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Electron cloud (e-cloud) effects are among the main performance limitations for the operation of the Large Hadron Collider (LHC) with 25 ns bunch spacing. A large number of electrons impacting on the beam-screens of the superconducting magnets induces significant heat load, reaching values close to the full cooling capacity available from the cryogenic system. A number of Machine Development (MD) sessions in 2018 was dedicated to characterizing the heat load as a function of beam and machine parameters, investigating in particular its distribution along the ring and its dependence on the filling pattern, bunch population and bunch length. The main results of these measurements have been compared against simulations performed with the PyECLOUD code in order to validate the underlying model.

This MD shows the feasibility of operating TI2 with an optics matched to the SPS Q22 optics.Optics studies in the transfer line (TL) were performed together with an injection voltage scan toassess, also, the longitudinal quality of the injected single bunch.

This note describes the performance limitations of the present LHC RF system on the injection plateau, in view of increased intensities in Run III and in the HL-LHC era. The minimum required injection voltage is derived from beam dynamics constraints and operational experience. The maximum available voltage is given by beam measurements with the half-detuning beam-loading compensation scheme. From these two constraints, the performance reach with increased intensities is evaluated. Various studies, such as a potential RF upgrade, or alternative beam-loading compensation scenarios, are recommended.

This MD note summarizes the measurements performed to study persistent longitudinal oscillations after injection into the LHC. It was found that they build up due to mismatch, and can lead to particle losses and uncontrolled bunch lengthening. For the first time, profile measurements and ObsBox data acquisitions were triggered at injection to obtain first-turn data. The measurements took place on 16th September 2017 between 14:30 and 19:30, and between 27th November 2017 20:00 and 28th November 2017 04:00.

This Note summarizes the results of the power loss calculations for FCC-ee machines with 400.79 MHz cavity options. The requirements for the single-cell cavity design and for the operation with beam are obtained from the results for the high-current FCC-ee machine (Z). For other machines the power loss is sufficiently low and can be absorbed and extracted by foreseen HOM couplers.

The main aim of this document is to have a clearly identified set of beam and machine parameters to be used for numerical simulations and performance assessment. Two scenarios (referring only to the operation at the nominal beam energy of 7 TeV) are discussed: i) Nominal scenario (levelling at a luminosity of 5E34 cm-2s-1) ii) Ultimate scenario (levelling at a luminosity of 7.5E34 cm-2s-1)

CERN's LHC injectors are delivering high-brightness proton and ion beams for the Large Hadron Collider LHC. We review the present operation modes and beam performance, and highlight the limitations. We will then give an overview of the upgrade program that has been put in place to meet the demands of the LHC during the High-Luminosity LHC era., Proceedings of the 61\textsuperscript{st} ICFA ABDW on High-Intensity and High-Brightness Hadron Beams, HB2018, Daejeon, Korea

One of the strong limitations for reaching higher beam intensities in the SPS, the injector of the LHC at CERN, are particle losses at flat bottom that increase with beam intensity. In this paper, different sources of these losses are investigated for two available SPS optics, using both measurements and simulations. Part of the losses originate from the PS-to-SPS bunch-to-bucket transfer, because the PS bunches are rotated in longitudinal phase space before injection and do not completely fit into the SPS RF bucket. The injection losses due to different injected bunch distributions were analyzed. Furthermore, at high intensities the transient beam loading in the SPS has a strong impact, which is (partially) compensated by the LLRF system. The effect of the present and future upgraded one-turn delay feedback system and phase loop on flat-bottom losses was studied using the longitudinal tracking code BLonD. Finally, the total particle losses are also affected by limitations in the SPS momentum aperture, visible for higher RF capture voltages in optics with lower transition energy and higher dispersion., Proceedings of the 61\textsuperscript{st} ICFA ABDW on High-Intensity and High-Brightness Hadron Beams, HB2018, Daejeon, Korea

Beam-based impedance measurements play an important role in benchmarking existing impedance models of the accelerator, as well as in elaborating them. Impedance measurements can be made with both stable and unstable beams. In the first case, one makes use of changes in stable bunch parameters, such as bunch length, synchrotron frequency distribution, or synchronous phase shift. In the second case, measurements of instability characteristics (threshold, growth rates, bunch spectrum) can be used for impedance search or evaluation, usually by comparison with results of particle simulations., CERN Yellow Reports: School Proceedings, Vol 3 (2017): Proceedings of the CAS-CERN Accelerator School on Intensity Limitations in Particle Beams

The purpose of this MD was to estimate the stability threshold due to longitudinal coupled-bunch instabilities (CBIs) driven by the RF cavities' fundamental impedance. These instabilities are not a concern for the LHC. A model was developed to study the stability threshold for the High-Luminosity LHC (HL-LHC). The goal of this MD was to validate this model and thus its predictions for the HL-LHC stability margins.

In future the SPS should be able to transfer to the LHC the beam produced by a completely new pre-injector chain and required by the LHC for different upgrade scenarios. The issues related to this extremely challenging task are presented together with some possible ways of overcoming the problems that arise. Besides an increase in injection energy provided by PS2, these measures can include both an SPS vacuum chamber upgrade against the e-cloud and operation with larger longitudinal emittance for beam stability. As a result the power plant of the SPS RF system must be doubled. The SPS upgrade will also need the improvement or replacement of many other machine elements.

The Super Proton Synchrotron (SPS) at CERN is the injector of the Large Hadron Collider (LHC), the world's largest particle collider. The High-Luminosity LHC (HL-LHC) project is a major step forward in the improvement of the LHC performances and it requires a doubling of the nominal bunch intensity of the current LHC beam. In the SPS, multi-bunch instabilities and particle losses limit the beam intensity that can be accelerated to 450 GeV/c and transferred to the LHC. Without mitigation measures, the bunch intensity threshold for longitudinal instabilities is three times below the nominal intensity of the LHC beam. Moreover, the present limited RF power is not sufficient to accelerate beams with intensities well above nominal without substantial particle losses and a reduction of the RF voltage available for the beam at the flat top energy. The SPS will undergo significant upgrades but they may not be sufficient to ensure the stability of the HL-LHC beam. The objectives of this doctoral research are to study the longitudinal intensity limitations of the LHC proton beam in the SPS and to find possible mitigation measures to ensure the beam stability and quality at HL-LHC intensity. Beam measurements and particle simulations are used in conjunction with analytical estimations to study the multi-bunch instabilities during the cycle in the SPS. This work attempts to identify the main sources of instabilities and beam quality degradation. Possible scenarios of mitigation measures are investigated to explore the future beam parameters achievable after upgrades. The effects on beam stability of the foreseen RF upgrade, the double RF operation and the reduction of various longitudinal beam-coupling impedances are analysed in detail. The scenario of a lower-harmonic RF system in the SPS, for particle losses reduction, is also studied.