Simulations, experiments, and analysis of beam target interaction

The onset of the growth of the electron beam spot due to partial charge neutralization by ions extracted from the target plasma has been predicted by theory and simulation. The concept of an electrically self-biased target was developed to control the length of the ion column and experiments were fielded on the Integrated Test Stand (ITS) for the Dual Axis Radiographic Hydro Test (DARHT) facility at Los Alamos National Laboratory. The experimental results confirmed the stability of the spot size when the target is self-biased at a potential of 350 kV. Our analyses and quantitative comparison between computer simulations and experiments show that the ions generated by the electron beam were from target materials and that the delay for onset of the spot growth was governed by the time needed for the ionization of target material and formation of the ion column with sufficient length.