Principle of charge-mass invariance of motion and possibility of steady-state solitary electrostatic waves in a nearly symmetric plasma

A quasi-neutral nearly symmetric plasma (i.e., a plasma in which particles with opposite charge polarity have identical charge-to-mass ratios but different masses) is considered. The possibility of the existence of steady-state solitary electrostatic waves in such a plasma is proved rigorously. This is associated with violation of the charge-mass invariance principle for a particle moving in a nearly symmetric plasma, which is in turn due to forces (1/n _±)?P _±/?x of a nonelectromagnetic origin.     

Physisorption kinetics of electrons at plasma boundaries

Plasma-boundaries floating in an ionized gas are usually negatively charged. They accumulate electrons more efficiently than ions leading to the formation of a quasi-stationary electron film at the boundaries. We propose to interpret the build-up of surface charges at inert plasma boundaries, where other surface modifications, for instance, implantation of particles and reconstruction or destruction of the surface due to impact of high energy particles can be neglected, as a physisorption process in front of the wall. The electron sticking coefficient s_e and the electron desorption time τ_e, which play an important role in determining the quasi-stationary surface charge, and about which little is empirically and theoretically known, can then be calculated from microscopic models for the electron-wall interaction. Irrespective of the sophistication of the models, the static part of the electron-wall interaction determines the binding energy of the electron, whereas inelastic processes at the wall determine s_e and τ_e. As an illustration, we calculate s_e and τ_e for a metal, using the simplest model in which the static part of the electron-metal interaction is approximated by the classical image potential. Assuming electrons from the plasma to loose (gain) energy at the surface by creating (annihilating) electron-hole pairs in the metal, which is treated as a jellium half-space with an infinitely high workfunction, we obtain s_e≈10^-4 and τ_e≈10^-2 s. The product s_eτ_e≈10^-6 s has the order of magnitude expected from our earlier results for the charge of dust particles in a plasma but individually s_e is unexpectedly small and τ_e is somewhat large. The former is a consequence of the small matrix elements occurring in the simple model while the latter is due to the large binding energy of the electron. More sophisticated theoretical investigations, but also experimental support, are clearly needed because if s_e is indeed as small as our exploratory calculation suggests, it would have severe consequences for the understanding of the formation of surface charges at plasma boundaries. To identify what we believe are key issues of the electronic microphysics at inert plasma boundaries and to inspire other groups to join us on our journey is the purpose of this colloquial presentation.     

Investigation of electrostatic charge distribution within the reactor wall fouling and bulk regions of a gas–solid fluidized bed

The distribution of charge within the wall fouling region and bulk of a fluidized bed reactor was investigated. Experiments were conducted in a 0.1 m in diameter carbon steel fluidization column under atmospheric conditions. Polyethylene particles were fluidized with extra dry air at 1.5 the minimum fluidization velocity (bubbling flow regime) for 1 h. Using an online Faraday cup measurement technique, the net charge-to-mass ratio (q/m), as well as the size distribution of all particles adhered to the column wall and those in the bulk of the bed was determined. The wall particles were found to be predominantly negatively charged while those which did not adhere to the wall were predominantly positively charged. The charge distribution within each region was then investigated by a custom made charged particle separator that separated the particles according to their charge magnitude and polarity. It was determined that although the net charge of the wall layer particles was negative, a significant amount of positively charged particles existed within each sample and therefore the entire wall particle layer. This suggests that the wall layer was formed through layering between positively and negatively charged particles. Particles in the bulk of the bed also consisted of bipolarly charged particles.     

Density Profiles in a Classical Coulomb Fluid Near a Dielectric Wall. I. Mean-Field Scheme

The equilibrium density profiles in a classical multicomponent plasma near a hard wall made with a dielectric material characterized by a relative dielectric constant ∈_w are studied from the first Born–Green–Yvon (BGY) equation combined with Poisson equation in a regime where Coulomb coupling is weak inside the fluid. In order to prevent the collapse between charges with opposite signs or between each charge and its dielectric image inside the wall when ∈_w>1, hard-core repulsions are added to the Coulomb pair interaction. The charge-image interaction cannot be treated perturbatively and the density profiles vary very fast in the vicinity of the wall when ∈_w≠1. The formal solution of the associated inhomogeneous Debye–Hückel equations will be given in Paper II, together with a systematic fugacity expansion which allows to retrieve the results obtained from the truncated BGY hierarchy. In the present paper the exact density profiles are calculated analytically up to first order in the coupling parameter. The expressions show the interplay between three effects: the geometric repulsion from the impenetrable wall; the electrostatic effective attraction (∈_w>1) or repulsion (∈_w<1) due to its dielectric response; and the Coulomb interaction between each charge and the potential drop created by the electric layer which appears as soon as the system is not symmetric. We exhibit how the charge density profile evolves between a structure with two oppositely-charged layers and a three-layer organization when ∈_w varies. (The case of two ideally conducting walls will be displayed elsewhere).     

Improved sensitivity to charged Higgs searches in top quark decays t→bH+→b(τ+ντ) at the LHC using τ polarisation and multivariate techniques

We present an analysis with improved sensitivity to the light charged Higgs (m_H⁺ < m_t-m_bm_{H^{+}} < m_{t}-m_{b}) searches in the top quark decays t→bH ⁺→b(τ ⁺ ν _τ )+c.c. in the t[`(t)]t\bar{t} and single t/[`(t)]t/\bar{t} production processes at the LHC. In the Minimal Supersymmetric Standard Model (MSSM), one anticipates the branching ratio B (H⁺ ?t⁺n_t) @ 1{\mathcal{B}} (H^{+} \to\tau^{+}\nu_{\tau})\simeq1 over almost the entire allowed tanb\tan\beta range. Noting that the τ ⁺ arising from the decay H ⁺→τ ⁺ ν _τ are predominantly right-polarized, as opposed to the τ ⁺ from the dominant background W ⁺→τ ⁺ ν _τ , which are left-polarized, a number of H ⁺/W ⁺→τ ⁺ ν _τ discriminators have been proposed and studied in the literature. We consider hadronic decays of the τ ^±, concentrating on the dominant one-prong decay channel τ ^±→ρ ^± ν _τ . The energy and p _T of the charged prongs normalised to the corresponding quantities of the ρ ^± are convenient variables which serve as τ ^± polariser. We use the distributions in these variables and several other kinematic quantities to train a boosted decision tree (BDT). Using the BDT classifier, and a variant of it called BDTD, which makes use of decorrelated variables, we have calculated the BDT(D)-response functions to estimate the signal efficiency vs. the rejection of the background. We argue that this chain of analysis has a high sensitivity to light charged Higgs searches up to a mass of 150 GeV in the decays t→bH ⁺ (and charge conjugate) at the LHC. For the case of single top production, we also study the transverse mass of the system determined using Lagrange multipliers.     

A measurement of the τ lifetime

We have reconstructed 695 three-track τ decay vertices using a high resolution drift chamber close to the interaction point. From the distribution of decay lengths we measure the lifetime to be (3.06 ±0.20±0.14)×10⁻¹³ s. Using this result we find that the ratio of charged weak coupling constant for the τ to that of the μ,G _τ/G _μ=0.967±0.040 consistent with the concept of lepton universality. On leave from Warsaw University, Poland Now at Hasylab, DESY Supported by Bundesministerium für Forschung und Technologie Supported by UK Science and Engineering Research Council Supported by CAICYT Supported by the Minerva Gesellschaft für Forschung GmbH Supported by US Dept. of Energy, contract DE-AC02-76ER000881 and by US Nat. Sci. Foundation Grant no INT-8313994 for travel Partially supported by grant CPBP 01.06     

Potential profile near the virtual cathode in presence of charged dust

In this work, concept of virtual cathode and its existence in dusty plasma has been studied by theoretical and numerical analysis. Using basic equations of charge dust, ions, and electrons, the non‐monotonic behaviour of the potential in presence of charged dust has been calculated and plotted as a function of dust density. It has been found that there is a change in potential between cathode and sheath potential and subsequently changes the threshold wall temperature as compared to that of without dust conditions. The threshold wall temperature has been increased due to the ability of micro‐particles acquiring electron charge and hence, reducing potential at the wall. Further, for different values of α (depends on dust density); threshold temperature remained the same for observed virtual cathode. Hence, behaviour of potential has been plotted as a function of α with increasing wall temperatures for two dust charge values (1 and 1,000). Considering no dust charge, it has been observed that, at lower dust density, double layer like structure is formed near the emissive wall. But this double layer structure gets diminishes with increasing dust density. Hence, below a threshold dust density, virtual cathode near to the emissive wall is not possible. While for Z_d = 1,000, the formation of virtual cathode appeared even at very small dust density. However, irrespective of variation of potential difference near the wall and existence of virtual cathode at different emission regime the threshold wall temperature remains same. Effect of dust potential dependency on threshold wall temperature has also been discussed in this study.     

Mean flow scaling along smooth and rough wall boundary layers

Effects of the upstream conditions and the degree of the wall roughness on the mean velocity profiles and some integral flow parameters in two dimensional zero-pressure-gradient boundary layer were characterized experimentally. The results were analyzed utilizing conventional and recent scaling flow parameters for 245< Re _θ ≤ 11·10³, where Re _θ is the Reynolds number based on the free stream velocity (Ū _∞) and the momentum thickness (θ). Good correlation of the quantity ΔŪ ⁺ as a function of the roughness parameter k ⁺ was obtained for sand roughness of 1.7 < k ⁺ ≤ 172, revealing a universality of the roughness effect, where ΔŪ ⁺ = = (Ū _∞ − Ū)/u _τ and K ⁺ = ku _τ /v.The mean flow structure of the outer flow was observed not to be influenced by the degree of the wall roughness, i. e., the outer flow of either the smooth or the rough surfaces scales similarly with the various scaling parameters regardless the degree of the wall roughness. However, it made flow confined to the wall region away from the classical universality, allowing similarity hypothesis not to be identical in the wall region at least for the current range of the Reynolds number.     

Jeans-Buneman instability in a dusty plasma

A self consistent formulation of the Jeans instability of a dusty plasma with proper inclusion of charge dynamics is described. It is shown that charge fluctuations significantly affect the Jeans as well as the Buneman mode. For plasma particles (electrons and ions) in local thermal equilibrium, the Jeans lengthλ _J is given byλ _J≈λ _g F(R, ε, β/η), whereλ _g is the Debye length of the charged grains,R is the square of the ratio of the Jeans to the plasma frequency of the grains,ε is the square of the ratio of the Debye length of the grains and the plasma particles andβ/η is the ratio of the attachment to the decay frequency of the electronic charges to the grain surface. The functional form ofF is given in the text. Numerical investigation of the Jeans-Buneman mode for a two and three component plasma shows that the Jeans mode dominates atkλ _D≪1 (wherek is the wave number andλ _D is the Debye length of plasma particles), whereas atkλ _D≫1 only the Buneman mode operates. Charge fluctuations reduce the area of overlap of the two modes. Furthermore, in the absence of gravity, there exists a new, charge fluctuation induced unstable mode in a streaming dusty plasma. Astrophysical applications of the results are discussed.     

De Haas-van Alphen effect studies in dilute alloys of silver and gold

De Haas-van Alphen experiments have been used to determine the scattering temperatures which characterize the [111] neck and belly extremal orbits in some dilute alloys of silver and gold. The relaxation time is anisotropic withτ _N/τ _B≃2 in both Ag(Au) and Au(Ag) when the scattering is dominated by the solute. This anisotropy is in the opposite sense to that observed in another homovalent alloy Ag(Cu) and to that observed in the presence of charged impurities.     

Charging of a conducting sphere moving in a weakly ionized gas under an arbitrarily oriented external uniform electric field

A charging conducting sphere moving in a weakly ionized gas is investigated. An external uniform electric field is applied with arbitrary orientation relative to the gas flow. The ion current is obtained analytically and investigated numerically in ballistic assumption. It is shown that charging regimes depend not only on the net charge of the sphere but also on the gas flow type, and the parameter ξ_± – the ratio of ion drift velocity far from the sphere to the gas velocity. The cases |ξ_±|<1 and |ξ_±|>1 yield two different charging regimes for Stokes and potential flows. For the potential flow, the ion current has been found analytically in continuous ξ_±-parameter space. The stationary charge of an isolated sphere is also calculated numerically as a function of α. It achieves maximum magnitudes in direct (α=0) and back (α=π) flows respectively.     

Collective behavior of laser-produced plasma from a multicomponent YBa2Cu3O7 target in air

2 Cu₃O₇, using a Q-switched Nd:YAG laser is investigated by time-resolved emission-spectroscopic techniques at various laser irradiances. It is observed that beyond a laser irradiance of 2.6×10¹¹ W cm^-2, the ejected plume collectively drifts away from the target with a sharp increase in velocity to 1.25×10⁶ cm s^-1, which is twice its velocity observed at lower laser irradiances. This sudden drift apparently occurs as a result of the formation of a charged double layer at the external plume boundary. This diffusion is collective, that is, the electrons and ions inside the plume diffuse together simultaneously and hence it is similar to the ambipolar diffusion of charged particles in a discharge plasma. Received: 30 January 1998/Revised version: 12 June 1998     

Ordered structures in a nonideal dusty glow-discharge plasma

The formation of ordered structures of charged macroparticles in a constant-current neon glow-discharge plasma is investigated. Experiments were performed with two types of particles: thin-walled glass spheres 50–63 μm in diameter and particles of Al₂O₃, 3–5 μm in diameter. Formation of quasicrystalline structures is observed in the standing strata and in an artificially created double electric layer. The formation of extended filamentary structures of macroparticles in the absence of visible stratification of the positive column has been observed for the first time. The influence of the discharge parameters on the formation of the ordered structures and their melting is examined. The form of the interaction potential between the charged macroparticles is considered, as well as changes in the conditions for maintaining the discharge in the presence of high concentrations of dust particles. Zh. éksp. Teor. Fiz. 112, 2030–2044 (December 1997)     

Deformation of viscoelastic coating in a turbulent flow

The rate and amplitude of compliant coating deformation by turbulent pressure pulsations were calculated. Complex compliance determined by a 2D model has two components: along and across the coating. Dependence of the components of dimensionless compliance on the wavelength — coating thickness ratio was determined for 0.3 < λ/H < 30 and dependence of these components on the ratio of flow velocity to velocity of wave propagation was determined for 0.1 < V/C < 10. Deformation amplitude and rate of surface displacement for the hard compliant coatings which can be used in practice were calculated within the range of 5–55 m/s for the water and air turbulent flow. The effects of the loss tangent and Poisson’s ratio of the coating material were also studied. It is shown that the mean-square displacement of their surface does not exceed the thickness of a viscous sublayer. However, the velocity of surface motion is comparable with velocity pulsations in a boundary layer near a wall. This can be a reason for drag reduction on a compliant wall. The calculated value of ratio between energy absorbed by the wall and energy dissipated within the flow because of drag was 10⁻⁴ for water and 10⁻⁶ for air. This estimate does not confirm the hypothesis explaining drag reduction by energy takeoff from the flow.     

Analysis and correction of the measurement of the neutron lifetime

Corrections have been introduced into the result τ_β = 885.4 ± 0.9_stat ± 0.4_syst s of our measurements of the neutron lifetime. The corrected value is τ_β = 881.6 ± 0.8_stat ± 1.9_syst s.     

Cross sections for single and double ionization of atomic helium under impact by fast multiply charged ions

Expressions for the cross sections for single and double ionization of atomic helium in collisions with fast multiply charged ions are obtained in the collision parameter range υ ²≫Z≳υ, υ ₀<c, where Z and υ are, respectively, the ion charge and ion velocity, υ ₀ is the characteristic velocity of electrons in the atomic helium ground state, and c is the velocity of light. Zh. Tekh. Fiz. 68, 1–7 (March 1998)     

Effects of charged Higgs bosons in the deep inelastic process ντN → τ?X and the possibility of detecting tau-neutrinos at cosmic neutrino detectors

We study the deep inelastic process ν _τ + N → τ ⁻ + X (with N ≡ (n + p)/2 an isoscalar nucleon), in the context of the two-Higgs doublet model Type II (2HDM(II)). We discuss the contribution to the total cross-section of diagrams, in which a charged Higgs boson is exchanged. We present results which show strong dependence of such contributions on tan β and M _H ^±. We show that for tan β ≈ 150 and M _H ^± ≈ 300 GeV, the contribution of the charged Higgs boson exchange diagrams to the cross-section of the charged current inclusive ν _τ N collision can become important. We find that this contribution for an inclusive dispersion generated through the collision of an ultra-high-energy tau-neutrino with E _ν ≈ 10²¹ eV on a target nucleon can be as large as 40% of the value of the contribution of the W ^± exchange diagrams, provided M _H ^± ≈ 300 GeV and tan β ≈ 150. Such enhancement and the induced variation on the mean inelasticity 〈y〉^CC could lead to sizeable effects in the acceptance of cosmic tau-neutrino detectors at experiments such as HiRes, PAO, and the CRTNT, which are anchored to the ground, and at experiments such as EUSO and OWL, which are proposed to orbit around the Earth. We also compare the contribution to σ _H+^tot from the different allowed initial quarks and we show that the contribution from the bottom quark dominates by far. This means that the H ^± contribution practically always gives a top quark in the final state. Such a large component of the cross-section having a top quark event in the final state could have recognizable features in the EAS experiments.      

On the existence and formation of small amplitude electrostatic double-layer structure in nonthermal dusty plasma

In the present article, we studied the effect of nonthermal electrons on the formation and existence of double-layer structures in a three-species plasma consisting of positive ions, nonthermal electrons, and immobile negative dust-charged grains. Employing the reductive perturbations, a modified Korteweg–de Vries (mKdV) type equation is derived for the dust-ion-acoustic waves (DIAWs) bearing nonthermality. We found that both positive and negative polarity shock structures (double layer) can exist such that it switches polarity while changing the dust charge concentrations. However, strong nonthemality favours only rarefactive structures irrespective of the ion temperature. It is also found that increasing the nonthermal electron in the system the width of the double layer is increased; furthermore, the shock structure forms with small dust charge concentration. For small ionic temperature, increasing the nonthermal electrons in the system makes the double layer potential to increase; however, for σ = 1 reverse phenomena occurs. Our results are relevant to the shock observations in Q machine experiments and in the ionospheric regime of the earth.     

Measurement of the τ lepton mass at the KEDR detector

A precise τ lepton mass measurement performed at the VEPP-4M collider with the KEDR detector is reported. The mass value is evaluated from the τ⁺τ⁻ cross section behavior around the production threshold. The result based on 6.7 pb⁻¹ of data is m _τ = 1776.81 _−0.23 ^+0.25 ± 0.15 MeV. Using 0.8 pb⁻¹ of data collected at the ψ′ peak, we have also determined that Γ _ee B _ττ(ψ′) = 9.0 ± 2.6 eV. The text was submitted by the authors in English.     

Flavor symmetry L μ-L τ and quasidegenerate neutrinos

Current data implies three simple forms of the neutrino mass matrix, each corresponding to the conservation of a nonstandard lepton charge. While models based on L _e and L _e-L _μ-L _τ are well known, little attention has been paid to L _μ-L _τ. A low-energy mass matrix conserving L _μ-L _τ implies quasidegenerate light neutrinos. Moreover, it is μ-τ symmetric and therefore (in contrast to L _e and L _e-L _μ-L _τ) automatically predicts maximal atmospheric neutrino mixing and zero U _e3. A seesaw model based on L _μ-L _τ is investigated and testable predictions for the neutrino mixing observables are given. Renormalization group running below and in between the seesaw scales is taken into account in our analysis, both numerically and analytically. The text was submitted by the authors in English.