Physical Processes in Compensated Negative-Ion Beams and Related Beam Transport Problems

This paper reviews resent theoretical and experimental research on physical processes in compensated negative-ion beams. A previous review was published by one of the authors in Ref. [1]. The present paper summarizes the new results of numerical calculations of the stationary electric field in negative-ion beams, and the resent results of experimental studies of suppression of ion-ion instability at low gas pressures. As in Ref. [1], the review addresses the following three main issues of the physics of compensated beams: 1) Spatial charge compensation in steady beams; 2) Dynamic decompensation of spatial charge, which occurs as a result of beam current modulation due to plasma instabilities in the ion source; 3) Collective processes. The results presented in this review enable one to determine how non-compensated spatial charge, nonresonant oscillations of the beam current, and collective oscillations of the ion-beam plasma influence the propagation properties of the beam. With this information, one can determine the optimal ion transportation parameters.