Particle Simulation of the Low- alpha Pierce Diode

摘要

The evolution of small initial perturbations of the uniform equilibrium of the ''classical'' Pierce diode is studied using particle simulations. These simulations have been performed with the new bounded-plasma code PDW1 and cover the parameter range 0 < alpha < 3 pi , where alpha = omega /sub p/L/v sub 0 . In the linear regime, three stages (initial-transit, adjustment, and dominant-eigenmode) are distinguished; oscillation frequencies, growth/damping rates, and potential profiles of the dominant eigenmode as well as oscillation frequencies of the next-to-dominant eigenmode are recovered and shown to agree quantitatively with recent analytical results. In the linearly unstable cases, the system evolves nonlinearly to a final state which may be either a new, nonuniform dc equilibrium, or a state of large-amplitude oscillations. In particular, for alpha = 1.5 pi the character of the final state is found to depend on the details of the initial conditions. (ERA citation 10:038427)