Accelerator physics challenges of the fs-slicing upgrade at the ALS
The goal of the Femtoslicing project at the ALS is to provide 100-200 fs long pulses of soft and hard x-rays with moderate flux and with a repetion rate of 10-40 kHz for experiments concerning ultrafast dynamics in solid state physics, chemistry and biology. The femtoslicing principle employs a femtosecond laser beam to interact resonantly (inverse FEL interaction) with the electron beam in the ALS. The induced energy spread over the femtosecond duration is converted to a transverse displacement by exploiting the dispersion of the storage ring. The displaced femtosecond electron pulse then radiates and produces femtosecond synchrotron radiation. To achieve the necessary spatial separation of the energy modulated slice from the rest of the bunch, a sizeable local vertical dispersion bump in the undulator used as radiator is required. This presents challenges in terms of the nonlinear dynamics and control of the vertical emittance.
