9,954 research outputs found
On O-X mode conversion in 2D inhomogeneous plasma with a sheared magnetic field
The conversion of an ordinary wave to an extraordinary wave in a 2D
inhomogeneous slab model of the plasma confined by a sheared magnetic field is
studied analytically.Comment: sub. to PPC
Constrains on parameters of magnetic field decay for accreting isolated neutron stars
The influence of exponential magnetic field decay (MFD) on the spin evolution
of isolated neutron stars is studied. The ROSAT observations of several X-ray
sources, which can be accreting old isolated neutron stars, are used to
constrain the exponential and power-law decay parameters. We show that for the
exponential decay the ranges of minimum value of magnetic moment, , and
the characteristic decay time, , , are excluded assuming the
standard initial magnetic moment, . For these
parameters, neutron stars would never reach the stage of accretion from the
interstellar medium even for a low space velocity of the stars and a high
density of the ambient plasma. The range of excluded parameters increases for
lower values of .
We also show, that, contrary to exponential MFD, no significant restrictions
can be made for the parameters of power-law decay from the statistics of
isolated neutron star candidates in ROSAT observations.
Isolated neutron stars with constant magnetic fields and initial values of
them less than never come to the stage
of accretion.
We briefly discuss the fate of old magnetars with and without MFD, and
describe parameters of old accreting magnetars.Comment: 18 pages, 6 PostScript figures, to be published in the Proceedings of
the XXVIII ITEP Winter Schoo
Finite temperature correlations and density profiles of an inhomogeneous interacting 1D Bose gas
We calculate the density profiles and density correlation functions of the
one-dimensional Bose gas in a harmonic trap, using the exact finite-temperature
solutions for the uniform case, and applying a local density approximation. The
results are valid for a trapping potential which is slowly varying relative to
a correlation length. They allow a direct experimental test of the transition
from the weak coupling Gross-Pitaevskii regime to the strong coupling,
'fermionic' Tonks-Girardeau regime. We also calculate the average two-particle
correlation which characterizes the bulk properties of the sample, and find
that it can be well approximated by the value of the local pair correlation in
the trap center.Comment: Final published version; updated references; 19 pages, 12 figure
Evolution of isolated neutron stars in globular clusters: number of Accretors
With a simple model from the point of view of population synthesis we try to
verify an interesting suggestion made by Pfahl & Rappaport (2001) that dim
sources in globular clusters (GCs) can be isolated accreting neutron stars
(NSs). Simple estimates show, that we can expect about 0.5-1 accreting isolated
NS per typical GC with in correspondence with observations.
Properties of old accreting isolated NSs in GCs are briefly discussed. We
suggest that accreting NSs in GCs experienced significant magnetic field decay.Comment: 6 pages, no figures. Submitted to Astronomical and Astrophysical
Transactions (style included
Low Threshold Parametric Decay Back Scattering Instability in Tokamak ECRH Experiments
The experimental conditions leading to substantial reduction of
backscattering decay instability threshold in ECRH experiments in toroidal
devices are analyzed. It is shown that drastic decrease of threshold is
provided by non monotonic behavior of plasma density in the vicinity of
magnetic island and poloidal magnetic field inhomogeneity making possible
localization of ion Bernstein decay waves. The corresponding ion Bernstein wave
gain and the parametric decay instability pump power threshold is calculated.Comment: 7 pages, 4 figure
RX J0720.4--3125 as a Possible Example of the Magnetic Field Decay of Neutron Stars
We studied possible evolution of the rotational period and the magnetic field
of the X-ray source RX J0720.4-3125 assuming this source to be an isolated
neutron star accreting interstellar medium. Magnetic field of the source is
estimated to be G, and it is difficult to explain observed
rotational period 8.38 s without invoking hypothesis of the magnetic field
decay. We used the model of ohmic decay of the crustal magnetic field. The
estimates of accretion rate (), velocity of the
source relative to interstellar medium ( km/s), neutron star age
( yrs) are obtained.Comment: 12 pages (LATEX), 2 PostScript figures. Also available at
http://xray.sai.msu.su/~polar/ (with the Russian variant of the article
Electron Bernstein waves in spherical tokamak plasmas with "magnetic wells"
In addition to traditional regimes with monotonously increasing magnetic
field, regimes with "magnetic wells" also occur in spherical tokamaks (STs).
The magnetic field profile inversion modifies significantly the whole picture
of the wave propagation and damping. Since the magnetic wells may become quite
common with further improvement of ST performance, analysis of such
configurations is of interest for assessment of EBW plasma heating an CD
perspectives. In this paper the basic features of the EBWs propagation and
damping for the second cyclotron harmonic in a slab model are considered.Comment: Proc. of 13-th Joint Workshop on ECE and ECRH, N.Novgorod, Russia May
17-20, 2004, 8 pages, 4 fig
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