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Nature Communications 12(1), 1638 (2021). doi:10.1038/s41467-021-21756-6, Key insights in materials at extreme temperatures and pressures can be gained by accurate measurements that determine the electrical conductivity. Free-electron laser pulses can ionize and excite matter out of equilibrium on femtosecond time scales, modifying the electronic and ionic structures and enhancing electronic scattering properties. The transient evolution of the conductivity manifests the energy coupling from high temperature electrons to low temperature ions. Here we combine accelerator-based, high-brightness multi-cycle terahertz radiation with a single-shot electro-optic sampling technique to probe the evolution of DC electrical conductivity using terahertz transmission measurements on sub-picosecond time scales with a multi-undulator free electron laser. Our results allow the direct determination of the electron-electron and electron-ion scattering frequencies that are the major contributors of the electrical resistivity., Published by Nature Publishing Group UK, [London]

Journal of synchrotron radiation 28(1), - (2021). doi:10.1107/S1600577520015052, This paper reports on nonlinear spectral broadening of 1.1 ps pulses in a gas-filled multi-pass cell to generate sub-100 fs optical pulses at 1030 nm and 515 nm at pulse energies of 0.8 mJ and 225 µJ, respectively, for pump–probe experiments at the free-electron laser FLASH. Combining a 100 kHz Yb:YAG laser with 180 W in-burst average power and a post-compression platform enables reaching simultaneously high average powers and short pulse durations for high-repetition-rate FEL pump–probe experiments., Published by Wiley-Blackwell, [S.l.]

Effects producing gain dilution in Free Electron Laser devices are well documented. We develop here a unified point of view allowing the introduction of space charge effects, along with the gain deterioration due to inhomogeneous broadening contributions and discuss the relevant interplay. We outline future developments and comment on the possibility of including in the formalism effects of quantum mechanical nature., 10 pages, 7 figures

The PixFEL collaboration has developed the building blocks for an X-ray imager to be used in applications at FELs. In particular, slim edge pixel detectors with high detection efficiency over a broad energy range, from 1 to 12 keV, have been developed. Moreover, a multichannel readout chip, called PFM2 (PixFEL front-end Matrix 2) and consisting of 32 × 32 cells, has been designed and fabricated in a 65 nm CMOS technology. The pixel pitch is 110 μm, the overall area is around 16 mm2. In the chip, different solutions have been implemented for the readout channel, which includes a charge sensitive amplifier (CSA) with dynamic signal compression, a time-variant shaper and an A-to-D converter with a 10 bit resolution. The CSA can be configured in four different gain modes, so as to comply with photon energies in the 1 to 10 keV range. The paper will describe in detail the channel architecture and present the results from the characterization of PFM2. It will discuss the design of a new version of the chip, called PFM3, suitable for post-processing with peripheral, under-pad through silicon vias (TSVs), which are needed to develop four-side buttable chips and cover large surfaces with minimum inactive area.

The Shanghai soft X-ray Free-Electron Laser facility (SXFEL) is being developed in two steps; the SXFEL test facility (SXFEL-TF), and the SXFEL user facility (SXFEL-UF). The SXFEL-TF is a critical development step towards the construction a soft X-ray FEL user facility in China, and is under commissioning at the Shanghai Synchrotron Radiation Facility (SSRF) campus. The test facility is going to generate 8.8 nm FEL radiation using an 840 MeV electron linac passing through the two-stage cascaded HGHG-HGHG or EEHG-HGHG (high-gain harmonic generation, echo-enabled harmonic generation) scheme. The construction of the SXFEL-TF started at the end of 2014. Its accelerator tunnel and klystron gallery were ready for equipment installation in April 2016, and the installation of the SXFEL-TF linac and radiator undulators were completed by the end of 2016. In the meantime, the SXFEL-UF, with a designated wavelength in the water window region, began construction in November 2016. This was based on upgrading the linac energy to 1.5 GeV, and the building of a second undulator line and five experimental end-stations. Construction status and the future plans of the SXFEL are reported in this paper.

In the context of a collaboration between LAL (Orsay) and DESY (Hamburg) a programme of development and tests of proto-type power couplers for superconducting cavities is underway in Orsay. Such couplers need to be developed for linear accelerators which require high gradient superconducting cavities, such as the European X ray Free Electron Laser or the International Linear Collider (ILC) project. We will describe the technical demands which have to be met to build such couplers and will present proto-type designs which are intended to meet these demands, taking the ILC as an example. A description of the infra-structure necessary for the coupler development will also be given along with first high power tests results on a series of power couplers built in industry.