Experimental Studies On The Excitation And Propagation Of Upstream Waves In An Ion-beam-plasma System And Electrostatic Ion-cyclotron Wave In A Magnetized Plasma

In plasma,there exist abundant collective waves and instabilities due to the pres-ence of multi-component charged particles and multiple time and space scales.There are also extrinsic modes such as ballistic modes and pseudo-waves.Ion-beam-plasma system is a typical plasma system,which is widely studied in the field of laboratory and space plasma.In this system,previous researchers have carried out a wealth of theoreti-cal and experimental research on the waves and instabilities existing in the downstream direction.However,almost no experimental research was carried out on waves prop-agating along the upstream direction.The first part of this thesis is mainly about the experimental excitation and identification of wave modes propagating in the upstream direction in a double plasma device.The waves were launched via a negatively biased excitation grid superimposed with a ramp signal.Through the experiments,it can be observed that there are two wave signals detected,one is the ion-acoustic wave and an-other is the burst ion signal.The two types of signals are distinguished by observing the change in the propagation velocity of the received signal with the ramp signal,and the change with the ion-beam energy.The velocity of the burst ion signal decreases as the rise-time of the ramp signal increases,and increases as the peak-to-peak amplitude of the ramp signal increases.The velocity of the ion-acoustic wave signal does not change with the change of the ramp signal.Moreover,by adjusting the velocity of the burst ions such that it closes to the speed of the ion-acoustic wave,the process of wave-particle interaction was observed.Besides,in the downstream direction,previous researchers have observed three eigenmodes,but none was observed about "pseudo-wave" formed by the burst ions.In recent years,the three eigenmodes together with one pseudo-wave were observed and identified in our group in the downstream direction.On this basis,a detailed experiment was carried out to study the wave propagation in the downstream direction for the cases of different ion-beam energies,and two groups of burst ions were observed that originate from the background ions and the beam ions,respectively.The phenomena of inverse Landau damping were also observed.The second part of this thesis is the study of electrostatic ion-cyclotron waves(EICWs)in a magnetized plasma.The electrostatic ion-cyclotron wave is a wave that propagates almost perpendicular to the magnetic field.Most of the previous ex-perimental works were carried out in a Q-machine,in which the waves were mainly excited by the current-driven instabilities caused by the electrons drifting parallel to the magnetic field.Due to the limited transverse scale of Q-machines,the studies on the propagation of the wave in space were seldomly reported.Only a few experiments using antenna excitation to excite the wave were reported,which can also study the harmonic waves.In this type of research,there has been little work studying the group velocity of the wave excited by the pulse signal.Besides,because the study of the dispersion relationship requires an external excitation method to control the frequency,and this excitation method was seldomly used before,the wave dispersion relationship was not well measured.In this thesis,the electrostatic ion-cyclotron wave was externally driven through an excitation grid placed in a magnetized plasma device.Both pulse signal and continuous signal were used for excitation,and the wave patterns were observed as well as the propagation process of the EICW in space.Using the time-of-flight method,both the group velocity and phase velocity were obtained.Furthermore,by changing the sig-nal frequency,the dispersion relation of the wave was measured.The results show that the dispersion relation measured by the experiment is more consistent with the disper-sion relation described by the kinetic theory.For group velocities and phase velocities,the results described by the fluid model and the kinetic model are consistent with the experimental results only within a limited range.