SLAC, Menlo Park, California, USA
LBNL, Berkeley, California, USA
SLAC, Menlo Park, California, USA
LANL, Los Alamos, New Mexico, USA
FACET produces high energy density electron beams for Plasma Wakefield Acceleration (PWFA) experiments. The high energy density beams are created by chirping the electron beam with accelerating sections and compressing the beam in magnetic chicanes. Precise control of the longitudinal beam profile is needed for the drive-witness bunch PWFA experiments currently underway at FACET. We discuss the simulations, controls, and diagnostics used to achieve FACET's unique longitudinal phase space.
SLAC, Menlo Park, California, USA
SLAC, Menlo Park, California, USA
The Facility for Advanced aCcelerator Experimental Tests (FACET) consists of the first two-thirds of the SLAC two-mile linac followed by a final focus and experimental end station. To date, wakefield-dominated emittance growth and dispersion in the linac, as well as dispersive and chromatic effects in the final focus have precluded regular reliable operation that meets the design parameters for final spot size. In this work, a 6-D particle tracking code (Lucretia) is used to simulate the complete machine, with input parameters taken directly from saved machine configurations. Sensitivities of various tuning parameters to the final spot sizes are compared with measurements taken from the real machine, and a set of tuning protocols is determined to improve regular machine operation.
SLAC, Menlo Park, California, USA
Two thirds of the SLAC Linac is used to generate a short, intense electron beam for the FACET experiments. The emittance growth along the Linac is a major concern to finally get small spot sizes for these experiments. There are two different approaches to get the required small emittances: a) lengthy iterative global tuning technique, and b) trying to identify locations of the main sources of the emittance growth and reducing their effect locally. How these approaches help to get good beam performances is discussed.
SLAC, Menlo Park, California, USA
The FACET accelerator facility is designed to provide short and intense e- or e+ bunches with small spot size for plasma wakefield accelerator research and other experiments. It is based on the SLAC linac with a compressor chicane in sector-10, and a second compressor chicane and final focus in sector-20 (S20). Originally, the S20 chicane was designed to be compatible with an upgrade to include a second S20 chicane for simultaneous transport of e- and e+ bunches. This placed additional optics constraints which lead to strong focusing in the S20 chicane. The latter increases the effects of errors causing emittance growth. Lately, it has been decided not to proceed with the upgrade option. Therefore, there is a potential for improving the optics by relaxing the constraints. In this study, we explore alternative optics designs where beta functions in the S20 chicane and final focus are reduced in order to minimize the error effects. The optics and non-linear aberrations are evaluated, and the chromatic correction is optimized for each design. Beam tracking simulations are performed using Elegant and Lucretia. The most optimal designs are identified based on these simulations.
SLAC, Menlo Park, California, USA
We report the first measurement of spectral line-width reduction in a self-amplified spontaneous emission (SASE) X-ray free-electron laser (FEL) obtained by introducing repeated delays of the electron bunch with respect to the radiation field pulse. The improved longitudinal coherence obtained by this method reduces the intensity spiking effect characteristic of a SASE FEL. The electron-photon delays introduced along the FEL undulator mix the spikes phase and amplitude, increasing the cooperation length and generating a smaller bandwidth than in the conventional SASE mode of operation of an FEL. We call this mode of operation, based on repeated electron-photon delays, ‘‘improved SASE'' (iSASE). We also show with theoretical and simulation analysis that in the iSASE mode it is possible to choose the separation and magnitude of the delays to obtain a nearly transform limited X-ray pulse. This analysis is carried out using a time dependent, one-dimensional model and with GENESIS numerical simulation, including three-dimensional effects.
