802 research outputs found
Spatial and Wavenumber Resolution of Doppler Reflectometry
Doppler reflectometry spatial and wavenumber resolution is analyzed within
the framework of the linear Born approximation in slab plasma model. Explicit
expression for its signal backscattering spectrum is obtained in terms of
wavenumber and frequency spectra of turbulence which is assumed to be radially
statistically inhomogeneous. Scattering efficiency for both back and forward
scattering (in radial direction) is introduced and shown to be inverse
proportional to the square of radial wavenumber of the probing wave at the
fluctuation location thus making the spatial resolution of diagnostics
sensitive to density profile. It is shown that in case of forward scattering
additional localization can be provided by the antenna diagram. It is
demonstrated that in case of backscattering the spatial resolution can be
better if the turbulence spectrum at high radial wavenumbers is suppressed. The
improvement of Doppler reflectometry data localization by probing beam focusing
onto the cut-off is proposed and described. The possibility of Doppler
reflectometry data interpretation based on the obtained expressions is shown.Comment: http://stacks.iop.org/0741-3335/46/114
The neutrino emission due to plasmon decay and neutrino luminosity of white dwarfs
One of the effective mechanisms of neutrino energy losses in red giants,
presupernovae and in the cores of white dwarfs is the emission of
neutrino-antineutrino pairs in the process of plasmon decay. In this paper, we
numerically calculate the emissivity due to plasmon decay in a wide range of
temperatures (10^7-10^11) K and densities (200-10^14) g cm^-3. Numerical
results are approximated by convenient analytical expressions. We also
calculate and approximate by analytical expressions the neutrino luminosity of
white dwarfs due to plasmon decay, as a function of their mass and internal
temperature. This neutrino luminosity depends on the chemical composition of
white dwarfs only through the parameter mu_e (the net number of baryons per
electron) and is the dominant neutrino luminosity in all white dwarfs at the
neutrino cooling stage.Comment: 19 pages, 3 figures, accepted for publication in MNRA
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