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Title of Thesis

Study of Soft X-rays From Depleted Uranium Assisted Pre-ionized Plasma In A Low Energy Mather Typeplasma Focus Device

Author(s)

Hamdullah

Institute/University/Department Details
Department of Physics / Quaid- I- Azam University, Islamabad
Session
2011
Subject
Physics
Number of Pages
126
Keywords (Extracted from title, table of contents and abstract of thesis)
Capacitor, Pressure, Energy, Uranium, Study, Focus, Emission, Low, Depleted, Xrays, Typeplasma, Discharge, Mather, Plasma, Preionization

Abstract
This thesis describes the experimental investigations of the soft X-ray emission and the plasma dynamics in a Mather type plasma focus device operated in different gases (Neon, Helium, Deuterium, Neon+Helium) by changing different parameters like charging voltage, capacitor bank energy, discharge current, anode shape, gas pressure and influence of preionization. The objectives of the studies are to enhance soft X-ray emission.The Rogowski coil, high voltage probe, PIN diodes and pinhole camera masked with appropriate absorption filters are used for diagnostics.Specifically attention is paid to tailor the radiation in different energy windows i.e. 1− 1.56 keV and 4−8.33 keV.A single 12.5 μF capacitor charged at 19-23 kV (2.25-3.3 kJ), with a field distortion type sparkgap as switch is used to transfer the energy to the system. In the first experiment, the effect of preionization caused by depleted uranium (92U238) on soft X-ray and total X-ray emission is investigated by varying the neon gas pressure with and without preionization.The X-ray yield and pinhole images are found strongly influenced by the preionization and the pressure of the working gas. The soft X-ray yield of 82.5 ± 4.0 J in 1.3–1.56 keV energy window is obtained with preionization of neon gas at the optimum pressure, leading to the conversion efficiency of 2.5% of the stored energy.The total X-ray yield with preionization is 195 ± 9.0 J in 4π geometry measured at the optimum pressure giving conversion efficiency of 5.9%.The time integrated images indicate the broadening of X-ray emission zone with preionization.
The second experiment is performed with helium as filling gas.The highest soft X-ray yield of 0.25 ± 0.01 J is obtained without preionization, which increases to 0.50 ± 0.02 J with preionization at optimum pressure.The total X-ray yield 1.50 ± 0.07 J without preionization, is enhanced to 2.44 ± 0.11 J with preionization.The plasma focus duration has been increased with preionization conforming enhancement and improvement in X-ray.This has also been conformed by the symmetric and enlarges pinch images with preionization.
The third experiment is performed in the mixture of helium and neon with a mixing ratio 50:50%.A decrease of 3-7 nsec is observed in the discharge time with preionization which was initially 20-30 nsec without preionization. Soft X-rays emission is increased from 2.3±0.11 J to 3.7±0.18 J and total X-rays emission from 9.5±0.47 J to 13.7±0.68 J by employing preionization.The preionization has also significant influences on the dynamics of the plasma focus.The focus peak amplitude, indicator of focusing efficiency of the system, has been increased from 2.3 to 3.5 and the focus duration from 67 ns to 93 ns while employing preionization. The time integrated pinhole images at the optimum pressure of the X-rays emission with preionization reveals that preionization not only enhances soft and total X-ray yield but it also significant influences plasma dynamics causing enhancement in focusing peak amplitude and focusing duration. The fourth and last experiment is performed in a 2.25 kJ Mather type plasma focus system with tapered anode operated in deuterium with and without preionization.The maximum Cu-Kα emission of 1.95±0.01 J with preionization and 1.62±0.08 J without preionization in 4π geometry is obtained at optimum filling pressure.The maximum total X-ray yield in 4π geometry is estimated about 2.64±0.13 J and 2.12±0.12 J with and without preionization respectively.It is found that Cu-Kα emission is emitted due to the impact of electrons in the current sheath with anode tip and the vapors ablated from the anode surface, which adds to the plasma and give rise to X-rays emission.
It is observed that the X-ray flux strongly depends upon the filling pressure as well as on preionization.There is a significant increase in soft X-rays, characteristics copper X-rays and total X-rays.Thus preionization employed prior to pulse discharge plays an important role in formation of a symmetric pinch filament, broadens X-ray emission pressure range and enhancement in X-ray emission.

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S. No. Chapter Title of the Chapters Page Size (KB)
1 0 CONTENTS

 

 
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INTRODUCTION

1.1 Literature survey on different available X-ray sources
1.2 Plasma and plasma focus device: an introduction
1.3 A brief review of Preionization in plasma focus
1.4 New generation plasma focus devices
1.5 Layout of the thesis

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3 2 EXPERIMENTAL SET UP OF PLASMA FOCUS AT QAU

2.1 Plasma focus system
2.2 Preionization arrangement

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4 3 X-RAYS AND ELECTRICAL DIAGNOSTICS TOOLS

3.1 X-ray detection and analysis
3.2 Basics diagnostic tools used for current and voltage measurement
3.3 Calculation of X-ray Yield

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5 4 ENHANCED SOFT X-RAY EMISSION WITH PREIONIZATION FROM PLASMA FOCUS

4.1 Enhanced X-rays yield with preionization from plasma focus operated in Neon
4.2 Enhanced X-ray yield with preionization from plasma focus operated in He
4.3 Effect of preionization on soft X-rays emission and plasma dynamics with neon-helium mixture
4.4 Enhanced Cu-Ká yield with preionization operated in Deuterium

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6 5 CONCLUSIONS AND SUGGESTIONS FOR FUTURE WORK

5.1 Conclusions
5.2 Suggested future work

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