FINITE ION VELOCITY EFFECTS ON THE STABILITY OF PIERCE-LIKE DIODES

The stability of Pierce-like plasma diodes is investigated for arbitra ry ion injection velocities. A recently developed integral formalism t hat accounts for ion dynamical effects is applied to derive a generali zed dispersion relation for electrostatic perturbations. Its evaluatio n exhibits several new features, such as the appearance of growing osc illatory modes, which become Pierce-Buneman modes in the limit of init ially resting ions, and of weakly damped oscillatory modes, which beco me undamped ion plasma oscillations in this limit. The stability of th is bounded plasma system is shown to be controlled by the new control parameter alpha = alpha(1 + mu)1/2, where alpha is the Pierce paramete r and mu = m(e)v(e0)2/m(i)v(i0)2 the ratio of electron and ion kinetic energy at the emitter.