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The dielectric properties of complex plasma containing either metal or dielectric spherical inclusions (macroparticles, dust) are investigated. We focus on surface plasmon resonances on the macroparticle surfaces and their effect on electromagnetic wave propagation. It is demonstrated that the presence of surface plasmon oscillations can significantly modify plasma electromagnetic properties by resonances and cutoffs in the effective permittivity. This leads to related branches of electromagnetic waves and to the wave band gaps. The conditions necessary to observe the band-gap structure in laboratory dusty plasma and/or space (cosmic) dusty plasmas are discussed.

The rotation of a dust cluster levitated in plasma sheath is investigated in the presence of magnetic field. In a cylindrical plasma chamber, a dust cluster is formed by micron sized dust particles and rotates under the influence of ion drag force driven by electric and magnetic field. When ion drag force is balanced with neutral drag force the cluster rotates at constant velocity. Ion temperature is determined by estimating the forces acting on the dust particle at room temperature as well as at cryogenic temperature.

A bow shock is observed in a two‐dimensional flow of charged micro particles in a complex plasma. A thin conducting wire is placed vertically against the flow to make a potential barrier as an obstacle against the flow. A void is formed around the potential barrier surrounding the wire. When the flow velocity exceeds the dust acoustic velocity, the density in front of the void increases and forms the bow shock.

Dust charges in a complex helium gas plasma, surrounded by cryogenic liquid, are studied experimentally. The charge is determined by frequency and equilibrium position of damped dust oscillation proposed by Tomme et al. (2000) and is found to decrease with ion temperature of the complex plasma.

Fine particles injected in a planar magnetron were pushed upward by diffusible plasma, leading to being suspended by the force balance with the gravity and forming three‐dimensional structures on the two‐dimensional structure formed by particle strings.

High-power microwave generation in an axially-extracted virtual cathode oscillator (VIRCATOR) is studied numerically using MAGIC which is a two-dimensional, finite-difference, time-domain particle-in-cell code. The simulation was motivated by the recent experiment of Yatsuzuka et al at the Himeji Institute of Technology in Japan. The Himeji experiment observed that, while pinching of the electron beam was found to be essential for microwave generation, the electron beam current remained below the critical pinching current when microwaves were detected. On the other hand, an earlier experiment by Benford et al showed that microwave emission occurred only when the diode current exceeded the critical current. In the simulation being developed for the Himeji VIRCATOR geometry, the preliminary phase space diagrams show the formation of a virtual cathode. A detailed simulation study is in progress on the effect of bipolar flow on the critical current for beam pinching and microwave emission. Bipolar flow consists of ion flow from the anode into the diode gap in addition to the electron flow and is known to increase the electron space charge limited current.

A 1.5 Watts FET amplifier with 5.8 dB gain over 27.5 to 28.4 GHz frequency band has been developed. This amplifier combines the output power of four multistage amplifier modules utilizing a 4 way combiner with low insertion loss.

Long-pulse high power microwave experiments are being conducted at the University of New Mexico (UNM) using a modified Physics International Pulserad 110A. The Pulserad 110A, which previously consisted of an 11-stage Marx bank followed by a Blumlein, has been modified by replacing the Blumlein with a parallel L-C network, as described by Cummings. Both the Marx bank and the L-C network together form a type-A pulse-forming network with an output impedance of 40 /spl Omega/, a pulse duration of 500-700 ns, and a peak voltage and current for a matched load of 570 kV and 14.3 kA, respectively. The UNM Pulserad 110A drives an electron beam diode having a graphite annular knife-edge cathode. The electron beam that is generated is injected into a slow wave structure (SWS) having 12 periods with variable ripple amplitudes. Microwave radiation in the TM/sub 01/ mode is observed with peak powers on the order of 170 MW and pulse widths at full-width, half-maximum of 20-25 ns. Longer pulse widths are observed for lower powers. Studies are being conducted to determine the effects of changes in the anode-cathode gap spacing and cathode diameter on pulse duration for a given SWS configuration. Both vacuum and plasma-filled experiments are being performed to investigate possible increase in pulse width using plasma filling. The system design will be presented along with experimental results.

An experiment is described in which microparticles are levitated within a rf sheath above a conducting plate in argon plasma. The microparticles forming a two-dimensional crystal structure are considered to possess Debye screening Coulomb potential ϕ(r)=(Q/4πe0r)exp(−r/λ), where Q is the electric charge, r is distance, and λ is the screening length. When the crystal structure is slanted with an angle θ, a particle experiences a force Mg sin θ, where M is the mass of the particle and g is acceleration due to gravity, which must be equal to the Debye screened Coulomb force from other particles. By changing θ, relations for λ(Q) are measured. The screening length λ and Q are determined uniquely from the crossing points of several relations. The electric charge Q is also estimated from a floating potential measured with a probe. The measured λ is nearly equal to an ion Debye length.

Summary form only given. The possibility of photon acceleration in a plasma was studied from the viewpoint of three-wave interaction. A photon with momentum h L q phi and energy h Lophi combines with a plasmon with momentum h L q pl and energy h Lopl to give a photon with momentum h L q phf and energy h Lophf. It was observed that the interaction vertex function for the plasmon-particle can be obtained by the use of the interaction Hamiltonian between particles and longitudinal quasiparticles. Calculation of the vertex function for a specified three-wave interaction process reveals that no transition occurs if the plasma is cold and stationary. It is found that the transition probability reaches a maximum when the plasma particles move in the direction of longitudinal plasma oscillations (plasmons) along with the direction of polarization of vector potential A , resulting in the upshifting of the frequency of the outgoing photon fields

Summary form only given. Recently, the authors (1989) studied the velocity diffusion process using the generalized Langevin equation derived by the projection operator method. Further study shows that the retarded frictional function plays an important role in suppressing particle diffusion in the velocity space in stronger turbulence. A theoretical formulation is presented for the retarded frictional effect, produced by the effective collisions due to the plasma turbulence. A test particle numerical experiment for Langmuir turbulence was carried out to test the theory. In stronger turbulence, a deviation of the diffusion rate from the one predicted by both the quasilinear and the extended resonance theories has been observed, and it is explained qualitatively by the present formulation

Fully developed incompressible turbulent flow in a two-dimensional channel has been simulated numerically. Turbulence promoters were arranged intermittently on one side of the channel walls. The two walls and promoters were heated individually. A large-scale flow field and a temperature field were calculated by integrating the filtered, three-dimensional time-dependent Navier-Stokes equations and time-dependent energy equation. Motions of turbulence field with small scales were simulated using eddy-viscosity models. The Reynolds and Peclet numbers were set at 1.1×l04 and 7.7×l0, respectively. Only 9, 000 grid points were distributed and three kinds of averaging were used in order to complement the grid points. Mean-velocity profiles, turbulence statistics, time-dependent features of flow and mean-temperature profiles are in good agreement with the experimental data. Calculations were carried out using a HITAC M 200/280 H system computer of the University of Tokyo.

Optimum structure parameters of GaAs hi-lo IMPATT diodes to give a high-efficiency and a high-output power are experimentally determined in the frequency range from 7 to 18 GHz. The highest efficiency is obtained at any frequency when a diode has a punch-through factor of about 0.6 and is depleted with an electric field strength of 10 kV/cm at the end of the lo region under operation. The optimum lo-region carrier concentration to achieve the highest efficiency and the upper limit of a junction area to obtain a high-output power without decreasing efficiency are found to be simply related to frequency by the following equations: (N_{L})_{\opt} = (4 \times 10^{14}) \cdot (f/7)^{3} cm-3and (S_{j})_{\max} = (20 \times 10^{-4}) \cdot (f/10)^{-1.9}) cm2), respectively, where f is in gigahertz.

Fully developed incompressible turbulent flow in two-dimensional channel with turbulence promoters has been predicted numerically by large eddy simulation. Parameter C in Smagorinsky model can be assumed constant generally in the range of high Reynolds numbers. In this paper, C is varied with SGS Reynolds number in low Reynolds number region and SGS eddy diffusivity near the solid boundary is considered as a function of the distance from the boundary, the velocity gradient and the molecular viscosity. These improvements of SGS eddy viscosity model and the boundary condition of SGS eddy diffusivity have little effect on the mean velocity distribution, but have a significant effect on the distributions of turbulences and turbulent shear stresses. Computed streaklines and Strouhal number of vortex shedding behind the turbulence promoter are compared with visual experiments. The Reynolds number in computation is set at 1.1×104 and 9000 grid points are distributed.

In this paper, a two-phase flow with randomly distributed particles is considered. The Navier-Stokes equation is integrated over the control volume fixed to the absolute co-ordinates, and then an exact volume-averaged momentum equation is derived. We remove the difficulty of mathematical treatment due to the random particle distribution by using a smooth weight-function. By the above volume-averaged equation, we can explain some phenomena of two-phase flow. As an example, the apparent viscosity of the two-phase parallel flow, where the particle concentration is distributed arbitrarily in the plane perpendicular to the flow direction, is obtained theoretically and compared with the summarized experimental data.