Pulsed Electron Lenses for Space Charge Mitigation

To produce the intense, high-quality hadron beams required by future nuclear and high-energy physics experiments, synchrotrons need to overcome the most prominent intensity limitation i.e., space charge. This Letter characterizes the potential of pulsed electron lenses in detailed 3D tracking simulations, key to which is a realistic machine and space charge model. The space charge limit, imparted by betatron resonances, is shown to be increased by up to 50% using a low symmetric number of electron lenses in application to the FAIR SIS100 synchrotron. Conceptually, a 100% increase is demonstrated with a larger number of electron lenses, which is found to rapidly saturate near the theoretical 2D limit.Comment: 6 pages, 5 figure

Flat Bunches with a Hollow Distribution for Space Charge Mitigation

Longitudinally hollow bunches provide one means to mitigate the impact of transverse space charge. The hollow distributions are created via dipolar parametric excitation during acceleration in CERN's Proton Synchrotron Booster. We present simulation work and beam measurements. Particular emphasis is given to the alleviation of space charge effects on the long injection plateau of the downstream Proton Synchrotron machine, which is the main goal of this study.Comment: Proceedings of International Particle Accelerator Conference 201

Active deep learning for nonlinear optics design of a vertical FFA accelerator

Vertical Fixed-Field Alternating Gradient (vFFA) accelerators exhibit particle orbits which move vertically during acceleration. This recently rediscovered circular accelerator type has several advantages over conventional ring accelerators, such as zero momentum compaction factor. At the same time, inherently non-planar orbits and a unique transverse coupling make controlling the beam dynamics a complex task. In general, betatron tune adjustment is crucial to avoid resonances, particularly when space charge effects are present. Due to highly nonlinear magnetic fields in the vFFA, it remains a challenging task to determine an optimal lattice design in terms of maximising the dynamic aperture. This contribution describes a deep learning based algorithm which strongly improves on regular grid scans and random search to find an optimal lattice: a surrogate model is built iteratively from simulations with varying lattice parameters to predict the dynamic aperture. The training of the model follows an active learning paradigm, which thus considerably reduces the number of samples needed from the computationally expensive simulations

An Overview of PyHEADTAIL

The macro-particle tracking code PyHEADTAIL simulates collective beam dynamics. The present paper documents its features and recent evolution

Single-Bunch Stability With Direct Space Charge

Previous studies have shown the suppressing effect of direct space charge on impedance-driven head-tail instabilities. The present work investigates transverse stability for the HL-LHC scenario based on our macro-particle simulation tool PyHEADTAIL using realistic bunch distributions. The impact of selfconsistent modelling is briefly discussed for non-linear space charge forces. We study how space charge pushes the instability threshold for the transverse mode coupling instability (TMCI) occurring between mode 0 and -1. Next we consider finite chromaticity: in absence of space charge, the impedance model predicts head-tail instabilities. For a selected case below TMCI threshold at Q0 = 5, we demonstrate the stabilising effect of space charge. Finally, we compare simulation results to past LHC measurements

Impact of Field Errors of Quadrupole Units on Beam Losses at SIS100 Injection

This report discusses heavy-ion beam losses due to the nominal transverse space charge and the field imperfections in SIS100 during accumulation based on recent cold measurements of the first 10 series quadrupole units. They are compared to the (stamped) First-of-Series quadrupole unit #2

Space Charge Effects and Advanced Modelling for CERN Low Energy Machines

The strong space charge regime of future operation of CERN’s circular particle accelerators is investigated and mitigation strategies are developed in the framework of the present thesis. The intensity upgrade of the injector chain of Large Hadron Collider (LHC) prepares the particle accelerators to meet the requirements of the High-Luminosity LHC project. Producing the specified characteristics of the future LHC beams imperatively relies on injecting brighter bunches into the Proton Synchrotron Booster (PSB), the downstream Proton Synchrotron (PS) and eventually the Super Proton Synchrotron (SPS). The increased brightness, i.e. bunch intensity per transverse emittance, entails stronger beam self-fields which can lead to harmful interaction with betatron resonances. Possible beam emittance growth and losses as a consequence thereof threaten to degrade the beam brightness. These space charge effects are partly mitigated by the upgrade of the PSB and PS injection energies. Nevertheless, the space charge tune spreads of the future injector beams are found to exceed the values reached by present LHC or other intense fixed target physics beams. This thesis project comprises three key tasks: detailed modelling of space charge effects, measurement at the CERN machines and mitigation of space charge impact. Throughout the course of this thesis, the simulation tool PyHEADTAIL has been developed and extended to model 3D space charge effects in circular accelerators across the wide energy range from PSB to SPS. The implementation for hardware-accelerating GPU architectures enables extensive studies, especially when employing the self-consistent particle-in-cell algorithm. The implemented models have been benchmarked with analytical results for space charge beam dynamics. In particular, the spectra of quadrupolar pick-ups – which provide a direct measurement method for the space charge tune shift – have been simulated and compared with the derived theory. The space charge situation at the SPS injection plateau has been extensively investigated in the course of comprehensive measurement studies, resulting in the identification of an optimal working point region for the SPS. The interplay of space charge and the horizontal quarter-integer resonance has been scrutinised in measurement, theory and simulation. Last but not least, a new LHC beam type with a hollow longitudinal phase space distribution has been developed for the PSB and proved to substantially mitigate space charge impact on the PS injection plateau

Requirements and Results for Quadrupole Mode Measurements

Direct space charge may be quantified, and hence the beam brightness observed, by measuring the quadrupolar beam modes in the CERN Proton Synchrotron (PS). The spectrum of the transverse beam size oscillations (i.e. the quadrupolar beam moment) contains valuable information: the betatron envelope modes and the coherent dispersive mode indicate optics mismatch, while their frequency shifts due to space charge allow a direct measurement thereof. To measure the quadrupolar beam moment we use the Base-Band Q-meter system of the PS which is based on a four electrode stripline pick-up. Past experiments with quadrupolar pick-ups often investigated coasting beams, where the coherent betatron and dispersion modes correspond to single peaks in the tune spectrum. In contrast, long bunched beams feature bands of betatron modes: the mode frequencies shift depending on the transverse space charge strength which varies with the local line charge density. By using the new transverse feedback in the PS as a quadrupolar RF exciter, we measured the quadrupolar beam transfer function. The beam response reveals the distinct band structure of the envelope modes as well as the coherent dispersive mode