Udit Narayan Pal

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.

Development of large volume double ring penning plasma discharge source for efficient light emissions

In this paper, the development of large volume double ring Penning plasma discharge source for efficient light emissions is reported. The developed Penning discharge source consists of two cylindrical end cathodes of stainless steel having radius 6 cm and a gap 5.5 cm between them, which are fitted in the top and bottom flanges of the vacuum chamber. Two stainless steel anode rings with thickness 0.4 cm and inner diameters 6.45 cm having separation 2 cm are kept at the discharge centre. Neodymium (Nd(2)Fe(14)B) permanent magnets are physically inserted behind the cathodes for producing nearly uniform magnetic field of ~0.1 T at the center. Experiments and simulations have been performed for single and double anode ring configurations using helium gas discharge, which infer that double ring configuration gives better light emissions in the large volume Penning plasma discharge arrangement. The optical emission spectroscopy measurements are used to complement the observations. The spectral line-ratio technique is utilized to determine the electron plasma density. The estimated electron plasma density in double ring plasma configuration is ~2 × 10(11) cm(-3), which is around one order of magnitude larger than that of single ring arrangement.

Spectroscopic Diagnostic of Volume Discharge Arrangement of a DBD Source and Comparison With PIC Simulation Code

This paper reports the spectroscopic analysis in volume discharge arrangement of a dielectric barrier discharge source in parallel plate geometry of a width of 2 mm. Helium is used as a working gas. The investigations are carried out using sinusoidal supply for the generation of discharges where two current pulses have been observed with different polarities in one period. The electron plasma density and temperature during the discharge have been estimated using the line-ratio technique from the observed visible neutral helium lines. To validate the results, a commercial particle-in-cell simulation code, OOPIC-Pro, has been used, which confirms filamentary as well as diffused discharges observed in the experiment. This code analysis also validates the estimated electron plasma density and temperature measurements at two different working pressures and at a fixed operating frequency.

Multiswitch Equivalent Electrical Model to Characterize Coaxial DBD Tube

In this paper, a quartz coaxial dielectric-barrier-discharge tube operated at different gas pressures and frequencies has been studied. A sinusoidal voltage up to 2.4 kVp with frequencies 34.5 and 47.5 kHz has been applied to the discharge electrodes for the generation of microdischarges. The experimental results confirm the filamentary nature of discharges when operated at different pressures (300, 600, and 1000 mbar) and at different frequencies (34.5 and 47.5 kHz). The relative influence of the given pressures and applied voltage waveforms on the discharge parameters has been analyzed. An equivalent electrical circuit model representing the multipeak phenomenon in the discharge has been developed, which validates the characteristics of the filamentary behavior. A series of simulations has been carried out in order to obtain the internal discharge parameters including discharge impedance which is not measurable during the experimental process. A close agreement between the simulated and experimental results has been obtained. From the experimental results and equivalent electrical circuit model, the dynamic nature of equivalent capacitance has also been reported.

Analysis of Geometrical Design Parameters for High-Energy and High-Current-Density Pseudospark-Sourced Electron Beam Emission

Four different configurations of plasma cathode electron (PCE) guns have been designed and developed in which pseudospark discharge concept has been used. Experimental studies have been performed to identify the dependence of geometrical design parameters like shape of aperture, distribution of apertures, and the number of gaps between hollow cathode and anode on high-energy and high-current-density electron beam emissions. The beam current density has been increased around five times by changing the shape of aperture from circular to sheet keeping the aperture area and other geometrical parameters identical. The perveance of the electron beam has also been increased by increasing the number of apertures on hollow cathode and anode surface. The beam current density from single aperture to multiple apertures has increased from 225 to 900 A/cm2 with low beam energy for the multiple-aperture case. The multiple gaps between hollow cathode and anode increase the electron beam energy. The maximum beam energy is found to be 16–14.5 keV at an applied gap voltage of 16 kV from the developed multigap PCE gun, which is much higher than that from the single gap configuration.

A multiple gap plasma cathode electron gun and its electron beam analysis in self and trigger breakdown modes

In the present paper, a pseudospark discharge based multiple gap plasma cathode electron gun is reported which has been operated separately in self and trigger breakdown modes using two different gases, namely, argon and hydrogen. The beam current and beam energy have been analyzed using a concentric ring diagnostic arrangement. Two distinct electron beams are clearly seen with hollow cathode and conductive phases. The hollow cathode phase has been observed for ∼50 ns where the obtained electron beam is having low beam current density and high energy. While in conductive phase it is high current density and low energy electron beam. It is inferred that in the hollow cathode phase the beam energy is more for the self breakdown case whereas the current density is more for the trigger breakdown case. The tailor made operation of the hollow cathode phase electron beam can play an important role in microwave generation. Up to 30% variation in the electron beam energy has been achieved keeping the same gas and by varying the breakdown mode operations. Also, up to 32% variation in the beam current density has been achieved for the trigger breakdown mode at optimized trigger position by varying the gas type.

Ultraviolet-B radiation enhancement in dielectric barrier discharge based xenon chloride exciplex source by air

A single barrier dielectric barrier discharge tube of quartz with multi-strip Titanium-Gold (Ti-Au) coatings have been developed and utilized for ultraviolet-B (UV-B) radiation production peaking at wavelength 308 nm. The observed radiation at this wavelength has been examined for the mixtures of the Xenon together with chlorine and air admixtures. The gas mixture composition, chlorine gas content, total gas pressure, and air pressure dependency of the UV intensity, has been analyzed. It is found that the larger concentration of Cl2 deteriorates the performance of the developed source and around 2% Cl2 in this source produced optimum results. Furthermore, an addition of air in the xenon and chlorine working gas environment leads to achieve same intensity of UV-B light but at lower working gas pressure where significant amount of gas is air.

Development of low-pressure high-current plasma cathode electron gun and use of associated techniques

A plasma cathode electron (PCE) gun has capabilities for generating high-current, broad, and focused beams for plasma-assisted microwave sources. A pseudospark-based hollow cathode PCE gun has been designed and developed for microwave generation which is operated in argon atmosphere. An analysis of the electron beam profile inside the drift space at different operating conditions has been carried out. This has been performed at several axial and radial locations inside the drift space which shows coherent phases of beam profiles in radial direction. The focusing and defocusing points in axial direction are also obtained. The beam current at different axial location for different applied voltages has been estimated. The obtained beam current is in close agreement with the beam current estimated by the particle-in-cell simulation code for the same geometry.