficient magnetic braking in the inner envelope. This result is consistent with the expectation from the MHD simulations with a typical ambipolar diffusivity and those without ambipolar diffusion. On the other hand, the high ambipolar drift velocity of 0.5–1.0 km s−1 on a 100 au scale predicted in the MHD simulations with an enhanced ambipolar diffusivity by removing small dust grains, where the minimum grain size is 0.1 μm, is not detected in our observations. However, because of our limited angular resolution, we cannot rule out a significant ambipolar drift only in the midplane of the infalling envelope. Future observations with higher angular resolutions (~0. ′′1) are needed to examine this possibility and ambipolar diffusion on a smaller scale.

Spin relaxation due to magnetic-field inhomogeneities: Quartic dependence and diffusion-constant measurements

1990 ◽  
Vol 41 (7) ◽  
pp. 3672-3688 ◽  
Author(s):  
K. C. Hasson ◽  
G. D. Cates ◽  
K. Lerman ◽  
P. Bogorad ◽  
W. Happer
Keyword(s):  
Magnetic Field ◽  
Spin Relaxation ◽  
Diffusion Constant ◽  
And Diffusion

Heat and Diffusion Fluxes in a Multicomponent Ionized Gas in a Magnetic Field

1969 ◽  
Vol 24 (6) ◽  
pp. 967-976
Author(s):  
R. S. Devoto
Keyword(s):  
Magnetic Field ◽  
Heat Flux ◽  
Thermal Diffusion ◽  
Diffusion Flux ◽  
Momentum Equation ◽  
Ionized Gas ◽  
Burnett Method ◽  
And Diffusion ◽  
Monatomic Gas

Ordinary and thermal diffusion as well as heat flux in a dilute, ionized, multicomponent monoatomic gas in a magnetic field are considered with the Chapman-Enskog-Burnett method. It is shown how, with certain modifications, the usual expressions for the properties of an un-ionized monatomic gas may be applied to this case. The expression for the diffusion flux is compared with the momentum equation suggested by Schliiter.

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