Plasma suppression and spot size stabilization in single and multiple pulse flash X-ray radiography

Summary form only given. Next generation X-ray radiography machines must use high electron beam current to provide the necessary dose and very small spot size to achieve the desired optical resolution. However, this combination of high current in a small area leads to undesirable side effects that were not important in old machines. Specifically, the intense local energy deposition from the high intensity electron beam causes vaporization of the bremsstrahlung target. The hot plasma thus generated provides a copious source of positive ions that are rapidly accelerated into the negative potential well of the incoming electron beam. As the ions propagate upstream, they partially charge neutralize the electron beam, causing its spot size to increase. We have studied the electron beam spot stabilization for the Dual Axis Radiographic Hydrotest Facility (DARHT).