Mahesh Kumar

Analysis of Power in an Argon Filled Pulsed Dielectric Barrier Discharge

In this paper an argon filled coaxial dielectric barrier discharge (DBD) has been studied to understand the detail of power transfer from a unipolar square pulse to plasma during discharge. A dielectric barrier discharge based diffuse pulse discharge and its electrical characteristics are investigated. A quartz coaxial DBD tube filled at different pressures is used in the experiment. A unipolar pulse voltage of different peak voltages and frequencies has been applied to the discharge electrodes for the generation of microdischarges. Two current pulses are used for two consecutive discharges per applied voltage pulse. The second discharge, which occurs at the falling flank of the voltage pulse, is induced by the charges stored on the dielectric barrier during the first discharge. It has been deduced that the power supplied to ignite the first discharge is partly stored to ignite the second discharge when the applied voltage decays. This process ultimately leads to much improved power transfer to the plasma. The knowledge obtained from dynamic processes of the DBDs in the discharge gap explains quantitatively the mechanism of ignition, development and extinction of the DBDs.

Pseudospark switch development for pulse power modulators

The Pseudospark switch is able to control high voltage and high current discharges and operates at low pressure like thyratron but much simpler in construction and does not suffer in electrodes wear. This switch is bipolar and has 100 % reverse current capability, much faster than thyratron and has applications in pulse power modulators, linear accelerators, laser systems etc. Such switch has been developed at CEERI Pilani and tested in a demountable setup. Switching behavior has been observed at 22 kV and 7 kA in hydrogen atmosphere (13 Pa). Electrodes shaping and high voltage gap has been simulated in ESTAT and designed accordingly. For this switch, as a cold cathode, a ferroelectric trigger source has also been developed and characterized. High dielectric material has been opted for such a source. The hold off voltage can be doubled if the gap of the electrodes is stacked to two single stage gaps. Such stack of two single stage switches has also been fabricated in a demountable setup. Switching behavior has been observed up to 40 kV and 2.9 kA. High voltage conditioning and characterization is still in progress. In this paper design of the electrodes, ferroelectric source, description of the demountable set up, fabrication, processing of the Pseudospark switch and switching behavior have been presented and discussed.

Discharge Characteristics of Dielectric Barrier Discharge (DBD) based VUV/UV Sources

Dielectric-barrier discharges (DBDs) are characterized by the presence of at least one insulating layer in contact with the discharge between two planar or cylindrical electrodes connected to an AC/pulse power supply. The dielectric layers covering the electrodes act as current limiters and prevent the transition to an arc discharge. DBDs exist usually in filamentary mode, based on the streamer nature of the discharges. The main advantage of this type of electrical discharges is that nonequilibrium and non-thermal plasma conditions can be established at atmospheric pressure. VUV/UV sources based on DBDs are considered as promising alternatives of conventional mercury-based discharge plasmas, producing highly efficient VUV/UV radiation. The experiments have been performed using coaxial and planar geometry of DBD (gas gap: 1–3 mm) made of quartz with N2/Ar/Xe gas at different pressures. A proper ultra high vacuum system and gas filing system has been made for the processing & characterization of DBD tubes. A RF generator (20-100 kHz, 0-2.4 kV peak) is used for discharges in DBD tube. A stable and uniform discharge is produced in the gas gap between the dielectric barrier electrodes. The discharge characteristics have been analyzed by V-I characteristics & Lissajous figure and found that the spatial discharge processes varies strongly according to the applied voltage waveform, pressure of filled gas and geometry of tube.

Experimental Investigation of Pseudospark generated electron beam

The pseudospark (PS) discharge is, however, more recently recognized as a different type of discharge which is capable of generating electron beams with the highest combined current density and brightness of any known type of electron source. PS discharge is a specific type of gas discharge, which operates on the left-hand side of the hollow cathode analogy to the Paschen curve with axially symmetric parallel electrodes and central holes on the electrodes. The PS discharge generated electron beam has tremendous applications in plasma filled microwave sources where normal material cathode cannot be used. Analysis of the electron beam profile has been carried out experimentally for different applied voltages. The investigation has been done at different axial and radial location inside the drift tube in argon atmosphere. This paper represents experimentally derived axial and radial variation of the beam current inside the plasma filled drift tube of PS discharge based plasma cathode electron (PCE) gun. With the help of current density estimation the focusing and defocusing point of electron beam in axial direction can be analyzed. It has been further confirmed the successful propagation of electron beam in confined manner without any assistance of external magnetic field.

Technological development for X-band Plasma Assisted Slow Wave Oscillator (PASOTRON)

Plasma assisted microwave devices are unique source for microwave radiation. This paper presents the status for development of X-band Plasma Assisted Slow Wave Oscillator (PASOTRON) of peak power 0.5MW.

Glass to silicon anodic bonding

Glass-to-silicon anodic bonding is a well known process for fabricating number of microelectromechanical components and subassemblies. Experiments have been carried out by varying bonding parameters, i.e. temperature and bias voltage, to get strong bond between silicon and 7740 pyrex glass pieces. Bias voltage in the range of 400 - 450 V at 420 degree(s)C appears to be appropriate for quality bonds between silicon and glass.

Batch Fabrication of Millimeter-Wave Silicon Impatts

Large number of millimeter wave Impatt diodes have been fabricated out of reasonably large size silicon wafer with very good uniformity in electrical characteristics using the technique reported here. Modification in processing adopted in the present work led to very high yield and improved thermal impedance during packaging of Impatts. These improvements are due to better surface finish in integral heatsink pads and controlled thinning. The present process has been tried on silicon SDR and DDR Impatts over a frequency range of 10 to 100 GHz. Other devices like silicon Baritts and GaAs transferred electron devices have also been batch fabricated successfully using the same technique.

Electrical and optical characterization of DBD based XeCl UV excimer source

In recent decades, interest in development of novel UV/VUV sources with spontaneous emission has grown1. Among the all UV/VUV sources, excimers occupy major attention due to the many characteristics, such as, technological features, design, the service life, the cost, etc. In all types of known excimer sources, Dielectric Barrier Discharge (DBD) is most effective and low cost technique2. In this work a DBD based XeCl UV excimer source has been developed. In the developed volume discharge (VD) configuration of DBD source, the temporal behaviour of the electrical quantities of the discharge has been obtained using an equivalent electrical circuit model3 to electrically characterize the developed source. Furthermore, to identify the dependency on diffusion process an emission spectroscopy analysis is also performed. The source is a single barrier DBD filled with binary mixture of xenon and chlorine gases. A unipolar pulse-like waveform has been used to excite the discharge. Based on the electrical and spectroscopy analysis, the discharge parameters are obtained which has been optimized to improve the radiation efficiency of the rare gas monohalide XeCl* (308nm) from this source. This particular spectral line is highly applicable for skin treatment. The nonexistence of the mercury in the excilamps is the creditable to cite and the DBD based excilamps are giving the competition to the mercury filled lamps which are ecological insecure for the human health.

Experimental study of single barrier DBD for the application of water treatment

A dielectric barrier discharge (DBD) based light source has been developed for the sterilization of water. For this a single barrier DBD cell with quartz (low dielectric loss and high breakdown strength) as dielectric has been used. Six numbers of linear strips of titanium gold are coated using magnetron sputtering technique on the diametrical opposite portions of the outer surface of the quartz tube. A helical tungsten electrode has been used as cathode to which a pulsed high voltage signal has been applied to strike the discharge. The outer striped electrodes are grounded. In this paper an effort has been made to evaluate the germicidal effect of the developed DBD tube. A series of experiments have been carried and decontamination study of autoclaved water has been performed using air as a working gas. The developed DBD cell is non-toxic and has advantages over the other conventional methods like dry heat, auto clave, γ-ray irradiation. Sterilization of the E. Coli bacteria (diluted in water) has been performed using this DBD source and results are illustrated.

Investigation of electron beam parameters inside the drift region of plasma cathode electron gun

This paper presents experimental studies for the production and propagation of an electron beam from a single gap pseudospark discharge based plasma cathode electron (PCE) gun. The generated electron beam has been successfully propagated for more than 25 cm in a gaseous environment without application of external guiding magnetic field at different operating conditions. The electron beam losses due to recombination with ions and collision with walls of drift space have been estimated. The electron beam profile has also been analyzed in the drift region of the gun.