Diagnosing the velocity-space separatrix of trapped particle modes

Trapped particle modes in pure electron plasmas are similar to modes in neutral plasmas and exhibit damping due to velocity diffusion across the separatrix between trapped and untrapped particles, as commonly occurs in neutral plasmas. Applied rf voltages cause resonant perturbation of particle velocities near the separatrix, giving a greatly enhanced mode damping. This diagnostic technique can determine the velocity-space separatrices for either electrostatic or magnetic trapping, or determine the particle distribution function along the separatrix.