CLIC est un des projets actuels de construction d'un collisionneur lineaire de haute energie. La taille verticale des faisceaux de 0,7nm lors de la collision et le mouvement rapide du sol de quelques nanometres imposent une stabilisation active des doublets finaux au cinquieme de nanometre au-dessus de 4Hz. La majorite de mon travail a porte sur l'etude des vibrations et de la stabilisation active de poutres en porte-a-faux et elancees afin de representer les doublets finaux de CLIC. Dans une premiere partie, les performances mesurees de differents types de capteurs de vibration associes a une instrumentation appropriee ont montre que des mesures precises du mouvement du sol sont possibles de 0,1Hz jusqu'a 2000Hz sur un site calme. Egalement, des capteurs electrochimiques repondant a priori au cahier des charges de CLIC peuvent etre incorpores dans la stabilisation active au cinquieme de nanometre. Dans une deuxieme partie, une etude experimentale et numerique des vibrations d'une poutre a permis de valider l'efficacite de la prediction numerique incorporee par la suite dans la simulation de la stabilisation active. Egalement, une etude de l'impact du mouvement du sol et du bruit acoustique sur les vibrations d'une poutre a montre qu'une stabilisation active est necessaire jusqu'a au moins 1000Hz. Dans une troisieme partie, les resultats sur la stabilisation active d'une poutre a ses deux premieres resonances sont montres jusqu'a des amplitudes d'un dixieme de nanometre au-dessus de 4Hz en utilisant en parallele un systeme commercial realisant une stabilisation passive et active de l'encastrement. La derniere partie a porte sur une etude d'un support pour les doublets finaux d'un prototype d'un collisionneur lineaire en phase de finalisation, le prototype ATF2. Ce travail a montre que le mouvement relatif entre ce support et le sol est en-dessous des tolerances imposees (6nm au-dessus de 0,1Hz) avec des conditions aux limites appropriees.

Etude des vibrations et de la stabilisation à l'échelle sous-nanométrique des doublets finaux d'un collisionneur linéaire

The luminosity that can be achieved in a linear collider strongly depends on the vertical emittance of the beams at the interaction point. One of the most important sources of emittance growth is the accelerating part of the main linac especially in the case of the compact linear collider, CLIC[1], where the wakefields are strong due to the high frequency of the accelerating structures (30GHz). Possible lattices for the main linacs for centre-of-mass energies of 1TeV and 3TeV are presented which allow the use of BNS-damping for emittance preservation. A new ballistic beam-based alignment technique to keep the emittance growth below the required limit is investigated. The influence of different prealignment and field errors on the correction efficiency is investigated.

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Emittance Preservation in the Main LINAC of CLIC

The Compact Linear Collider (CLIC) is a high energy (0.5 to 5 TeV) e/sup /spl plusmn// linear collider that uses a high-current electron beam (the drive beam) for 30 GHz RF power production by the two-beam acceleration (TBA) method. Recently, a new cost-effective and efficient generation scheme for the drive beam has been developed. A fully-loaded normal-conducting linac operating at lower frequency (937 MHz) generates and accelerates the drive beam bunches, and a compression system composed of a delay-line and two combiner rings produces the proper drive beam time structure for RF power generation in the drive beam decelerator. In this paper, a preliminary design of the whole compression system is presented. In particular, the fundamental issue of preserving the bunch quality along the complex is studied and its impact on the beam parameters and on the various system components is assessed. A first design of the rings and delay-line lattice, including path length tuning chicanes, injection and extraction regions is also presented together with the simulation results of the beam longitudinal dynamics.

/pdf/the-drive-beam-pulse-compression-system-for-the-clic-rf-1asjdvqxbl.pdf

The drive beam pulse compression system for the CLIC RF power source

In this paper we describe the latest version of a program we have used for several years to acquire and analyze turn-by-turn data from pick-up electrodes in the AGS Booster during injection. The program determines several parameters of the injected beam including the tunes and the position and angle of the incoming beam. Examples are given for bath proton and gold injection.

/pdf/turn-by-turn-analysis-of-proton-and-gold-beams-at-injection-i8aecuxloh.pdf

Turn-by-turn analysis of proton and gold beams at injection in the AGS booster

This paper presents a possible design for the CLIC Injector Linac, where both electrons and positrons are accelerated from 0.2 to 2.4 GeV, prior to injection into the damping rings. The most stringent constraints on the design are set by the positron beam, which has by far the largest transverse emittance. The proposed optics is based on a FODO lattice wrapping the first six 1.5 GHz accelerating structures, followed by a succession of quadrupole triplets and accelerating structures for the rest of the linac.

/pdf/design-study-of-the-clic-main-beam-injector-linac-2d4fr8ohvz.pdf

Design study of the CLIC main beam Injector Linac

In this paper we discuss a new approach to two-beam acceleration. The energy for RF production is initially stored in a long-pulse electron beam which is efficiently accelerated to about 1.2 GeV by a fully loaded, conventional, low frequency (∼1 GHz) linac. The beam pulse length is twice the length of the high-gradient linac. Segments of this long pulse beam are compressed using combiner rings to create a sequence of higher peak power drive beams with gaps in between. This train of drive beams is distributed from the end of the linac against the main beam direction down a common transport line so that each drive beam can power a section of the main linac. After a 180-degree turn, each high-current, low-energy drive beam is decelerated in low-impedance decelerator structures, and the resulting power is used to accelerate the low-current, high-energy beam in the main linac. The method discussed here seems relatively inexpensive, is very flexible and can be used to accelerate beams for linear colliders over the entire frequency and energy range.

/pdf/a-new-method-for-rf-power-generation-for-two-beam-linear-2vb3e3kyr0.pdf

A new method for RF power generation for two-beam linear colliders

The Compact Linear Collider (CLIC) study of an e+/e- linear collider in the TeV energy range is based on Two-Beam Acceleration (TBA) in which the overall RF power needed to accelerate the beam is extracted from high intensity relativistic electron beams, the so-called drive beams. Due to the high beam power, acceleration and transport of the drive beams in an efficient and reliable way is specially challenging. An overview of a potentially effective scheme is presented. It is based on the generation of trains of short bunches, accelerated in low frequency c.w. superconducting cavities, stored in an isochronous ring and combined at high energy by funneling before injection by sectors into the drive linac. The various systems of the complex are discussed as well as the beam dynamics all along the process. An original method has been specially developed to stabilize such an intense beam during deceleration and RF power production in the drive linac.

/pdf/a-multi-drive-beam-scheme-for-two-beam-acceleration-in-a-tev-3osxzv8nt3.pdf

A. Riche

Papers

A new method for RF power generation for two-beam linear colliders

A multi-drive beam scheme for two-beam acceleration in a TeV linear collider