The Compact Linear Collider (CLIC) - 2018 Summary Report

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

High-Gradient RF laboratory at IFIC for medical applications

General interest has been shown over the last years for compact and more affordable facilities for hadron-therapy. The High-Gradient (HG) know-how and technology for normal-conducting accelerating RF (Radio-Frequency) electron linac (linear accelerator) structures recently developed for projects such as CLIC (CERN), has raised the achievable accelerating gradient from 20-30 MV/m up to 100-120 MV/m. This gain has come through a better understanding of the high-power RF vacuum arcs or breakdowns (BD) phenomena, the development of quantitative HG RF design methods and refinements in fabrication techniques. This can allow for more compact linacs also for protons, which is potentially important in the new trend in hadron-therapy of using linacs able to provide protons of 70-230 MeV or light ions of 100-400 MeV/u. Linacs are of particular interest for medical applications because they can provide a high degree of flexibility for treatment, such as running at 100-400 Hz pulse rate and pulse-to-pulse beam energy (and intensity) variations. This kind of accelerator is very well suited to treat moving organs with 4D multi-painting spot scanning technique. HG operation is limited by the BD phenomena and is characterized by the BD-Rate. New fresh structures initially operate at a reduced performance and must be conditioned through extended high-power rf operation until the maximum operational gradient is reached. This process is a time consuming, and consequently costly task (> 350 million pulses) which is important to understand and reduce. The IFIC HG-RF laboratory is designed to host a high-power and high-repetition rate facility for testing S-Band (2.9985 GHz) normal-conducting RF structures. This facility will allow the development, RF conditioning and studies of the BD phenomena in HG structures.General interest has been shown over the last years for compact and more affordable facilities for hadron-therapy. The High-Gradient (HG) know-how and technology for normal-conducting accelerating RF (Radio-Frequency) electron linac (linear accelerator) structures recently developed for projects such as CLIC (CERN), has raised the achievable accelerating gradient from 20-30 MV/m up to 100-120 MV/m. This gain has come through a better understanding of the high-power RF vacuum arcs or breakdowns (BD) phenomena, the development of quantitative HG RF design methods and refinements in fabrication techniques. This can allow for more compact linacs also for protons, which is potentially important in the new trend in hadron-therapy of using linacs able to provide protons of 70-230 MeV or light ions of 100-400 MeV/u. Linacs are of particular interest for medical applications because they can provide a high degree of flexibility for treatment, such as running at 100-400 Hz pulse rate and pulse-to-pulse beam energy (and intensity) variations. This kind of accelerator is very well suited to treat moving organs with 4D multi-painting spot scanning technique. HG operation is limited by the BD phenomena and is characterized by the BD-Rate. New fresh structures initially operate at a reduced performance and must be conditioned through extended high-power rf operation until the maximum operational gradient is reached. This process is a time consuming, and consequently costly task (> 350 million pulses) which is important to understand and reduce. The IFIC HG-RF laboratory is designed to host a high-power and high-repetition rate facility for testing S-Band (2.9985 GHz) normal-conducting RF structures. This facility will allow the development, RF conditioning and studies of the BD phenomena in HG structures

RF Design of the X-band Linac for the EuPRAXIA@SPARC_LAB Project

We illustrate the RF design of the X-band linac for the upgrade of the SPARC_LAB facility at INFN-LNF (EuPRAXIA@SPARC_LAB). The structures are travelling wave (TW) cavities, working on the 2π/3 mode, fed by klystrons with pulse compressor systems. The tapering of the cells along the structure and the cell profiles have been optimized to maximize the effective shunt impedance keeping under control the maximum value of the modified Poynting vector, while the couplers have been designed to have a symmetric feeding and a reduced pulsed heating. In the paper we also present the RF power distribution layout of the accelerating module and a preliminary mechanical design

Manufacturing of X-band Accelerating Structures: Metrology Analysis and Process Capability

The fabrication tolerances of RF components are essential for CLIC X-band accelerating structures to perform efficiently. On one hand, the capability of high power accelerating structures depends on the shape accuracy and the asperity of the inner surfaces, when microwaves pass through the cavity. On the other hand, surface flatness and dimensional tolerances are necessary to guarantee a correct assembly process. Hence, the discs that build up the structure require sub-micrometre specifications and, in order to meet all the needs, ultra-precision machining using single crystal diamond tools is mandatory. This paper shows the analysis of the metrology results of the fabrication of 118 discs (4 accelerating structures). Dimensional and form tolerances are studied following the production order to find drifts in the production and to predict the impact on the assembly process. Finally, process capability is evaluated

Pre-Alignment Techniques Developments and Measurement Results of the Electromagnetic Center of Warm High-Gradient Accelerating Structures

In the framework of the PACMAN project we have developed a test set-up to measure the electromagnetic centre of high gradient accelerating structures for alignment purposes. We have demonstrated with previous simulation studies that a resolution of 1 m is possible. The improvements applied on the technique and on the set-up, calibrations and the equipment instrumentation allows the measurement of the electromagnetic centre, with a final precision of 1.09 m in the horizontal plane and 0.58 m in the vertical plane. The experimental measurements and the simulation studies as a support to justify the numbers obtained are presented and discussed

Calorimetric Power Measurements in X-band High Power RF

With the aim to test prototype accelerating structures for CLIC at high-gradient, new klystron-based, X-band high power test stands are being built at CERN. These tests stands are referred to as Xboxes with Xbox1 and Xbox2 being already operational. Stainless steel loads are placed in the end of the Xbox-1 system to absorb the remaining power which comes out of the accelerating structure. Power information is important and needs to be measured precisely. A new power measuring method based on calorimetry is proposed independent from RF measurements subject to frequent calibration. The principles of the method and simulations are presented and the results of actual experimentation are used to validate the method. The results show calorimetric measurement is feasible method and have a good precision at this power level

High-Power Testing Results of X-Band RF-Window and 45 Degrees Spiral Load

The X-Band test facilities at CERN have been running for some years now qualifying CLIC structure prototypes, but also developing and testing high power general-purpose X-Band components, used in a wide range of applications. Driven by operational needs, several components have been redesigned and tested aiming to optimize the reliability and the compactness of the full system and therefore enhancing the accessibility of this technology inside and outside CERN. To this extent, a new high-power RF-window has been designed and tested aiming to avoid unnecessary venting of high-power sections already conditioned, easing the interventions, and protecting the klystrons. A new spiral load prototype has also been designed, built, and tested, optimizing the compactness, and improving the fabrication process. In these pages, the design and manufacturing for each component will be shortly described, along with the last results on the high-power testing

Pre-alignment of Accelerating Structures for Compact Acceleration and High Gradient using In-situ Radiofrequency Methods

International audienceTo achieve a high accelerating gradient of 100 MV/m, the CLIC project under study at CERN uses a 23 cm long tapered normal-conducting travelling wave Accelerating Structure (AS) operating at 12 GHz. Minimisation of the long-range wakefields (WF) is assured by damping of the HOM through four radial waveguides in each cell without distorting the accelerating mode. As an extension of them, there are four bent waveguides called WF monitors (WFM) in the middle cell with two RF pick-ups. To obtain a small beam emittance in the collision point, micro-metric pre-alignment of the AS is required. We work to find the electrical centre of the AS through the use of the asymmetry in the RF scattering parameters created by an off-centre conductive wire, stretched along the axis. The accuracy required is of 7 μm with a resolution of 3.5 μm for the WFM signals including the acquisition electronics. Our simulations have shown that a resolution of 1 μm is possible using a calibrated VNA. Measurement results and improvements of the final accuracy will be presented and discussed

Electromagnetic Field Pre-alignment of the Compact Linear Collider (CLIC) Accelerating Structure with help of Wakefield Monitor Signals

The CLIC project, currently under study at CERN is an electron-positron collider at 3 TeV centre-of-mass energy and luminosity of 2*1034 cm⁻²s^{−1}. Achieving such luminosity requires a beam dimension of 1 nm in the vertical plane and high beam stability. The TD24 is a traveling wave structure operating at 12 GHz designed to reach 100 MV/m at constant gradient. It consists of two coupling cells and 24 disks. The RF is coupled from cell to cell though an iris of 5.5 mm. To minimize the occurrence of wake-fields and minimize the emittance growth Δεy below 5%, the pre-alignment precision of the electrical centre of the accelerating structure (AS) on its support has to be better than 7 μm. Following, the AS is actively aligned with beam using the wake-field monitor (WFM) signals, with a resolution of 3.5 μm. A test bench for laboratory measurements has been designed and exploits the asymmetry created by RF scattering parameters of an off-centre conductive wire, stretched to locate the electromagnetic centre of the AS. Simulations and preliminary measurement results are presented