Excitation of solitons and surface waves in three dimensional beam neutralization*

Ion beams are used in various engineering applications such as particle accelerators, ion-thrusters, and ion-implantations. The rate of neutralization of beams is affected by the energy and the location of the electron source relative to the ion beam. In recent numerical works by Lan and Kaganovich, electrostatic-solitary-waves (ESWs) were observed when the electrons were injected in a 2D planar ion beam. We will present the beam neutralization in 3D and show the formation of solitons and their movement along the beam axis using the Particle-in-Cell (PIC) method. Prediction of electron solitons is important as they may cause the heating of electrons and slow down the process of neutralization in the beam. A hybrid MPI-GPU code, CHAOS, is used for this work, in which an argon beam is neutralized by the electrons emitted from a circular source along the beam axis. We will present our findings on the formation of solitons and long wavelength surface waves in cylindrical and planar beams for different beam widths. Prediction of the surface waves and their frequencies is important in experimental diagnostics and passive measurements in plasma beams. By comparing our results with the theory of planar surface waves, we will show how the long-wavelength surface waves get excited differently in a 2D planar and 3D cylindrical beam.