Speaker: Speaker needed

Speaker: Speaker needed

Location: Zoom 

Meeting ID: 919 0856 4931  Passcode: 476937

Title: Theoretical Characterization of the Nanoblade Optical Field Emission Cathode   

Abstract: Optical field emission enhanced by nanostructure-induced focusing beyond the diffraction imit promises high-current,  high-brightness electron beams. The nanoblade, an atomically sharp wedge with a metallic coating, has boasted enhanced fields up to 80 V/nm at a wavelength of 800 nm. Furthermore, the associated rescattering process produces high harmonic generation which may be of greater intensity than that of gas sources. In this thesis we aim to theoretically and computationally characterize the nanoblade cathode. In studying quasi-static field emission, we produce an effective source distribution applicable for any conductor, finding strong deviations from free-electron gas results for tungsten and copper-group (111) surfaces. We consider the near-field ponderomotive dynamics under the existence of a strong field gradient, finding modifications to existing classical rescattering cutoffs which will become of import particularly in high-wavelength ventures. In finding the limits of such a cathode, we perform a simple comparative thermomechanical study of tips and blades and find that structures with large opening angles perform better than their narrower counterparts. We explore the distribution of emitted radiation and consider the addition of gratings to improve high harmonic generation prospects. To estimate the emittance, brightness, and radiation yield, we develop an object-oriented time-dependent density-functional theory code, in C++ with a Python wrapper, which projects the grander system down to a single dimension. The following unprojection scheme permits the efficient estimation of these critical beam properties.

1:00 PM PST|3:00 PM CST|4:00 PM EST

Speaker: Brian Schaap, UCLA

Host: Philippe Piot

Abstract: Inverse Compton scattering by relativistic electrons off intense laser pulses is becoming an increasingly prevalent compact source of tunable radiation in X-ray spectral range. The brightness of typical Compton sources, unfortunately, remains small compared to large scale facilities. The Compton brightness can be enhanced significantly via a shallow angle scattering geometry and superradiant emission from a density modulated electron beam, which are shown to be complementary methods via the use of inverse free electron laser microbunching. Furthermore, we will discuss our experimental efforts towards the observation of superradiant Compton scattering at the UCLA Pegasus laboratory, including diagnostics of strongly compressed electron bunches -such as longitudinal phase space tomography, electro-optic sampling, and THz streaking- and the recent demonstration of shallow angle Compton scattering.

Visitors: Those from outside Argonne who wish to attend in person must contact  accelerator@anl.gov  to arrange a gate pass.

Title: Advanced Temporal and Phase-Space Diagnostics for X-ray Free-Electron Lasers

Host: Nathan Sitaraman 

Abstract: Precise characterization of electron and photon beams is vital for advancing the performance and scientific capabilities of X-ray free-electron lasers (XFELs). In this seminar, we present recent breakthroughs in time-resolved diagnostics and phase-space reconstruction techniques for XFEL applications. First, we discuss attosecond-resolution measurements enabled by a variable polarization X-band radiofrequency transverse deflecting structure (TDS) at SwissFEL’s Athos beamline, which allow full reconstruction of FEL power profiles with pulse durations as short as 300 attoseconds. Second, we introduce a novel approach for five-dimensional (5D) phase-space tomography, experimentally demonstrated at FLASHForward and later applied at SwissFEL, offering comprehensive insight into the spatial and momentum distributions of GeV-class electron beams. Finally, we explore a self-synchronized, cost-effective diagnostic method using wakefield streaking in corrugated structures, achieving femtosecond temporal resolution without active synchronization. Together, these techniques represent a significant leap forward in ultrafast beam diagnostics, enabling new levels of control and optimization for current and future XFEL facilities.