Linear Collider Project Research Articles

Wakefield damping in a distributed coupling linear accelerator

The number of cells in a π-mode standing wave (SW) accelerating structure for the Compact Linear Collider (CLIC) project is limited by mode overlap with nearby modes. The distributed coupling scheme avoids mode overlap by treating each cell as independent. Designs of cells suitable for distributed coupling with strong wakefield suppression by waveguide damping have not previously been studied. In this paper we develop a SW cell to be used in a distributed coupling structure that can satisfy the CLIC transverse wake potential limit. From the middle cell of the CLIC-G* traveling wave (TW) structure, a SW cell is designed and then adapted to perform as a cell in a distributed coupling structure. Its wake potentials in an ideal case of open boundaries are reduced to satisfy the wake potential threshold. An electric boundary is added to the model to simulate total reflection at the distribution network. A horizontal coupler cell that connects to the distribution network such that the reflected wakefields remain similar to the open boundary case is simulated. A triplet module which takes advantage of cell-to-cell coupling to reduce reflected wake potential is presented.

Characterization and alignment of a resonant cavity beam position monitor for the Compact LInear Collider (CLIC) project at CERN

Beam diagnostic devices are essential tools to sense the properties of the beam in particle accelerators. Beam Position Monitors (BPMs) are used to detect the transverse beam spatial coordinates. A large number of high-resolution resonant cavity BPMs, operating at 14GHz, are proposed to monitor the orbit of the two main beam linacs of the CLIC project. This paper discusses innovative calibration techniques on a dedicated test bench in the frame of the PACMAN project. The particular location of the electromagnetic center of the resonant cavity BPM is detected utilizing a stretched-wire measurement approach. Measurements, RF characterization and final fiducialization of the BPM electrical offset are treated with details. Initial studies through EM simulations of the cavity BPM are covered. The presented experimental results prove the feasibility of the alignment methodology with nanometric resolution.

Key4hep, a framework for future HEP experiments and its use in FCC

The road map to the FCC Feasibility Study Report, for submission to the next Update of the European Strategy for Particle Physics, will require detailed simulation and advanced reconstruction algorithms to explore and maximise the physics reach of proposed detector solutions. The optimisation process will require maximal flexibility in changing detector geometries, materials and sensitive areas, and efficient tools to quantify the overall performance. To synergise such developments, the CEPC, CLIC, FCC, ILC and SCT communities have engaged in the commissioning of a ‘Turnkey Software Stack’ (Key4hep), which would provide all the necessary ingredients, from simulation to analysis, for future experiments. This approach is based on the positive experience of the linear collider projects ILC and CLIC, which have developed and used a common software stack (iLCSoft) over the last decade. Key4hep aims to cover most, if not all, future linear and circular machines colliding leptons (electrons, muons) and hadrons. The common software ecosystem will facilitate writing specific components for experiments ensuring coherency and maximising the re-use of established solutions. Project-specific software frameworks will require adaptation to fully profit from the common software base. In this essay, we present the status and plans for re-framing the FCC software framework, FCCSW, around Key4hep and discuss the challenges associated with the transition.

Dual beam delivery system serving two interaction regions for the Compact Linear Collider

The Compact Linear Collider (CLIC) could provide ${e}^{+}{e}^{\ensuremath{-}}$ collisions in two detectors simultaneously possibly at a bunch train frequency in the linac twice the baseline design value. In this paper, a novel dual beam delivery system (BDS) design is presented in order to serve two interaction regions (IR1 and IR2) including optics designs and the evaluation of luminosity performance with synchrotron radiation (SR) and solenoid effects for both energy stages of CLIC, 380 GeV and 3 TeV. IR2 features a larger crossing angle than the current baseline. The luminosity performance of the novel CLIC scheme was evaluated by comparing the different BDS designs with and without the detector solenoid field effects. It has to be highlighted that the impact of the detector solenoid on luminosity had not been evaluated for the current CLIC baseline, which amounts to a loss of about 4% that corresponds to the same value of the old baseline design. At 380 GeV the novel dual BDS design features same luminosities than the current baseline. However at 3 TeV the luminosity performance is reduced by 2% from the baseline design for the IR1 and by 33% for the IR2. The dual CLIC BDS design provides adequate luminosities to two detectors and proves to be a viable candidate for future linear collider projects.

Operation of a high-current drive beam electron gun prototype for the Compact Linear Collider

The high-average current electron gun low energy electrons from a thermionic cathode at high intensity is the prototype of the drive beam source for the Compact Linear Collider project. The electromagnetic design of the gun was done originally with 2D simulations to minimize the beam emittance for high-current operation (of the order of 8 A) at 140 keV. This paper reports on the first experimental measurements of beam extraction and transport. For the first time, 3D tracking simulations, which take into account precisely the cathode-grid geometry, have been compared with experimental optical transition radiation images of the beam, and we obtained impressive agreement. In addition, we have confirmed that the details of the cathode-grid assembly can impact significantly the beam emittance.

Applying Superconducting Magnet Technology for High-Efficiency Klystrons in Particle Accelerator RF Systems

An MgB2 superconducting solenoid magnet has been developed for electron beam focusing in X-band (12 GHz) klystrons for particle accelerator RF systems, to provide a central field of 0.8 T at 57 A and at ≥20 K. It has successfully realized significant AC-plug power saving in one order of magnitude compared with that for a conventional Cu solenoid magnet. The large-scale application may be expected for the Compact Linear Collider (CLIC) project proposed as a future accelerator candidate at CERN. It requires ~5,000 klystrons, and the MgB2 magnet application will realize significant AC-plug power saving. This paper describes progress in a prototype MgB2 superconducting solenoid magnet development and discusses the future prospect.

Low Loss Microwave Ceramic and other Microwave Dielectric Materials for Beam Physics Applications

Introduction. Relativistic, high intensity and small emittance electron bunches are the basis of a future linear collider and free electron laser projects. Drive beam generation in a wakefield structure employing for power extraction and acceleration low loss dielectrics like microwave ceramics, fused silica and Chemical Vapor Deposition (CVD) diamond were considered.Objective. We report here our experimental testing of a ceramic material with extremely low loss tangent at GHz frequency ranges allowing the realization of high efficiency wakefield acceleration. We also present Barium Strontium Titanium oxides (BST) ferroelectric material, which is a critical tuning element of the 400 MHz superconducting radiofrequency (RF) tuner developed and tested by the CERN/Euclid Techlabs collaboration. The materials discussed here also include quartz and CVD diamonds that are capable of supporting the high RF electric fields generated by electron beams or pulsed high power microwaves. These materials have been optimized or specially designed for accelerator applications.Materials and methods. The ceramic materials for accelerators, commonly used for the dielectric based accelerating structures, have to withstand high gradient accelerating fields, and prevent potential charging by electron beams. Correspondingly, the ceramic materials, fused silica and CVD diamond were tested with high power wakefield accelerating structures at Argonne Wakefield Accelerator of Argonne National Laboratory. Some of the presented here ceramic materials were tested at X-band 11.4 GHz magnicon high power source.Results. Low loss microwave ceramics, fused silica, and CVD diamonds have been considered as materials for dielectric based accelerating structures to study of the physical limitations encountered driving > 100 MV/m at microwave and ~ GV/m at THz frequencies in a dielectric based wakefield accelerator. Various ceramic compositions were high power and electron beam tested at X-band 11.4 GHz magnicon power source and Argonne Wakefield Accelerator correspondingly. Special attention was paid to the CVD diamond cylindrical Ka-band 35 GHz wakefield structure development. Finally, the dielectric based structure tuning was demonstrated by varying the permittivity of the BST ferroelectric layer by temperature changes and by applying an external direct current electric field across the ferroelectric. This allows us to control the effective dielectric constant of the composite system and therefore, to control the structure frequency during operation. The same type of ferroelectric material was used for the Ferroelectric Fast Reactive tuner (FE-FRT) development. In a world first, CERN has tested the prototype FE-FRT with a superconducting cavity, and frequency tuning has been successfully demonstrated.Conclusion. Recent results on the development and experimental testing of advanced dielectric materials for accelerator applications are presented. Low loss microwave ceramics, quartz and CVD diamond are considered. We presented our experimental results on wakefield generation in microwave frequency ranges with the dielectric based accelerating structures. Special attention was paid to the experimental results on high power testing at X-band of the externally powered dielectric based components. Finally, we present here first experimental demonstration of ferroelectric tunable microwave ceramic for accelerator application, which includes both tunable dielectric wakefield accelerating structure and ferroelectric based fast high power tuner for superconducting cavities. The experimental results presented here are critical for the advanced dielectric wakefield accelerating structures and other components development intended for the future linear collider projects.

Demonstration of a cavity-based pulse compression system for pulse shape correction

A compact X-band correction cavity chain (CC) has been successfully designed, fabricated and high power tested for the Compact Linear Collider (CLIC) project. The CC consists of eight spherical cavities and four polarizers, and each spherical cavity has a ${Q}_{0}$ of 45 000 and a diameter of 7 cm. The compact CC can correct a decaying pulse shape generated by a storage cavity without need of low efficiency pulse modulation or a solution based on long delay lines. A flattop output with small ripples can be obtained if the CC and the storage cavity are matched. Experiments of the CC with a barrel open cavity (BOC) were conducted on the XBOX2 test facility at CERN, and the high power results match the theoretical calculations. The appliance of the CC only reduces the pulse compression efficiency by 6% relatively if the transmission attenuation is ignored.

Power Test of the Second-Generation Compact Linear Collider (CLIC) Nb3Sn Damping Wiggler Short Model

In the frame of the compact linear collider project, a high-field short-period superconducting damping wigglers will be required to reduce the emittance of the electron and positron beams. The use of Nb 3 Sn as superconducting material is being investigated, as a valid option for its smaller size and increased working margin. At CERN, Geneva, Switzerland, a second Nb 3 Sn damping wiggler short model has been developed, assembled, and tested. In this paper, the cold power test of that magnet is discussed in terms of training, quench detection, protection, endurance, and other tests.

Vibration Control Using a Dedicated Inertial Sensor

The Compact Linear Collider (CLIC) project is right in the development phase. In this prospect, the main objective of the final focus stabilization is to succeed in damping ground motion vibration at the sub-nanometer scale to avoid any unwanted motion of the two last final focus magnets. Active vibration control using high-resolution industrial seismic sensors has already shown its limits in the desired range of attenuation [4–100] Hz. Hence, a dedicated inertial sensor has been designed, tuned to fit CLIC requirements. It doesn’t contain any feedback or coil which would linearize its dynamic in its bandwidth [0.1–100] Hz, avoiding electrical noise or thermal noise, and when used for active control, enhancing its performances thanks to the internal resonance. An analytical modeling of the sensor dynamic behavior also shown experimentally gives a first internal resonance around 11 Hz. This paper is complemented by a comparative measurement with high precision industrial sensors. A noise level 2.5 times better (0.04 nm at 4 Hz) has been achieved. This sensor has also been tested in the context of vibration rejection with a sub-nanometer active vibration rejection support. Experimental results have been compared with the one obtained with the state-of-the-art industrial sensors. Vertical seismic motion attenuation results have shown unprecedented performances. A damping ratio of 8.5 has been achieved at 4 Hz, leading to an rms displacement of the support of 0.25 nm thanks to the active support prototype and the dedicated sensor.

Low emittance design of the electron gun and the focusing channel of the Compact Linear Collider drive beam

For the Compact Linear Collider project at CERN, the power for the main linacs is extracted from a drive beam generated from a high current electron source. The design of the electron source and its subsequent focusing channel has a great impact on the beam dynamic considerations of the drive beam. We report the design of a thermionic electron source and the subsequent focusing channels with the goal of production of a high quality beam with a very small emittance.

Optimization of an hybrid positron source using channeling

The hybrid positron source made of a crystal-radiator, as a source of channeling radiation, and an amorphous converter is briefly described. Optimization of the heating effects and thermal shocks led to a granular converter made of small tungsten spheres. Simulation results with application to two linear collider projects CLIC and ILC are presented. A test operated with this kind of source at KEK is described and the results gathered last year, reported. Plans for the future are briefly described.

Performance of the SDHCAL technological prototype

The SDHCAL technological prototype is a 1 × 1 × 1.3 m3 high-granularity Semi-Digital Hadronic CALorimeter using Glass Resistive Plate Chambers as sensitive medium. It is one of the two HCAL options considered by the ILD Collaboration to be proposed for the detector of the future International Linear Collider project. The prototype is made of up to 50 GRPC detectors of 1 m2 size and 3 mm thickness each with an embedded semi-digital electronics readout that is autotriggering and power-pulsed. The GRPC readout is finely segmented into pads of 1 cm2. This proceeding describes the prototype, its operation and its performance in energy reconstruction. Aspects of the GRPC readout modelling and comparisons with simulations are also presented.

In vacuum diamond sensor scanner for beam halo measurements in the beam line at the KEK Accelerator Test Facility

The investigation of beam halo transverse distributions is important for the understanding of beam losses and the control of backgrounds in Future Linear Colliders (FLC). A novel in vacuum diamond sensor (DSv) scanner with four strips has been designed and developed for the investigation of the beam halo transverse distributions and also for the diagnostics of Compton recoil electrons after the interaction point (IP) of ATF2, a low energy (1.3GeV) prototype of the final focus system for the ILC and CLIC linear collider projects. Using the DSv, a dynamic range of ∼106 has been successfully demonstrated and confirmed for the first time in simultaneous beam core (∼109 electrons) and beam halo (∼103 electrons) measurements at ATF2. This report presents the characterization, performance studies and tests of diamond sensors using an α source, as well as using the electron beams at PHIL, a low energy <5MeV photo-injector at LAL, and at ATF2. First beam halo measurement results using the DSv at ATF2 with different beam intensities and vacuum levels are also presented. Such measurements not only allow one to evaluate the different sources of beam halo generation but also to define the requirements for a suitable collimation system to be installed at ATF2, as well as to optimize its performance during future operation.

Prospects of high energy photon colliders

Photon colliders (γγ, γe) have been considered a natural addition to e+e− linear-collider projects for more than 30 years [1, 2]. It was a common opinion that such linear collider with four types of colliding beams (plus e+e−) would be the best instrument for the study of particles physics at energies from 100 GeV to several TeV where a lot of new physics was expected, including the dark matter. Following the discovery of the Higgs boson at LHC (and nothing else), the physics community has been actively considering various approaches to building a Higgs factories for precision measurement of the Higgs properties, among them there are several proposals of photon colliders (PC). In this paper, following a brief discussion of general situation in particles physics and the place of the photon collider among candidates for future colliders, I give an overview of photon colliders based on linear colliders ILC and CLIC and of more recently proposed photon-collider Higgs factories (with no e+e− collision option) based on recirculation linacs in ring tunnels.

Physics at ILC

The physics case for the International Linear Collider (ILC) project is discussed. The project is proposed to be built in Japan and a final decision has to be taken in 2016 on a government level. The initial data taking with e +e - beams is planned at the center-of-mass energy of 500 GeV with following runs at 250 GeV and 350 GeV. Potential physics studies at ILC are discussed with a special attention to the measurements, which are expected to have a better sensitivity at ILC in respect to the LHC experiments.

Environmentally Benign Electrofinishing Process for Selective Material Removal and Reduced Surface Roughness of Materials (like Nb, Ti, Ta, SS and Mo) in Low Viscosity Water Based Electrolytes

Post finishing processes are used to within every material manufacturing process. Various techniques are used to remove burrs, radius edges, and polish to a desired surface finish. These techniques improve the overall performance of the material for its application and generally improve the overall appearance of the material. This paper will discuss a range of applications and materials in which a pulse reverse electrochemical approach, in water based HF-free electrolytes, has been used to obtain these desired finish properties. A specific application of interest that requires a high quality surface finish to obtain the desired performance is the Niobium superconducting radio frequency cavities (SRF) required for the International Linear Collider and other high energy physics projects. In order for these cavities to achieve the required particle acceleration gradients, electropolishing is conducted as a final surface finishing operation. Conventional electropolishing of SRF cavities is based on the well-established viscous salt film theory[1] and utilizes a viscous electrolyte consisting of a mixture of sulfuric acid (95-98%) and hydrofluoric acid (49%), in a 9:1 volume ratio.[2] The HF is included to depassivate the niobium oxide film during electropolishing.[3]Based on prior surface finishing activities using pulse reverse waveforms in low viscosity aqueous electrolytes,[4] we speculated that a new paradigm was evolving and could be applied to electropolishing of SRF cavities. Within this activity Faraday used guidelines and observations from 1”x1” (6.4 cm2) and 3”x3” (58.1 cm2) coupons to scale the bipolar EP process to single cell SRF cavities of ~1,800 cm2 surface area. We recently reported these results at the 16th International Conference on RF Superconductivity in collaboration with Fermi National Accelerator Laboratory (FNAL) who declared that this cavity demonstrated the highest performance of any cavity previously processed at FNAL. This presentation will focus pulse/pulse reverse electrofinishing processes being developed by Faraday Technology. It will explore various strongly passive materials and their applications specific surface finishing requirements. These materials include but are not limited to titanium alloys, tantalum alloys, nickel alloys, stainless steels, niobium, and molybdenum alloys.

Status and Prospects of {$e^+e^-$} Linear Collider Projects

Status and Prospects of {$e^+e^-$} Linear Collider Projects

Cherenkov radiation from short relativistic bunches: general approach.

In recent years new interest in Cherenkov radiation has arisen based on progress in its new applications like biomedical imaging, photonic structures, metamaterials, and beam physics. These new applications require Cherenkov radiation theory of short bunches to be extended to rather more complicated media and structures than considered originally. We present a new general approach to the analysis of Cherenkov fields and loss factors for relativistic short bunches in arbitrary slow wave guiding systems. This new formalism is obtained by considering a general integral relation that allows calculation of the fields in the vicinity of the charge. The proposed approach dramatically simplifies simulations using analytical fields near the moving source of Cherenkov radiation.

A hadronic calorimeter with Glass RPC as sensitive medium

The SDHCAL technological prototype is a 1 × 1 × 1.3 m3 high-granularity Semi-Digital HadronicCALorimeter using Glass Resistive Plate Chambers as sensitive medium.It is one of the two HCAL options considered by the ILD Collaborationto be proposed for the detector of the future International LinearCollider project. The prototype is made of up to 50 GRPC detectors of1 m2 size and 3 mm thickness each with an embedded semi-digitalelectronics readout that is autotriggering and power-pulsed. The GRPCreadout is finely segmented into pads of 1 cm2. Measuredperformances of the GRPC and the full SDHCAL prototype in terms ofhomogeneity, low noise and energy resolution are presented in thisproceeding.