498 research outputs found
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
Cooling of Neutron Stars: Two Types of Triplet Neutron Pairing
We consider cooling of neutron stars (NSs) with superfluid cores composed of
neutrons, protons, and electrons (assuming singlet-state pairing of protons,
and triplet-state pairing of neutrons). We mainly focus on (nonstandard)
triplet-state pairing of neutrons with the projection of the total
angular momentum of Cooper pairs onto quantization axis. The specific feature
of this pairing is that it leads to a power-law (nonexponential) reduction of
the emissivity of the main neutrino processes by neutron superfluidity. For a
wide range of neutron critical temperatures , the cooling of NSs with
the superfluidity is either the same as the cooling with the superfluidity, considered in the majority of papers, or much faster. The
cooling of NSs with density dependent critical temperatures and
can be imitated by the cooling of the NSs with some effective
critical temperatures and constant over NS cores. The
hypothesis of strong neutron superfluidity with is inconsistent
with current observations of thermal emission from NSs, but the hypothesis of
weak neutron superfluidity of any type does not contradict to observations.Comment: 10 pages, 6 figure
Dark Matter Search Perspectives with GAMMA-400
GAMMA-400 is a future high-energy gamma-ray telescope, designed to measure
the fluxes of gamma-rays and cosmic-ray electrons + positrons, which can be
produced by annihilation or decay of dark matter particles, and to survey the
celestial sphere in order to study point and extended sources of gamma-rays,
measure energy spectra of Galactic and extragalactic diffuse gamma-ray
emission, gamma-ray bursts, and gamma-ray emission from the Sun. GAMMA-400
covers the energy range from 100 MeV to ~3000 GeV. Its angular resolution is
~0.01 deg(Eg > 100 GeV), and the energy resolution ~1% (Eg > 10 GeV). GAMMA-400
is planned to be launched on the Russian space platform Navigator in 2019. The
GAMMA-400 perspectives in the search for dark matter in various scenarios are
presented in this paperComment: 4 pages, 4 figures, submitted to the Proceedings of the International
Cosmic-Ray Conference 2013, Brazil, Rio de Janeir
A separation of electrons and protons in the GAMMA-400 gamma-ray telescope
The GAMMA-400 gamma-ray telescope is intended to measure the fluxes of gamma
rays and cosmic-ray electrons and positrons in the energy range from 100 MeV to
several TeV. Such measurements concern with the following scientific goals:
search for signatures of dark matter, investigation of gamma-ray point and
extended sources, studies of the energy spectra of Galactic and extragalactic
diffuse emission, studies of gamma-ray bursts and gamma-ray emission from the
active Sun, as well as high-precision measurements of spectra of high-energy
electrons and positrons, protons, and nuclei up to the knee. The main
components of cosmic rays are protons and helium nuclei, whereas the part of
lepton component in the total flux is ~10E-3 for high energies. In present
paper, the capability of the GAMMA-400 gamma-ray telescope to distinguish
electrons and positrons from protons in cosmic rays is investigated. The
individual contribution to the proton rejection is studied for each detector
system of the GAMMA-400 gamma-ray telescope. Using combined information from
all detector systems allow us to provide the proton rejection from electrons
with a factor of ~4x10E5 for vertical incident particles and ~3x10E5 for
particles with initial inclination of 30 degrees. The calculations were
performed for the electron energy range from 50 GeV to 1 TeV.Comment: 19 pages, 10 figures, submitted to Advances and Space Researc
Poloidal inhomogeneity of the particle fluctuation induced fluxes near of the LCFS at lower hybrid heating and improved confinement transition at the FT-2 tokamak
This paper deals with the new spectral and microturbulence experimental data
and their analysis, which show, that the radial electric field Er generated at
the LH heating (LHH) in the FT-2 is high enough to form the transport barriers.
The ETB is formed when LHH is switched off. The radial fluctuation-induced
EB drift flux densities near LCFS in SOL are measured at two different
poloidal angles. For this purpose two Langmuir probes located at low and high
field sides of the torus are used. Registration of the poloidal and radial
components of the electric field and density fluctuations at the same time
during one discharge permits to measure the poloidal asymmetry of the transport
reduction mechanism of the radial and poloidal particle fluxes in the SOL. The
absolute E(~) fluctuation levels show dependence on the sign of Er
shear. The modification of the microscale turbulence by the poloidal Er x B
rotation shear EB at the L - H transition near LCFS is also
studied by X-mode fluctuation Reflectometry. The new data were obtained by
spatial spectroscopic technique.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
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