The CERN Proton Synchrotron (PS) routinely crosses transition energy at around 6 GeV in order to accelerate protons that are injected in the Super Proton Synchrotron (SPS) or transferred to users of fixed target experiments. Depending on the beam parameters and intensity, a fast vertical coherent instability occurs during transition crossing. The instability, characterized by beam losses and a frequency spectrum in the range of 500-900 MHz, represents an important intensity limitation for the neutron time-of-flight (nTOF) beam, and in general could represent a bottleneck for future high intensity beams. In order to better understand the nature and the source of the instability and to find possible mitigations, a dedicated measurement campaign took place. Parallel to the measurements, beam dynamics simulations have been performed to study the observed instability. In particular, single bunch effects have been simulated using the PS transverse beam coupling impedance model developed over recent years. In this paper we present the measurements results along with the obtained instability thresholds. Different beam configurations and stabilizing effects, such as the gamma jump scheme and the octupole-induced tune spread, are also considered. The measurements results are compared with simulations.

Complementary to the physics research at the LHC, several fixed-target facilities receive beams from the LHC injector complex. To serve the fixed-target physics programme at the super proton synchrotron, high-intensity proton beams from the proton synchrotron are extracted using the multiturn extraction technique based on trapping parts of the beam in stable resonance islands. Considering the number of protons requested by future experimental fixed-target facilities, such as the proposed search for hidden particles experiment, the currently delivered beam intensities are insufficient. Experimental studies were conducted to optimize the multiturn extraction technique, pushing its capabilities in the domain of highintensity proton beams, and their results are presented in this paper. The success of these studies led to the decision to discontinue the former continuous transfer and remove the related hardware from the accelerator. Therefore, the multiturn extraction becomes standard operational practice for delivering proton beams for the fixed-target physics programme at the CERN super proton synchrotron.

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Due to its effective pumping ability, nonevaporable getter (NEG) coating is considered for the vacuum chambers of the Compact Linear Collider (CLIC) electron damping rings (EDR). The aim is to suppress fast beam ion instabilities. The electromagnetic (EM) characterization of the NEG properties up to ultrahigh frequencies is required for the correct impedance modeling of the damping ring (DR) components. The properties are determined using rectangular waveguides which are coated with NEG. The method is based on a combination of complex transmission coefficient S 21 measurements with a vector network analyzer (VNA) and 3D simulations using CST Microwave Studio® (CST MWS). The frequency ranges discussed in this paper are 220-330 and 500-750 GHz.