Document Details

Document Type : Thesis 
Document Title :
A comparative study of the physical processes responsible for the breakdown of He and Kr gases by excimer laser pulses.
دراسة مقارنة للعمليات الفيزيائية المسئولة عن انهيار غازي الهيليوم والكريبتون بواسطة نبضات ليزر الاكسيمر
 
Subject : x-Ray Laser 
Document Language : Arabic 
Abstract : Numerical analysis is presented to investigate the electrical breakdown of helium and Krypton gases over a pressure range 4.5-3000 torr induced by a 248 nm an excimer laser source of pulse length 18 ns operated at threshold intensity varies between, 4.0 X 1011 and 2.0 X 1013 W/cm2 (Turcu et al 1997). The investigations are based on a modified electron cascade model, which solves numerically the time dependent Boltzmann equation for the electron energy distribution function (EEDF) and a set of rate equations describing the rate of change of the formed excited states population. In this work the He and Kr atom are treated as a four state atoms namely; a ground state an ionized state and two exited states. For more realistic results, the rate coefficients and cross sections of the physical processes involved into the model are taken to vary with the electron energy. The result of computations showed a reasonably good agreement between the calculated threshold irradiance and the measured ones for both gases over the whole range of the gas pressure examined experimentally. A study of the effect of the physical processes on the breakdown threshold revealed that multi-photon ionization of the ground and excited states are the main process which contributes to the breakdown of Kr . For He however, only photoionization of the formed excited atoms are responsible for the generation of the seed electrons which execute the plasma formation. More over inspection of the actual contribution of loss processes to the breakdown of helium gas showed that No evidence for diffusion and recombination losses is observed for the whole gas pressure range. On the contrary for Kr diffusion losses are found to play a major role over the low pressure regime. Analysis of the calculated electron energy distribution function and its parameters, viz, the time evolution of electrons, excited states population, ionization rate………..etc, reflected the importance of photo-ionization of the excited atoms in comparison with collisional ionization processes as a physical mechanism responsible for the breakdown of both gases under the experimental condition used in this work. 
Supervisor : Yosr Ezz Eldin Gamal Hassan 
Thesis Type : Master Thesis 
Publishing Year : 1432 AH
2011 AD 
Number Of Pages : 216 
Added Date : Monday, March 3, 2014 

Researchers

Researcher Name (Arabic)Researcher Name (English)Researcher TypeDr GradeEmail
حمده عبد الله الزهرانيAL-Zahrani, Hamdah AbdullahInvestigatorMaster 

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 36630.pdf pdf 

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