B. L. Meena

Discharge analysis and electrical modeling for the development of efficient dielectric barrier discharge

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 two coaxial quartz double barrier DBD tubes, which are filled with Xe/Ar at different pressures. A sinusoidal voltage up to 2.4 kV peak with frequencies from 20 to 100 kHz has been applied to the discharge electrodes for the generation of microdischarges. A stable and uniform discharge is produced in the gas gap between the dielectric barrier electrodes. By comparisons of visual images and electrical waveforms, the filamentary discharges for Ar tube while homogeneous discharge for Xe tube at the same conditions have been confirmed. The electrical modeling has been carried out to understand DBD phenomenon in variation of applied voltage waveforms. The simulated discharge characteristics have been validated by the experimental results.

Analysis of Discharge Parameters in Xenon-Filled Coaxial DBD Tube

In this paper, a xenon-filled coaxial dielectric barrier discharge (DBD) has been studied to understand the high-pressure nonequilibrium nonthermal plasma discharge. A quartz coaxial DBD tube (ID: 6 mm, OD: 12 mm) at 400-mbar xenon-filled pressure has been used in the experiment. A unipolar pulselike voltage up to a-6-kV peak working at 30 kHz has been applied to the discharge electrodes for the generation of microdischarges. A single discharge is observed per applied voltage pulse. Visual images of the discharge and electrical waveform confirm the diffused-type discharges. The knowledge obtained by dynamic processes of DBDs in the discharge gap explains quantitatively the mechanism that is obtained in the ignition, development, and extinction of DBDs. The behavior of different discharge parameters has also been analyzed. From the experimental results and equivalent electrical circuit, the dynamic nature of equivalent capacitance has been reported. The relative intensity analysis of the Xe peak in the optical emission spectra (172 nm) has also been carried out for different supplied powers, and it is found that the radiation power has increased with supplied power.

Characterization of High Power Pseudospark Plasma Switch (PSS)

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. For this switch, as a cold cathode based 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 23 kV and 7 kA in single stage. High voltage conditioning and characterization is still in progress. The paper includes the introduction with working principle, description of the demountable set up, simulation by TriComp, AMaze and OOPIC Pro (Without Comparison among them), and switching behavior.

Investigations of a high current linear aperture radial multichannel pseudospark switch

In this paper, a high current linear aperture radial multichannel Pseudospark switch (LARM-PSS) is reported which has been analyzed for its high current characteristics. In order to enhance hold-off voltage and support hollow cathode effect for the ignition of the discharge in this configuration, the field penetration analysis through circular and linear apertures of the electrodes has been carried out. The linear apertures in the electrodes increase the current handling capacity than that of circular aperture electrodes without significant compromise of the hold-off capacity. The developed LARM-PSS switch is capable to hold voltage up to 25 kV at gas pressure between 10 and 50 Pa for hydrogen. The switch has been operated using a 800 nF capacitor bank and conducted an effective charge up to 1.5 C with peak switch current ∼20 kA at applied voltage 19 kV.

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.

Design and development of a high current pseudospark switch for pulse power applications

Recently it has been realized that for high current applications a radial channel Pseudospark Switch (PSS) is a right choice whereas a coaxial PSS is better suited for medium power applications. An effort has been made to design and develop a high current PSS for pulse power applications and the initial results of the same are presented in this paper. It utilizes linear discharge apertures (length greater than width) in the electrodes geometry. The linear aperture helps in significantly higher current conduction without discharge constriction. The electrostatic simulations of the geometry have been carried out using Omni Track code to analyze voltage penetration through the linear apertures. To study the voltage profile, discharge phenomenon and dynamics of the charge particles in the radial channel PSS, a particle-in-cell (PIC) simulation code “Oopic-Pro” has also been used. The simulated results have been applied as a feedback to design and develop this PSS on the specified parameters. A demountable high current pseudospark switch with radial discharge channel is ready for experimentation.

Electron beam analysis of pseudospark sourced electron gun

Summary form only given. Recently, the pseudospark (PS) discharge is recognized for producing electron beams with the highest combined current density and brightness of any known type of electron sources1. In the PS discharge there is fast voltage breakdown together with fast current rise and development of complex discharge with different discharge phases useful for high power plasma switches, EUV radiation, high density electron beam generation, etc2. In this type of discharge there is self consistent formation of electron beam during the breakdown process1–2. We have recently designed and developed a PS discharge based plasma cathode electron gun (PCE-Gun)3. Experimental investigations are carried out using this electro n gun at different operating conditions in argon and hydrogen atmospheres. Studies of the production and propagation of the electron beam from the PS discharge has also been carried out. The electron beam profile is investigated in axial and radial direction with the help of circular ring arrangement inside the drift region. It is observed that the electron beam propagates more than 250 mm without external guiding magnetic field. The current density estimation of the focusing and defocusing point of electron beam is also analyzed which is helpful for the development of plasma assisted microwave sources. The PIC simulation complements the results. The plasma generation process by impact ionization is examined from the simulations, showing the effect on supplying the electrons that determine the density of the beam.

Investigation of discharge parameters in Xenon filled coaxial DBD tube

In this paper a Xenon filled coaxial dielectric barrier discharge (DBD) has been studied to understand the high pressure, non-equilibrium, nonthermal plasma discharge. A quartz coaxial DBD tube (ID: 6mm, OD: 12 mm) at 400 mbar Xenon filled pressure has been used in the experiment. Different applied voltage waveforms at 30 kHz using RF generator as well as pulse power source have been applied to the discharge electrodes for the generation of microdischarges. Visual images of discharge and electrical waveform confirm the diffused type discharges. The knowledge obtained by dynamic processes of DBDs in the discharge gap explains quantitatively the mechanism that is obtained in ignition, development and extinction of DBDs. The behaviour of different discharge parameters has also been analyzed. From the experimental results and equivalent electrical circuit, the dynamic nature of equivalent capacitance has been reported. The relative intensity analysis of the second continuum of the Xe discharge (172 nm) has been carried out for different applied voltages and it is found that the radiation power has increased with voltage.

Investigation of beam parameters to design plasma filled BWO

Plasma assisted devices are unique source for microwave radiation [1]. The Plasma assisted BWO is a novel combination of plasma cathode electron-gun (PCE gun) and plasma filled slow-wave structure to produce microwave radiation. In Plasma-assisted microwave generator the electron beam exhibits two dimensional motions in the slow wave structure. In these devices, the beam self electrostatic fields, which play a destructive role in the beam transport, can largely be compensated by ions. The electron beam propagates in the ion-focusing regime (Bennett pinch)[2], which eliminates the requirement of external magnetic field. For efficient operation of these devices it is important to know the dynamics of beam generated by plasma cathode electron gun. The present work deals with the results of simulated studies of stationary and non stationary effects in the beam dynamics in X- band plasma assisted BWO and their theoretical interpretation. The simulation of the slow wave structure (SWS) has been done using different CAD tools for designing the plasma assisted BWO. The simulation has been performed for analysis of beam dynamics in the periodically rippled SWS in cylindrical form. A series of experiments has been performed for generating high intensity electron beam [3] from PCE gun under different operating condition. The particle in cell code has been used to investigate the different beam parameters. Comparative measurement for beam energy at different locations in drift region has also been performed experimentally.