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Le Compact Linear Collider (CLIC), ou Collisionneur Linéaire Compact est un accélérateur de particules en projet au CERN. Il doit prendre la relève du Large Hadron Collider pour approfondir les futures découvertes de celui-ci. Le CLIC sera un accélérateur linéaire d'une quarantaine de kilomètres permettant de faire des collisions entre des électrons et des positrons à une énergie de 3 TeV. Le CLIC est basé sur le principe d'accélération à deux faisceaux. Le faisceau principal, de grande énergie et de faible intensité est accéléré grâce à un deuxième faisceau d'électrons relativistes de grande intensité et de faible énergie, le faisceau d'entraînement, parallèle au faisceau principal. Cette technologie devrait permettre une accélération d'environ 100 MV/m. Voir aussi Articles connexes

Accélérateur de particules
Large Hadron Collider, l'accélérateur de particules principal du CERN

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Optics design and performance of an ultra-low emittance damping ring for the compact linear collider

A high-energy (0.5-3.0 TeV centre of mass) electron-positron Compact Linear Collider (CLIC) is being studied at CERN as a new physics facility. The design study has been optimized for 3 TeV centre-of-mass energy. Intense bunches injected into the main linac must have unprecedentedly small emittances to achieve the design luminosity 1035cm-2s-1 required for the physics experiments. The positron and electron bunch trains will be provided by the CLIC injection complex. This thesis describes an optics design and performance of a positron damping ring developed for producing such ultra-low emittance beam. The linear optics of the CLIC damping ring is optimized by taking into account the combined action of radiation damping, quantum excitation and intrabeam scattering. The required beam emittance is obtained by using a TME (Theoretical Minimum Emittance) lattice with compact arcs and short period wiggler magnets located in dispersion-free regions. The damping ring beam energy is chosen as 2.42 GeV. The lattice features small values of the optical functions, a large number of compact TME cells, and a large number of wiggler magnets. Strong sextupole magnets are needed for the chromatic correction which introduces significant nonlinearities, decreasing the dynamic aperture. The nonlinear optimization of the lattice is described. An appropriate scheme of chromaticity correction is determined that gives reasonable dynamic aperture and zero chromaticity. The nonlinearities induced by the short period wiggler magnets and their influence on the beam dynamics are also studied. In addition, approaches for absorption of synchrotron radiation power produced by the wigglers are discussed. Realistic misalignments of magnets and monitors increase the equilibrium emittance. The sensitivity of the CLIC damping ring to various kinds of alignment errors is studied. Without any correction, fairly small vertical misalignments of the quadrupoles and, in particular, the sextupoles, introduce unacceptable distortions of the closed orbit as well as intolerable spurious vertical dispersion and coupling due to the strong focusing optics of the damping ring. A sophisticated beam-based correction scheme has been developed in order to bring the design target emittances and the dynamic aperture back to the ideal value. The correction using dipolar correctors and several skew quadrupole correctors allows a minimization of the closed-orbit distortion, the cross-talk between vertical and horizontal closed orbits, the residual vertical dispersion and the betatron tune coupling. The small emittance, short bunch length, and high current in the CLIC damping ring could give rise to collective effects which degrade the quality of the extracted beam. A number of possible instabilities and an estimate of their impact on the ring performance are briefly surveyed. The effects considered include fast beam-ion instability, coherent synchrotron radiation, Touschek scattering, intrabeam scattering, resistive-wall wake fields, and electron cloud.

EPFL2006

Study and Experimental Characterization of a Novel Photo Injector for the CLIC Drive Beam

Öznur Mete

In this thesis, the transverse and longitudinal beam properties of the PHIN photoinjector are characterized. The objective of the research is to demonstrate the reliable and stable production of a 1.3 µs long bunch train, with 2.33 nC charge per bunch and 4.5 µC of total charge, by the PHIN photoinjector. The results of this thesis are the important steps towards the feasibility demonstration of a photoinjector as the Compact Linear Collider's drive beam source. The PHIN photoinjector has been conceptualized by a collaboration between "Laboratoire de l'Accélérateur Linéaire (LAL)", "Rutherford Appleton Laboratory (RAL)" and "Organisation Européenne pour la Recherche Nucléaire (CERN)". Within this collaboration, LAL and RAL have committed to the design and the construction of the RF gun and laser, respectively. The photocathode production as well as the overall coordination and commissioning were under the responsibility of CERN. The project is in the framework of the second Joint Research Activity PHIN of the European CARE program. The photoinjector has been installed, in 2008, on a dedicated test-stand at CERN. During the commissioning of the PHIN photoinjector, the beam properties have been studied by rigorous systematic measurements and simulations. The maximum charge per bunch yield of the Cs2Te cathode has been found to be 4.4 nC, in agreement with the theoretical limit of 4.7 nC. The transverse normalized emittance, beam energy and energy spread have been measured both in a single shot and the time-resolved manner. The single shot measurements revealed useful information about the shot-to-shot stability of the beam properties, whereas the time-resolved measurements have reflected the stability along the bunch train. The multi-slit emittance measurement set-up, OTR profile monitors with gated CCD cameras and a segmented beam dump have been designed, implemented and utilized for the main measurements. The experimental characterization and the numerical studies clearly indicate the feasibility of a photoinjector within the specifications defined by the existing CLIC test facility. Further simulation and design studies have been conducted based on several modifications of the current PHIN RF gun design. In this successive model an RF gun with the specifications of the CLIC drive beam has been investigated and proposed as the preliminary design for the future CLIC drive beam injector studies.

EPFL2011

High Frequency Effects of Impedances and Coatings in the CLIC Damping Rings

Eirini Koukovini Platia

The Compact Linear Collider (CLIC) is a 3 TeV e+e- machine, currently under design at CERN, that targets to explore the terascale particle physics regime. The experiment requires a high luminosity of 2x10^34 cm^2 s^-1, which can be achieved with ultra low emittances delivered from the Damping Rings (DRs) complex. The high bunch brightness of the DRs gives rise to several collective effects that can limit the machine performance. Impedance studies during the design stage of the DR are of great importance to ensure safe operation under nominal parameters. As a first step, the transverse impedance model of the DR is built, accounting for the whole machine. Beam dynamics simulations are performed with HEADTAIL to investigate the effect on beam dynamics. For the correct impedance modeling of the machine elements, knowledge of the material properties is essential up to hundreds of GHz, where the bunch spectrum extends. Specifically, Non Evaporable Getter (NEG) is a commonly used coating for good vacuum but its properties up to high frequencies were still widely unexplored. A new method using rectangular waveguides is proposed, benchmarked and applied for the first time to characterize NEG up to hundreds of GHz. The numerical tools used for the DR studies are applied and benchmarked with measurements in other light sources. In particular, single bunch measurements were performed in the ALBA light source and compared to the model prediction using HEADTAIL. The impedance budget of ALBA was estimated before and after the installation of a pinger magnet. Furthermore, studies were also carried out for the Swiss Light Source (SLS) upgrade to investigate the machine performance in terms of single bunch instabilities for lattices with negative momentum compaction factor.

EPFL2015

Optics design and performance of an ultra-low emittance damping ring for the compact linear collider

EPFL2006

Study and Experimental Characterization of a Novel Photo Injector for the CLIC Drive Beam

Öznur Mete

EPFL2011