Computer Simulation of Gas-filled Neutron Tube Ion-optic System

Computer simulation of gas-filled neutron tube has been fulfilled. Fully relativistic electromagnetic particle-in-cell finite difference, time-domain cod SUMA [1,2] has been used to investigate ion-optic system, the ionization and knock on processes and their influence on the deuteron beam and the output neutron flow parameters. When deuteron and ionized particles space charge self-field forces become the same order of magnitude as external one, virtual cathode may occurs. It happens because the injected from ion source deuterons cannot overcome their own space charge potential wall and move in transverse direction. However, electrons, produced by ionization, are trapped within the deuteron beam space charge potential wall and decrease it significantly. Thus, space charge neutralization of deuteron beams by electrons, may considerably increase target current and, as a result, output neutron flow. Moreover, own longitudinal electric field rise near the target leads to reduction of accelerating electrode target potential wall, which was made to prevent knock on emission from the target. As a result, additional knocked on electrons may appear in the region and should be taken into account. The data obtained were compared with experimental results.