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We consider the singularity crossing phenomenon in differential-algebraic equations (DAEs) of Hall MHD systems in one spatial dimension. The Hall MHD DAEs have singularities with impasse points, pseudoequilibrium points, or singularity-induced bifurcation (SIB) points. The pseudoequilibrium and SIB points allow for smooth transitions between the plus (supersonic) and minus (subsonic) Riemann sheets. Within the singular pseudoequilibrium points, there may exist only one analytic trajectory crossing the sonic curve (as in the case of SIB point), two analytic and two other trajectories of lower degree of smoothness in the case of pseudosaddle points, or two analytic and an uncountable number of trajectories of lower smoothness in the case of singular pseudonodes. In this paper, we show examples of singular points in Hail MHD systems described by DAEs and explain the singularity (also called the sonic or forbidden curve) crossing phenomenon by using the recent developments in the qualitative analysis of DAEs. Index Terms--Bifurcations, differential-algebraic equations (DAEs), Hall MHD, singularities.

In this paper, a chemical model to predict barium oxide depletion from hollow cathode insert will be developed. This model is based on the knowledge of the ternary diagram that describes the BaO-CaO-[Al.sub.2][O.sub.3] system and takes also into account the diffusive motion of barium oxide inside the insert. A comparison between numerical and experimental data is made to determine the diffusion coefficient inside the insert. The diffusion coefficient found presents an Arrhenius trend with activation energy similar to the one of barium oxide evaporation. A 2-D model is used to demonstrate how the temperature profile along the insert is a key parameter to calculate barium depletion. This is the first model the authors are aware of that includes both the complex chemistry of the BaO-CaO-[Al.sub.2][O.sub.3] system and the diffusion motion of BaO from the insert core to the surface. Index Terms--Barium oxide depletion, hollow cathode lifetime, insert chemistry.

In this paper, two designs of the rectangle-pulse Marx generator based on pulse-forming network (PFN) for pulse-power application are reported. The PFN is composed of inductors and capacitors. Proposed schemes consist of several identical PFNs that are connected according to Marx generator scheme. PFN Marx generators can output rectangle pulse several hundreds of nanoseconds in duration and several tens of nanoseconds in rising time. The effect of component parameter to the waveform is studied. Prototypes made of four PFNs have been tested. One of the prototypes is designed according to classical Marx mode, while another is designed as an L--C Marx generator in which only one command switch and one isolating switch is needed. In a 500-ns duration, 65-ns rising-time rectangle pulse has been achieved on the matching load. Index Terms--Classical mode, L--C mode, Marx generator, pulse-forming network (PFN), rectangle pulse.

Fast neutrons from deuteron-deuteron fusion reactions were used for a study of fast deuterons in the PF-1000 plasma-focus device. The energy spectrum of neutrons was determined by the time-of-flight method using ten scintillation detectors positioned downstream, upstream, and side-on the experimental facility. Neutron energy-distribution functions enabled the determination of axial and radial components of energy of deuterons producing the fusion neutrons, as well as a rough evaluation of the total energy distribution of all fast deuterons in the pinch. It was found that the total deuteron energy-distribution function decreases with the deuteron energy more slowly than the tail of the Maxwellian distribution for 1-2-keV deuterons. Index Terms--Energy spectrum of fast deuterons, neutron production, plasma diagnostics, plasma focus (PF).

Byline: W.W. Plotczyk, A. Resztak, A. Szymanski The paper presented selected problems of brown coal as well as another solid carbonaceous materials pyrolysis and gasification in a plasma jet. Introduction of the coal into thermal plasma caused its decomposition into simpler components. Among the gaseous products the most important are: CH.SUB.4, C.SUB.2H.SUB.2, C.SUB.2H, H.SUB.2, CO and CO.SUB.2. In an active plasma containing oxygen and/or water, coal conversion to synthesis gas is very high, up to 90%. The content of CO in the after reaction gas is nearly 60% and that of CO.SUB.2 does not exceeded 3 vol.%. Effective coals pyrolysis to C.SUB.2H.SUB.2, and CO.SUB.2 take place in hydrogen and argon plasma. Total decomposition into gaseous products is close to or exceeded the volatile matter content in the substrates. Studies performed at Warsaw University on brown coal pyrolysis in H.SUB.2 and Ar plasma confirmed this statement.

Near space, the region between controlled commercial airspace and LEO offers capabilities critical to emerging national defense needs. Two emerging technologies, high-altitude buoyant lift systems and plasma thrust technology are explained. Exploiting near space for defense purposes will depend on success of emerging air plasma technologies.

Results of high-speed electrical and optical diagnostics are used as a basis to discuss a new surface flashover model. Outgassing, caused by electron stimulated desorption, is found to play a crucial role in the temporal flashover development. Dielectric unipolar surface flashover under vacuum is experimentally characterized by a three-phase development, which covers a current range from [10.sup.-4] A to 100 A. Phase one comprises a fast (several nanoseconds) buildup of a saturated secondary electron avalanche reaching current levels of 10 to 100 mA. Phase two is associated with a slow current amplification reaching currents in the Ampere level within typically 100 ns. The final phase is characterized by a fast current rise up to the impedance-limited current on the order of 100 A. The development during phase two and three is described by a zero-dimensional model, where electron-induced outgassing leads to a Townsend-like gas discharge above the surface. This is supported by time-resolved spectroscopy that reveals the existence of excited atomic hydrogen and ionic carbon before the final phase. The feedback mechanism toward a self-sustained discharge is due to space charge leading to an enhanced field emission from the cathode. A priori unknown model parameters, such as outgassing rate and gas density buildup above the surface, are determined by fitting calculated results to experimental data. The significance of outgassing is also discussed with a view to microwave surface flashover. Index Terms--Electric breakdown, flashover, high power microwave, optical spectroscopy, outgassing, pulse measurements, surface flashover.

Capacitively coupled rf plasma sources are used extensively in the microelectronics industry, for commercial production as well as laboratory research and development. This paper deals with the physics of the processes involved and development, both theoretical and analytical, that have helped in understanding the discharge processes. The review begins with a description of the rf discharge. A literature survey provides the experimental efforts that have been directed towards investigating the physics of the capacitively coupled discharges. Measurements of the various plasma parameters are dealt with. Analytical and numerical methods that have been successfully used to model the discharge processes are treated in considerable detail. The paper concludes with a brief comparison of the various techniques.

Tokamak magnetic fusion research has progressed to an advanced project, i.e., ITER (International Thermonuclear Experimental Reactor). Therefore, existing tokamaks must explore operational scenarios necessary for a high-performance plasma while simultaneously suppressing any disruptive instabilities. To implement this investigation, various advanced real-time controls using processed profile data and all available actuators should be tested in the experiments. To satisfy these requirements at the large tokamak JT-60, we are upgrading its original real-time control system [I] completely. Two criteria for the new system configuration have been adopted: (i) The distributed processors for the measurements, actuators, and supervisory controllers (SVCs) are linked through a 'reflective memory (RM)' network for fast, real-time communication. The profile data in the RM modules are also updated in real time. (ii) For efficient parallel and pipeline processes performed by multiple controllers, synchronization is provided from two sources: external hardware clocks and software counters in the RMs, which are updated by the SVCs. For a control function, the following simple and flexible method has been employed to perform various experimental proposals: New test control methods are first registered in the supervisory controllers. In accordance with the preprogrammed waveforms that indicate which control method to use, the SVCs select the correct control method in real time. The upgraded configuration of the JT-60 plasma control system and its effectiveness in seeking advanced operational scenarios applicable to ITER are discussed in detail.

The timing system is an essential part of the tokamak Tore Supra. It provides the synchronisation of all of the triggers necessary for a plasma discharge. Operational since 1988, it has been used for 26000 pulses of Tore Supra without significant change or upgrade. However in 1999 it has been undergoing a staged modernisation. Hence this new timing system with a designed flexible and open-ended architecture, together with a more user-friendly man-machine interface, is ready to accept new concepts which will be necessary for the control of long discharges (up to 1000 s).