In 2023 the LHC restarted after the yearly winter shutdown with a new machine configuration optimized for intensities of up to 1.8e+11 protons per bunch. In the first two months of the 2023 run the bunch intensities were pushed up to 1.6e+11 protons per bunch until a severe vacuum degradation, caused by a damaged RF bridge, occurred close to the ATLAS experiment. Following repair, the decision was taken to stop the intensity increase. After a period of smooth operation, a leak developed between the cold mass and insulation vacuum of a low-beta quadrupole, leading to an abrupt stop of the LHC. Thanks to a rapid intervention, the leak could be repaired without warning up large parts of the machine, and the LHC was ready for beam again early September. Special runs at very large beta* were completed in the remaining time before switching to Lead ion operation. The performance achievements and limitations as well as the issues that were encountered over the year will be discussed in this paper.

The question of the mitigation of the Transverse Mode Coupling Instability (TMCI) by space charge has been discussed for more than two decades. Since few years, it has become clear that the ABS model, which has been often used in the past and which assumes an air-bag bunch in a square well, is not sufficient to properly describe the complexity of the interaction between impedance and space charge. Considering a more realistic longitudinal Gaussian distribution, a fully self-consistent treatment of space charge was performed few years ago using the circulant matrix model, which revealed the usual TMCI mechanism but with oscillation modes shifted both by impedance and space charge. In this paper, a non self-consistent treatment of space charge is analyzed, still using a Gaussian distribution, to look at the evolution of the coherent direct space charge modes. It is shown in particular that it leads to exactly the same result as the self-consistent treatment for space charge parameters below 1 and that it is a much better approximation than the ABS model for space charge parameters above 1, as it reveals clearly how the positive modes lead to negative tune shifts.

The intrabunch motion for independent longitudinal or transverse beam oscillation modes has been explained analytically for impedance driven bunched-beam coherent instabilities already several decades ago by Laclare and they have been observed in many measurements and simulations. These oscillation patterns do not depend on the bunch intensity, they are head/tail symmetric and they exhibit a number of nodes equal to the radial mode number. However, in many measurements and simulations of transverse beam instabilities (due to impedance only, impedance and beam-beam, impedance and space charge, or electron cloud), asymmetric patterns are observed depending on the bunch intensity. The latter can be described theoretically considering the interaction between several modes, i.e. mode coupling, which explains why and how different kinds of asymmetric intrabunch signals can be observed. In this paper, the intrabunch motion in the presence of mode coupling is explained first without maths and then with maths, considering the case of a bunch interacting with a transverse impedance, using the GALACTIC Vlasov solver.

CERN is pursuing several initiatives to reduce its impact on the environment through an integrated approach to address all the objectives set by the relevant United Nations (UN) Sustainable Development Goals (SDG). In particular CERN is committed to respect the net-zero paradigm for future machines and has established a Sustainable Accelerators Panel to harmonize the approach to sustainability of the various studies for future accelerators. In this paper we will describe the efforts taken in managing responsibly our technical installations and the process we are setting up to perform the lifecycle assessment of the different future projects to better understand the main drivers of CO2 emissions in order to minimize them by design.