PONDEROMOTIVE FORCE DRIVEN SELF GENERATED MAGNETIC FIELD IN LASER PLASMA INTERACTIONS

Abstract

In my thesis a differential equation governing magnetic field depending on plasma frequency(𝜔𝑝𝑒 ), laser intensity parameter (𝑎0), laser frequency (𝜔𝑙 ), plasma density which varies along transverse direction (𝑛0) and Electric field (𝐸(𝜉)) is derived. This differential equation is second order linear and inhomogeneous. For deriving this differential equation I have done literature review on laser plasma interaction. I have studied basics of plasma and laser systems. I have also gone through the process of generating ultra-short laser pulse which is very important for my research as these ultra-short laser pulse are described by high peak intensities. These ultra-short laser pulse are amplified by Chirped Pulse Amplification as conventional amplifying methods have lot of limitations. Also these ultra-short laser pulse can introduce the effect of non linearities in the plasma which can catalyse (Pondermotive Force) the process of generation of magnetic field. The purpose of my research is to study the characteristics and behaviour of magnetic field for respective electric field envelope. Since this magnetic field is self-induced after laser irradiation of the target, I have to study the process of self-induced plasma magnetisation such as Biermann Battery, Inverse Faraday Effect, Plasma Magnetisation Due to Fast Currents or Fountain Effect, magnetisation by Pondermotive force, Weibel Instability etc. I had analytically solved the differential equation for different piece wise electric field pulse profile such as Sine, Triangular, Sawtooth Increasing, Sawtooth Decreasing, Rectangular Triangular and Square pulse. The response of the magnetic field for these profiles were analysed and maximum amplitude compared to all other electric field pulse profile was found for Square pulse but with heavy oscillations. The second best amplitude was with Sawtooth Decreasing and interestingly it had minor oscillation unlike Square profile. The maximum amplitudes of Sine, Triangular, Sawtooth Increasing, Rectangular triangular electric field pulse profiles were found to be nearly same with minor fluctuations. I have also tried to see the variation of magnetic field with laser intensity parameter (𝑎0), plasma density (𝑛0), and differential length (𝑑𝑙 ) for all electric field pulse profiles and analysed that the magnetic field increases with increase in laser intensity parameter (𝑎0) and plasma density (𝑛0) and decreases with increase in differential length (𝑑𝑙 ) and this result matches computational and theoretical results. My results can be applied in applications where shape of electric field and magnetic field along with their peak amplitude are considered. We can choose Square electric field Pulse profile if only matter of consideration is peak amplitude and not the oscillations in envelope. If oscillations in the envelope and peak both are important better option is Sawtooth Decreasing electric field pulse profile.