Flash X-Ray (FXR) Accelerator Optimization - Beam-induced Voltage Simulation and TDR Measurements

Ong, M M ; Vogtlin, G E

Lawrence Livermore National Laboratory

关键词: Lawrence Livermore National Laboratory;    43 Particle Accelerators;    Computerized Simulation;    Simulation;    42 Engineering;   

DOI  :  10.2172/15014170
RP-ID  :  UCRL-TR-205798
RP-ID  :  W-7405-ENG-48
RP-ID  :  15014170

美国|英语

来源: UNT Digital Library

【 摘 要 】

Lawrence Livermore National Laboratory (LLNL) is evaluating design alternatives to improve the voltage regulation in our Flash X-Ray (FXR) accelerator cell and pulse-power system. The goal is to create a more mono-energetic electron beam that will create an x-ray source with a smaller spot-size. Studying the interaction of the beam and accelerator cell will generate improved designs for high-current accelerators at Livermore and elsewhere. When an electron beam crosses the energized gap of an accelerator cell, the electron energy is increased. However, the beam with the associated electromagnetic wave also looses a small amount of energy because of the increased impedance seen across the gap. The phenomenon is sometimes called beam loading. It can also be described as a beam-induced voltage at the gap which is time varying. This creates beam energy variations that we need to understand and control. A high-fidelity computer simulation of the beam and cell interaction has been completed to quantify the time varying induced voltage at the gap. The cell and pulse-power system was characterized using a Time-domain Reflectometry (TDR) measurement technique with a coaxial air-line to drive the cell gap. The beam-induced cell voltage is computed by convoluting the cell impedance with measured beam current. The voltage was checked against other measurements to validate the accuracy. The simulation results predicted that there are significant beam-induced gap voltage variations. Beam-induced voltages from different current profiles and cell impedances were simulated and compared. This allows us to predict the effect on voltage regulation for different design alternatives before making hardware changes and high-voltage testing. The beam-induced voltages are incorporated into a larger accelerator system-model to quantify their effect on total beam energy variations.