Production and Transport of Convoy Electrons

Results are presented of doubly-differential (in energy and angle) cross section (DDCS) measurements for production of convoy electrons from 36 MeV/u Ar ^{15+}, Ar^{17+ }, and Ar^{18+} ions in thin amorphous carbon foils. The observed electron emissions are fitted to a multipole expansion of the DDCS, frequently employed to characterize ion-atom electron-loss to the continuum (ELC) and electron-capture to the continuum (ECC) cusp shapes. Thinner target data agree reasonably well with ion-atom predictions of component multipole moments, beta_{k}. The results also reveal a rapid evolution of beta_ {k} with increasing target thickness. A quantitative model of the multipole evolution bridging the transition from the single- to the plural-collision regime is presented which demonstrates significant competition between one-step and multi-step production mechanisms. Excellent agreement is found for the first two even-ordered moments, beta_2 and beta _4, while the lack of good agreement for the dipole moment, beta_1, suggests the need to include additional continuum electron transport phenomena.