28 research outputs found
Wake-mediated propulsion of an upstream particle in two-dimensional plasma crystals
The wake-mediated propulsion of an "extra" particle in a channel of two
neighboring rows of a two-dimensional plasma crystal, observed experimentally
by Du et al. [Phys. Rev. E 89, 021101(R) (2014)], is explained in simulations
and theory. We use the simple model of a pointlike ion wake charge to reproduce
this intriguing effect in simulations, allowing for a detailed investigation
and a deeper understanding of the underlying dynamics. We show that the
nonreciprocity of the particle interaction, owing to the wake charges, is
responsible for a broken symmetry of the channel that enables a persistent
self-propelled motion of the extra particle. We find good agreement of the
terminal extra-particle velocity with our theoretical considerations and with
experiments.Comment: 7 pages, 4 figures, PRL (https://journals.aps.org/prl/), updated
version with correct author affiliation
Network analysis of 3D complex plasma clusters in a rotating electric field
Network analysis was used to study the structure and time evolution of driven
three-dimensional complex plasma clusters. The clusters were created by
suspending micron-size particles in a glass box placed on top of the rf
electrode in a capacitively coupled discharge. The particles were highly
charged and manipulated by an external electric field that had a constant
magnitude and uniformly rotated in the horizontal plane. Depending on the
frequency of the applied electric field, the clusters rotated in the direction
of the electric field or remained stationary. The positions of all particles
were measured using stereoscopic digital in-line holography. The network
analysis revealed the interplay between two competing symmetries in the
cluster. The rotating cluster was shown to be more cylindrical than the
nonrotating cluster. The emergence of vertical strings of particles was also
confirmed.Comment: 9 pages, 9 figures; corrected Fig.4 and typo
All-fiber highly chirped dissipative soliton generation in the telecom range
A high-energy (0.93 nJ) all-fiber erbium femtosecond oscillator operating in the telecom spectral range is proposed and realized. The laser cavity, built of commercially available fibers and components, combines polarization maintaining (PM) and non-PM parts providing stable generation of highly chirped (chirp parameter 40) pulses compressed in an output piece of standard PM fiber to 165 fs. The results of the numerical simulation agree well with the experiment. The analyzed intracavity pulse dynamics enables the classification of the generated pulses as dissipative solitons
Network analysis of 3D complex plasma clusters
Network analysis was used to study the structure and time evolution of driven
three-dimensional complex plasma clusters. The clusters were created by suspending
micron-size particles in a glass box placed on top of the rf electrode in
a capacitively coupled discharge. The particles were highly charged and manipulated
by an external electric �eld that had a constant magnitude and rotated
uniformly in the horizontal plane. Depending on the frequency of the applied electric
�eld, the clusters rotated in the direction of the electric �eld or remained stationary.
The three-dimensional positions of all particles were measured using stereoscopic
digital in-line holography.
The network approach was used to elucidate the structural changes in the cluster
consisting only of a very limited number of particles (64). The Analysis revealed an
interplay between two competing symmetries in the cluster. Spherical and cylindrical
ordering of the particles was examined by comparing network measures of the
experimental data with null models. The null models were arti�cial data with a certain
number of points in perfectly spherical order, and the rest in cylindrical order.
The well established network measures local connectivity, clustering coe�cient and
average path length were considered. Network analysis of the clusters showed
that the rotating cluster was more cylindrical than the nonrotating cluster.
These �ndings were in agreement with the estimate of the radial con�nement
with the aid of a dynamical force balance. Neglecting friction and inertial forces due
to the low particle velocities in the cluster, the pro�le of the electrical con�nement
could be estimated by calculating the repulsing Yukawa-type interaction between
the particles. The radial con�nement was shown to be stronger in the case of cluster
rotation, increasing the cylindricity of the cluster.
The emergence of vertical strings of particles was also con�rmed by using a network
analysis. While the traditional method of a �xed threshold has limitations such
as erroneously including passing by particles and a somewhat arbitrary threshold,
community �nding algorithms yield a more elegant approach of �nding structures
in complex systems. With the aid of multislice networks, it is possible to examine
the whole time series at once and thus resolve the time evolution of the strings.
As we demonstrated, network analysis is a powerful tool to analyze the structure
of complex plasma clusters and may have numerous applications in other complex
systems where the characertization of the spatial structure plays a vital role.
Second harmonic generation in SiC polytypes
LMTO calculations are presented for the frequency dependent second harmonic
generation (SHG) in the polytypes 2H, 4H, 6H, 15R and 3C of SiC. All
independent tensor components are calculated. The spectral features and the
ratios of the 333 to 311 tensorial components are studied as a function of the
degree of hexagonality. The relationship to the linear optical response and the
underlying band structure are investigated. SHG is suggested to be a sensitive
tool for investigating the near band edge interband excitations.Comment: 12 pages, 10 figure
Wave Phenomena in a Stratified Complex Plasma
PK-4 is a plasma facility that uses a dc discharge inside a glass tube for experiments on complex (dusty) plasmas in microgravity onboard the International Space Station. It was launched in October 2014. During development, several models of PK-4 were built. The experiments described here took place in the engineering model of PK-4. During a test run, we injected particles with different diameters. They formed a stratified complex plasma where an instability generated waves inside the strata. The analysis of the video data is shown and the type and the cause of the instability are discussed here
Wave turbulence observed in an auto-oscillating complex (dusty) plasma
We study a complex plasma under microgravity conditions that is auto-oscillating due to a heartbeat instability and contains quasi-solitary wave ridges —oscillons. We demonstrate that this system can serve as a nearly ideal model system to mimic weak Kolmogorov-Zakharov–type wave turbulence. The slopes of the structure functions agree reasonably well with power laws assuming extended self-similarity. The energy spectrum displays multiple cascades, which we attribute to the influence of friction, the heartbeat instability and a modulational instability
Anisotropic confinement effects in a two-dimensional plasma crystal
The spectral asymmetry of the wave-energy distribution of dust particles during mode-coupling-induced melting, observed for the first time in plasma crystals by Couedel et al. [Phys. Rev. E 89, 053108 (2014)], is studied theoretically and by molecular-dynamics simulations. It is shown that an anisotropy of the well confining the microparticles selects the directions of preferred particle motion. The observed differences in intensity of waves of opposed directions are explained by a nonvanishing phonon flux. Anisotropic phonon scattering by defects and Umklapp scattering are proposed as possible reasons for the mean phonon flux