Beam-target interaction for high-dose, multi-pulse radiography

Summary form only given. The conversion of an intense relativistic electron beam into X-rays for radiographic imaging is achieved through the bremsstrahlung process of electrons in a tantalum or tungsten target of some optimal thickness. A high-dose radiographic source with small spot size is needed to achieve desirable resolution for thick objects. Consequently, an extremely high brightness electron beam is used and a significant amount of electron beam energy can be deposited in a small area of the target. Vaporization of the target material and plasma generation can result. We describe a computational methodology used to model the beam-target interaction and the evolution of the resultant plasma. Several codes, including particle-in-cell (PIC), Monte Carlo transport, and magnetohydrodynamic (MHD) codes, contribute to simulate different parts of the problem in a linked fashion. Multi-dimensional PIC calculations provide detailed characterization of the beam transmitted to the target foil. Electron-photon Monte Carlo transport codes calculate beam scattering and energy deposition in the target. These energy source conditions are used in 1-D and 2-D MHD codes to model the foil expansion and the evolution of the target plasma issues addressed by the calculations include: the effects of the time dependence of the energy profile deposited in the target; the influence of the external magnetic field on plasma expansion; the influence of the expanding plasma on the guide magnetic field (and, consequently, on the beam quality); radiation effects; and multi-dimensional effects.