Novel Beam Excitation System Based on Software-Defined Radio
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P.J. Niedermayer, R. Singh
GSI, Darmstadt, Germany
Funding:This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under GA No 101004730. A signal generator for transverse excitation of stored particle beams is developed and commissioned at GSI SIS18. Thereby a novel approach using a software-defined radio system and the open-source GNU Radio ecosystem is taken. This allows for a low cost yet highly flexible setup for creating customizable and tuneable excitation spectra. Due to its open-source nature, it has the potential for long term maintainability and integrability into the accelerator environment. Furthermore, this opens up the possibility to easily share algorithms for the generation of waveforms across accelerator facilities. As a first application, the device is used to control the coherence and amplitude of transverse oscillations by excitation in the vicinity of betatron sidebands. It enables measurement of beam parameters like tune and chromaticity. On a longer term, it will be used for more complex tasks such as beam shaping, extraction and automated parameter scans towards these complex processes.
The beam quadrupole moment of stored beams can be measured with a four-plate quadrupole pick-up. The frequency spectrum of the quadrupole moment contains not only the usual first-order dipole modes (the betatron tunes) but also the second-order coherent modes, comprising of (1.) (even) normal envelope modes, (2.) odd (skew) envelope modes and (3.) dispersion modes. As a novel diagnostic tool, the measured frequencies and amplitudes provide direct access to transverse space charge strength through the tune shift as well as linear coupling (and mismatch thereof), along with the benefit of a non-invasive beam-based measurement. Technically, quadrupole moment measurements require a pick-up with non-linear position sensitivity function. We discuss recent developments and depict measurements at the GSI SIS18 heavy-ion synchrotron.
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Simulation and Measurements of the Fast Faraday Cups at GSI UNILAC
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R. Singh, P. Forck, T. Reichert, A. Reiter
GSI, Darmstadt, Germany
S. Klaproth
THM, Friedberg, Germany
G.O. Rodrigues
IUAC, New Delhi, India
Funding:This work is supported by the German Federal Ministry of Education and Research (BMBF) under contract no. 05P21RORB2. Joint Project 05P2021 - R&D Accelerator (DIAGNOSE) The longitudinal charge profiles of the high intensity heavy ion beam accelerated at the GSI UNILAC upto 11.4 MeV/u can differ significantly in consecutive macro-pulses. Variations in bunch shape and mean energy were also observed within a single macro-pulse. In order to have an accurate and fast determination of bunch shape and its evolution within a macro-pulse, a study of fast Faraday Cup designs is underway at GSI. In this contribution, we present CST particle in cell (PIC) simulations of radially coupled co-axial Fast Faraday Cup (RCFFC) and conventional axially coupled FFC (ACFFC) design. The simulation results are compared to the measurements performed under comparable beam conditions primarily with RCFFCs. A rather large impact of secondary electron emission is observed in simulations and experiments. The biasing of the FFC central electrode as a mitigation mechanism on the measured profiles is discussed.
Beam Characterization of Slow Extraction Measurement at GSI-SIS18 for Transverse Emittance Exchange Experiments
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J. Yang, P. Boutachkov, P. Forck, T. Milosic, R. Singh, S. Sorge
GSI, Darmstadt, Germany
Funding:This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under GA No 101004730. The quality of slowly, typically several seconds, extracted beams from the GSI synchrotron SIS18 is characterized with respect to the temporal beam stability, the so-called spillμstructure on the 100 µs scale. A pilot experiment was performed utilizing transverse emittance exchange to reduce the beam size in the extraction plane, and the improvement of spillμstructure was found. Important beam instrumentation comprises an Ionization Profile Monitor for beam profile measurement inside the synchrotron and a plastic scintillator at the external transfer line for ion counting with up to several 106 particles per second and 20 µs time slices. The performant data acquisition systems, including a scaler and a fast Time-to-Digital Converter (TDC), allow for determining the spill quality. The application of the TDC in the measurement and related MAD-X simulations are discussed.
Studies on Radially Coupled Fast Faraday Cups to Minimize Field Dilution and Secondary Electron Emission at Low Intensities of Heavy Ions
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G.O. Rodrigues, S. Kumar, K. Mal, R. Mehta, C.P. Safvan
IUAC, New Delhi, India
R. Singh
GSI, Darmstadt, Germany
Fast Faraday Cups (FFCs) are interceptive beam diagnostic devices used to measure fast signals from sub-nanosecond bunched beams and the operation of these devices is a well-established technique. However, for short bunch length measurements in non-relativistic regimes with ion beams, the measured profile is diluted due to field elongation and distortion by the emission of secondary electrons. Additionally, for short bunches with the expected intensities envisaged in the High Current Injector at the Inter University Accelerator Centre, the impedance matching of the EM structure puts severe design constraints. This work presents a detailed study on the modification of a radially-coupled coaxial FFC [1]. The field dilution and secondary electron emission aspects are modelled through EM simulations and techniques to minimise these effects are explored. This has resulted in a new design, which has a better signal to noise ratio and benefits from a more accurate bunched beam measurement. [1] Carneiro, J.-P., et al. ’Longitudinal Beam Dynamics Studies at the Pip-II Injector Test Facility.’ International Journal of Modern Physics A, vol. 34, no. 36, 2019, p.1942013
Application of Machine Learning towards Particle Counting and Identification
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S.E. Engel
University of Essex, Physics Centre, Colchester, United Kingdom
P. Boutachkov, R. Singh
GSI, Darmstadt, Germany
An exploration into the application of three machine learning (ML) approaches to identify and separate events in the detectors used for particle counting at the GSI Helmholtz Centre for Heavy Ion Research. A convolutional neural network (CNN), a shape-based template matching algorithm (STMF) and Peak Property-based Counting Algorithm (PPCA) were developed to accurately count the number of particles without domain-specific knowledge required to run the currently used algorithm. The three domain-agnostic ML algorithms are based on data from scintillation counters commonly used in beam instrumentation and represent proof-of-work for an automated particle counting system. The algorithms were trained on a labelled set of over 150 000 experimental particle data. The results of the three classification approaches were compared to find a solution that best mitigates the effects of particle pile-ups. The two best-achieving algorithms were the CNN and PPCA, achieving an accuracy of 99.8\%. This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under GA No 101004730.
