In recent years new processes of ion-plasma technology of thin-film coating in which rather dense mono-kinetic ion flows on processable substrates are used have been developed. In the processing of optical film coating, e.g., ion beams of argon, oxygen, and other heavy gases with a cross section of up to 100 mm in diameter, with a current density of up to 2 mA/cm2and energy 50–70 eV are required. Such beams are difficult for receiving in “classical” ion sources because of restriction on ion space charge. The new approach to resolve this problem consists of the application of decelerating the ions. In this method a broad ion beam is formed in an ion source of known type with the ion energy 500–1000 eV, and then the ions are decelerated in a specially developed ion decelerator. Devices on breaking of ion—ion decelerators based on the discharge with closed electron drift in crossed EXE fields were proposed and technological decelerators of ions, intended for processing of substrates with a diameter of up to 100 mm, were developed. The properties of the system consisting of an ion source and an ion decelerator, were investigated. It was shown that the researched system effectively produces ion beams with above-mentioned parameters. But in case of submission of breaking potential on DE, positive in relation to the output electrode of a source, potential of a beam also grows. The increase of the beam potential causes the reduction of the axial component of the ions’ velocity and preservation of their transversal velocity component constant. The divergency of a beam thus increases, and the ion current density on DE falls. Essential influence of a decelerating degree is shown at deep (more than 50&percent;) decelerating of ions on the ion current density distribution and on the plasma potential of the beam body. Probe measurements of the local plasma properties and ion beam parameters in the space of ion beam transportation were done and show that the change of the beam potential is observed in wide area of the beam, and only 30&percent;–40&percent; of the potential drop is concentrated in a short layer near DE. The analysis of balances of currents of ions and electrons in the investigated system are brought forward for cases, when no special means were used for the ion beam space charge compensation and when on the source output there a neutralizer in kind of a heated filament was applied. ©1998 American Institute of Physics.