The reliable operation of superconducting LINACs hinges on robust cryogenic systems, yet commissioning often reveals complex dynamics such as thermoacoustic oscillations, cavity instabilities, and nonuniform heat loads. This work presents a detailed account of SPIRAL2 cryogenics from initial commissioning to routine beam delivery, highlighting advances in thermodynamic modelling, linear-quadratic control, and physics-informed state observers. By coupling these approaches with machine learning diagnostics, the study establishes new methods for stabilizing superconducting cavities and enhancing long-term accelerator performance.

We present a novel bimodal radio frequency (RF) cavity that integrates fundamental and harmonic modes within a single structure, enhancing spatial efficiency and operational flexibility for multi-frequency RF systems. Unlike conventional approaches, this cavity allows for the independent and simultaneous operation of each mode, while effectively suppressing higher-order modes (HOMs).

We developed the Azimuthal Modulation Method to precisely sculpt the electromagnetic fields inside radiofrequency (rf) cavities used for accelerating, deflecting, or focusing particle beams. By azimuthally modifying the cavity wall geometry, this technique enables precise control of the multipole components in the longitudinal electric field. It can be used to remove undesired multipoles introduced by features such as power couplers, yielding multipole free accelerating structures that reduce beam degradation, or to add desired multipoles for beam shaping applications. As an example, we demonstrate an rf cavity that transforms a transverse Gaussian beam distribution into uniform.

A compact radially magnetized permanent magnetic solenoid (PMS) delivering a 1 T peak field has been designed, fabricated, and experimentally validated. Beam tests with 7 MeV electrons confirm a focal length of less than 10 cm, demonstrating the PMS’s potential for high-brightness MeV-scale applications. This power-free, compact solution offers a practical and cost-effective alternative to electromagnetic solenoids, with applications ranging from ultrafast electron diffraction to inverse Compton sources.

In electron storage rings, modulating the radiofrequency (RF) accelerating field with harmonics of the synchrotron oscillation frequencies results in a dynamic change in the longitudinal particle distribution of the bunches. The optimization of electron bunch elongation, which relaxes the Touschek effect, depends on modulation and beam parameters. Our focus is on the frequency detuning characteristics of RF phase modulation with double synchrotron frequencies, which are introduced using a frequency detuning curve. Nonlinear effects due to phase modulation lead to a peak frequency shift in the negative direction from the double synchrotron frequency.

The unique LEM beamline at PSI delivers low-energy muons for studying the magnetic and electronic properties of thin films, surfaces, and multilayers. Its ultrathin carbon foil, essential for muon tagging, can degrade silently, and changes in tagging efficiency directly reflect variations in beam quality. We present a noninvasive method to monitor the foil condition in real time by extracting the tagging efficiency from standard low-energy muSR decay histograms.

Beam experiments were carried out on the ALBA synchrotron to evaluate different methods to introduce coupling with special attention to the compatibility with operations. The first experiments intend to achieve full coupling by tuning the working point onto the coupling resonance. Our second attempt is based on the excitation of the resonance with an A.C. skew quadrupole driven at a frequency equal to the difference of the tunes. Unfortunately the unavoidable small fluctuation of the tunes, did not allow to keep a stable beam size. A stable excitation was finally achieved using a phase-locked loop system which generates a reference of the tunes to drive the A.C. skew quadrupole.

This study demonstrates that the magnetic horn employed in the NuMI beamline functions predominantly as a linear focusing element. This characteristic is verified through analytical modeling and numerical simulations, and further validated using muon‑monitor measurements. Moreover, it is shown that the horn current can be reconstructed from muon monitor signals with an accuracy of 0.05%, highlighting the potential of this technique for non-invasive, real-time beam diagnostics with high precision for future long baseline neutrino experiments.

After nearly a decade of operation under high-intensity proton beams, the LHC beam dumps - measuring 8.5 m in length, 720 mm in diameter, and weighing over 6 t - were dismantled and examined in an unprecedented operation at CERN. The installation of a dedicated facility with remote handling systems, along with the development of a custom cutting strategy, enabled the safe opening of the highly activated duplex stainless-steel vessel to access and inspect the carbon-based core. The results assess the viability of the absorber materials under long-term exposure to high energy densities and demonstrate how large radioactive accelerator components can be safely decommissioned.

In environments subjected to hydrogen ion irradiation or high beam losses, residual hydrocarbons may result in carbon contamination of the metal surfaces. Under these conditions, it has been assessed that surface carbon contamination leads to a decrement of the surface electric field holding properties. This study explores the efficacy of Oxygen Plasma Cleaning (OPC) on metal electrodes irradiated by low energy hydrogen ion beam with the purpose of reducing surface carbon contamination. The study indicates a significant reduction in carbon contamination by OPC, enough to allow irradiated materials to achieve performances comparable with the electric field strength of raw surfaces.

This work proposes a novel high-repetition-rate pulsed surface muon source driven by the 8 GeV electron beam at the SHINE facility. Unlike conventional proton-based sources operating at low repetition rates or in continuous mode, the proposed design achieves 50 kHz pulsed operation with a surface muon intensity of 3×10⁶ μ⁺/s, which is comparable to existing facilities. The resulting time structure is ideal for μSR and several fundamental muon experiments. This study demonstrates how existing GeV electron beamlines can be cost-effectively leveraged to generate intense muon beams.

It has already been shown before that the sum of a transport matrix and its inverse can be a key to the description of a fully coupled particle motion in an accelerator. Here a number of hidden symmetry properties offered by this approach are studied in detail. A new index formalism has been introduced, and a special type of matrix equations has been investigated thoroughly for this purpose.

This paper presents two general methods for beam optics ramping in under-constrained systems, motivated by the Electron-Ion Collider Hadron Storage Ring cooling section design. Direct interpolation between matched optics at injection and top energy often fails due to large separations in knob space. An intermediate-penalty method maintains ramp continuity when identical constraints are enforced along the path, while a continuation-based scheme with adaptive weighting constructs feasible ramps under strict, differing constraints at both ends. These approaches provide broadly applicable strategies for lattice design where endpoint optics differ significantly.

A modified maximum-entropy algorithm facilitates six-dimensional phase space tomography.

Maintaining stable, high-quality electron beams is critical for synchrotron light sources, but beam optics and coupling are constantly disturbed by insertion device movements during operation. This study introduces a novel real-time feedback system that tackles this challenge. By applying deep learning directly to turn-by-turn beam position data, the system rapidly extracts key optics parameters and predicts necessary corrections. Successfully demonstrated at the Shanghai Synchrotron Radiation Facility (SSRF), this approach reduces optics distortion and suppresses emittance coupling variations, enabling continuous monitoring and correction within each injection cycle.