High Efficiency Klystrons Using the COM Bunching Technique

Energy consumption is a major concern for future large-scale high-energy accelerator projects such as the compact linear collider (CLIC), future circular collider (FCC), and international linear collider (ILC). Thus, efficient generation of microwave power recently gained new attention by the accelerator community. In response, we propose an innovative two-stage multibeam klystron (TS-MBK) concept. It combines a very high RF power generation efficiency (84%) with a compact and cost effective electro-mechanical configuration. This article presents the concept and design study of a 1.0-GHz, 24-MW klystron. The technological novelties and mitigation of issues specific to this concept are described. TS-MBK performance has been validated using particle-in-cell computer simulations.

This report describes the physics potential and experiments at a future multi- TeV e+e collider based on the Compact Linear Collider (CLIC) technology. The physics scenarios considered include precision measurements of known quantities as well as the discovery potential of physics beyond the Standard Model. The report describes the detector performance required at CLIC, taking into account the interaction point environment and especially beaminduced backgrounds. Two detector concepts, designed around highly granular calorimeters and based on concepts studied for the International Linear Collider (ILC), are described and used to study the physics reach and potential of such a collider. Detector subsystems and the principal engineering challenges are illustrated. The overall performance of these CLIC detector concepts is demonstrated by studies of the performance of individual subdetector systems as well as complete simulation studies of six benchmark physics processes. These full detector simulation and reconstruction studies include beaminduced backgrounds and physics background processes. After optimisation of the detector concepts and adopting the reconstruction algorithms the results show very efficient background rejection and clearly demonstrate the physics potential at CLIC in terms of precision mass and cross section measurements. Finally, an overview of future plans of the CLIC detector and physics study is given and a list of key detector R&D topics needed for detectors at CLIC is presented.

A bstract We study the electromagnetic form factors of electrically neutral dark-sector particles in this paper. Concretely speaking, we focus on the operators that can lead to interactions of fermionic dark states with the Standard-Model (SM) photon, including both dimension-5 (the magnetic and electric dipole moments) and dimension-6 (the anapole moment and charge radius) operators. Correspondingly, instead of the SM-photon form factors, we employ hypercharge gauge-field form factors that can induce additional couplings to the SM Z -boson. Utilizing the mono-photon production channel at future linear electron-positron colliders, the International Linear Collider (ILC) and the Compact Linear Collider (CLIC), we demonstrate that tuning beam polarization allows for simultaneous enhancement of signal-event rates and suppression of dominant SM background events, i.e. neutrino-induced processes, and hence improvement of sensitivity reach. Our analysis reveals that ILC and CLIC can probe electromagnetic form factors of dark-sector particles up to about two orders of magnitude beyond existing experimental limits. We also estimate, at the order-of-magnitude level, the validity range of the effective-field-theory (EFT) approach we adopt, finding that for the dimension-5 operators the EFT remains valid in most of the parameter regions to which the ILC and CLIC can be sensitive, while it breaks down in the entire sensitivity region for the dimension-6 operators.

The International Linear Collider (ILC) and the Compact Linear Collider (CLIC) are the two options for a future high-energy, high-luminosity linear electron-positron collider. Both are expected to be built in stages, optimised for their physics potential. The main goals are the precision measurements of Higgs-boson and top-quark properties as well as direct and indirect searches for new physics Beyond Standard Model. In my talk I will review some of the latest results from both ILC and CLIC demonstrating their physics potential, pointing to similarities and complementarity of both projects.

We discuss the production of the doubly charged leptons in future linear electron positron colliders, such as the International Linear Collider and Compact Linear Collider. Such states are introduced in extended weak-isospin multiplets by composite models. We discuss the production cross section of and carry out analyses for hadronic, semi-leptonic and pure leptonic channels based on the full simulation performance of the silicon detector. The 3- and 5-sigma statistical significance exclusion curves are provided in the model parameter space. It is found that the hadronic channel could offer the most possible detectable signature.

One of the primary goals of the proposed future collider experiments is to search for dark matter (DM) particles using different experimental approaches. High energy e$^+$e$^-$ colliders offer unique possibility for the most general search based on the mono-photon signature. As any e$^+$e$^-$ scattering process can be accompanied by a hard photon emission from the initial state radiation, analysis of the energy spectrum and angular distributions of those photons can be used to search for hard processes with invisible final state production and to test the nature and interactions of the DM particles. Dedicated procedure of merging the matrix element calculations with the lepton ISR structure function was developed to model the Standard Model background processes contributing to mono-photon signature with WHIZARD. We consider production of DM particles at the International Linear Collider (ILC) and Compact Linear Collider (CLIC) experiments. Detector effects are taken into account within the DELPHES fast simulation framework. Limits on the light DM production in a generic model are set as a function of the mediator mass and width based on the expected two-dimensional distributions of the reconstructed mono-photon events. Limits on the mediator coupling to electrons are presented for a wide range of mediator masses and widths. For light mediators, for masses up to the centre-of-mass energy of the collider, results from the mono-photon analysis are more stringent than the limits expected from direct resonance search in SM decay channels.

Opportunities for searches for axionlike particles (ALPs) coupling to photons in e+e− collisions at the Future Circular Collider (FCC-ee) and International Linear Collider (ILC) are investigated. We perform a study of the photon-fusion production of ALPs decaying into two photons, e+e−→γγe+a(γγ)e−, over the light-by-light continuum background, for the planned FCC-ee and ILC center-of-mass energies and integrated luminosities. An analysis of the feasibility measurements is presented using parametrized simulations for two types of detectors. Upper limits at 95% confidence level (C.L.) on the cross section for ALP production, σ(γγ→a→γγ), and on the ALP-photon coupling are obtained over the ma≈0.1–1000 GeV ALP mass range, and compared to current and future collider searches. Production cross sections down to σ(γγ→a→γγ)≈1 fb (1 ab) will be probed at ma≈1 (300) GeV, corresponding to constraints on the axion-photon coupling as low as gaγγ≈2×10−3 TeV−1. Published by the American Physical Society 2024

The Compact Linear Collider (CLIC) is a multi-TeV high-luminosity linear e+e- collider under development. For an optimal exploitation of its physics potential, CLIC is foreseen to be built and operated in a staged approach with three centre-of-mass energy stages ranging from a few hundred GeV up to 3 TeV. The first stage will focus on precision Standard Model physics, in particular Higgs and top-quark measurements. Subsequent stages will focus on measurements of rare Higgs processes, as well as searches for new physics processes and precision measurements of new states, e.g. states previously discovered at LHC or at CLIC itself. In the 2012 CLIC Conceptual Design Report, a fully optimised 3 TeV collider was presented, while the proposed lower energy stages were not studied to the same level of detail. This report presents an updated baseline staging scenario for CLIC. The scenario is the result of a comprehensive study addressing the performance, cost and power of the CLIC accelerator complex as a function of centre-of-mass energy and it targets optimal physics output based on the current physics landscape. The optimised staging scenario foresees three main centre-of-mass energy stages at 380 GeV, 1.5 TeV and 3 TeV for a full CLIC programme spanning 22 years. For the first stage, an alternative to the CLIC drive beam scheme is presented in which the main linac power is produced using X-band klystrons.

The Compact Linear Collider (CLIC) is a concept for a future linear collider that would provide e + e - collisions at up to 3 TeV. The physics aims require a detector system with excellent jet energy and track momentum resolution, highly efficient flavour tagging and lepton identification capabilities, full geometrical coverage extending to low polar angles, and timing information of the order of nanoseconds to reject beam-induced background. To deal with these requirements, an extensive R&D programme is in place to overcome current technological limits. The CLIC detector concept includes a low-mass all-silicon vertex and tracking detector system and fine-grained calorimeters designed for particle flow analysis techniques, surrounded by a 4 T solenoid magnet. An overview of the requirements and design optimisations for the CLIC detector concept is presented.

The post-linac energy collimation system of future e+e− multi-TeV linear colliders is designed to fulfil an essential function of protection of the Beam Delivery System (BDS) against miss-steered or errant beams likely generated by failure modes in the main linac. For the case of the Compact Linear Collider (CLIC), the energy collimators are required to withstand the impact of a full bunch train in case of failure. This condition makes the design of the energy collimation system especially challenging, if we take into account the need to dispose of an unprecedented transverse beam energy density per beam of the order of GJ/mm2, when assuming the nominal CLIC beam parameters at 3 TeV centre-of-mass energy, which translates into an extremely high damage potential of uncontrolled beams. This leads to research activities involving new collimator materials and novel collimation techniques. The increase of the transverse spot size at the collimators using nonlinear magnets is a potential solution to guarantee the survival of the collimators. In this paper we present an alternative nonlinear optics based on a multipole magnet pair for energy collimation. In order to preserve an acceptable luminosity performance, we carefully study the general conditions for self-cancellation of optical aberrations between two multipoles. This nonlinear optics scheme is adapted to the requirements of the post-linac energy collimation system for the CLIC BDS, and its performance is investigated by means of beam tracking simulations. Although applied to the CLIC case, this nonlinear protection system could be adapted to other future colliders.

The Compact Linear Collider (CLIC) project is exploring the possibility of constructing a multi- TeV linear electron-positron collider for high-energy frontier physics studies beyond the LHC era. The CLIC concept is based on high-gradient normal-conducting accelerating structures. The RF power for the acceleration of the colliding beams is produced by a two-beam acceleration scheme, where power is extracted from a high current drive beam that runs parallel with the main linac. The key ongoing studies involve accelerator parameter optimisation, technical studies and component development, alignment and stability, and include a number of system performance studies in test-facilities around the world. The CLIC physics potential and main detector issues, as well as possible implementation staging, are being studied in parallel. A summary of the progress and status of the corresponding studies will be given, as well as an outline of the preparation and work towards developing a CLIC implementation plan by 2018/19.

The Compact Linear Collider (CLIC) is a proposed TeV-scale linear electron-positron collider based on a novel two-beam acceleration technology. With its high luminosity and a broad energy range, from 380 GeV to 3 TeV, CLIC presents a mature option for a future Higgs factory and discovery machine. Detailed studies of the CLIC physics potential have been performed, mostly based on full Geant4 simulations using a dedicated detector concept, CLICdet. In this contribution, a general introduction to the CLIC programme and highlights of CLIC physics studies are reported.

The Stanford Linear Accelerator Center (SLAC) version of the 1 TeV next linear collider (NLC) requires a 4:1 increase in drive frequency, from the 2.85 GHz of the 1 TeV Stanford Linear Collider (SLC) to 11:4 GHz for the NLC. More than eight years have gone into the development of a new 75-MW klystron for powering the NLC. The increase in power density and surface RF gradient at the higher frequency have rendered previous RF window and circuit designs unusable. Following numerous catastrophic gun, cavity, and window failures, new designs have evolved that solved the problems. As history's most ambitious klystron development enters its last year, the result includes a robust 75-MW peak power solenoid-focused, 50% efficient klystron. Not far behind is a 60-75-MW periodic permanent magnet (PPM)-focused 60% efficient version that will reduce the NLC electric power bill by tens of millions of dollars per year.

The Next Linear Collider (NLC) will require unprecedented amounts of power at a higher frequency than has been used previously for such applications. Two general applications have been considered and/or are still under consideration as RF power sources: systems that use RF pulse compression and systems that directly generate and use the large peak power needed to drive a section of an accelerator. Conventional klystrons and gyroklystrons are examples of RF sources that would require pulse compression to meet the requirements of the NLC. The relativistic klystron and variations of the two-beam accelerator have been considered for directly generating the peak power needed. Cost and efficiency arguments further restrict the range of options. A recent candidate is the cross field amplifier (CFA), which may have a cost advantage if it can be used in a mode without a pulsed modulator and without a thermionic cathode. The CFA could fit into either of the above categories or could be a category of its own if economy of large scale production allowed one to consider using from 10/sup 4/ to 10/sup 5/ relatively low peak power sources. >

We study phenomenological consequences of the strong first-order electroweak phase transition in an extension of the standard model with an inert doublet and vector-like leptons motivated by the muon $g-2$ anomaly and dark matter. We find that a condition for the strong first-order electroweak phase transition inevitably induces a large logarithmic enhancement in $Z$ boson decays, which relegates the explanation of the anomalous muon $g-2$ at below 2$\sigma$ level. Our analysis shows that future lepton collider experiments, especially the Giga-$Z$ at the International Linear Collider and Tera-$Z$ at the Circular Electron Positron Collider as well as Future Circular Collider have great capability to explore the nature of the electroweak phase transition, which is complementary to conventional approaches via measurements of the triple Higgs boson coupling and gravitational waves.