724 research outputs found

### Magnetic explosions: role of the inductive electric field

Inclusion of the inductive electric field, ${\bf E}_{\rm ind}$ due to the
temporally changing ${\bf B}$, in magnetic explosions is discussed, with
emphasis on solar flares. Several roles played by ${\bf E}_{\rm ind}$ are
identified: on a global scale, ${\bf E}_{\rm ind}$ produces the EMF that drives
the explosion; the associated ${\bf E}_{\rm ind}\times{\bf B}$ drift is
identified with the inflow of magnetic field lines into a reconnection region;
the polarization current, associated with $\partial{\bf E}_{\rm ind}/\partial
t$, implies a ${\bf J}\times{\bf B}$ force that accelerates this inflow; and
the component of ${\bf E}_{\rm ind}$ parallel to ${\bf B}$ accelerates the
energetic electrons that cause hard X-ray emission and type III radio bursts.
Some simple models that describe these effects are presented. A resolution of
the long-standing "number problem" in solar flares is suggested

### Linear acceleration emission: 2 Power spectrum

The theory of linear acceleration emission is developed for a large amplitude
electrostatic wave in which all particles become highly relativistic in much
less than a wave period. An Airy integral approximation is shown to apply near
the phases where the electric field passes through zero and the Lorentz factors
of all particles have their maxima. The emissivity is derived for an individual
particle and is integrated over frequency and solid angle to find the power
radiated per particle. The result is different from that implied by the
generalized Larmor formula which, we argue, is not valid in this case. We also
discuss a mathematical inconsistency that arises when one evaluates the power
spectrum by integrating the emissivity over solid angle. The correct power
spectrum increases as the 4/3rd power of the frequency at low frequencies, and
falls off exponentially above a characteristic frequency.
We discuss application of linear acceleration emission to the emission of
high frequency photons in an oscillating model for pulsars. We conclude that it
cannot account for gamma-ray emission, but can play a role in secondary pair
creation.Comment: 25 pages; Accepted for publication in Ap

### Faraday rotation: effect of magnetic field reversals

The standard formula for the rotation measure, RM, which determines the
position angle, $\psi={\rm RM}\lambda^2$, due to Faraday rotation, includes
contributions only from the portions of the ray path where the natural modes of
the plasma are circularly polarized. In small regions of the ray path where the
projection of the magnetic field on the ray path reverses sign (called QT
regions) the modes are nearly linearly polarized. The neglect of QT regions in
estimating RM is not well justified at frequencies below a transition frequency
where mode coupling changes from strong to weak. By integrating the
polarization transfer equation across a QT region in the latter limit, I
estimate the additional contribution $\Delta\psi$ needed to correct this
omission. In contrast with a result proposed by \cite{BB10}, $\Delta\psi$ is
small and probably unobservable. I identify a new source of circular
polarization, due to mode coupling in an asymmetric QT region. I also identify
a new circular-polarization-dependent correction to the dispersion measure at
low frequencies.Comment: 25 pages 1 figure, accepted for publication in The Astrophysical
Journa

### Dynamics of spin 1/2 quantum plasmas

The fully nonlinear governing equations for spin 1/2 quantum plasmas are
presented. Starting from the Pauli equation, the relevant plasma equations are
derived, and it is shown that nontrivial quantum spin couplings arise, enabling
studies of the combined collective and spin dynamics. The linear response of
the quantum plasma in an electron--ion system is obtained and analyzed.
Applications of the theory to solid state and astrophysical systems as well as
dusty plasmas are pointed out.Comment: 4 pages, 2 figures, to appear in Physical Review Letter

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