A compact and cost-effective hard X-ray free-electron laser driven by a high-brightness and low-energy electron beam

We present the first lasing results of SwissFEL, a hard X-ray free-electron laser (FEL) that recently came into operation at the Paul Scherrer Institute in Switzerland. SwissFEL is a very stable, compact and cost-effective X-ray FEL facility driven by a low-energy and ultra-low-emittance electron beam travelling through short-period undulators. It delivers stable hard X-ray FEL radiation at 1-Å wavelength with pulse energies of more than 500 μJ, pulse durations of ~30 fs (root mean square) and spectral bandwidth below the per-mil level. Using special configurations, we have produced pulses shorter than 1 fs and, in a different set-up, broadband radiation with an unprecedented bandwidth of ~2%. The extremely small emittance demonstrated at SwissFEL paves the way for even more compact and affordable hard X-ray FELs, potentially boosting the number of facilities worldwide and thereby expanding the population of the scientific community that has access to X-ray FEL radiation

Investigating the role of photoemission in the e-cloud formation at the LHC

The presence of electron clouds at the LHC gives rise to sev-eral problems, among them is the heat deposited by the elec-trons on the beam screens of the superconducting magnets,which constitutes a significant load for the cooling system.To improve the understanding of this phenomenon, simula-tion studies of the e-cloud build-up are performed using thededicated simulation tool PyECLOUD. Photoelectrons gen-erated by synchrotron radiation can significantly enhancethe e-cloud formation. In this contribution, the availableliterature on photoelectric properties of the material usedfor the LHC beam screens is reviewed, and the number ofphotons emitted by the beam is calculated. This allows thedefinition of suitable simulation parameters for modeling theelectrons from photoemission within the PyECLOUD code.The simulations with photoemission seeding are comparedto those that neglect photoemitted electrons. The predictedheat loads are compared against measurements from LHCcryogenic cells. Since these cells include several kinds ofmagnets, simulations with dierent configurations of theexternally applied magnetic field had to be combined. Fur-thermore a sensitivity study on the modeling of synchrotronradiation is presented

Overview on heat loads in the LHC

A consequence of the formation of electron cloud in beam chambers is the deposition of energy on their walls due to electron impacts. In cryogenic devices this can cause a significant heat load for the cryogenics system, posing constraints on machine design and operation At the LHC this effect is found to be quite strong and needs to be addressed to avoid performance limitations in view of the planned HL-LHC upgrade. Unexpectedly the eight LHC arcs show very dierent heat loads. These differences, which appeared after the 2013-14 shut-down period, are still unexplained and have been the subject of thorough investigations and characterizations. This contribution describes the main observations on the heat loads deposited on the arc beam screens with different beam conditions and in dierent moments of the LHC operational experience

Single- and two-color attosecond hard x-ray free-electron laser pulses with nonlinear compression

We report on the generation of one- and two-color attosecond hard x-ray pulses at SwissFEL by appropriately tailoring the nonlinear compression of the electron beam. For achieving very short [about 300 attoseconds (as)] and stable single-color pulses, we minimize the collective effects of the longitudinal space-charge forces by strongly compressing the electron beam right before the undulator, utilizing the energy collimator chicane as a third compression stage. For achieving two-color short pulses, we exploit enhanced space-charge forces splitting the beam into two energy components.ISSN:2643-156

Electron cloud effects at the CERN accelerators

Electron cloud eects have been identified as one of themain performance limitations for some of the synchrotronsof the CERN accelerator complex. The tools for the simula-tion of the electron cloud build-up and its eects on beamstability have significantly evolved in recent years, leadingto a much better understanding of all machine observations.At the same time, electron cloud mitigation measures havebeen tested (e.g. surface treatments) and implemented inoperation (e.g. beam induced scrubbing). The combinationof a deeper understanding of the electron cloud and a handleon its mitigation has been the key to reach and exceed thenominal luminosity in the LHC during Run 2 as well as todefine strategies to cope with the High Luminosity (HL)operation of the LHC as from 2026

Frequency and spatially chirped free-electron laser pulses

We have produced hard x-ray free-electron laser (FEL) pulses, which are chirped both in photon energy and in spatial position. The experiments have been carried out at the hard x-ray beamline Aramis at SwissFEL, located at the Paul Scherrer Institute in Switzerland. The FEL beamline was operated without any external focusing and with a tilted, energy-chirped electron bunch, whose properties are then transferred to the photon beam. The resulting FEL pulses were used for a single-shot absorption x-ray spectroscopy experiment at the Alvra endstation. But, as will be outlined, applications of this type of tailored FEL pulse go beyond such experiments, allowing for x-ray pulse compression and control of the transverse coherence within the puls