Papers presented at EPAC 2006

Accelerator Division
Damping Rings (DR) designs to achieve ultra-low emittance beams in Linear Colliders (ILC and CLIC) will be reviewed pointing out the major issues both from the beam dynamics and the technological point of view and comparing the required performances with the one achieved at SLC. The design, beam simulations, benchmarking and performances already achieved in test facilities, especially the KEK-ATF1 facility, will be presented. Finally, future R&D plans and schedule in terms of beam performances,
more » ... beam stability and technological development as well as the world-wide organization to achieve them will be discussed. -13 - Abstract The CLIC Test Facility, (CTF3), under construction and test at CERN is the product of a multilateral international collaboration to address all the key issues of the CLIC technology. The presentation, after the description of the CLIC scheme towards multi-TeV Linear Collider and of the main advantage of the two beams accelerator scheme, will focus on the status of the CTF3 project and of the technological developments; in particular the performances already achieved in the high field accelerating structures and in the RF power production. The results of the recombination process for the drive beam as well as the plans and schedule for the future are reported. Abstract Future light sources based on high gain free electron lasers, require the production, acceleration and transport up to the undulator entrance of high brightness (low emittance, high peak current) electron bunches. Wake fields effects in accelerating sections and in magnetic bunch compressors typically contribute to emittance degradation, hence the injector design and its operation is the leading edge for high quality beam production and for the success of the future light sources. DC and RF guns, photo-cathode materials, laser pulse shaping and sub-ps synchronization systems are evolving towards a mature technology to produce high quality and stable beams. Nevertheless reduction of thermal emittance, damping of emittance oscillations and bunch compression are still the main issues and challenges for injector designs. With the advent of Energy Recovery Linacs, superconducting RF guns have been also considered in many new projects as a possible electron source operating in CW mode. An overview of recent advancements and future perspectives in FEL injectors will be illustrated in this talk. Abstract There are several potential advantages for a collider operation with a lattice with negative momentum compaction factor (alfa, c ). Since the lattice of the Frascati e+e--factory DA NE is flexible enough to provide collider operation even with alfa < 0, we have exploited this possibility for an experimental study of the beam dynamics. The negative momentum compaction lattices have been successfully implemented and stable 1 A currents have been stored in both electron and positron rings without any problem for RF cavities and feedback systems operation. First collisions have been tested at low currents. In this paper we describe the experimental results and compare them with expectations and numerical simulations. Present limitations to DA NE operation with alfa < 0 and ways to overcome them are also discussed. Abstract Obtaining very short bunches is an issue for colliders and Coherent Synchrotron Radiation (CSR) sources. In strong RF focusing regime (SRFF) bunch length is not constant along the ring, but a bunch length modulation (BLM) occurs; thus allowing to obtain short bunches at a given position in the ring. Until now the bunch length modulation has been studied only in the limit of zero current; in this paper we present a simulation code suitable to study the effects of CSR and of the vacuum chamber wakefields on the single bunch longitudinal dynamics in a regime of strong RF focusing. The code has been applied to lattices that can be realized in DAΦNE for a possible experiment on bunch length modulation. Abstract This communication describes the research work plan that is under implementation at the SPARC FEL facility in the framework of the DS4 EUROFEL programme. The main goal of the collaboration is to study and test the amplification and the FEL harmonic generation process of an input seed signal obtained as higher order harmonics generated both in crystals (400 nm and 266 nm) and in gases (266 nm, 160 nm, 114 nm). The SPARC FEL can be configured to test several cascaded FEL layouts that will be briefly analysed. Abstract A density modulated electron beam generated at the photocathode of a radio-frequency electron gun evolves within an accelerator towards a homogenous beam but with an energy modulation. The density modulation is changed into energy modulation. This energy distribution can be exploited to restore the initial density profile, called comb beam, with a proper rf phase of the accelerating cavities and by adding a proper compressor. The comb beam at the cathode is generated driving the photocathode by the relative laser pulse train. This laser pulse is obtained with a shaping device inserted into the laser system. The dynamics is studied within the SPARC system with the PARMELA code. Abstract The Frascati photo-injector SPARC (Pulsed Self Amplified Coherent Radiation Source) will be equipped with a Xband RF cavity for linearizing emittance to enhance bunch compression and for reducing bunch longitudinal energy spread. A biperiodic cavity working on the π/2-mode offers some advantages in comparison to a conventional (periodic) cavity despite the need of accurate machining. A copper prototype made of seventeen separated cells has been built following numerical simulation. In this paper we report on preliminary measurements of its RF properties. The main characteristics of the cooling system for the final device are also addressed. Abstract Advanced high brightness injectors require photocathodes with fast response, high quantum efficiency and good surface uniformity. Both Mg films deposited by laser ablation and Pb films deposited by vacuum arc could satisfy these requirements. Their emission and morphology are compared. Abstract The Frascati photo-injector SPARC (Pulsed Self Amplified Coherent Radiation Source) will be equipped with a Xband RF cavity for linearizing emittance to enhance bunch compression and for reducing bunch longitudinal energy spread. The nine cells standing wave cavity prototype made of separated cells has been already built and measured. In this paper we report on characterisation of the first brazed prototype. Heat load studies have been performed as well to design the cooling system for the final device. Abstract In the framework of the LHC Luminosity Upgrade, we develop a new layout of the interaction region (IR) with β * equal to 25cm in which the combination-separation dipoles come first with respect to the triplet assembly (dipole first) in opposition of the nominal layout (quadrupole first). The new layout presents several advantages (separate channel for multipole error correction, straightforward crossing angle scheme with no crossing in the triplet, early separation of the beam). The payoff is a large β function in the triplet, which enhances the chromaticity, non-linear effects and eats up aperture. We investigate options for local chromaticity correction and their effects on long-term stability. Abstract The implementation of a crab crossing scheme at the Frascati -factory DA NE is under consideration, together with several other ideas and upgrades to increase the collider luminosity. The crab crossing is beneficial to the luminosity because it is expected to optimize the geometrical superposition of the colliding bunches and to weaken the synchro-betatron beam-beam resonances. The basic specifications of such a system, the expected luminosity increase, a preliminary design of the crab cavities and the architecture of the dedicated RF system are presented. Abstract The CLIC Test Facility CTF3, built at CERN by an international collaboration, aims at demonstrating the feasibility of the CLIC scheme of multi-TeV electronpositron linear collider by 2010. In particular, one of the main goals is to study the generation of high-current electron pulses by interleaving bunch trains in delay lines and rings using transverse RF deflectors. This will be done in the 42 m long delay loop, built under the responsibility of INFN/LNF, and the 84 m long combiner ring that will follow it. The delay loop installation was completed and its commissioning started at the end of 2005. In this paper the commissioning results are presented, including the first tests of beam recombination. Abstract The DA NE Beam Test Facility is operating since 2002, providing electrons, positrons and photons from the single particle up to 10 10 particles per spill and from 25 to 750 MeV. During these years, the facility has hosted tens of high energy physics test and experiments from all over Europe, operating in very different conditions of multiplicity and energy. Operation performance and parameters, tools and diagnostics, as well as the main results obtained, are presented. RINGS * Abstract The damping rings for the International Linear Collider must be capable of accepting large beams from the electron and positron sources, and producing highly damped beams meeting demanding stability specifications, at the machine repetition rate of 5 Hz. Between March and November 2005, a program of studies was undertaken by an international collaboration of 50 researchers, to compare a number of configuration options, including ring circumferences between 3 and 17 km. Here, we outline the studies and discuss the principle considerations in the choices of the baseline and alternative damping ring configurations. Abstract The three-dimensional fully relativistic and selfconsistent code RETAR has been developed to model the dynamics of high-brightness electron beams and, in particular, to assess the importance of the retarded radiative part of the emitted electromagnetic fields in all conditions where the electrons experience strong accelerations. In this analysis we evaluate the radiative energy losses in the electron emission process from the photocathode of an injector, during the successive acceleration of the electron beam in the RF cavity and the focalization due to the magnetic field of the solenoid, taking also into account the e.m. field of the laser illuminating the cathode. The analysis is specifically carried out with parameters of importance in the framework of the SPARC and PLASMONX projects. Abstract In this paper, we illustrate the electromagnetic and beam dynamics design procedure of a new class of photoinjector, a hybrid standing/traveling wave structure. In this device a standing wave RF gun section is integrated with a downstream traveling wave structure through a coupling cell that feeds simultaneously the two sections. We discuss the advantages in RF and beam performance of the hybrid photoinjector compared to conventional systems. The electromagnetic design has been performed using the 3D electromagnetic code HFSS. Results of beam dynamics simulations in different operating conditions are also discussed. Abstract We describe a possible layout and parameters of a polarized positron source for CLIC, where the positrons are produced from polarized gamma rays created by Compton scattering of a 1.3-GeV electron beam off a YAG laser. This scheme is very energy effective using high finesse laser cavities in conjunction with an electron storage ring. We point out the differences with respect to a similar system proposed for the ILC.
doi:10.15161/ fatcat:2beci4umx5asvps2jmfewfvlci