In the studies of optical injections in laser or beam-driven wakefield accelerators, there is a frequent demand for using obliquely propagating assistant lasers in particle-in-cell simulations. In conventional methods, this is only possible in either two- or three-dimensional Cartesian geometries, which have the drawbacks of either lack of fidelity for the actual situation or requiring a huge amount of computational resources. In this work, we develop a new method that uses an expression-defined oblique laser field to simulate such situations in quasicylindrical geometry particle-in-cell simulations, having the advantages of both maintaining good fidelity and saving computational resources. As an example, we use this method in the scissor-cross ionization injection scheme for the optimization of the injected beam quality. This method is widely applicable to particle injections with assistant lasers in wakefield accelerators, as long as the assistant lasers only influence the injected particles during the injection process.

ThomX is a compact x-ray source based on Compton scattering, installed at IJCLab (Laboratoire de physique des 2 infinis-Irène Joliot-Curie) in Orsay. The machine uses a small electron storage ring and an intense laser pulse stored in a high-finesse optical cavity. This article describes the various subsystems of the machine and their initial results of the commissioning, which began in mid-2021. This first commissioning phase led to the production of ${10}^{10}$ x-rays/s with an on-axis energy of 45 keV. The main steps to be taken to reach the nominal flux are outlined at the end.

A high-current, long-pulsed beam operation without beam loss was demonstrated at the Superconducting rf Test Facility (STF) of the High Energy Accelerator Research Organization. The primary purpose of the STF was to validate the superconducting radio-frequency (rf) acceleration technology for the International Linear Collider (ILC) using accelerator components in line with the ILC design. Thus, the most critical objective of STF was to perform beam operations with a pulse length ($726\text{−}\mathrm{\mu }\sec$) and current (5.8 mA) equal to those of the ILC. Severe radiation caused by beam loss hinders stable beam operation. In a $100\text{−}\mathrm{\mu }\sec$ pulsed beam operation, a gradient drop in the accelerating cavities owing to beam loading causes beam loss. This beam loading was suppressed by imposing an additional driving power as feedforward control (BeamFF) to compensate for the gradient drop. BeamFF can completely suppress the gradient variation from a flattop to a 0.4% level with an amplitude stability of 0.3%–0.4%. Based on the knowledge obtained in the $100\text{−}\mathrm{\mu }\sec$ beam operation, we achieved a stable $726\text{−}\mathrm{\mu }\sec$, 5.8-mA beam operation, and a beam power of 5.6 kW. The maximum energy variation of the pulsed beam was 1.5%. This value is significantly less than the threshold of 4%, which causes beam loss. We thus verified the stable beam acceleration technology for the ILC at the STF.

A significant contribution to the temporal resolution of an ultrafast electron diffraction (UED) instrument is arrival time jitter caused by amplitude and phase variation of radio-frequency (rf) cavities. In this paper, we present a semianalytical approach for calculating rf-induced temporal jitter from klystron and rf cavity parameters. Our approach allows fast estimation of temporal jitter for MeV-UED beamlines and can serve as a virtual timing tool when shot-to-shot measurements of rf amplitude and phase jitters are available. A simulation study for the SLAC MeV-UED instrument is presented, and the temporal resolution of several beamline configurations is compared.

This work studies the suitability of a set of different materials for manufacturing more efficient and durable radio-frequency quadrupole (RFQ) structures compared to that currently used in many linear particle accelerators, traditionally made out of copper. RFQs are susceptible to vacuum breakdowns caused by the exposure to high electric fields, resulting in surface degradation. Additionally, a further limitation of present-day copper RFQs is surface blistering under hydrogen ion beam exposure, due to beam halo losses. Irradiation is associated with a further reduction of the breakdown field strength of the metal surface thereby affecting the overall efficiency of the RFQ. The investigated materials, Cu-OFE, CuCr1Zr, CuBe2, Ti6Al4V, SS316LN, Nb, and Ta, were submitted to low-energy (45 keV) ${\mathrm{H}}^{-}$ irradiation and tested in a direct-current (dc) system with pulsed high voltage. For comparison, the maximum surface electric field was measured for both irradiated and pristine (nonirradiated) surfaces of the same material. The effects of irradiation on the surface of the materials, before and after being submitted to high electric fields, were studied with the help of microscopic imaging and chemical analysis. Blistering caused by ${\mathrm{H}}^{-}$ irradiation has been observed in all copper and copper alloy materials. Despite reductions in breakdown field strength postirradiation, no indications were found that the blisters on the surface have a direct cause in triggering breakdowns during high electric field tests. SS316LN, Ti6Al4V, CuBe2, and CuCr1Zr showed maximum surface electric fields higher than copper, making these promising candidate materials for future RFQs manufacturing. This paper focuses on the results with CuCr1Zr, CuBe2, SS316LN, and Ta, complementing and expanding previous work exploring Cu-OFE, Nb, and Ti6Al4V.

Recently, nonlinear effects have been used to cool a special beam represented by an annular distribution in a 2D phase space. This outcome was accomplished using an ac dipole combined with amplitude detuning generated by static nonlinear magnets. In this paper, we investigate a more realistic scenario, in which a beam distribution in a 4D phase space includes the presence of a beam halo and demonstrate how the latter can be removed using nonlinear effects. The proposed approach employs high-order nonlinear ac magnets to trap into nonlinear resonances and to perform an adiabatic transport of the beam halo in phase space. Theoretical models are formulated and examined using numerical simulations to evaluate their efficacy.

The baseline configuration of the Compact Linear Collider positron source is optimized at three different collision energy stages for both drive beam-based and klystron-based acceleration modes. The hybrid target is replaced with a single amorphous tungsten target with the target thickness and electron beam spot size optimized. As a result of the optimization, compared with the old baseline configuration, the positron yield has been improved by a factor of 1.65, enabling the same reduction in the bunch charge and beam power of the primary electron beam. The total deposited power in the target is reduced by a factor of 2.1. The most realistic start-to-end simulation to date of the system from the target to the injector linac is performed taking into account new design of essential hardware. The impact of misalignments is studied for the first time and is found to be small and acceptable. Possibility for reducing the primary electron beam energy is investigated. With a bunch charge below 1 nC, it is possible to reduce the energy from 5 GeV to a minimum of 2.3 GeV with the linac length and costs reduced accordingly. The deposited power in the target is also reduced with the energy.

A quadrupole wiggler consisting of a row of alternating-polarity permanent magnet-excited quadrupoles is used in a collinear wakefield accelerator under development at Argonne National Laboratory. Fine translational and angular adjustment mechanisms are implemented in all quadrupoles to obtain a better than $1\text{−}\mathrm{\mu }\mathrm{m}$ precision in the alignment of quadrupole wiggler assemblies. The quadrupole’s magnetic and mechanical designs are described. Two wiggler prototypes were fabricated, aligned, and characterized performing pulsed wire magnetic measurements. The sensitivity of the quadrupole wiggler alignment to the ambient temperature was measured.

The electron-ion collider crab Cavities will present a significant transverse impedance to the beam. The low-level radio frequency system will have to reduce the crab cavity impedance to prevent transverse instabilities, while regulating the crabbing voltage and minimizing the radio frequency noise levels injected into the beam. This work presents an estimate of the crab cavity impedance in the presence of feedback and the resulting stability margins using simplified stability criteria. Generalized stability criteria are also presented in this work and are used to more accurately estimate stability margins.

Hybrid multibend achromat (MBA) lattice with a pair of dispersion bumps separated by $-I$ transformation is used in some diffraction-limited storage ring (DLSR) designs, which can obtain relatively large dynamic apertures. However, the $-I$ transformation also largely restricts the horizontal tune of the lattice cell. In this paper, an MBA lattice with four dispersion bumps is proposed, which has relatively good flexibility in adjusting the number of bends in the lattice cell and the lattice cell tunes, while also achieving the effective sextupole cancellation within the lattice arc section. The new lattice can have a larger horizontal cell tune than the hybrid MBA lattice with the same number of bends, which is beneficial for reducing the emittance. In the new lattice, $-I$ transformation is not necessary for the sextupole cancellation between paired bumps, and a general relation of sextupole cancellation is used. Following this lattice concept, a 7BA lattice is preliminarily designed for a 1.5 GeV DLSR. This lattice concept can also be extended to the case of MBA lattice with more bumps.

In this contribution, we present the design of a resonant slow extraction based on the radio-frequency knockout (rf-KO) scheme, where we make use of the transverse resonance islands bucket (TRIB) optics. The generation of the TRIB optics is presented in two example lattices, which are considered for the potential upgrade of the current booster at DESY. The slow extraction studies are motivated to potentially supply high energy electron beams to the high energy physics beamline users. Simulations show an extraction efficiency in excess of 90% with a septum blade thickness of $100\mathrm{\mu }\mathrm{m}$.

GaAs-based photocathodes are the only viable source capable of providing spin-polarized electrons for accelerator applications. This type of photocathode requires a thin surface layer, in order to achieve negative electron affinity (NEA) for efficient photoemission. However, this layer is vulnerable to environmental and operational effects, leading to a decay of the quantum efficiency $\eta$ characterized by a decay constant or lifetime $\tau$. In order to increase $\tau$, additional agents can be introduced during the activation procedure to improve the chemical robustness of the surface layer. This paper presents the results of recent research on Li as an enhancement agent for photocathode activation using Cs and ${\mathrm{O}}_2$, forming Cs-${\mathrm{O}}_2$-Li as an enhanced NEA layer. Measurements yielded an increase in lifetime by a factor of up to $19\pm 2$ and an increase in extracted charge by a factor of up to $16.5\pm 2.4$, without significant reduction of $\eta$. This performance is equal to or better than that reported for other enhanced NEA layers so far.

Proton therapy presents an interesting and important challenge to accelerator physics. Practical restrictions such as room size, gantry weight, and cost have led to a demand for more compact and affordable devices. Success would benefit a significant number of patients every year. Dielectric wall accelerators could provide this breakthrough, but there is limited work available regarding their feasibility or possible integration into medical devices, and no solutions exist for longitudinal beam control. In this work, we discuss the development of a linear beam dynamics model for dielectric wall accelerators. The model is implemented as part of the open-source code transoptr. It is tested against the rf LINAC subroutine in transoptr and is used to study bunch injection and transport. Building on recent work, the effect of time-varying fields on beam dynamics is also investigated. Conditions for limiting transverse beam size and maintaining longitudinal stability are discussed, and considerations are given to accelerator and beamline design.

We investigate properties of optical elements in the optical cavity of an x-ray laser oscillator with emphasis on the power loss of a monochromatic Gaussian radiation beam upon passing through them using analytical and numerical approaches. Here we assume the optical cavity comprises of refractive lenses and Bragg crystals exploiting symmetric Bragg scattering. For the lens, we include focusing and curvature effects while we include angular filtering due to finite Darwin width of the Bragg crystal. Our results indicate the feasibility of x-ray power out-coupling in the range of 0.5%–28% with intracavity reflectivity of 67%–95% at 10.321 keV for nominal ($\ge 65\%$ reflectivity) cases. We also show the possibility of achieving high out-coupling of 35%–80% while restricting the intracavity reflectivity in the 19%–62% by adopting lossy cavities with $10–20\mathrm{\mu }\mathrm{m}$ thin crystals.