Implementation of Radio-Frequency Deflecting Devices for Comprehensive High-Energy Electron Beam Diagnosis

Abstract

In next-generation light sources, high-brightness electron beams are used in a free-electron laser configuration to produce light for use by scientists and engineers in numerous fields of research. High-brightness beams are described for such light sources as having low transverse and longitudinal emittances, high peak currents, and low slice emittance and energy spread. The optimal generation and preservation of such high-brightness electron beams during the acceleration process and propagation to and through the photon-producing element is imperative to the quality and performance of the light source. To understand the electron beam's phase space in the accelerating section of a next-generation light source machine, we employed radio-frequency cavities operating in a deflecting mode in conjunction with a magnetic spectrometer and imaging system for both low (250 MeV) and high (1.2 GeV) electron energies. This high-resolution, high-energy system is an essential diagnostic for the optimization and control of the electron beam in the FERMI light source generating fully transversely and longitudinally coherent light in the VUV to soft x-ray wavelength regimes. This device is located at the end of the linear accelerator in order to provide the longitudinal phase space nearest to the entrance of the photon-producing beam-lines. Here, we describe the design, fabrication, characterization, commissioning, and operational implementation of this transverse deflecting cavity structure diagnostic system for the high-energy (1.2 GeV) regime

Coherent soft X-ray pulses from an echo-enabled harmonic generation free-electron laser

“…. The longitudinal phase space distribution at the end of the linac was measured by vertically stretching the electron beam using a radiofrequency deflecting cavity and dispersing it horizontally with a dipole magnet 47 .…”

Characterisation of microbunching instability with 2D Fourier analysis

“…The beam longitudinal phase space was measured at the Diagnostic Beam Dump (DBD) station (see Fig. 1) by means of a vertical RF deflector (VRFD) located at the end of L4, followed by a horizontal spectrometer magnet (SP) 48 . A screen in the DBD line provides a measurement of the energy of particles in the horizontal plane via the dispersion function of the spectrometer, and the arrival time of the particles in the beam through the calibration of the VRFD.…”

Two-bunch operation with ns temporal separation at the FERMI FEL facility

“…FEL-1 covers the spectral range between 20 and 100 nm, in FEL-2 this process of harmonic conversion is repeated twice and the range of operation is between 20 and 4 nm. Both the FEL lines are driven by the same linac, as sketched in figure 1, starting from the photoinjector [33], the S-band accelerating sections, the two magnetic bunch compressors, the energy spectrometer beam lines and the deflecting cavities [34].…”

“…The electron longitudinal phase space is routinely measured at the end of the linac, by combining the use of the rf deflector with the dispersion in the DBD [34]. The deflector stretches the beam vertically, imposing a correlation between the displacement of each electron and its temporal position, while the spectrometer disperses the particles horizontally according to their energy [40].…”