We discuss the inductively heated plasma generator (IPG) facility in application to the generation
of the thermal dusty plasma formed by the positively charged dust particles and the electrons
emitted by them. We develop a theoretical model for the calculation of plasma electrical
conductivity under typical conditions of the IPG. We show that the electrical conductivity of dusty
plasma is defined by collisions with the neutral gas molecules and by the electron number density.
The latter is calculated in the approximations of an ideal and strongly coupled particle system and
in the regime of weak and strong screening of the particle charge. The maximum attainable electron
number density and corresponding maximum plasma electrical conductivity prove to be independent of
the particle emissivity. Analysis of available experiments is performed, in particular, of our
recent experiment with plasma formed by the combustion products of a propane–air mixture and the CeO
2 particl...

The Sagdeev potential technique has been employed to study the dust ion
acoustic solitary waves and double layers in an unmagnetized collisionless
dusty plasma consisting of negatively charged static dust grains, adiabatic
warm ions, and isothermally distributed electrons and positrons. A
computational scheme has been developed to draw the qualitatively different
compositional parameter spaces or solution spaces showing the nature of
existence of different solitary structures with respect to any parameter of the
present plasma system. The qualitatively distinct solution spaces give the
overall scenario regarding the existence of different solitary structures. The
present system supports both positive and negative potential double layers. The
negative potential double layer always restricts the occurrence of negative
potential solitary waves, i.e., any sequence of negative potential solitary
waves having monotonically increasing amplitude converges to a negative
potential double layer. However, there exists a parameter regime for which the
positive potential double layer is unable to restrict the occurrence of
positive potential solitary waves. As a result, in this region of the parameter
space, there exist solitary waves after the formation of positive potential
double layer, i.e., positive potential supersolitons have been observed. But
the amplitudes of these supersolitons are bounded. A general theory for the
existence of bounded supersolitons has been discussed analytically by imposing
the restrictions on the Mach number. For any small value of positron
concentration, there is no effect of very hot positrons on the dust ion
acoustic solitary structures. The qualitatively different solution spaces are
capable of producing new results for the formation of solitary structures.

This paper shows that several known properties of the Yukawa system can be
derived from the isomorph theory, which applies to any system that has strong
correlations between its virial and potential-energy equilibrium fluctuations.
Such "Roskilde-simple" systems have a simplified thermodynamic phase diagram
deriving from the fact that they have curves (isomorphs) along which structure
and dynamics in reduced units are invariant to a good approximation. We show
that the Yukawa system has strong virial potential-energy correlations and
identify its isomorphs by two different methods. One method, the so-called
direct isomorph check, identifies isomorphs numerically from jumps of
relatively small density changes (here 10%). The second method identifies
isomorphs analytically from the pair potential. The curves obtained by the two
methods are close to each other; these curves are confirmed to be isomorphs by
demonstrating the invariance of the radial distribution function, the static
structure factor, the mean-square displacement as a function of time, and the
incoherent intermediate scattering function. Since the melting line is
predicted to be an isomorph, the theory provides a derivation of a known
approximate analytical expression for this line in the temperature-density
phase diagram. The paper's results give the first demonstration that the
isomorph theory can be applied to systems like dense colloidal suspensions and
strongly coupled dusty plasmas.

Simple practical approach to estimate thermodynamic properties of strongly
coupled Yukawa systems, in both fluid and solid phases, is presented. The
accuracy of the approach is tested by extensive comparison with direct computer
simulation results (for fluids and solids) and the recently proposed
shortest-graph method (for solids). Possible applications to other systems of
softly repulsive particles are briefly discussed.

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.

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.

The Sagdeev potential technique has been employed to study the dust ion
acoustic solitary waves and double layers in an unmagnetized collisionless
dusty plasma consisting of negatively charged static dust grains, adiabatic
warm ions, and isothermally distributed electrons and positrons. A
computational scheme has been developed to draw the qualitatively different
compositional parameter spaces or solution spaces showing the nature of
existence of different solitary structures with respect to any parameter of the
present plasma system. The qualitatively distinct solution spaces give the
overall scenario regarding the existence of different solitary structures. The
present system supports both positive and negative potential double layers. The
negative potential double layer always restricts the occurrence of negative
potential solitary waves, i.e., any sequence of negative potential solitary
waves having monotonically increasing amplitude converges to a negative
potential double layer. However, there exists a parameter regime for which the
positive potential double layer is unable to restrict the occurrence of
positive potential solitary waves. As a result, in this region of the parameter
space, there exist solitary waves after the formation of positive potential
double layer, i.e., positive potential supersolitons have been observed. But
the amplitudes of these supersolitons are bounded. A general theory for the
existence of bounded supersolitons has been discussed analytically by imposing
the restrictions on the Mach number. There is no effect of very hot positrons
on the dust ion acoustic solitary structures. The qualitatively different
solution spaces are capable of producing new results for the formation of
solitary structures.

A new approximate expression for the potential distribution around an absorbing particle in isotropic collisionless plasma is proposed. The approximate expression is given by the sum of the Debye-Hückel potential with an effective screening length and the far-field asymptote obtained from the solution of the linearized Poisson equation. In contrast to analogous models, the effective screening length is not fixed but depends on the distance from the particle. This allows us to obtain a more accurate approximation for the potential distribution in the entire range of distances. The dependence of the screening length on the distance is predicted from the analysis of the charge density
distribution function. This dependence contains two adjustable parameters, which are calculated by applying the procedure based on charge balance considerations. Using the obtained results, simple expressions for the parameters of the model are proposed. In addition, a simple expression for the characteristic screening length, which can be used to approximate the potential distribution near the particle, is obtained. The developed model potential is shown to be in excellent agreement with the solution of the nonlinear
Poisson equation for typical conditions used in experiments with complex plasmas.

Author(s): Johannes Feist and Francisco J. Garcia-Vidal

We demonstrate that exciton conductance in organic materials can be enhanced by several orders of magnitude when the molecules are strongly coupled to an electromagnetic mode. Using a 1D model system, we show how the formation of a collective polaritonic mode allows excitons to bypass the disordered...

[Phys. Rev. Lett. 114, 196402] Published Tue May 12, 2015