Stabilization of electron beam spot with gas cells in high-dose X-ray radiography

Summary form only given. Stability of radiographic spot has been under intensive study in recent years because of its importance in high-dose flash X-ray radiography. We have investigated a concept of placing a gas cell in front of the target to improve the stability of the spot size. The idea is to use the incoming electron beam to ionize the gas cell to a favorable density (in a time scale of pulse rise time), which causes charge and current neutralization on the electron beam. For an electron beam such as the DARHT beam (2 kA and 20 MeV), which is well below the Alfven current limit, we believe that there is an intermediate gas pressure regime where the stable beam propagation can be achieved. In our study, we first use a simple rate equation to calculate the ionization of the gas cell by the DAHRT beam. The model includes avalanche and recombination of the ionized electrons.