Cold Plasma Particle-Particle Collisions and Self-Heating

Summary form only given. Using the input file coldplas.inp from our venerable electrostatic periodic particle-in-cell (PIC) code XES1 (available at http://ptsg.eecs.berkeley.edu), we observe cold plasma oscillations excited in the fundamental mode. Our purpose is to examine the electron-electron collisions. Let two electrons be loaded at x=L/4 and at x=3L/4 for a system of length L. The ions form a uniform stationary background that makes the periodic system net neutral. The particle excitation at t=0 is an x-velocity v1=A sin kx in fundamental mode, with amplitude A and kL=2pi. With small A, the Vx-x phase space shows two ellipses, each centered at the starting positions and with oscillations at the input plasma frequency, as expected. As A is increased, the two particles collide at x=L/2 and reflect. The particle oscillatory and colliding motion histories are observed by tracing their Vx-x motions. Next, 64 electrons are loaded uniformly in x and excited in the fundamental mode using small A and producing 64 non-colliding elliptical orbits with an envelope in mode. When A is increased, we now ask, "Which electrons collide first?" We observe crossing first at x=0 or at x=L/2 , where neighboring orbits have opposite x-velocities. These collisions randomly scatter the particles, and the field, kinetic, and total energies grow non-physically with time