In 2023, an RF technique known as empty-bucket channelling was implemented operationally at the CERN Super Proton Synchrotron (SPS) to improve the quality of the spill provided to the North Area experiments. Empty-bucket channelling suppresses particle-flux variations during resonant slow extraction by accelerating particles between empty RF buckets and rapidly displacing particles into the tune resonance via chromatic coupling. The flux variations are often caused by the power converter ripple present in the synchrotron’s magnets, which modulates the beam dynamics during the extraction process. In a chromatic extraction, the quadrupole ripple is the main contribution to the modulation as it directly perturbs the transverse tune. When empty-bucket channelling is applied, however, dipole ripple additionally modulates the size of the empty RF bucket. In this contribution, the phenomenon is explored and the consequences for empty bucket channelling in the SPS are outlined.

The CERN Super Proton Synchrotron (SPS) offers slow-extracted, high-intensity proton beams at 400 GeV/c for 3 fixed targets in the CERN North Experimental Area (NA) with a spill length of about 5 seconds. Since first commissioning in the late seventies, the NA has seen a steady increase in users, many of which requiring improved spill quality control. Slow extraction is sensitive to small perturbations with the effect of reduced spill quality. While some of these effects have been addressed in recent years, continuous compensation of intensity fluctuations at 50 Hz harmonics originating from power converter ripple has been particularly difficult to achieve. In 2023, the deployment of two techniques - "Empty-Bucket Channeling" and active control with Adaptive Bayesian Optimization – resulted in a significant suppression of these intensity modulations. This paper focuses on using Adaptive Bayesian Optimization for 50 Hz harmonic control. The chosen algorithm is described, together with details of integration in the CERN control system. The 2023 results are presented and complemented with an overview of the next steps.

Testing of space-bound microelectronics plays a crucial role in ensuring the reliability of electronics exposed to the challenging radiation environment of outer space. This contribution describes the beam optics studies carried out for the run held in November 2023 in the context of the CERN High-Energy Accelerators for Radiation Testing and Shielding (HEARTS) experiment. It also delves into an investigation of the initial conditions at the start of the transfer line from the CERN Proton Synchrotron (PS) to the CERN High Energy Accelerator Mixed-field (CHARM) facility. Comprehensive optics measurement and simulation campaigns were carried out for this purpose and are presented here. Using a validated optics model of the transfer line, the impact of air scattering on the beam size was quantified with MAD-X and FLUKA, providing valuable insights into the current performance and limitations for Single Event Effects (SEE) testing at CHARM.