The Beam Coupling Impedance (BCI) is a crucial aspect in the realm of accelerator physics, as it describes the electromagnetic interactions between charged particle beams and the accelerator structure. The measurement and quantification of BCI is an essential requirement to assess and mitigate its impact, particularly when introducing new components or addressing problems within existing devices. The stretched Wire Method (WM) is a well-established technique for BCI evaluations, although with well-known limitations. These are particularly prominent when dealing with cavity-like structures. In that case, the estimates obtained below the cut-off frequency of the beam pipe can be inaccurate. It is worth noting that this frequency range is particularly relevant for many accelerator applications. To overcome these well-recognized limitations, a different bench measurement technique has been identified and thoroughly examined. This novel approach has been subjected to comprehensive testing in both virtual and real measurements, with a particular focus on a pillbox cavity.

The beam loading effect results in a gradient reduction of the accelerating structures due to the excitation of the fundamental mode when the beam travels through the cavity. A recent implementation of this process in the tracking code RF-Track allows the simulation of realistic scenarios, thus revealing the impact of this phenomenon in start-to-end accelerator designs. In this paper, we present the latest update of the beam loading module which allows the simulation of the compensation of this effect and we explore the potential of the developed tool in heavy-loaded scenarios.

In the context of the HL-LHC upgrade, RF Crab Cavities (CCs) are one of the key components. Due to the increased intensity, the collider will operate with a large crossing angle scheme and these CCs will be used to counteract the geometrical reduction factor coming from the crossing angle. Amplitude and phase noise injected from the Low-Level RF, are known to induce transverse bunch emittance growth. This contribution presents the latest measurements of emittance growth induced by amplitude noise. The measurement was performed thanks to the SPS Beam Synchrotron Radiation Telescope (BSRT), that has been used to characterize the evolution of the transverse distributions. The measured emittance growth was found to be dependent on the amplitude detuning induced by the SPS octupoles, although no dependence was predicted by the available theories and models. In this paper, the measurement results will be presented and discussed.

Metamaterials could allow developing superconductive-like materials at ambient temperature, with consequent drastic reduction in energy consumption. They are therefore promising materials for future accelerators of small and big scale. Here, electromagnetic metamaterials to synthesize an equivalent structure that approaches superconductive-like properties, i.e. extremely high electrical conductivity, are investigated. The underlying electromagnetic model is formalized analytically using transmission line theory and supported by electromagnetic simulations and experimental measurements.

During the third run of the Large Hadron Collider in 2023, which had the highest intensity bunch population compared to previous runs, increased losses attributed to pressure spikes within a warm vacuum sector triggered a beam dump. Subsequent inspections revealed localised annealing and plasticisation of the tension spring in the sliding contact radio-frequency finger module, alongside traces of vapour deposition on the various module components with the stainless-steel spring material. A comprehensive analysis involving vacuum and beam impedance studies was conducted to investigate the triggering mechanisms behind the radio-frequency finger module failure. The findings indicate localised beam-induced heating, which could lead to the annealing of the spring with a consequent cascade of effects. Additionally, investigations of potential mitigation measures were performed.

SIRIUS, a brazilian 4th generation synchrotron light source, currently operates in top-up mode at 100mA in uniform fill. The main limiting factor for reaching higher currents is the temporary RF system in use. It is comprised of one PETRA 7-Cell cavity and two solid state amplifier towers that combined provide at most 120kW of power. By mid 2024, two superconducting RF cavities will replace the current cavity and two amplifier towers will be added to the system, allowing operation at higher currents. The design current of SIRIUS storage ring is 350mA, which can only be achieved once a third harmonic cavity is installed to lengthen the bunches to avoid excessive wake-induced heating of sensitive components. However, the installation of such cavity is not foreseen in the near future, which raises the question of which is the maximum current in uniform fill SIRIUS can be operated. This work will present some theoretical and experimental studies carried out to answer this question.

A new high-luminosity Electron-Ion Collider (EIC) is being developed at BNL. Beam collisions occur at IP-6, involving two rings: the Electron Storage Ring (ESR) and the Hadron Storage Ring (HSR). The vacuum system of both rings is newly developed and impedance optimization is progressing. Beam-induced heating and thermal analysis are performed for both rings to manage and control thermal distribution. The study explores collective effects across the Rapid Cycling Synchrotron (RCS), ESR, and HSR using simulated single bunch wakefields. Discussions encompass impedance analysis, collective effects and beam interactions, and the impact of ion and electron clouds on beam dynamics.

The impedance of in-vacuum undulators (IVU) is a significant part of the total broadband impedance determining collective effects of beam dynamics in synchrotrons. It is computationally difficult to simulate the full few-meter-long 3D structure, which includes bellows, flanges, and taper transitions with a variable gap. So, the impedance is usually calculated separately for a simplified geometry of every component and the resistive-wall impedance is calculated using analytical formulas. The ECHO3D code based on a low-dispersive numerical technique provides an opportunity to compute the wakefield induced by a very short bunch in the full 3D model of the NSLS-II IVU. Here, we discuss the numerical simulations in comparison with beam-based measurements.

We summarize recent experimental studies of the impedance and beam-induced heating of titanium-coated ceramic vacuum chambers used in the NSLS-II injection kickers. We installed a spare chamber (SN003) in test section C01, demonstrating that beam-induced power is effectively dissipated in the titanium coating. Equipped with 12 temperature detectors, we measured temperatures and beam currents during operational fill patterns. The results, highlighting the heating of chamber, will be thoroughly presented.

ECHO3D has been used for calculating the geometric impedance for several beamline vacuum components in the hadron storage ring (HSR) of the EIC (Electron-Ion Collider) in the past few years. In this paper, we present the geometric impedances calculated from ECHO3D for the beam screen with pump slots, the polarimeter and the bellow with pump ports in the HSR. We also discuss some findings while cross-checking these results with what calculated from GdfidL and CST.

Boosters in synchrotron injector systems have traditionally had more relaxed designs than storage rings, and consequently impedance has not been considered an important factor in their designs. In 4th generation light sources like Diamond-II, it is desirable to increase the extracted charge per shot to reduce filling times and enable advanced injection schemes. As such, the vacuum chamber impedance becomes a significant design parameter. An impedance database has been created for the Diamond-II booster, using the same AT-style lattice concept as for the storage ring, to be used as input into particle tracking and other simulations. We present here an overview of the database, including details of significant components and current progress on engineering designs.

Impedance is a significant concern in modern storage rings like Diamond-II, due to instabilities limiting maximum bunch charge and other potential effects such as emittance dilution. Significant changes have been made to the Diamond-II impedance database, partly driven by progress in engineering design work, and partly by the requirements of particle tracking simulations and increase in available computing resources. We present an overview of the current state of the Diamond-II impedance database, focusing on the most significant updates and additions.

The beam wire scanners of the CERN Super Proton Synchrotron (SPS) experienced multiple failures of their carbon wires caused by the high-intensity beam during a very short period in April 2023. Different modifications of the existing instrument were therefore studied to reduce the beam-induced power without compromising its functionality nor negatively affecting the beam coupling impedance. Amongst these options were the implementation of ferrite absorbers, a change of the scanner mechanism and the installation of an RF coupler in the vacuum tank. In this paper, we introduce the electromagnetic simulation results for the installed ferrite loads and the RF coupler, as well as their impact on the on-axis beam impedance. The final improvement for the configuration to be installed during the end-of-year stop of the accelerator will be summarized.

During the last long shutdown of the accelerators at CERN (LS2), the main radio frequency system of the Proton Synchrotron Booster (PSB) was upgraded. A wideband system with Finemet magnetic alloy cavities driven by solid-state amplifiers replaced several different ferrite-loaded cavities. In measurements post-LS2, the longitudinal beam stability did not match predictions, which triggered a survey of the PSB impedance model. This started with the Finemet RF system, which are expected to be the dominant impedance contribution. Single stretched wire measurements were carried out with a 6-cell Finemet test cavity with different amplifier configurations. Measurement results and electromagnetic simulations are presented in this paper and compared to the previous impedance model. The electromagnetic characterization presented in this contribution will complement the beam-based impedance and low-level RF measurements as an input for the simulations of beam stability.

The Beam Coupling Impedance (BCI) is a crucial aspect in the realm of accelerator physics, as it describes the electromagnetic interactions between charged particle beams and the accelerator structure. The measurement and quantification of BCI is an essential requirement to assess and mitigate its impact, particularly when introducing new components or addressing problems within existing devices. The stretched Wire Method (WM) is a well-established technique for BCI evaluations, although with well-known limitations. These are particularly prominent when dealing with cavity-like structures. In that case, the estimates obtained below the cut-off frequency of the beam pipe can be inaccurate. It is worth noting that this frequency range is particularly relevant for many accelerator applications. To overcome these well-recognized limitations, a different bench measurement technique has been identified and thoroughly examined. This novel approach has been subjected to comprehensive testing in both virtual and real measurements, with a particular focus on a pillbox cavity.

The beam gas ionization monitors (BGIs) are non-destructive instruments to measure the transverse beam profiles. With the goal to double the beam intensity in the injector chain for the High-Luminosity Large Hadron Collider (HL-LHC), any element contributing to the overall beam coupling impedance requires an in-depth impedance evaluation from the design stage. This paper presents the beam coupling impedance optimization and mitigation study of the beam gas ionization monitors for the Super Proton Synchrotron (SPS) at CERN. Detailed electromagnetic simulations of the 3D model were carried out already before the construction of the prototype. Consequently, geometrical modifications required for impedance mitigation were still possible and were investigated while keeping the functionality of the device. We present different mitigation measures as coatings, RF-fingers and the introduction of additional loss mechanisms to dampen resonances of the geometry. At last, a comparison of the instrument design before and after impedance reduction is shown.

The 40 MHz and 80 MHz Radio Frequency (RF) systems in the CERN Proton Synchrotron (PS) are required to perform non-adiabatic bunch shortening before beam ejection. This manipulation allows to fit the bunches into the short RF buckets of the 200 MHz Super Proton Synchrotron (SPS). Although the impedance of the cavities is strongly reduced by feedback, the detailed understanding of the beam-cavity interaction is essential to evaluate their impact on the beam. This contribution focuses on the impedance characterization of the 80 MHz RF systems to describe how the RF amplification chain behaves as a function of beam current changes. Complementary measurement techniques, both beam and RF-based, were adopted. The results of the different measurements show good agreement. The aim is to study and predict possible beam quality degradation at beam intensities required by the High Luminosity LHC (HL-LHC), as well as to propose future consolidation to the high-frequency RF systems in the PS.

The beam loading effect results in a gradient reduction of the accelerating structures due to the excitation of the fundamental mode when the beam travels through the cavity. A recent implementation of this process in the tracking code RF-Track allows the simulation of realistic scenarios, thus revealing the impact of this phenomenon in start-to-end accelerator designs. In this paper, we present the latest update of the beam loading module which allows the simulation of the compensation of this effect and we explore the potential of the developed tool in heavy-loaded scenarios.

The impedance of the Large Hadron Collider (LHC) is a source of instabilities and has to be monitored closely. It is usually assessed by measuring the tune-shift vs intensity, in particular at top energy where it is the most critical, as the collimators are the closest to the beam. However, to get information on the real part of the impedance, growth rate measurements are required. These are difficult to perform at flat-top because triggering the instability in a sharp and fast manner remains a challenge. Moreover, the length of the full cycle, including an energy ramp, prevents the measurement repetition. Instead, measuring growth rates at injection is more natural and allows rapid cycling, with the downside that the impedance at injection is not dominated by collimators but rather by fixed-gap devices. Here, we present measurements at injection energy, placing the collimators in tighter positions than the nominal ones, in an attempt to obtain a similar configuration as the flat top situation. The measurements are performed at several negative chromaticities to study the evolution of the growth rate of the rigid bunch mode instability. Results are finally compared to simulations.

The High Energy Photon Source (HEPS) is a fourth-generation synchrotron radiation facility with design beam emittance of less than 60 pm. Impedance modelling is an important subject due to the adopted small beam pipe as well as the tight requirements from beam collective effects. Narrowband impedances can be generated by the discontinuity of the vacuum chamber or the finite conductivity of the beam pipe. The coupled bunch instabilities caused by the narrowband impedances could restrict the beam current or perturb the synchrotron radiations. In this paper, the narrowband impedances in the HEPS storage ring are investigated element by element.

The transverse narrow-band impedance makes a major contribution to the transverse coupled-bunch instability, which may deteriorate the beam quality in multi-bunch, high-intensity circular accelerators. Thus, strict restriction on the transverse narrow-band impedance are implemented during the initial accelerator design phase. However, slight component structure deviations during the construction of accelerators and component modifications during the subsequent operation may lead to impedance difference from the design value. It is therefore more meaningful to obtain the impedance parameters of circular accelerators by beam experimental measurement during the machine operation. In this paper, by mode distribution of coupled-bunch instability and its growth rate, a method was proposed to obtain the transverse narrow-band impedance which is represented with an LRC resonator. In order to verify the effectiveness of the method, the numerical calculation with three known LRC resonators was used to check their difference and the fitted LRC resonator parameters are in good agreement with the setting values.

Previous studies have identified turbulent mode coupling instability (TMCI) as one of the most severe single-bunch instabilities in the FCC-ee collider, potentially limiting its performance. Its threshold is influenced by both transverse and longitudinal wakefields arising from vacuum chamber resistive wall effects, discontinuities, and beam-beam interactions, the latter of which can be seen as a transverse cross-wake force. In this paper, we investigate the TMCI using the most recent collider parameters and an updated impedance model. We also explore various mitigation techniques aimed at increasing the instability threshold, including positive chromaticity and a feedback system.

Due to the small vacuum apertures, impedance serves as a significant cause of beam instabilities in the 4th generation storage ring. These instabilities are directly affected by the bunch charge, thereby placing a limit on the maximum achievable beam current within the storage ring. The Korea-4th generation storage ring (Korea-4GSR) is currently under construction with the aim of reaching a maximum beam current of 400 mA. To meet this goal, we've conducted estimations and optimizations of the current storage ring’s impedance. In this presentation, we show the impedance of Korea-4GSR and the corresponding instabilities.

The beam coupling impedance is a key design parameter for all accelerator structures. Recently, we have introduced a novel simulation approach for impedance calculations in 3D-geometry. Unlike conventional methods, this approach is based on the solution of Maxwell’s equations in the frequency domain using a high-order finite element technique. The main challenge for all impedance simulations, however, is the huge amount of computational resources that is required for the numerical discretization of electromagnetically large accelerator structures. In this contribution, we introduce a specialized domain decomposition technique for impedance simulations. The technique allows to handle large accelerator structures by decomposing the computational domain into subdomains that interact by means of suitably chosen boundary conditions. We describe a class of such boundary conditions that accurately take into account the modal wave contributions traveling through domain interfaces in the presence of a particle beam. An application of the method considered in the paper is the full impedance characterization of a large in-vacuum undulator for the PETRA IV synchrotron source.

In the context of the HL-LHC upgrade, RF Crab Cavities (CCs) are one of the key components. Due to the increased intensity, the collider will operate with a large crossing angle scheme and these CCs will be used to counteract the geometrical reduction factor coming from the crossing angle. Amplitude and phase noise injected from the Low-Level RF, are known to induce transverse bunch emittance growth. This contribution presents the latest measurements of emittance growth induced by amplitude noise. The measurement was performed thanks to the SPS Beam Synchrotron Radiation Telescope (BSRT), that has been used to characterize the evolution of the transverse distributions. The measured emittance growth was found to be dependent on the amplitude detuning induced by the SPS octupoles, although no dependence was predicted by the available theories and models. In this paper, the measurement results will be presented and discussed.

We present an impedance model of the Fermilab Recycler ring using PyHEADTAIL. The model is constructed by incorporating analytical expressions for the wakefields of beamline components that contribute significantly to impedance. The effects of indirect space charge are included as an inductive impedance. Benchmarking against measured coherent Betatron tune shifts, the impedance model is found to capture 73.4% of observed tune shifts. Our findings serve as a stepping stone for the development of a realistic impedance model crucial for studying impedance-driven instabilities at higher intensity.