Plasmons, Wakes and Clusters

A charged particle moving with velocity v¿ in a medium having electron collective resonant frequency ¿o sets up electron density fluctuations of two types. Collective fluctuations train the particle composing a conical pattern in a relatively extended periodic wake of wavelength 2¿¿/¿o. These fluctuations constitute a mode of energy transport from the particle track, leading eventually to particle-hole excitations. Single-particle interactions give rise to bow waves ahead of the particle and to periodic crispations in the collective fluctuations of wavelength ~ h/mv. The electric field associated with the wake gives rise to a retarding force on the particle and to a mixing of energy levels of electrons bound to the particle. The superposition of wake potentials in a dicluster causes forces on the constituent ions which account quantitatively for measurements of the break-up behavior of swift molecular ions in thin foils.