Plasma Crystal in (3 + 1) Dimensions

JETP Letters - A quasi-two-dimensional plasma crystal in (3 + 1) dimensions has been experimentally observed for the first time; i.e., three spatial coordinates of each microparticles of the...     

Measurements of the Dalitz plot parameters for K ± → π±π0π0 decays

The g, h, and k Dalitz plot parameters, which are coefficients in a series expansion of the squared module of the matrix element |M(u, v)|² ∝ 1 + gu + hu ² + kv ² (u, v are invariant variables), have been measured for K ^± → π^±π ⁰π⁰ decays using 35 GeV/c hadron beams at the IHEP (Protvino) accelerator. Dependences of parameters and fit quality on the π⁰π⁰ mass cut were investigated for the first time. It is shown that the expansion mentioned above does not fit the experimental data near the π⁺π^? mass threshold and that addition of the cubic terms only slightly improves the fit quality. This result indicates the important role of nonanalytical terms in the matrix element that are connected with pion rescattering. A comparison of our data with previous measurements is presented.     

Direct observation of muon-pair production by high-energy muons in the liquid-argon calorimeter BARS

Experimental data accumulated over a long-term exposure of the big liquid-argon spectrometer BARS at the Institute for High Energy Physics (IHEP, Protvino) in a horizontal flux of cosmic rays are analyzed with the aim of selecting events that correspond to muon-pair production by muons in the sensitive volume of the detector. The results obtained in this way make it possible to perform, for the first time, a direct experimental test of various theoretical estimates of the total cross section for electromagnetic muon-pair production by high-energy muons.     

Dusty plasma induced by solar radiation under microgravitational conditions: An experiment on board the Mir orbiting space station

The dynamics of the formation of ordered structures of macroparticles charged by photoemission under the action of solar radiation under microgravitational conditions without the use of electrostatic traps to confine the particles is studied experimentally and theoretically. The working conditions needed for the formation of structures of charged macroparticles are chosen as a result of a numerical solution of the problem posed, the particle charges and the interparticle interaction parameter are determined, and the characteristic times specifying the dynamics of the formation of an ordered system of macroparticles are calculated. The behavior of an ensemble of macroparticles under the effect of solar radiation is observed experimentally on board the Mir space station. An analysis and comparison of the results of the experimental and theoretical investigations permit drawing a conclusion regarding the possibility of the existences of extended ordered formations of macroparticles charged by photoemission under microgravitational conditions. Zh. éksp. Teor. Fiz. 114, 2004–2021 (December 1998)     

The dynamics of macroparticles in a direct current glow discharge plasma under microgravitation conditions

The dynamics of large-sized (70-180 μm) spherical bronze particles in a direct current glow discharge plasma was studied experimentally under microgravitation conditions. The temperatures, velocities, pair correlation functions, and self-diffusion coefficients of macroparticles were measured at various discharge currents. The charges of dust particles (on the order of 10⁶ e) corresponded to high surface potentials of about 30–40 V. The experimental data were in close agreement with the simulation data on Yukawa systems with weak screening of dust charges. The influence of macroparticles on equilibrium ionization in a dense dust cloud was considered.     

Propagation of the 3D Crystallization Front in a Strongly Nonideal Dusty Plasma

We have analyzed the data obtained at the PK-3 Plus Laboratory onboard the International Space Station from analysis of the crystallization front propagation in a dusty plasma. We have developed the “axial” algorithm for identifying “crystal-like” particles, which makes it possible to recognize different crystalline domains and their surface. We have proposed a method for determining the 3D front velocity, presuming the existence of a small region of the domain surface, which propagates along a certain line perpendicular to this region. It is shown that the front velocity is almost independent of time and amounts to about 60 μm/s. We have proposed a theory of the crystallization front propagation in the dust cloud under the assumption that the flux of particles being crystallized is proportional to the difference in the self-diffusion coefficients for the liquid and crystalline phases. The upper estimate of the front velocity correlates with the results of processing of experimental data.     

Study of K ± → e ± νπ 0 decays at the KMN setup

K ^± → e ^± νπ ⁰ decays have been studied using the KMN setup at the Institute for High Energy Physics (Protvino). The experiment has been performed in the 36-GeV/c hadron beams of the IHEP accelerator. The accumulated data allow us to select ～1.08M candidates for K _e3 decays. Analyzing the Dalitz plot of these events, we estimate the linear slope of the charge form factor to be λ ₊ = [30.44 ± 0.83(stat.) ± 0.74(syst.)] × 10^?3.     

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. The evolution of complex plasma structural properties upon pressure variation is studied. Theoretical estimates allow us to identify the main factors responsible for the observed behavior.     

Void Closure in Complex Plasmas under Microgravity Conditions

We describe the first observation of a void closure in complex plasma experiments under microgravity conditions performed with the Plasma-Kristall (PKE-Nefedov) facility on board the International Space Station. The void--a grain-free region in the central part of the discharge where the complex plasma is generated--has been formed under most of the plasma conditions and thought to be an inevitable effect. However, we demonstrate in this Letter that an appropriate tune of the discharge parameters allows the void to close. This experimental achievement along with its theoretical interpretation opens new perspectives in engineering new experiments with large quasi-isotropic void-free complex plasma clouds in microgravity conditions.     

Transport of microparticles in weakly ionized gas-discharge plasmas under microgravity conditions

Measurements of effective structural (pair correlation function) and transport (diffusion constant) characteristics of the system of microparticles in dc and rf gas-discharge plasmas under microgravity conditions are reported. The comparison between these measurements and numerical simulations is used for complex plasma diagnostics.