In future storage rings, precise control of the electron-beam phase space will become increasingly important. A key challenge in these dynamics is maintaining the lattice’s isochronicity, which is crucial for applications such as optical stochastic cooling and steady-state microbunching. In particular, path-length deviations induced by intrabeam scattering (IBS) could limit the performance of steady-state microbunching light sources. In this paper, we present a more accurate formula for calculating the IBS-induced path-length deviation of an electron beam traversing the lattice, which can aid in lattice optimization. Additionally, we have developed a tool to simulate IBS-kick effects on beam dynamics. It can directly compute the IBS equilibrium emittance in storage rings and efficiently evaluate the associated path-length deviations for an electron beam traversing a lattice.
We have constructed a 324-MHz interdigital H-mode drift tube linear accelerator (IH-DTL) with an alternating phase focusing method. This IH-DTL will be part of a muon linear accelerator (linac) being developed at the Japan Proton Accelerator Research Complex for a precise measurement of the muon anomalous magnetic moment and a search for the muon electric dipole moment. The IH-DTL is 1.45 m long and accelerates muons from β=v/c=0.08 to 0.28. Low-power tuning was performed using six slug tuners, which reduced the peak-to-peak on-axis field error to 1.4%. Following 94 h of high-power conditioning, the IH-DTL demonstrated stable operation at the nominal peak power of 390 kW and a duty factor of 0.1%, corresponding to the designed accelerating field (E_{0}) of 3.6 MV/m. This paper presents the construction, low-power rf tuning, and high-power performance of the 324-MHz IH-DTL.
The maximum secondary electron yield, δ_{max}, is a key parameter governing electron cloud buildup in high-intensity proton accelerators, yet its direct in situ determination under operational conditions remains challenging. This paper presents a novel method to estimate δ_{max} in the Large Hadron Collider (LHC) using electron cloud measurements performed in the Vacuum Pilot Sector. The approach exploits the characteristic evolution of electron cloud intensity during beam injection, in particular the transition from an initial build-up regime to a linear scaling of electron flux with the number of injected bunches. Electron cloud currents measured with dedicated electron pickups are compared with PyECLOUD simulations performed for varying δ_{max} values. The threshold number of injected bunches required to reach the linear regime provides a robust observable from which δ_{max} can be extracted with limited sensitivity to other surface-emission parameters. The method is applied to multiple LHC fills and surface materials. For conditioned copper liners, δ_{max} values between approximately 1.16 and 1.30 are obtained, in agreement with independent analyses and literature values. Applying the technique over extended operation periods enables the reconstruction of surface conditioning curves as a function of cumulative electron dose. These curves show a rapid initial decrease in δ_{max} before approaching an apparent plateau, which may lie below the detection limit of the method depending on the beam pipe material and location. The method is compatible with routine LHC operation and enables systematic monitoring of vacuum-surface conditioning.
This manuscript proposes a method to enable controlled high gradient particle acceleration when requiring self-modulation (SM) of the drive bunch. While electron bunch seeding of self-modulation has been realized at a plasma electron density [L. Verra et al., (AWAKE Collaboration), Controlled growth of the self-modulation of a relativistic proton bunch in plasma, Phys. Rev. Lett. 129, 024802 (2022)10.1103/PhysRevLett.129.024802], it has not been demonstrated at higher plasma densities due to limitations of available seed bunch properties. As experimentally shown in this manuscript, truncating available seed bunches with a relativistic ionization front allows these limitations to be overcome. This seeding method is called truncated electron bunch seeding of self-modulation (teSSM), and experiments confirm that—when using teSSM—self-modulation becomes reproducible. Additionally, the seed wakefield amplitude is also increased, which is known to be advantageous because it shortens the length needed to reach self-modulation saturation. The presented results establish teSSM as a method for achieving controlled, high gradient particle acceleration with long drivers and available seed bunches.
Inverse Compton scattering (ICS) is a promising method for generating coherent and tunable x-rays in a compact setup. In this paper, we present a theoretical framework describing the output of an ICS x-ray source for arbitrary interaction angles between pulsed electron and laser beams in the Thomson regime. This allows for analytic optimization of the x-ray beam properties by varying the parameters defining the geometry. In general, different x-ray applications require optimization of different x-ray beam properties, such as energy spread for x-ray spectroscopy and angular spread for x-ray scattering measurements. In this paper, we restrict ourselves to optimization of the x-ray brilliance, which is a comprehensive figure of merit for x-ray beam quality. The framework can be used, however, to optimize other x-ray properties. We investigate two specific ICS interaction geometries in particular: head-on scattering of a laser beam off an electron beam and scattering of a laser beam off an electron beam in a co-propagating geometry, interacting under a grazing angle. For head-on scattering, we show that a tightly focused, cylindrically symmetric laser pulse, which balances laser intensity and interaction time, optimizes the x-ray brilliance. For a co-propagating, grazing angle geometry, an elliptical focus of the laser pulse is required to mitigate the geometric reduction of the interaction time. We find that the latter geometry is especially useful for soft x-ray generation.
Superconducting magnets enable energy-frontier accelerators by generating strong magnetic fields to steer and focus the particles. Although high-temperature superconductors such as REBa_{2}Cu_{3}O_{x} (rebco, RE = rare earth) hold a strong potential for generating a higher magnetic field than Nb-Ti and Nb_{3}Sn, the associated magnet and conductor technology for accelerator applications is still in its infancy. The U.S. Magnet Development Program is developing rebco magnet technology in collaboration with industry. Here we report an experiment of making a dipole magnet called C3 using commercial high-temperature superconducting corc® wires. The magnet, following a canted cosθ design, generated a dipole field of 5.99 T at 4.2 K in its clear aperture of 65 mm at 6.795 kA when a resistive voltage of 105 μV appeared across one of the coils in the magnet. The stored energy was 53 kJ at the peak field. The magnet showed no degradation in the current-carrying capability at 4.2 K after the thermal cycle. We report on the detailed design, fabrication, and performance of the C3 magnet that can be of interest to potential users of this emerging technology. We also discuss issues and research needs to inform future rebco magnet development. The experiment represented another step to addressing if the high-temperature superconducting accelerator magnet technology can increase the discovery capability of future particle accelerators.
At the 1.5-GeV synchrotron light source DELTA operated by TU Dortmund University, intense and ultrashort radiation pulses in the vacuum ultraviolet and terahertz regimes are generated by the interaction of femtosecond laser pulses with electron bunches in an undulator. The resulting periodic modulation of the electron energy is converted into a density modulation in a dispersive section, giving rise to coherent radiation emission at harmonics of the seed wavelength in a second undulator. This process is known as coherent harmonic generation (CHG). This paper describes the experimental setup and concentrates on the spectral aspects of CHG radiation under variation of properties of the seed laser pulse and the dispersive section. CHG spectra at the second harmonic of the 800 nm seed wavelength were recorded using a grating spectrometer equipped with an image-intensified CCD camera. Numerical simulations to model the CHG spectra for different group-delay dispersion and third-order dispersion were carried out, and a convolutional neural network was implemented to predict these parameters from measured CHG spectra. The results show that the tunable laser parameters directly translate into the spectrotemporal properties of the coherently emitted pulses.
The High Energy Photon Source is the first fourth-generation light source in China, featuring a hybrid multibend achromat lattice. This innovative design incorporates high gradient quadrupoles with an aperture of 26 mm, a gradient of about 80 T/m, and high-order field harmonics of less than 4×10^{−4}. This paper details the optimized magnetic design, precise fabrication techniques, batch field measurements, and a method for field harmonic compensation utilizing a magic finger. A comparative analysis was conducted on nine types of the 480 pure quadrupole magnets that share the same cross section but differ in iron lengths. These variations include laminated or solid cores and closed or open yokes. The cross section, characterized by a narrow concave and convex pole contour, a tapered pole root, and saddle coils, is designed to mitigate magnetic saturation while enhancing the iron filling ratio. The impact of iron saturation on the transfer function and the evolution of current-dependent multipole fields has been systematically investigated, along with the effects of mechanical errors and inhomogeneities in the magnetic properties of the iron core on harmonics. We demonstrate a comprehensive engineering solution for high gradient small-aperture quadrupole magnets, which has been validated through mass production.
The inverse-Cherenkov dielectric laser accelerator (ICR-DLA) holds great promise as a compact, on-chip accelerator for a wide range of future applications. However, two significant challenges—bunch dispersion/deflection and phase slippage—have hindered its development in the subrelativistic regime. In this paper, we propose an approach that addresses both issues simultaneously by utilizing a single laser pulse to illuminate a staged dielectric prism. Our method leverages the phase slippage experienced by subrelativistic electrons during high-gradient acceleration, allowing these electrons to encounter alternating focusing and defocusing forces throughout the acceleration process. This technique enables stable, long-range bunch transport within a miniaturized acceleration channel. We show that cascading focusing and acceleration of subrelativistic electrons can be achieved in a multistage acceleration structure, laying a foundation to bridge the gap between subrelativistic and relativistic regimes, which is crucial for the realization of a practical on-chip particle accelerator.
It is significantly challenging to protect the power source against the reflected power when standing-wave rf structures operate, in particular under overcoupled conditions. Conventionally, nonreciprocal circulators, usually operating under pressurized SF_{6} atmosphere, are employed to isolate the power source from the reflected power. However, breakdowns, rf losses, and thermal stress make these devices unusable in rf structures operating at high frequencies (6–12 GHz) and can limit the maximum power or the repetition rate, all of which are critical aspects for next-generation accelerators or rf photoinjectors, as an example. Furthermore, the use of SF_{6} gas is becoming increasingly problematic due to its environmental impact. In this paper, two novel rf networks are proposed to compensate reflections from standing-wave structures, thus avoiding the use of circulators. They are based on specifically designed hybrids that, combined with rf structures, allow to strongly reduce the reflected power. The design of hybrids with arbitrary power ratios between different ports constitutes a multiobjective optimization problem. To address this challenge, a new optimization methodology is proposed to simplify the optimization process into a single-objective problem. These novel rf networks are then applied to a new C-band photoinjector recently developed at the Italian National Institute of Nuclear Physics INFN (Frascati, Rome, Italy) and to a new proposal of X-band rf photoinjector for National Synchrotron Radiation Laboratory (NSRL).
Undulator tapering is an important technique in free-electron lasers and synchrotron radiation sources, used to enhance radiation efficiency, broaden spectral bandwidth, and perform other related functions. However, conventional tapering methods, such as gap variation or electromagnetic control of individual magnets, involve complex mechanical structures or power supply systems, posing challenges in tuning the taper profile while maintaining good field integral performance in practice. This paper presents a beat frequency undulator that enables dynamic control of undulator tapering over a wide range. The concept employs two permanent magnet arrays with slightly different periods, whose magnetic field superposition generates a longitudinal beat frequency envelope, creating a tunable taper profile without gap adjustment or electromagnetic tuning. By longitudinally shifting one array, the taper strength and direction can be reconfigured in real time. This approach offers inherent advantages in mechanical simplicity and maintains a field integral comparable to that of a standard planar undulator, providing a robust and flexible solution for undulator tapering.
We present a methodology for modeling the photoemission process in nanopatterned photocathodes using finite-difference time domain (FDTD) and 3D Monte Carlo (MC) methods adapted for tasks with 3D nanopattern geometry. Using MC, we calculated the electron transport inside the alkali semiconductor. The FDTD method was used to simulate light absorption in a photocathode. This coupled approach self-consistently models resonant effects, electron excitation, transport to the cathode surface, and emission into vacuum. Furthermore, this approach enables the study of two-dimensional (2D) nanopatterned structures. We studied semiconductor photocathodes with 1D and 2D nanopatterned metal substrates. We calculated the quantum efficiency and intrinsic emittance at photon energies from 1.8 to 2.4 eV. We have demonstrated that the quantum efficiency of a nanopatterned photocathode is significantly higher than that of a photocathode with a flat interface. We also demonstrated that the quantum efficiency of a two-dimensional nanostructured photocathode is polarization-independent. At the same time, the cathode intrinsic emittance remains unchanged upon nanopatterning.
Pulsed high-power radio frequency (rf) systems frequently employ pulse compressors to augment peak output power, thereby reducing the required number of rf sources and enhancing cost efficiency. A prominent class of these devices utilizes single resonant cavities supporting two degenerate modes to achieve high performance within a compact footprint. However, the inherent coupling of these modes complicates experimental characterization, a challenge exacerbated by the fact that these units are typically nondismountable. This paper proposes a novel analytical method to disentangle the complex electromagnetic data encoded within these systems. By separately extracting the parameters of the individual degenerate modes and the characteristics of the associated waveguide network, the method provides a granular view of device performance. This approach enables a more comprehensive interpretation of measurement data, offering a pathway for the precise tuning and optimization of monolithic rf pulse compression systems.
Future electron-positron linear colliders require extremely small beam sizes at the interaction point (IP) to achieve high luminosity. The Accelerator Test Facility (ATF) at KEK has been developed to demonstrate the required beam focusing scheme, achieving a vertical size of 37 nm at the virtual IP using a low-emittance beam generated in a damping ring. However, as nanometer scale focusing requires specialized optics, even small kicks in the beamline can lead to significant distortions at the IP. Transverse wakefield effects have previously been observed as beam size growth with increasing bunch intensity and have been primarily interpreted as static effects arising from orbit distortion and misalignment. Dynamic wakefield effects caused by pulse-by-pulse beam orbit fluctuations have also been suggested by previous measurements and investigated through numerical simulations; however, a direct experimental and quantitative evaluation has not been reported. In this paper, we present the first experimental and quantitative study of dynamic wakefield effects on nanometer scale beams at the ATF. Controlled orbit fluctuations were introduced using steering magnets, enabling systematic measurements over a wide range of fluctuation amplitudes without changing the beam optics configuration. The resulting beam size growth was quantitatively evaluated through both experiments and simulations incorporating all wakefield sources in the beamline. The results demonstrate that dynamic wakefield effects can significantly contribute to beam size growth and must therefore be taken into account to achieve stable nanometer scale beams in future linear colliders.
Beam-driven plasma wakefield acceleration represents a promising strategy for producing high-energy electron and positron beams in future accelerator facilities. A key challenge in realizing high-quality acceleration is the production of high-charge, high-stability double-bunch beams, as existing methods are often limited to low charges or suffer from significant charge loss. In this paper, we propose a coherent synchrotron radiation-tolerant beam-merging scheme using twin isochronous beamlines that share a common dipole magnet to generate a high-charge double-bunch beam with excellent stability. Numerical simulations indicate that the proposed scheme generates a 5 nC/1 nC electron double-bunch beam that exhibits no charge loss, with emittance growths of both bunches constrained to approximately 0.1 mm mrad, and an interbunch timing jitter maintained below ±2 fs. The robustness of the scheme is evaluated, and its potential use in large-scale accelerator facilities is emphasized for supplying high-quality drive beams for plasma wakefield accelerators.
In order to reduce the increase in bunch energy dispersion caused by the beam loading effect, beam loading compensation in the acceleration structure is required. In this paper, a novel scheme is proposed to use microwave pulse compression to compensate for the beam loading effect in the traveling wave structure. The compression system consists of an energy storage cavity and a correction chain of six cavities working in S band. Through parameter optimization, the optimal coupling factors of the energy storage cavity and the correction cavity are obtained to generate microwave pulses with increasing amplitude. Through this scheme, the S-band traveling wave acceleration structure achieves an acceleration voltage of 50.14 MV with a power input of 16.6 MW and a beam current of 2.5 A. The relative energy dispersion is 0.77%, and the effective system power gain reaches 10.56, significantly surpassing that of conventional microwave pulse compression systems.
Historically, the design and operation of secondary beamlines at CERN’s North and East Areas relied on simplified particle distributions and a beamline acceptance determined solely by collimators. The formalism presented here makes as few simplifying assumptions as possible and can be used to match and design secondary beamlines without time-consuming HPC tracking studies. In this study, the formalism is applied to the development of a new neutrino beamline within the Physics Beyond Colliders framework at CERN. The code is expressed generically, providing tools for designing secondary beamlines with small relative losses.
A new beam delivery system has been developed to explore the feasibility of extending the energy reach of Compact Linear Collider (CLIC) to 7 TeV, either through an extension of existing CLIC linacs or by integrating novel acceleration technologies. This study provides key insights for the design of future multi-TeV collider concepts, including a potential 10 TeV plasma-wakefield acceleration-based collider. Particular emphasis is placed on developing a more compact final focus system capable of achieving a luminosity higher than that of previous designs. An in-depth analysis of higher-order optical aberrations and their impact on beam size and luminosity performance is presented.
The injection of positrons in a plasma wakefield has long been challenging due to the demand for an appropriate field structure. Here, we propose a novel approach whereby a positron source is positioned at the front of a hollow, positively charged driver. This configuration allows the plasma wakefield to continuously catch up with the positrons, enabling self-adaptive capture into the accelerating and focusing phase. Our analytical model demonstrates that positrons with varying angles, energies, and initial positions can be effectively injected into similar phases for further acceleration. In addition, introducing a transversely asymmetric driver can substantially enhance the energy gain without affecting the injection. Three-dimensional quasistatic PIC simulations show that injected positrons with a charge of 12 pC can be accelerated to energies exceeding 14 GeV using a 10 GeV hollow positron driver, corresponding to an acceleration gradient of 16 GV/m. These results provide a proof-of-principle demonstration for a new positron injection and acceleration scheme in plasma wakefields.
The P ¯ ANDA experiment at the High Energy Storage Ring (HESR) of the Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, will be a unique setup to study the strong interaction in antiproton-proton collisions. The combination of a windowless cluster-jet target and a high-intensity antiproton beam, cooled by stochastic cooling down to momentum spreads of 4 × 10 − 5 in the presence of the target, is ideal to study, e.g., the line shape of exotic candidates in the charmonium spectrum, such as the χ c 1 ( 3872 ) . For first studies on the performance of the cluster-jet target and the stochastic cooling, both were installed at the COoler SYnchrotron (COSY) at the Forschungszentrum Jülich, Germany. Detailed studies on the beam quality for different target settings with different densities were performed and will be presented in this paper. The results show that the cluster-jet target is able to provide the required hydrogen target thickness of more than 2 × 10 15 atoms / cm 2 for the P ¯ ANDA experiment and that the stochastic cooling is able to efficiently cool the beam in presence of such a target thickness, although the system is not yet complete compared to the setup foreseen for the HESR. The presented results strengthen the theoretical understanding of the beam-target interaction and stochastic cooling performance and will provide important input for operation later at the HESR.
