Ferrite-Enhanced U-Shaped Internal Antenna for Large-Area Inductively Coupled Plasma System

A Ni–Zn ferrite-enhanced U-shaped internal inductive antenna (240 mm $times$ 2300 mm) operated at 2 MHz was used as a linear plasma source for an ultralarge-area plasma, and its plasma and electrical characteristics were investigated and compared with those of the antenna operated at 13.56 MHz without the ferrite. By the magnetic field enhancement, the operation of the source showed higher power transfer efficiency, lower antenna impedance, and lower RF rms voltage compared to that operated at 13.56 MHz without the ferrite. When photoresist etch uniformity was measured by etching the photoresist using a 40-mtorr $hbox{Ar/O}_{2} (7:3)$ mixture at 2 MHz by locating three U-shaped antennas in parallel, the etch uniformity less than 11% could be obtained on the substrate size of 2300 mm $times$ 2000 mm.      

Plasma-Pretreated Catalyst for Methanol Synthesis From Syngas

A new catalyst preparation method by combining the traditional coprecipitation method with an oxygen plasma pretreatment was developed in this paper. The ternary Cu/Zn/Al catalyst powders were first prepared by coprecipitation method, and then pretreated by the plasma in a fluidized-bed dielectric barrier discharge reactor with a carrier gas of a molar ratio of $hbox{O}_{2}/hbox{Ar} = 5/95$ . Then, the plasma-pretreated catalyst was conducted with the methanol synthesis test at the following conditions: $hbox{H}_{2}/hbox{CO}/hbox{N}_{2} = 64/32/4$, $Q = 900 hbox{sccm}$, $P = 4 hbox{MPa}$, and $T = 255 ^{circ}hbox{C}$. The plasma pretreatment could enhance the catalytic activity, e.g., the methanol selectivity increased from 28% to 72% and the methanol yield from 0.19 to 0.52 $hbox{g/g}_{rm cat.}cdothbox{h}$ , although the CO and $hbox{H}_{2}$ conversions were slightly decreased. On the other hand, the BET, inductively coupled plasma/optical emission spectroscopy, and X-ray diffraction analysis found that the catalytic properties did vary after plasma pretreatment. In short, this paper reveals that the plasma pretreatment is a viable process for preparation of Cu/Zn/Al catalyst in terms of methanol synthesis.      

Design and Numerical Optimization of a Cusp-Gun-Based Electron Beam for Millimeter-Wave Gyro-Devices

A novel thermionic cusp electron gun operating in the temperature-limited regime that produces a large-orbit electron beam through a nonadiabatic magnetic-field reversal was designed, analyzed, and optimized to give an electron-beam ideal for driving gyro-devices, particularly in the millimeter-to-submillimeter-wavelength range due to its small cross-sectional size. The annular-shaped axis-encircling electron beam had a beam current of 1.5 A at an acceleration potential of 40 kV, a tunable velocity ratio $alpha (= v_{ perp}/v_{z})$ between one and three, an optimized axial velocity spread $Delta v_{z}/v_{z}$ of $sim$ 8%, and a relative alpha spread $Deltaalpha/alpha$ of $sim$10% at an alpha value of 1.65.      

Energy Efficiency Analysis of the Discharge Circuit of Caltech Spheromak Experiment

The Caltech spheromak experiment uses a size A ignitron in switching a 59-$ muhbox{F}$ capacitor bank (charged up to 8 kV) across an inductive plasma load. Typical power levels in the discharge circuit are $sim$200 MW for a duration of $sim!! 10 muhbox{s}$. This paper describes the setup of the circuit and the measurements of various impedances in the circuit. The combined impedance of the size A ignitron and the cables was found to be significantly larger than the plasma impedance. This causes the circuit to behave like a current source with low energy transfer efficiency. This behavior is expected to be common with other pulsed plasma experiments of similar size that employ an ignitron switch.      

Low-Pressure Helicon-Plasma Discharge Initiation via Magnetic Field Ramping

Discharge initiation at low pressures and flow rates is investigated in the Madison Helicon Experiment flowing helicon source. At low pressures (below 14-sccm flow rate), a threshold magnetic field exists for discharge initiation which depends on RF power and gas flow rate. Above the threshold magnetic field, RF discharges start only after a significant delay (approximately seconds) and sometimes will not start at all. This threshold magnetic field is interpreted using electron multipactor arguments. A technique is described for initiating discharges at low flow rates and pressures $(lambda_{{rm en}, {rm iz}} ≫ L_{rm system})$ and high magnetic fields (above the threshold value). Without a static magnetic field present, the RF power is turned on, and a lower density $(≪ 10^{11} hbox{cm}^{-3})$ unmagnetized discharge occurs. The magnetic field is then applied, and the discharge transitions to the higher density (up to $10^{13} hbox{cm}^{-3}$) regime. Using this method, magnetized discharges can be started at flow rates as low as 1 sccm ( $1.8 times 10^{-4} hbox{torr}$ at $z = -91 hbox{cm}$ , $1.7 times 10^{-5} hbox{torr}$ at $z = 105 hbox{cm}$) at 500 W in a 1.04-kG magnetic field. This technique can be used to initiate low-pressure helicon discharges for basic plasma science experiments and other applications.      

Proof of Principle Experiments on Direct Generation of the $hbox{TE}_{11}$ Mode in a Coaxial Vircator

Experiments on a coaxial vircator with a sectioned emitter are reported. The emitting area is sectioned to form two opposing emitters in order to favor growth of the $hbox{TE}_{11}$ mode and inhibit growth of the $hbox{TM}_{01}$ mode that is usually excited in a coaxial vircator. Experiments are performed using a compact 320-J 400-kV Marx generator and a compact coaxial vircator built in a standard 8$^{primeprime}$ vacuum tube. The radiated magnetic-field strength is measured by means of four free-field (B-dot) probes, and experiments show that sectioning the emitter does, in fact, lead to generation of the $hbox{TE}_{11}$ mode.      

Generation of Plasma Wave at Pump-Wave Frequency and Second Harmonic Generation at Ultrarelativistic Laser Power

In this paper, the influence of ponderomotive and relativistic nonlinearities on the filamentation of an ultraintense laser pulse is investigated in three dimensions within the paraxial ray approximations. Generation of electron plasma wave (EPW) structure at pump-wave frequency and the second harmonic generation in these filamentary structures are reported. The generation of the plasma wave is due to intensity gradient (in the transverse direction of the laser beam in filamentary structure) and density gradient (due to ponderomotive-force effect). For typical laser–plasma parameters: The $hbox{laser intensity} = 2.5timesbreak 10^{20} hbox{W/cm}^{2}$; the $hbox{particles density} = 1.9 times 10^{19} hbox{cm}^{-3}$; and it is found that the maximum intensity of EPW is in the range of $2.0 times 10^{13} hbox{W}/hbox{cm}^{2}$. Interaction of the plasma wave with the incident laser beam leads to second harmonic generation, and the yield comes out to be $approx! 2.1 times 10^{-7}$.      

Atmospheric Pressure DC Glow Discharge in Semiconductor Gas Discharge Electronic Devices

The stabilization of dc glow discharges in a dc plasma is studied experimentally in air and neon media functions of pressure $p$, interelectrode distances $d$, and diameter $D$ of the cathode areas in the semiconductor gas discharge electronic devices (SGDED) with GaAs cathode. Comparision of current and discharge light emission (DLE) from SGDED are used for the determination of the stabilization under low- and atmospheric-pressure glow microdischarge conditions. It is found that uniform DLE can be generated in Ne up to atmosphere pressure different from the case in air under specific conditions. Apart from the homegeneous results, nonhomogeneous current–voltage characteristic forms are also observed for some parameter sets. The experimental results reveal different discharge behaviors in both gas media at atmospheric pressure.      

Computational Studies of Atmospheric-Pressure Methane–Hydrogen DC Micro Glow Discharges

Atmospheric-pressure methane–hydrogen micro glow discharges were computationally investigated using a 2-D hybrid model. The plasma model was solved simultaneously with a model for the external circuit. Simulations were conducted for a pin-to-plate electrode configuration with an interelectrode separation of 400 ${rm mu}hbox{m}$. The spatiotemporal evolutions of electrons, species densities, electric field, and electron and gas temperatures were studied. A total of 81 reactions were considered, which included electron–neutral, electron–ion, ion–neutral, and neutral–neutral reactions. An 84-step reaction mechanism consisting of 15 surface species and four deposited bulk species was considered. A time-stepping technique was employed to address the time scales of plasma transport (in microseconds) and neutral and fluid transport (in milliseconds) in 2-D simulations with detailed volume and surface chemistry. The simulations indicated $hbox{H}_{3}^{+}$ and $hbox{CH}_{5}^{+}$ ions to be the most prominent hydrogen and hydrocarbon ions. The gas temperature predictions suggested the discharge to be operating as a nonthermal glow discharge. The effect of discharge current on both plasma and deposition characteristics was studied. The simulations predicted a flat voltage–current characteristic, indicating the discharge to be operating in normal glow mode. The predicted voltage–current characteristic was found to be in favorable agreement with the experimental measurements. With an increase in discharge current, the deposition rate profile expanded in the lateral direction, suggesting that deposition occurred at the cathode spot.      

Dynamics of the Current Distribution in a Discharge of the PF-3 Plasma Focus Facility

In this paper, results are presented from studies of the dynamics of the plasma-current sheath and current distribution in the PF-3 facility, one of the largest plasma focus machines in the world. The experiments were done at input energy of $W = 290 hbox{kJ}$ and discharge current of $I sim 2 hbox{MA}$, with the chamber being stationary filled with the working gas. The current sheath parameters were measured with absolutely calibrated magnetic probes installed at different distances from the system axis and at different heights above the anode plane. The possibility is demonstrated of the formation of closed current loops due to the development of shunting breakdowns in the insulator region. The maximum residual plasma density at which the electrode gap remains magnetically self-insulated is estimated.      

Preliminary Study on Applications of an Atmospheric-Pressure Argon Plasma Discharge With a Single-Electrode Configuration

An atmospheric-pressure (AP) argon plasma discharge generated in a single-electrode configuration with the power supply operating at a frequency of 45 kHz is employed to perform some applications, such as the treatment of the interior surface of a medical infusion tube, hydrophilic modification of insulator surface, hardening of metal surface, and acidification treatment of water. It is shown that the active gases ( $hbox{O}_{2}$ and $hbox{N}_{2}$) mixed in a carrier gas (Ar) play a significant role in carrying out such applications. A preliminary study on its applications is presented to demonstrate the promising potential of AP single-electrode-configuration plasma jet.      

Performance Analysis of a Diagonal MHD Accelerator for Space Propulsion

The performance of a diagonal magnetohydrodynamic (MHD) accelerator has been numerically investigated. Studies were carried out using air plasma as a working gas in an equilibrium condition based on the MHD Augmented Propulsion Experiment channel designed by NASA. The MacCormack scheme is employed in order to solve the set of differential equations with MHD approximations. The fundamental performance of a diagonal MHD accelerator considering both flow performance along the channel and propulsion performance has been evaluated under various applied input currents and magnetic fields. The optimum performance is dominated by ${bf j} times {bf B}$ Lorentz body force acceleration, while it is increased with Joule heating and the ${bf u} times {bf B}$ term's contribution, which are detrimental to the propulsion performance. Moreover, friction forces resist the flow performance, particularly near the channel exit.      

Production of Capacitively Coupled Atmospheric Plasma Jet With Multiring Electrodes for the Medical Plasma Tool

An atmospheric capacitively coupled plasma jet has been developed by using multiring-electrode configurations for medical applications. It was found that the discharge conditions for plasma-jet production expanded with the increase of the number of pairs of multiring electrodes. The length of the plasma jet increased with the increase of the injected power and helium-gas flow rate. The temperature of the plasma jet, measured by a thermocouple, decreased with the increase of gas flow rate and was then attained to be around 50 $^{circ}hbox{C}$ at a helium flow rate of 30 L/min. Optical measurements of plasma-jet emission showed various optical emissions from helium atoms, nitrogen atoms, hydroxyl radicals, and metal atoms originating from the electrode material.      

Modeling of the Dynamic Plasma Pinch in Plasma Focus Discharges Based in Von Karman Approximations

Dynamic plasma pinches occur in a variety of devices, as $Z$ -pinches and plasma focus. In this paper, a lumped parameter model of a dynamic plasma pinch produced in a plasma focus discharge is presented. The model is based in Von Karman approximations of the radial density and velocity profiles, which leads to the reduction to a system of ordinary differential equations describing the dynamic evolution of the pinch compression and expansion. The model was coupled with a fusion kernel to produce an estimate of the neutron yield per pulse. The calculations were tested against available data of the pressure–yield curve of seven experimental devices ranging from 1 to 250 kJ, showing excellent agreement, particularly regarding the curvature of the pressure–yield curve.      

Optimization of Sustain Electrode Gap for High-Efficiency Plasma Display by Using a Counter-Electrode Structure

A counter-electrode structure as a microscaled dielectric barrier discharge for an application to the alternating-current plasma display has been investigated with six in-test panels fabricated by using a thick-film ceramic-sheet method. Based on observations of infrared (IR) emission, the optimum sustain electrode gap to generate an efficient positive-column-like microdischarge plasma was suggested. The IR emission as well as the firing and sustain voltages increases with the increasing electrode gap, and the positive-column-like microdischarge plasma was built up for electrode gaps over 400 $muhbox{m}$, which can be used for an intense vacuum ultraviolet source. Furthermore, the luminance and luminous efficiency, as well as the panel capacitance of the counter-electrode structure, were compared with those of the conventional reference structure.      

Studies on the Measuring Method of Number Density of Ions in the High Speed Flow Field

At present, the method of using a parallel-plate probe to measure the number density of ions at atmosphere has some limitations such as big size of probe, low velocity of gas flow allowed to measure, and low accuracy. In this paper, a detector with a spherical probe is fabricated and is used to measure the number density of ions. The diameter of probe can be reduced to 6 mm. The highest velocity that can be measured is extended to 28 m/s, and the collecting rate is up to 100%. The spatial distribution diagram of ion number density is also given, with a cross section of 0.36 $hbox{m}^{2}$. Then, an effective method is provided to measure the number density of ions generated from the miniature ion source or in the gas flow with high velocity.      

Fabrication and characteristics of solution‐processed graphene oxide–silicon heterojunction

We demonstrate the fabrication of a solid state heterojunction photovoltaic device with solution‐processed graphene oxide (GO) and n‐Si. Partially reduced GO with a high optical gap (2.8 eV) was spin‐coated on the n‐Si substrate and a heterojunction device was fabricated with the structure of Au/pr‐GO/n‐Si. In the fabricated device, incident light was transmitted through the thin GO film to reach the junction interface, generating photoexciton, and thereby a photovoltaic action was observed. By means of a built‐in electric potential at the GO/n‐Si junction, photoexcited electrons and holes can be separated, transported and collected at the electrodes.

     

Epitaxial growth of titanium oxide thin films on c-cut and α-cut sapphire substrates

C-cut and α-cut sapphire substrates are used to grow epitaxial titanium oxide films by pulsed-laser deposition at 700 °C under a controlled oxygen pressure in the 10⁻¹-10⁻⁵ mbar range. The rutile phase is evidenced in films whatever the substrate and the oxygen pressure while the anatase phase is only observed on c-cut sapphire substrate and for oxygen pressure down to 10⁻³ mbar. No other titanium oxide phases (i.e. TiO, Ti₂O₃ or Magneli phases) are identified despite the oxygen-deficiency observed in films grown at low oxygen pressure. According to asymmetric X-ray diffraction measurements performed on films, the main axis growth and the in-plane epitaxial relationships between titanium oxide films and sapphire substrates are found to be depending on the orientation of the sapphire basal plane and on the oxygen pressure. The anatase crystallites are highly oriented with the following epitaxial relationship . The rutile phase is (2 0 0) oriented on c-cut sapphire substrate and displays two distinct in-plane relationships: . The use of α-cut sapphire substrate leads to the growth of rutile crystallites (2 0 0) or (1 0 1) oriented. In these cases, the in-plane orientations are , respectively. For the two substrates used, schematic views of atomic arrangement of the different interfaces are proposed.     

Pb2CrO5 photovoltaic device for the detecting light-beam position

A light position detector operating through a photovoltaic effect of a Pb₂CrO₅ ceramic disk with a pair of Au planar electrodes is investigated. A fabrication technique and the basic characteristics of the photovoltaic device for position detection are described. A peak photovoltage is obtained around the edge of the electrode for an incident light beam. The incident light beam shape and the electrode pattern are important factors for obtaining a linear relation between the light-beam position and the output signal from the device. A device fabricated for detecting one-dimensional light position has a high position resolution of 0.5 m and a good linearity of ±2 m or less. A two-dimensional device can be fabricated in the same way as the one-dimensional device, except for the electrode pattern. A method for two-dimensional light position detection using a Pb₂CrO₅ photovoltaic cell is demonstrated for a green LED as a light source.     

A novel preparation method and investigation of sprayed CdS films

The main reason for the low photovoltaic efficiency of Cu₂S/CdS cells, in which the CdS film is deposited by solution spraying, is the very small average dimensions of the crystalline grains. The difficulty in depositing films with transverse dimensions of crystalline grains larger than 1 m is due to the fast decrease of substrate temperature during the spraying deposition of the CdS film. We have since arranged an experimental set-up able to maintain the surface temperature of the substrate constant. In this way it is possible to control the parameters which affect the deposition and to obtain a high degree of reproducibility of morphological properties. Average grain sizes of more than 1 m are obtained. We have investigated the crystalline grain sizes and the film thickness as a function of the deposition temperature and the spraying rate.Work supported by Ministero Pubblica Istruzione and Centro Regionale Ricerche Nucleari e Struttura della materia