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We present an initiative to foster new ideas about the applications of accelerators to the Environment. Called "Challenge Based Innovation" this initiative will gather four teams each of six master-level students each coming from different academic backgrounds. As part of the EU-funded I.FAST project (Innovation Fostering in Accelerator Science and Technology), they will gather during 10 days in Archamps near CERN to receive high level lectures on accelerators and the environment and to brainstorm on possible new applications of accelerators for the environment. At the end of the gathering, they will present their project at CERN to a jury made of experts., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

We report the design of the pre-injector chain for the Future Circular e⁺ e⁻ Collider (FCC-ee) system. The electron beam from a low-emittance RF gun is accelerated by an S-band linac up to 6 GeV. A damping ring at 1.54 GeV is required for emittance cooling of the positron beam. The intermediate energy step from the exit of the S-band linac at 6 GeV to the 20 GeV injection energy of the top-up booster can be provided by the modified Super Proton Synchrotron (SPS), serving as a pre-booster ring (PBR). An alternative option to reach 20 GeV energy would be to extend the S-band linac with a C- or X-band linac. An overall cost optimisation will determine the choice of the final configuration. Beam loss and emittance dilution in the linac due to space charge effects, wakefields, and misalignment of accelerator components can be mitigated by RF phasing and orbit steering. Start-to-end simulations examine the beam transport through the linac up to either 6 GeV or 20 GeV. The results indicate large design margins. Simulations of the beam dynamics in the damping ring (DR) demonstrate a sufficiently large momentum acceptance. Effects of intrabeam scattering and electron cloud instability in the DR are also studied., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The FCC-ee is a high-luminosity, high-precision circular collider to be constructed in a new 100 km tunnel in the Geneva area. The physics case is well established and the FCC-ee operation is foreseen at 91 GeV (Z-pole), 160 GeV (W pair production threshold), 240 GeV (Higgs resonance) and 365 GeV (t-tbar threshold). Due to the large 6D production emittance and important thermal load in the production target, the positron injector, in particular the positron source, is one of the key elements of the FCC-ee, requiring special attention. To ensure high reliability of the positron source, conventional and hybrid targets are currently under study. The final choice of the positron target will be made based on the estimated performances. In this framework, we present a preliminary design of the FCC-ee positron source, with detailed simulation studies of positron production, capture and primary acceleration., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The Future Circular electron-positron Collider (FCC-ee) requires fast cycling injectors with very low extraction emittances to provide and maintain extreme luminosities at center of mass energy varying between 91.2-385 GeV in the collider. For this reason, the whole injector complex table is prepared by putting into consideration the minimum fill time from scratch, bootstrapping, transmission efficiency as well as store time of the beams in synchrotrons to approach equilibrium emittances. The current injector baseline contains 6 GeV S-band linac, a damping ring at 1.54 GeV, a prebooster to accelerate from 6 to 20 GeV, which is followed by 98-km top up booster accelerating up to final collision energies. Acceleration from 6 GeV to 20 GeV can be provided either by Super Proton Synchrotron (SPS) of CERN or a new synchrotron or C-Band linac, distinctively, which all options are retained. In this paper, the current status of the whole FCC-ee injector complex and injection strategies are discussed., Proceedings of the 62th ICFA ABDW on High Luminosity Circular e$^+$e$^-$ Colliders, eeFACT2018, Hong Kong, China

We present a first rough estimate for the electrical power consumption of the FCC-ee lepton collider. This electrical power is dominated by the RF system, which provides the motivation for the ongoing R&D on highly efficient RF power sources. Other contributions come from the warm arc magnets, the cryogenics systems, cooling, ventilation, general services, the particle-physics detectors, and the injector complex., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

The Future Circular e⁺e⁻ Collider pre-injector chain consists of a 6 GeV S-Band linac, a damping ring at 1.54 GeV and pre-booster ring to reach 20 GeV for injection to the main booster. The electron and positron beams use the same accelerator chain alternatively. The e⁺ beam is generated from a novel low level RF-gun providing 6.5 nC charge at 11 MeV with 0.5 micron geometric emittance. The e⁺ beam is produced by the impact of a 4.46 GeV e⁻ beam onto a hybrid target, accelerated in the linac up to 1.54 GeV, and injected to the damping ring for emittance cooling. Simulations on the performance of the DR are presented for reaching the required equilibrium emittances at the required damping time. As an alternative option, a 20 GeV linac is considered utilising C-Band cavities and simulations studies have been undertaken regarding the beam transport and transmission efficiency up to that energy., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

This report sums up in two volumes the first 50 years of operation of the CERN Proton Synchrotron. After an introduction on the genesis of the machine, and a description of its magnet and powering systems, the first volume focuses on some of the many innovations in accelerator physics and instrumentation that it has pioneered, such as transition crossing, RF gymnastics, extractions, phase space tomography, or transverse emittance measurement by wire scanners. The second volume describes the other machines in the PS complex: the proton linear accelerators, the PS Booster, the LEP pre-injector, the heavy-ion linac and accumulator, and the antiproton rings.

The baseline of the CLIC study considers non-polarized e+ for the 3 TeV centre of mass energy. The e+ source is based on the hybrid targets scheme, where a crystal-radiator target is followed by an amorphous-converter target. Simulations have been performed from the exit of the amorphous target up to the entrance of the Pre-Damping Ring. Downstream the amorphous target, there is an Adiabatic Matching Device (AMD) followed by a Pre-Injector Linac accelerating the e+ beam up to around 200 MeV. Then a common Injector Linac (for both e+ and e-) accelerates the beams up to 2.86 GeV before being injected into the Pre-Damping Ring. In this note, the characteristics of the AMD and the other sections are described and the beam parameters at the entrance of the Pre-Damping Ring are given.

Compton sources are capable to produce intense beams of gamma-rays necessary for numerous applications, e.g. production of polarized positrons for ILC/CLIC projects, nuclear waste monitoring. These sources need high current of electron beams of GeV energy. Storage rings are able to accumulate a high average current and keep it circulating for a long time. The dynamics of circulating bunches is affected by large recoils due to emission of energetic photons. We report results of both an analytical study and a simulation on the dynamics of electron bunches circulating in storage rings and interacting with the laser pulses. The steady-state transverse emittances and energy spread, and dependence of these parameters on the laser pulse power and dimensions at the collision point were derived analytically and simulated. It is shown that the transverse and longitudinal dimensions of bunches are dependent on the power of laser pulses and on their dimensions as well. Conditions of the laser cooling were found, under which the electron bunches shrink due to scattering off the laser pulses. The beam behavior in rings with the longitudinal strong focusing lattices is discussed., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The CLIC damping rings should produce the ultra-low emittance necessary for the high luminosity performance of the collider. This combined to the high bunch charge present a number of beam dynamics and technical challenges for the rings. Lattice studies have been focused on low emittance cells with optics that reduce the effect Intra-beam scattering. The final beam emittance is reached with the help of super-conducting damping wigglers. Results from recent simulations and prototype measurements are presented, including a detailed absorption scheme design. Collective effects such as electron cloud and fast ion instability can severely limit the performance and mitigation techniques have been identified and tested. Tolerances for alignment and technical system design such as kickers, RF cavities, magnets and vacuum have been finally established., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The CLIC study considers the hybrid source using channeling as the baseline for unpolarised positron production. The hybrid source uses a few GeV electron beam impinging on a crystal tungsten target. With the tungsten crystal oriented on its 111 > axis it results an intense, relatively low energy photon beam due mainly to channeling radiation. Those photons are then impinging on an amorphous tungsten target producing positrons by e⁺e⁻ pair creation. The downstream capture section is based on an adiabatic matching device and a 2 GHz pre-injector linac. The resulting studies are presented here., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

We propose a viable positron source scheme that uses circularly polarized gamma rays generated from the main 250 GeV electron beam. The beam passes through a helical superconducting undulator with a magnetic field of ~ 1 Tesla and a period of a few centimeters. The gamma-rays produced in the undulator in the energy range between ~ 3 MeV ~ 100 MeV will be directed to a titanium target and produces polarized positrons. The positrons are then captured, accelerated and transported to a damping ring. Detailed parameter studies of this scheme including positron yield, undulator parameter dependence and target composition and geometry will be presented. Effects on the 250 GeV drive beam, including emittance, energy spread and energy loss from the beam passing through the undulator will also be discussed., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

This note presents a particle tracking study in the CLIC Injector Linac, which accelerates both electrons and positrons from 200 MeV to 2.42 GeV, prior to their injection into the damping rings. For the positrons, a growth of the emittance and a large energy spread are observed at the end of the linac, but both effects can be minimized by using a bunch compressor at the exit of the e+ Pre-Injector Linac. For the electrons, no significant increase of the emittance is noticed and the energy spread remains small.

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.

The aim of the CLIC Test Facility CTF3 at CERN is to demonstrate the feasibility of key points of the Two-Beam Acceleration based Compact Linear Collider (CLIC) study. In particular, it addresses the efficient generation of a drive beam with the appropriate time structure of the electron bunches in order to produce high power RF pulses at a frequency of 30 GHz. This time structure requires a high bunch repetition frequency. It is obtained by successive injections of bunch trains into an isochronous ring using transversely deflecting RF structures. The major goal of the now completed first phase of CTF3 was to achieve the bunch train combination at low charge. In this paper, we give a description of the project and summarize the experimental results, with a focus on the successful bunch frequency multiplication for various factors up to five.

A collaboration meeting of the CLIC Test Facility, CTF3, took place at CERN on 23-25 November 2004. The present summary of the CTF3 status, results obtained in 2004 and plans for the coming year 2005 is based on presentations given during this meeting.

In the framework of the CLIC RF power source studies, the feasibility of the electron bunch train combination by injection with RF deflectors into an isochronous ring has been successfully demonstrated in the preliminary phase of CTF3. A new method, based on beam frequency spectrum analysis, was experimented to monitor this scheme. A coaxial pick-up and its read-out electronics were designed and mounted in the CTF3 ring to allow comparison of the amplitudes of five harmonics of the fundamental beam frequency (3 GHz) while combining the bunch trains. The commissioning of the monitor was a successful proof of principle for this new method, despite the short length of the bunch trains and the presence of parasitic signals associated to high-order waveguide modes propagating with the beam inside the pipe.

The CTF3 preliminary phase at CERN has demonstrated the feasibility of the bunch frequency multiplication process, by injection of subsequent bunch trains into an isochronous ring. In order toobserve the bunch interleaving at each stage of this process, a new method based on frequency spectrum analysis has been developed. For this purpose, a coaxial RF pick-up and its detection system were designed and mounted in the CTF3 ring, in order to allow comparison of the amplitudes of five harmonics of the fundamental beam frequency (9, 12, 15, 18 and 21 GHz) while combining bunch trains. The commissioning of this monitor was a successful proof of principle for this new method, however with two limitations: the short length of the bunch trains and the presence of parasitic signals associated with waveguide modes propagating with the beam inside the pipe.

In 1999 and 2000 experiments were carried out in the EPA machine to investigate the shielding properties of a ceramic vacuum chamber with a thin Titanium coating on the inside. A single electron bunch was extracted and sent consecutively through two ceramic chambers. The upstream chamber was coated, the downstream was not and served as a reference. The magnetic field was measured in the horizontal plane close to the outer ceramic wall on both chambers. Four different configurations of the upstream chamber were measured. In the first configuration no second shield was installed. Then three different shields were installed at the outside of the ceramic. The penetration of the electro-magnetic fields through the thin Titanium layer was very small in the first case (reduction of nearly 40dB) but substantial in the three other cases.

The Two-Beam Accelerator concept is one of the most promising methods for producing RF power for future linear colliders. In particular it allows upgrades to multi-TeV energies. One of its challenges is the production of the high current drive beam, which as it passes through decelerating structures, produces rf power for acceleration of the main beam. These challenges must be studied at a smaller scale test facility.

The CLIC (Compact Linear Collider) positron source is based on the conventional scheme, using a metal converter target and an Adiabatic Matching Device (AMD) composed of a Flux Concentrator (FC) and a constant magnetic field along the positron Pre-Injector linac. The positrons are accelerated with L-band RF structures. Beam dynamics simulations are described for the positron production in the target and capture section in the AMD. The distribution of the energy deposition in the target is studied with the EGS4 code. The dependence of the positron yield on several parameters is studied and optimised using both EGS4 and analytical calculations. Following this optimisation, a new set of design parameters is proposed and particle tracking simulations are performed to estimate the overall performance.

The seventh CTF3 collaboration meeting was held at CERN on 12th and 13th June 2002. Representatives from INFN-Frascati, LAL, RAL, SLAC, Uppsala University and CERN participated. The main focus was the work for the nominal phase, but also very spectacular results were reported from the preliminary phase. Progress was reported on all activities. The design and layout studies are far advanced and very active hardware design and prototyping is going on. The construction of major systems has started. The major milestones for 2003 are the commissioning of the injector, the first part of the Drive Beam Accelerator and a 30 GHz high power RF source after the first four accelerator sections.

In the framework of the CLIC RF power source studies, the new scheme of electron pulse compression and bunch frequency multiplication, using injection by RF deflectors into an isochronous ring, will be tested at CERN during the CTF3 preliminary phase. The present LPI complex will be modified in order to allow a test of this scheme at low charge. The design of the new front-end, of the modified linac, of the matched transfer line, and of the isochronous ring lattice is presented here.The results of the related beam dynamics studies are also discussed.

The CLIC positron source is based on the conventional scheme, using a metal converter target and an Adiabatic Matching Device (AMD) composed of a Flux Concentrator and a DC magnetic field along the e+ Pre-Injector linac. Positrons are accelerated with L-band RF structures. In this paper extensive beam dynamics simulations are described for the e+ production in the target and for the e+ capture in the matching and focusing sections. The distribution of the energy deposition in the target is studied with the EGS4 code. The AMD acceptance is expressed by analytic formulae. The dependence of the e+ yield on several parameters (incident beam radius, target thickness, aperture radius, longitudinal acceptance, accelerating field) is studied and optimized. With these new parameters, detailed particle tracking simulations are performed. Based on the analysis of the results, the transverse and longitudinal acceptances of the capture system and of the e+ Pre-Damping Ring are derived. Finally a new set of design parameters is proposed for the CLIC e+ production.

SLAC and LAL collaborators, together with CERN people made a review of the work done on the beam dynamics and on the design of several components. The latter includes the thermionic gun, the bunching system and the solenoids. The workshop treated the possibility to increase both the beam current and the repetition rate. Both have direct consequences on the injector. A higher beam current would allow implementing a new mode of CTF3 to generate 30 GHz RF power at the end of the Drive Beam Accelerator. A higher repetition rate would ease the RF conditioning of the 30 GHz accelerating structures. The buncher designs being on the critical path will be finished mid-February 2001, while the final injector design will be finished in June 2001.

The CLIC study of a high energy (0.5 - 5 TeV), high luminosity (1034 - 1035 cm-2 sec-1) e± linear collider is presented. Beam acceleration using high frequency (30 GHz) normal-conducting structures operating at high accelerating fields (150 MV/m) significantly reduces the length and, in consequence, the cost of the linac. Based on new beam and linac parameters derived from a recently developed set of general scaling laws for linear colliders, the beam stability is shown to be similar to lower frequency designs in spite of the strong wake-field dependency on frequency. A new cost-effective and efficient drive beam generation scheme for RF power production by the so-called "Two Beam Acceleration (TBA)" method is described. It uses a thermionic gun and a fully-loaded normal-conducting linac operating at low frequency (937 MHz) to generate and accelerate the drive beam bunches, and RF multiplication by funnelling in compressor rings to produce the desired bunch structure. Recent 30 GHz hardware developments and results from the CLIC Test Facility (CTF), assessing the feasibility of the scheme, are described.

The progress of the Compact LInear Collider (CLIC) study of a multi-TeV (0.5 - 5 TeV) high-luminosity (5'1033 to 1.5'1035 cm-2 sec-1) e± linear collider based on Two-Beam Acceleration (TBA) is presented. The length and, in consequence, the cost of the overall complex is reduced by the use of high accelerating fields (150 MV/m), which are generated by specially damped 30 GHz normal-conducting accelerating structures. The large amount of RF power (400 MW/m) required to generate these high fields is provided by a novel RF power generating scheme which is potentially both cost and power efficient. After summarising the progress made in the developments of 30 GHz components and the performance obtained in the present phase of the CLIC Test Facility (CTF2), the design of a new test facility (CTF3), which will demonstrate the feasibility of the RF power generating scheme, is described

The longitudinal and lateral shower profiles for 500 MeV electrons in iron are studied using dosimetry and activation techniques. The results are compared with Monte Carlo simulations and other previously published data. These studies were necessary for estimating the dose and its profile for the CMS quartz fiber calorimeter radiation damage work performed at LIL ( CERN).

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 (approx. 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 between. This train of drive beams is distributed from the end of the linac in the opposite direction to the main beam 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.

The CLIC study of a high energy (0.5 - 5 TeV), high luminosity (10^34 - 10^35 cm^-2 sec^-1) e± linear collider is presented. Beam acceleration using high frequency (30 GHz) normal-conducting structure s operating at high accelerating fields (100 to 200 MV/m) significantly reduces the length and, in consequence the cost of the linac. Based on new beam and linac parameters derived from a recently dev eloped set of general scaling laws for linear colliders, the beam stability is shown to be similar to lower frequency designs in spite of the strong wake-field dependency on frequency. A new cost effe ctive and very efficient drive beam generation scheme for RF power production by the so-called "Two Beam Acceleration (TBA)" method is described. It uses a conventional thermionic gun and a fully-load ed normal-conducting linac operating at low frequency (937 MHz) to generate and accelerate the drive beam bunches and RF multiplication by funneling in compressor rings to produce the desired bunch st ructure. Recent 30 GHz hardware developments and results from the CLIC Test Facility (CTF) assessing the feasibility of the scheme are described.

The exploitation of the enhancement of positron sources by channeling effects, in particular for Linear Colliders (LC), relies on the long term resistance of the crystal to radiation damage. Such dama ge has been tested on a 0.3 mm thick tungsten monocrystal exposed during 6 months to the 30 Gev incident electron beam of the SLAC Linear Collider (SLC). The crystal was placed in the converter region , orientated in a random direction and received an integrated flux of e- (fluence) of 2 x 10^18 e-/mm^2. The crystal was analyzed before and after irradiation by X and Gamma diffractometry. No damage was observed, the mosaic spread remained unchanged during irradiation (0.4 mrad FWHM). Implications for use of orientated crystal as converter for positron sources of future LCs are discussed.

The feasibility study for an e+e- linear collider based on two beams accelerator and working at 30 GHz is investigated with the CLIC (Compact Linear Collider). A new set of beam parameters has been presented at the LC 97 Workshop. Compared to the previous reference scheme for the injector complex, several major changes occurred. The two options, 0.5 TeV and 1 TeV (centre of mass), are discussed. Several issues concerning the RF gun and the associated laser, the beam loading compensation, the positron source, the damping rings and the bunch compressors are presented. This note presents the study of the new CLIC injector complex.