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Planar channeling and quasichanneling oscillations in a bent crystal
Particles passing through a crystal under planar channeling experience
transverse oscillations in their motion. As channeled particles approach the
atomic planes of a crystal, they are likely to be dechanneled. This effect was
used in ion-beam analysis with MeV energy. We studied this effect in a bent
crystal for positive and negative particles within a wide range of energies in
sight of application of such crystals at accelerators. We found the conditions
for the appearance or not of channeling oscillations. Indeed a new kind of
oscillations, strictly related to the motion of over-barrier particles, i.e.
quasichanneling particles, has been predicted. Such oscillations, named planar
quasichanneling oscillations, possess a different nature than channeling
oscillations. Through computer simulation, we studied this effect and provided
a theoretical interpretation for them. We show that channeling oscillations can
be observed only for positive particles while quasichanneling oscillations can
exist for particles with either sign. The conditions for experimental
observation of channeling and quasichanneling oscillations at existing
accelerators with available crystal has been found and optimized.Comment: 25 pages, 11 figure
Oscillation modes of dc microdischarges with parallel-plate geometry
Two different oscillation modes in microdischarge with parallel-plate
geometry has been observed: relaxation oscillations with frequency range
between 1.23 and 2.1 kHz and free-running oscillations with 7 kHz frequency.
The oscillation modes are induced by increasing power supply voltage or
discharge current. For a given power supply voltage, there is a spontaneous
transition from one to other oscillation mode and vice versa. Before the
transition from relaxation to free-running oscillations, the spontaneous
increase of oscillation frequency of relaxation oscillations form 1.3 kHz to
2.1 kHz is measured. Fourier Transform Spectra of relaxation oscillations
reveal chaotic behaviour of microdischarge. Volt-Ampere characteristics
associated with relaxation oscillations describes periodical transition between
low current, diffuse discharge and normal glow. However, free-running
oscillations appear in subnormal glow only.Comment: Submitted to: New Journal of Physic
Frequency versus relaxation oscillations in a semiconductor laser with coherent filtered optical feedback
We investigate the dynamics of a semiconductor laser subject to coherent delayed filtered optical feedback. A systematic bifurcation analysis reveals that this system supports two fundamentally different types of oscillations, namely relaxation oscillations and external roundtrip oscillations. Both occur stably in large domains under variation of the feedback conditions, where the feedback phase is identified as a key quantity for controlling this dynamical complexity. We identify two separate parameter regions of stable roundtrip oscillations, which occur throughout in the form of pure frequency oscillations
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