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2022 Status Report of the Advanced Wakefield Experiment AWAKE

Journal of Instrumentation 17(05), P05036 (2022). doi:10.1088/1748-0221/17/05/P05036, Linear colliders are an attractive platform to explore high-precision physics of newly discovered particles. The recent significant progress in advanced accelerator technologies has motivated their applications to colliders which has been discussed in the alegro workshop. In this paper we discuss structure wakefield acceleration, namely collinear wakefield acceleration and two-beam acceleration. We especially discuss available drive and witness beam sources based on L and S-band radiofrequency technology, and also summarize available and forthcoming longitudinal shaping techniques to improve the overall acceleration efficiency via the transformer ratio., Published by Inst. of Physics, London

This report describes the electron pre-injector of the FCC-ee injector chain. There are two main options for electron sources for such a machine, an RF-photo injector or a thermionic gun. The study comprises the source itself and a linear accelerator to accelerate the electrons up to 200 MeV.

During the preparatory phase of the International Linear Collider (ILC) project, all technical development and engineering design needed for the start of ILC construction must be completed, in parallel with intergovernmental discussion of governance and sharing of responsibilities and cost. The ILC Preparatory Laboratory (Pre-lab) is conceived to execute the technical and engineering work and to assist the intergovernmental discussion by providing relevant information upon request. It will be based on a worldwide partnership among laboratories with a headquarters hosted in Japan. This proposal, prepared by the ILC International Development Team and endorsed by the International Committee for Future Accelerators, describes an organisational framework and work plan for the Pre-lab. Elaboration, modification and adjustment should be introduced for its implementation, in order to incorporate requirements arising from the physics community, laboratories, and governmental authorities interested in the ILC., 48 pages, 5 figures

Positron source is very important for many accelerator experiments. The optimisation of positron source is therefore a crucial problem to be solved. In this report, a new simple, general and effective optimisation strategy is proposed, based on iterations of scan of free parameters, which has the advantage of easily handling realistic parametric problems. The new strategy in principle can be 25 times faster than the old optimisation method. The optimisation of the CLIC positron source at the 3 TeV and 1.5 TeV stages with the new strategy is presented. Positron yield is improved by 43% compared with previous studies, mainly due to the removal of the distance between the targets. The validation of the simulation code is carried out with a cross-check with the ILC positron source results. In addition, studies on mesh grid size for PEDD estimation and matching of positron beam to the latest design of the injector linac are also presented. Positrons can be transported in the matched injector linac almost without losses, with a final accepted yield of 2.14 e+/e-.

Conjugate heat transfer simulations were performed for the two-beam module of the Compact Linear Collider (CLIC). A full approach using ANSYS Fluent is presented for the determination of heat dissipation values from the main beam portion of the module to the cooling air and water. A transient model for heat dissipated through the tunnel to the outside soil is presented as well. Structural stress-strain simulations and modal analyses were performed for the adjustable supports with the finite-element method using ANSYS Mechanical. The operating range of the adjustable supports was determined.

The AWAKE experiment reached all planned milestones during Run 1 (2016-18), notably the demonstration of strong plasma wakes generated by proton beams and the acceleration of externally injected electrons to multi-GeV energy levels in the proton driven plasma wakefields. During Run~2 (2021 - 2024) AWAKE aims to demonstrate the scalability and the acceleration of electrons to high energies while maintaining the beam quality. Assuming continued success of the AWAKE program, AWAKE will be in the position to use the AWAKE scheme for particle physics applications such as fixed target experiments for dark photon searches and also for future electron-proton or electron-ion colliders. With strong support from the accelerator and high energy physics community, these experiments could be installed during CERN LS3; integration and beam line design studies show the feasibility of a fixed target experiment in the AWAKE facility, downstream of the AWAKE experiment in the former CNGS area. The expected electrons on target for fixed target experiments exceeds the electrons on target by three to four orders of magnitude with respect to the current NA64 experiment, making it a very promising experiment in the search for new physics. Studies show that electrons can be accelerated to 70 GeV in a 130 m long plasma cell installed in an extended TI 2 extraction tunnel from SPS to the LHC and transported to collision with protons/ions from the LHC. The experiment would focus on studies of the structure of matter and QCD in a new kinematic domain. The AWAKE scheme offers great potential for future high energy physics applications and it is the right moment now to support further development of this technology leading to unique facilities.

Temperature changes lead to unwanted thermo-mechanical deformations in the components of the Compact Linear Collider (CLIC) module. There are several sources and sinks of heat around the CLIC two-beam module. Heat is generated in the components that produce, transfer, and extract radio frequency (RF) power. Excess heat is removed from the components by cooling water as well as dissipated to air by convection from the outer surfaces of the components. The ambient temperature might also vary along the tunnel during the operation of CLIC. Due to tight assembling and alignment tolerances, it is necessary to minimize the thermo-mechanical deformations in the components. In this paper, the steps of thermal-structural Finite Element Analysis (FEA) of CLIC lab module type 0#2 are described from geometry model simplification to setting up the simulation. The description is accompanied by useful hints for CATIA and ANSYS users performing similar modelling tasks. A reliable computer simulation is important for studying the effects of different operational parameters as well as evaluating future two-beam module designs.

The requirement of luminosity loss below 1% raises tight tolerances for the phase and power stability of the CLIC drive beam (DB) klystrons and consequently for the high voltage pulse ripple of the modulators. A low-level RF (LLRF) feedback system needs to be developed and combined with the modulator in order to guarantee the phase and amplitude tolerances. To this aim, three feedback control strategies were investigated, i) Proportional Integral (PI) controller, ii) Linear Quadratic Integral Regulator (LQI) and iii) Model Predictive Controller (MPC). The klystron, as well as the incident phase noise were modelled and used for the design and evaluation of the controllers. First simulation results are presented along with future steps and directions.

Within the CLIC (Compact Linear Collider) project, feasibility studies of a photo injector option for the drive beam as an alternative to its baseline design using a thermionic electron gun are on-going. This R&D program covers both the laser and the photocathode side. Whereas the available laser pulse energy in ultra-violet (UV) is currently limited by the optical defects in the 4thharmonics frequency conversion crystal induced by the0.14 ms long pulse trains, recent measurements of Cs3Sbphotocathodes sensitive to green light showed their potential to overcome this limitation. Moreover, using visible laser beams leads to better stability of produced electron bunches and one can take advantages of the availability of higher quality optics. The studied Cs3Sbphotocathodes have been produced in the CERN photo emission laboratory using the co-deposition technique and tested in a DC gun set-up. The analysis of data acquired during the cathode production process will be presented in this paper, as well as the results of lifetime measurements in the DC gun

A photoinjector, PHIN (PHotoINjector), has been realized at CERN by a joint effort of several institutes within the European Coordinated Accelerator Research in Europe program. The test facility has been installed and commissioned at CERN with the aim to demonstrate the beam parameters needed for the CLIC Test Facility 3 (CTF3). This beam is unique with respect to its long bunch train and high average charge per bunch requirements. The nominal beam for CTF3 consists of 1908 bunches each having a 2.33 nC charge and a bunch frequency of 1.5 GHz. Thus, a total charge of similar to 4.4 mu C has to be extracted and accelerated. The stability of the intensity and the beam parameters along this exceptionally high average current train is crucial for the correct functioning of the CLIC drive beam scheme. Consequently, extensive time-resolved measurements of the transverse and longitudinal beam parameters have been developed, optimized, and performed. The shot-to-shot intensity stability has been studied in detail for the electron and the laser beams, simultaneously. The PHIN photoinjector has been commissioned between 2008 and 2010 during intermittent operations. This paper reports on the obtained results in order to demonstrate the feasibility and the stability of the required beam parameters.

As part of a SLAC-CERN-KEK col­lab­o­ra­tion on high gra­di­ent X-band struc­ture re­search, sev­er­al pro­to­type struc­tures for the CLIC lin­ear col­lid­er study have been test­ed using two of the high power (300 MW) X-band rf sta­tions in the NLCTA fa­cil­i­ty at SLAC. These struc­tures dif­fer in terms of their man­u­fac­tur­ing (brazed disks and clamped quad­rants), gra­di­ent pro­file (amount by which the gra­di­ent in­creas­es along the struc­ture which op­ti­mizes ef­fi­cien­cy and max­i­mizes sus­tain­able gra­di­ent) and HOM damp­ing (use of slots or waveg­uides to rapid­ly dis­si­pate dipole mode en­er­gy). The CLIC goal in the next few years is to demon­strate the fea­si­bil­i­ty of a CLIC-ready base­line de­sign and to in­ves­ti­gate al­ter­na­tives which could bring even high­er ef­fi­cien­cy. This paper sum­ma­rizes the high gra­di­ent test re­sults from the NLCTA in sup­port of this ef­fort.

In this deliverable we report an overview of the possible injector options suitable to match the CompactLight X-band high brightness linac able to drive short wavelength FELs user facilities. Different schemes have been investigated including RF gun injectors at different operating frequency (S, C and X band) and a DC gun based design. The electromagnetic and RF designs for all cases are reported and discussed, including a preliminary evaluation of the laser/cathode system requirements. Matchings with the downstream linac are also investigated with beam dynamics simulations. State of the art S-band injectors look appropriate to achieve the required parameters at low repetition rate ( 100 Hz). On the other end a compact C-band (or X-band) RF gun design is expected to have even better performances at low repetition rates and moreover, due to the lower thermal load, could allow higher repetition rates operation, up to 1 kHz, with acceptable performances degradation. DC guns are also very promising solutions for kHz range operation.

In this deliverable we report an overview of the possible injector options suitable to match the CompactLight X-band high brightness linac able to drive short wavelength FELs user facilities. Different schemes have been investigated including RF gun injectors at different operating frequency (S, C and X band) and a DC gun based design. The electromagnetic and RF designs for all cases are reported and discussed, including a preliminary evaluation of the laser/cathode system requirements. Matchings with the downstream linac are also investigated with beam dynamics simulations. State of the art S-band injectors look appropriate to achieve the required parameters at low repetition rate ( 100 Hz). On the other end a compact C-band (or X-band) RF gun design is expected to have even better performances at low repetition rates and moreover, due to the lower thermal load, could allow higher repetition rates operation, up to 1 kHz, with acceptable performances degradation. DC guns are also very promising solutions for kHz range operation., On behalf of the CompactLight Collaboration