Patrick Krämer

Resolving Competing Ultraviolet Photoinduced Ring-Opening and Dissociation Pathways in Iodothiophenes by Ultrafast Electron Diffraction

Aaron Ghrist, Matthew Bain, Yusong Liu, Weronika O Razmus et autres

Abstract The ultraviolet photochemistry of halothiophenes is thought to proceed via competing pathways, prompt C–X (X = halogen) bond fission, and parent ring opening followed by fragmentation, yet direct structural evidence distinguishing these mechanisms is limited. Here, time-resolved gas-phase ultrafast electron diffraction …

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Two-stage constrained Bayesian optimization for particle accelerator tuning

Fuhao Ji, Alex Reid, Auralee Edelen, Daniel Ratner et autres

Particle accelerators are highly complex, non-linear systems that require rapid tuning during operation to meet requirements on beam qualities for applications in different scientific disciplines. Multi-objective Bayesian Optimization (MOBO) has been recently demonstrated at SLAC MeV-UED facility for speeding up online electron …

The UV Photoinduced Ring-Closing Reaction of Cyclopentadiene Probed with Ultrafast Electron Diffraction

J. Lederer, Lauren Bertram, Lisa Huang, Surjendu Bhattacharyya et autres

Conjugated cyclic organic molecules are common across many fields such as pharmaceuticals, are naturally occurring in biological systems, and are used in synthetic materials. One particular area of interest from a photochemical point of view is the formation of highly strained cyclic …

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Response of fs-Laser-Irradiated Diamond by Ultrafast Electron Diffraction

Franky Bernal, Erika J. Riffe, Shane W. Devlin, Sébastien Hamel et autres

Structural details of the proposed solid–liquid phase transition of carbon have remained elusive, despite years of study. While it is theorized that novel carbon materials form from a liquid precursor, experimental studies have lacked the temporal and spatial resolution necessary to fully …

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Multi-objective Bayesian active learning for MeV-ultrafast electron diffraction

Fuhao Ji, Auralee Edelen, Ryan Roussel, Xiaozhe Shen et autres

Ultrafast electron diffraction using MeV energy beams(MeV-UED) has enabled unprecedented scientific opportunities in the study of ultrafast structural dynamics in a variety of gas, liquid and solid state systems. Broad scientific applications usually pose different requirements for electron probe properties. Due to …

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Impedance minimization of the CERN Super Proton Synchrotron cavities using the generalized coupled S -parameter method

Shahnam Gorgi Zadeh, Erion Gjonaj, Thomas Flisgen, Patrick Krämer et autres

In the context of the Large Hadron Collider (LHC) injector upgrade, components with high contribution to the beam coupling impedance of the injector chain have to be identified and optimized to ensure the delivery of high-intensity proton beams to the LHC. The …

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Improved HOM-mitigation for future SPS 33-Cell 200 MHz traveling-wave accelerating structures

Patrick Krämer, Christine Völlinger

The CERN SPS 200 MHz traveling-wave (TW) accelerating structures pose an intensity limitation for the planned High Luminosity (HL-) LHC upgrade. Higher-order modes (HOMs) around 630 MHz have been identified as one of the main sources of longitudinal multi-bunch instabilities. Improved mitigation …

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Measurement of rf voltage in long traveling wave accelerating structures with application to the CERN Super Proton Synchrotron

Patrick Krämer, Christine Völlinger

Since its inauguration in 1976, the Super Proton Synchrotron (SPS) at CERN relies on a traveling wave system for particle acceleration instead of making use of standing wave cavities that are more common in circular accelerators. These traveling wave structures (TWSs) are …

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Splitting methods for nonlinear Dirac equations with Thirring type interaction in the nonrelativistic limit regime

Patrick Krämer, Katharina Schratz, Xiaofei Zhao

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Verification by RF Measurements of New HOM Mitigation Scheme Developed for Future SPS 33-Cell Accelerating Structures

Patrick Krämer, Aaron Farricker, Christine Völlinger

Longitudinal higher-order modes (HOMs) at a frequency of around 630 MHz in the 200 MHz travelling wave RF structures currently limit the beam intensities in the CERN SPS to less than that required by the High Luminosity (HL-) LHC. In the framework …

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Building the Impedance Model of a Real Machine

Benoît Salvant, David Amorim, Sergey Antipov, Sergey Arsenyev et autres

A reliable impedance model of a particle accelerator can be built by combining the beam coupling impedances of all the components. This is a necessary step to be able to evaluate the machine performance limitations, identify the main contributors in case an …

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Needs and Solutions for Machine Impedance Reduction

Christine Völlinger, Aaron Farricker, T. Kaltenbacher, Patrick Krämer et autres

Particle beams with highest possible beam intensities are requested nowadays, hence in modern circular accelerators, the consideration of beam coupling impedance issues is of increasing relevance. Classical sources of beam coupling impedance are RF-systems, injection and extraction kickers, but also beam diagnostic …

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