The dynamics of space charge compensation

The classical operation of EBIS (electron beam ion source) avoided to use confinement times close to the compensation time. However the results of EBIT (electron beam ion trap) as well as of EBIS sources operating with a gas mixture--purposely or due to a too high residual gas pressure--have shown, that advantage may be taken from confinement times longer than the compensation time. By numerical simulations it has been found that compensation by thermal ions does not lead to a complete loss of radial confinement. Instead, the compensated electron beam acts as a radial energy filter for the ions produced: Hot ions are lost, cold ions become confined to the beam even better. By a dynamical simulation of space charge compensation, the time dependence of important features can be studied and interpreted with respect to experimental results, like electron-ion-overlap, ion cooling by newly born ions and by evaporated ions, and the loss of thermal ions until compensation is reached