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 CLIC acceleration scheme, in which the RF power used to accelerate the main high energy beam is extracted from a second high intensity but low energy beam, places strict requirements on the phase stability of the power producing drive beam. To limit luminosity loss caused by energy jitter leading to emittance growth in the final focus to below 1%, 0.2 degrees of 12 GHz, or 50 fs, drive beam phase stability is needed. A low-latency phase feedforward correction with bandwidth above 17.5 MHz will be used to reduce the drive beam phase jitter to this level. The proposed scheme corrects the phase using fast electromagnetic kickers to vary the path length in a chicane prior to the drive beam power extraction. A prototype of this system has been installed at the CLIC test facility CTF3 to prove its feasibility. The latest results from the system are presented, demonstrating phase stabilisation in agreement with simulations given the beam conditions and power of the kicker amplifiers. Necessary improvements in the phase monitor CLIC – Note – 1092 performance and optics corrections made to remove the phase-energy dependence via R56 in order to achieve this level of stability are also discussed. 7th International Particle Accelerator Conference, Busan, Korea, 8 13 May 2016 Geneva, Switzerland 11 May 2016 DEMONSTRATION OF CLIC LEVEL PHASE STABILITY USING A HIGH BANDWIDTH, LOW LATENCY DRIVE BEAM PHASE FEEDFORWARD SYSTEM AT THE CLIC TEST FACILITY CTF3∗ J. Roberts, CERN, Geneva, Switzerland; JAI, Oxford, UK A. Andersson, R. Corsini, P.K. Skowroński, CERN, Geneva, Switzerland P.N. Burrows, G.B. Christian, C. Perry, JAI, Oxford University, UK A. Ghigo, F. Marcellini, INFN/LNF Frascati, Italy

The Compact Linear Collider (CLIC) is a multi-TeV high-luminosity linear e+e- collider under development. For an optimal exploitation of its physics potential, CLIC is foreseen to be built and operated in a staged approach with three centre-of-mass energy stages ranging from a few hundred GeV up to 3 TeV. The first stage will focus on precision Standard Model physics, in particular Higgs and top-quark measurements. Subsequent stages will focus on measurements of rare Higgs processes, as well as searches for new physics processes and precision measurements of new states, e.g. states previously discovered at LHC or at CLIC itself. In the 2012 CLIC Conceptual Design Report, a fully optimised 3 TeV collider was presented, while the proposed lower energy stages were not studied to the same level of detail. This report presents an updated baseline staging scenario for CLIC. The scenario is the result of a comprehensive study addressing the performance, cost and power of the CLIC accelerator complex as a function of centre-of-mass energy and it targets optimal physics output based on the current physics landscape. The optimised staging scenario foresees three main centre-of-mass energy stages at 380 GeV, 1.5 TeV and 3 TeV for a full CLIC programme spanning 22 years. For the first stage, an alternative to the CLIC drive beam scheme is presented in which the main linac power is produced using X-band klystrons.

The two-beam acceleration scheme envisaged for CLIC will require a high degree of phase stability between two beams at the drive beam decelerator sections, to allow efficient acceleration of the main beam. There will be up to 48 such decelerator sections for the full 3 TeV design, and each decelerator section will be instrumented with a feed-forward system to correct the drive beam phase to a precision of 0.2 degrees at 12 GHz relative to the main beam, using a kicker system around a four-bend chicane. A prototype system has been developed and tested at the CLIC Test Facility (CTF3) complex, where the beam phase is measured upstream of the combiner ring and corrected with two kickers in a dog-leg chicane just upstream of the CLEX facility, where the resulting phase change is measured. This prototype is designed to demonstrate correction of a portion of the CTF3 bunch train to the level required for CLIC, with a bandwidth of greater than 30 MHz, and within a latency constraint of 380 ns as set by the beam time-of-flight through the combiner ring complex. A description of the hardware will be given and initial results from the first phase of the experiment will be presented.

In the CLIC two beam acceleration concept the phase synchronisation between the main beam and the RF power extracted from the drive beam must be maintained to within 0.2 degrees of 12 GHz [1, 2]. A drive beam phase feedforward system with bandwidth above 17.5 MHz is required to reduce the drive beam phase jitter to this level [3]. The system will correct the drive beam phase by varying the path length through a chicane via the use of fast strip line kickers. A prototype of the system is in the final stages of installation at the CLIC test facility CTF3 at CERN. This paper presents results from preparations for the phase feedforward system relating to optics improvements, the development of a slow phase feedback that will be run in parallel with the feedforward system and first tests of the kicker amplifier and kickers.

The Compact Linear Collider international collaboration is pursuing an extensive R&D program towards a multiTeV electron-positron collider. In particular, the development of two-beam acceleration technology is the focus of the CLIC test facility CTF3. In this paper we summarise the most recent results obtained at CTF3: the results of the studies on the drive beam generation are presented, the achieved two beam acceleration performance is reported and the measured breakdown rates and related observations are summarised. The stability of the deceleration process performed over 12 subsequent modules and a comparison of the obtained results with the theoretical expectations are discussed. We also outline the future experimental program.

The Compact Linear Collider international collaboration is pursuing an extensive R&D program towards a multiTeV electron-positron collider. In particular, the development of two-beam acceleration technology is the focus of the CLIC test facility CTF3. In this paper we summarise the most recent results obtained at CTF3: the results of the studies on the drive beam generation are presented, the achieved two beam acceleration performance is reported and the measured breakdown rates and related observations are summarised. The stability of the deceleration process performed over 12 subsequent modules and a comparison of the obtained results with the theoretical expectations are discussed. We also outline the future experimental program.

A new electro-optic bunch profile monitor has recently been installed in CLIC Test Facility 3 at CERN. The monitor is based on an electro-optic spectral decoding scheme which reconstructs the longitudinal profile of the electron bunch by measuring its Coulomb field. The system uses a 780 nm fibre laser system, transported over a 20m long distance to the interaction chamber, where a ZnTe crystal is positioned close to the beam. The assembly also contains a traditional OTR screen, which is coupled to a second optical line and used to adjust the temporal overlap between the laser and the electron pulse. This paper presents the detection system in detail, as well as reporting on the first measurements performed with beam. Presented at: 4th International Particle Accelerator Conference, Shanghai, China, 12 17 May 2013 Geneva, Switzerland Date 12/05/2013 CLIC – Note – 1015

Comprehensive user manual for the phase-coding system setup and operation with PHIN including the measurements performed with the beam

The future Compact Linear Collider (CLIC) e−/e+ collider is based on the two-beam acceleration concept, whereby interleaving electron bunches of the drive beam through a delay loop and combiner rings as well as high peak RF power at 12GHz are created locally to accelerate a second beam, the main beam. One of the main objectives of the currently operational CLIC Test Facility (CTF3) is to demonstrate beam combination from 1.5GHz to 12GHz, which requires satellite-free fast phase-switching of the drive beam with sub-ns speed. The PHIN photo-injector, with the photo-injector laser, provides flexibility in the time structure of the electron bunches produced, by direct manipulation of the laser pulses. A novel fiber modulator-based phase-switching technique allows clean and fast phase-switch at 1.5GHz. This paper describes the switching system based on fiber-optic modulators, and the measurements carried out on both the laser and the electron beam to verify the scheme.

The high charge PHIN photo-injector was developed within the framework of the European CARE program to provide an alternative to the drive beam thermionic gun in the CTF3 (CLIC Test Facility) at CERN. In PHIN 1908 electron bunches are delivered with bunch spacing of 1.5 GHz and 2.33 nC charge per bunch. Furthermore the drive beam generated by CTF3 requires several fast 180 deg phase-shifts with respect to the 1.5 GHz bunch repetition frequency in order to allow the beam combination scheme developed at CTF3. A total of 8 subtrains, each 140 ns long and shifted in phase with respect to each other, have to be produced with very high phase and amplitude stability. A novel fiber modulator based phase-switching technique developed on the laser system provides this phase-shift between two consecutive pulses much faster and cleaner than the base line scheme, where a thermionic electron gun and sub-harmonic bunching are used. The paper describes the fiber-based switching system and the measurements verifying the scheme. The paper also discusses the latest 8nC charge production and cathode life-time studies on Cs2Te.

In the two beam acceleration scheme the Main Beam must be precisely synchronized with respect to the RF power produced by the Drive Beam. Timing errors would have an impact on the collider performances. The Drive Beam phase errors should be controlled, by means of a feed forward system, within 0.1° (23fs @ 12GHz) to avoid a luminosity reduction larger than 2%. A beam phase arrival monitor is an essential component of the system. Its design has been based on the following main requirements: resolution of the order of 20fs, very low coupling impedance due to the very high beam current and integrated filtering elements to reject RF noise and weak fields in the beam pipe that could otherwise affect the measurements.

The deliverables of TPMON task within the "Diagnostics" work package (DIAG) have been achieved, and are presented. The main results are described and key additional references are provided.