974 research outputs found
Measurement of the speed of sound by observation of the Mach cones in a complex plasma under microgravity conditions
We report the first observation of the Mach cones excited by a larger
microparticle (projectile) moving through a cloud of smaller microparticles
(dust) in a complex plasma with neon as a buffer gas under microgravity
conditions. A collective motion of the dust particles occurs as propagation of
the contact discontinuity. The corresponding speed of sound was measured by a
special method of the Mach cone visualization. The measurement results are
incompatible with the theory of ion acoustic waves. The estimate for the
pressure in a strongly coupled Coulomb system and a scaling law for the complex
plasma make it possible to derive an evaluation for the speed of sound, which
is in a reasonable agreement with the experiments in complex plasmas.Comment: 5 pages, 2 figures, 1 tabl
Fluid-solid phase transitions in 3D complex plasmas under microgravity conditions
Phase behavior of large three-dimensional complex plasma systems under
microgravity conditions onboard the International Space Station is
investigated. The neutral gas pressure is used as a control parameter to
trigger phase changes. Detailed analysis of structural properties and
evaluation of three different melting/freezing indicators reveal that complex
plasmas can exhibit melting by increasing the gas pressure. Theoretical
estimates of complex plasma parameters allow us to identify main factors
responsible for the observed behavior. The location of phase states of the
investigated systems on a relevant equilibrium phase diagram is estimated.
Important differences between the melting process of 3D complex plasmas under
microgravity conditions and that of flat 2D complex plasma crystals in ground
based experiments are discussed.Comment: 13 pages, 10 figures; submitted to Phys. Rev.
Freezing and melting of 3D complex plasma structures under microgravity conditions driven by neutral gas pressure manipulation
Freezing and melting of large three-dimensional complex plasmas under
microgravity conditions is investigated. The neutral gas pressure is used as a
control parameter to trigger the phase changes: Complex plasma freezes (melts)
by decreasing (increasing) the pressure. Evolution of complex plasma structural
properties upon pressure variation is studied. Theoretical estimates allow us
to identify main factors responsible for the observed behavior.Comment: Phys. Rev. Lett. (in press); 4 pages, 4 figure
Dynamics of lane formation in driven binary complex plasmas
The dynamical onset of lane formation is studied in experiments with binary
complex plasmas under microgravity conditions. Small microparticles are driven
and penetrate into a cloud of big particles, revealing a strong tendency
towards lane formation. The observed time-resolved lane formation process is in
good agreement with computer simulations of a binary Yukawa model with Langevin
dynamics. The laning is quantified in terms of the anisotropic scaling index,
leading to a universal order parameter for driven systems.Comment: 4 pages, 3 figures, movies available at
http://www.mpe.mpg.de/pke/lane-formation
A search for J^{PC}=1^{-+} exotic mesons in the pi- pi- pi+ and pi- pi0 pi0 systems
A partial wave analysis (PWA) of the pi-pi-pi+ and pi-pi0pi0 systems produced
in the reaction pi- p -> (3pi)-p at 18 GeV/c was carried out using an isobar
model assumption. This analysis is based on 3.0M pi-pi0pi0 events and 2.6M
pi-pi-pi+ events and shows production of the a2(1320), pi2(1670) and \pi(1800)
mesons. An earlier analysis of 250K pi-pi-pi+ events from the same experiment
showed possible evidence for a J^{PC}=1^{-+}$ exotic meson with a mass of 1.6
GeV/c^2 decaying into rho pi. In this analysis of a higher statistics sample of
the (3pi)- system in two charged modes we find no evidence of an exotic meson.Comment: 4 pages, 5 figures, added comment about the negative reflectivity
exotic wave
Phenomena in Complex (Dusty) Plasma Studied under Microgravity Conditions
Complex (dusty) plasmas are composed of weakly ionized gas and charged microparticles and represent the plasma state of soft matter. The investigations which are not available on ground have been per-formed onboard the International Space Station (ISS) with the help of the “Plasma Crystal-3 Plus” (PK-3 Plus) laboratory. A number of interesting phenomena has been observed. The phase transition from iso-tropic plasma into electrorheological plasma was initiated. The crystal-liquid phase transition was ob-tained in large 3D isotropic dusty plasma. The slow compression of the dust particle subsystem has been investigated
Shear flow in a three-dimensional complex plasma in microgravity conditions
Shear flow in a three-dimensional complex plasma was experimentally studied
in microgravity conditions using Plasmakristall-4 (PK-4) instrument on board
the International Space Station (ISS). The shear flow was created in an
extended suspension of microparticles by applying the radiation pressure force
of the manipulation-laser beam. Individual particle trajectories in the flow
were analyzed and from these, using the Navier-Stokes equation, an upper
estimate of the complex plasma's kinematic viscosity was calculated in the
range of --. This estimate is much lower than previously
reported in ground-based experiments with 3D complex plasmas. Possible reasons
of this difference are discussed.Comment: 5 pages, 4 figure
Dust density waves in a dc flowing complex plasma with discharge polarity reversal
We report on the observation of the self-excited dust density waves in the dc
discharge complex plasma. The experiments were performed under microgravity
conditions in the Plasmakristall-4 facility on board the International Space
Station. In the experiment, the microparticle cloud was first trapped in an
inductively coupled plasma, then released to drift for some seconds in a dc
discharge with constant current. After that the discharge polarity was
reversed. DC plasma containing a drifting microparticle cloud was found to be
strongly non-uniform in terms of microparticle drift velocity and plasma
emission in accord with [Zobnin et.al., Phys. Plasmas 25, 033702 (2018)]. In
addition to that, non-uniformity in the self-excited wave pattern was observed:
In the front edge of the microparticle cloud (defined as head), the waves had
larger phase velocity than in the rear edge (defined as tail). Also, after the
polarity reversal, the wave pattern exhibited several bifurcations: Between
each of the two old wave crests, a new wave crest has formed. These
bifurcations, however, occurred only in the head of the microparticle cloud. We
show that spatial variations of electric field inside the drifting cloud play
an important role in the formation of the wave pattern. Comparison of the
theoretical estimations and measurements demonstrate the significant impact of
the electric field on the phase velocity of the wave. The same theoretical
approach applied to the instability growth rate, showed agreement between
estimated and measured values.Comment: 7 pages, 4 figure
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