Electron Beam Delivery Systems
Production of electron beams for x-ray FELs is a difficult and elaborate process consisting of the electron generation, acceleration, compression, and transport. A significant understanding of the underlying physics such as space charge effects, wake-fields, and coherent synchrotron radiation (CSR) has been gained over the past decade. Radical improvements in the electron beam quality may be needed to be able to build a cost effective VUV-soft x-ray FEL facility. We are developing understanding of the beam phase space evolution, and means to control and manipulate emittances, using both theoretical approaches and high-resolution numerical modeling. We have developed a parallel code suite, IMPACT, for advanced supercomputer modeling of high intensity, high brightness beams in rf linacs and photoinjectors. An example is provided by 100 million macroparticle simulations of the microbunching instability, simulations that cannot be sensibly performed on today’s single-processor computers. Figure 1 shows a multiprocessor simulation using IMPACT for the longitudinal phase space of a beam. The figure shows the sensitivity to macroparticle number of the evolution of the microbunching instability. We are augmenting our present particle loading approach with “quiet-start” techniques, and in parallel we are also developing a direct Vlasov-Maxwell solution.
Following the accelerator, electron beams will be switched into each FEL in the array, in a time-sliced manner dependent on user needs. Techniques for switching the electron beam between FEL’s are being studied, using pulsed ferrite magnets in a linear array, selectively switching the beam into FEL beamlines.
FIGURES:
Longitudinal phase space distribution calculated using 10 million (red) and 1 billion (green) macroparticle IMPACT simulations. Blue shows the model with no space-charge or CSR effects.
