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The dynamic aperture is an essential concept in circular particle accelerators, providing the extent of the phase space region where particle motion remains stable over multiple turns. The accurate prediction of the dynamic aperture is key to optimising performance in accelerators such as the CERN Large Hadron Collider and is crucial for designing future accelerators like the CERN Future Circular Hadron Collider. Traditional methods for computing the dynamic aperture are computationally demanding and involve extensive numerical simulations with numerous initial phase space conditions. In our recent work, we have devised surrogate models to predict the dynamic aperture boundary both efficiently and accurately. These models have been further refined by incorporating them into a novel active learning framework. This framework enhances performance through continual retraining and intelligent data generation based on informed sampling driven by error estimation. A critical attribute of this framework is the precise estimation of uncertainty in dynamic aperture predictions. In this study, we investigate various machine learning techniques for uncertainty estimation, including Monte Carlo dropout, bootstrap methods, and aleatory uncertainty quantification. We evaluated these approaches to determine the most effective method for reliable uncertainty estimation in dynamic aperture predictions using machine learning techniques.

The Super Proton Synchrotron at CERN is equipped with a scraping system for halo cleaning at beam transfer to the Large Hadron Collider. The system is composed of movable graphite blades mechanically swept through the beam to remove tails immediately before beam transfer. Due to the mechanical movement, beam particles are intercepted by a small volume of material with consequent concentration of energy deposition and high thermal loads. The blades were tested with beam to verify their resistance to the most extreme scraping conditions. Even though the beam was prematurely dumped by the beam loss monitoring system, the microstructural analysis of the blades following the test found signs of material sublimation. The test setup was reproduced in simulation to reconstruct the levels of energy deposition actually reached in the blades during the test; values are compatible with local material sublimation, in agreement with the microstructural analysis. Simulations were carried out by coupling the sixtrack tracking code, used for single particle beam dynamics in circular accelerators for high energy physics, to the fluka Monte Carlo code, for particle-matter interactions. The time evolution of the beam intensity measured during scraping and the distribution of losses around the ring were used for an extensive benchmark of the simulation tool against measurements taken during the test. This work presents the endurance test together with simulation results and the benchmark of the simulation tool. The quantitative agreement between simulations and measurements proves the quality of the analyses and the maturity of the simulation tool, which can be reliably used to predict the performance of cleaning systems in circular accelerators.

Staged acceleration, driven by terahertz (THz) frequency radiation pulses in a lattice with alternating orientation dielectric-lined waveguides and intervening matching optics, is shown to mitigate transverse emittance and energy spread growth, opening a route to multistage THz linacs. Decomposition of the longitudinal THz field into the multipolar components reveals a quadrupole field component with strong radial dependence. As such, it induces a transverse energy correlation in the beam during acceleration due to the large variation in the electric field with radius and azimuthal position of the electrons. An alternating orientation of stages separated by a matching section provides a compensation of transverse energy spread correlation induced in the beam during its interaction with the THz field. Furthermore, the monopolar component of the acceleratingLSM11mode was found to be constant with respect to transverse position, entailing zero monopolar transverse voltage and preventing emittance growth, unlike conventional radio-frequency structures. We demonstrate in a rectangular dielectric-lined waveguide structure that, when used for the acceleration of relativistic electrons, the slice transverse emittance is conserved and the growth in the slice energy spread is reduced by 70%–80% simultaneously over a system of two stages, each providing an interaction length of 4 mm and an energy gain of up to 2 MeV.

Particle accelerators driven by laser-generated terahertz (THz) pulses promise unprecedented control over the energy–time phase space of particle bunches compared with conventional radiofrequency technology. Here we demonstrate acceleration of a relativistic electron beam in a THz-driven linear accelerator. Narrowband THz pulses were tuned to the phase-velocity-matched operating frequency of a rectangular dielectric-lined waveguide for extended collinear interaction with 35 MeV, 60 pC electron bunches, imparting multicycle energy modulation to chirped (6 ps) bunches and injection phase-dependent energy gain (up to 10 keV) to subcycle (2 ps) bunches. These proof-of-principle results establish a route to whole-bunch linear acceleration of subpicosecond particle beams, directly applicable to scaled-up and multistaged concepts capable of preserving beam quality, thus marking a key milestone for future THz-driven acceleration of relativistic beams.Relativistic 35 MeV electron bunches with charges of 60 pC are accelerated in a terahertz-wave-driven dielectric waveguide. When the terahertz pulse energy is 0.8 μJ, an accelerating gradient of 2 MeV m−1 and energy gain of 10 keV are achieved.

Merlin++ is a C++ particle accelerator and particle tracking library originally developed at DESY for use in International Linear Collider (ILC) simulations. Merlin++ has more recently been adapted for High-Luminosity Large Hadron Collider (HL-LHC) collimation studies, utilizing advanced scattering physics. However, as is all too common in long-standing high-energy physics software, recent developments have focused on functional additions rather than code design and maintainability. This has resulted in usability issues for users and developers alike. The following presents recent improvements in adhering to modern software sustainability practices to address these issues. Quantifiable improvements in code complexity and maintainability are presented via appropriate test metrics and the evolution of the software architecture is analyzed. Experiences and conclusions of applying modern sustainability methodology to longstanding scientific software are discussed.

Purpose: To evaluate and compare the deliverability of ‘sawtooth’ proton arc therapy (PAT) plans relative to static intensity modulated proton therapy (IMPT) at a cyclotron-based clinical facility. Methods: The delivery of single and dual arc Sawtooth PAT plans for an abdominal CT phantom and multiple clinical cases of brain, head and neck (H&N) and base of skull (BoS) targets was emulated under the step-and-shoot and continuous PAT delivery regimes and compared to that of a corresponding static IMPT plan. Results: Continuous PAT delivery increased the time associated with beam delivery and gantry movement in single/dual PAT plans by 4.86/7.34 min (brain), 7.51/12.40 min (BoS) and 6.59/10.57 min (H&N) on average relative to static IMPT. Step-and-shoot PAT increased this delivery time further by 4.79 min on average as the delivery was limited by gantry motion. Conclusions: The emulator can approximately model clinical sawtooth PAT delivery but requires experimental validation. No clear benefit was observed regarding beam-on time for sawtooth PAT relative to static IMPT.

Strong beam-beam effects at the interaction point of a high-energy e+e− linear collider such as the Compact Linear Collider (CLIC) lead to an emittance growth for the outgoing beams, as well as to the production of beamstrahlung photons and e+e− coherent pairs. In this paper, we present a conceptual design of a 150 m long post-collision extraction line for the CLIC machine at 3 TeV, which separates the various components of the outgoing beam using a vertical magnetic chicane, before transporting them to their respective dump. In addition, detailed studies are performed in order to compute the power losses along the CLIC post-collision line. For the vacuum window at the exit of the post-collision line, we propose a thick (1.5 cm) layer of carbon-carbon composite, with a thin (0.2 mm) aluminum leak-tight foil. The stress levels in this exit window are estimated. Finally, we discuss the use of diagnostics along the post-collision line for monitoring and improving the quality of the e+e− collisions and, in turn, the luminosity of the CLIC machine.

Superconducting, curved magnets can reduce accelerator footprints by producing strong fields (>3T) and reducing the total number of magnets through their capability for combined-function multipolar fields, making them an attractive choice for applications such as heavy ion therapy. There exists the problem that the effect of strongly curved harmonics and fringe fields on compact accelerator beam dynamics is not well represented: existing approaches use integrated cylindrical multipoles to describe and model the fields for beam dynamics studies, which are invalid in curved coordinate systems and assume individual errors cancel out over the full machine. In the modelling of these machines, the effect of strongly curved harmonics and fringe fields on compact accelerator beam dynamics needs to properly included. An alternative approach must be introduced for capturing off-axis fields in a strongly curved magnet, which may affect long-term beam stability in a compact accelerator. In this article, we investigate the impacts of deploying a curved canted-cosine-theta (CCT) superconducting magnet in a compact medical synchrotron for the first time. We develop a method to analyse and characterise the 3D curved fields of an electromagnetic model of a CCT developed for the main bending magnets of a 27m circumference carbon ion therapy synchrotron, designed within the Heavy Ion Therapy Research Integration Plus European project, and the CERN Next Ion Medical Machine Study (NIMMS). The fields are modelled in the compact synchrotron in MAD-X/PTC to study their effects on beam dynamics and long-term beam stability. The insights gained through the methods presented allow for the optimisation of both magnet and synchrotron designs, with the potential to impact the operational performance of future ion therapy facilities.

Laser-plasma wakefield acceleration (LWFA) offers ultrahigh accelerating gradients in compact setups, but the complex non-linear nature of the process makes it challenging to generate high-quality beams. Injection of electron bunches from an external source into a plasma accelerator provides a promising route to improved performance; however, electron bunches from conventional radio-frequency (RF)-based injectors suffer from non-linear compression and laser-beam asynchrony, leading to energy jitter and emittance growth. We present a fundamental concept of terahertz-controlled electron bunches for external injection into LWFA. This terahertz-frequency approach provides temporal locking between the electron beam and the drive laser, and enables the compression of high-quality beams to sub-10-fs durations before injection into the LWFA. Numerical simulations demonstrate that GeV-scale acceleration with excellent beam quality and stability -- energy jitter and energy spread around 0.2% -- can be achieved using this method. This concept opens new opportunities for stable, multi-stage laser-driven accelerators and supports the development of next-generation applications such as free-electron lasers (FELs).

We demonstrate that narrowband multi-cycle terahertz (MC-THz) sources based on periodically-poled lithium niobate (PPLN) wafer stacks can be driven by high repetition-rate, high energy femtosecond ytterbium-doped lasers. Operating at 10-kHz repetition rate with up to 104 W of pump power on a 10-wafer stack, we measure 26.4 mW of THz average power for a narrowband multi-cycle source. We identify and quantify strong lensing effects causing dramatic beam focusing in 47 wafer stacks which act as a primary limitation in the current configuration, and present mitigation strategies for future scaling. This first study of high average power narrowband multi-cycle THz sources offers a path forward to Watt-level high repetition rate sources using thin lithium niobate plates.