The hard X-ray twisted photons and relativistic massive particles with orbital angular momentum – vortex electrons, muons, protons, etc. – have many potential applications in high-energy and nuclear ...physics. However, such states can be obtained so far mainly via diffraction techniques, not applicable for relativistic energies. Here we show that the vortex states of different particles, including hadrons, ions, and nuclei, can be generated in a large class of processes with two final particles simply by altering a postselection protocol. Thanks to entanglement and to the uncertainty relations, an evolved state of a final particle becomes twisted if the momentum azimuthal angle of the other particle is measured with a large uncertainty. We give several examples, including Cherenkov and undulator radiation, particle collisions with intense laser beams,
e
μ
→
e
μ
,
e
p
→
e
p
. This technique can be adapted for ultrarelativistic lepton and hadron beams of linear colliders, and it can also facilitate the development of sources of X-ray and
γ
-range twisted photons at storage rings and free-electron lasers.
Physics of structured waves is currently limited to relatively small particle energies as the available generation techniques are only applicable to the soft X-ray twisted photons, to the beams of ...electron microscopes, to cold neutrons, or non-relativistic atoms. The highly energetic vortex particles with an orbital angular momentum would come in handy for a number of experiments in atomic physics, nuclear, hadronic, and accelerator physics, and to generate them one needs to develop alternative methods, applicable for ultrarelativistic energies and for composite particles. Here, we show that the vortex states of in principle arbitrary particles can be generated during photon emission in helical undulators, via Cherenkov radiation, in collisions of charged particles with intense laser beams, in such scattering or annihilation processes as
e
μ
→
e
μ
,
e
p
→
e
p
,
e
-
e
+
→
p
p
¯
, and so forth. The key element in obtaining them is the postselection protocol due to entanglement between a pair of final particles and it is largely not the process itself. The state of a final particle – be it a
γ
-ray, a hadron, a nucleus, or an ion – becomes twisted if the azimuthal angle of the other particle momentum is measured with a large error or is not measured at all. As a result, requirements to the beam transverse coherence can be greatly relaxed, which enables the generation of highly energetic vortex beams at accelerators and synchrotron radiation facilities, thus making them a new tool for hadronic and spin studies.
Fourth-generation X-ray light sources are being developed to deliver laser-like X-ray pulses at intensities and/or repetition rates that are beyond the reach of table-top devices. An important class ...of experiments at these new facilities comprises pump-probe experiments, which are designed to investigate chemical reactions and processes occurring on the molecular or even atomic level, and on the timescale of a few femtoseconds. Good progress has been made towards the generation of ultrashort X-ray pulses (for example, at FLASH or LCLS), but experiments suffer from the intrinsic timing jitter between the X-ray pulses and external laser sources. In this Letter, we present a new approach that provides few-femtosecond temporal resolution. Our method uses coherent terahertz radiation generated at the end of the X-ray undulator by the same electron bunch that emits the X-ray pulse. It can therefore be applied at any advanced light source working with ultrashort electron bunches and undulators.
OCELOT is a novel multiphysics simulation toolkit, which has been in development at European XFEL in collaboration with NRC Kurchatov Institute and DESY since 2011. In this paper we describe its ...architecture, implementation, and applications in the area of synchrotron light sources and FELs.
Abstract
The FEL performance strongly correlates with the undulator field quality. The definition of mechanical tolerances for the undulator magnets allows us to achieve the wished field quality. ...These mechanical tolerances should be defined both on short and long-range errors. With long-range errors, we address problems like deformations of the yoke caused by the support structures or unwanted tapering, which can arise in the positioning procedure of the ideally parallel undulator coils. In this contribution, we quantify the effect and set tolerances of a few types of long-range errors on the FEL radiation generated specifically from superconducting undulator coils.
FOCUS (Fast Monte CarlO approach to Coherence of Undulator Sources) is a new GPU‐based simulation code to compute the transverse coherence of undulator radiation from ultra‐relativistic electrons. ...The core structure of the code, which is written in the language C++ accelerated with CUDA, combines an analytical description of the emitted electric fields and massively parallel computations on GPUs. The combination is rigorously justified by a statistical description of synchrotron radiation based on a Fourier optics approach. FOCUS is validated by direct comparison with multi‐electron Synchrotron Radiation Workshop (SRW) simulations, evidencing a reduction in computation times by up to five orders of magnitude on a consumer laptop. FOCUS is then applied to systematically study the transverse coherence in typical third‐ and fourth‐generation facilities, highlighting peculiar features of undulator sources close to the diffraction limit. FOCUS is aimed at fast evaluation of the transverse coherence of undulator radiation as a function of the electron beam parameters, to support and help prepare more advanced and detailed numerical simulations with traditional codes like SRW.
FOCUS (Fast Monte CarlO approach to Coherence of Undulator Sources), a new GPU‐based code to compute the transverse coherence of X‐ray radiation from undulator sources as a function of the electron beam parameters, is described. FOCUS is validated with the Synchrotron Radiation Workshop (SRW) and SPECTRA codes. Examples of application to coherence studies in third‐ and fourth‐generation light sources are shown.
Abstract
Minimizing projected emittance of high brightness electron beam is important for efficient overlap between electron beam and radiation pulse in an FEL facility. Coherent synchrotron ...radiation (CSR) emission in a single bending section in the beam transport system usually introduces different slice energy modulation hence different slice transverse kicks in the designed dispersion-free lattice, causing projected emittance growth. Here we present theoretical and simulation study of CSR effect on the projected emittance growth in the beam switchyard arc before SASE2 undulator beamline at the European XFEL. We analyze arc optics impact on CSR effect and discuss possible schemes for emittance degradation compensation.
Abstract
We propose to develop, characterize and operate a superconducting undulator (SCU) afterburner consisting of 5 undulator modules (1 module = 2 SCU coils of 2 m length and 1 phase shifter) ...plus a pre-series prototype at the SASE2 hard X-ray beamline of European XFEL. This afterburner will produce an output in the order of 10
10
ph/pulse at photon energies above 30 keV. The project is divided into the production of a pre-series prototype module and a small-series production of 5 modules. Central goals of this R&D activity are: the demonstration of the functionality of SCUs at an X-ray FEL, the set up of the needed infrastructure to characterize and operate SCUs, the industrialization of such undulators, and the reduction of the price per module. In this contribution, the main parameters and specifications of the pre-series prototype module are described.
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