The Nonlinear Electrostatic Waves In An Electron-positron Plasma

Electron-positron plasma generally widely exists in the early universe of nature.At the same time,it has been found that electron-positron plasma can also be produced in laboratory experiments on the long human way of scientific exploration research,which has opened up a new direction for plasma physics,and naturally also attracted the strong interest of researchers.With the development and progress of technology and the innovation of scientific research,the research of electrostatic wave in an electron-ion plasma and the analysis of its physical significance have been extensively explored,and many conclusions and breakthroughs that are conducive to the expansion of scientific research have been obtained.However,the data about the study and analysis of some phenomena in an electron-positron plasma are still to be explored.Therefore,the main innovation and emphasis of this paper is to study the excitation and properties of nonlinear electrostatic waves in an electron-positron plasma.The main contents of this paper are as follows:(1)In order to make a more detailed and accurate study of the nonlinear electrostatic wave in an electron-positron plasma,through a lot of investigation and reading,first of all,on the basis of previous researches on the excitation of nonlinear electron-acoustic wave(EAW)in the electron-ion plasma,we know that electron-acoustic wave(EAW)is a kind of Bernsteingreen-Kruskal(BGK)nonlinear mode,in which electrons are trapped in the wave trough,and the number of trapped particles must be generated during the excitation process.For the collisionless plasma,the external driver with the low amplitude is app lied to the simulation process.When the driver is turned on,the amplitude of the resonance point rises to a larger value,and the maximum amplitude is almost constant after the external driver is turned off.The excited electron-acoustic wave(EAW)is a high-frequency nonlinear wave involving only electrons,which is quite different from the ion-acoustic wave(IAW).On this basis,we carry out a simulation,using a new simulation method-Vlasov simulation.At the same time,different simulation parameters are set,and the same conclusion is obtained that electron-acoustic wave(EAW)is a kind of nonlinear wave,however,the difference is that under the condition of constant wave number k,Vlasov simulation is carried out by changing the value of the driving phase velocity,and the data is processed.We have drawn the resonance peak diagram,showing a broad peak(which is different from the previous one).The broad peak is due to the same excitation resonance at the two adjacent phase velocities.In addition,the evolution of the vortex structure of the phase space diagram with the simulation time obtained only by increasing the length of the simulation domain with other parameters are constant is also different from the previous results,which is analyzed in Chapter 2.(2)On the basis of(1),we obtain a new research direction,the excitation of nonlinear electrostatic wave in an electron-positron plasma.In this work,the excitation of nonlinear electrostatic waves in an unmagnetized collisionless electron-positron plasma is analyzed and studied in detail from two aspects of theoretically and numerically simulation,and the dispersion relation of undamped nonlinear electrostatic waves is derived.We mainly analyze and discuss the modes of these waves excited in an electron-positron plasma with positron to electron temperature ratio of T_R=1 and T_R=0.1,respectively.By theoretical analysis,when T_R=1,the dispe-rsion relationship is similar to the"thumb"curve,and the upper and lower branches represent the Langmuir wave(LW)and IBK wave,respectively;and when T_R=0.1,the dispersion relationship presents a new type of curve,which is called"thumb-teardrop"curve.Through Vlasov simulation,we can get that in the long wavelength limit,only Langmuir wave(LW)and IBK wave exist,and the electronic-acoustic wave(EAW)and ion-acoustic wave(IAW)disappear.Then,we find that the dispersion curve obtained by Vlasov simulation is more inward than the theoretical dispersion curve,which is due to the nonlinear frequency shift and wavenumber shift.Finally,we analyze the properties of these waves by Fourier transform and do further research.(3)In order to enrich our work,based on previous studies on strongly enhanced stimulated Brillouin backscattering in an electron-positron plasma.We have learned that the previous studies on the three wave coupling process of the two kinds of plasmas by means of analysis and numerical simulation,and predicted theoretically and numerically the opposite of stimulated Brillouin sca ttering and Raman scattering in the electron positron plasma.In this work,stimulated Raman or stimulated Brillouin backscattering is used to amplify the relative propagating laser beam by plasma laser,thus producing ultra-short pulse with ultra-high intensity.When approp-riately phase-matching conditions for the frequency(?)and wave vector(k)of the pump,seed,and plasma waves,i.e.,conservation of energy(?_pump=?_seed+?_{p lasma})and momentum(k_pump=k_seed+k_plasma),the fluctuations grow rapidly in time,and producing massive amplification.These relationships are used to t heoretically calculate and simulate the analytically determined dispersion relation of plasma,because resonance amplification is observed at k_seed which satisfies the phase matching condition.And we use the EPOCH program to simulate the previous work,an d make a more detailed analysis of the conclusions,and expand the new research direction this work by changing the laser intensity and pulse width.The specific process will be discussed and analyzed in Chapter 4.The main innovations of this paper are as follows:(1)A broad peak is obtained in the excitation resonance of the nonlinear electron-acoustic wave in an electron-ion plasma;(2)In an electron-positron plasma,the dispersion relation of nonlinear electrostatic wave generally presents a“thumb-teardrop”curve;(3)In the study of laser pulse amplification in an electron-positron plasma,the characteristics of pulse amplification are analyzed by changing the laser intensity and the pulse width of the simulation setting.