238 research outputs found
Fast Neutron Detector for Fusion Reactor KSTAR Using Stilbene Scintillator
Various neutron diagnostic tools are used in fusion reactors to evaluate
different aspects of plasma performance, such as fusion power, power density,
ion temperature, fast ion energy, and their spatial distributions. The stilbene
scintillator has been proposed for use as a neutron diagnostic system to
measure the characteristics of neutrons from the Korea Superconducting Tokamak
Advanced Research (KSTAR) fusion reactor. Specially designed electronics are
necessary to measure fast neutron spectra with high radiation from a gamma-ray
background. The signals from neutrons and gamma-rays are discriminated by the
digital charge pulse shape discrimination (PSD) method, which uses total to
partial charge ratio analysis. The signals are digitized by a flash
analog-to-digital convertor (FADC). To evaluate the performance of the
fabricated stilbene neutron diagnostic system, the efficiency of 10 mm
soft-iron magnetic shielding and the detection efficiency of fast neutrons were
tested experimentally using a 252Cf neutron source. In the results, the
designed and fabricated stilbene neutron diagnostic system performed well in
discriminating neutrons from gamma-rays under the high magnetic field
conditions during KSTAR operation. Fast neutrons of 2.45 MeV were effectively
measured and evaluated during the 2011 KSTAR campaign.Comment: 15 pages, 14 figures, conferenc
Enhancement of near-cloaking. Part II: the Helmholtz equation
The aim of this paper is to extend the method of improving cloaking
structures in the conductivity to scattering problems. We construct very
effective near-cloaking structures for the scattering problem at a fixed
frequency. These new structures are, before using the transformation optics,
layered structures and are designed so that their first scattering coefficients
vanish. Inside the cloaking region, any target has near-zero scattering cross
section for a band of frequencies. We analytically show that our new
construction significantly enhances the cloaking effect for the Helmholtz
equation.Comment: 16pages, 12 fugure
Seesaw tau lepton mass and calculable neutrino masses in a 3-3-1 model
In a version of the 3-3-1 model proposed by Duong and Ma the introduction of
the scalar sextet for giving mass to the charged leptons is avoided by adding a
singlet charged lepton. We show that in this case the lepton gains mass
through a seesaw--like mechanism. Besides we show how to generate neutrino
masses at the tree and at the 1-loop level with the respective
Maki-Nakagawa-Sakata leptonic mixing matrices.Comment: revtex, 5 pages and one eps figure. Published versio
Proximity and Josephson effects in superconductor - antiferromagnetic Nb / \gamma-Fe50Mn50 heterostructures
We study the proximity effect in superconductor (S), antiferromagnetic (AF)
bilayers, and report the fabrication and measurement of the first trilayer
S/AF/S Josephson junctions. The disordered f.c.c. alloy \gamma-Fe50Mn50 was
used as the AF, and the S is Nb. Micron and sub-micron scale junctions were
measured, and the scaling of gives a coherence length in the AF of
2.4 nm, which correlates with the coherence length due to suppression of
in the bilayer samples. The diffusion constant for FeMn was found to be 1.7
\times 10 m s, and the density of states at the Fermi level was
also obtained. An exchange biased FeMn/Co bilayer confirms the AF nature of the
FeMn in this thickness regime.Comment: 6 pages, 5 figures, accepted for Phys. Rev.
Measurement of the Bottom contribution to non-photonic electron production in collisions at =200 GeV
The contribution of meson decays to non-photonic electrons, which are
mainly produced by the semi-leptonic decays of heavy flavor mesons, in
collisions at 200 GeV has been measured using azimuthal
correlations between non-photonic electrons and hadrons. The extracted
decay contribution is approximately 50% at a transverse momentum of GeV/. These measurements constrain the nuclear modification factor for
electrons from and meson decays. The result indicates that meson
production in heavy ion collisions is also suppressed at high .Comment: 6 pages, 4 figures, accepted by PR
The PHENIX Experiment at RHIC
The physics emphases of the PHENIX collaboration and the design and current
status of the PHENIX detector are discussed. The plan of the collaboration for
making the most effective use of the available luminosity in the first years of
RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program
available at http://www.rhic.bnl.gov/phenix
Topical Issues for Particle Acceleration Mechanisms in Astrophysical Shocks
Particle acceleration at plasma shocks appears to be ubiquitous in the
universe, spanning systems in the heliosphere, supernova remnants, and
relativistic jets in distant active galaxies and gamma-ray bursts. This review
addresses some of the key issues for shock acceleration theory that require
resolution in order to propel our understanding of particle energization in
astrophysical environments. These include magnetic field amplification in shock
ramps, the non-linear hydrodynamic interplay between thermal ions and their
extremely energetic counterparts possessing ultrarelativistic energies, and the
ability to inject and accelerate electrons in both non-relativistic and
relativistic shocks. Recent observational developments that impact these issues
are summarized. While these topics are currently being probed by
astrophysicists using numerical simulations, they are also ripe for
investigation in laboratory experiments, which potentially can provide valuable
insights into the physics of cosmic shocks.Comment: 13 pages, no figures. Invited review, accepted for publication in
Astrophysics and Space Science, as part of the HEDLA 2006 conference
proceeding
Application of Hénon method in numerical estimation of the stick–slip transitions existing in Filippov-type discontinuous dynamical systems with dry friction
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