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 high-intensity 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.

In the framework of the LHC Injectors Upgrade (LIU) project, the investigation and quantification of the optics mismatch between the CERN Proton Synchrotron Booster (PSB) and PS is a crucial step in understanding the source of horizontal emittance growth between the two machines. Extensive studies were carried out to estimate the mismatch from single-pass measurements in the transfer line and to rematch the transfer line to reduce the dispersive mismatch at PS injection while keeping the betatron matching unaltered. This paper presents the results of the data analysis of more recent multi-turn measurements, which profited from a new turn-by-turn beam profile monitor in the PS ring, to assess the achieved level of matching and corresponding emittance growth. The results confirm the improved matching and demonstrate the feasibility of the multi-turn technique as a fundamental tool that will be important for the recommissioning of the renovated transfer line after Long Shutdown 2.

This contribution gives an overview of the beam performance of the LHC injector chain during Run 2. In the first part the various beam types used for LHC luminosity production with protons (e.g. 25 ns standard, 25 ns BCMS, 8b4e, 8b4e BCS) are described. The present performance limitations along the injector chain together with the achieved beam parameters at LHC injection (e.g. transverse emittance, intensity, batch spacing) are summarised. Also the special high intensity beams, which were studied within the LIU framework and also extracted to the LHC for Machine Development studies, are mentioned. The second part describes the evolution of the ion beams for the LHC throughout Run 2 and their optimisation for luminosity production.

In the framework of the LHC Injectors Upgrade project the improvements required to achieve the parameters of the future beams for the High-Luminosity LHC are being studied and implemented. In order to deliver high brightness beams, control over the beam intensity and emittance is fundamental. Therefore, a highly accurate and reliable transverse emittance measurement is essential. Presently at the CERN Proton Synchrotron, the only operationally available emittance monitors not impacting the facility beam production are the flying wire scanners used to measure the circulating beam profile. The wire scanners will be replaced with a new generation in the next two years and a prototype is already installed. The prototype has been commissioned with beams featuring a wide range of intensities and emittances. This paper evaluates the performance of the prototype with respect to the present system via beam-based measurements. The transverse emittance measurement is discussed, considering the different potential error contributions to the measurement, such as knowledge of the machine optics and the dispersive contribution to the beam size.

Radio frequency breakdown rate is a crucial performance parameter that ensures that the design luminosity is achieved in the CLIC linear collider. The required low breakdown rate for CLIC, of the order of 10(-7) breakdown pulse(-1) m(-1), has been demonstrated in a number of 12 GHz CLIC prototype structures at gradients in excess of the design 100 MV/m accelerating gradient, however without the presence of the accelerated beam and associated beam loading. The beam loading induced by the approximately 1 A CLIC main beam significantly modifies the field distribution inside the structures, and the effect on breakdown rate is potentially significant so needs to be determined. A dedicated experiment has been carried out in the CLIC Test Facility CTF3 to measure this effect, and the results are presented.

The new Linear Electron Accelerator for Research (CLEAR) facility at CERN started its operation in fall 2017. CLEAR results from the conversion of the CALIFES beam line of the former CLIC Test Facility (CTF3) into a new testbed for general accelerator R&D and component studies for existing and possible future accelerator applications. CLEAR can provide a stable and reliable electron beam from 60 to 220 MeV in single or multi bunch configuration at 1.5 GHz. The experimental program includes studies for high gradient acceleration methods, e.g. for CLIC X-band and plasma technology, prototyping and validation of accelerator components, e.g. for the HL-LHC upgrade, and irradiation test capabilities for characterization of electronic components and for medical applications. An overview of the facility capabilities and a summary of the latest results will be presented.

The conversion of the CALIFES beamline of CTF3 into the “CERN Linear Electron Accelerator for Research” (CLEAR) facility was approved in December 2016. The primary focus for CLEAR is general accelerator R&D and component studies for existing and possible future accelerator applications. This includes studies for high gradient acceleration methods, e.g. for CLIC and plasma technology, and prototyping and validation of accelerator components, e.g. for the HL-LHC upgrade. The facility also provides irradiation test capabilities for characterisation of electronic components and for medical applications. A description of the facility with details on the achievable beam parameters, and the status and plans are presented.

One of the objective of The CLIC Test Facility (CTF3) at CERN is to demonstrate the CLIC Drive Beam Recombination concept. An accurate control of the transverse beam parameters is necessary in order to succeed in preserving the beam quality after the recombination. During the activity of the facility we improved our tools and technique for characterising the beam transverse phase space before and after recombination. The common quadrupole scan technique was improved by performing constant-beam-size measurement and it was enriched by a tomographic reconstruction of the phase-space. More over studies have been performed in order to estimate and subtract the impact of dispersion on such a measurements. An overview of these techniques will be presented with actual measurements performed over the last year of operation of the facility. 8th International Particle Accelerator Conference, Copenhagen, Denmark, 14 19 May 2017 Geneva, Switzerland 15 May 2017 CLIC – Note – 1115 TRANSVERSE BEAM PHASE-SPACE MEASUREMENT EXPERIENCE AT CTF3 D. Gamba∗, B. Constance, R. Corsini, S. Doebert, L. Malina, F. Tecker, T. Persson, J. Roberts, A. P. Rollings, P. K. Skowronski, CERN, Geneva 1217, Switzerland L. Martin, L.A.P. Serratosa, University of Oxford, Oxford OX1 3RH, United Kingdom Abstract One of the objective of The CLIC Test Facility (CTF3) at CERN is to demonstrate the CLIC Drive Beam Recombination concept. An accurate control of the transverse beam parameters is necessary in order to succeed in preserving the beam quality after the recombination. During the activity of the facility we improved our tools and technique for characterising the beam transverse phase space before and after recombination. The common quadrupole scan technique was improved by performing constant-beam-size measurement and it was enriched by a tomographic reconstruction of the phase-space. Moreover studies have been performed in order to estimate and subtract the impact of dispersion on such a measurements. An overview of these techniques will be presented with actual measurements performed over the last year of operation of the facility.One of the objective of The CLIC Test Facility (CTF3) at CERN is to demonstrate the CLIC Drive Beam Recombination concept. An accurate control of the transverse beam parameters is necessary in order to succeed in preserving the beam quality after the recombination. During the activity of the facility we improved our tools and technique for characterising the beam transverse phase space before and after recombination. The common quadrupole scan technique was improved by performing constant-beam-size measurement and it was enriched by a tomographic reconstruction of the phase-space. Moreover studies have been performed in order to estimate and subtract the impact of dispersion on such a measurements. An overview of these techniques will be presented with actual measurements performed over the last year of operation of the facility. INTRODUCTION The CLIC Test Facility (CTF3) [1] at CERN aims to demonstrate the feasibility of the key technologies of the Compact Linear Collider (CLIC) design [2]. One of the key aspects of CLIC is its Drive Beam recombination. At CTF3 an initially 1.2 μs long train of bunches at 1.5 GHz is recombined with itself in a complex of delay lines and rings in order to produce a 140 ns long train at 12 GHz. During the recombination process different parts of the initial train undertake different paths before being merged together. In order to preserve the projected emittance of the beam an optics that produces the same transverse (and longitudinal) phase-space distribution irrespectively of the path is necessary. At CTF3 the quadrupole scan technique has been the primary tool to verify the optics and the orbit closure between the different paths, as well as to identify dispersion leakage and chromatic aberrations. In the following sections we introduce the basic mathematical concept used, and we discuss some actual measurements performed at CTF3. QUADRUPOLE SCAN TECHNIQUE The quadrupole scan technique is one of the main methods for measuring the transverse Twiss parameters of relativistic beams in transfer lines, and it is extensively documented in the literature (e.g. in [3]). Here we recall only the basic principles for the simplest case of a linear and uncoupled transfer line, where one can treat the horizontal and vertical phase-spaces independently using a 2D matrix formalism. ∗ davide.gamba@cern.ch A quadrupole scan consists in reconstructing the transverse phase-space distribution at some location along a beam line by measuring the beam profile downstream. In linear optics the transfer matrix from a reconstruction (R) to a measurement (M) location can be written as: ( x x ′ ) M = [ A B C D ] ( x x ′ )

The Compact Linear Collider (CLIC) is a TeV-scale high-luminosity linear $e^+e^-$ collider under development at CERN. Following the CLIC conceptual design published in 2012, this report provides an overview of the CLIC project, its current status, and future developments. It presents the CLIC physics potential and reports on design, technology, and implementation aspects of the accelerator and the detector. CLIC is foreseen to be built and operated in stages, at centre-of-mass energies of 380 GeV, 1.5 TeV and 3 TeV, respectively. CLIC uses a two-beam acceleration scheme, in which 12 GHz accelerating structures are powered via a high-current drive beam. For the first stage, an alternative with X-band klystron powering is also considered. CLIC accelerator optimisation, technical developments and system tests have resulted in an increased energy efficiency (power around 170 MW) for the 380 GeV stage, together with a reduced cost estimate at the level of 6 billion CHF. The detector concept has been refined using improved software tools. Significant progress has been made on detector technology developments for the tracking and calorimetry systems. A wide range of CLIC physics studies has been conducted, both through full detector simulations and parametric studies, together providing a broad overview of the CLIC physics potential. Each of the three energy stages adds cornerstones of the full CLIC physics programme, such as Higgs width and couplings, top-quark properties, Higgs self-coupling, direct searches, and many precision electroweak measurements. The interpretation of the combined results gives crucial and accurate insight into new physics, largely complementary to LHC and HL-LHC. The construction of the first CLIC energy stage could start by 2026. First beams would be available by 2035, marking the beginning of a broad CLIC physics programme spanning 25-30 years.

The injectors have delivered different beam types for luminosity production in the LHC during the 2017 run. Besides the nominal beam with 25 ns spacing and 72 bunches at PS extraction, the batch-compression-merging-splitting (BCMS) beam with multiples of 48 bunches at extraction from the SPS has been produced. The reduced number of bunches per batch from the PS is compensated by almost twice as smaller transverse emittance. The vacuum related issues in the LHC (16L2 cell) could be mitigated by switching to the so-called 8b4e beam, where mini-batches of 8 bunches are followed by 4 empty bunch positions in between. Thanks to the flexibility of the injectors, a higher brightness version of the 8b4e has been prepared to quickly react to the needs of the LHC. In this paper, an overview of the beams from the injector complex is given, describing how the beams are produced and summarizing their characteristics, achieved performance and specific limitations. In view of the operation in 2018, the expected beam parameters are presented, as well as a reminder of possible alternative beam types from the injectors. BEAM PRODUCTION SCHEMES All the accelerators in the LHC injector chain contribute to the definition of the beam parameters. The transverse emittance is initially defined at injection in the PS Booster (PSB) and increases linearly with the bunch intensity (brightness curve [1]). The beam pattern is then defined in PS, where rf manipulations are performed to split, merge and compress the beam. The versatility of the rf systems in the PS allows to produce various beam patterns and the rf manipulations used during the 2017 run are shown in Fig. 1. At extraction from the PS, the bunch spacing is 25 ns with the longitudinal emittance adjusted to εL = 0.35 eVs per bunch as a compromise for low capture losses and beam stability in the SPS. The nominal bunch intensity at PS extraction is Nb = 1.3 × 1011 protons per bunch (p/b). Finally, 1 to 4 batches are extracted from the PS to the SPS to maximize the number of bunches per injection into the LHC. An important limitation for beam brightness occurs at the transfer from the PSB to the PS. The longitudinal emittance extracted from the PSB should bemaximized to reduce space charge effects on the PS flat bottom [2]. However, the maximum bunch length for extraction from the PSB to the PS is limited by the rise time of the recombination kickers [3]. In addition, too large momentum spread leads to transverse emittance blow-up due to a known, and unavoidable with ∗ alexandre.lasheen@cern.ch h = 9 .. 1 4 m 7 1 4 2 1 h = 9 .. 1 4 .. 2 1 h = 7 → 2 1 25 ns BCMS 8b4e BC 8b4e standard h = 7 1 4 2 1 Standard h = 2 1 → 4 2 → 8 4

The CLIC Test Facility CTF3 was build, commissioned and operated at CERN by an international collaboration, with the aim of validating the CLIC two beam acceleration scheme, in which the RF power used to accelerate e+/e− beams is extracted from a high intensity electron beam. In the past years the main issues of such a scheme were assessed, demonstrating its feasibility. The CTF3 experimental programme is complementing these results by addressing cost and performance subjects, mainly using the CALIFES test beam injector and a full scale two-beam module. In this paper we document the present status and give an outlook to next year run, when the experimental programme should be completed. 7th International Particle Accelerator Conference, Busan, Korea, 8 13 May 2016 Geneva, Switzerland 12 May 2016 CLIC – Note – 1101 BEAM-LOADING EFFECT ON BREAKDOWN RATE IN HIGH-GRADIENT ACCELERATING STRUCTURES∗ F. Tecker†, N. Catalan-Lasheras, R. Corsini, A. Degiovanni1, A. Grudiev, G. McMonagle, J.L. Navarro Quirante1, I. Syratchev, W. Wuensch, B. Woolley, CERN, Geneva, Switzerland R. Rajamaki2, Aalto University, Espoo, Finland T. Argyropoulos2, J. Giner-Navarro2, IFIC (CSIC-UV), Valencia, Spain D. Gamba2, JAI, Oxford, United Kingdom J. Tagg, National Instruments Switzerland, Ennetbaden, Switzerland E. Senes2, University of Torino, Torino, Italy 1 present affiliation: ADAM, Geneva, Switzerland 2 also at CERN, Geneva, Switzerland

The RF breakdown rate is crucial for the luminosity performance of the CLIC linear collider. There quired breakdown rate at the design gradient of 100 MV/m has been demonstrated, without beam presence, in a number of 12 GHz CLIC prototype structures. Nevertheless, the beamloading at CLIC significantly changes the field profile inside the structures, and the behaviour with beam needs to be understood. A dedicated experiment in the CLIC Test Facility CTF3 to determine the effect of beam on the breakdown rate has been collecting breakdown data throughout the year 2016. The complete results of the experiment and the effect of the beamloading on the break down rate are presented. 8th International Particle Accelerator Conference, Copenhagen, Denmark, 14 19 May 2017 Geneva, Switzerland 16 May 2017 CLIC – Note – 1122 RESULTS OF THE BEAM-LOADING BREAKDOWN RATE EXPERIMENT AT THE CLIC TEST FACILITY CTF3∗ E. Senes† 1, N. Catalan-Lasheras, R. Corsini, D. Gamba, A. Grudiev, G. McMonagle, I. Syratchev, F. Tecker, W. Wuensch, CERN, Geneva, Switzerland T. Argyropoulos2, J. Giner-Navarro2,3, IFIC (CSIC-UV), Valencia, Spain R. Rajamaki, Aalto University, Espoo, Finland X. Stragier2, TU/e, Eindhoven, The Netherlands 1also at University of Torino, Torino, Italy, 2also at CERN, Geneva, Switzerland, 3present affiliation, UCLA, Los Angeles, CA, USA

Due to the secondary showers generated when a particle hits the vacuum chamber, beam losses at an accelerator may be detected via radiation detectors located near the beam line. Several sources of background can limit the sensitivity and reduce the dynamic range of a Beam Loss Monitor (BLM). This document concentrates on potential sources of background generated near high gradient RF cavities due to dark current and voltage breakdowns. An optical fibre has been installed at an experiment of the Compact Linear Collider (CLIC) Test Facility (CTF3), where a dedicated study of the performance of a loaded and unloaded CLIC accelerating structure is undergoing. An analysis of the collected data and a benchmarking simulation are presented to estimate BLM sensitivity limitations. Moreover, the feasibility for the use of BLMs optimised for the diagnostics of RF cavities is discussed.

Six UK institutes are engaged in a collaborative R&D programme with CERN aimed at demonstrating key aspects of technology feasibility for the Compact Linear Collider (CLIC). We give an overview and status of: 1) Drive-beam components: quadrupole magnets and the beam phase feed-forward prototype. 2) Beam instrumentation: stripline and cavity beam position monitors, an electro-optical longitudinal bunch profile monitor, and laserwire and diffraction and transition radiation monitors for transverse beam-size determination. 3) Beam delivery system and machinedetector interface design, including beam feedback/control systems and crab cavity design and control. 4) RF structure design. In each case we report on the status of prototype systems and performance tests with beam at the CTF3, ATF2 and CESRTA test facilities, including plans for future experiments.

The CLIC Test Facility CTF3 has been built at CERN by the Compact Linear Collider (CLIC) International Collaboration, in order to prove the main feasibilit y issues of the two-beam acceleration technology on which the collider is based. After the successful completion of its initial task, CTF3 is continuing its experimental prog ram in order to give further indications on cost and performance issues, to act as a test bed for the CLIC technology, and to conduct beam experiments aimed at mitigating technological risks. In this paper we di scuss the status of the ongoing experiments and present the more recent results, including improvements in beam quality and stability .