4,352 research outputs found

### Fast growing instabilities for non-parallel flows

Unstable modes growing when two plasma shells cross over a background plasma
at arbitrary angle $\theta$, are investigated using a non-relativistic three
cold fluids model. Parallel flows with $\theta=0$ are slightly more unstable
than anti-parallel ones with $\theta=\pi$. The case $\theta=\pi/2$ is as
unstable as the $\theta=0$ one, but the fastest growing modes are oblique.
While the most unstable wave vector varies with orientation, its growth rate
slightly evolves and there is no such thing as a stable configuration. A number
of exact results can be derived, especially for the $\theta=\pi/2$ case.Comment: 4 pages, 3 figures, to appear in Phys. Lett.

### Connection between the two branches of the quantum two-stream instability across the k space

The stability of two quantum counter-streaming electron beams is investigated
within the quantum plasma fluid equations for arbitrarily oriented wave
vectors. The analysis reveals that the two quantum two-stream unstable branches
are indeed connected by a continuum of unstable modes with oblique wave
vectors. Using the longitudinal approximation, the stability domain for any k
is analytically explained, together with the growth rate

### Anisotropic enhanced backscattering induced by anisotropic diffusion

The enhanced backscattering cone displaying a strong anisotropy from a material with anisotropic diffusion is reported. The constructive interference of the wave is preserved in the helicity preserving polarization channel and completely lost in the nonpreserving one. The internal reflectivity at the interface modifies the width of the backscatter cone. The reflectivity coefficient is measured by angular-resolved transmission. This interface property is found to be isotropic, simplifying the backscatter cone analysis. The material used is a macroporous semiconductor, gallium phosphide, in which pores are etched in a disordered position but with a preferential direction

### Oblique electromagnetic instabilities for an ultra relativistic electron beam passing through a plasma

We present an investigation of the electromagnetic instabilities which are
trig gered when an ultra relativistic electron beam passes through a plasma.
The linear growth rate is computed for every direction of propagation of the
unstable modes, and temperatures are modelled using simple waterbag
distribution functions. The ultra relativistic unstable spectrum is located
around a very narrow band centered on a critical angle which value is given
analytically. The growth rate of modes propagating in this direction decreases
like k^(-1/3).Comment: 5 pages, 3 figures, to appear in EuroPhysics Letter

### Stable transport in proton driven Fast Ignition

Proton beam transport in the context of proton driven Fast Ignition is
usually assumed to be stable due to protons high inertia, but an analytical
analysis of the process is still lacking. The stability of a charge and current
neutralized proton beam passing through a plasma is therefore conducted here,
for typical proton driven Fast Ignition parameters. In the cold regime, two
fast growing Buneman-like modes are found, with an inverse growth-rate much
smaller than the beam time-of-flight to the target core. The stability issue is
thus not so obvious, and Kinetic effects are investigated. One unstable mode is
found stabilized by the background plasma protons and electrons temperatures.
The second mode is also damped, providing the proton beam thermal spread is
larger than $\sim$ 10 keV. In Fusion conditions, the beam propagation should
therefore be stable.Comment: Submitted to Po

### Harmonic analysis of irradiation asymmetry for cylindrical implosions driven by high-frequency rotating ion beams

Cylindrical implosions driven by intense heavy ions beams should be
instrumental in a near future to study High Energy Density Matter. By rotating
the beam by means of a high frequency wobbler, it should be possible to deposit
energy in the outer layers of a cylinder, compressing the material deposited in
its core. The beam temporal profile should however generate an inevitable
irradiation asymmetry likely to feed the Rayleigh-Taylor instability (RTI)
during the implosion phase. In this paper, we compute the Fourier components of
the target irradiation in order to make the junction with previous works on RTI
performed in this setting. Implementing a 1D and 2D beam models, we find these
components can be expressed exactly in terms of the Fourier transform of the
temporal beam profile. If $T$ is the beam duration and $\Omega$ its rotation
frequency, "magic products" $\Omega T$ can be identified which cancel the first
harmonic of the deposited density, resulting in an improved irradiation
symmetry.Comment: 19 pages, 8 figures, to appear in PR

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