"Real-Life" Pulse Flattening on the LLNL Flash X-Ray (FXR) Machine

Abstract

Summary form only given. High-resolution radiography using high-current electron accelerators based on the induction linac principle requires the linac's final spot on the X-ray target to be millimeter-sized. The requisite final focusing solenoid must then be adjusted for a specific beam energy at its entrance. Temporal variation of entrance beam energy then results in a less than optimal time- averaged spot size. The now-mature FXR (Flash X-Ray) induction linac facility at Lawrence Livermore National Laboratory will be briefly described with an emphasis on its pulsed power system. In principle, the pulsed Blumleins at the heart of the system output a square pulse, so that with correct cell timing synchronization, the effective beam output into the final focusing solenoid should be optimally flat. We have found that real-life considerations of transmission line and pulse power details in both the injector and accelerator sections of the machine results in significant energy variations in the final beam. We have implemented methods of measurement and analysis that permits this situation to be quantified and improved upon. This methodology will be described and before and after results documented. The improvement will be linked to final beam spot size and enhancement in expected radiographic resolution.