A study of electron strings and their use for efficient production of highly charged ions

An electron string is a state of a one component electron plasma, which can arise when multiply reflected electrons are accumulated in a strong solenoidal magnetic field. Based on the electron beam ion source (EBIS) in the reflex mode of operation the processes of the string formation and its decay were observed and the characteristic times of the processes have been measured. Information about the electron energy distribution in electron strings has been obtained using four independent methods. It was shown, the distribution is broad and, moreover, there is some amount of electrons, having energies higher than the energy of the electrons used for feeding the string. An instability was observed as a starting point of electron string formation. The instability is strongly suppressed and the string is formed when the injecting electron current reaches a threshold value, which depends on a quality of electron focusing. Most likely the instability observed is responsible for the string electron energy spread. The results of the string formation using various constructions of electron gun and electron repeller, situated in magnetic fields of various induction, are presented. Similar to electron beams in EBIS, electron strings were successfully used for production of highly charged ions. The first attempts of a theoretical description of the electron string phenomenon are briefly discussed. (C) 2000 American Institute of Physics. [S0034-6748(00)60402-1].