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Summary form only given. An appropriate boundary condition describing electron balance at the cathode surface is of fundamental importance to fluid modeling of gas discharges. This boundary condition is conventionally formulated in terms of the escape factor. Various approaches have been applied to evaluation of escape factors. Recently, escape factors for argon have been obtained by means of Monte...
Summary form only given. Radiofrequency helicon waves are excited in argon, helium, and deuterium at a frequency of 13.56 MHz with input RF powers of up to 2.5 kW using a half-turn double helix antenna. The effect on radial density profiles and ionization efficiency due to nonuniform axial static magnetic field profiles is investigated, with peak magnetic fields of up to 1 kG. The ionization efficiency...
Summary form only given. A He/O2 plasma jet has been developed that operates using radio frequency (RF) power and produces a stable homogeneous discharge at atmospheric pressure. An optical emission spectroscopy has been used to observe the electronically excited species from the plasma jet and the discharge characteristics for the different gas mixture of He/O2 were studied with a current and a voltage...
Summary form only given. The current density profile associated to the current sheath produced in a 5.6 muF Mather type plasma focus operated at 20 kV was studied by means of a magnetic probe placed in the interelectrodic space at different axial positions along the gun. From the probe signal, both, the arrival time and the temporal width of the current sheath, were measured during the run down phase...
Summary form only given. Cylindrical Langmuir probes are widely used in a variety of applications. Nevertheless, many non-ideal characteristics have not been fully investigated. In this work, we examine the relationships between probe length, radius, and plasma Debye length and their effect on experimentally obtained I-V curves. The plasmas investigated are low pressure weakly collisional plasmas...
Summary form only given. The radial compression of cylindrical plasmas induces acceleration voltages considerably higher than those used to charge the capacitor bank employed in the discharge. These phenomena typically occur in Z-pinches and plasma focus devices, where 100 keV X-rays are commonly observed in machines operated with charging voltages of 50 kV or less. Several accelerating mechanisms...
Summary form only given. Ready neutralization of ion beams by a source of electrons is a well known phenomenon, but the physics behind that process is not well understood. As electric propulsion devices move into the micro and macro regimes with colloids, FEEPs, and large arrays of thrusters, the interactions between the neutralizer and the thruster are under examination. A series of 2D particle-in-cell...
Summary form only given. Electron sheaths are normally only present near small probes when they are biased more positive than the plasma potential or at electron emitting surfaces in weakly collisional low pressure plasma. Here, electron sheaths created along the axis of a large positively biased plate (diameter = 10 cm) located in a multi-dipole argon plasma are described. Experimental data show...
Summary form only given. Low-frequency (LF) wave activity in the megahertz frequency range, which has been detected in various helicon plasmas excited by m=1 antennas, is thought to be a substantial factor in the discharge performance. In this report, LF turbulence is characterized comparatively in two different plasma sources excited at 13.56 MHz by m=0 antennas: in a conventional helicon plasma...
Summary form only given. We have recently employed data obtained from laser-induced fluorescence (PLIF) measurements to provide the initial density distribution for 2D-MHD calculations of argon Z-pinches. In previous studies those data were derived from hydrodynamics calculations. The measured data introduce a feature not present in the calculated initial conditions, namely, the presence of sub-millimeter...
Summary form only given. The transport properties of dense plasmas, which are usually produced by strong shock wave compression or capillary discharge, exhibit nonideal characteristics, e.g., insulator-metal transition, that can not be described by classical theories. This paper presents a practical computational model to evaluate the ionization balances and electrical conductivities of a dense plasma...
Summary form only given. When simulating high power microwave tubes, tube operation can influence the pulsed power network as well as vice versa. Commonly used approximations, such as a wave emitting/absorbing boundary condition, do not capture the dynamic mutual interaction of pulsed power with the microwave tube. For example, impedance collapse due to diode closure will cause both a drop in the...
Summary form only given. When a plane electromagnetic wave, traveling in free space, falls on an object, it gives rise to a scattered field in all directions. The ratio of the scattered field to the incident field intensity is related to the radar cross-section (RCS). A collisional unmagnetized plasma; which has a complex dielectric constant, can be used as a good absorber of electromagnetic waves...
Summary form only given. Researchers are interested in rapid switching high-current diodes for applications including accelerators, microwave sources, and flat panel displays. Gas-filled diodes, such as the pseudospark, are one class of candidates for such high-current applications. To yield a better understanding of their operation, numerical simulations of these devices must include a number of...
Summary form only given. Intense laser ablation induced shocks have been found use in the field of high pressure and high energy density physics studies viz. equation of state (EOS) measurements, phase transformations, understanding astrophysical high density plasma phenomena etc. Several megabars of pressures can now be generated, under laboratory conditions using modest laser intensities. To achieve...
Summary form only given. The state-of-the-art in first principles physics software has greatly advanced in the last few years though the advent of highly efficient, scalable parallel software and ubiquitous Beowulf-class clusters. In the arena of high power microwave and X-ray sources, it is not unusual to simulate multi-dimensional (2- and 3-D), fully electromagnetic situations with fidelity sufficient...
Summary form only given. A direct simulation Monte Carlo (DSMC) method is being added to VORPAL to model dilute (large Knudsen number) gases. VORPAL is a multi-dimensional, parallel particle-in-cell (PIC) plasma simulation code that supports a variety of models for both plasma and electromagnetic fields. The addition of the DSMC capabilities will allow VORPAL to run hybrid simulations of gas/plasma...
Summary form only given. Global positioning satellites (GPS) have been experiencing an anomalous, accelerated degradation of solar array power. This phenomenon, analyzed since the early 80's, remains unexplained. Recently, low-energy (<50 keV) oxygen ions (O+) have been identified as a possible, still unexplored, cause of degradation of solar panel coverglass materials. Oxygen ion implantation...
Summary form only given. In the past there has been considerable research performed using electromagnetic plasma thrusters as the primary ion source in sputtering applications. In the experiments conducted here, thin film coatings of various hard metallic alloys and oxides were applied to stainless steel electrodes using ion beam deposition. An SPT type Hall effect thruster capable of producing an...
Summary form only given. One of the main advantages of the plasma cathode electron guns is its ability to produce electron beam under the higher operation pressure up to fore-pump pressure range. Present work is devoted to plasma electron guns that were designed especially to generate narrow focusing electron beams under the high pressure. To produce narrow focusing beam two contradictory requirements...
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