Rashmita Das

Low voltage operation of plasma focus

Plasma foci of compact sizes and operating with low energies (from tens of joules to few hundred joules) have found application in recent years and have attracted plasma-physics scientists and engineers for research in this direction. We are presenting a low energy and miniature plasma focus which operates from a capacitor bank of 8.4 muF capacity, charged at 4.2-4.3 kV and delivering approximately 52 kA peak current at approximately 60 nH calculated circuit inductance. The total circuit inductance includes the plasma focus inductance. The reported plasma focus operates at the lowest voltage among all reported plasma foci so far. Moreover the cost of capacitor bank used for plasma focus is nearly 20 U.S. dollars making it very cheap. At low voltage operation of plasma focus, the initial breakdown mechanism becomes important for operation of plasma focus. The quartz glass tube is used as insulator and breakdown initiation is done on its surface. The total energy of the plasma focus is approximately 75 J. The plasma focus system is made compact and the switching of capacitor bank energy is done by manual operating switch. The focus is operated with hydrogen and deuterium filled at 1-2 mbar.

Characterization of High Power Microwave Radiation by an Axially Extracted Vircator

Characterization results of high-power microwave radiation, from an axial vircator driven by pulsed electron beam accelerator AMBICA-600 are reported in this paper. We present a study on variation in pulsed microwave power output and dominant frequency by discretely varying anode-cathode (A-C) gap. While keeping the cathode diameter fixed at 40 mm, for the A-C gap distance in the range 5-9 mm, dominant frequencies have been measured to be lying in the range 4.7-9.8 GHz. The trend of a subsequent increase in the dominant frequency at lower A-C gap distances (and vice versa) revealed that center frequency is mainly governed by the longitudinal size of the potential well. The highest microwave power of ~ 14 MW for ~ 75-ns pulse duration was obtained at A-C gap of 7 mm having the dominant frequency in C-band at ~ 6.9 GHz. The beam-to-microwave power conversion efficiency of ~ 1.2% has been demonstrated in our experiments. On the basis of power distribution pattern obtained by the gas breakdown technique, the dominant mode of emission is believed to be transverse magnetic mode. Relative analysis of frequency spectrums obtained for various A-C gap distances evidenced experimental recognition of optimum A-C spacing as a generation of narrowband distinct frequency peak of large magnitude with minimal mode hopping.

Development of compact D-D neutron generator

In recent years, due to specific features of compact neutron generators, their demand in elemental analysis and detection of the illicit materials has been increased in scientific community. Compact in size, controlled operation and radiation safety like features of neutron generator is suitable for research work with illicit materials. An accelerator based neutron generator can be operated in steady mode as well as in pulse mode. The main embodiment of this type of generator includes ion source, ion acceleration system and target. We are developing such type of neutron generator. This consists of one in-house developed penning ion source, a single electrode acceleration gap and one deuteriated titanium target or virgin titanium target. The neutron generator was operated at 80 kV acceleration potential, a deuterium pressure of 0.1 mTorr and ion source potential at 1 kV. The neutron generation was confirmed by the solid state nuclear track detector CR-39. In this report, we will discuss various physics and technical issues related to the important components of this generator, operation of the generator and neutron detection.

Experimental study of exploding wire method for production of metal nanoparticles

In an effort to characterize the exploding wire method for efficient production of nanoparticles, we are involved for studying this method in our laboratory. The copper wire of 0.26 mm diameter was exploded inside an enclosure made off stainless steel. The explosion was done by passing electric current through the wire by discharging the capacitor. In this paper we discuss the behavior of the electrical circuit in explosion process and the production of the nanoparticles after explosion.

Particle distribution of nanocrystalline copper produced by exploding wire method

This paper presents the experimental study of electrical explosion of wire method. The sample was prepared by exploding copper wire of 0.26mm diameter in the nitrogen environment. In each time of explosion overheating factor was varied. Prepared samples were characterized by X-ray diffraction and transmission electron microscope. The result reveals the presence of copper nanoparticles and decrease of the percentage of higher size particles with increase of overheating factor.

Generation of copper nanoparticles by electro-exploding wire technique for various pressures of the surrounding medium

This paper presents the experimental results on explosion of copper wire at a discharge voltage of 9kV for the generation of Cu nanoparticles in nitrogen environment at different pressures. The current and voltage waveforms for different pressures of the nitrogen gas have been recorded by a current transformer and a high voltage probe. Nanoparticles generated by the electro exploded wire method were characterized by both optical microscopy and transmission electron microscopy. Experiments show that the variation of pressure of nitrogen gas inside the exploding chamber determines the size of the particles formed during the explosion of the copper wire. It is observed that for a pressure of less than 230 mbar of nitrogen gas, the wire does not explode and the copper wire remains intact. Micro particle generation occurred at a pressure of 2.3×10 2 mbar of nitrogen gas and nanoparticles were formed when the pressure was further increased to 1×10 3 mbar. Experimental results show that we could deposit maximum energy into the metal core when the wire was exploded by working in the high pressure regime of the nitrogen gas resulting in the production of nanoparticles. Transmission electron microscopy reveals the size of the nanoparticles to be in the range of 35 to 75 nm.

Production of nanocrystalline copper by exploding wire method

Nanostructured materials have generally been synthesized by condensation from the vapor phase. Different methods are developed and used for nano sized metal powder production Exploding wire method is a vapor phase method in which the nanoparticles are formed by discharging the electrical pulse into a thin wire. Nanocrystalline powder of copper has been produced by the electrical explosion of wire. Wire was exploded in the nitrogen environment. Sample was characterized by X-ray diffraction (XRD). Grain size was measured by using Scherrers Formula. Average grain size was found to be 59.68nm.

Issues related to nanoparticles generation by exploding wire method

Nano science and nanotechnology continue to grow as fields of scientific research and commercial development. At this time, focus is to develop the particles of desired size with significant change of properties than bulk material. But the sample preparation methods involved in each process, surface functionlization and existing characterization techniques remains an important and complicated issue of nanoscience for the development of new materials till the present date. Thus for a science, that is all about size, these important size issues need to be fully understood as it impacts not only the electronic and optical properties but also environmental and biological interactions. We are producing metal nanoparticles by exploding wire method. Vacuum plays an important role in the production of pure nanopowder as well as to avoid contamination and storage of the material to produce stable nanoparticles. In this paper we will discuss about the complications and intermediate process involved in the production of nano crystalline by exploding wire method.

Deuterium Gas Analysis by Residual Gas Analyzer

Hydrogen gas is generated by electrolysis method in a compact hydrogen generator. A simple procedure reduces handling and storage of hydrogen cylinders for laboratory applications. In such a system, we are producing deuterium gas from heavy water by electrolysis method. After production of the deuterium gas, we have checked the purity level of the outgoing deuterium from the electrolyser. The test was carried out in a high vacuum system in which one residual gas analyser (RGA) was mounted. The deuterium gas was inserted by one manual gas leak valve in to the vacuum system. In this study, the effect of the emission current of the RGA on the detection of the deuterium was performed. In this paper, we will discuss the detail analysis of the deuterium gas and the effect of the emission current on the partial pressure measurement.

A Low Impedance Marx Generator as a Test bed for Vacuum Diodes

A low impedance Marx generator was developed, which will serve as a test bed for Vacuum diodes of various electrode materials and geometries. The vacuum diodes will be used for high power microwave generation. The generator is capable to supply ~3GW of pulsed power to the vacuum diodes which is sufficient enough to produce plasma within the diode for electron beam generation. A vacuum of 10−5Torr is required for virtual cathode formation within the diode, when the beam current exceeds the space charge limiting current. A vacuum diode of reflex triode geometry has been designed and vacuum of 10−5 Torr has been achieved. The repetitive operation of the vacuum diode depends upon the recovery of the diode, the importance of the vacuum system on the recovery of the diode will be explained. A vacuum system with high voltage isolator has been installed for getting the desired vacuum within the diode. The design criterion of the vacuum system will be discussed. The 300kV/1.8kJ Marx generator which will power the vacuum diode has six stages with stage capacitance and voltage of 240nF and 50kV respectively. It has an impedance of ~7 ohm and can deliver 200kV voltage across the diode in critically damped load condition. The generator has a very fast rise time of 200ns.The operational characteristics of the Marx generator are determined experimentally. The results have been analyzed and compared to an equivalent circuit model of the system.