1,731 research outputs found
Phase and Power Control in the RF Magnetron Power Stations of Superconducting Accelerators
Phase and power control methods that satisfy the requirements of
superconducting accelerators to magnetron RF sources were considered by a
simplified kinetic model of a magnetron driven by a resonant injected signal.
The model predicting and explaining stable, low noise operation of the tube
below the threshold of self-excitation (the Hatrree voltage in free run mode)
at a highest efficiency, a wide range of power control and a wide-band phase
control was well verified in experiments demonstrating capabilities of the
magnetron transmitters for powering of state of the art superconducting
accelerators. Descriptions of the kinetic model, the experimental verification
and a conceptual scheme of the highly-efficient magnetron RF transmitter for
the accelerators are presented and discussed.Comment: 10 pages, 15 figure
Neutrino emission in neutron matter from magnetic moment interactions
Neutrino emission drives neutron star cooling for the first several hundreds
of years after its birth. Given the low energy ( keV) nature of this
process, one expects very few nonstandard particle physics contributions which
could affect this rate. Requiring that any new physics contributions involve
light degrees of freedom, one of the likely candidates which can affect the
cooling process would be a nonzero magnetic moment for the neutrino. To
illustrate, we compute the emission rate for neutrino pair bremsstrahlung in
neutron-neutron scattering through photon-neutrino magnetic moment coupling. We
also present analogous differential rates for neutrino scattering off nucleons
and electrons that determine neutrino opacities in supernovae. Employing
current upper bounds from collider experiments on the tau magnetic moment, we
find that the neutrino emission rate can exceed the rate through neutral
current electroweak interaction by a factor two, signalling the importance of
new particle physics input to a standard calculation of relevance to neutron
star cooling. However, astrophysical bounds on the neutrino magnetic moment
imply smaller effects.Comment: 9 pages, 1 figur
Quantum Interference Controls the Electron Spin Dynamics in n-GaAs
Manifestations of quantum interference effects in macroscopic objects are
rare. Weak localization is one of the few examples of such effects showing up
in the electron transport through solid state. Here we show that weak
localization becomes prominent also in optical spectroscopy via detection of
the electron spin dynamics. In particular, we find that weak localization
controls the free electron spin relaxation in semiconductors at low
temperatures and weak magnetic fields by slowing it down by almost a factor of
two in -doped GaAs in the metallic phase. The weak localization effect on
the spin relaxation is suppressed by moderate magnetic fields of about 1 T,
which destroy the interference of electron trajectories, and by increasing the
temperature. The weak localization suppression causes an anomalous decrease of
the longitudinal electron spin relaxation time with magnetic field, in
stark contrast with well-known magnetic field induced increase in . This
is consistent with transport measurements which show the same variation of
resistivity with magnetic field. Our discovery opens a vast playground to
explore quantum magneto-transport effects optically in the spin dynamics.Comment: 8 pages, 3 figure
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