Wave-Particle Interaction And Electron Acoustic Solitary Structures In Space Plasmas Using Particle In Cell Simulations And Satellite Observations

Wave-particle interactions are very important phenomena in the space plasma environment.Using 1D particle-in-cell(PIC)model,we study the trapping of plasma particles by waves and the formation of electron-acoustic solitary structures in a plasma which consists of immobile ions,and cold,beam and hot electrons.We have also presented a more generalized form of the non-Maxwellian distribution function for space plasmas.Moreover,using the data from the Magnetospheric Multiscale(MMS)spacecraft,we studied the two-way direct measurement of wave-particle energy exchange simultaneously by two distinct plasma species(H+and He+).The principal results are shown as follows.1.By performing one-dimensional(1-D)particle-in-cell(PIC)simulations,nonlinear effects of the electron-acoustic waves are investigated in a multispecies plasma,whose constituents are the hot electrons,cold electrons and beam electrons with immobile neutralized positive ions.Numerical analyses have identified that electron-acoustic waves with a sufficiently large amplitude tend to trap cold electrons.Because the electron-acoustic waves are dispersive,where the wave modes with different wave numbers have different phase velocities and so the trapping may lead to the mixing of cold electrons.The cold electrons finally get thermalized or heated.The investigation also shows that the excited electron-acoustic waves give rise to a broad range of wave frequencies,which may be helpful for understanding the broadband-electrostatic-noise(BEN)spectrum in the Earth's auroral region.2.Electrostatic solitary(ES)structures have been frequently observed in the solar wind,Earth's and other planetary magnetosphere and are the most widely theoretically studied waves in literature.However,there are very few studies in which simulations and theoretical studies have been performed simultaneously.In this study,we perform 1-D electrostatic Particle-in-Cell(PIC)simulations of electrostatic solitary(ES)waves in a plasma which consists of immobile ions,and cold,beam and hot electrons.It is found that for a small value of electron beam velocity,ES structures are formed due to the steepening of initially quasi-monochromatic electron acoustic(EA)waves.We interpret these ES structures as electron acoustic solitary(EAS)structures,which agree with the rarefactive(negative electrostatic potential)electron acoustic solitary structures obtained theoretically as a solution of the Korteweg de-Vries(KdV)equation.We have found that polarity of solitary structures depends on the drift velocity of electron beam and formation of electric field spikes are consistent with the ES waves observations from Earth's magnetosphere.3.A more generalized form of the non-Maxwellian distribution function,i.e.,the AZ-distribution function is presented.Its fundamental properties are numerically observed by the variation of three parameters:?(rate of energetic particles on the shoulder),r(energetic particles on a broad shoulder),and q(superthermality on the tail of the velocity distribution curve of the plasma species).It has been observed that(i)the AZ-distribution function reduces to the(r,q)-distribution for ??0:(ii)the AZ-distribution function reduces to q-distribution for a?0 and r?0:(iii)the AZ-distri'bution function Cairns-distribution function for r?0 and q??:(iv)the AZ-distribution reduces to Vasyliunas Cairns distribution for r?0 and q??+1:(v)finally,the AZ-distribution reduces to Maxwellian distribution for ??0,r?0,and q??.The uses of this more generalized AZ-distribution function in various space plasmas are briefly discussed.4.Wave and particle may interchange their energy in the collisionless space plasmas.We have studied the wave-particle energy exchange simultaneously by two distinct plasma species(H+and He+)using the Magnetospheric Multiscale(MMS)spacecraft.The distribution of ions around the magnetic field is not symmetric.It is observed that the due to cyclotron resonance the H+ transfer energy to electromagnetic ion cyclotron(EMIC)waves,whereas the EMIC waves transfer energy to He+ by nonresonant interaction.