Steady-state solutions of split beams in electron storage rings

Recently, a novel operation method for synchrotron light sources with transversely split beams has been explored to fulfill the rising demand for flexible and high-throughput X-ray sources required in such diverse fields as time-resolved X-ray spectroscopy, molecular chemistry in organic cells, high-resolution medical imaging, quantum materials science or sustainable energy research. Within that novel operation mode, additional stable regions are produced in the horizontal phase space by operating an electron storage ring on a resonance that is driven by the nonlinear sextupole or octupole magnets. In the longitudinal phase space, a similar split can be produced by introducing an oscillation of the synchrotron phase via a modulation of the phase of the radiofrequency resonator. Strong radiation damping in electron storage rings, however, has to be overcome before additional regions in phase space can become populated by particles and form stable islands. This damping mechanism changes the dynamics of the system and causes diffusion between the different islands in phase space, raising the question what kind of equilibrium state exists in the asymptotic temporal limit. In this paper, a finite-differences approximation in rotating action-angle coordinates is used to solve the Vlasov–Fokker–Planck equation and to study the obtained equilibrium states for the longitudinal as well as the transverse case. The number of solution vectors and the magnitude of the corresponding singular values of the matrix of the underlying finite-differences equation are used as abstract indicators to define the required parameter set that provides stable additional beamlets. As a consequence, the beamlets have a stability that is close to that of the main beam in terms of diffusion caused by the radiation damping and quantum excitation

Stadtbahn und U-Bahn in Wien

Ein erster großer Wettbewerb zur Errichtung einer Stadtbahn in Wien endete im Jahre 1873. Doch es sollten noch 25 Jahre vergehen, ehe die Wiener Dampfstadtbahn den Betrieb aufnehmen konnte. Die Wiener Stadtbahn sollte das erste Schnellverkehrsmittel der Stadt werden, doch der ihr beschiedene Erfolg blieb bescheiden. Es war nur ein Grundgerüst geschaffen worden, das zwar dem Arbeitsverkehr nicht genügte, sich allerdings bei Ausflüglern am Wochenende großer Beliebtheit erfreute. Erst durch die Elektrifizierung Mitte der 1920er Jahre trat der erhoffte Erfolg der neuen "Wiener elektrischen Stadtbahn" ein. Während in der frühen Phase der Massenmotorisierung nach dem Zweiten Weltkrieg die Meinung vorherrschte, die Stadt müsse dem Verkehr angepasst werden, kam es im Laufe der 1960er Jahre langsam zu einem Meinungsumschwung. Mit der Wiener U-Bahn kam es zu einem neuen Leitparadigma in der kommunalen Verkehrs- und Planungspolitik: Dem öffentlichen Verkehr wurde gegenüber dem motorisierten Individualverkehr der Vorzug gegeben. Der Verkehr sollte nun der Stadt angepasst werden, die U-Bahn wurde zum Impulsgeber, an deren Liniennetz sich die Entwicklung der Stadt orientieren sollte

Effective wound closure with a new two-component wound closure device (Prineo™) in excisional body-contouring surgery: experience in over 200 procedures

In excisional body-contouring surgery the surgeon is often confronted with time-consuming closure of long wounds. Recently, a new combination of a self-adhering mesh together with a liquid 2-octyl cyanoacrylate adhesive (Prineo™; Ethicon, Inc., Somerville, NJ, USA) has been introduced to replace intracutaneous running suture

Attoclock Ptychography

Dedicated simulations show that the application of time-domain ptychography to angular photo-electron streaking data allows shot-to-shot reconstruction of individual X-ray free electron laser pulses. Specifically, in this study, we use an extended ptychographic iterative engine to retrieve both the unknown X-ray pulse and the unknown streak field. We evaluate the quality of reconstruction versus spectral resolution, signal-to-noise and sampling size of the spectrogram

Laser-induced inner-shell excitations through direct electron re-collision versus indirect collision

The dynamics and the decay processes of inner-shell excited atoms are of great interest in physics, chemistry, biology, and technology. The highly excited state decays very quickly through different channels, both radiative and non-radiative. It is therefore a long-standing goal to study such dynamics directly in the time domain. Using few-cycle infrared laser pulses, we investigated the excitation and ionization of inner-shell electrons through laser-induced electron re-collision with the original parent ions and measured the dependence of the emitted x-ray spectra on the intensity and ellipticity of the driving laser. These directly re-colliding electrons can be used as the initiating pump step in pump/probe experiments for studying core-hole dynamics at their natural temporal scale. In our experiment we found that the dependence of the x-ray emission spectrum on the laser intensity and polarization state varies distinctly for the two kinds of atomic systems. Relying on our data and numerical simulations, we explain this behavior by the presence of different excitation mechanisms that are contributing in different ratios to the respective overall x-ray emission yields. Direct re-collision excitation competes with indirect collisions with neighboring atoms by electrons having "drifted away" from the original parent ion. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Propagation-enhanced generation of intense high-harmonic continua in the 100-eV spectral region

The study of core electron dynamics through nonlinear spectroscopy requires intense isolated attosecond extreme ultraviolet or even X-ray pulses. A robust way to produce these pulses is high-harmonic generation (HHG) in a gas medium. However, the energy upscaling of the process depends on a very demanding next-generation laser technology that provides multi-terawatt (TW) laser pulses with few-optical-cycle duration and controlled electric field. Here, we revisit the HHG process driven by 16-TW sub-two-cycle laser pulses to reach high intensity in the 100-eV spectral region and beyond. We show that the combination of above barrier-suppression intensity with a long generation medium significantly enhances the isolation of attosecond pulses compared to lower intensities and/or shorter media and this way reduces the pulse duration as well as field-stability requirements on the laser driver. This novel regime facilitates the real-time observation of electron dynamics at the attosecond timescale in atoms, molecules, and solids

A self-referenced in-situ arrival time monitor for X-ray free-electron lasers

We present a novel, highly versatile, and self-referenced arrival time monitor for measuring the femtosecond time delay between a hard X-ray pulse from a free-electron laser and an optical laser pulse, measured directly on the same sample used for pump-probe experiments. Two chirped and picosecond long optical supercontinuum pulses traverse the sample with a mutually fixed time delay of 970 fs, while a femtosecond X-ray pulse arrives at an instant in between both pulses. Behind the sample the supercontinuum pulses are temporally overlapped to yield near-perfect destructive interference in the absence of the X-ray pulse. Stimulation of the sample with an X-ray pulse delivers non-zero contributions at certain optical wavelengths, which serve as a measure of the relative arrival time of the X-ray pulse with an accuracy of better than 25 fs. We find an excellent agreement of our monitor with the existing timing diagnostics at the SACLA XFEL with a Pearson correlation value of 0.98. We demonstrate a high sensitivity to measure X-ray pulses with pulse energies as low as 30 $\mu$J. Using a free-flowing liquid jet as interaction sample ensures the full replacement of the sample volume for each X-ray/optical event, thus enabling its utility even at MHz repetition rate XFEL sources