We present the design and initial characterization of a multi-mode cavity, a novel electromagnetic structure with potential benefits such as compactness, efficiency, and cost reduction. The 2nd Harmonic mode was chosen to linearize the fundamental mode for use as an accelerating and bunching cavity. The reduction in the number of cavities required to bunch and accelerate promises cost and space savings over conventional approaches. Superfish and COMSOL simulations were used to optimize the cavity's geometry with the goal of balancing various design parameters, such as quality factor (Q-factor), harmonic modes, and mode coupling. A 3D-printed copper-plated cavity was used to validate code predictions. The cavity's multi-mode nature positions it for use with other harmonic modes with small deviations in design. For example, a 3rd Harmonic can be used to decrease energy spread by widening the peak of the fundamental. This research lays the foundation for further exploration of the cavity's applications and optimization for specific use cases, with potential implications for a wide range of accelerator fields.

The luminosity of particle colliders depends, among other parameters, on the transverse profiles of the colliding beams. At the LHC at CERN, heavy-tailed transverse beam distributions are typically observed in routine operation. The luminosity is usually modelled with the assumption that the 𝑥-𝑦 planes are independent (i.e. statistically uncorrelated particle distributions between the planes) in each beam. Analytical calculations show that the solution of inverting 1D heavy-tailed beam profiles to transverse 4D phase-space distributions is not unique. For a given transverse beam profile, the distributions can be dependent (i.e. statistically correlated) or independent in the transverse planes, even in the absence of machine coupling. In this work, the effect of transverse 𝑥-𝑦 dependence of the 4D phase space distribution on the luminosity of a particle collider is evaluated for heavy-tailed beams.

In the High Luminosity Large Hadron Collider (HL-LHC) era, the intensity of the circulating bunches will increase to 2.2e+11 protons per bunch, almost twice the nominal LHC value. Besides detailed studies of known and new failure cases for HL-LHC, it is also required to investigate failures beyond nominal design. A consequence of such failures can be the impact of a large number of high-energy particles in one location, resulting in a significantly increased dam- age range due to an effect called hydrodynamic tunnelling. This phenomenon is studied by coupling FLUKA, an energy deposition code, and Autodyn, a hydrodynamic code. This paper presents the simulated evolution of the deposited energy, density, temperature and pressure for the impact of the HL-LHC beam on a graphite target. It then computes the resulting tunnelling range and finally compares the outcome with previous studies using LHC intensities.

The Electron Ion Collider design strategy for reaching unprecedented luminosities and detection capabilities involves collision of flat bunches at a relatively large crossing angle. Effective head-on collisions are restored using crab cavities, which introduce a correlation of the particles' transverse coordinates with their longitudinal positions in the bunch, or crab dispersion. The collision geometry is further complicated by a tilt of the Electron Storage Ring plane with respect to that of the Hadron Storage Ring. In addition, the interaction point is placed inside the field of a detector solenoid. Reaching the design luminosity requires precise control of the 6D bunch distribution at the IP accounting for all of the aforementioned design features. This paper describes correction of the detector solenoid effect on the beam optics of the Hadron Storage Ring using a combination of local and global skew quadrupoles.

Distributed-coupling structures has been proposed as an advanced type of high-gradient accelerators, RF power flow independently into each cavity.This method has few advantages such as high shunt impedance, superior power efficiency, and low costs. And the most distributed-coupling structures typically set 0° or 180° as the phase advance which can simplify the design.In this study we introduces a new-designed distributed-coupling structures with phase advance greater than 180°. This choice of angle will significantly reduce costs without affecting the shunt impedance.

The Electron Ion Collider (EIC), to be constructed at Brookhaven National Laboratory, will collide polarized high-energy electron beams with hadron beams, achieving luminosities up to 1e+34 cm^−2 s^−1 in the center-mass energy range of 20-140 GeV. The Hadron Storage Ring (HSR) of the EIC will utilize the arcs of the Relativistic Heavy Ion Collider (RHIC) and construct new straight sections connecting the arcs. In this article, we will examine all available skew quadrupoles currently in the HSR lattice and explore possible schemes for future global betatron coupling correction with RHIC-like decoupling feedback system. The effects of detector solenoids and quadrupole rolls are estimated at injection and stored energies. We also studied the decoupling requirements for generating and maintaining large transverse emittance ratio beams in the HSR.

We present a novel method for minimizing the effects of radiative depolarization in electron storage rings by use of vertical orbit bumps in the arcs. Electron polarization is directly characterized by the RMS of the so-called spin orbit coupling function in the bends. In the Electron Storage Ring (ESR) of the Electron-Ion Collider (EIC), as was the case in HERA, this function is excited by the spin rotators. Individual vertical orbit bumps in the arcs can have varying impacts on this function globally. In this method, we use a singular value decomposition of the response matrix of the spin-orbit coupling function with each orbit bump to define a minimal number of most effective groups of bumps, motivating the name “Best Adjustment Groups for ELectron Spin” (BAGELS) method. These groups can then be used to minimize the depolarizing effects in an ideal lattice, and to restore the minimization in rings with realistic closed orbit distortions. Furthermore, BAGELS can be used to construct groups for other applications where a minimal impact on polarization is desirable, e.g. global coupling compensation or vertical emittance creation. Application of the BAGELS method has significantly increased the polarization in simulations of the 18 GeV ESR, beyond achievable with conventional methods.

In a radiofrequency accelerating structure with ceramic insertion, high shunt impedance (162 megaohm/m) and high group velocity (3.1% of the speed of light) are achieved simultaneously. The ceramic insertion is in the form of a cylinder, sandwiched between copper endplates with the beam aperture opened at the center. We report our theoretical study on this novel type of traveling wave accelerating structure that operates with a 2pi/3-mode at 5.7 GHz. The high shunt impedance is realized by the low-loss, highly reflective ceramic insertion confining the accelerating mode at the center. The high group velocity, or fast filling time of the radiofrequency wave, is made possible by the side coupling slots designed with large dimensions. As a result, this novel traveling wave accelerating structure enhances the power efficiency significantly, by two means. The high shunt impedance allows providing a greater accelerating gradient with a given amount of radiofrequency power. The fast filling time allows an earlier start of the beam acceleration within each radiofrequency power pulse, thus leading to a higher duty factor of the accelerator beam production. This type of the structure design allows using metallic iris features, which minimizes the electric field magnitude witnessed by the ceramic component. We also discuss the scheme of using periodic permanent magnets to focus an electron beam in the accelerating structure. The unique radiofrequency coupler design is also addressed.

High field radio frequency (RF) accelerating structures are an essential component of modern linear accelerators (linacs) with applications in photon production and ultrafast electron diffraction. Most advanced designs favor compact, high shunt impedance structures in order to minimize the size and cost of the machines as well as the power consumption. However, breakdown phenomena constitute an intrinsic limitation to high field operation which ultimately affects the performance of a given structure requiring dedicated tests. The introduction of a recent design based on cryogenic distributed coupling structures working at C-band (~6 GHz) allows to increase the shunt impedance by use of alternative distribution schemes for the RF power while mitigating the breakdowns thanks to the low temperature. In this paper we introduce the plan for high field and breakdown tests envisioned for a simple two-cell version of the aforementioned structure. Moreover, we discuss the joining procedure utilized to unify the two fabricated halves of such a structure and relying on the diffusion bonding technique which constitutes an attractive alternative to the brazing approach.

Plasma temperature dynamics provide significant insight when evaluating ion source performance. Quantities such as beam emittance, or mean transverse energy, are strongly correlated with the source plasma temperature. At LANSCE there is currently no method implemented for measuring initial source emittance or implementing tunability of mean transverse energy through ion source control parameters. In this work we will discuss our demonstration of a new laser diagnostic tool for measuring H- beam emittance on the LANSCE H- ion source laser diagnostic stand. Our investigated method will be an extension of systems outlined for NIFS, and will be optimized for rapid response times, scanning the Doppler broadened Hydrogen-alpha emission line at a rate 10x faster than the plasma ignition time window (800 microseconds). We will show that our real-time, non-intrusive measurement approach will enable characterization and study of source control parameter effects on source plasma temperature for future emittance optimization.

This work aims to improve the ability of particle accelerator researchers to develop high-performance accelerator cavity designs by creating an overall multiphysics framework that integrates and couples existing application codes. This framework will allow accelerator researchers to build multiphysics models that will optimize cavity design, improve understanding of whole-device performance, and reduce the development and fabrication costs of accelerator research. We utilize the open-source VizSchema data standard as an intermediate data structure interface layer to standardize interfaces between individual application codes. VizScema is extensively documented online, and plugins for VizSchema are available for popular visualization packages, including VisIt and ParaView. Currently, the work focuses on coupling the EM field solver COMSOL and the electron gun code MICHELLE to allow COMSOL field-solve results to be seamlessly used by MICHELLE for particle-solve. Later work will extend this integration to include other fields, particles, and thermodynamics simulation codes.

Recent studies have investigated a longitudinal instability that may develop in electron storage rings featuring higher-harmonic cavities. The instability, also referred to as periodic transient beam loading (PTBL), manifests as a slow oscillation of bunch longitudinal profiles following a coupled-bunch mode 1 pattern. In this contribution, we applied a well-established theory of longitudinal mode-coupling to assess the thresholds for this instability. Results obtained through this semi-analytical approach, considering different storage ring and harmonic cavity parameters, were validated using macroparticle tracking and compared against other methods proposed in previous investigations.

Elettra 2.0, will be a 4th generation synchrotron radiation source that will replace Elettra, the 3rd generation light source that has been in operation since 1993 at Trieste. In this paper, the effects of the quadrupolar wake fields are investigated, and the transverse mode coupling threshold is presented. Also, the incoherent tune shift for multi-bunch operation is examined considering the rhomboidal vacuum chamber of Elettra 2.0.

The question of the mitigation of the Transverse Mode Coupling Instability (TMCI) by space charge has been discussed for more than two decades. Since few years, it has become clear that the ABS model, which has been often used in the past and which assumes an air-bag bunch in a square well, is not sufficient to properly describe the complexity of the interaction between impedance and space charge. Considering a more realistic longitudinal Gaussian distribution, a fully self-consistent treatment of space charge was performed few years ago using the circulant matrix model, which revealed the usual TMCI mechanism but with oscillation modes shifted both by impedance and space charge. In this paper, a non self-consistent treatment of space charge is analyzed, still using a Gaussian distribution, to look at the evolution of the coherent direct space charge modes. It is shown in particular that it leads to exactly the same result as the self-consistent treatment for space charge parameters below 1 and that it is a much better approximation than the ABS model for space charge parameters above 1, as it reveals clearly how the positive modes lead to negative tune shifts.

The intrabunch motion for independent longitudinal or transverse beam oscillation modes has been explained analytically for impedance driven bunched-beam coherent instabilities already several decades ago by Laclare and they have been observed in many measurements and simulations. These oscillation patterns do not depend on the bunch intensity, they are head/tail symmetric and they exhibit a number of nodes equal to the radial mode number. However, in many measurements and simulations of transverse beam instabilities (due to impedance only, impedance and beam-beam, impedance and space charge, or electron cloud), asymmetric patterns are observed depending on the bunch intensity. The latter can be described theoretically considering the interaction between several modes, i.e. mode coupling, which explains why and how different kinds of asymmetric intrabunch signals can be observed. In this paper, the intrabunch motion in the presence of mode coupling is explained first without maths and then with maths, considering the case of a bunch interacting with a transverse impedance, using the GALACTIC Vlasov solver.

SOLEIL II is an upgrade project of the existing Synchrotron SOLEIL facility. It aims to reach fourth-generation light source parameters. This includes reductions of the transverse beam emittance, vacuum chamber dimensions and momentum compaction factor. A new impedance model of the SOLEIL II storage ring was developed. This paper demonstrates the evaluation of transverse single- and coupled-bunch instabilities with an up-to-date impedance model. Storage ring operation with a harmonic cavity is an essential component of the project. A harmonic cavity provides bunch lengthening and perturbs synchrotron motion. Its effects on transverse instabilities in SOLEIL II are reported in this contribution.

Imparting designed nonlinear correlation on the longitudinal phase space is nontrivial task. While RF cavities operating at different frequencies can generate arbitrary correlation in principle, it is hard to realize such system due to the lack of RF power sources and their costs. We present a new method that may overcome such practical limitation by adopting transverse wigglers and transverse deflecting cavities. Deflecting cavities introduce and eliminate linear correlation between longitudinal and transverse coordinates. We located transverse wigglers, which impart arbitrary correlation on the transverse phase space, where the longitudinal-to-transverse correlation is maximized. In principle, this system only requires deflecting cavities operating in the same frequency and several magnets such as transverse wigglers and quadrupoles.

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.

In the latest years Machine Learning (ML) has seen an unprecedented diffusion in the most different fields in simulations and real life as well. Probably two of the first and most used ML applications in accelerators are the optimization of the final performance of the machines, and the so called virtual diagnostics. In the latest years ML was successfully applied to improve the machine safety performing fault detection or to prevent interlocks. In this work we explored the possibility to use a ML approach to efficiently steer the beam in case the lattice contains high order magnets (sextupolar order and higher). We applied this scheme to SLS 2.0, the synchrotron upgrading at the Paul Scherrer Institut.

Proton polarization is preserved in the AGS by using helical dipoles partial snakes to avoid depolarizing vertical resonances. These same helical dipoles also drive numerous (82) weak horizontal resonances that result in polarization loss. These horizontal resonances occur at the same energy (and therefore frequency) as depolarizing resonances driven by linear betatron coupling. A new scheme has therefore been implemented to correct the snake-driven resonances with the placement of skew quadrupoles in the AGS ring powered to cancel the resonance driving term at each horizontal resonance crossing. The skew quadrupoles are required to pulse independently for each resonance to account for the variation of drive term phasing with energy. Fifteen thin skew quadrupoles have been installed in the AGS ring to implement this correction. We describe the correction principle, the magnet design and commissioning results from RHIC Run 24.

Beam profile measurements in the LHC and its injector complex show heavy tails in both transverse planes. From standard profile measurements, it is not possible to determine if the underlying phase space distribution is statistically independent. A measurement campaign in the CERN PSB was carried out to introduce cross-plane dependence in bunched beams in controlled conditions, in view of characterizing the LHC operational beam distributions. The results of the measurement campaign demonstrate how heavy tails can be created via coupled resonance excitation of the lattice in the presence of space charge, in accordance with predictions from the fixed line theory. The coupled resonance introduces dependence between the different planes, which persists after the resonance excitation is removed.

We present the optics design of the solenoid compensation scheme at the FCC-ee. The 2T solenoids from the experiments induce coupling on the beams, generating an increase on vertical emittance. This compensation scheme minimizes emittance growth, with a final value of approximately 5% of the nominal.
 A screening solenoid is placed around the Final Focus Quadrupoles to protect them from the experiment’s field. 
A skew quadrupole component is added to the Final Doublet, aligning the magnet axis to the rotated reference frame of the beam. 
Two anti-solenoids placed approximately ±20 m from the IP are used to cancel the field integral. The vertical orbit generated by the horizontal crossing angle in the detector field is compensated by vertical correctors placed right after the beam pipe separation and next to the final focus quadrupoles.
 We describe the IR optics in this scheme, including the detector solenoid and the magnetic elements used for compensation.

The X-ray beam position monitors (XBPMs) installed in the front end system of the Taiwan Photon Source (TPS) is discussed in this article. This XBPM has an Advanced Photon Source (APS) blade type. Calibration has been finished for most XBPMs in the front end of the insertion device beamline. The stability and resolution of the XBPMs will be introduced in the article. The problems encountered during functioning will also be men-tioned.

In this study, we present the design of a candidate lattice for the Shanghai Synchrotron Radiation Facility Upgrade (SSRF-U) storage ring, targeting the soft X-ray diffraction limit. Due to its ultra-low emittance, intra-beam and Touschek scattering are significant and require attention. We conducted simulations to examine the emittance growth and beam lifetime of different machine configurations in the SSRF-U storage ring. Equilibrium beam emittance variations due to beam coupling and bunch lengthening were identified through simulations. Additionally, Touschek scattering and beam lifetime were calculated.

The upgrade of PETRA III to PETRA IV at DESY is currently in its design phase. To achieve the desired beam parameters a 3rd harmonic cavity is necessary for the accelerating system. An investigation of three types of cavity structures thus is conducted to find the most cost effective and environmentally sustainable option. A high focus in this investigation is placed on the damping of higher order modes. Therefore, two of the investigated structures are so called single mode structures. Such structures have its cavity directly coupled to an RF-absorber, allowing for damping of all resonant modes but the desired ground mode. The design considered in this paper is from a conceptual test of Helmut Herminghaus (MAMI, Mainz, DE). Taking the requirements of PETRA IV into account, the design is adapted, numerically simulated and optimized.

The Advanced Photons Source (APS) storage ring (SR) underwent an upgrade to the multi-bend achromat (MBA) lattice recently. As part of the upgrade, four out of the sixteen Radio Frequency (RF) cavities were removed from the storage ring. The remaining twelve cavities were left in place during the entire upgrade process and restored to full operating power to support beam commissioning once the installation activities were completed. This paper provides details on the planning and preparations made to preserve the cavity integrity during the installation period, challenges faced while restoring the cavities and how the cavity power coupler beta values were determined.

For the future multi-TeV muon collider, ionization cooling is a critical step to achieve the required beam emittance for a proton-driven muon beam. Ionization cooling of intense muon beams requires the operation of high-gradient, normal-conducting RF structures in the presence of strong magnetic fields. The MAP modular cavity study at Fermilab has demonstrated the RF breakdown threshold at 13 MV/m for copper surface and 50 MV/m for beryllium surface in a 3 T solenoid B field. Based on these surface E field limits, we design a new 805 MHz copper cavity with thin curved beryllium windows that can achieve a gradient (without the transit time factor) of ~27 MV/m, which is comparable to the current 6D cooling lattice design. We also explore the distributed coupling for feeding the RF power to multiple cavities in the cooling lattice to accommodate the tight space in the superconducting solenoids. This cavity design study can be applied to the muon collider demonstrator program to experimentally evaluate the 6D muon emittance cooling.

Future colliders will require injector linacs to accelerate large electron bunches over a wide range of energies. For example the Electron Ion Collider requires a pre-injector linac from 4 MeV up to 400 MeV over 35 m*. Currently this linac is being designed with 3 m long traveling wave structures, which provide a gradient of 16 MV/m. We propose the use of a 1 m distributed coupling design as a potential alternative and future upgrade path to this design. Distributed coupling allows power to be fed into each cavity directly via a waveguide manifold, avoiding on-axis coupling**. A distributed coupling structure at S-band was designed to optimize for shunt impedance and large aperture size. This design provides greater efficiency, thereby lowering the number of klystrons required to power the full linac. In addition, particle tracking analysis shows that this linac maintains lower emittance as bunch charge increases to 14 nC and wakefields become more prevalent. We present the design and fabrication of this distributed coupling structure, as well as cold test data and plans for higher power tests to verify on the structure's real world performance.

As compared to conventional travelling-wave (TW) structures, parallel-coupled accelerating structures eliminate the requirement for the coupling between cells, providing greater flexibility in optimizing the shape of cells. Each cell is independently fed by a periodic feeding network for this structure. In this case, it has a significantly short filling time which allows for ultrashort pulse length, thereby increasing the achievable gradient. In this paper, a design of an X-band parallel-coupled TW structure is presented in detail.

Pulse compressors have been widely used to generate very high peak RF power in exchange for a reduction in the RF pulse length for linear accelerators. A C-band spherical pulse compressor is numerically studied for the linac of Super Tau-Charm Facility in this paper. Utilizing a dual-mode coupler for producing two orthogonal polarized TE11 modes, TE114 mode is chose for storing energy in resonant cavity enabling a Q0 over 1.3×105. By modulating the coupling factor to 8.6, an optimum average power gain of 4.8 can be achieved in the case of combing with a 3π/4 travelling wave accelerator. This paper concludes the optimum RF parameters of the pulse compressor, as well as the geometry tolerance is given for the next step machining.

Numerical optimizations on couplers of the traveling wave accelerating structures usually require lots of calculation resources. This paper proposes a new technique for matching couplers to an accelerating structure in a more efficient way. It combines conventional Kroll method with improved Kyhl method, thereby simplifying the tuning and simulation process. We will present the detailed design of a constant-gradient C-band accelerating structure based on this new method.

To meet phase stability requirements, a high peak power coaxial magnetron-based RF system with >70% efficiency would normally be injection locked to an RF source by using a circulator to send the locking signal into the magnetron through the antenna. This added requirement of a high-power circulator pushes the inherently low coaxial magnetron’s cost-per-watt to a high overall RF Power Source system cost-per- watt. For this project, the injected phase locking signal for the magnetron will use a novel input port that does not require a high- power circulator. The new input port uses the cathode stalk assembly to turn the filament-cathode into an antenna that couples to the resonant circuit of the magnetron. The coupling system between the cathode stalk, which runs at high voltage, and the RF input includes isolation for high voltage.

As part of the Electron-Ion Collide (EIC) upgrade at Brookhaven National Laboratory (BNL), the development of new beam screens for the vacuum system is underway. The mechanical design of the beam screens received support from CERN, particularly in addressing the mechanical response during a magnet quench, i.e. a resistive transitions in the superconducting magnets. Maintaining an overall elastic behavior in this component is crucial for the efficient functioning of the collider. The mechanical behavior of the EIC beam screen during a quench was initially analyzed using analytical methods and subsequently validated through a Multiphysics FEM model developed for the High-Luminosity LHC (HL-LHC) beam screen. The FEM model underwent an initial verification against analytical formulations in its simpler 2D magnetic-based version. Following this, thermal and mechanical physics were fully coupled with the magnetic model in a 3D framework. Various features, including partial weld penetration, pumping holes, and guiding rings, were then taken into consideration. Additionally, the plastic behavior of the beam screen materials was considered too. The assessment included an analysis of the maximum deformation and stress experienced by the EIC beam screen during a magnet quench, resulting in an overall elastic response for the proposed design.

A setup of in-house made Goubau (G-) Line system for measuring the broadband impedance of vacuum components has been developed at the NSRRC for improving the beam-stability of the Taiwan Photon Source (TPS). A thin copper wire of 0.287 mm in diameter with polyimide-coating ~0.02 mm in thickness connects two horn-shape aluminum launchers face-to-face at a distance ~1.2 m far in between via two impedance-matching copper tapers welded on both ends of the wire that transports the surface waves through the vacuum duct under test (DUT) allocated at the middle of wire. Measurement of time domain reflection (TDR) for the G-Line has verified the systematic performance of matching the impedance of 50 ohms. A vector network analyzer measures the transmission parameters of S21 of the DUT from the G-Line that the longitudinal impedance of DUT can be obtained. Various DUTs of vacuum components e.g. flanges without gasket were measured for inspecting the G-Line performance, besides, the special designed aluminum gaskets with rf-shielding property sealed flanges were also inspected that must feature with ultra-low impedance. The detail design and the test results of the G-Line will be described.

Compact synchrotrons, such as those proposed for cancer therapy, use short and highly bent dipoles. Large curvature drives non-linear effects in both body and fringe fields, which may be critical to control to obtain the desired dynamic aperture. Similarly to current practice, for straight magnet, our long-term goal is to aim at finding a parametrization of the field map that requires few terms to capture the relevant long term dynamical effects. This parametrization will then be used to optimize the performance of the synchrotron by long-term tracking simulations and, at the same time, drive the development of the magnet design by providing measurable quantities that can be computed from field maps. This paper presents the first steps towards the goal of representing the field with a few key parameters.

Pairs of Siberian Snakes allow the avoidance of first-order spin resonances during energy ramping. However, a high density of first-order resonances correlates with the presence of higher-order resonances after the installation of snakes. Thus, one effective tactic of mitigating higher-order resonances is by weakening the surrounding first-order ones, equivalent to minimizing the spin-orbit coupling integrals. Such a proxy helps sidestep a multi-hour polarization transmission simulation for each lattice configuration. In a three-fold super-periodic ring, using 12 snakes is a sufficient condition for completely eliminating the spin-orbit coupling integrals at all energies and tunes. Since the HSR will only have up to 6 snakes, we opt to focus on suppressing the strongest first-order resonances instead of the whole spectrum. By varying the snake reflection axes and the betatron phase advance in two of the arcs, we search in a 7-dimensional lattice space for the weakest resonance structure using a variety of metrics and find the configuration with highest polarization transmission.

The successful injection of proton beams into the Large Hadron Collider (LHC) depends on an efficient scraping mechanism in the Super Proton Synchrotron (SPS). The beams accelerated in the SPS contain a significant non-Gaussian tail population. If not removed, this transverse tail population can cause high losses in the transfer lines and in the LHC injection elements. Subsequently, the Beam Loss Monitor (BLM) system may trigger a beam dump reducing the machine availability. As beam intensities increase to meet the parameters set by the LHC Injector Upgrade (LIU), the efficiency of the scraping operation becomes increasingly crucial. To fully cope with higher beam intensities in the framework of the High-Luminosity LHC (HL-LHC) project, an upgrade of the scraper system, consisting of two movable graphite blades, is being developed and scheduled for installation in January 2025. This article presents the results of a comprehensive simulation study that employs the FLUKA code coupled with SixTrack to assess energy deposition in the scrapers.

SSRF (Shanghai Synchrotron Radiation Facili-ty)/SXFEL (Shanghai Soft X-ray FEL) Facility has de-veloped an advanced variable polarization transverse deflecting structure TTDS (two-mode transverse deflect-ing structure) to perform variable polarization based on the design of a dual-mode RF structure. The 15-cell prototype of the TTDS was fabricated at SSRF/SXFEL. Because the two modes operate in the same structure, any geometric change will affect both modes. A new RF design of the regular cell is proposed to improve rf per-formance. The two modes are coupled independently in two pairs of side coupling holes. The work presented in this paper is focused on the new design and the rf param-eters compared with the initial design.

Compact accelerator systems are assuming an increasingly significant role within the domain of radiotherapy. As processing technology continues to mature, X-band accelerators have garnered extensive utilization. This study introduces a design for a side-coupled traveling-wave Ku-band accelerator tube, leveraging established processing methodologies. The envisaged particle output energy stands at 2.5 MeV, with a microwave power source requiring a 300 kW input sourced from a klystron. The microwave design outcomes, derived using ANSYS HFSS, are delineated herein, alongside considerations pertaining to dynamic output and engineering design. Subsequent stages will subject this accelerator tube to processing tests, with the overarching objective of effectively supplanting the natural radiation source Co60 within the realm of radiotherapy.

Hefei Advanced Light Facility (HALF) injector comprises 40 S-band 3-meter traveling wave accelerating structures, capable of delivering electrons of full energy 2.2 GeV into the storage ring. To mitigate the emission degradation caused by dipole and quadrupole fields in the coupler cavity, the coupler design incorporates a racetrack and a short-circuit waveguide to eliminate this impact. This article presents an introduction to design of the traveling wave structure and the results of cold and high-power testing. We performed tuning and preliminary measurements on accelerating structure, resulting in meeting the single-cell phase deviation and accumulated phase deviation requirements of the project objectives while maintaining good measurement consistency.

With the recently implemented lattice tool LOCOM, which combines the precision of LOCO as well as the speed of multi-frequency AC-LOCO, it takes only a few minutes for the NSLS-II lattice measurement and correction of both linear optics and coupling. Besides, LOCOM can be applied to characterize linear optics at the extremely high chromaticity condition, thus, greatly speeding up the development of a new operational mode with x/y chromaticity of +10/+10. The high chromaticity lattice could potentially enable a reliable operation of the storage ring with high single-bunch current. Moreover, to characterize the errors of chromatic sextupoles with high precision, we are in the process of implementing the NOECO based on the LOCOM method. Preliminary simulation study indicates that 1-2% precision can be achieved for the calibration of chromatic sextupole errors. If such high accuracy can be achieved, it could potentially help in resolving some long-standing challenges of NSLS-II, e.g., the discrepancy between the designed and measured tune shift with amplitude. Finally, to have an independent crosscheck, we have implemented the TBT based ICA NOECO method with a confirmed 2% accuracy.

All wires of the four CERN SPS rotational wirescanners broke when increasing the beam intensity towards the target for the LHC Injector Upgrade in 2023. Impedance and thermal studies were immediately launched, with simulations and measurements indicating that beam induced heating from resonant modes on the thin wire could be sufficient to cause these breakages. Mitigation measures to displace electromagnetic losses away from the wire were proposed and implemented. This allowed a much higher beam intensity to be reached, close to the LIU target. Simulations now predict that the modified wirescanners can sustain the LIU beam parameters.

The WS superconducting systems are based on scintillator detectors and wavelength shifting fibers are mounted on the beam pipe. The detectors are coupled to long haul optical fibers, which carry the signals to custom front end electronics sitting in controls racks at the surface. The acquisition chain have been characterized at IHEP (Protvino), CERN PSB, COSY Juelich and SNS before installation in the ESS tunnel. The beam test results of this system design, differing from the standard approach where photomultipliers are coupled to the scintillator will be presented.

The Fermilab Side-Coupled Linac contains seven 805 MHz modules accelerating H- beam from 116 MeV to 400 MeV. Each module contains at least one wire scanner, yielding beam intensity at positions along a transverse direction. These wire scanners each contain three wires, mounted at different angles: "X", "Y", and 45° between "X" and "Y" to analyze coupling. Recently, a significant amount of transverse X-Y coupling was identified within wire scanner data from the Side-Coupled Linac, which has been present in data from the past decade. This realization has prompted an investigation into the wire scanner's utility as a diagnostic tool in the Fermilab Linac. This work presents efforts to better characterize the wire scanners' limitations and the phenomenon occurring in the Side-Coupled Linac.

To realize very precise measurement of the muon spin precession frequency in the level of sub-ppm, a muon beam is injected into a precisely adjusted storage magnet of sub-ppm uniformity via “Three-dimensional spiral beam injection scheme [1]” at J-PARC muon g-2/EDM experiment. This injection scheme requires a strongly X-Y coupled beam which is applied by eight rotating quadrupoles on the 10m of beam transport line [2]. Currently we have two scenarios of set of rotation angles (1) 45 or 60 degrees fixed, (2) any angles. In this presentation, strategy to precise control of the X-Y coupling at the beam transport line is discussed: how to control/monitor X-Y coupled phase space with eight rotatable quadrupole magnets including its alignment requirements for the case of (1) and (2). Results of alignment of the newly developed mount system for the rotating quad is also introduced. A pair of dedicated magnets called active shield multipole magnet (ASXM) will be set at the entrance and the exit of the beam channel of the storage magnet yoke. These devices will guarantee how well the beam phase space is matched with requirements at the reference point inside the storage magnet [3].

To develop a high-power, high-efficiency electron irradiation accelerator system with an adjustable electron beam, a novel constant-gradient backward-travelling-wave (BTW) accelerating structure has been designed. This accelerator tube implements a backward-travelling-wave design, which offers the advantages of short filling time and low power reflection, which are characteristic of traveling-wave acceleration structures, and can incorporate a nosecone design to achieve high shunt impedance. The constant-gradient concept is adopted to further enhance the electron beam power and beam efficiency. This paper presents the design of the BTW accelerating structure, encompassing parameter estimation and comprehensive three-dimensional simulations to validate the concept.

The Future Circular electron-positron Collider (FCC-ee) is a proposed accelerator with 91 kilometres circumference that should serve as a Higgs and electroweak factory, with unprecedented luminosity. Unavoidable misalignments and field errors will generate optics errors at the interaction point (IP), whose effect will be amplified by the beam-beam collisions, which will make it challenging for the collider to reach its intended luminosity goals. Hence, there is a need for correction tools that will enable the precise correction of the optics at the IP, such as linear coupling parameters and spurious dispersion. This will be essential both for FCC-ee commissioning and during routine operation. This paper describes the construction, simulated effectiveness, and constraints of IP tuning tools.

Plasma processing of superconducting radio frequency (SRF) cavities has shown an improvement in accelerating gradient by reducing the radiation due to field emission and multipacting. Plasma processing is a common technique where the free oxygen produced by the plasma breaks down and removes hydrocarbons from surfaces. This increases the work function and reduces the secondary emission coefficient. The hydrocarbon fragments of H2, CO, CO2, and H2O are removed from the system with the process gas which is flowing through the system. Here, we present COMSOL for the first time to simulate the plasma processing of an SRF cavity. In this work, we use Jefferson Lab's C75 SRF cavities design as our case study. Using simulation, we predict the condition of plasma ignition inside the SRF cavity. The simulation provides information about the optimal rf coupling to the cavity, mode for plasma ignition, choice of gas concentration, power, and pressure.

The SuperKEKB IR is designed to achieve extremely small vertical and horizontal beta functions at the IP. Superconducting magnets provide the focusing magnetic field required to squeeze down the beta functions. The Belle II detector solenoid field is fully compensated with the superconducting anti-solenoids on each side of the IP. For further luminosity improvement, an upgrade of the superconducting final focus quadrupole magnets is required; a new canceling scheme for the Belle-II solenoid field, based on new anti-solenoids, is to be implemented. The design concept of the new IR is to make the beam trajectory as parallel to the QC1 magnet axis as possible to cancel the X-Y coupling and chromaticity between the IP and QC1s and minimize vertical emittance by redesigning the anti-solenoid profile. Moving QC1P closer to the IP results in an increase in the required field strength and current density. Nb3Sn is selected as the cable material instead of the present NbTi. While superconducting properties are better, Nb3Sn magnet fabrication is quite difficult because of the brittleness of the material. New IR design idea and the technical challenges of the new IR magnets are described.

Even though the strengths are weaker, different from quadrupole offsets, sextupole offsets are causing more complicated disturbances on the storage ring optics. They are making orbit distortion and quadrupole kicks as well as couplings. The offsets in chromatic sextupoles can affect the correction of chromaticity too. The closed orbit corrections in modern storage rings are fast and reliable, but their main focus is correcting the orbit to the quadrupole centers and the orbit distortion from a sextupole offset can make orbit offsets at other sextupoles which can be iterated. In this paper, we study the impact of the sextupole offsets on the linear optics in NSLS-II storage ring.

We propose to correct nonlinear lattice optics with the closed-orbit modulation technique. Closed orbit modulation with large amplitude samples the nonlinear optics. Fitting such data measured on the machine to the lattice model with appropriate lattice parameters would reveal the nonlinear errors and provide a means for correction. The method is tested in simulation and is shown to work in principle. Experimental data were also taken. However, more work is needed to understand the other effects on the mode amplitude dependence on modulation amplitude on a real machine.

For the injection into the SOLEIL II storage ring a beam with small transverse and longitudinal sizes is necessary, which requires the booster synchrotron to be upgraded. The new booster is designed as a multi-bend 16BA Higher-Order Achromat lattice with a small emittance of 5 nm∙rad at 2.75 GeV. Robustness of the lattice has been studied with realistic errors in magnet alignment and calibration, but also taking into account specific errors as mismatch in the RF frequency and circumference error, as RF frequency is driven by the main storage ring. Also, power supply tracking errors have been considered and their reduction will be discussed. On top of these error studies an emittance exchange is performed to allow more flexibility in the injection parameters into the storage ring. Different methods are compared within the framework of a very realistic machine.

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 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 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.

Space charge has been a limiting effect for low energy accelerators inducing emittance growth and tune spread. Tune shift and tune spread parameters are important for avoiding resonances, which limits intensity of the beam. Circular modes are round beams with intrinsic flatness that are generated through strong coupling, where intrinsic flatness can be transformed to real plane flatness through decoupling. It is understood that flat beams increase the quality parameters of a beam due to one of the plane emittances being smaller than the other plane since luminosity and beam brightness depend inversely on the beam emittances. We show that circular mode beams manifest smaller space charge tune spread compared to uncorrelated round beams, which allows better systematic control of operating point of the beam. Minimized tune spread allows flexible operating points on the tune map. We also dedicate current and intrinsic flatness ratio limits on circular modes, which increase quality parameters without detrimental effects on the emittance increase.

Advanced Photon Source Upgrade (APS-U) Fast Orbit Feedback (FOFB) system uses 160 fast and 160 slow corrector magnets to stabilize orbit measured at 560 Beam Position Monitors (BPM). We plan to operate both fast and slow correctors in a unified feedback algorithm at 22 kHz correction rate. Mid-ranging control is a proven approach for feedback systems with two manipulated inputs each exerting distinct dynamic effects to regulate a single output. This method resets the fast input to its chosen DC setpoint and proves beneficial when cost of fast input is more than the slower one. Unified operation of fast and slow correctors is a fitting application to mid-ranging concept which is well founded for two input one output systems. In this work, based on the cross-directional nature of the FOFB system we developed a multi-variable approach to mid-ranging control. It can be applied to FOFB with multiple fast and slow correctors, and multiple BPMs. Performance of proposed scheme is tested in simulations with APS-U FOFB prototype model in MATLAB. The feedback loop with fast and slow correctors is stable with mid-ranging algorithm, and the fast corrector drives effectively tracked setpoints.

The novel Coupling-Loss-Induced-Quench (CLIQ) concept will be part of the quench protection system of the High Luminosity Large Hadron Collider (HL-LHC) Inner Triplet superconducting magnets at CERN. Several units of two distinct CLIQ prototype variants were produced to validate the CLIQ novel protection concept and define the system parameters for the required performance. Subsequently, these units were further enhanced by introducing additional redundancy, advanced monitoring systems, and improved safety features. These improvements culminated in the development of the third and final version. This paper provides insights into the evolution from prototypes to the final version to be installed in the machine, shedding light on the outcomes of comprehensive safety and electromagnetic compatibility (EMC) tests, coupled with extensive operational assessments.

We present a method for coupling particle dynamics, particle-matter interaction, and hydrodynamics codes to model the effects of high-intensity electron beams in Fourth Generation Storage Rings for the purpose of machine protection. The coupled codes determine if high-energy-density conditions (>100 J/mm^3) are present in beam-intercepting components. Elegant is used to simulate the dynamics of a whole-beam abort by muting the high-power cavity RF. Within the APS-U, the impacting beam begins interacting with a horizontal collimator, at which point elegant is interrupted and the beam impact process is modeled using MARS and FLASH. MARS simulates the interaction of the beam with the collimator, passes the energy density to FLASH, and returns the transmitted particle distribution to elegant. FLASH uses the energy deposition to determine the density of the collimator material. The surviving beam is propagated again through the APS-U lattice and the process is repeated until the beam is fully lost. The input MARS geometry is updated each step to reflect the changing material properties. The coupled codes also examine the effects of synchrotron radiation within the vacuum beam chambers.

The Institute for Applied Physics (IAP) installed a permanent test setup for up to \SI{60}{\kilo\watt} of RF power in cw mode for conditioning. The goal is to establish a time efficient test procedure for the future MYRRHA CH-cavities. Three test stands were designed to accommodate up to three cavities simultaneously. All stations are curently tested via the \SI{175}{\mega\hertz} MAX RFQ prototype at IAP with the new test setup. Vacuum, Low-level-, and high-power measurements have been successfully performed.

An exact solution for the radiation field of a particle in a helical undulator, valid for an arbitrary point in space and an arbitrary particle energy, was obtained by the partial domain method, generalized for the case of spiral motion of a particle. The interface between the regions is a cylindrical surface containing the spiral trajectory of the particle. A comparison is made with the existing solution, which is valid in the far zone at high particle energies.

SIRIUS is the Brazilian 4th generation synchrotron light source. Currently, SIRIUS is in its Phase 1 stage of the project, with 14 beamlines proposed, some of which are already used by external users. Recently, the SABIÁ beamline underwent a transition where its commissioning insertion device (ID) was replaced by the beamline’s titular ID, an in-house developed DELTA undulator. This device offers versatility in generating various polarizations of light depending on the relative positions of the ID cassettes. However, each permissible configuration engenders distinct perturbations in beam dynamics, particularly affecting beam orbit, optics, and equilibrium parameters. This paper reports the impacts of the DELTA on beam dynamics and outlines the correction strategies implemented to mitigate these effects