| Transport of ion beams in plasmas includes hot research topics such as energy loss or energy deposition of ion beams,self-focusing effects of ion beams and ion beam filamentation instability.In the fields of heavy ion-driven inertial confinement fusion,proton fast ignition,neutral beam injection in magnetic confinement fusion,and proton-boron beam-target fusion,the occurrence of fusion reactions is closely related to the energy loss or energy deposition of ion beams.Studying this topic is beneficial to grasp the energy evolution of ion beams and the temperature changes of plasma targets,which is conducive to improving the acquisition of fusion energy.In addition,the study of the self-focusing effects and ion beam filamentation instability in plasmas can also help to analyze the ion beam density modulation that may occur in the above experiments,and provide theoretical support for using plasmas as the transport medium to improve the quality and application values of ion beams as well.In this thesis,at first the evolution of the self-generated electromagnetic field of ion beams in plasmas is derived,and the self-focusing conditions of high-energy low-density ion beams in plasmas are analytically obtained.In the theoretical framework of this thesis,the plasma is constantly heated as the ion beam transports.The results show that the selffocusing conditions are strongly dependent on the degree to which the plasma is heated.When the plasma is weakly heated,the ion beam is focused towards the center as a whole,forming a denser ion beam.When the plasma is strongly heated,the ion beam forms a hollow structure in the middle,creating a ring-shaped focus.Then,taking the proton-boron beam-target fusion as an example,the influences of quantum degeneracy effects and collective electromagnetic effects on the energy loss of ion beams and the fusion reaction rate are studied through theory and simulation.The results show that the interaction of a proton beam with a boron target in the plasma state can generate more fusion reaction products α particles than injecting the proton beam to a solid boron target.The reason lies in that after the solid boron target becomes a plasma,quantum degeneracy effects will become stronger,and collective electromagnetic effects will be weakened.These two factors can reduce the energy loss of the proton beam in the boron target,so that more protons with sufficient energy are able to participate in the proton-boron fusion reaction.Subsequently,the hybrid-PIC simulation program LAPINS is used to simulate the selffocusing effects of ion beams under weak heating,and the self-focusing conditions derived analytically are verified through the simulation results.Finally,the ion beam filamentation instability is explored through simulations,and it is found that the greater the ion beam density and kinetic energy are,the greater the growth rate of filamentation instability will be.It is also found that the ion beam filamentation instability can be suppressed by applying a longitudinal magnetic field,and the required magnetic field strength depends on the density and kinetic energy of the ion beam. |
