A resistive transverse damper is often needed in particle accelerators operating with many bunches and it is usually very efficient as it can considerably reduce the necessary amount of nonlinearities needed to reach beam stability through Landau damping. In the CERN LHC for instance, the required current in the Landau octupoles is predicted to be reduced by an order of magnitude for zero chromaticity (for the beam and machine parameters used during the last year of Run 2, in 2018, this corresponded to $\sim 2000\mathrm{A}$ without damper and $\sim 200\mathrm{A}$ with damper, knowing that the maximum current available in the Landau octupoles is $\sim 550\mathrm{A}$). However, a resistive transverse damper also destabilizes the single-bunch motion below the transverse mode coupling instability intensity threshold (for zero chromaticity), introducing a new kind of instability, which has been called ITSR instability (for imaginary tune split and repulsion). Until now, only one type of impedance-driven transverse coherent instability has been explained for a single bunch in a circular particle accelerator, at zero chromaticity and without a multiturn wake: the transverse mode coupling instability. A transverse mode coupling instability can also be observed in the presence of Landau damping, beam-beam, electron cloud or space charge. However, the ITSR instability exhibits a different mechanism, which is not due to mode coupling. The purpose of this article is to explain in detail both this new instability mechanism and its mitigation using a simplified analytical model, which has been carefully benchmarked, using the pyheadtail macroparticle tracking code, by Oeftiger (one of the code’s developers).

As one of the leading acceleration mechanisms in laser-driven underdense plasmas, direct laser acceleration (DLA) is capable of producing high-energy-density electron beams in a plasma channel for many applications. However, the mechanism relies on highly nonlinear particle-laser resonances, rendering its modeling and control to be very challenging. Here, we report on novel physics of the particle resonances and, based on that, define a potential path toward more controlled DLA. Key findings are acquired by treating the electron propagation angle independently within a comprehensive model. This approach uncovers the complete particle resonances over broad propagation angles, the physical regimes under which paraxial/nonparaxial dynamics dominates, a unified picture for different harmonics, and crucially, the physical accessibility to these particle resonances. These new insights can have important implications where we address the basic issue of particle trapping as an example. We show how the uncovered trapping parameter space can lead to better acceleration control. More implications for the development of this basic type of acceleration are discussed.

We have designed a tool to measure the bunch length of an electron beam in a minimally invasive way by means of coherent Smith-Purcell radiation (SPR). The technique has been employed successfully at a test apparatus for the Mainz Energy-recovery Superconducting Accelerator MESA, demonstrating it is possible to determine the bunch length while losing less than 0.6% of the electron beam. The impact of the space charge on the bunch length can be reduced while tuning the longitudinal bunch preparation system during a live measurement at beam currents up to 1 mA. Doing so, RMS bunch lengths of $70\mu \mathrm{m}$ can be achieved in a typical operating mode of the low-energy beam transport system of MESA. In addition to the bunch length measurements, typical properties of the generated SPR are demonstrated.

The Super Proton Synchrotron at CERN is equipped with a scraping system for halo cleaning at beam transfer to the Large Hadron Collider. The system is composed of movable graphite blades mechanically swept through the beam to remove tails immediately before beam transfer. Due to the mechanical movement, beam particles are intercepted by a small volume of material with consequent concentration of energy deposition and high thermal loads. The blades were tested with beam to verify their resistance to the most extreme scraping conditions. Even though the beam was prematurely dumped by the beam loss monitoring system, the microstructural analysis of the blades following the test found signs of material sublimation. The test setup was reproduced in simulation to reconstruct the levels of energy deposition actually reached in the blades during the test; values are compatible with local material sublimation, in agreement with the microstructural analysis. Simulations were carried out by coupling the sixtrack tracking code, used for single particle beam dynamics in circular accelerators for high energy physics, to the fluka Monte Carlo code, for particle-matter interactions. The time evolution of the beam intensity measured during scraping and the distribution of losses around the ring were used for an extensive benchmark of the simulation tool against measurements taken during the test. This work presents the endurance test together with simulation results and the benchmark of the simulation tool. The quantitative agreement between simulations and measurements proves the quality of the analyses and the maturity of the simulation tool, which can be reliably used to predict the performance of cleaning systems in circular accelerators.

Crab crossing scheme is an essential collision scheme to achieve high luminosity for the future colliders with large crossing angles. However, when bunch length of one or both colliding beams is comparable with the wavelength of the crab cavity voltage, the nonlinear dependence of the crabbing kick may present a challenge to the beam dynamics of the colliding beams and impact the beam quality and the luminosity lifetime. In this paper, the results of nonlinear dynamics in the crab crossing scheme are presented, using both analytical and numerical approaches. The result indicates that higher-order synchrobetatron resonances may be excited in the crab crossing scheme with large crossing angle, which causes the beam quality deterioration and luminosity degradation. The studies also reveal possible countermeasures to suppress the synchrobeta resonance, hence mitigate the degradation of beam quality and luminosity.

The new generation internal beam dump of the Super Proton Synchrotron (SPS) at CERN will have to dissipate approximately 270 kW of thermal power, deposited by the primary proton beam. For this purpose, it is essential that the cooling system features a very efficient heat evacuation. Diffusion bonding assisted by hot isostatic pressing (HIP) was identified as a promising method of joining the cooling circuits and the materials of the dumps core in order to maximize the heat transfer efficiency. This paper presents the investigation of HIP assisted diffusion bonding between two CuCr1Zr blanks enclosing SS 316L tubes and the realization of a real size prototype of one of the dump’s cooling plates, as well as the assessments of its cooling performance under the dump’s most critical operational scenarios. Energy-dispersive x-ray spectroscopy, microstructural analyses, measurements of thermal conductivity, and mechanical strength were performed to characterize the HIP diffusion bonded interfaces (CuCr1Zr-CuCr1Zr and CuCr1Zr-SS 316L). A test bench allowed to assess the cooling performance of the real size prototype. At the bonded interface, the presence of typical diffusional phenomena was observed. Moreover, measured tensile strength and thermal conductivity were at least equivalent to the lowest ones of the materials assembled and comparable to its bulk properties, meaning that a good bonding quality was achieved. Finally, the real size prototype was successfully tested with an ad hoc thermal test bench and with the highest operational thermal power expected in the new generation SPS internal beam dump. These results demonstrated the possibility to use HIP as a manufacturing technique for the cooling plates of the new generation SPS internal beam dump, but they also open up the way for further investigations on its exploitability to improve the cooling performance of any future high intensity beam intercepting device or in general devices requiring very efficient heat evacuation systems.

A transverse beam profile monitor that visualizes a two-dimensional beam-induced fluorescent image was developed. The monitor employs a sheet-shaped gas flow formed by a technique of rarefied gas dynamics. A simplified analysis method was developed to reconstruct the beam intensity profile from the obtained image. The developed profile monitor and the analysis method were applied to measure the J-PARC 3 MeV ${\mathrm{H}}^{-}$ beam profile. The root mean square values of the profiles were consistent with the ones obtained by a wire-scanning-type beam profile monitor. The beam loss due to the gas sheet injection was measured as a beam-current reduction. The amount of the beam current decreased in proportion to the gas sheet flux and the reduction ranged from 0.004 to 2.5%. The assembled system was capable of reconstructing a beam profile from a single shot beam pulse ($1.7\times {10}^{13}$ protons in $50\mu \mathrm{s}$).

An electron-ion collider (EIC) at Brookhaven National Laboratory is being proposed as a new discovery machine for the nuclear physics and quantum chromodynamics. The hadron beam cooling plays an important role in the EIC machine to achieve its physics goals. The most challenging is cooling of protons at the highest energy in the EIC. In this paper, we present a possible design of a ring-based electron cooler for the high energy hadron beam cooling. In the proposed approach, the electrons will cool the hadrons while being cooled themselves by radiation damping in the storage ring. For the design of the cooler using the storage ring approach several aspects become very important, including electron ring optics design, chromaticity correction, calculating the dynamic aperture, radiation damping, quantum excitation, and intrabeam scattering. In addition, such effects as beam-beam scattering due to interaction of electrons with hadrons becomes of special concern, and we develop a generalized approach to it. In this paper, we take all of the above effects into the design, and discuss the beam lifetime and instabilities in the ring. A special feature of our design is an effective use of dispersion in the cooling section, both for the ions and electrons, to redistribute the cooling rate between the longitudinal and horizontal planes. Finally, the cooling performance is simulated for proton beam at the top energy of the EIC. Our conclusion is that such ring-based cooler could be a feasible approach to provide required parameters of hadron beam at the top energy of 275 GeV for the EIC.

Detrimental beam dynamics effects limit the performance of high-intensity rapid cycling synchrotrons (RCSs) such as the 8 GeV proton Fermilab Booster. Here we report the results of comprehensive experimental studies of various beam intensity dependent effects in the Booster. In the first part, we report the dependencies of the Booster beam intensity losses on the total number of protons per pulse and on key operational parameters, such as the machine tunes and chromaticities. Then we cross check two methods of the beam emittance measurements (the MultiWires proportional chambers and the ionization profile monitors). Finally, we used the intensity dependent emittance growth effects to analyze the ultimate performance of the machine in the present configuration, with the maximum space-charge tuneshift parameter $\mathrm{\Delta }{Q}_{\mathrm{SC}}\sim 0.6$, and after its injection energy is upgraded from 0.4 to 0.8 GeV.

We propose a novel scheme for the calculation of bunch profiles and synchronous phase shifts for arbitrary fill patterns in electron storage rings considering both the effects of the passive harmonic cavity and the short range wakefield. This scheme treats the bunch as a charge distribution rather than a point charge with a bunch form factor, and divides the voltage induced in the cavity into two groups: that induced by the previous passages and that by the present passage, where the latter is integrated with the short range wakefield from all the other vacuum components. An iteration loop for computing the bunch profiles, including a subloop using Newton iteration for calculating the synchronous phase deviations, is built and implemented into a matlab-based code. Using this code, we study the bunch lengthening and centroid transient effects for several possible fill patterns in the Hefei Advanced Light Facility storage ring under design. We find the method is very efficient, and the CPU time for the whole calculation on a regular personal computer is less than 30 seconds for each case even with more than 700 bunches. Using the case of a long gap fill as a benchmark example, both the results given by our code and the multiparticle tracking simulation with elegant are in very good agreement.

This paper deals with the determination of the wake-function, impedance and energy loss due to surrounding accelerator components of two countermoving beams, i.e., two beams moving in opposite directions. Differently from the classical case, the distance between source and test charges cannot be considered constant. The paper defines a generalized wake-function, independent of the source and test particle’s direction of motion. From this generalized wake-function a wake-potential is derived. The paper focuses in particular on the longitudinal direction. The expression of the energy dissipated by two beams transiting in the same vacuum chamber is obtained. This expression is valid both in the comoving and countermoving beam scenario. Subsequently, the proposed model is benchmarked by calculating the longitudinal co and countermoving wake-functions, the corresponding impedances and wake-potentials for two simple geometries (a circular pipe and a pillbox cavity) traversed by two countermoving beams, and by comparing the results with the ones of the electromagnetic code CST Studio Suite. Finally, for the pillbox geometry, the energy loss of the two countermoving beams and their rf-heating are investigated.

In response to recommendations in the 2013 update of the European Strategy for Particle Physics, a conceptual design effort for an energy upgrade of the Large Hadron Collider (LHC) at CERN, the so-called high-energy LHC (HE-LHC), was launched as part of the Future Circular Collider study. The HE-LHC machine, which is meant to use 16 T magnet technologies in the existing LHC tunnel, would provide proton collisions at a center-of-mass energy of 27 TeV ($\sim 2\times \mathrm{LHC}$) with a total stored energy of 1.34 GJ ($\sim 4\times \mathrm{LHC}$) per beam. By adapting the LHC collimation system, a first layout of the HE-LHC’s betatron cleaning insertion was conceived, with the requirement to sustain—for at least 10 seconds—the impact of about 1.86 MW, corresponding to a beam lifetime of 12 minutes, without inducing any magnet quench nor any damage to other accelerator components. In this article, we evaluate the power deposition on the collimation insertion for proton beam operation in the HE-LHC machine at top energy, by means of particle tracking and interaction calculations. The beam loss effects on the warm elements as well as on the superconducting dispersion suppressor magnets are assessed through a three-step simulation approach. In particular, for the proposed future high-energy LHC, we demonstrate the necessity of adding local collimators in the dispersion suppressor, and we uncover the harmful consequences of a potential removal of the beam line “dogleg” in the collimation insertion.

Photocathodes based on bialkali antimonides have great potential in the field of high-brightness electron sources. In this paper, the influence of incident light absorption on the performance of ${\mathrm{K}}_2\mathrm{CsSb}$ photocathodes was studied using Monte Carlo simulations. The surface plasmon polaritons (SPPs) were first introduced into ${\mathrm{K}}_2\mathrm{CsSb}$ photocathodes employing a nanopattern structure to improve the effective absorption of incident light and adjust the initial distribution of the photoelectrons. To evaluate the effect of SPPs on the photocathode performance, photoemission from such photocathodes was modeled using Monte Carlo simulations. Simulations show the quantum efficiency of the ${\mathrm{K}}_2\mathrm{CsSb}$ photocathode increases by 2–3 times that of the photocathode without SPPs. Moreover, the thermal emittance of the photocathode remains unchanged. These results are crucial to the future development of high-brightness electron beams.

The multibend achromat (MBA), which often serves as a building block for modern low-emittance storage rings, is composed of a repetition of unit cells with optimized optical functions for low emittance in the achromat center, as well as end cells for dispersion and optics matching to insertion devices. In this work, we describe the simplest stable class of unit cells that are based on a longitudinal Fourier expansion, transforming Hill equations to Mathieu equations. The resulting cell class exhibits continuously changing dipolar and quadrupolar moments along the beam path. Although this elementary model is defined by only three parameters, it captures a significant amount of notions that are applied in the design of MBAs. This is especially interesting as Mathieu cells can be viewed as an elementary extension of Christofilos’ original model of alternating-gradient focusing, while their sinusoidal bending and focusing functions lend themselves to future applications in undulatorlike structures. Mathieu cells can be used to estimate the range of reasonable cell tunes and put an emphasis on the combination of longitudinal gradient bending and reverse bending, as well as on strong horizontal focusing to reach emittances lower than the classic theoretical minimum emittance cell. Furthermore, the lowest emittances in this model are accompanied by small absolute momentum compaction factors.

A negative muonium ion (${\mathrm{Mu}}^{-}$) source using an aluminum foil target (Al target) was developed as a low-energy muon source. ${\mathrm{Mu}}^{-}$ ions are produced by irradiating the Al target with a 3-MeV positive muon (${\mu }^{+}$) beam and observed using a microchannel plate. An experiment to produce ${\mathrm{Mu}}^{-}$ ions was conducted to evaluate the performance of this ${\mathrm{Mu}}^{-}$ ion source. The measured event rate of ${\mathrm{Mu}}^{-}$ ions was $(1.7\pm 0.3)\times {10}^{-3}{\mathrm{Mu}}^{-}/\mathrm{s}$ when the event rate of the incident ${\mu }^{+}$ beam was $1.3\times {10}^6/\mathrm{s}$. The experiment was conducted at the Muon Science Establishment, D-line in the Materials and Life Science Experimental Facility within the Japan Proton Accelerator Research Complex. The formation probability, defined as the ratio of the ${\mathrm{Mu}}^{-}$ ions to the incident muons on the Al target, was $(1.1\pm 0.2(\mathrm{stat}{)}_{+0.1}^{-0.0}(\mathrm{syst}))\times {10}^{-6}$. This ${\mathrm{Mu}}^{-}$ ion source was first adopted in the commissioning of the muon accelerator at the D-line, and the event rate of the accelerated ${\mathrm{Mu}}^{-}$ ions was consistent with the expectation. This ${\mathrm{Mu}}^{-}$ ion source boosted the development of the muon accelerator, and the practicality of this low-energy muon source obtained using a relatively simple apparatus was demonstrated.

Proposals aimed at measuring the electric dipole moment (EDM) for charged particles in storage rings require a good understanding of the systematic errors that can contribute to a vertical spin buildup mimicking the EDM signal to be detected. In what follows, a method of averaging emanating from the Bogoliubov-Krylov-Mitropolski method is employed to solve the Thomas-Bargmann-Michel-Telegdi equation and calculate the Berry phases arising for the storage ring frozen spin concept. The formalism employed proved to be particularly useful to determine the evolution of the spin at the observation point, i.e., at the location of the polarimeter. Several selected cases of lattice imperfections were simulated and benchmarked with the analytical estimates. This allowed the proof of the convergence of the numerical simulations and helped gain better understanding of the systematic errors.

Stripline kickers are commonly used for on-axis injection in the low emittance rings. The beam coupling impedances of the kickers normally show large contributions to the total impedance budget. In the High Energy Photon Source, the necessity of the short pulse bottom width (less than 10 ns) and strong deflection field requires the kicker to have a short length and a small gap between the electrodes, respectively. A new five-cell stripline kicker is proposed in order to save longitudinal space as well as to reduce the beam coupling impedance. Comprehensive studies have been undertaken to characterize the impedance of the stripline kicker. The beam coupling impedance and heat load dissipation on the kicker due to the beam passage are studied numerically. Strategies to further reduce the impedance are discussed. In addition, impedance bench measurements are launched to identify the impedance of the kicker experimentally. The longitudinal beam coupling impedance is measured with different terminations by using coaxial wire method. A satisfactory agreement has been reached between the numerical predictions and the measurements. A novel fasten block design with ceramic is proposed for the wire stretching and the center holding of the inner conductor in a small beam pipe.