The PolariX TDS (Polarizable X-Band Transverse Deflection Structure) is an innovative TDS-design operating in the X-band frequency-range. The design gives full control of the streaking plane, which can be tuned in order to characterize the projections of the beam distribution onto arbitrary transverse axes. This novel feature opens up new opportunities for detailed characterization of the electron beam. In this paper we present first measurements of the Polarix TDS at the FLASHForward beamline at DESY, including three-dimensional reconstruction of the charge-density distribution of the bunch and slice emittance measurements in both transverse directions. The experimental results open the path toward novel and more extensive beam characterization in the direction of multi-dimensional-beam-phase-space reconstruction.

/pdf/experimental-demonstration-of-novel-beam-characterization-14i9g43bmi.pdf

Experimental demonstration of novel beam characterization using a polarizable X-band transverse deflection structure.

Virtual Diagnostic (VD) is a computational tool based on deep learning that can be used to predict a diagnostic output. VDs are especially useful in systems where measuring the output is invasive, limited, costly or runs the risk of altering the output. Given a prediction, it is necessary to relay how reliable that prediction is, i.e. quantify the uncertainty of the prediction. In this paper, we use ensemble methods and quantile regression neural networks to explore different ways of creating and analyzing prediction's uncertainty on experimental data from the Linac Coherent Light Source at SLAC National Lab. We aim to accurately and confidently predict the current profile or longitudinal phase space images of the electron beam. The ability to make informed decisions under uncertainty is crucial for reliable deployment of deep learning tools on safety-critical systems as particle accelerators.

Uncertainty Quantification for Virtual Diagnostic of Particle Accelerators

X-ray free-electron lasers (FELs) are state-of-the-art scientific tools capable to study matter on the scale of atomic processes. Since the initial operation of X-ray FELs more than a decade ago, several facilities with upgraded performance have been put in operation. Here we present the first lasing results of Athos, the soft X-ray FEL beamline of SwissFEL at the Paul Scherrer Institute in Switzerland. Athos features an undulator layout based on short APPLE-X modules providing full polarisation control, interleaved with small magnetic chicanes. This versatile configuration allows for many operational modes, giving control over many FEL properties. We show, for example, a 35% reduction of the required undulator length to achieve FEL saturation with respect to standard undulator configurations. We also demonstrate the generation of more powerful pulses than the ones obtained in typical undulators. Athos represents a fundamental step forward in the design of FEL facilities, creating opportunities in FEL-based sciences. 

An X-ray free-electron laser with a highly configurable undulator and integrated chicanes for tailored pulse properties

We demonstrate the generation of widely tunable two-color x-ray free-electron laser (FEL) pulses at SwissFEL. In a split-undulator configuration, each color is produced in a different undulator section, and a chicane between the two sections allows for a variable time separation between the two pulses of up to 500 fs. We show an unprecedented photon energy ratio between the two colors of about three (350 and 915 eV), with each individual pulse having a peak power of a few gigawatts and a duration down to the femtosecond level. Moreover, we demonstrate the reduction of the required undulator length via the optical klystron mechanism and the time-resolved diagnostics of the FEL pulses utilizing the same beam setup as for the pulse generation. The unique combination of widely tunable energy and time separation of the two-color pulse pair offers opportunities to study ultrafast x-ray-induced energy transfer and relaxation processes in physics, chemistry, and biology.Received 21 February 2022Accepted 4 April 2022DOI:https://doi.org/10.1103/PhysRevResearch.4.L022025Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBeam diagnosticsX-ray lasersPhysical SystemsFree-electron lasersLinear acceleratorsAccelerators & BeamsAtomic, Molecular & OpticalParticles & Fields 

/pdf/widely-tunable-two-color-x-ray-free-electron-laser-pulses-1rh9h0pv.pdf

Widely tunable two-color x-ray free-electron laser pulses

X-ray free-electron lasers (XFELs), with pulse durations of a few tens of femtoseconds or shorter, are cutting-edge instruments capable of observing structure and dynamics at the atomic scale. Temporal diagnostics are challenging but of fundamental importance for XFEL performance and experiments. In this paper, we demonstrate a method to characterize on a single-shot basis the temporal profile of both the electron beam and the XFEL radiation with femtosecond resolution. The approach consists in streaking the electron beam after the undulator using the wakefields of a corrugated structure. Its merits are arrival time stability and cost-effectiveness. Our method allows access to self-synchronized femtosecond diagnostics to any XFEL facility at low cost. 

/pdf/self-synchronized-and-cost-effective-time-resolved-1j0381z8.pdf

Self-synchronized and cost-effective time-resolved measurements at x-ray free-electron lasers with femtosecond resolution

A collaboration between DESY, PSI and CERN has developed and built an advanced modular X-band transverse deflection structure (TDS) system with the new feature of providing variable polarization of the deflecting force. The prototype of the novel X-band TDS, the polarizable $X$-band (PolariX) TDS, was fabricated at PSI following the high-precision tuning-free production process developed for the C-band Linac of the SwissFEL project. Bead-pull rf measurements were also performed at PSI to verify, in particular, that the polarization of the dipole fields does not have any rotation along the structure. The high-power test was performed at CERN and now the TDS is at DESY and has been installed in the FLASHForward beamline, where the first streaking experience with beam has been accomplished. We summarize in this paper the rf design of the TDS and its key components, such as the $X$-band pulse compressor, E-rotator, and phase shifter, the results of the bead-pull measurements and the high power test and finally the rf setup at DESY.

/pdf/novel-x-band-transverse-deflection-structure-with-variable-3nw1v35e5p.pdf

Novel $X$-band transverse deflection structure with variable polarization

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Novel $X$-band transverse deflection structure with variable polarization