| Paper | Title | Page |
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| MOPGW017 | Feedback Design for Control of the Micro-Bunching Instability based on Reinforcement Learning | 104 |
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| The operation of ring-based synchrotron light sources with short electron bunches increases the emission of coherent synchrotron radiation (CSR) in the THz frequency range. However, the micro-bunching instability resulting from self-interaction of the bunch with its own radiation field limits stable operation with constant intensity of CSR emission to a particular threshold current. Above this threshold, the longitudinal charge distribution and thus the emitted radiation vary rapidly and continuously. Therefore, a fast and adaptive feedback system is the appropriate approach to stabilize the dynamics and to overcome the limitations given by the instability. In this contribution, we discuss first efforts towards a longitudinal feedback design that acts on the RF system of the KIT storage ring KARA (Karlsruhe Research Accelerator) and aims for stabilization of the emitted THz radiation. Our approach is based on methods of adaptive control that were developed in the field of reinforcement learning and have seen great success in other fields of research over the past decade. We motivate this particular approach and comment on different aspects of its implementation. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW017 | |
| About • | paper received ※ 15 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019 | |
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| MOPGW018 | Perturbation of Synchrotron Motion in the Micro-Bunching Instability | 108 |
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| Short electron bunches in a storage ring are subject to complex longitudinal dynamics due to self-interaction with their own CSR. Above a particular threshold current, this leads to the formation of dynamically changing micro-structures within the bunch, generally known as the micro-bunching instability. The longitudinal dynamics of this phenomenon can be simulated by solving the Vlasov-Fokker-Planck equation, where the CSR self-interaction can be added as a perturbation to the Hamiltonian. This contribution particularly focuses on the comprehension of synchrotron motion in the micro-bunching instability and how it relates to the formation of the occurring micro-structures. Therefore, we adopt the perspective of a single particle and comment on its implications for collective motion. We explicitly show how the shape of the parallel plates CSR wake potential breaks homogeneity in longitudinal phase space and propose a quadrupole-like mode as potential seeding mechanism of the micro-bunching instability. The gained insights are verified using the passive particle tracking method of the Vlasov-Fokker-Planck solver Inovesa. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW018 | |
| About • | paper received ※ 15 May 2019 paper accepted ※ 18 May 2019 issue date ※ 21 June 2019 | |
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| MOPTS017 | Status of Operation With Negative Momentum Compaction at KARA | 878 |
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Funding: We are supported by the DFG-funded ’Karlsruhe School of Elementary and Astroparticle Physics: Science and Technology’ and European Union’s Horizon 2020 research and innovation programme (No 730871) 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. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPTS017 | |
| About • | paper received ※ 14 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019 | |
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| TUPGW016 | New Operation Regimes at the Storage Ring KARA at KIT | 1422 |
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| The storage ring Karlsruhe Research Accelerator (KARA) at KIT operates in a wide energy range from 0.5 to 2.5 GeV. Initially, the ring was designed to serve as a Light Source for synchrotron radiation facility ANKA. Since then different operation modes have been implemented at KARA: in particular, the double bend achromat (DBA) lattice with non-dispersive straight sections, the theoretical minimum emittance (TME) lattice with distributed dispersion, and different versions of low compaction factor optics with highly stretched dispersion function. Short bunches of a few ps pulse width are available at KARA. Low alpha optics have been tested and implemented in a wide operational range of the ring and are now routinely used at 1.3 GeV for studies of CSR-induced beam dynamics and THz bursting in the micro-bunching instability. Different non-linear effects, in particular, residual high order components of magnetic fields generated in insertion devices have been studied and cured. A new operation mode at high vertical tune implemented at KARA essentially improves beam performance during user operation as well as at low alpha regimes. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPGW016 | |
| About • | paper received ※ 23 April 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019 | |
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| WEPTS015 | Synchronous Measurements of Electron Bunches Under the Influence of the Microbunching Instability | 3119 |
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Funding: This work has been supported by the German Federal Ministry of Education and Research (Grant No. 05K16VKA). We acknowledge the support by the Helmholtz International Research School for Teratronics. The microbunching instability is a longitudinal collective instability which occurs for short electron bunches in a storage ring above a certain threshold current. The instability leads to a charge modulation in the longitudinal phase space. The resulting substructures on the longitudinal bunch profile vary over time and lead to fluctuations in the emitted power of coherent synchrotron radiation (CSR). To study the underlying longitudinal dynamics on a turn-by-turn basis, the KIT storage ring KARA (Karlsruhe Research Accelerator) provides a wide variety of diagnostic systems. By synchronizing the single-shot electro-optical spectral decoding setup (longitudinal profile), the bunch-by-bunch THz detection systems (THz power) and the horizontal bunch size measurement setup (energy spread), three important properties of the bunch during this instability can be measured at every turn for long time scales. This allows a deep insight into the dynamics of the bunch under the influence of the microbunching instability. This contribution will discuss effects like the connection between the emitted CSR power and the deformations in the longitudinal bunch profile on the time scale of the instability. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS015 | |
| About • | paper received ※ 14 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019 | |
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| WEPTS016 | Longitudinal Beam Manipulation by RF Phase Modulation at the Karlsruhe Research Accelerator | 3123 |
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| At the storage ring KARA (Karlsruhe Research Accelerator) of the Karlsruhe Institute of Technology (KIT) we have installed a function for the RF phase modulation to the low-level RF system. By choosing proper conditions of the modulation, the electron distribution on the longitudinal phase space can be changed in a large range. There are several applications of this longitudinal manipulation to the accelerator operation: an improvement of the beam lifetime and suppression of collective instabilities. We have performed tracking simulations for the longitudinal beam manipulation by the RF phase modulation. The results have implied that the longitudinal phase space distribution strongly depends on the modulation frequency. We have also performed experiments, which aimed at improving the beam lifetime in 2.5 GeV KARA multi-bunch operations. In this contribution, the low-level RF system at KARA, the simulation and experimental results under the RF phase modulation will be presented. As one of the options of the modulation, we consider manipulation of the internal fine structure in the longitudinal phase space by the modulation. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS016 | |
| About • | paper received ※ 15 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019 | |
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