Comprehensive Analysis of Micro-Structure Dynamics in Longitudinal Electron Bunch Profiles

Der Betrieb von Synchrotronstrahlungsquellen mit kurzen Elektronenpaketen führt zur Ausbildung von Mikro-Strukturen innerhalb der Pakete, was wiederum einen Anstieg der abgestrahlten kohärenten Synchrotronstrahlungs-Leistung zur Folge hat. Die dynamische Entwicklung dieser Mikro-Strukturen kann indirekt durch die Messung der resultierenden Fluktuationen der emittierten Strahlungsleistung untersucht werden. Diese Fluktuationen konnten an verschiedenen Synchrotronstrahlungsquellen gemessen werden, so auch an ANKA, KIT. Für die direkte Beobachtung der Mikro-Strukturen stehen zwar bereits einige Methoden zur Messung der Elektronenverteilung in den Paketen zur Verfügung, der kleine Maßstab stellt hier allerdings hohe Anforderung an die jeweilige Messtechnik. Zum Zwecke dieser Masterarbeit wurde die longitudinale Dynamik daher mittels des neu entwickelten Programms Inovesa simuliert. Da dies schnell zu großen Datenmengen führen kann, wurden Methoden des maschinellen Lernens eingesetzt, um die dominanten Mikro-Strukturen in den longitudinalen Elektronenverteilungen zu identifizieren. Anhand der so gewonnenen Resultate wird anschließend die Charakteristik und Dynamik der Mikro-Strukturen und deren Korrelation zur abgestrahlten kohärenten Synchrotronstrahlung ausführlich untersucht

Continuous bunch-by-bunch spectroscopic investigation of the micro-bunching instability

Electron accelerators and synchrotrons can be operated to provide short emission pulses due to longitudinally compressed or sub-structured electron bunches. Above a threshold current, the high charge density leads to the micro-bunching instability and the formation of sub-structures on the bunch shape. These time-varying sub-structures on bunches of picoseconds-long duration lead to bursts of coherent synchrotron radiation in the terahertz frequency range. Therefore, the spectral information in this range contains valuable information about the bunch length, shape and sub-structures. Based on the KAPTURE readout system, a 4-channel single-shot THz spectrometer capable of recording 500 million spectra per second and streaming readout is presented. First measurements of time-resolved spectra are compared to simulation results of the Inovesa Vlasov-Fokker-Planck solver. The presented results lead to a better understanding of the bursting dynamics especially above the micro-bunching instability threshold.Comment: 12 pages, 11 figure

On the Perturbation of Synchrotron Motion in the Micro-Bunching Instability

The self-interaction of short electron bunches with their own radiation field can have a significant impact on the longitudinal beam dynamics in a storage ring. While higher bunch currents increase the power of the emitted CSR which can be provided to dedicated experiments, it simultaneously amplifies the strength of the self-interaction. Eventually, this leads to the formation of dynamically changing micro-structures within the bunch and thus fluctuating CSR emission, a phenomenon that is generally known as micro-bunching or micro-wave instability. The underlying longitudinal dynamics can be simulated by solving the VFP equation, where the CSR self-interaction can be added as a perturbation to the Hamiltonian. In this contribution, we focus on the perturbation of the synchrotron motion that is caused by introducing this additional wake field. Therefore, we adopt the perspective of a single particle and eventually comment on its implications for collective motion. We explicitly show how the shape of the parallel plates CSR wake potential breaks homogeneity in the longitudinal phase space and propose a quadrupole-like mode as potential seeding mechanism of the micro-bunching instability. Moreover, we consider synchrotron motion above the instability threshold and thereby motivate an approach to control of the occurring micro-bunching dynamics. Using dynamically adjusted RF amplitude modulations we can directly address the continuous CSR-induced perturbation at the timescale of its occurrence, which allows for substantial control over the longitudinal charge distribution. While the approach is not limited to this particular application, we demonstrate how this can significantly mitigate the micro-bunching dynamics directly above the instability threshold. The gained insights are supported and verified using the VFP solver Inovesa and put into context with measurements at KARA

Status of Operation With Negative Momentum Compaction at KARA

For fu­ture syn­chro­tron light source de­vel­op­ment novel op­er­a­tion modes are under in­ves­ti­ga­tion. At the Karl­sruhe Re­search Ac­cel­er­a­tor (KARA) an op­tics with neg­a­tive mo­men­tum com­paction has been pro­posed, which is cur­rently under com­mis­sion­ing. In this con­text, the col­lec­tive ef­fects ex­pected in this regime are stud­ied with an ini­tial focus on the head-tail in­sta­bil­ity and the mi­cro-bunch­ing in­sta­bil­ity re­sult­ing from CSR self-in­ter­ac­tion. In this con­tri­bu­tion, we will pre­sent the pro­posed op­tics and the sta­tus of im­ple­men­ta­tion for op­er­a­tion in the neg­a­tive mo­men­tum com­paction regime as well as a pre­lim­i­nary dis­cus­sion of ex­pected col­lec­tive ef­fects

Detuning Properties of RF Phase Modulation in the Electron Storage Ring KARA

In electron storage rings, it is possible to increase the electron bunch length by applying a phase modulation on the radio frequency accelerating field by choosing appropriate parameters for the modulation. Such a bunch lengthening effect improves beam parameters such as the beam lifetime, which can help us to get better beam stability. The dependence of the bunch lengthening on the modulation frequency, the so-called detuning property, tends to have a peak with asymmetric slopes around it. The modulation amplitude and the beam current also affect the properties of the detuning condition of such bunch lengthening. We have investigated the detuning property with systematic measurements at the electron storage ring KARA. The experimental results agree with the theoretical model and the simulation results