A maximal electron current in a neutralized electron beam is constrained by
the beam-drift instability of the primary electrons and the neutralizing i
ons. To suppress this instability and to increase the threshold of the elec
tron current, the active methods are usually used. As a result of the appli
cation of these methods the spectrum of neutralizing ions is changed. The m
easurement of the ion mass spectrum is performed with the special ion mass
analyzer. The experiments on the JINR test bench show that the presence of
light ions (hydrogen) in the beam decreases the threshold beam current rela
ted to the beam-drift instability. (C) 2000 Elsevier Science B.V. All right
s reserved.