RF Coaxial Resonator for Investigating Multipactor Discharges on Metal and Dielectric Surfaces

http://accelconf.web.cern.ch/AccelConf/LINAC2014/html/auth0693.htmTHPP096International audienceMultipactor discharge is a phenomenon in which electrons impact one or more material surfaces in resonance with an alternating electric field. The discharge can occur for a wide range of frequencies, from the MHz range to tens of GHz, and in wide array of geometries if the impacted surface has a secondary electron emission (SEE) yield larger than one. The discharge can take place on a single surface or between two surfaces. A novel coaxial resonator to investigate two-surface multipactor discharges on metal and dielectric surfaces in the gap region under vacuum conditions has been designed and tested. The resonator is ~ 100 mm in length with an outer diameter of ~ 60 mm (internal dimensions). A pulsed RF source delivers up to 30 W average power over a wide frequency range 650-900 MHz to the RF resonator. The incident and reflected RF signals are monitored by calibrated RF diodes. An electron probe provides temporal measurements of the multipacting electron current with respect to the RF power. These experiments were successful in identifying multipacting and allowed us the evaluation of a home made sputtered titanium nitride (TiN) thin layers as a Multipactor suppressor

Polarized Positron Source with a Compton Multiple Interaction Point Line

ISBN 978-3-95450-115-1International audiencePositron sources are critical components of the future lepton colliders projects. This is essentially due to the high luminosity required, orders of magnitude higher than existing ones. In addition,polarization of the positron beam rather expands the physics research potential of the machine by increasing the precision of the measurements and enhancing certain types of interactions. In this framework, the Compton sources for polarized positron production are taken into account where the high energy gamma rays are produced by the Compton scattering and subsequently converted in the polarized electron-positron pairs in a target. The Compton multiple IPs line is proposed as one of the solutions to increase the number of captured positrons. This allows a significant increase in the emitted gamma ray flux impinging on the target. The gamma ray production with the Compton multiple IPs line is simulated and used for polarized positron generation. Later, a capture section based on an adiabatic matching device followed by a pre-injector linac is simulated to capture and accelerate the positron beam. The results obtained are presented and discussed

Titanium Nitride Coating of RF Ceramic Windows by Reactive DC Magnetron Sputtering

International audienceLAL-Orsay is developing an important effort on R&D and technology studies on RF power couplers for superconductive cavities. These are complex and high technology devices due to their basic functions: vacuum and temperature separation form the environment to the cavity. One of the most critical components of high power couplers is the ceramic RF window that allows the power flux to be injected in the coaxial line. The presence of a dielectric window on a high power RF line has in fact a strong influence on the multipactor phenomena, a resonant electron discharge that is strongly limiting for the RF components performances. The most important method to reduce the multipactor is to decrease the secondary emission yield of the ceramic window. Due to its low secondary electron emission coefficient, TiN thin film is used as a multipactor suppressor coating on RF ceramic coupler windows. In the framework of the EU program FP6 the LAL-Orsay and the LNL-Legnaro establish a collaboration to develop a coating bench that takes into account the different strong constraints on stoechiometry and film coating thickness given by coupler operating conditions. Reactive magnetron sputtering technology was chosen to obtain such deposit. A full description of a sputtering bench recently installed in LAL, and its main characteristics are given. Stoechiometric TiN films are obtained by optimization of reactive gas flow (N2), for a given bias and a given ionisation gas flow (Ar). XRD analysis was performed to control film composition. From the data obtained, lattice parameter is calculated for each deposit and film stoechiometry is determined. XPS analysis of stoechiometric film had shown the existence of oxygen and carbon mainly in the surface. However, it shows also that the ratio Ti/N in atomic percentage is equal to 1

Positron Production and Capture based on Low Energy Electrons for SuperB

TUPEB057International audienceProviding a high quality and sufficient high current positron beam for the ultra high luminosity B-factory SuperB is a major goal. In this paper a proposition for positrons production and capture scheme based on low energy electrons up to1 GeV is presented. For this technique, several types of flux concentrator used to capture the positrons are being studied. The following accelerating section bringing the positrons up to 280 MeV and the total yield for L-band and S-band type accelerators are given. Also the result of the benchmark between ASTRA and a LAL code based on Geant4 toolkit simulation is discussed

PHIL Accelerator at LAL - Diagnostic status

http://accelconf.web.cern.ch/AccelConf/BIW2010/papers/tupsm100.pdfInternational audienceThe "Photo-Injector at LAL" (PHIL : http://phil.lal.in2p3.fr/) is a new electron beam accelerator at LAL. This accelerator is dedicated to test and characterise electron photo-guns and high-frequency structures for future accelerator projects (like the next generation lepton colliders, CLIC, ILC). This machine has been designed to produce low energy (E<10 MeV), small emittance (epsilon < 10 pi.mm.mrad), high current (charge 2 nC/bunch) electrons bunch at low repetition frequency (frep<10Hz) [1]. The first beam has been obtained on the 4th of November 2009. This paper will describe the current status and the futures developments of the diagnostics devices on this machine

PHIL photoinjector test line

LAL is now equiped with its own platform for photoinjectors tests and Research and Developement, named PHIL (PHotoInjectors at LAL). This facility has two main purposes: push the limits of the photoinjectors performances working on both the design and the associated technology and provide a low energy (MeV) short pulses (ps) electron beam for the interested users. Another very important goal of this machine will be to provide an opportunity to form accelerator physics students, working in a high technology environment. To achieve this goal a test line was realised equipped with an RF source, magnets and beam diagnostics. In this article we will desrcibe the PHIL beamline and its characteristics together with the description of the first two photoinjector realised in LAL and tested: the ALPHAX and the PHIN RF Guns

Low Energy Beam Measurements Using PHIL Accelerator at LAL, Comparison with PARMELA Simulations

http://accelconf.web.cern.ch/AccelConf/PAC2011/papers/wep210.pdfInternational audiencePHIL ("PHo­to-In­jec­tor at LAL") is a new elec­tron beam ac­cel­er­a­tor at LAL. This ac­cel­er­a­tor is ded­i­cat­ed to test and char­ac­ter­ize elec­tron RF-guns and to de­liv­er elec­tron beam to users. This ma­chine has been de­signed to pro­duce and char­ac­terise low en­er­gy (E<10 MeV), small emit­tance (e<10 p.​mm.​mrad), high bril­liance elec­trons bunch at low rep­e­ti­tion fre­quen­cy (n<10Hz). The first beam has been ob­tained on the 4th of Novem­ber 2009. The cur­rent RF-gun test­ed on PHIL is the Al­phaX gun, a 2.5 cell S-band cav­i­ty de­signed by LAL for the plas­ma ac­cel­er­a­tor stud­ies per­formed at the Strath­clyde uni­ver­si­ty. This paper will pre­sent the first Al­phaX RF-gun char­ac­ter­i­za­tions per­formed at LAL on PHIL ac­cel­er­a­tor, and will show com­par­isons be­tween mea­sure­ments and PARMELA sim­u­la­tions

Baseline Design of the SuperB Factory Injection System

TUPPR088International audienceThe injection complex of the SuperB, B-factory project of INFN consists of a polarized electron gun, a positron production system, electron and positron linac sections, a positron damping ring and the transfer lines connecting these systems and the collider main rings. To keep the ultra high luminosity nearly constant, continuous injection of 4 GeV electrons and 7 GeV positrons in both Low Energy Ring (LER) and High Energy Ring (HER) is necessary. In this paper we describe the baseline design and the beam dynamics studies performed to evaluate the system performance

The CLIC positron source based on compton schemes

The CLIC polarized positron source is based on a positron production scheme in which polarized photons are produced by a Compton process. In one option, Compton backscattering takes place in a so-called “Compton ring”, where an electron beam of 1 GeV interacts with circularly-polarized photons in an optical resonator. The resulting circularly-polarized gamma photons are sent on to an amorphous target, producing pairs of longitudinally polarized electrons and positrons. The nominal CLIC bunch population is 4.2x109 particles per bunch at the exit of the Pre-Damping Ring (PDR). Since the photon flux coming out from a "Compton ring" is not sufficient to obtain the requested charge, a stacking process is required in the PDR. Another option is to use a Compton Energy Recovery Linac (ERL) where a quasicontinual stacking in the PDR could be achieved. A third option is to use a "Compton Linac" which would not require stacking. We describe the overall scheme as well as advantages and constraints of the three options