Study of the space charge potential of ion beams

Abstract

The energy distribution of slow residual gas ions created by an ion beam in collisions with the residual gas molecules inside an ion beam transport system has been measured with an electrostatic spectrometer. For this investigations Ar + ion beams (dc) were used, with energies between 15 and 45 keV. The beam current has been varied from 0.01 up to 1.6 mA. Further parameters were the residual gas pressure, the gas composition, the beam diameter and the potentials of several clearing electrodes in the beam transport system. The experimental results are compared with the calculated values of the space charge potentials of the ion beam. In operating the spectrometer in a gated mode the time could be measured which is necessary to build up the space charge compensation in a pulsed ion beam. Additional residual gas ions produced at different radial distances from the ion beam axis by an electron beam allowed to determine the radial potential distribution.