225 research outputs found
Polarized beam operation of the Hybrid Spectrometer at the pulsed Spallation Neutron Source
The concept of a neutron Hybrid Spectrometer (HYSPEC) combines the
time-of-flight spectroscopy with the focusing Bragg optics and incorporates a
polarized beam option. Here we describe the polarization analysis scheme
proposed for HYSPEC and quantify its performance via the Monte-Carlo
simulations. We find that the broadband supermirror-bender transmission
polarizers provide reasonably good polarization analysis capability within
about 8-10 meV energy window for scattered neutron energies in the thermal
range up to about 25 meV.Comment: Preprint, to appear in Physica B. 10 pages, 4 figure
Continuum in the spin excitation spectrum of a Haldane chain, observed by neutron scattering in CsNiCl3
The spin excitation continuum, expected to dominate the low-energy
fluctuation spectrum in the Haldane spin chain around the Brillouin zone
center, q=0, is directly observed by inelastic magnetic neutron scattering in
the S=1 quasi-1D antiferromagnet CsNiCl3. We find that the single mode
approximation fails, and that a finite energy width appears in the dynamic
correlation function S(q,omega) for q < 0.5pi. The width increases with
decreasing q, while S(q,omega) acquires an asymmetric shape qualitatively
similar to that predicted for the 2-magnon continuum in the nonlinear
sigma-model.Comment: 4 pages, 3 figures, submitted to PR
Excitation of zonal flow by the modulational instability in electron temperature gradient driven turbulence
The generation of large-scale zonal flows by small-scale electrostatic drift
waves in electron temperature gradient(ETG) driven turbulence model is
considered. The generation mechanism is based on the modulational instability
of a finite amplitude monochromatic drift wave. The threshold and growth rate
of the instability as well as the optimal spatial scale of zonal flow are
obtained.Comment: 10 pages, 3 figure
- …