Study On Acceleration Of Electron Beam In Laser-plasma Wakefield And The Self-focusing Effects

With the rapid development of laser technology, the research of laser technology for people isalso growing; the interaction of the laser and plasma is one of the hot research topics. Electronacceleration in the wake-field and self-focusing of strong laser have been studied in thelaser-plasma interaction.Firstly, article introduces the history of laser technology and self-focusing, and thetechnology of laser to accelerate the electrons and PIC simulation method are made a summary. Itdescribes the basic principles of the laser-plasma interaction, and studies the generation ofwake-field and the process of the electron acceleration and the injection. We obtain the best initialmomentum and density of the electrons in injection and acceleration by studying the effects ofelectron density on the energy of the captured electrons. Further the influence of the accelerationof the injection electrons on the wake-field is studied. Then the self-focusing mechanism andself-focusing critical power are introduced, and it’s good for studying the self-focusing in theinteraction of laser-plasma.In this paper, the main conclusions include:1. Electrons with certain initial momentum can be trapped and accelerated forward in thewake-field，while electron with px0=0participates in the wake field oscillation. But the larger theelectronic initial momentum is, the smaller the vertical momentum is. So, according to the initialmomentum threshold, electrons can have the most effective acceleration and the accessibledistance can be comparable to the length of loss phase. The smaller the plasma density is, thelarger the electronic ultimate longitudinal momentum is. And it is conform to the theory of LuWeietc. The lower the plasma density is, the more obvious the electronic longitudinal momentumincrease trend is. At the same time, with the decrease of the density, the width of the wake-fieldand electronic phase acceleration range is bigger, and it is not conducive to the generation ofmonoenorgetic electron beam.2. When without the injected electrons, the minimum value of electrostatic field is located atthe bottom of the wake field. As the electrons of sheath layer injecting, the shape of the wake-fieldwill be extended along direction. The electrons with a higher longitudinal initial momentum in thesheath layer can be injected into the wake-field. When the coulomb field of electron beams islarger than electrostatic field, the electron beams, as a driver, can accelerate the high energyelectrons. The initial momentum threshold increases as the absolute value of the scalar potential inthe electrostatic field decrease.3. The self-focusing of intense laser with plasma density linear up-ramp profile is studied andthe dielectric constant expressions and spot size equation are obtained. We use the four ordersRunge-Kutta methods for numerical solution. The results show that the density gradient scale issmaller, the faster the electron density increasing, the self-focusing effect is more obvious; thelarger the laser intensity is, the greater the diffraction effect is, the poorer the self-focusing effect is.The results may be significant theoretically to the mechanism of self-focusing of intense laser inthe linear up-ramp density of plasma.