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Atmospheric microwave plasma jets generated in Ar gas or Ar/[O.sub.2] and Ar/[H.sub.2] gas mixtures were applied to a surface modification of metal. The nozzle-type microwave plasma jet is excited in a rectangular waveguide, operated at a frequency of 2.45 GHz, and is stabilized by the flowing channel of a working gas through the nozzle. The charged particles, with a high kinetic energy produced from the plasma jet, caused a surface in a rough morphology to be smooth, showing a change in the water contact angle. A scanning electron microscopy and a water contact-angle analyzer characterized the samples treated in different gas mixtures. The water contact angles of the samples were plotted as a function of the recovery time, showing that the sample treated by Ar/[H.sub.2] plasma jet has the smallest contact angle (~ 3[degrees]) and the slowest recovery of the angle. In the estimation of the aluminum-surface free energy, after the [H.sub.2]/Ar plasma treatment, the total surface free energy of the Al sample increased from 18.71 to 82.81 mJ/[m.sup.2] drastically. Index Terms--Contact angle, metal, plasmas material-processing applications, surface treatment.

Stability properties of the resistive hose instability is investigated for a rounded current-density profile of a charged particle beam propagating through a background plasma where the electron collision time (1/[[nu].sub.c]) is comparable to or longer than the magnetic decay time ([[tau].sub.d]). The eigenvalue equation is derived based on the energy group model, including the stabilizing influence of a finite magnetic decay time. The dispersion relation of the resistive hose instability in a charged particle beam with an arbitrary current density profile is derived, assuming that the eigenfunctions can be represented by the rigid displacement of the self magnetic field in the plasma. Stability analysis for perturbations propagating through the beam pulse from its head to tail is carried out for an arbitrary current profile of the beam. It is shown from the stability analysis that the width of the range [[OMEGA].sup.2] corresponding to instability decreases drastically as the value of parameter [[nu].sub.c][[tau].sub.d] decreases from infinity to zero, thereby being a very narrow bandwidth of instability. It is also shown for arbitrary current profile that any perturbation with frequency [OMEGA] higher than the maximum betatron frequency [[omega].sub.[beta]m] is stable. Here, [OMEGA] is the Doppler-shifted frequency seen by beam particles. Index Terms--Beam instability, beam propagation, charged particle beam, resistive hose.

We have investigated the influence of anode-cathode (A-K) gap distance on the output characteristics of high-power microwave from coaxial virtual cathode oscillator (vircator). This high-power microwave generator is powered by the 'Chundoong' (Max 600 kV, 88 kA, 60 ns), which is an intense relativistic electron beam-pulse generator. In this experiment, it was observed that the microwave power has been strongly dependent upon the A-K gap distance, where the A-K gap has been varied from 4 to 8 mm. The maximum microwave power is observed to be 244 MW, whose efficiency is about 2.75% at the A-K gap distance 4 mm. Also the microwave frequencies are measured to be 5.1 [less than or equal to] f [less than or equal to] 5.9 GHz from the combination of a coupled line band pass filter with a 1-GHz bandwidth and dispersive delay line method. It is noted that measured output microwave frequency is in good agreement with that of simulation. It is also found that the dominant mode of output microwave is a [TM.sub.01] in this simulation result. Index Terms--Coaxial vircator, high-power microwave, relativistic diode.

The microwave plasma-torch and its application for decomposition of chemical warfare agent using a moderate microwave power are investigated. Decomposition of chemical warfare agents is demonstrated for phosgene (CO[Cl.sub.2]) as a sample example. The main byproducts of phosgene decomposition are CO and [Cl.sub.2]. The [Cl.sub2] gas was completely converted to HCI by injecting N[H.sub.3] into the microwave plasma-torch as an additive gas. The HCl is, in turn, eliminated by passing the exhaust gas through a wet-scrubber. Detailed decomposition properties of phosgene by microwave plasma-torch at the atmospheric pressure are also investigated by making use of Fourier transform infrared, mass spectroscopy, and ion chromatography. Index Terms--Chemical warfare agents, microwave plasma-torch, phosgene.

A stability analysis of a propagating ion beam through a plasma medium is carried out in terms of transverse conductivity of the background plasma. Coupled eigenvalue equations are obtained for the flat-top density profiles of beam ions and plasma electrons. The dispersion relation of the transverse instability in an intense ion beam propagating through the background plasma is derived, including the plasma conductivity (4[pi][sigma][perpendicular to]/[omega]), the magnetic decay time [[tau].sub.d] and fractional charge neutralization f. It is shown that the obtained dispersion relation recovers the previous one of the electron-ion two-stream instability in the limit of [sigma][perpendicular to] [right arrow] 0. On the other hand, the dispersion relation of the resistive-hose instability is recovered when [sigma][perpendicular to] [right arrow] [infinity]. Influence of the finite transverse conductivity [sigma][perpendicular to] on the resistive hose stability properties are investigated for the ion beam propagating through a plasma channel. The growth rate of the resistive hose instability decreases considerably as the transverse conductivity 4[pi][sigma][perpendicular to]/[omega] decreases from infinity. Index Terms--Instability, ion beam, plasma conductivity, resistive-hose, two-stream.

A novel slow-wave structure (SWS), the coaxial inverted helical groove structure, is presented and those of its properties used for wide-band traveling-wave tube (TWT) are investigated. The first part of the paper concerns the wave properties of this structure in the case of a vacuum. The influence of the geometrical dimensions on dispersion characteristics and interaction impedance are investigated. The theoretical results reveal a very weak dispersion for the fundamental wave in the structure. The negative dispersion can be realized by a suitable selection of the structural parameters. The interaction impedance of the fundamental wave is about 10 [OMEGA]. The interaction impedance of the -1 space harmonic wave is much lower than that of the fundamental wave. Thus, the risk of backward wave oscillation is reduced. The software high frequency structure simulator (HFSS) is also used to calculate the dispersion property of the SWS. The simulation results from HFSS and the theoretical results agree well, which supports the theory. In the second part, a self-consistent linear theory of a coaxial inverted helical groove TWT is presented. The typical small signal gain per period is about 0.5 dB and the 3-dB small-signal gain bandwidth can exceed 25% with a 33-dB gain of tube. Index Terms--Dispersion relation, interaction impedance, inverted helical-groove waveguide, slow-wave structure, small signal analysis, traveling-wave tube.

Theoretical simulation of the dispersion and interaction impedance characteristics of a semivane loaded negative dispersion helical slow-wave structure, which is a slight variant of a conventional vane-loaded helix of a wide-band traveling-wave tube (TWT), was validated for the nonresonant perturbation measurement. While the experimental and theoretical results agreed well with respect to interaction impedance for both the semivane structure and the structure without vanes, there was disagreement found with respect to the dispersion characteristics of the semivane structure, which was explained quantitatively by the deformation that had taken place in assembling the structure. The output performance of a TWT using the semivane structure fairly agreed with the prediction by an in-house one-dimensional nonlinear Lagrangian code, with respect to saturated output power (~50 W), saturated gain (~40 dB), and lower-band-edge second harmonic level (~ -5 dBc), in the operating frequency range of 6-18 GHz, except at the low frequency end of the operating band, where the saturated power was less and the second harmonic level higher than predicted, a finding that may be attributed to the departure of the deformed structure from exhibiting a negative dispersion at the lower band edge. Index Terms--Helical slow-wave structure, negative dispersion, traveling-wave tube, wide-band.

The dispersion relation of the electromagnetic waves propagating through a helix is obtained for the helix inserted into a magnetron-type cylindrical conductor. The resultant dispersion relation consists of a combination of helix and magnetron dispersion relations. In special cases, they decouple from each other and recover the previous results. For example, in the case when the magnetron vane structures disappear, the dispersion relation recovers the typical helix dispersion relation. On the other hand, the resultant dispersion relation recovers the magnetron-transverse electric mode when the helix pitch angle [PHI] approaches [pi]/2. Index Terms--Electromagnetic waves, helix, magnetron.

The performance of a klystrode is investigated for annular electron beams. Numerical simulations of the output cavity in the klystrode device are carried out by making use of the fully electromagnetic three-dimensional code, HFSS, and the fully electromagnetic, two-and-one-half-dimensional, self-consistent PIC code, MAGIC. In addition, an analytical expression to predict the efficiency and gap-field strength of the device is developed to investigate klystrode performance over a wide range of parameters. This analytical expression for the annular klystrode is developed based on the Maxwell's equations and Newton's second law of motion. The analytical results agree fairly well with data obtained numerically from the MAGIC code. The presented results indicate that the theoretical formula obtained from the analytical calculation may be useful for designing the klystrode microwave tubes. Index Terms--Analytic calculation, annular beam, HFSS, klystrode, MAGIC, microwave tube.

Cavity excitation due to beam head effects in high power klystrons behaviour was studied.

The propagation properties of an electron beam whose energy and current are simultaneously premodulated at the cathode are investigated by computer simulation using the two-dimensional (2-D) particle-in-cell code, MAGIC. The simulation is carried out to investigate the influence of the initial energy modulation and the phase difference between current and energy modulation. With appropriate initial energy modulation, the amplitude of the downstream current modulation can be kept as high as the initial modulation level. Appreciable growth of high harmonic components is also observed as the electron beam debunches. The simulation data are compared with results obtained from a nonlinear theory of the current modulation in an electron beam propagating through a drift tube. It is shown that the simulation data agree remarkably well with the analytical theory. Index Terms - Electron beam, premodulation.

The self-consistent nonlinear theory of a relativistic electron beam propagation through a waveguide loaded with a sheath helix was formulated. A close integrodifferential equation for the normalized beam current was derived in terms of normalized time and propagation distance using Maxwell equations. It was then examined analytically by the Fourier decomposition of the current modulation with the harmonic number used. The mode strength derived was expressed in terms of the spatial oscillation frequency and growth rate of the mode amplitude.

An examination on the influence of the initial energy modulation caused by the self-potential depression on the premodulated electron-beam propagation through a drift tube is conducted. The beam's kinetic energy at the injection varies according to the potential depression k which varies due to the initial current modulation. Results show that the initial energy modulation caused by the self-potential depression at injection plays a significant role in the current modulation for long range propagation.

The distribution of hydrogen concentration in a palladium lattice subjected to a temperature gradient is investigated. A palladium rod coated with a diffusion barrier film that regulates the outflux of hydrogen atoms is used in the study. A constant temperature gradient is imposed upon the one-dimensional rod. Results show thatthe linear temperature increase causes a significant redistribution in the hydrogen concentration of the rod.

A theoretical model was used to analyze neutron thermalization in a medium. The results showed that thermal neutron flux was a function of the diffusion constant, the reciprocal length and the Fermi age of the moderator material. The thermal neutron flux at the origin was found to be proportional to the square of the moderator density. Increased Fermi age resulted in a proportional increase in the thermal neutron flux volume.

Properties of the valence band structure in boron-zinc oxide (BZO) films were investigated using the secondary electron emission due to the Auger neutralization of helium ions, with respect to the application of BZO films to the development of solar cells, in which the conductivity of the BZO films plays a critical role in improving cell performance. The characteristic energy &eh;0 corresponding to the peak density of states in the valence band showed that BZO film prepared with a 3000 SCCM B2H6 gas flow rate (SCCM denotes cubic centimeters per minute at standard temperature and pressure) had a shallow characteristic energy &eh;0 = 5 eV, whereas film without boron doping had a deep characteristic energy &eh;0 = 8.2 eV, suggesting that a high concentration of boron impurity in BZO films might enhance the transition of electrons and holes through the bandgap from the valence to the conduction band in zinc oxide crystals, thereby improving the conductivity of the film. The measurement method developed here demonstrates that the secondary electron emission is very useful in the determination of the band structure in various synthetic films. [ABSTRACT FROM AUTHOR]

Time-resolved spectroscopic measurements of a capillary discharge plasma of helium gas were carried out to obtain detailed information about dynamics of the discharge plasma column, where the fast plasma dynamics is determined by the electron density and temperature. Our measurements show that the electron density of the capillary plasma column increases sharply after gas breakdown and reaches its peak of the order of 1018 cm-3 within less than 100 ns, and then it decreases as time goes by. The result indicates that a peak electron density of 2.3×1018 cm-3 occurs about 65 ns after formation of the discharge current, which is ideal for laser wakefield acceleration experiments reported by Karsch et al. [New J. Phys. 9, 415 (2007)]. [ABSTRACT FROM AUTHOR]

A comprehensive decontamination scheme of the chemical and biological agents, including airborne agents and surface contaminating agents, is presented. When a chemical and biological attack occurs, it is critical to decontaminate facilities or equipments to an acceptable level in a very short time. The plasma flame presented here may provide a rapid and effective elimination of toxic substances in the interior air in isolated spaces. As an example, a reaction chamber, with the dimensions of a 22 cm diameter and 30 cm length, purifies air with an airflow rate of 5000 l/min contaminated with toluene, the simulated chemical agent, and soot from a diesel engine, the simulated aerosol for biological agents. Although the airborne agents in an isolated space are eliminated to an acceptable level by the plasma flame, the decontamination of the chemical and biological agents cannot be completed without cleaning surfaces of the facilities. A simulated sterilization study of micro-organisms was carried out using the electrolyzed ozone water. The electrolyzed ozone water very effectively kills endospores of Bacillus atrophaeus (ATCC 9372) within 3 min. The electrolyzed ozone water also kills the vegetative micro-organisms, fungi, and virus. The electrolyzed ozone water, after the decontamination process, disintegrates into ordinary water and oxygen without any trace of harmful materials to the environment. [ABSTRACT FROM AUTHOR]

A theoretical model of the plasmas generated by a sheath-helix antenna is developed for axisymmetric perturbations. The system configuration consists of a cylindrical plasma column inside a dielectric tube of radius R[sub c]. The eigenvalue equation is obtained and the eigenfunction is identified as the Bessel function J[sub 0](x) of the first kind of order zero. The radial wave numbers ξ and η for the eigenfunction are described in terms of the rf frequency and plasma density. A full dispersion relation is analytically obtained, including influence of the finite plasma size, antenna effects, the electron inertia, and ion mass contributions. It is shown from the dispersion relation that the radial mode number ξ approaches infinity at the lower-hybrid frequency, exhibiting a resonance condition. Meanwhile, the radial wave number η approaches 3.83/R[sub c] at the lower-hybrid frequency. A cross-sectional view of the light emission in experiment indicates that the helicon-plasma density at the lower-hybrid frequency has a hollow profile. The azimuthal component E[sub θ](r) of the perturbed electric field observed experimentally is very similar to the theoretical model of J[sub 1](3.83r/R[sub c]) at the lower-hybrid frequency. The emission peak coincides with the radial location of the strongest electric-field intensity. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Striations observed in a coplanar or a wedge-shaped planar ac-type discharges are reported in this article. The observed data indicate that the striations are related to ion charge waves of the wall generated by the self-sustained perturbations that originate from the force balance between the ion and the electron wall-charge clouds accumulated on the dielectric layers over the metal electrodes. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on a study which proposed a model for resistive filamentation of a self-pinched slab electron beam. Components of the lowest order modes; Comparison of the modes' dispersion relation with the results from a linearized particle simulation mode; Application of the analytic model and simulation mode to the interpretation of an experiment in which filamentation was observed in a self-pinched annular electron beam propagating in low-pressure air.

Presents a scheme to generate high-dose, steady-state neutrons from plasma ion implantation. Theoretical calculations and assumptions on plasma ion implantation; Influence of temperature on the deuterium concentration inside palladium; Dynamics of ion sheath.

Introduces the existence of a return current when the electron beam propagates through the background plasma. Influence of the return current on the equilibrium and stability properties; Equilibrium state of the beam-plasma configuration; Dispersion relation for the eigenfrequencies of the perturbed configurations.