CRYSTAL ASSISTED PROCESSES IN ION CHANNELING

Channeled ions experience a restoring force from adjacent atomic rows or planes that govern their trajectories and hence limit their interac tions to those with valence or conduction electrons. Trajectory inform ation can be gained from emergence patterns and studies of radiative e lectron capture (REC) can give information on the electron momentum di stributions and densities in the channel. With this knowledge, one can study ion-electron collisions in dense media; in particular, dielectr onic excitation and recombination. The states of the energetic channel ed ions can be influenced by the crystal field and by the wake field t hat follows them. They can also be perturbed by the periodic electroma gnetic force with a frequency depending on their velocity and the peri odicity of the lattice. When the frequency of the perturbation nu caus ed by passing along a given crystal direction with atomic spacing d at velocity upsilon reaches a resonance, nu(res) = (upsilon/d)K, where K = 1, 2, 3,..., resonant coherent excitation (RCE) can occur to non-de generate eigenstates of the ion. Ions in these excited states can then be ionized by the channel electrons or, if not ionized, can escape fr om the crystal and radiate, RCE has been studied in both axial and pla nar channeling by varying the ion velocity or, in the case of planar c hanneling, by varying the apparent interatomic spacing by changing the angle with respect to an axis. In both cases, information can be gain ed concerning the states of channeled ions and the nature of the cryst al channel.